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+Project Gutenberg's The Preparation of Plantation Rubber, by Sidney Morgan
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Preparation of Plantation Rubber
+
+Author: Sidney Morgan
+
+Contributor: Henry P. Stevens
+
+Release Date: March 7, 2011 [EBook #35510]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK RUBBER ***
+
+
+
+
+Produced by Chris Curnow, Harry Lamé, Robin Curnow and
+the Online Distributed Proofreading Team at
+http://www.pgdp.net
+
+
+
+
+
+
+
+
+
+  +----------------------------------------------------------------------+
+  |                       TRANSCRIBER'S NOTES:                           |
+  |                                                                      |
+  | * Minor typographical and lay-out errors have been corrected.        |
+  | * Inconsistencies in spelling (e.g. hyphenated vs. non-hyphenated    |
+  |   words) have not been corrected.                                    |
+  | * Italics are represented by underscores as in _text_.               |
+  | * The original book uses a V symbol to describe V-shaped cuts. These |
+  |   V symbols are represented as [V].                                  |
+  | * Changes made to original text:                                     |
+  |   * Table of Contents:                                               |
+  |     * "Early collection of latex transport" changed to "Early        |
+  |       collection of latex--Transport".                               |
+  |     * "Roof brick built houses" changed to "Roof--Brick built        |
+  |       houses".                                                       |
+  |     * The order of the sections under Chapters XII and XXII has been |
+  |       changed slightly to reflect the order of the sections in the   |
+  |       text.                                                          |
+  |   * "Tephrosia candiad" changed to "Tephrosia candida".              |
+  |   * "Archiev" changed to "Archief".                                  |
+  |   * "about 1/2 square" changed to "about 1/2 inch square".           |
+  |   * "asbesto-slate" changed to "asbestos-slate" as elsewhere.        |
+  |   * "Formaline" changed to "Formalin" as elsewhere.                  |
+  | * Footnotes moved to under the paragraph they belong to.             |
+  | * Page 141: "The lengths of crepe were weighed carefully at 8 a.m.   |
+  |   and 4 a.m." should probably read "The lengths of crepe were weighed|
+  |   carefully at 8 a.m. and 4 p.m."                                    |
+  +----------------------------------------------------------------------+
+
+
+
+
+                       THE PREPARATION OF PLANTATION
+                                   RUBBER
+
+
+
+
+                              THE PREPARATION
+                                    OF
+                             PLANTATION RUBBER
+
+                                    BY
+
+                          SIDNEY MORGAN, A.R.C.S.
+
+ VISITING AGENT FOR ESTATES IN THE EAST; FORMERLY SENIOR SCIENTIFIC OFFICER
+        AND NOW HONORARY ADVISER TO THE RUBBER GROWERS' ASSOCIATION
+                                 IN MALAYA
+
+               WITH A PREFACE AND A CHAPTER ON VULCANIZATION
+
+                                    BY
+
+      HENRY P. STEVENS, M.A. (OXON.,) PH.D., F.I.C.
+
+      CONSULTING CHEMIST TO THE RUBBER GROWERS' ASSOCIATION IN LONDON
+
+
+                           CONSTABLE & CO. LTD.
+                         LONDON : BOMBAY : SYDNEY
+                                   1922
+
+
+                        PRINTED IN GREAT BRITAIN BY
+                BILLING AND SONS, LTD., GUILDFORD AND ESHER
+
+
+
+
+PREFACE
+
+
+Mr. Sidney Morgan's work on Plantation Rubber in the East is so well known
+that he hardly needs introduction.
+
+An earlier book, published in 1914, by the Rubber Growers' Association,
+entitled "The Preparation of Plantation Rubber," was well received and
+widely read. This book dealt in a very practical manner with problems with
+which the industry had to contend. A second edition was subsequently
+published. Both editions are now out of print. The present opportunity was
+therefore taken to revise the original work, with the result that it has
+been enlarged and practically rewritten. The information given is brought
+up-to-date, and covers the whole process of production, commencing with the
+planting of the tree, passing on to the collection, coagulation, and curing
+of the rubber, and concluding with the packing for export. In the course of
+his work for the Association, Mr. Morgan carried out a great deal of
+industrial research in rubber production, including lengthy experiments on
+tapping, the use of different coagulants and different conditions of
+coagulation, and also on varying modes of rolling, drying, and smoking
+rubber. He also went very fully into the types of construction and details
+of the machinery and buildings employed on estates.
+
+Much of this valuable work has escaped notice, owing to its having been
+published in reports with limited circulation. Also a great deal of
+information was supplied to planters in a quiet and unobtrusive fashion, in
+interviews, visits to estates, and on other similar occasions. The
+knowledge and experience thus accumulated has been embodied in the present
+volume. The subject-matter should interest not only those actually engaged
+in rubber planting, but those otherwise directly or indirectly connected
+with the industry, such as importers, brokers, and particularly the rubber
+manufacturers in this country and in America. My experience has been that
+manufacturers as a whole have but a vague idea as to the methods employed
+in the preparation of plantation rubber, and this work provides them with
+the opportunity of obtaining an insight into the actual operations on the
+estates. It is most desirable that a closer bond should unite the
+plantation and manufacturing rubber industries. Such a result is best
+promoted by a better understanding of the problems with which each is
+confronted. Perhaps I may go so far as to suggest that some leading
+scientific officer in the employment of one of the large manufacturing
+concerns may take in hand a book which will give the planters the
+equivalent of information in regard to the manufacturing industry which the
+planters are now offering to the manufacturers.
+
+The photographs in the earlier part of the book will give the layman some
+conception of the enormous amount of labour that must be expended in the
+opening up, planting, trenching, and weeding the plantations which have
+replaced the virgin jungle. The authors are indebted for most of these
+photographs to Mr. H. Sutcliffe, one of the mycologists of the Rubber
+Growers' Association. The pictures of spotless coagulating tanks and tiled
+verandahs regularly hosed down will indicate the cleanliness necessary for
+the preparation of the beautifully clean sheet and crepe rubber which
+became available with the advent of plantation rubber. These results are
+largely due to the work of Sidney Morgan and his colleagues, on whom the
+planters have relied for technical guidance and advice.
+
+As regards my own contribution this is confined to a general outline of the
+subject. I have, therefore, omitted reference to a number of matters which
+would have been dealt with in detail had space permitted. The information
+given is based on researches on vulcanisation carried out for the Rubber
+Growers' Association by the writer over a period of nine or ten years. It
+was not found practicable to give detailed references in all cases. The
+reports on which the conclusions are based will, however, be found among
+the regular quarterly reports made by the writer for the Association up to
+June, 1919. Subsequent reports have been published in the Monthly Bulletin
+of the Rubber Growers' Association. We are indebted to the Association for
+permission to publish details from these reports, and also for the use made
+of numerous earlier reports published both in London and in the East.
+
+
+
+
+CONTENTS
+
+
+  PART I
+  _FIELD OPERATIONS_
+
+                                                                      PAGE
+  CHAPTER I
+  PLANTING
+
+  Seeds--Seed selection--Strain improvement by bad propagation--
+  Nurseries--Stumps--Seed at stake--Basket plants--Preparation
+  of land--Danger of disease--Clean clearing--Loss of top-soil--
+  Silt-trenches on slopes                                                1
+
+  CHAPTER II
+  FIELD MAINTENANCE
+
+  Clean weeding--Selective weeding--Loss of top-soil--Grass
+  ridges--Lallang eradication--_Mimosa gigantea_ (_M.
+  invisa_)--Green cover-plants--Connection between weeding,
+  soil conservation, and soil improvement                               13
+
+  CHAPTER III
+  THINNING OF AREAS
+
+  Original planting per acre--Ultimate stand per acre--Close-
+  planting _versus_ wide-planting--When to commence
+  thinning operations--How to select in preliminary rounds--
+  Later selections based on yields of individuals--Yields per
+  tree, present and future--Trees per acre                              19
+
+  CHAPTER IV
+  TAPPING SYSTEMS
+
+  Former methods--Former systems--Tendency to reduce number of
+  tapping cuts and frequency of tapping--Period allowed for
+  bark-renewal--Modern systems--Superimposed cuts--Single cuts,
+  etc.--Tapping experiments--R.G.A. experiment--Alternate-daily
+  _versus_ daily tapping                                                28
+
+  CHAPTER V
+  TAPPING AND COLLECTING
+
+  Tapping knives--Personal equation in use of knives--Choice of
+  latex cups--Cleaning of cups--Water in cups--Premature
+  (spontaneous) coagulation--Prevention of spontaneous
+  coagulation--The use of anti-coagulants in the field--
+  Collecting pails--Payment by result--Methods for calculation
+  of yields per coolie--Tree-scrap, oxidation of--Prevention of
+  oxidation--Bark-shavings--Collection and storage of shavings--
+  Treatment of shavings--Collection of earth-scrap                      38
+
+  CHAPTER VI
+  TRANSPORT OF LATEX AND COAGULUM
+
+  Percentages of "first" latex and other grades--Early
+  collection of latex--Transport, nature of--Light railways--
+  Motor-lorries--Bullock-carts--Care of transport vessels--Use
+  of an anti-coagulant during transport--Transport by coolie--
+  Coagulation centres (stations)--Transport of coagulum                 59
+
+
+  PART II
+  _FACTORY OPERATIONS_
+
+  CHAPTER VII
+  PRELIMINARY TREATMENT OF LATEX
+
+  Reception at store--Receptacles--Jars--Tanks--Necessity for
+  close supervision--Need for utmost cleanliness--Straining of
+  latex--Strainers--Facilitation of straining--Bulking of latex
+  --Standardised dilution of latex--Facilities for receiving and
+  handling latex--Reception verandahs--Receiving vessels--Types
+  of installations                                                      65
+
+  CHAPTER VIII
+  COAGULATION
+
+  Choice of coagulant--Strength of acid solution--Making stock
+  solution--Quantity for use--Quantities under modern
+  requirements--Care in mixing--Method of mixing with latex--Use
+  of sodium bisulphite as an anti-oxidant--Quantities for use--
+  Formulæ--Abuse of the chemical--Residual traces in the dry
+  rubber--Use of sodium sulphite as an anti-coagulant,
+  quantities for use--Formulæ--Use of Formalin as anti-coagulant
+  --Formulæ for use                                                     74
+
+  CHAPTER IX
+  PREPARATION OF SHEET RUBBER
+
+  Pale (air-dried) sheets--Uniformity of product--Pans _versus_
+  tanks--The ideal tank--Modern installations--Care of tanks--
+  Standardised dilution of latex--Variation in dimensions and
+  density of coagulum--Standardising instruments--Method of
+  using--Skimming latex--Style of sheets--Standard sheets--
+  Rolling and marking--When to work the coagulum--Hand-rolling--
+  Power smooth-rolling--Marking rolls--Preparation for smoke-
+  curing--Caution against accumulation of wet sheets--Hot-water
+  treatment--Dripping in the open air--When to place in smoke-
+  house                                                                 89
+
+  CHAPTER X
+  PREPARATION OF CREPE RUBBER
+
+  First consideration, fine pale crepe--Standardised dilution of
+  latex--Coagulation and coagulant--Quantities of coagulant--
+  Colour of rubber--Sodium bisulphite (use of)--Evaluation and
+  deterioration of the bisulphite and sulphite of sodium--To
+  distinguish between these two chemicals--Care of sodium
+  bisulphite--Mixing solution with latex--Former methods of
+  making pale rubber--Working the coagulum--Lower grades of
+  crepe--Naturally coagulated lump--Skimmings and washings--
+  Tree-scrap--Bark-shavings--Earth-scrap--Fibrous matter in low-
+  grade rubbers--Scrap-washers--Compound crepes--Increased care
+  with lower grades--Block rubber from crepe--Smoked crepe
+  _versus_ sheet clippings                                             110
+
+  CHAPTER XI
+  DRYING OF RUBBER
+
+  Air-drying of crepes--Artificial driers for crepes--Vacuum
+  drying--Hot-air driers--Michie-Golledge system--Rate of air-
+  drying--When drying takes place--Increase in weight of drying
+  crepe--Differences in weight--Aids to normal drying--Smoke-
+  curing of sheet rubber--Instruments for recording temperature
+  --Temperatures of smoke-house--Period of drying--Fuels for
+  smoking--Sun-drying of sheet rubber--Artificial driers for
+  sheet rubber                                                         132
+
+  CHAPTER XII
+  SORTING, GRADING, AND PACKING
+
+  Reducing number of grades--Reduction carried too far--R.G.A.
+  recommendations--Care in sorting--Choice of packing cases--
+  Bags--Bales--Folding of crepe--Mechanical folders--Care in
+  assembling--Methods of packing--Weight of contents--Short
+  weights                                                              150
+
+
+  PART III
+  _MACHINERY AND BUILDINGS_
+
+  CHAPTER XIII
+  MACHINES
+
+  Quality of metal in rolls--Nature of roll-bearings--Brass
+  liners--Liners of alloy or of cast-iron--Adequacy of machines
+  --Arrangement of battery--Speed of machines--Gear ratios--
+  Grooving of rolls--Heating of rolls--Sheeting machines--
+  Lubrication--Trays--Position of battery--Drainage of battery--
+  Access to back of machines--Engines--Power                           159
+
+  CHAPTER XIV
+  FACTORIES
+
+  General construction--Plenty of light--Floors--Drainage of--
+  How many storeys--Verandahs--Tanks, situation of--Designs and
+  lay-out--Drains--Water supply                                        172
+
+  CHAPTER XV
+  OTHER BUILDINGS
+
+  Drying-houses for crepe rubber--How many storeys--Ventilation
+  --Windows--Effect of light--Effect of direct sun-rays--Hot-air
+  houses--Smoke-houses--Various types--Ordinary smoke-houses--
+  General ventilation--Windows--Racks of supports--Floors--
+  Furnaces in general--Pit-fires--Pot-fires--Iron stoves--
+  Horizontal drum-furnaces--Rate of combustion--Brick stoves--
+  Pataling type of--Consumption of fuel--Floor of furnace room--
+  Roof--Brick built houses--"Third Mile" type--Jackson cabinet--
+  Devon type--Detailed description of--Barker patent design            178
+
+  CHAPTER XVI
+  OTHER BUILDINGS (_continued_), AND SITUATION OF BUILDINGS
+
+  Sorting-room--Packing room--Store rooms--Storage of rubber--
+  Need for special accommodation--Floor of store room--Local
+  conditions--Temperature and humidity--Incidence of moulds--
+  Effect upon smoked sheets--Tool-sheds and stores--Situation of
+  buildings--Position with respect to points of the compass--
+  Choosing a factory site--Centralisation--Decentralisation            211
+
+
+  PART IV
+  _THE FINISHED RUBBER_
+
+  CHAPTER XVII
+  DEFECTS IN CREPE RUBBERS
+
+  General style of finish--Dirty edges--Iron-stains--Rust-stains
+  --Oil-marks--Trays--Dirt--Holes--Greenish and tacky streaks--
+  Not due to oil _per se_--Tackiness and copper--Cotton and
+  other fibre--Bark and grit--Sand--Oxidation streaks--Yellow
+  streaks--Bisulphite streaks--Spot disease--Cause of--Influence
+  of rate of drying--Percentage of moisture--Humidity of
+  atmosphere--Prevention of disease--Infection by contact--
+  Outbreak of dormant spores--Rules to be observed--Surface
+  moulds or mildew--Tackiness in general--Full discussion of--
+  Experimental reproduction--Lack of uniformity in colour--
+  Defects in block rubber                                              223
+
+  CHAPTER XVIII
+  DEFECTS IN SHEET RUBBER
+
+  Defective coagulation--Coloured surface blotches--General
+  darkening of surface--Soft coagulum--Spongy underface--Tearing
+  --"Pitting" of surface--Thick ends or edges--Mis-shapen sheets
+  --Thick patches--Torn sheets--"Dog-ears"--Creases--Greasiness
+  of surface before smoking--Surface blemishes--Uneven
+  appearance--Variation due to oxidation--Colour when dry--
+  Surface gloss--Dull surface--Moist glaze and greasiness--
+  Virgin spots--Surface moulds or mildew--Black streaks or spots
+  --White or grey streaks--Rust--Theories on formation of--
+  Prevention of--Two methods--Other views on causation--Bubbles
+  --Causes of formation--In the field--In the factory--Blisters
+  --"Spot" disease in sheet rubber--Support marks--Stickiness--
+  Surface pattern--Sheet clippings--Other infrequent defects--
+  Dirt--Ash--Bark--Splinters                                           249
+
+  PART V
+  _GENERAL_
+
+  CHAPTER XIX
+  CHOICE OF COAGULANT
+
+  Acetic acid in general use--Is a coagulant necessary?--Acetic
+  acid--Formic acid--Citric acid--Tartaric acid--Oxalic acid--
+  Sulphuric acid--Hydrochloric and nitric acids--Hydrofluoric
+  acid--Alum--Pyroligneous acid--Smoked water--Chinese vinegar--
+  Sulphurous acid--Sugars--Various salts--Proprietary compounds
+  --Carbonic acid gas--Alcohol--Vegetable extracts                     278
+
+  CHAPTER XX
+  SPECIAL METHODS OF PREPARATION
+
+  Da Costa process--Byrne curing process--Freezing process--
+  Wickham process--Derry process--Spontaneous coagulation--
+  Definition of--Discussion of types--Ærobic--Anærobic--
+  Organisms--Maude-Crosse patent--Method of operation--
+  Accelerating action of sugars--Accelerating action of soluble
+  calcium salts--Ilcken-Down process--Slab rubber                      290
+
+
+  PART VI
+  _VULCANISATION_
+
+  CHAPTER XXI
+  INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION
+
+  Wild rubber contrasted with plantation rubber--Milling and
+  mixing--Preparation for vulcanising--Vulcanising                     301
+
+  CHAPTER XXII
+  TESTING OF PLANTATION RUBBER
+
+  Tests on raw rubber--Breaking strain--Behaviour of rubber
+  during milling, etc.--Preparation for testing--Tests on
+  vulcanised rubber--Choice of a formula--Physical tests               309
+
+  CHAPTER XXIII
+  THE PROPERTIES OF RUBBER
+
+  Raw rubber--Physical tests--Vulcanised rubber--"Inner
+  qualities" of raw rubber--Defects of crepe and sheet--
+  Variation in physical properties--Rate of cure--Influence of
+  various factors in raw rubber on rate of cure--Other types of
+  plantation rubber--Fine para                                         313
+
+  INDEX                                                                327
+
+
+
+
+LIST OF ILLUSTRATIONS
+
+
+                                                                    PAGE
+  SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING                       2
+  FELLING LIGHT (SECONDARY) JUNGLE                                       3
+  SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED                 4
+  NEW CLEARING                                                           5
+  TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON
+    VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING                   6
+  LIGHT JUNGLE                                                           7
+  DENSE JUNGLE                                                           8
+  CLEARING READY FOR PLANTING                                            9
+  NEW CLEARING: SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING
+    DRAINED                                                             11
+  TYPICAL YOUNG CLEARING, WITH TIMBER                                   15
+  TYPICAL YOUNG CLEARING, WITH TIMBER                                   17
+  TYPICAL YOUNG PLANTED AREA                                            20
+  ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA                            21
+  WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO
+    TAPPING                                                             24
+  FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED
+    TOO LONG                                                            25
+  TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE                   31
+  THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE AND
+    ON RENEWED BARK                                                     33
+  SINGLE CUT ON HALF CIRCUMFERENCE (HALF-SPIRAL)                        35
+  A [V]-CUT ON HALF THE CIRCUMFERENCE                                   37
+  SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE                             41
+  EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING                         44
+  ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING               45
+  1. SHOWING EFFECT OF "WINTERING"                                      48
+  2. NEW GROWTH OF YOUNG LEAF ON SAME TREE                              49
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      50
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      51
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      52
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      53
+  RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED WITH
+    FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER
+    COOLIE" BY SAMPLING OF LATEX                                        66
+  END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD
+    FOR RECEIVING LATEX AND FILLING TANK                                70
+  RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX                   71
+  ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH                      72
+  TWO VIEWS OF DILUTION AND MIXING TANKS                                81
+  UNIT MODERN COAGULATING TANK (TWO VIEWS)                              91
+  ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON THE
+    RIGHT                                                               92
+  CLOSER VIEW OF FOREGOING                                              93
+  ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF
+    GRAVITATING LATEX                                                   95
+  A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION             96
+  A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION
+    TANKS, RAISED, ON THE LEFT                                          97
+  THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN THE
+    FACTORY                                                            108
+  THE NEWER METHOD OF HANGING IN THE OPEN AIR                          109
+  THREE GRADES OF CREPE RUBBER                                         111
+  A WASHING SHED                                                       112
+  DRYING GRAPH. PALE CREPE (THIN)                                      140
+  A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT                 155
+  ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT                   157
+  A BATTERY OF MACHINES                                                165
+  "THIRD MILE" TYPE; HORIZONTAL DRUM                                   190
+  "THIRD MILE" TYPE OF FURNACE, USED IN CONJUNCTION WITH "THIRD
+    MILE" SMOKE-HOUSE                                                  190
+  SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE)                  193
+  PATALING TYPE OF FURNACE                                             193
+  LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED
+    VENTILATORS PERMANENTLY OPEN                                       194
+  BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE
+    BUILDING, BUT FED FROM OUTSIDE                                     195
+  GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES             196
+  NEAR VIEW OF SHELTER                                                 197
+  "THIRD MILE" TYPE OF SMOKE-HOUSE                                     199
+  GENERAL VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE                   201
+  GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND FACTORY
+    BUILDINGS                                                          202
+  VIEW OF PLATFORM OF "DEVON" SMOKE-HOUSE; DOORS OF COMPARTMENTS
+    OPEN, AND ONE RACK PARTIALLY WITHDRAWN                             203
+  DOUBLE "DEVON" SMOKE-HOUSE OF BRICK, WITH ROOF OF CHINESE
+    TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM
+    SMOKING CHAMBERS                                                   204
+  SIDE-VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL
+    ARRANGEMENT FOR STOKING FURNACES                                   205
+  FRONT VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE                     206
+  SIDE-VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE                      207
+  THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT                   210
+  SUGGESTED ARRANGEMENT OF BUILDING                                    218
+  THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM "SPOT"
+    DISEASE                                                            237
+
+
+
+
+THE PREPARATION OF PLANTATION RUBBER
+
+
+
+
+PART I
+
+FIELD OPERATIONS
+
+
+
+
+CHAPTER I
+
+_PLANTING_
+
+
+To criticise the methods of the pioneer planters of _Hevea Brasiliensis_
+presents no difficulty in the light of present comparative knowledge, and
+to be "wise after the event" is a failing which is not confined to those
+interested in modern planting methods. Looking at the matter broadly,
+however, it must be acknowledged that the pioneers, wrong though they may
+have been on some points, did remarkably well, considering that there
+existed no real knowledge on the subject and that the methods employed were
+perforce of an empirical nature. Although we know a little more concerning
+the scientific aspects of rubber planting, the sum total of that knowledge
+does not justify any drastic criticism of the methods employed by our
+predecessors. In fact, although we may be of opinion that on general lines
+there is little now to be learned regarding the planting of _Hevea
+Brasiliensis_, our present knowledge does not preclude the possibility that
+future investigations may bring against us charges similar to those
+sometimes levelled at the earlier planters.
+
+The main theme of the present volume is that of the preparation of rubber
+for the market. Hence it is not proposed to deal in detail with the work
+attaching to the opening and development of rubber estates. For this the
+reader is referred to the literature dealing specifically with rubber
+planting. Certain points in connection with planting may advantageously be
+treated in a general way according to modern knowledge, and of these it is
+proposed to discuss a few in the following pages.
+
+[Illustration: SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING.]
+
+SEEDS.--The view is now generally held that many areas were planted from
+seed which was not collected in a discriminate manner; and that probably
+the comparatively low yields obtained on areas of some estates may be due
+to the employment of seed from a poor strain. To be able to decide whether
+such explanation fits the case demands a full knowledge of all the possible
+factors governing the question of yields. It may, or may not, be a fact
+that seed from a poor strain is wholly or partially accountable for low
+yields; but whatever the degree in which the seed influences the result, it
+is an axiom that to obtain the best results in all planting industries a
+most judicious selection of seed should be made. In short, seed obtained
+from good-yielding specimens by selective treatment will eventually produce
+progeny of good-yielding strain.
+
+[Illustration: FELLING LIGHT (SECONDARY) JUNGLE.]
+
+The recognition of these principles as applied to the planting of _H.
+Brasiliensis_ has focussed recent attention upon the desirability of
+planting nurseries with seeds obtained from those trees which are known to
+be good producers of latex of normal consistency. It does not follow that
+the tree of most rapid growth and development is necessarily the best
+yielder; such is often not the case. In the matter of selection, therefore,
+one has to take other standards than that of size; and the issue is
+narrowed chiefly to a consideration of the yields of latex given by
+individual trees. It has been found by various experimenters that there is
+no necessity to proceed to such a refinement as the determination of the
+actual weight of rubber yielded. The dry rubber content of latices from the
+same trees is found to be so comparatively regular, allowing for climatic
+changes, that it is sufficient for the purposes of selection to measure the
+volumes of latex yielded by individual trees.
+
+[Illustration: SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED.]
+
+Unfortunately the industry is so young that the question of seed selection
+yet awaits study. The task presents certain practical difficulties, and
+would be by no means so easy to control as in the case of seed selection
+from other plants. It will be obvious that several generations of trees
+raised from selected seed would have to be under observation before any
+sound deductions could be made from statistics obtained in the course of
+the work. Thus the problem of seed-selection as it concerns the
+establishment of a high-yielding strain would involve many years of
+observation on the part of a trained man. Unfortunately neither the man nor
+the facilities for such experimental work exist at the present moment in
+the Federated Malay States. On the scientific side the industry is
+incommensurably staffed, and most of the workers' time is occupied with
+routine work connected with estate practice.
+
+[Illustration: NEW CLEARING.
+
+In the middle distance, felled trees awaiting burning; in the foreground, a
+flat and wet area with main drainage outlined.
+
+(_By courtesy of the manager of Membakut Estate, British North Borneo._)]
+
+[Illustration: TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON
+VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING.]
+
+SELECTION.--It is possible, however, that the question of strain
+improvement will be solved in another manner than that of successive
+breeding from the seeds of high-yielding trees. Such investigatory work is
+now occupying the attention of scientific organisations in the East, and
+credit is due to the stations in Java which have begun experimental work in
+this direction. In brief, the scheme may be outlined as follows. Trees
+known to be uniformly good yielders are kept under observation, and the
+seeds gathered carefully. These seeds are germinated in a special nursery,
+and the best-grown seedlings are selected for further operations. At a
+certain stage a bud is taken from a high-yielding parent tree and grafted
+upon the stem of the seedling. When this has "struck" the original head of
+the seedling is removed. This ensures that one has in the seedling both the
+stem and future branch system of the same strain as the parent
+high-yielding trees. It is possible to go a step farther, and by certain
+processes induce a new root system to grow above the existing roots, which
+are then removed. One is then able to guarantee that the roots, stem, and
+branches will be of the original high-yielding strain. An objection
+sometimes made against the third operation of inducing a new root system is
+that the original tap-root is removed and that the subsequent system
+consists only of laterals. Against this argument may be quoted the observed
+fact that in actual development any one of the laterals may under such
+circumstances function eventually as a tap-root.
+
+[Illustration: LIGHT JUNGLE.]
+
+On the whole, this system of propagation receives the approval of
+investigators, and removes the objections which may be advanced against the
+development of a scheme entirely founded upon successive breedings from
+selected seed. The course of the investigations, also, are thereby
+shortened considerably. Care must be exercised in the work of obtaining and
+grafting the buds, but it has now been proved that by exercising reasonable
+precautions which are not beyond the intelligence and ability of
+subordinates, an extremely high percentage of success can be attained.
+
+[Illustration: DENSE JUNGLE.]
+
+Until such time as this process becomes practicable the inception of a
+planted area must follow the lines usually adopted.
+
+NURSERIES.--The usual practice is to obtain seeds from some estate which
+has a reputation for good yields and for exercising care in the gathering
+and shipping of seeds. The seed is planted in specially prepared beds, and
+the percentage of germination noted for future reference. The plants should
+be tended carefully, and close observation made for the detection of
+disease or pests. It is not uncommon to find that owing to lack of care in
+the preparation of the seed-bed, the young plants are attacked by disease.
+
+[Illustration: CLEARING READY FOR PLANTING.
+
+Surface timber removed, but stumps remaining.]
+
+STUMPS.--At a stage, varying according to the requirements of the estate,
+when the plants are from twelve to eighteen months old, they are lifted
+from the earth. The roots and head are cut off, and the "stump" is ready
+for immediate planting in the field. Naturally any appreciable delay in
+planting, or unfavourable weather conditions, will militate against the
+chances of successful "striking"; and it is not uncommon to find that a
+certain number of "supplies" will be necessary.
+
+SEED AT STAKE.--A method sometimes adopted is to put out seed in the field,
+in prepared holes which indicate the exact position of the future trees.
+Usually three seeds are placed in each hole, and if two or three germinate,
+the plant having the healthiest appearance is retained, and the others
+removed. The possible objections to this method of planting are obvious to
+those acquainted with field conditions, but in actual practice planting
+seed "at stake" has often proved highly successful. Naturally the results
+obtained must depend upon the selection of good seeds, the care exercised
+in the preparation of the "holes," weather conditions, and the
+discrimination exercised in the selection of the plants to be
+retained--apart from such disabilities as the depredations of rats and
+other pests.
+
+BASKET PLANTS.--Yet another and perhaps the most popular method at present
+is the germination and growth of seedlings in baskets specially constructed
+for the purpose. These plants are kept under observation until of the
+required age and growth. They are then conveyed to the field, and the
+baskets are planted in prepared holes. The baskets, being of vegetable
+material, are liable to be attacked by various diseases while in the
+nursery or after planting. It is considered advisable, therefore, to treat
+them by dipping into some disinfectant such as tar, or a mixture of tar and
+one of the common proprietary disinfectants. Otherwise a disease may be
+conveyed from the basket to the seedling.
+
+PREPARATION FOR PLANTING.--There can be no other opinion than that ideally
+all land required for planting should be perfectly clear of timber of every
+description. After felling and burning, under ordinary conditions a certain
+amount of clearing is effected, but in actual practice this amounts to
+comparatively little. Big logs and stumps are left because the cost of
+clean clearing is judged to be prohibitive and non-economic. Surface timber
+is gradually cleared in the course of development, and usually large stumps
+are the last to be tackled. The objection to this procedure is really not
+strong, but unfortunately an important point is generally overlooked.
+Granted that most of the dreaded diseases travel beneath the surface of the
+ground by means of buried timber, it is plain that as far as stumps are
+concerned, the chief source of danger lies in the existence of the roots.
+If these were carefully exposed and removed, the isolated stumps would then
+not be such potential infection points. It follows from this argument that
+the importance of removing buried timber cannot be too strongly insisted
+upon. It is not uncommon to find that some years after the opening of an
+estate, and after surface timber has been removed, a large number of trees
+are affected with _Fomes lignosus_ (formerly known as _Fomes semitostus_).
+Such cases are directly attributable to the existence of buried timber, and
+no local treatment will be successful unless the whole of the area is dug
+over carefully, and all pieces of timber removed.
+
+[Illustration: NEW CLEARING; SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING
+DRAINED.
+
+(_By courtesy of manager, Membakut Estate, British North Borneo._)]
+
+SILT CATCHMENT TRENCHES.--Granted the ultimate necessity of clean clearing,
+it becomes necessary to take some precautions to prevent loss of soil by
+"wash" in young areas planted on sloping land. An argument often used in
+extenuation of the practice of allowing large surface timber to remain
+until it becomes rotten is that it is an aid in preventing loss of soil by
+wash. Its removal necessitates the institution of some method of preventing
+"wash." The establishment of terraces on steep slopes tends to the
+achievement of the desired result, but this method is not extended to more
+moderate slopes where loss by wash is still considerable. It is the opinion
+of the writers and others that the general case calls for the institution
+of silt catchment trenches, which, as the name denotes, fulfil the duty of
+catching any surface soil and of retaining rainwater. These trenches are
+usually laid out on contour, and do not exceed a length of 20 feet. They
+are usually from 18 inches to 2 feet wide and deep, and are so arranged on
+the slope that they occupy overlapping positions. The actual number of
+trenches required will depend upon the angle of slope; the steeper the
+slope the greater the number required--_i.e._, the shorter will be the
+length of slope between any two trenches. Given a clean area, it is obvious
+that the momentum acquired by running water (and hence the amount of soil
+removed) on any one slope will depend upon the distance travelled. It is
+advisable, therefore, to place a larger proportion of the trenches on the
+upper part of the slope than on the lower, so as to guard against the
+breaking down of the trench system under an abnormal downpour of rain.
+
+On land thus prepared the writer has seen areas successfully planted,
+which, under ordinary conditions, were condemned as being too steep for
+planting. It is true that these trenches necessitate continual upkeep until
+the soil becomes well shaded by trees, but the actual amount of work
+demanded in cleaning and maintaining the trenches will depend largely upon
+the thoroughness with which the original work was planned and executed.
+Whatever may be the weaknesses exposed as a result of providing an
+insufficient number of trenches of inadequate dimensions, there can be no
+question that they are a necessity.
+
+
+
+
+CHAPTER II
+
+_FIELD MAINTENANCE_
+
+
+CLEAN WEEDING.--Intimately connected with the growth and development of the
+rubber tree one has to consider the conditions under which it is allowed to
+mature. The argument has been used that, since the habitat of _Hevea
+Brasiliensis_ is in the jungle, we should be proceeding against nature by
+introducing conditions unlike those under which the "wild" rubber tree
+grows. It is difficult to treat such an argument seriously, as by quoting
+parallel instances in arboriculture it could be shown that growth,
+development, and yields are improved by cultivation of "wild" plants.
+
+It needs small experience with rubber-tree plantations to be convinced of
+the necessity for dealing with other growths, which would otherwise soon
+surround and overshadow young rubber trees.
+
+Apart from checking and preventing woody undergrowths it is considered
+advisable to keep the ground more or less free from light vegetable
+growths, which are roughly grouped under the heading of "weeds."
+
+Naturally, if these weeds are allowed to flourish and seed, their eventual
+eradication may be a matter of extreme difficulty and expense. It is the
+aim, therefore, of properly conducted estates generally to institute such a
+system of work that the weeding-gangs cover the whole estate at regular
+intervals; and, as a general rule, it may be accepted that the shorter the
+interval between successive visits by the gang to any particular area, the
+easier it is to keep weeds in check, and the cheaper the work will
+eventually be done. This procedure defines roughly what is implied by the
+term "clean weeding," and it is the policy adopted by most estates.
+
+Strict adherence to this practice in rubber cultivation has been inculcated
+by the older school of planters who obtained their experience in the
+cultivation of other crops such as tea, coffee, tobacco, etc.
+
+In latter years the wisdom of scrupulous clean weeding under all conditions
+has been questioned; and there can be no doubt that under certain special
+conditions a continuation of the policy of clean weeding is calculated to
+produce, in course of time, more harm than benefit. As an instance, the
+case might be cited of steep slopes on poor land. Continual clean weeding
+on such areas will lead eventually to a great loss of the surface soil,
+unless some precautions are adopted for catching and retaining the fine
+silt particles. It is to be noted that such a type of soil and slope, when
+the shade is appreciable, often produces no weeds heavier in growth than a
+very light grass. It is urged that the necessity for strict clean weeding
+on such soils does not exist, and, in fact, that it would be an injurious
+policy. Such arguments appear to be well founded in experience, and the
+writers are in thorough agreement that such special cases deserve special
+consideration. Rigid adherence to a policy of clean weeding, without regard
+to special conditions, would be most inadvisable.
+
+Nevertheless, such exceptional cases do not detract from the wisdom of
+clean weeding in general. Every planter of experience realises how easily
+fields become infested with weeds if the regular work is suspended or
+delayed. It is probably quite true that the harm due to the presence of
+some weeds on an occasion is negligible; but apart from this debatable
+point, there is the solid fact that if once an area is allowed to become
+weedy it may soon demand a much greater expenditure to bring it back to
+normal condition than if it had been regularly weeded. This is common
+experience, and for that reason alone a general policy of clean weeding is
+thoroughly sound; especially if combined with some system of
+silt-retention.
+
+GRASS SQUARES.--On some estates the practice of clean weeding is undertaken
+in combination with a system of silt-retention, which depends upon the
+development and maintenance of ridges. These are built up from the débris
+of weeding in the form of hollow squares. Grass is allowed to sprout and
+grow in these ridges, and when it attains a certain height it is trimmed
+down so as to keep it within bounds. The soil within the hollow square is
+clean weeded; and it is maintained that loss of soil by wash is avoided.
+Under certain conditions there is a great deal to be said in favour of the
+method, but in the opinion of the writers it should be regarded only as a
+method of expediency. It is not to be preferred to the more thorough
+practice of soil-retention by means of silt-trenches, although the latter
+method may be slightly more expensive in the end.
+
+[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER.
+
+Planted "rubber-stump" in foreground.]
+
+"LALLANG" ERADICATION.--The greatest bugbear of the planter in connection
+with weeding is the incidence of lallang. Many proposals have been put
+forward at various times for the complete eradication of this pest; but at
+present, under ordinary circumstances, there would seem to be no better
+method than by heavy and deep digging, followed by regular attention. The
+method is acknowledged to be expensive, but any half-hearted measure
+otherwise taken will eventually prove to be even more costly.
+
+One has to differentiate, of course, between the incidence of lallang
+attributable to negligence on the estate itself, and the occasional
+outbreaks near boundaries, due to seeds having been wind-borne from patches
+of lallang outside the boundaries But, in general, it would be safe to
+remark that the appearance of lallang could be taken as evidence of a
+failure to cover the area at sufficiently short intervals.
+
+As already intimated, the usual method of eradication of areas of lallang
+is by thorough digging, and the exposure of the strong root system to the
+sun. As a matter of interest it may be noted that recently some success has
+been obtained by another method[1] on areas which one may have in view for
+planting at some future date.
+
+[1] "Eradication of Lallang," W. P. Handover, _The Planter_, Vol. I., No.
+1, August, 1920.
+
+It consists in the employment of _Mimosa gigantea_, which eventually
+smothers the growth of lallang.
+
+The seeds are sown broadcast, in drills, or in pockets, amongst the
+lallang. In the course of about three months it overtops the grass and
+proceeds to travel. At this stage the whole mass is pressed down, and the
+pressing is repeated at regular intervals. Under favourable conditions, in
+about twelve months, an impenetrable mat has been formed, which gradually
+forms a good mulch. When it is desired to remove the Mimosa, the mass
+(pressed down) is cut and rolled up like a carpet. Cleared in this manner,
+the area then needs regular weeding, in order to check the development of
+any stray lallang shoots. In actual practice it was found that the cost of
+this method was approximately two-thirds that of the usual digging method.
+
+GREEN COVER PLANTS.--Some years ago it was quite common to find green
+cover-plants employed on estates with the primary idea of minimising
+weeding costs. With most of these it was found later that their value was
+not real, and that they harboured diseases, and pests. Moreover, when they
+were removed, it was often found that an abundant crop of lallang and
+weeds resulted.
+
+There can be no question that certain plants can be employed with
+advantage, not only in the control of weeds, but also by reason of benefit
+to the soil in which they are established. These plants are leguminous, and
+their use is restricted almost entirely to young areas, inasmuch as they
+will not continue to grow when shade becomes marked. Of those best known in
+modern practice might be mentioned _Tephrosia candida_ (Boga bean),
+_Centrosema Plumerii_, and _Dolichos Hoseii_ (Sarawak bean).
+
+[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER.
+
+Young rubber plants in foreground. Two of these are easily distinguishable,
+both with small crowns of leaves.]
+
+It is wrong to imagine, however, that the establishment of such leguminous
+cover-plants obviates weeding. So far is this from being the case, that in
+practice it is found that the weeding "rounds" must be conducted at first
+with the same regularity as in ordinary working, but that naturally there
+is much less work to be done.
+
+As the plants develop, they can be pruned or dug into the soil, as the case
+may be. The addition of the green material to the soil, either by digging
+or by burying in open trenches, is calculated to cause improvement in the
+condition of the soil. There may thus be a close connection between
+weeding, soil conservation, and soil improvement.
+
+
+
+
+CHAPTER III
+
+_THINNING OF AREAS_
+
+
+On this subject there is unanimity regarding the necessity for the
+operation. Divergence of opinion exists only as to a matter of degree.
+
+On the one hand there is the school of planters who would advocate the
+advisability of planting up to, say, 200 trees per acre, with subsequent
+thinning out by selection. At the other extreme there is the opinion that
+we should plant only a few more trees per acre than it is intended
+eventually to maintain, the argument being that by this method the growth
+and development of individual trees will be so much greater than in close
+planting that the necessity for drastic thinning out will not arise.
+
+Unfortunately for the latter school, a very important point is
+overlooked--viz., that size and general development are not criteria of
+yielding capacity. It might thus follow that a stand of ninety well-grown
+trees per acre might give very disappointing yields per acre. In a few
+instances this has been noted with 30 by 30 feet planting, but it is
+doubtful whether the factor influencing such results has been appreciated.
+
+The apostles of close-planting have this in their favour: that if the trees
+to be removed are selected on proper lines, it is possible to have all
+remaining trees of comparatively high-yielding strain. This is a very sound
+argument, but its practicability is limited very largely by the question of
+early growth and development. It would seem the sane course in any event
+not to plant more trees per acre than may grow normally, and without branch
+or root interference up to the fifth year (the normal first year of
+tapping).
+
+Before this stage has been reached, stunted or deformed trees will have
+been noted and removed, so that in the first year of tapping thinning
+proper can be commenced. In the past this has been effected wholly by
+selection of trees according to their general appearance and situation; but
+it is now safe to predict that future operations will be based upon sounder
+and more scientific lines.
+
+Trees will be selected for removal according to their individual yields, a
+standard which we have been advocating for years without much practical
+success. In Java and Sumatra much good work has been done in this
+direction, and recently a commencement has been made in the F.M.S.
+
+[Illustration: TYPICAL YOUNG PLANTED AREA.
+
+Heavy original jungle timber.]
+
+It is within the daily observation of all planters that certain trees
+regularly give greater yields than others, and that such trees are not to
+be distinguished by size or general development. Moreover, with slight
+variations, it has been found that a good yielding tree is consistently a
+good yielder, and the converse holds true.
+
+If, therefore, measurements of individual yields are taken at intervals,
+and the results recorded during the first year of tapping of an area, an
+excellent guide is obtained for the first round of thinning. It is found
+in actual practice that five, or even three, readings during the year are
+sufficient to give the indication required. It is not essential that
+simultaneous readings should be taken over a large area; in fact, such a
+step is really impracticable at first. The simplest method is to employ
+either--
+
+(_a_) A small uniform vessel in which the latex is measured by means of a
+thin slip of bamboo upon which graduations are marked.
+
+(_b_) A glass measure graduated regularly.
+
+[Illustration: ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA.]
+
+In both cases it is immaterial what units are represented by the
+graduations--whether cubic centimetres, quarter ounces, half-ounces, or
+ounces, as long as the unit is not too large. It is preferable to employ a
+fairly small unit, so that in taking readings from young trees a wider
+range may be obtained between poor yields and good yields. In the case of
+older trees a larger unit may be taken.
+
+The first stage in the operations is to number all trees in the field to
+be tested, and to prepare a rough register, with three or five vacant
+columns opposite each tree number.
+
+It is not advisable to commence the record of yields until the panel of
+bark has been under tapping for a month or two. It is found that an
+intelligent coolie can be taught the method of measuring and rough
+recording. The latter is accomplished by means of marks made upon the
+virgin bark of the tree above the tapped area. The marks may be made with a
+tapping knife, by means of paint, or with a lead pencil. The simplest form
+of record consists in putting one mark for each graduation of reading.
+
+In practice it is found that, commencing about an hour after the first tree
+has been tapped (in the case of young trees) and following the course taken
+by the tapper, the measurer of yields is able to do about 2 full tasks (650
+to 750 trees) per diem. Each day progress is made through the field.
+
+Obviously on such a small scale and utilising only one measuring coolie the
+comparison is restricted very much; but in any case this is immaterial as,
+owing to the personal equation of the tapper, comparison strictly should be
+limited and internal--_i.e._, it should really be confined to one task only
+at a time. In this way the worst trees in any task are indicated.
+
+The keeping of the records may be entrusted to a field clerk, but is better
+placed in the hands of a European. The register is taken into the field and
+the rough records found on the trees are noted in the columns against the
+tree number.
+
+Most planters are aware in a general way of the disparity between the
+yields of individual trees, but they would probably be surprised if they
+undertook the institution of such records.
+
+The following figures must not be taken as typical. They represent the
+average results from several tasks in a young field from which all
+ill-grown and deformed trees had been removed. It is immaterial what the
+units represent, as they are purely arbitrary and were selected for the
+purpose of obtaining a fairly wide range.
+
+Any trees which failed to yield sufficient latex to reach the first mark
+were registered at zero. The following percentages were obtained:
+
+  Zero                  3 per cent.
+  Above mark 1          6    "
+    "     "  2         16    "
+    "     "  3         42    "
+    "     "  4         12    "
+    "     "  5         14    "
+    "     "  6          6    "
+    "     "  7          0    "
+    "     "  8          1    "
+    "     "  9          0    "
+                      ---
+                      100    "
+
+It may be remarked that, judging by ordinary standards, it was impossible
+to discriminate between good yielders and others, and if thinning were to
+be done on the usual lines it is quite possible that some of the best
+yielding trees would be removed.
+
+Taking the mark No. 5 as the datum line, it will be noted that 79 per cent.
+of the trees come below and 21 per cent. above. In the latter proportion
+the majority lie close to the datum line. It will be seen that there are
+outstanding yielders even amongst these young trees, and that it would be
+possible to mark about 10 per cent. of the stand per acre at once for
+removal in the first round of thinning.
+
+In the case of old trees it is possible that one would encounter greater
+extremes of yields than those shown in the foregoing table, especially if a
+certain amount of thinning had been done previously on empirical lines.
+Sufficient has been written to show that the only reasonable basis for
+selection of trees in thinning is that of yields; and it is obvious that if
+the method be adopted the future yield per acre of any area is bound to be
+in excess of the same area as thinned on rule-of-thumb lines.
+
+YIELDS PER TREE.--A great feature is made in estate reports of the figure
+showing the average yield per tree per annum. Assuming an area to be
+yielding at the average high rate of 540 lbs. per acre per annum, with an
+average stand of ninety trees per acre, the yield per tree per annum
+averaged over all trees is 6 lbs. Keeping in mind the test-figures on a
+previous page, it will be obvious that some of these trees may have given
+very much more than 6 lbs. during the year, and some less. In view of
+present information it would not be surprising to find that a few might
+have been yielding upwards of 15 lbs. per annum. Unfortunately this
+information is only to be obtained by individual tests, and under normal
+estate conditions the facts escape notice. Cases are known in which
+out-standing individual trees have been known to yield at the rate of 25
+lbs. and more per annum.
+
+[Illustration: WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO
+TAPPING.]
+
+[Illustration: FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED
+TOO LONG.
+
+Note height and comparative lack of girth.]
+
+FUTURE YIELDS PER TREE.--It has been shown that by selective methods based
+on yields, poor trees can be eliminated. Whether by a process of
+seed-selection or by means of propagation based on bud-grafting and
+marcotting, it needs no great stretch of imagination to forecast future
+conditions under which trees may be bred which will be capable eventually
+of giving an average yield of 25 lbs. per annum over any given area.
+Yields of 1,000 lbs. per acre per annum should be obtained easily.
+
+TREES PER ACRE.--This brings us to the question as to how many trees one
+should leave to the acre after thinning operations. Figures have been given
+by various authorities, but it appears to the writer at the present time to
+be impossible to lay down a general rule. So much depends upon conditions.
+In certain cases where the soil is admittedly poor, the average growth
+below normal, and thinning has been postponed too long, the writer has been
+forced to the conclusion that it would be most inadvisable, and
+commercially unsound, to reduce the stand of trees below 120 per acre. In
+such instances the average yield per tree equalled only 3 lbs. per annum,
+and although the trees were upwards of nine or ten years old the crowns
+were small and sparse. It is doubtful whether such trees will ever exhibit
+any further development, and to thin them further would probably lead only
+to a diminution in the crop per acre.
+
+Under normal conditions of growth an arbitrary figure of eighty trees per
+acre has been selected as a standard by many estates. In these cases it
+would probably be correct to state that thinning was undertaken on almost
+purely empirical lines--_i.e._, that trees were not selected by tests of
+individual yields. As far as such a method retained the apparently most
+vigorous trees it was successful; but in view of what has been written it
+might explain some of the disappointing results which have followed upon
+such a system of thinning.
+
+It will be clear that any decision regarding the number of trees to be
+retained must be derived from a study of the detailed results of individual
+tests. If the large majority of the trees appear to be fairly uniform in
+yields the first thinning must be confined to comparatively few trees.
+Where there is, on the other hand, a good percentage of high-yielding trees
+the final stand per acre may be appreciably less. Unless and until such
+information is available, one cannot give any definite opinion as to the
+requisite number of trees to be retained per acre.
+
+Similarly, intelligence must be displayed in deciding which of several
+uniformly-yielding trees should be removed. In the average sense of this
+consideration one must pay no attention to symmetry of spacing, but when
+dealing with trees of fairly uniform yields one needs to study the
+characteristic development of the trees individually, in order to retain
+those which would appear to be most favourably situated with regard to
+surrounding trees.
+
+
+
+
+CHAPTER IV
+
+_TAPPING SYSTEMS_
+
+
+Broadly there are only two methods employed in obtaining the latex from
+_Hevea Brasiliensis_. The first is that employed in South America, where
+incisions are made by means of a light axe. The other is the system of
+excision, or paring, of the bark practised on plantations in the East.
+
+In the early days of the plantation industry, the South American method
+seems to have been employed, and the writer has knowledge of trees on one
+of our best-known estates in Malaya which still exhibit the outward and
+visible signs of that method. At a comparatively early stage, however, the
+method of excision was introduced. Curiously enough there appears to be no
+record of its inception or of the individual who was responsible for the
+substitution of this method. We have been so accustomed to regard it as one
+of the ordinary facts of estate procedure, that this point seems to have
+escaped notice and enquiry.
+
+As a variant of these two main methods, a slight vogue was for a short
+while obtained by the operation known as "pricking." This was generally
+combined with excision of bark, and was then known as the "paring and
+pricking" method; but the simple operation of pricking alone had its
+adherents, and various forms of instruments were designed to achieve the
+object. As a means for obtaining a flow of latex, pricking may have been
+effective, but the general difficulties attaching to the collection of the
+latex was such as to put the method out of favour.
+
+In the employment of "paring and pricking," a thin shaving of bark was
+excised on one occasion. At the next tapping no bark was excised, but a
+pricking instrument was used along the previously cut surface. It was not
+proved that any advantage was gained by this method, which was more
+commonly employed in Ceylon than elsewhere, and it would be surprising to
+find it in use at the present day.
+
+In the ordinary way the method of excision is practised in such a manner
+that the "cut" gradually descends to the base of the tree.
+
+Planters with original views, and of an enquiring nature, often query the
+common practice; and it has been suggested that "as the latex descends by
+the force of gravity," one's paring should be done in an upward direction,
+thus obtaining a greater pressure of latex--and hence a greater flow. It
+will be obvious that it would be no simple matter to collect effectively
+the latex thus obtained from the under edge of a sloping cut, but apart
+from this the argument would appear to be founded upon what is now accepted
+to be a fallacy--viz., that the latex _per se_ is manufactured in the
+leaves and gravitates down the tree.
+
+FORMER SYSTEMS OF TAPPING.--To hark back ten years in the plantation rubber
+industry is equivalent to delving into history, since development has been
+so rapid. It was then thought necessary to place upon the trees a number of
+simultaneous cuts which the modern planter would judge to be inconceivably
+excessive. Were it not for evidence in the shape of photographs extant, it
+would be difficult to convince a young planter that such systems were
+employed.
+
+It was not uncommon for trees to have from six to ten cuts, sometimes all
+placed on one half of the tree in a herring-bone fashion, and sometimes
+divided into two portions, each of which tapped the opposite quarter panel
+of the tree's circumference. Such superimposed cuts were spaced from 1 foot
+to 18 inches apart.
+
+On other occasions, a spiral cut was employed, commencing at a height of,
+say, 5 feet, and gradually descending to the cup at the base of the tree.
+
+Later systems varied from several cuts on a half-circumference, or on a
+quarter of the tree, tapped either daily, or on alternate days, to cases in
+which one-third or one-fifth of the tree was employed. Also popular were
+the systems of the [V] and half-spiral cuts on half the circumference.
+
+It did not take long to be recognised that with all these systems demanding
+a number of simultaneous parings from the same panel of bark, the rate of
+excision was so heavy that the period available for the renewal of bark was
+insufficient for continuous tapping.
+
+As a result most of the systems specified have fallen into desuetude, and
+the tendency has since been to reduce the number of cuts, or the
+periodicity of tapping, so as to allow for increasing periods of bark
+renewal.
+
+In the earlier days, a period of four years was thought to be an extremely
+generous allowance, whereas six years is now becoming recognised as a
+minimum necessity. Eight years is not regarded as extravagant, while with
+older bark on some estates periods of ten and twelve years have to be
+allowed for full renewal. Even so no finality has been reached, and no
+general rule can be laid down. Local conditions of planting and growth
+exercise great influence, and the writers have in mind instances in which a
+period of eight years has proved to be insufficient even for a first
+renewal after the excision of virgin bark.
+
+In the main the most popular systems of tapping are:
+
+     (_a_) One cut on a quarter of the tree, tapped daily.
+
+     (_b_) One cut on a third of the tree, tapped daily.
+
+     (_c_) One cut on half the circumference, tapped on alternate days.
+
+     (_d_) A [V] cut on half the circumference, tapped on alternate days.
+
+Variants and extremes are:
+
+     (1) One cut on a quarter, tapped on alternate days.
+
+     (2) One cut on a half, tapped daily.
+
+Superficially viewed the latter is four times as strenuous as the former,
+and the relative position seems to be inexplicable. It may be explained
+that as a rule the former system is practised on old trees with poorly
+renewed bark, in order to allow for adequate bark renewal; and the latter
+is employed in opening young trees just brought into tapping, when the rate
+of bark renewal is at a maximum.
+
+[Illustration: TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE.]
+
+A few estates in this country still continue to tap trees by means of two
+superimposed cuts on a quarter of the tree. This was a very popular system
+some four or five years ago, but it has come to be recognised by practical
+experience that any system employing superimposed cuts leads to a high
+consumption of bark without proportionate increase in yield. For instance,
+if one compares the system of two cuts on a quarter tapped daily with a
+similar system employing only one cut, one finds that the major quantity of
+latex is yielded by the lower cut, and that the single-cut system which
+excises approximately half the amount of bark gives about 80 per cent. of
+the yield obtained by the tapping of two superimposed cuts.
+
+Of experiments to test the relative values of different systems of tapping
+there have been many. Most of them suffered from the initial handicap that
+they dealt with systems which were then popular. In order to obtain any
+valid result they had to be undertaken over a long period. Meantime there
+was a progressive movement in actual estate practice towards a greater
+conservatism in bark removal, and hence the experiments as originally
+planned lost value.
+
+Moreover, in Malaya it was difficult for experimenters to obtain practical
+support in the form of areas of trees suitable for experiment. As a result
+experiments were often confined to small blocks of trees, and a small
+number of blocks, from which any conclusions derived were subject to
+considerable errors of experiment. Often comparisons were made between only
+two blocks, and no allowance was made for varying factors, such as initial
+differences in yielding capacities of the trees, soil conditions, or the
+personal equation of the tappers. As a general rule, therefore, the results
+were vitiated to a very appreciable extent.
+
+All these factors were later taken into consideration in an experiment
+undertaken on behalf of the Rubber Growers' Association. In this instance
+unique facilities were provided by the London Asiatic Rubber Company on
+their property at Semenyih Estate, and it is only fitting that the company
+should receive the recognition which its enterprise deserves.
+
+It would have been a great advantage to have included in that experiment
+other features which have since come into prominence, but the original
+scope of the experiment had to be confined to the point of comparing yields
+obtained in making comparative tests based on one system of tapping with
+different frequencies. Such data were required as a check upon a Ceylon
+tapping experiment which had attracted much attention. In that experiment
+trees were tapped at intervals ranging from one day to seven days; and it
+was concluded that after a period of three and a half years trees tapped
+with greater intervals gave yields equalling or exceeding those obtained
+from trees tapped with shorter intervals.
+
+[Illustration: THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE
+AND ON RENEWED BARK.]
+
+In the Semenyih experiment the system chosen was that which had the
+greatest contemporary vogue--viz., two superimposed cuts on a quarter of
+the tree. The various blocks were tapped respectively every day, every
+second day, and every third day.
+
+It was found that the conclusions drawn from the Ceylon experiment were not
+confirmed. After a period of three and a half years' continuous tapping
+neither the alternate-day system nor the third-day system gave results in
+any way approximating to the yield of the daily system.
+
+The actual average yields from these systems over the whole period were in
+the order of--
+
+    _Daily._          _Two Days._      _Three Days._
+  100 per cent.      60 per cent.      45 per cent.;
+
+and throughout the course of the experiment neither of the other sections
+showed any appreciable improvement in position relative to the daily
+section.
+
+In actual yields "per tapping" over the whole period the alternate-day and
+the third-day divisions showed advantages of 20 and 35 per cent.
+respectively over the daily portion.
+
+At the beginning of the second year of experiment another section of blocks
+was opened with a single cut on a quarter, tapped daily. This enabled
+direct comparison between the values of one cut and two cuts on a quarter
+in daily tappings and between a daily single cut and two cuts tapped
+alternate daily.
+
+It appeared that the daily single cut yielded over the period of experiment
+80 per cent. of that obtained by tapping two cuts daily; and that in the
+comparison between two cuts tapped alternate-daily and a single cut tapped
+daily the latter had an advantage of about 40 per cent. in yield.
+
+This result has been used by advocates of daily tapping generally, but it
+does not constitute a fair argument, inasmuch as the single cut was tapped
+twice as often, and its position was always relatively low on the hole of
+the tree. It has been shown in the comparison between the daily single cut
+and the two cuts daily that the influence on yields of the superimposed cut
+is relatively small. A fairer comparison would have been obtained if the
+two cuts tapped alternate-daily had been either amalgamated to form one
+long cut on half the tree or to form a [V] on half the tree, thus placing
+the cuts in the opposing sections on the same level. With the knowledge
+that the yield obtained from cuts is _always greater per tapping_ by using
+the alternate-daily system, it would appear to be plain that the one long
+cut on half the tree would at least equal the yield of the single short cut
+tapped daily on a quarter tree.
+
+[Illustration: SINGLE CUT ON HALF CIRCUMFERENCE (HALF SPIRAL).
+
+_Note._--In this particular instance the cut is changed to the opposite
+half of the tree every half-year.]
+
+Unfortunately no opportunity has been afforded up to the present of
+definitely proving this point by prolonged experiment under strict
+conditions. It is true that the view is held strongly in some quarters as a
+result of the experience of managers, chiefly on their own estates, that
+alternate-daily tapping generally gives better yields than daily tapping.
+
+In a number of instances this view is probably correct, and the writers are
+in agreement; but it is necessary to clear away some misconceptions which
+confuse the issue. In the main there are two schools, one of which plumps
+for alternate-daily tapping, while the other adheres strongly to daily
+excision. Great confusion exists, inasmuch as in many instances the
+disciples of these schools are really discussing different matters. In the
+case of managers who argue for alternate-daily tapping their experience is
+gained, with very few exceptions, from systems in which the excision covers
+half the circumference of the tree; whereas in almost all cases daily
+tapping is confined to a single cut on a quarter of the girth. Bearing on
+such a comparison there are, as far as the writers are aware, no reliable
+published experimental results. To compare the results obtained from one
+system practised on one estate with the results of the other system
+established on another estate is not strictly permissible, as we know that
+conditions generally may vary to an enormous degree.
+
+The controversy has raged, however, to such an extent that many who are not
+directly engaged in estate practice have obtained confused impressions. For
+instance, it appears to be the belief in some quarters that alternate-daily
+tapping, when applied to a single cut on a quarter of the tree, will yield
+more than an exactly similar cut tapped daily. In support of such a
+statement there does not appear to be any confirmation under normal
+conditions; although such a result might be obtained in the case of old
+trees which have been heavily over-tapped in the past, and on which the
+rate of bark renewal has been appreciably retarded. It might also be the
+case eventually when trees with the opposing frequencies have been tapped
+for a period extending into many years; but it is the opinion of the
+writers that under normal conditions such a result would be extremely
+doubtful.
+
+When we come, however, to a comparison of daily tapping on a single cut on
+a quarter with double the length of that cut on half the circumference, at
+the same height, tapped alternate-daily--whether in the form of one long
+cut or in the form of a [V]--we arrive at a contrast which gives a clear
+issue. As already stated, facts and figures of reliable experiment are
+wanting; but it is the opinion and experience of the writers that the
+alternate-daily system at least suffers no disadvantage on the point of
+yields, and in other respects, such as conservation of labour and costs, is
+superior to the daily system.
+
+[Illustration: A [V]-CUT ON HALF THE CIRCUMFERENCE.]
+
+
+
+
+CHAPTER V
+
+_TAPPING AND COLLECTING_
+
+
+TAPPING KNIVES.--The choice of a tapping knife is a subject upon which
+there is much divergence of opinion. This must be so because no known knife
+has such apparent outstanding superior features or claims as would enable
+one to settle the point. Moreover, the personal factor is so large that, as
+far as the knives in common use are concerned, it appears to exert the
+greatest influence. The possibility of obtaining the ideal knife, which
+will go to sufficient depth into barks of varying thickness to yield the
+maximum quantity of latex without wounding, is quite as remote at the
+present time as it was some years ago. Meanwhile the search for that ideal
+knife continues, and occasionally one learns of the alleged merits of some
+new instrument which, it is said, fulfils all requirements. It is only to
+be regretted, both for the sake of the inventor and for the expectant
+buyers, that the claims always fail in some one or more particulars.
+
+In Malaya probably the number of different types of tapping knives may
+amount to a half-dozen, but those most commonly in use are:
+
+     (1) The gouge--straight or bent.
+
+     (2) The ordinary farrier's knife.
+
+     (3) Modifications of the farrier's knife, such as the "Jebong."
+
+Argument on the respective merits of knives is popular, and discussion
+seems endless. It is claimed for the bent gouge that it is superior to the
+straight instrument, because, the leverage being downwards on the handle,
+the tendency is to lift the cutting edge upwards and out of the bark,
+whereas with a straight gouge the tendency is to push the knife downwards
+into the bark. It is claimed, therefore, that the average shavings taken
+off by the bent gouge should be thinner than those obtained by the use of
+the straight instrument.
+
+For similar reasons it is asserted that the "Jebong" and other
+modifications are superior to the original form of the farrier's knife.
+These points are generally accepted without great argument, but when
+comparisons are made between the gouge and the farrier's knife (with its
+modifications) the opinions of planters are so varied and conflicting as to
+be almost irreconcilable. Two opinions based on experience with both types
+of knives are often wholly contradictory.
+
+There can be no doubt that the likes and dislikes of operative coolies have
+a considerable influence in determining the measure of success obtained
+with any one knife. Should coolies have been accustomed to the use of a
+particular form of instrument they become quite expert, and any proposed
+change creates in the minds of coolies a prejudice which is considerable in
+effect on the quality of the handicraft. Such prejudice may be overcome in
+course of time, but in the interval not a little damage may have been done
+in the shape of tapping wounds. So considerable is this question of
+personal favour that even on estates where a standard pattern of knife is
+issued coolies often modify that knife slightly on their own accord. Such
+alteration is ignored by the superintendents as long as the quality of the
+tapper's work is maintained at a high standard.
+
+Naturally there is a limit to such leniency, and this limit is soon reached
+in the case of knives having adjustable parts controlled by screws, or nuts
+and bolts, etc. Some knives of this description really merit a much wider
+use than is afforded them at present; but in view of the potential damage
+which might be done as a result of adjustments made by the coolies these
+knives do not become popular.
+
+It is not proposed here to enter into a description of even recent
+instruments for which strong claims are being made by their inventors or
+vendors. If they possess the merits attributed to them they will soon find
+favour, as managers are always keen on studying the points of any new knife
+which will lead to a conservation of bark and a reduction in the number of
+wounds. On the whole, it may be advanced that the best general results are
+obtained by the adoption of a simple non-adjustable knife and the retention
+of its use.
+
+THE CHOICE OF LATEX CUPS.--It has come to be recognised that the maximum
+possible cleanliness is essential in all details of estate work, and the
+younger generation of planters could scarcely be aware that a few years ago
+it was deemed sufficient to use coco-nut shells for the reception of latex
+on individual trees.
+
+Terne-plate cups ousted the coco-nut shell, and they had the merit of being
+cheap. The interior coating of tin did not last long if the cups were
+properly cleaned. The iron being exposed, with a minutely roughened
+surface, each microscopic projection served as a point around which latex
+coagulated. Scrapping the film of interior rubber became more and more
+difficult, and often the cups were burnt in order to get rid of the
+accumulation of rubber. The last state of such cups was worse than the
+preceding one. On some estates fairly successful attempts were made to keep
+these cups clean by making the coolies bring them into the store each day.
+Terne-plate cups are not now in common use.
+
+Aluminium cups have their advocates, but much the same argument applies to
+the difficulty of keeping them clean as was used in the foregoing
+paragraph. On many estates, however, they are used with success, the usual
+method of treatment being to make the coolies bring them into the store and
+clean them there. Owing to the comparative lightness of the material such a
+scheme is more feasible than was the case with terne-plate cups.
+
+The cups now most in general use are either of glass or white-ware, and
+probably those of glass are the most extensively employed. There are many
+details to be studied in the choice between these two types of
+cups--_e.g._, percentage of breakage in transport and in the field, price
+when breakage is taken into account, etc.; but these apart the glass cups
+have one advantage--namely, the ability of the superintendents to see
+whether the cups have been properly cleaned. In the case of white-ware cups
+this means an inspection and handling of individual cups, whereas in the
+case of glass the point is settled by visual examination at a comparative
+distance.
+
+[Illustration: SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE.
+
+The opening cut covers two-fifths. Subsequent cuts occupy one-fifth of
+circumference.]
+
+Glass cups are made in two patterns, one having a flat bottom and the other
+a conical base. The latter is convenient for use when wire supports are
+employed, the cup fitting into a loop placed beneath the spout. Used on the
+ground its shape is an obvious disadvantage, as, unless a hole is scooped
+for its reception, it has to be propped up with sticks or stones. Often a
+touch is sufficient to upset the balance, and latex is lost.
+
+The flat-bottomed cup, on the other hand, may be used with success equally
+on a wire support or on the ground. It is sometimes said that owing to its
+shape the ease of cleaning, as compared with the half-spherical cup, is
+diminished, and that if the cups when not in use are kept inverted upon
+sticks placed near the foot of the tree the breakage is apt to be high.
+This latter objection is being rapidly removed as the practice of using
+these sticks is losing vogue for various reasons, and wire cup-holders will
+be in general use as soon as the cost of material becomes normal.
+
+There are on the market, and in fairly wide use, cups of Chinese and
+Japanese manufacture. These generally consist of brown earthenware with an
+interior glass finish. These are cheap in comparison with glass and
+white-ware cups, but it is a pity that the glass does not extend over the
+whole of the cup. The outer surface has a tendency to collect rubber and
+dirt. On some few estates small china bowls or saucers are still used and
+are quite satisfactory, except for the favour with which they are regarded
+by natives on the outskirts of the estates.
+
+CLEANING CUPS.--The question of cup-cleaning would appear to be a very
+simple one; but in practice it is quite a source of worry to managers,
+especially where a mixed labour force is employed. Tamil coolies can be
+made to clean their cups in the day's task and at odd times. Chinese
+coolies, more often than not, either refuse to give the necessary attention
+or else demand extra pay for the work.
+
+The method of cup-cleaning employed more popularly within recent years was
+that of daily washing. The tapper carried two buckets, one for receiving
+the latex and the other containing water. Pouring the latex in the bucket
+the coolie then added a little water to the cup and added these rinsings to
+the latex collected. The cup was next washed hastily in the bucket of water
+and replaced. By the time the coolie has emptied and washed some 200 cups
+(about half the task generally) the water has the consistency of dilute
+latex, and the wet cup when replaced becomes coated with a thin film of
+rubber. If the latex is always collected in one direction it will be clear
+that, while the cups at one end of the task are comparatively clean, those
+at the other end have the chance of being correspondingly dirty.
+
+Controversy has raged respecting this question of cup-washing, and many
+estates have abandoned it as a daily practice. Coolies have not to carry an
+extra bucket of water. The contents of the cups are poured into the
+latex-bucket, and the bulk of the latex film remaining is also removed by
+the aid of a finger. The cup is then replaced, a thin skin of rubber
+forming on the interior surface. As a general rule this is easily removed
+on the next occasion, except perhaps in dry weather. It is the custom on
+most estates employing this practice to have all cups receive special
+attention at regular intervals.
+
+There are certain economic factors entering into the difference of opinion
+regarding the two broad methods employed. In some cases--_e.g._, on old
+areas--it would be practically impossible to follow the older method of
+daily cup-washing, as the tappers have to employ two buckets for the
+collection of the latex. The employment of special coolies for cup-washing
+would be necessitated, such as may be seen sometimes on estates working
+Chinese "squatter" labour--where the man taps, a child assists in
+collecting, and another child, or the mother, washes the cups. It may be
+pointed out that in such instances the helpers are not paid by the estate.
+Their services merely mean a saving in time which is spent in the
+squatter's garden, and perhaps the permission to the tapper to work a
+larger number of trees than would be allotted ordinarily to a task.
+
+Again, on some estates, the tappers, while not being required to carry a
+bucket of water for cup-washing, are given an increased number of trees to
+tap. Furthermore, on hilly areas under tapping, it is often manifestly
+unfair to expect the tapper to be able to carry two buckets during
+collection, when the slope is such, as to make the manipulation of even one
+bucket a matter of difficulty.
+
+It will be seen, therefore, that there is no clear issue for argument
+concerning the two methods, and that the point must be decided on the
+economic factors peculiar to each estate or district.
+
+[Illustration: EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING.
+
+Note uneven surface and callosities.]
+
+[Illustration: ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING.]
+
+WATER IN CUPS.--Much discussion used to take place regarding the necessity
+or otherwise for placing a small quantity of water in the cups when
+tapping. It was recognised that the permission to use water (with the idea
+of preventing coagulation) led to much abuse, apart from the question as to
+the utility of the method. Dirty water was often used, although clean water
+may have been placed in the buckets when coolies left the muster-ground.
+The small quantity of water often exceeded the actual yield of pure latex
+by hundreds per cent., with the result that on arrival at the factory the
+diluted latex was below the standard desirable for the preparation of a
+good sheet-rubber.
+
+PREMATURE COAGULATION.--Other opinion to the contrary it is now generally
+acknowledged that the possibility of premature coagulation in the cup or
+bucket is at least not diminished by the addition of even clean water. The
+use of water often obtained from estate drains clearly led to increased
+trouble. The extent to which such premature coagulation takes place varies
+greatly under the influence of many factors--_e.g._:
+
+     (_a_) Cleanliness of cups and spouts (the latter an important item
+     often overlooked, and involving the presence of certain organisms
+     which effect coagulation).
+
+     (_b_) Climatic conditions.
+
+     (_c_) Rate and volume of flow of latex.
+
+     (_d_) Size of tappers' tasks (involving the length of interval between
+     tapping, and the collection of latex).
+
+     (_e_) Distance to be traversed between the site of the task and the
+     store.
+
+     (_f_) Care in collecting, to exclude extraneous matter.
+
+     (_g_) Nature of transport; agitation of the latex to be reduced to a
+     minimum.
+
+     (_h_) Nature of the soil, and situation of the estate.
+
+The last mentioned factor is of great importance. As a general rule it is
+noted that premature coagulation is less marked on estates situated on
+comparatively hilly land. The greatest effect is remarked on estates
+situated on the flat lands of the coastal area where peaty soils are a
+feature. On many such estates, in spite of the observance of all ordinary
+precautions, it is not possible to receive the latex at the factory without
+a large percentage of prematurely coagulated rubber being found in the
+transport vessels.
+
+ANTI-COAGULANTS.--For this reason on these (and other) estates, the use of
+small quantities of anti-coagulants is common. The effect of these is to
+keep the latex liquid and thus render possible the preparation of a higher
+percentage of first-grade rubber than would be otherwise obtained.
+
+Among the better known agents which have such an effect upon latex,
+formalin and sodium sulphite (not bisulphite) are the chief. The latter is
+the more popular as it is slightly cheaper and much more stable. As now
+used, it is in the form of an easily soluble powder (anhydrous sodium
+sulphite). The ordinary crystalline form of sodium sulphite as used in
+photography is not recommended, on account of its comparative lack of power
+and its poor keeping qualities.
+
+It will be obvious that, given two equal quantities of different latices,
+different amounts of an anti-coagulant may be required to produce the same
+effect. Hence it should be remembered that a formula which suits the needs
+of one field or one estate will not necessarily prove suitable in the case
+of another field or estate. Unless this point is appreciated trouble may
+ensue. On some estates it has been the custom to give equal quantities of
+sodium sulphite solution to all coolies irrespective of the ages of the
+trees in the fields to be tapped. Thus it happened that the latex from one
+field was found to have insufficient anti-coagulant present, while that
+from another field could only be coagulated by the addition of an excess of
+acid. In this matter the experience of the preliminary trials should have
+caused some discrimination to be exercised as to the quantities of solution
+to be issued in each field or division. It has been found sometimes that a
+moist glossiness in the smoked sheet could be attributed to the use of an
+excess of sodium sulphite. Traces of the salt remained in the rubber, and
+as the substance is hygroscopic, moisture was being absorbed from the air,
+to cause a surface deposit which often returned even after the sheets were
+surface-washed and re-dried.
+
+If sodium sulphite is to be used in the field, the following formula, which
+is in wide use, may serve as a basis for trials.
+
+
+_Formula for Use of Sodium Sulphite in the Field._
+
+     (_a_) Dissolve anhydrous sodium sulphite in water at the rate of 1
+     pound to 3 gallons.
+
+     (_b_) Of this solution each coolie is given about 3/4 pint. This is
+     usually sufficient for a task of 350 trees. The solution is used by
+     shaking a few drops into the cup or, diluted with an equal volume of
+     water, it is run down the main channel when the latex flows.
+
+[Illustration: 1. SHOWING EFFECT OF "WINTERING."]
+
+On some estates it is found either unnecessary or impracticable to use the
+solution in this manner. Instead the anti-coagulant is placed in the bottom
+of the bucket prior to the commencement of collection. The solution is made
+as in (_a_) above, and roughly half an ordinary latex-cupful is placed in
+each bucket.
+
+[Illustration: 2. NEW GROWTH OF YOUNG LEAF ON SAME TREE.]
+
+COLLECTING PAILS.--All vessels intended for the transport of latex should
+have a smooth and curved interior, so that cleansing may be easy.
+Preferably the interior and exterior surfaces should be glazed, but it is
+often found that the enamel chips easily, and that the handles are too
+frail in construction. The shoulder-pieces, to which the handles are
+joined, are often too lightly attached to the bucket. Something stouter in
+the shape of enamelled ware is required, without an appreciable increase in
+weight. Until such a utensil is available, the heavily galvanised and
+brass-bound milk-pails used on some estates are as good as anything at
+present in vogue, providing they are kept scrupulously clean.
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_a_) Note on right hand the panel next in order for tapping; a hopeless
+position.]
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_b_) The present cut badly infected; above there is no renewal of bark.]
+
+The collecting pails should be kept under cover, when not in use, either at
+the muster grounds or at the factory. On some estates coolies are allowed
+to take them to their quarters, where they are used for various purposes.
+Curious effects of this practice have sometimes been noticed. As an
+example might be quoted an instance in which premature coagulation was
+found to take place to a surprising degree. It was discovered eventually
+that the coolies (Javanese in this case) were in the habit of utilising the
+buckets for the preparation of their food. A liquid extract of a popular
+fruit was often made. This extract was very markedly acid in character,
+and as the buckets were not afterwards thoroughly cleansed, the latex of
+the following day suffered.
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_c_) As in (_b_); another tree.]
+
+Preferably all buckets should have a lid of slightly funnel shape. This is
+inverted during collection, and thus prevents much dirt falling into the
+latex.
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_d_) At close quarters. Note wounds due, apparently, to bad tapping, but
+really caused by the disease.]
+
+PAYMENT BY RESULT.--The arguments for and against the institution of this
+practice are many. In actual result there can be no question that a higher
+yield is obtained by the adoption of a scheme under which the coolie is
+either given a bonus based on result or is paid at a definite rate per
+pound. It is fully recognised, both by advocates and opponents of payment
+by result, that the personal equation of the tapper is a very important
+factor. A good skilled tapper will always obtain a higher yield than an
+ordinary individual from the same task of trees, and without any more
+injury to the trees. It is argued, therefore, that such an operative should
+be given the benefit of his skill. Apart from this, it is claimed that even
+the average tapper does not do his best work if he knows that he will get
+his daily wage, no matter what his yield may be, as long as he does not
+injure the trees by wounding. It is claimed that this sense of security
+leads to shallow tapping which, while it has an agreeable appearance, does
+not produce the available amount of rubber.
+
+On the other hand, it is advanced in opposition that under a scheme of
+payment by result the tappers' only consideration is the matter of
+obtaining rubber, and that considerable damage in the form of wounds is
+done by over-deep tapping. That there is a great deal of truth in these
+statements is not to be doubted. Much, of course, depends upon the amount
+and quality of the supervision possible, and upon the standard demanded. It
+is a notable fact, however, that on estates which first introduced the
+system some years ago the quality of the tapping compares favourably with
+that of average estates, and in a few instances within the experience of
+the writer the tapping is of a high standard. Possibly these are
+exceptional instances, and there can be no doubt that the opposition of
+many managers of considerable experience is founded upon the deterioration
+in the standard of tapping which often follows the institution of payment
+of tappers by result.
+
+It will be recognised by planters that apart from the personal factor in
+tapping, the worker might be so unfortunate as to be placed in an area from
+which the yield is naturally low, either by reason of its youth or from
+other natural causes. Obviously such individuals are entitled to special
+consideration in respect of the rate per pound paid for the rubber
+obtained. Again, on very hilly land it may be not humanly possible for a
+worker to tap the usual number of trees. Hence to place him on a parity
+with other tappers, as far as wage-earning capacity is concerned, a higher
+rate than ordinary must be given. It will be plain, therefore, that on any
+one estate it is generally impossible to set a standard rate per pound for
+payment by result; the rate may vary, for example, from, say, 3 cents per
+pound in old and high-yielding tasks to 12 cents or more per pound on young
+areas of the same estate.
+
+Naturally the actual rates paid will primarily depend upon the average
+yield per tree or yield per acre, and the lower the average yield the
+higher the rates to be paid per pound. Thus, on low-yielding properties
+where the natural conditions render a high yield impossible the rate per
+pound may reach a figure of 22 cents (approximately 6d.).
+
+The methods of arriving at the yield of rubber brought in by individual
+tappers vary, but broadly they fall into two classes:
+
+     (_a_) That in which the volume of latex is ascertained (either by
+     measuring or by weighing), a sample is drawn, and the final
+     calculation made from the weight of the more or less dry sample.
+
+     (_b_) That in which, after noting the volume, the calculation is based
+     upon a reading of the dry rubber content of the latex, obtained by
+     means of an instrument such as the "Metrolac," or any other instrument
+     working on the same principle.
+
+Quite a number of estates which have not adopted the full system of payment
+by result yet employed some such method of checking the yields of
+individual coolies, as the observed results act as a great deterrent
+against various malpractices, such as neglecting to tap trees, adulteration
+of the latex, etc.
+
+TREE-SCRAP.--The thin film of latex which coagulates naturally upon the
+surface of the tapping cut after the latex has ceased to flow is known as
+"tree-scrap." Normally it is collected on all estates, but the method of
+collection varies according to the class of labour employed. On most
+estates, where the labour is Tamil or Javanese, it is supposed to be
+removed as fully as possible before the tapping cut is reopened. The narrow
+strips are then placed in a bag or basket carried by the tapper. Chinese
+tappers usually decline to follow this practice of first peeling off the
+scrap, and remove it by the operation of tapping, with the result that the
+scrap when brought into the store has adhering to it various shavings of
+bark. Unless these can be thoroughly cleaned off the scrap cannot truly be
+classed as "tree-scrap."
+
+OXIDATION OF TREE-SCRAP.--It is often noted that some scrap is dark in
+colour, and in this condition it is generally spoken of as "oxidised"
+scrap. The oxidation is probably due to an enzyme, and also to the presence
+of chemical substances of a phenolic nature. In the course of laboratory
+experiments with normal latex, it was found possible to reproduce this
+darkening due to oxidation by the addition of very small quantities of
+various phenols used in general chemical processes, and the rapidity with
+which the darkening was effected depended upon the quantity of the phenol
+added. If this rapidly oxidising latex be mixed with normal latex, it would
+seem that the whole bulk of the latex is affected by this tendency to rapid
+oxidation. It is observed that this condition under which any tree may
+yield rapidly oxidising latex is not a permanent one.
+
+CARE OF TREE-SCRAP.--As these scraps eventually give a grade of rubber
+which compares well with other and better-looking grades care should be
+exercised in collection and treatment so that its quality is not impaired
+in any way.
+
+TO PREVENT OXIDATION.--As a rule the scraps are picked over, and heavily
+oxidised pieces are sorted out; otherwise the crepe rubber prepared
+exhibits black streaks. The scraps should not be allowed to remain in the
+sun (which induces "tackiness"), and if they have to be kept over night
+they may be placed in a weak solution (1 per cent.) of sodium bisulphite to
+arrest oxidation. It should be recognised that such a solution will not
+"bleach" already darkened scrap-rubber, and the nature of its action is
+only anti-oxidant.
+
+BARK SHAVINGS.--In the matter of collecting bark-shavings much depends upon
+the organisation and nature of the labour force. Probably, on the majority
+of estates bark-shavings are collected systematically, but on quite a
+number considerable laxity in this respect has been noted. This may arise
+from lack of adequate supervision or from the peculiar systems of working
+which seem to pertain to Chinese labour. Granted that the trees are well
+"scrapped," and that the percentage of rubber obtained from shavings under
+such circumstances would be extremely small (say 2 per cent. by weight on
+the total output), it does not need much calculation to see that annually
+the loss of rubber to the estate must be considerable. It would also seem
+to follow that, if the adult labour declines to pick up bark-shavings
+carefully, it might pay to employ children for the purpose. Or, as is done
+in some places, the adult labour might find it advantageous to collect
+bark-shavings at low rates per pound.
+
+It is a well-known fact that if bark-shavings be allowed to accumulate in a
+heap for any but a short period, a fermentative and heating action is set
+up. The heat developed in these piles of shavings is so considerable that
+it is impossible to keep the hand in a heap for more than a second or two.
+Should this be allowed to persist, as would happen in the case of a
+breakdown of engine or machines, it usually results in the final crepe
+rubber becoming tacky when approaching dryness.
+
+To avoid this heating effect it is necessary to have spare jars or proper
+tanks in which the shavings may be soaked in water. In this condition
+bark-shavings may be kept for many days.
+
+For the same reason (_i.e._, the heating effect and consequent tackiness)
+the custom followed on some estates of allowing coolies to keep
+bark-shavings in their "lines" until they have accumulated a fair quantity
+cannot be commended, quite apart from the possibility of actual loss by
+theft, which is thus rendered easy.
+
+It will be clear that where the trees are scrapped efficiently before
+tapping, the amount of rubber to be obtained from the treatment of pure dry
+shavings would be almost nil, and would scarcely repay the cost of
+collection and working. In actual practice, however, it is not possible to
+guarantee that the shavings are free from some scrap-rubber. Shavings
+brought in by Tamils and Javanese carry only a small amount of rubber,
+whereas where Chinese tappers are employed the yield of rubber may be as
+high as 35 to 40 per cent. upon the total weight of the material treated.
+
+Few estates now are not equipped with "scrap-washers"--machines specially
+designed for removing the bark from the rubber--and if they function
+efficiently the resulting crepe should be free from bark-particles.
+
+COLLECTION OF EARTH-SCRAP.--This, the lowest grade of rubber, is found at
+the base of the tree. Theoretically, if proper precautions are observed,
+the amount should be comparatively small, but in actual practice it may be
+very appreciable. The usual contributory causes are:
+
+     (_a_) Failure to replace cups beneath the spouts of trees which
+     continue to drip latex after collection.
+
+     (_b_) Collection of latex at too early a stage.
+
+     (_c_) Failure on the part of the tapper to ensure the flow of latex,
+     by means of the spout, into the cup.
+
+     (_d_) Flowing of latex over the edge of the cut before it reaches the
+     vertical channel.
+
+     (_e_) "Wash-cuts" on wet days, when the volume of rainwater down the
+     tree is sufficient to wash the latex out of the cup.
+
+The amount of earth-scrap collected on any estate will depend, all other
+things being equal, upon the labour expended in its collection. Certainly
+on well-organised estates, having ample labour, the amounts collected are
+huge in comparison with other estates. The ground at the base of the tree
+below the latex-spout is systematically turned over with pointed sticks and
+large clots of rubber are often picked up. Here, again, it is advised that
+the collected earth-scrap should not be allowed to remain in heaps upon the
+floor of the factory. It should be placed in suitable tanks containing
+water, and quite a considerable portion of the cleansing work is thus taken
+from the machines.
+
+
+
+
+CHAPTER VI
+
+_TRANSPORT OF LATEX AND COAGULUM_
+
+
+PERCENTAGE OF FIRST LATEX AND OTHER GRADES.--One of the problems
+confronting any manager is the question of the percentage of first-grade
+rubber calculated upon the whole output. Inquiries are constantly being
+received for advice as to what the various percentages of each grade of
+rubber should be. This is a question to which no definite list of figures
+can apply. There are so many little factors influencing the result. Some
+estates are not particularly careful in collecting tree-scrap. Hence quite
+a quantity of tree-scrap finds its way into the crepe made from
+bark-shavings. On the other hand, bark-shavings are not collected
+systematically on some estates, and the total output is thereby diminished.
+In consequence the first-grade rubber shows a higher percentage than it
+would otherwise. Again, if the earth-rubber is not regularly collected the
+percentages of the best grades are higher than they should be. In comparing
+the percentages of each grade of rubber from any two estates, therefore,
+one should have all the information possible as to the various working
+details of the estates. Without wishing to lay down any definite
+proportions which can be applied to all estates it might be said that,
+taking averages over a large number of estates, the percentages to be aimed
+at are:
+
+  First-grade latex   75 per cent. to 80 per cent.
+  Other grades        20    "      "  25    "
+
+For these figures one promises that all lower grades are collected and
+accounted for carefully and regularly. The distribution of the lower grades
+will depend upon the field practices of the particular estate, but the
+following list might be given for an estate keeping all lower grades
+distinctly separate:
+
+  First-grade latex         75 per cent.
+  Cup-washings            }
+  Coagulated lump, etc.   } 10    "
+  Tree-scrap                 9    "
+  Bark-shavings              4    "
+  Earth rubber               2    "
+                           ---
+                           100    "
+
+Emphasis is again laid on the statement that these figures must not be
+accepted as a standard. Nevertheless, they may prove of some service to
+managers in giving an idea of what the general line of percentages may be.
+There are special circumstances, such as distance of transport and the
+nature of the land, which at present would render the attainment of more
+than 75 per cent. first-grade rubber impossible on some estates. Still the
+fact remains that if the percentage is low through distance of transport,
+etc., some method will have to be discovered by means of which the
+difficulty maybe overcome. On a few estates the percentage of first-grade
+rubber obtained sometimes reaches 85, but these results are rather out of
+the ordinary. An estate which collects all lower grades properly is doing
+well if the percentage of first-grade rubber is 75 or over.
+
+EARLY COLLECTION.--As already noted in the preceding chapter, one of the
+factors influencing premature coagulation is that of the interval elapsing
+between the commencement of tapping and the collection of latex. It will be
+seen that this ordinarily would depend, in turn, upon such considerations
+as the size of the tappers' tasks, the spacing of the trees, and the
+natural conformation of the land over which the tappers have to perform
+their tasks. In general it need only be remarked that every possible
+consideration should be given to this question, and that any delay should
+be avoided.
+
+TRANSPORT.--Wherever possible it is endeavoured to convey latex from field
+to factory by man-power. Tamil coolies, as a rule, place the bucket on the
+head; Chinese and Javanese coolies like to use a balanced carrying-pole.
+Where distance renders these methods too costly in time and labour, it is
+usual to have field centres where the latex is collected and dispatched to
+the factory generally (_a_) by means of vessels conveyed on light railways;
+(_b_) in large cans placed on motor-lorries; (_c_) in cylindrical
+galvanised drums supported on two wheels and drawn by bullocks. There may
+be variants, but these are the chief means of transport in bulk over a
+distance.
+
+Where possible, the best system is that employing a trolley-line, as great
+agitation of the latex is avoided, and the time in transit is much reduced.
+
+The usual method of transport by bullock power is slow, and as estate roads
+(and even Government roads) are often below the standard expected in this
+country, the jolting undergone by the latex is, to say the least, not
+calculated to afford a high yield of first-grade rubber. The late Mr. F. W.
+F. Day advocated the use of a circular perforated wooden grid, to be
+floated on the latex, in order to moderate the wave effect produced by
+jolting.
+
+Whatever the means of bulk-transport employed, it should be the care of
+those in charge to see that vessels are not allowed to remain in the sun
+longer than is necessary. Even during the journey they should be shaded in
+the best possible manner.
+
+These large transport vessels usually receive what is really only
+perfunctory attention in the matter of cleaning. They should receive the
+same care as would be exercised in dealing with milk cans in other
+countries. Ordinary sluicing with water is not sufficient, and if they
+cannot be sterilised by means of boiling water, they should be treated,
+after ordinary washing, with a 5 per cent. solution of sodium bisulphite
+every day.
+
+ANTI-COAGULANT FOR TRANSPORT.--When anti-coagulants are not used in the
+cups or buckets, it is advisable to use them in the bulk-transport vessels.
+Either formalin or sodium sulphite is of service, but the great objection
+advanced against the former is its loss due to evaporation while the carts
+are going to the fields or waiting at the centres. For this reason sodium
+sulphite is now generally employed.
+
+
+_Formula for Use of Sodium Sulphite in Transport._
+
+     (_a_) Dissolve 1 pound of powder in 3 gallons of water.
+
+     (_b_) Of this solution, place half a gallon in the vessel for every 30
+     to 40 gallons of latex.
+
+TRANSPORT BY COOLIE.--As already pointed out, the extent to which man-power
+can be used in transport of latex is generally limited. On small estates it
+is an easy matter for coolies to carry the latex to the factory, but on
+larger estates many difficulties may arise, which may also militate against
+the successful use of other means of transport. It is not uncommon to find,
+therefore, that a policy of decentralisation has been adopted.
+
+COAGULATION CENTRES.--Divisions of the estate have their own small stations
+at which latex is received and coagulated. In this way it is possible to
+receive latex without much delay, and with benefit to the resultant rubber,
+especially if prepared in sheet form. Much controversy has arisen regarding
+these decentralised establishments, but the fact remains that on large
+estates, which are efficiently controlled, the scheme has been highly
+successful from all points of view. On the other hand, it is alleged that
+this method of working increases costs, and often gives an unsatisfactory
+quality of rubber. Concerning the latter point it seems to be reasonable to
+expect that the European in charge of any division should be conversant
+with the method of preparation required, and should be capable of seeing
+that no mistakes are made. Given uniform equipment in all stations, and
+uniform rules for treatment of the latex, there does not appear to be any
+valid reason why the product of one station should be inferior to that of
+the others. Neither is it so in the case of several estates which might be
+quoted.
+
+In the matter of costs of working the writer has had to investigate several
+cases regarding which there was dissatisfaction. In some instances it was
+found that the stations had not been placed advantageously with respect to
+a water-supply; and instead of one or two coolies pumping for an hour or
+two, a larger number had to be employed for hours in the carriage of water
+from the nearest available source. This meant that, as the coolies were on
+daily wage, the force appeared to be much bigger than that usually
+required. In other cases there were too many store coolies, when often the
+place of some could have been taken for the necessary period by tappers
+arriving early from the nearer fields. Sometimes costs were increased by
+reason of the use of an excess of chemicals, owing to the lack of uniform
+rules throughout the several stations. In spite of all that has been
+written, and the verbal instructions that have been given, it was not
+uncommon to find unstable chemicals such as sodium bisulphite exposed to
+the moist air. In this way not only was there waste of material, but also
+the probability of inferior rubber being made.
+
+TRANSPORT OF COAGULUM.--On the whole if it is a question between the
+transport of latex and the transport of coagulum, the writer would always
+favour the latter, for reasons which have possibly been made clear in the
+preceding paragraphs. In effect, it should be recognised that the less
+handling and transport the latex receives the better the general result.
+
+If proper precautions are taken, the transport of coagulum intended for the
+preparation of crepe should present no difficulty, and should have no
+injurious effect upon the quality of the resultant rubber. It is only too
+common, nevertheless, to note defects, in the finished crepes, which can
+only be attributed to a failure to observe reasonable care in the transport
+of the coagulum. For example, it has been observed that a mass of coagulum
+from a coagulation station has been conveyed on the floor of a
+bullock-cart, or motor-lorry, previously used in the carriage of other
+materials. Unless the boards have been most scrupulously cleansed, the
+coagulum is found to be contaminated, often to a marked degree. Again,
+although the cart may be clean, it may have to travel some distance on
+roads carrying a fair amount of motor traffic. Even should the cart have a
+canopy, road-dust is often whirled through the open sides of the cart; and
+in the districts where red laterite roads are common, the stain of such
+dust often persists in the finished crepe. It scarcely need be remarked
+that coagulum should be transported in closed wooden boxes or in galvanised
+iron drums fitted with lids; and that preferably sufficient water should
+be present in these receptacles to allow the coagulum to float. All such
+containers should receive the same scrupulous attention as the vessels
+employed in the transport of latex.
+
+The successful transport of coagulum for sheet-making is fraught with much
+greater disabilities, and it is usual to note on most estates that the
+resulting sheets from out-stations are always inferior, in final result, to
+those coagulated and prepared at the central factory. If the flat pieces of
+coagulum are placed in piles of any height it is common to find, on arrival
+at the factory, that much adhesion has been caused. There is great
+difficulty in separating the pieces, and often the successful operation is
+impossible. It is usual to hand-roll the coagulum before transport, but it
+is often found that by the time the rubber reaches the factory it has
+become too hard for subsequent good results.
+
+One of the strong arguments in favour of the establishment of divisional
+stations is to be found in the preceding paragraph. Sheet-making, as it
+necessitates the employment of only light machines suitable for hand-power,
+is a feasible proposition in a field station. There is no reason for sheets
+made thus to be in any way inferior to those made at a central factory; in
+fact, they are often better, as the latex has the chance of being treated
+when comparatively fresh.
+
+If it is found necessary to transport sheet-coagulum, every possible
+precaution should be taken against piling the pieces.
+
+After hand-rolling some estates bring the rubber from the field-stations to
+the central factory in drums of water, others in shallow boxes containing
+not more than half a dozen sheets in a pile. A method proposed long ago,
+but not in practice, was to have a number of shallow trays subdivided so
+that each compartment held one sheet only. If these trays were properly
+made and carefully fitted there appeared to be no reason why they should
+not form sliding parts of a large box, in which squeezing and adhesion of
+the pieces of coagulum would be avoided. Naturally any such device would
+increase appreciably the weight to be transported, and on this ground would
+not find popular favour except where motor-power is used for road
+transport.
+
+
+
+
+PART II
+
+FACTORY OPERATIONS
+
+
+
+
+CHAPTER VII
+
+_PRELIMINARY TREATMENT OF LATEX_
+
+
+RECEPTION OF LATEX AT THE STORE.--Bearing in mind the remarks in Chapter
+VI. on the conditions under which latex is transported, it follows that
+nothing but the very best and most suitable vessels should be used in the
+store. A point to which adequate attention is not given in many factories
+might be mentioned here. Considering the importance attached to colour in
+the dry rubber by brokers and consumers, and knowing how extremely trivial
+are the causes which may mar the colour, it is rather surprising that
+better provision is not made for the reception and handling of latex in
+factories. Too often the receiving vessels are placed on the floor of the
+store close to the entrance. Coolies bringing in latex cannot avoid
+bringing with them quite a considerable amount of dirt. Presuming that a
+hose-pipe has been installed, and that the floor is constantly being
+sluiced down with water, no great harm will result. But would it not be
+ever so much better if the dirt were kept out? In how many factories is
+provision made for this? Such an arrangement is not difficult to make, and
+is already in practice on a few estates. A verandah is built outside the
+wall of the factory and all latex is received there. In another place open
+chutes are provided which terminate in the straining sieves. The coolie
+thus stands on the verandah where he removes coagulated lump and impurities
+from the latex, which is then poured down the chute, passing through the
+sieve into large coagulating jars or tanks.
+
+Too often it would appear, from the writers' observation, there is a lack
+of adequate supervision on the arrival of latex at the store. Much can be
+learned from an inspection of the coolies' buckets, and the cause of small
+defects in the finished rubber can often be thus traced. Leaves, stems,
+bark-shavings, and dirt appear in the buckets, and it is a source of
+constant surprise to imagine how even unintelligent coolies can allow such
+things to happen. These objects are removed before or during straining, but
+still they ought not to be there in the first place, and the fact that such
+a state of things exists is evidence of neglect on the part of the coolies
+or lack of supervision. Efforts are made in a large number of cases to cope
+with these troubles, but on some estates things are allowed to proceed in
+the same slipshod way, and too much responsibility is thrown on the
+straining process.
+
+[Illustration: RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED
+WITH FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER COOLIE" BY
+SAMPLING OF LATEX.]
+
+It is suggested that it should be the business of a European to supervise
+the reception of latex every day. This is at present quite impossible on
+some estates, but it does not alter the fact that this supervision should
+be provided, and is extremely necessary.
+
+It is surprising how the point is overlooked in many factories--not that
+they are in a dirty state, but they fall short of being classed as clean
+factories for want of the little that makes the difference. Possibly those
+in charge do not believe that all this fuss need be made, but the writers
+can assure them, from a practical knowledge of a very large number of
+factories, that cleanliness does pay.
+
+It might not be credited to Tamil coolies, but yet it is probably true,
+that the moral effect of working under the cleanest and best conditions has
+an influence upon the store coolies, and that their work is better in
+consequence. Everything which will tend to simplify the cleansing of the
+factory should therefore be installed. Hose-pipes, glazed tiles, clean
+floors, plenty of light and air are not fads or fancies, but considerable
+factors in determining the final quality of the rubber. There is
+considerable truth in the suggestion that the coagulating room and machine
+room should be as "spick and span" as a modern home dairy.
+
+STRAINING OF LATEX.--This is a most necessary process, and one which
+usually entails much trouble and time which one could wish avoided. It will
+be admitted that the trouble could be reduced greatly if the regulation of
+field processes could be made more stringent. In spite of knowledge that
+impurities must not be allowed to enter the cups, coolies will ignore the
+rule that the cup must not be placed in position until the bark shaving has
+been cut. The result is that pieces of bark fall into the cups, and coolies
+are generally too careless or too hurried to remove them.
+
+Again, when cups are placed on the ground, it is easy to see that dirt may
+adhere to them. In the collection of latex some of this dirt may fall into
+the bucket. Since the introduction of cup-holders on many estates the
+trouble from this source has decreased considerably, but, nevertheless, it
+may be taken for granted that even under the best of conditions all latex
+requires straining.
+
+The best type of strainer has yet to be evolved. Usually it consists in
+principle of a piece of fine brass mesh contained in some form of holder.
+Theoretically such a strainer should work well, but in actual practice
+nearly all strainers are a source of continual worry. Undiluted latex, as
+received at the factory, is of a rich consistency, containing very fine
+particles of dirt and often minute particles of prematurely coagulated
+rubber. The latter soon clog a fine mesh strainer, while the former may
+pass through. When the flow through the strainer becomes slow, the coolie
+in charge generally rubs the top surface of the sieve with a piece of
+coagulum, thus forcing material through the mesh. He then rubs the
+under-surface, with the result that undesirable matter falls into the
+strained latex. In theory it seems a simple matter to have a number of
+sieves ready so that a clean one may be substituted for a clogged one,
+which should be cleansed at once with water. In practice the factory coolie
+will probably only carry out instructions when the eye of the
+superintendent is alert. As a result of the rubbing and consequent strain,
+the brass mesh usually breaks away from its support and the fracture may
+not be detected for some time, during which irreparable damage may have
+been done to the resultant rubber.
+
+In view of the presence of the fine particles of dirt, to which allusion
+has been made, fine sieving of the latex appears to be essential,
+especially when sheet-rubber is to be prepared. The fine sieves are
+generally of the type known as "60 mesh," and they do not usually give
+thoroughly satisfactory results even when the gauze is supported and
+strengthened by means of cross-wires placed underneath. The general fault
+with these strainers is that a sufficiently wide "selvage" is not allowed
+in the clamped edges of the gauze, or that the edges of the support are so
+sharp and abrupt that the strands of the gauze are soon severed by the
+strain imposed in vigorous cleaning.
+
+Many estates use two strainers; the first a more robust one containing "30
+mesh" gauze, and the second the fine "60 mesh." Even this device does not
+bring about the desired immunity from trouble. Relief could be obtained if
+the latex were always in a more freely fluid form. Estates employing
+anti-coagulants in the field benefit in this respect. Other estates,
+although finally using the finest of mesh, experience far less trouble than
+most estates by reason of a difference in method of working. This can be
+explained by an outline of the system adopted on a particular estate:
+
+     (_a_) On arrival of the rich latex at the store, all visible
+     coagulated lumps and other extraneous matter are removed by the
+     tapper.
+
+     (_b_) Each tapper's latex is diluted with a quantity of water.
+
+     (_c_) The diluted latex passes through two sieves, one above the
+     other. The top sieve is of stout perforated zinc sheet, with 10
+     circular holes to the inch. This removes all large particles. The
+     lower is of "30 mesh" brass gauze, and practically no rubbing is
+     required. The latex is now in glazed-tile tanks, in which it is
+     further diluted to the required standard by means of a recording
+     instrument.
+
+     (_d_) The latex flows by means of a chute into the coagulating tanks,
+     passing through a large "60 mesh" sieve.
+
+It is not guaranteed that this method will furnish a complete absence of
+very fine particles of dirt in sheet rubber, as the human element enters so
+largely into the question; but it can be stated that no complaints have
+been received on the point of "specks of dirt" since this system was
+inaugurated.
+
+On the same estate fine sieving in the preparation of pale crepe has been
+abandoned as an unnecessary refinement. The two coarse sieves mentioned
+above are employed only, and it is to be acknowledged that the results
+justify the procedure.
+
+BULKING OF LATEX.--Not long ago advanced estates used to combine all latex
+before coagulation, in order to obtain uniformity of product. Previously it
+had been the custom to deal only with comparatively small separate volumes
+of latex, with obviously great disadvantage.
+
+Since the introduction of instruments such as the "Metrolac," by means of
+which any volume and all volumes of latex may be reduced to a common
+standard of dry rubber content, the necessity for "bulking" has passed. It
+is not now necessary to keep latex standing, perhaps for two hours,
+awaiting the arrival of other latex from distant fields.
+
+STANDARDISATION OF LATEX.--In modern practice, as already pointed out, it
+is possible now to handle any volume of latex with a view to its reduction
+to any required standard of dilution for the purpose of obtaining a
+uniform product. For the reception and subsequent handling of the latex
+various schemes have been devised, and they are usually planned in
+connection with coagulating tanks used in the preparation chiefly of sheet
+rubber.
+
+[Illustration: END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD
+FOR RECEIVING LATEX AND FILLING TANK.
+
+T, Sheet coagulation tank; C, cylinder for reception and dilution of latex;
+GG, gutter; PP, raised platform on verandah; SS, steps leading to platform;
+W, dwarf wall; EE, expanded metal partition; OO, open.]
+
+In the successful working of a tank it is necessary, in order to obtain the
+best results, to standardise all latex. This cannot be effected properly in
+the tank itself, and hence it is the practice to dilute each lot of latex
+to standard before it is run into the tank. In the ordinary way this would
+entail a great deal of labour in handling the diluted latex. To obviate
+this, the scheme outlined in the accompanying sketch has been suggested on
+several occasions and in various quarters. Such a scheme or modification of
+it has been put into successful practice on several estates. Although the
+drawing was made some considerable time ago when estates were not then
+prepared to go so far in this direction, subsequent modifications show only
+minor differences which, while leaving the original principle intact,
+testify to a fertility of resource in adapting the idea to existing
+circumstances and buildings. The drawing is _in toto_ almost a replica of
+the original installation now in successful use on the Kinrara Estate of
+the Ledbury Rubber Company. On this company's Ledbury Estate likewise a
+similar system is employed, except that the reception verandah is part of a
+natural formation and needed no such direct raising. Several other estates
+have now adopted the scheme, which has been proved to be of practical
+value. The writers make no claim to originality in the idea, which might
+have occurred to many independently on the introduction of coagulating
+tanks.
+
+[Illustration: RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX.]
+
+VERANDAH.--In reproducing the drawing it is believed that the sketch will
+convey practically all the information required. It may be explained that
+the coolies are allowed to enter only the outer part of the verandah. The
+buckets are handed across the low wall into the care of factory coolies,
+who strain the latex through gauze sieves into the latex cylinders.
+
+LATEX RECEPTION VESSELS.--These cylinders may be similar to the tanks
+commonly used for transport of latex from distant fields to the factory. An
+80-gallon cylinder is easily mounted by its trunnions on a suitable iron
+framework which is superimposed on a skeleton truck.
+
+[Illustration: ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH.]
+
+The latex is diluted down to standard in the cylinders, the truck is moved
+opposite the compartment to be filled, and a light movable gutter is placed
+beneath the vent of the outlet pipe. This pipe is fixed in the bottom of
+the cylinder, and is provided with a large stop-cock which is operated by a
+spanner key. The stop-cock should be of the simplest type, capable of being
+taken apart and assembled in a minute or so. The orifices should be large
+enough for a coolie to insert at least two or three fingers so as to
+facilitate cleaning, and the pipe should have no right-angle bends.
+
+On the inside of the cylinder a scale of gallons may be painted, so that
+one may possess a knowledge of the quantities run into, or required for the
+completion of, any compartment.
+
+A SCREW PLUG UNSATISFACTORY.--It may be of benefit to managers who
+contemplate such an installation to know that the adoption of a stop-cock
+in the vent pipe of the cylinder is the outcome of experience. In one
+instance the vent pipe as designed was fitted with a screw plug at the end.
+Unfortunately with this arrangement the flow could not be regulated, and
+owing to the "head" of the latex it dashed violently down the gutter,
+struck the bottom of the coagulating tank, and thence was scattered over
+the factory.
+
+ANOTHER INSTALLATION.--In another type of installation, in place of the
+vessels travelling upon a raised verandah platform, the standardised latex
+is conveyed to the coagulating tanks by means of drums supported by hooks
+to a chain-block and pulley which travels on an overhead gantry. This
+method is practicable, but may be regarded as less satisfactory in general
+working than the verandah method of treatment.
+
+A MODERN INSTALLATION.--In the most recent scheme for dealing with the
+reception of latex, its standardisation, and conveyance to the coagulating
+tank, the main principle of the first system outlined is retained; but the
+receptacles are not mobile. Glazed-tile tanks are employed, the capacity of
+each being approximately equivalent to that of each unit coagulating tank.
+
+The accompanying illustrations show the general arrangement and some
+details of the system of reception tanks employed on the well-known
+Pataling Estate.
+
+
+
+
+CHAPTER VIII
+
+_COAGULATION_
+
+
+Whether it is necessary to employ any coagulant, or whether latex should be
+allowed to coagulate naturally, will not be discussed at this stage.
+Neither will mention be made of any patent processes of coagulation which
+employ other than acid mediums. These subjects will be treated in a
+subsequent section of the book.
+
+CHOICE OF COAGULANTS.--It is not proposed here to enter into a discussion
+as to the merits of the dozens of known coagulants. Suffice it to state
+that acetic acid, although the oldest general coagulant, still remains the
+best and safest at the present time. There is a deal to be said in favour
+of the use of another organic acid, formic acid. It is equally as safe as
+acetic acid, and quite efficacious; the only drawback is that, taking all
+things into consideration, it is very slightly more expensive. Acetic acid,
+therefore, will always be implied in this chapter when the word "acid" is
+used.
+
+STRENGTH OF ACID SOLUTION.--In the old days it was the rule rather than the
+exception to find pure, undiluted acid used in coagulation. In many cases
+no harm resulted, for the simple reason that, owing to the large proportion
+of water in the latex, the acid was thereby very much diluted. The estates
+had to thank the over-dilution of the latex for the non-injury of the
+resulting rubber.
+
+Some estates make up a stock solution of 1 part acid to 20 of water, and
+use this with success because of the fair amount of added water present in
+the latex.
+
+It must be understood that what is being referred to now is not the
+absolute quantity necessary for coagulation, but the proportions--_i.e._,
+the respective volumes of acid and water in the solution of acid made up
+every day. That the strength of the acid solution, as well as the quantity
+used, has an effect upon coagulation can be easily demonstrated in the
+following way:
+
+Take separate and equal lots of the same latex, and to each add the same
+quantity of pure acid, but in each case diluted with varying quantities of
+water. It will be found that coagulation is quickest where pure acid is
+employed, and slowest where the acid is most dilute. It will also be found
+that, providing the quantity of acid employed was sufficient for
+coagulation, the best and most uniform coagulation is obtained from the use
+of the most dilute acid, within limits. It will often be found that where
+pure acid has been employed coagulation is local--_i.e._, we have lumpy
+coagulation, and often a very milky remaining liquor. This is due to the
+fact that, as coagulation is immediate upon the spot which is first touched
+by the pure acid, a deal of the acid is enclosed within the rubber at that
+spot, and hence other portions of the latex are deprived of acid. It is in
+such cases that most air-bubbles are enclosed.
+
+As the dilution of the acid solution is increased the mixing is more
+thorough and uniform. Coagulation is slower, and air-bubbles can escape to
+the surface.
+
+METHOD OF MAKING STOCK SOLUTION.--Experiments have been repeatedly made in
+the laboratory with acid solutions of varying dilution, from pure acid down
+to 1 part of acid in 500 parts of water. While it has been found that a 1
+in 5 solution can be used where the latex is very dilute (say, 1 part of
+latex to 5 parts of water), and a 1 in 20 solution may be used in fairly
+dilute latex (for crepe-making), it is undoubtedly a fact that for latex as
+generally "standardised" on estates a much more dilute solution of acid
+should be used--_e.g._, 1 in 100, or even 1 in 200, of water. It must be
+borne in mind that the quantity of acid necessary for coagulation is not
+changed, but merely the dilution. Let us take a concrete case to illustrate
+the point:
+
+     On an estate at present the stock solution is made up by diluting 1
+     pint of acid with 20 pints of water, and 1 gallon of this is necessary
+     to coagulate 50 gallons of pure latex.
+
+     It is desired to use a stock solution of 1 pint of acid to 100 pints
+     of water. Evidently, therefore, 5 gallons of this stock solution
+     contain only the same quantity of pure acid as 1 gallon of the old
+     solution contained, and it will be necessary to add 5 gallons for
+     every 50 gallons of pure latex. Thus:
+
+          1 to 20; 1 gallon necessary for 50 gallons pure latex.
+          1 to 100; 5 gallons necessary for 50 gallons pure latex.
+
+It may be pointed out that the quantities worked out in the foregoing
+examples are not absolutely and mathematically correct, but they are quite
+close enough for all practical purposes.
+
+It may be advanced by someone that if a dilute solution of acid, such as 1
+in 100, is used the bulk of this stock solution (5 gallons to 50 gallons of
+latex) is very great, and might be injurious to the quality of the
+resulting rubber. A moment's consideration will show that, after all, the
+volume of acid solution is only one-tenth that of the volume of latex. This
+can have no effect upon the quality of the rubber. Even dilution of the
+pure latex with half its bulk of water in the factory will have no effect
+upon the quality of the resulting rubber. It is to be remembered that,
+except in cases where the proportion of added water to latex is absurdly
+large, the main argument against putting water into the latex-cups is
+against the possible poor quality of the water rather than against the
+actual small quantity theoretically added. It is acknowledged that, where
+the water to be put into the cups can be guaranteed to be of good quality,
+no great objection would be raised against placing the smallest possible
+quantity of such water in the cups. But how many estates have such good
+water easily available to the coolies, and how many estates can be sure
+that only that smallest possible quantity would be used? It is a notorious
+fact that, even on estates where the quantity of water used was supposed to
+be a minimum, the proportion of water to latex in some cups often exceeded
+even three or four to one. In any case it may be stated as an elementary
+truism that the absence of water is more to be desired than water of
+doubtful quality.
+
+QUANTITY OF ACID.--As a result of repeated experimental work it has been
+found that, for pure average latex, the quantity of acid necessary for
+complete coagulation, reckoned in parts of pure acid to parts of latex, is:
+
+     1 part pure acid; 1,000 parts average latex.
+
+Where the latex is rather richer than average (above 30 per cent. dry
+rubber) probably a little more acid would be required, and similarly if the
+dry rubber content is lower the quantity of acid must be less.
+
+It used to be a common belief that the more dilute the latex the greater
+the quantity of acid necessary, but this would only apply to cases of
+extreme dilution of latex.
+
+As a matter of fact, up to certain limits of added water, the reverse is
+actually the case--_i.e._, the more water in the latex the less acid must
+be added, assuming that for pure latex the proportion of pure acid to latex
+is taken as 1 part to 1,000 parts. This was found to be the case up to
+dilutions of three or four times the volume of latex. To take concrete
+examples which will perhaps make the truth more clear:
+
+     Assuming we commence by making up our stock solution of acid by adding
+     100 parts of water to 1 part of pure acid, this gives us a mixture of
+     1 to 100. For 1 gallon of pure latex it would be necessary to add
+     one-tenth of its volume of the above mixture--_i.e._, 16 ozs.
+
+     Suppose we take a gallon of pure latex and add a gallon of water, we
+     now have 2 gallons of so-called latex. But we still have only 1 gallon
+     of real latex present in the diluted latex, and it is only necessary
+     to add sufficient acid to coagulate this gallon--_i.e._, 16 ozs.
+
+     Further, if 1 gallon of latex be diluted with 2, 3, or even 4 gallons
+     of water it is still only necessary to add 16 ozs. of the acid
+     mixture.
+
+     At dilutions beyond this limit, however, it is necessary to add a
+     little more acid to obtain complete coagulation.
+
+In the process of preparing sheet rubber it is very necessary to see that
+the minimum quantity of acid is used, otherwise visible defects are caused.
+But in coagulating latex intended for preparing crepe, where the rubber
+undergoes protracted washing on the machines, the presence of a slight
+excess of acid in coagulation is not calculated to cause any deterioration
+in the quality of the rubber. Advantage must not be taken of this statement
+to argue that more than a slight excess may be used without injury to the
+rubber, as it can be shown that the use of a large excess of acid results
+in an inferior rubber.
+
+QUANTITIES NECESSARY FOR MODERN REQUIREMENTS.--It may be commended to the
+notice of the beginner that any further experimental work as to the
+quantity of acetic acid necessary for complete coagulation would only
+involve a waste of time and energy.
+
+The general figure given in a preceding paragraph (1 part pure acid to
+1,000 parts of latex) may be accepted as the rough basis for working. In
+modern practice, however, undiluted latex is usually diluted to a standard
+which may vary on different estates from 1-1/4 lbs. to 1-1/2 lbs. dry
+rubber per gallon.
+
+Latices of these strengths can be coagulated at a ratio of 1 part pure acid
+to 1,200 parts of standardised latex; and this quantity need not be
+exceeded, except in cases where an appreciable amount of some
+anti-coagulant is present in the latex. The proportion may then be raised
+to 1 in 1,000.
+
+If considered advisable the acid may be used in a 1/2 per cent. solution
+for sheet preparation; but in any case it is advised for the sake of
+uniformity that a 1 per cent. solution should be employed in the
+preparation of both sheet rubber and crepe rubber. In most modern
+factories, measuring vessels of various capacities are to be found, and it
+is always more satisfactory to have the solution made up in approximately
+correct strength at the rate of 1 oz. of pure acid to 5 pints of water.
+Often, however, on some estates European supervision of this work is not
+possible, and the preparation of the acid solution has to be left in the
+hands of a (more or less) skilled coolie. It is thus necessary to find some
+less fine, but still approximately correct, method of procedure. In the
+East the kerosene tin is in universal favour for the carriage of water, and
+there is no reason why it should not be utilised as a standard measure for
+preparing the dilute acid solution, _providing it is not allowed to become
+rusty_. The capacity of the tin is 4 gallons (640 fluid ozs.), so that a
+one-hundredth part would be approximately 6-1/2 ozs. It is suggested that
+this quantity should be measured out by means of a glass graduated vessel,
+and then that an aluminium cup should be cut down so as to hold the exact
+quantity.
+
+This would reduce the making of a solution, sufficiently approximate to 1
+per cent. strength for all practical purposes, into a simple operation of
+mixing pure acid and water in the ratio of one cupful of acid to 1 kerosene
+tin of water.
+
+The actual quantity of solution required for the coagulation of any volume
+of standardised latex can be calculated easily from the ratio 1:1,200. As
+the strength of solution is 1:100 it will be seen that the quantity to be
+taken is _always one-twelfth_ that of the volume of latex--_e.g._:
+
+     (_a_) If the latex tank holds 90 gallons of standardised latex, 7-1/2
+     gallons of dilute acid solution are required.
+
+     (_b_) A tank containing 120 gallons of latex would need 10 gallons of
+     the 1 per cent. acid solution.
+
+It is assumed that all estates, not only in the preparation of sheet
+rubber, but also in the making of crepe rubber, always employ the system of
+standardising latex in order to obtain uniformity. They are ill-advised if
+they do not follow this practice; but in case average undiluted latex is
+treated in coagulation, the quantity of acetic acid to be used should be
+calculated from the ratio 1:1,000.
+
+If the acid solution is to be employed in 1 per cent. strength, _one-tenth_
+of the volume of latex to be treated will indicate the required quantity of
+solution necessary for complete coagulation unless anti-coagulants have
+been used, when the quantity must be increased as experience directs. It
+will be recognised, of course, that undiluted latex may only be used in any
+case for the preparation of crepe rubber; or in some exceptional case, such
+as the special preparation of "slab" rubber.
+
+CARE IN MIXING.--It is essential that the mixture of dilute acid and latex
+should be thoroughly intimate. This can only be attained by careful
+manipulation, especially in the case of sheet preparation. Where crepe
+rubber is to be made it may be permissible to employ a solution stronger
+than 1 per cent., but it is not advised. The acid should be poured into
+the latex while stirring, and the agitation should continue for such a
+period as to ensure thorough mixing in all parts.
+
+It will be appreciated that in the preparation of sheet rubber this period
+may not be unduly prolonged, otherwise the latex will have begun to
+coagulate before skimming and the placing of the partitions in their
+respective slots can be effected. Furthermore, while in the preliminary
+treatment for crepe rubber, the formation of enclosed bubbles and surface
+froth is immaterial. For sheet preparation it is essential that the
+stirring shall be done so carefully as to try to avoid internal bubbles and
+to reduce surface froth to a minimum. For crepe-making a perforated board,
+with handle attached at right angles to the face of the board, may be used;
+but in shallow sheet-coagulating tanks, broad paddles (which may or may not
+be perforated) give good results as long as there is a sufficient number
+used to cover the area of the tank in reasonable time. Obviously also,
+where the area of any tank or compartment is of any appreciable size, the
+dilute acid solution should be poured in from various points so as to
+obtain a good even distribution. In some cases the acid is distributed from
+a sprinkling can, but this is a refinement which experience shows to be
+unnecessary. In actual practice, working on a tank measuring 12 ft. by 4
+ft., no difficulty is found if coolies pour in acid solution from four
+points. The degree of success depends entirely upon experience and
+efficient supervision. This remark applies equally to the use of various
+devices, such as rakes with broad teeth, used as stirring implements. There
+is room for display of ingenuity in this direction, and it is found often
+that, while they are used successfully on one estate, they may be condemned
+on another.
+
+[Illustration: TWO VIEWS OF DILUTION AND MIXING TANKS.
+
+Below, on the right, coagulating tanks. At the far end strainers. Each
+dilution tank is of equal capacity to the corresponding coagulating tank.]
+
+USE OF SODIUM BISULPHITE.--Some few years ago a demand for pale crepe
+rubbers sprang up, and this demand has been maintained. The total quantity
+of pale rubber put on the market previously could only have amounted to
+very little, and that little was obtained by luck and various tricks in
+manipulation. It must be premised that if coagulation is allowed to take
+place, either naturally or with the aid of acetic acid, the resulting
+rubber will almost inevitably oxidise on the surface, except in the cases
+of very dilute or young latices. Even supposing that this darkening of the
+surface does not take place in the wet stage, it is often found that a
+rubber expected to dry to a pale colour does not fulfil expectations, and a
+dull neutral shade results. This darkening of crepe rubber may be
+attributed to a slow process of oxidation, which continues until the rubber
+is dry. From these remarks it will be seen that the process of oxidation is
+a natural one, and that any pale rubber formerly shipped was the outcome of
+circumstances outside the control of the estate, except in such cases where
+boiling of the coagulum, etc., was resorted to. The fact that one rubber
+happened to be a shade darker than another was absolutely no criterion as
+to the value of the rubber, but apparently the market thought, and still
+thinks, otherwise, although the actual necessities of manufacturers for a
+pale crepe to be employed in special processes must be comparatively small.
+
+The prevention of this natural oxidation was a problem which exercised the
+minds of all responsible for the preparation of pale rubbers, and much time
+and thought were expended upon it. Various theories were propounded, and
+the chief conclusion arrived at was that the darkening of rubber was to be
+prevented by excluding all the light possible from the drying houses. To
+this end windows were to be kept shut, or else they were provided with
+ruby-coloured glass, which incidentally kept out the air. In spite of these
+precautions, little success attended the expenditure of so much energy and
+thought. It was absolutely necessary that some chemical agent should be
+discovered which would make the preparation of pale crepe possible for any
+estate. This chemical would have to fulfil several requirements before it
+could become popular:
+
+     1. It must be a simple substance capable of being easily handled.
+
+     2. It must be very soluble, so that solutions could easily be made up
+     by inexpert workers.
+
+     3. It must be cheap.
+
+     4. It must be quite innocent of any harmful effect upon the quality of
+     the rubber.
+
+After months of investigation into the properties of other chemicals the
+writers decided that the only one which satisfactorily answered all
+requirements was sodium bisulphite. The writers make no pretension to any
+claim of having discovered the properties of this substance, which was a
+common chemical, and widely known. Even its action on latex was suspected
+before they engaged upon the work. These matters are only mentioned because
+the credit, if any, should be given to the laboratories of the Rubber
+Growers' Association.
+
+As soon as it began to be known on the market that sodium bisulphite was
+being used in the preparation of pale crepe, a great outcry was made, and
+estates were warned that no more rubber prepared in this way would be
+accepted. It was said that the chemical would destroy the "nerve" of the
+rubber,[2] and it was definitely stated that rubber prepared with this
+chemical was brittle. It must be remembered that brokers had some
+legitimate excuse in raising objections to the introduction of new and
+strange chemicals for preparing rubber, as they were quite without means of
+judging whether the rubber had suffered harm or not. Still, on the other
+hand, private tests had been made in conjunction with Messrs. Beadle and
+Stevens for fully eight months before the name of the chemical was
+mentioned in reports, and they had decided from the results of
+vulcanisation tests that the chemical was quite innocuous. Then, and only
+then, did we consider it advisable to recommend the use of sodium
+bisulphite in general estate practice. Owing to the initial prejudice
+against rubber prepared with sodium bisulphite, the results of our
+preliminary work were published by permission of the Rubber Growers'
+Association.[3] The original instructions to estates regarding the proper
+employment of this chemical were given in the private reports issued by the
+Rubber Growers' Association in 1911. At the present time it is probably
+accurate to state that it is now used by all estates preparing fine crepes.
+Representatives of manufacturers have sometimes given us to understand
+that the question of paleness of colour in such rubber is of no such
+importance as is impressed upon us as producers. While we are prepared to
+believe, we can only plead that from our point of view the supply arises
+from the demand. Such are the conditions governing the sale of rubber that,
+irrespective of the requirements of the ultimate user, we have to market
+rubber which is valued almost completely upon its appearance at the time of
+sale.
+
+[2] Williams, International Rubber and Allied Congress, London, 1914.
+
+[3] "The Employment of Sodium Bisulphite in the Preparation of Plantation
+Rubber," Beadle, Stevens, and Morgan, _India-rubber Journal_, August 2,
+1913.
+
+As long as such conditions prevail estates must continue to adopt any
+device of proved harmlessness, in order to obtain the best possible price
+for their product, and not because we desire to continue a practice which
+some assure us to be unnecessary, and which, moreover, adds somewhat to the
+cost of production.
+
+QUANTITIES OF SODIUM BISULPHITE.--It must be premised that, although sodium
+bisulphite is employed on some few estates in the preparation of sheet
+rubber, we do not advise the practice. It is unnecessary, and may lead to
+some little trouble and delay in drying. In any case, sodium sulphite gives
+the results desired for sheet rubber (see following). It must be
+understood, therefore, that we are concerned here, in the case of sodium
+bisulphite, with its employment in the preparation of fine pale crepe only.
+
+As the dry rubber contents of latices vary with the age of the trees, the
+general health of the trees, the seasons and general climatic conditions,
+the relative strain imposed by depletion of reserves through tapping, etc.,
+it will be clear that the effect produced by a definite quantity of sodium
+bisulphite in any given volume of latex will also vary--_i.e._, the effect
+depends upon the potential amount of rubber present. A dilute latex needs
+less sodium bisulphite than a richer latex to produce the same effect in
+colour.[4]
+
+[4] Incidentally there are certain occasions, as in the opening of areas of
+bark rested for long periods, when the latex is of a rich yellow colour.
+Sodium bisulphite will not "bleach" this colour, and it is well to remark
+again at this stage that the action of the chemical is only to avoid or
+arrest oxidation (darkening).
+
+Hence it follows that if in any factory uniform quantities of the solution
+are used for any given volume of undiluted latices from different areas of
+the estate, the effect upon the dry rubbers will vary. This explains why
+some estates obtain different shades of rubber in their fine pale crepes.
+
+The remedy obviously is to reduce the variation in latices by diluting them
+all to a standard rubber content as is done in sheet preparation. One is
+thus assured that the prescribed quantities of sodium bisulphite will meet
+requirements in every case, and that waste will be avoided.
+
+Working with a standard of 1-1/2 lbs. dry rubber per gallon the following
+formula should serve as a _maximum_:
+
+
+_Formula for Use of Sodium Bisulphite._
+
+     (_a_) Dissolve sodium bisulphite in water at the rate of 1 lb. to 10
+     gallons.
+
+     (_b_) Of this solution use 1 gallon to every 10 gallons of latex.
+
+MAKING A SOLUTION.--The making of a solution of the chemical would seem to
+be a simple matter, but to judge by the ill-effects sometimes observed in
+the dry rubber the simplicity of the operation appears to have been
+overrated. Great care must be exercised in preparing the solution, and the
+work should not be left to the few minutes preceding its actual
+requirement; such has been found to be the case in several factories, so
+that it is not surprising if the rubber is defective.
+
+The powder should be added gradually to water with thorough stirring, which
+should be continued for five minutes at least. Even then there may often be
+seen at the bottom undissolved particles, sand, and other impurity. It is
+necessary, therefore, in such cases to decant the solution through a piece
+of cotton cloth before using. No solid particles should be allowed to enter
+the latex.
+
+ABUSE OF SODIUM BISULPHITE.--It is now generally recognised that the abuse
+of sodium bisulphite, in the form of an excess, leads mainly to delay in
+the period of drying and the production of an overpale rubber.[5] It is
+probable that few estates, if any, now experience trouble due to this
+non-observance of the rules and quantities laid down for use.
+
+[5] "The Preparation of Plantation Rubber," Morgan, 1913, p. 74.
+
+RESIDUAL TRACES OF SODIUM BISULPHITE.--The prolongation of the drying
+period was attributed to the fact that traces of substances caused by the
+decomposition of sodium bisulphite remained in the rubber if the rubber
+were not sufficiently worked and washed on the rolls. These traces must
+have been very minute, but they were sufficient to retard the progress of
+drying. That much depended on the care exercised in washing is evident from
+the fact that samples prepared with varying quantities of the chemical show
+varying results on extraction. These samples were tested for the presence
+of sulphates. Of the series tested that sample prepared with bisulphite in
+the proportion of 1 part to 600 parts latex showed only a trace of sulphate
+present; while the one prepared 1:2,400 gave an equal quantity.
+Intermediate samples contained no trace of sulphate. On the whole,
+therefore, the presence of sulphate in crepe rubber is adventitious, and
+properly washed crepe prepared with moderate quantities of bisulphite may
+be taken as free from any residual quantities. Meanwhile there cannot
+possibly be any doubt of the advantages gained by the use of sodium
+bisulphite, and it would not be very wide of the mark if the statement were
+made that, in the event of this chemical being discarded, most contracts
+for pale crepe could not be fulfilled.
+
+SODIUM SULPHITE.--It would not be amiss to insist upon the point that while
+the nature of sodium _bisulphite_, as employed in the preparation of
+rubber, is anti-oxidant, sodium sulphite is employed chiefly for its
+anti-coagulant property. It is not used, therefore, in the making of crepe
+rubber, but is of service in the preparation of sheet rubber, where the aim
+is to keep the latex in good fluid condition as long as is necessary, and
+to retard coagulation slightly so that enclosed bubbles of gas or air may
+escape. Formulæ have been given for its use in the field when required. On
+some estates this practice is not found necessary, but a quantity of
+solution is always placed in the bottom of the reception vessels prior to
+the straining of latex into them. Only a small quantity is used, and as a
+working basis the following formula may be adopted:
+
+
+_Sodium Sulphite: For Use in the Factory._
+
+     (_a_) Dissolve 2 ozs. of anhydrous sodium sulphite in a gallon of
+     water.
+
+     (_b_) The gallon of solution, placed in the bottom of the reception
+     jar or tank, is sufficient for the treatment of 40 gallons of
+     standardised latex (1-1/2 lbs. dry rubber per gallon).
+
+The warning previously given regarding the necessity for thoroughness in
+the preparation of solutions is here reiterated. Stirring should be
+thorough, say for five minutes, and if there is any sediment or undissolved
+matter the solution should be strained through cloth before using.
+
+Where uniform jars or tanks are in use, the majority of which will contain
+uniform quantities of latex daily, the practice of using the chemical can
+be made almost fool-proof even in the hands of coolies. A calculation is
+made of the quantity of powder required for each vessel daily. The
+necessary number of lots is weighed out each morning and each placed in an
+envelope. The process is thus simplified by the fact that the contents of
+an envelope, neither more nor less, are required for each unit reception
+vessel. Even the weighing can be done by a coolie if he is given a
+counterpoise (of lead, for example) equivalent to the required weight.
+
+It will not be found necessary to do any vigorous stirring of the solution
+with the latex, as the latter is strained into the solution and the
+continued addition of successive quantities is sufficient to give a good
+mixture.
+
+USE OF FORMALIN.--Few estates now use formalin (formaldehyde) as an
+anti-coagulant. It must be acknowledged that when not abused there are
+points in favour of its employment in preference to sodium sulphite, but
+these are outbalanced by certain disadvantages. The argument may be stated
+thus:
+
+     _Points for_: (1) If made up freshly it is an effective
+     anti-coagulant.
+
+     (2) Formalin being the solution of a gas in water, there is no
+     residual substance left in the rubber to delay drying.
+
+     (3) Its use gives a bright clear rubber.
+
+     _Points against_: (1) Its cost at all times is greater than that of
+     sodium sulphite.
+
+     (2) If the jar is not sealed there is loss by evaporation, thus
+     increasing the cost.
+
+     (3) Its effect upon the rubber is uncertain. Even in normal quantity
+     it is said to cause "brittleness" or "shortness."
+
+Certain few estates, however, have continued its use, and no trouble is
+claimed to ensue. The following formula is stated to give satisfactory
+results in the preparation of sheet rubber, when applied as in the
+preceding paragraphs bearing on the employment of sodium sulphite:
+
+
+_Formula for Use of Formalin (Formaldehyde)._
+
+     (_a_) 1 pint of formalin is diluted with 5 gallons of water.
+
+     (_b_) Of this solution 1 gallon is required for 50 gallons of
+     standardised latex.
+
+In noting this formula the writer gives no recommendation regarding its
+use. Whatever may be the actual facts regarding the effect of formalin upon
+the vulcanisation of rubber, when used in minimum proportions, there can be
+no question concerning its injurious effect if used in excess. Beyond this
+the factors of cost and loss militate against its wider employment.
+
+
+
+
+CHAPTER IX
+
+_PREPARATION OF SHEET RUBBER_
+
+
+PALE SHEET.--The first form in which plantation rubber was prepared was as
+"biscuits" or sheets. This form remained in favour for some years. The
+first biscuits or sheets were rather dark in colour owing to the natural
+oxidation which followed. Then it was discovered that by diluting the latex
+the degree of oxidation was diminished, and later it was found that if the
+soft coagulum were placed in almost boiling water for a short time the
+resulting rubber was pale. Thus there arose gradually a demand for pale
+sheet. With our present knowledge we are in a position to state that the
+pale biscuits were not in any way superior to the darker ones, and they
+were in most cases actually inferior.
+
+It was found also as time progressed that sheet rubber, on air-drying,
+became covered with external surface moulds, and that, more often than not,
+the smell of the drying rubber was the reverse of pleasant. Even when dry
+the sheets had to be continually brushed free from moulds, and by the time
+the rubber reached the market it was again usually mouldy. Such are, even
+now, the handicaps under which those who prepare pale sheets have to
+labour. Few, however, are the estates making pale sheets, and they are
+confined almost entirely to native holdings.
+
+To those accustomed only to the preparation of crepe rubber, where
+coagulation can be effected in large batches, the preparation of sheet
+rubber always seems to demand much more labour. As a matter of fact,
+although the preliminary operations certainly do demand more care and
+labour than in crepe-making, there are compensating advantages in the
+machining stage. For the preparation of sheet of the highest quality on any
+but the largest scale, elaborate installations of machinery are quite
+superfluous, as equal results can be obtained with pairs of rolls worked by
+hand.
+
+UNIFORMITY OF PRODUCT.--There will be no need to enter again into a
+discussion of the preliminary operations of receiving and straining latex
+for sheet-making. They have been fully dealt with in Chapter VII. It used
+to be the general custom to mix the acid and latex in each individual dish,
+and in some small or non-progressive factories that is still the procedure.
+Quite apart from the question of labour entailed, the process is quite
+unnecessary. Even if comparatively small volumes of latex are handled,
+standardisation by dilution should be the rule, and the acid solution
+should be added to the bulk. It is possible to stir in the acid and to
+ladle out uniform quantities in each pan or dish from a bulk volume of up
+to 40 gallons if the organisation is efficient.
+
+On any but a small scale the labour entailed in the handling and cleaning
+of pans is excessive, and shallow tanks are now employed on most estates.
+The reception and standardisation of latex by dilution has already been
+discussed in Chapter VII. The combination of this practice with the
+employment of shallow coagulating tanks has simplified working and reduced
+the cost of labour. It is not intended to enter into any lengthy discussion
+relative to the merits of sheets made in pans as against those made in
+tanks. It is granted that it is possible to make a "pan" sheet superior in
+appearance to the general average of "tank" sheets; but from an economic
+standpoint the introduction of the use of tanks into all but the smallest
+factories is only a matter of time, if the demand for this class of rubber
+persists.
+
+THE IDEAL TANK.--Even the most modern installations of sheet-coagulating
+tanks must be regarded as merely temporary devices, as, given facilities,
+the room for improvement is so wide.
+
+The first tanks made erred in being too large, and as the result of
+experience the size of units has now been reduced to a maximum of 12 feet
+by 4 feet by 1 foot deep.
+
+[Illustration: UNIT MODERN COAGULATING TANK (TWO VIEWS).
+
+Construction of brick and cement with lining of glazed tiles. Note slots
+incorporated in side tiles. Partition boards in piles in the background.]
+
+Tanks are at present constructed either of hard timber or of brick and
+cement faced with glazed tiles; both types have inherent drawbacks. The
+wooden tanks are difficult to keep clean and in "sweet" condition. The
+glazed tiles, unless extremely well laid, allow the acid serum (from which
+the rubber is removed) to percolate between the interstices. Thus "pockets"
+of liquid collect beneath the tiles, and in process of the decomposition of
+certain constituents dissolved in the serum evil-smelling gases are set
+free.
+
+[Illustration: ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON
+THE RIGHT.
+
+Note drainage cocks, chute, and sieve in position.]
+
+It should not be a matter of difficulty for manufacturers to make sheets of
+thick glass sufficiently large to form the bed-plate and side-pieces
+necessary in the lining of a tank. If such adjuncts could be secured, the
+disabilities indicated above would be perhaps wholly removed. Unless there
+is a demand from estates, however, it is idle to expect a supply to be
+forthcoming.
+
+An even greater improvement would take the form of unit tanks cast in
+glazed white-ware with the necessary slots incorporated in the sides. At
+present no known firm makes such tanks of sufficient size. A unit could
+measure (internally) 6 feet by 4 feet by 1 foot deep, with slots 1-1/2
+inches apart, and 3/8 inch in width. The tanks might be reinforced with
+iron bars, so that they could either be used alone or embedded in the usual
+brick structure. The junctions of the bed-plate and side-pieces could be
+finely rounded so as to facilitate cleaning, and at one end a draining-hole
+could be made, say, 1 inch in diameter.
+
+[Illustration: CLOSER VIEW OF FOREGOING.
+
+Note partitions in position and coagulum being removed.]
+
+Meantime both the hard-wood tanks and those of glazed tiles find their
+particular applications. The former is generally employed in smaller
+factories, or where future large increases of crop preclude the present
+installation of a fixed system. The latter find use in large factories, or
+where no new areas remain to come into bearing.
+
+MODERN INSTALLATION.--As an example of a modern installation of coagulating
+tanks, we can do no better than offer reproductions of the system now in
+use on Pataling Estate.
+
+A warning must be given against employing all tanks of stone-ware or cement
+unless well glazed. Almost without exception, irrespective of the material
+used in the construction of coagulating tanks, wooden partitions are
+employed. In the few exceptional cases the partitions are either of glass
+or of aluminium. The former would appear to be the ideal substance, were it
+not for initial cost and loss by breakage. These disabilities may possibly
+be overcome in course of time.
+
+CARE OF TANKS.--The use of aluminium would have been wider had it not been
+for lack of supplies and the question of cost during the War. A novel
+method of employing aluminium partitions was introduced in the factory of
+Tremelbye Estate. There were no slots in the sides of the glazed-tile
+tanks, but the necessary slots were very ingeniously created by means of
+aluminium "distance-pieces," the two long edges of which were turned at
+right angles to the face of each piece to a depth of about 1/4 inch. The
+ends of the thin aluminium partition moved in the slot thus formed between
+two adjacent "distance-pieces." The friction between the surfaces was
+sufficient to allow all the partitions, when in position, to be raised well
+above the floor of the tank, so that a uniform level of latex was obtained.
+Slight hand-pressure only was then required to push the partitions down.
+
+Naturally the cleansing of glass or aluminium partitions presents no
+difficulty, but in the case of wood failure to ensure thorough cleanliness
+leads to possible defects in the finished dry rubber. Provided the wood
+could be made waterproof, no trouble would ensue, and hence various
+measures have been tried with that object in view. When new the boards have
+been surface-waxed or varnished, and the treatment has been repeated on
+occasions. But in course of time the surface film of waterproof material
+has disappeared, partially or wholly, and the trouble recurs. When
+partitions become sodden with serum, the surfaces are liable to be coated
+with a slime, consisting largely of organic growths which have an effect
+upon the latex, causing "pitting" on the surface of the coagulum and
+enclosed bubbles within.
+
+[Illustration: ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF
+GRAVITATING LATEX.]
+
+It is recommended, therefore, that wooden tanks, after ordinary cleansing
+daily, should be swabbed out with a 5 per cent. solution of sodium
+bisulphite. Wooden partitions should receive the same treatment, and once a
+week at least (or every day if possible) they should be placed in the sun
+for an hour or two, care being taken that both sides of a partition are
+exposed in turn. Before being placed in the latex, all wooden partitions
+should be made wet on the surfaces.
+
+Some years ago the writers had made a partition of vulcanite, which
+apparently would have proved of great service but for the initial cost. The
+advent of the War put the matter out of the question, but it is possible
+now that such a material would be worthy of extended trial. Except in the
+matter of cost, it would appear to have advantages over any substance yet
+tried; and if it were possible for estates to supply their own lower grade
+rubbers direct, the cost might be reduced considerably.
+
+[Illustration: A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION.
+
+Behind wall in background are the tanks in which latex is standardized.
+Note vent, to the left, through which latex flows and wooden "stopper" on
+edge of tank.]
+
+STANDARD LATEX.--Enough has been written (see Chapter VII.) to familiarise
+the reader with the use of this term for the description of latex diluted
+daily to a level of dry rubber content. Whatever may be the practice
+elsewhere, it is now fairly general on estates in Malaya to reduce all
+latices to a uniform "strength" for the preparation of sheet rubber. It is
+claimed that only in this manner can uniformity of product be achieved.
+
+The selection of a standard has been the outcome of general experience. It
+has been found that if too high a standard is taken difficulties arise,
+such as (1) unsatisfactory and uneven coagulation, (2) too thick a coagulum
+for easy working in general, (3) too extended a period of drying and
+smoke-curing, and hence too dark a colour in the finished rubber.
+
+[Illustration: A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION
+TANKS, RAISED, ON THE LEFT.]
+
+On the other hand, too low a standard also brings trouble in its train. The
+coagulum is too porous, will not stand handling, and the resultant sheet is
+too thin unless an abnormal thickness of coagulum is prepared. Furthermore,
+over-dilution means an increase in the number of tanks required for any
+original volume of latex. This involves an increase in floor area, and
+perhaps in the size of the building. The soft sheets, when rolled, may
+spread to such a width as to cause the edges to be squeezed under the
+cheek-blocks of the machines, etc.
+
+For all practical purposes, whether sheets are prepared in pans or in
+tanks, it has been found that the optimum results are obtained by the
+adoption of a standard approximating and not exceeding 1-1/2 lbs. dry
+rubber per gallon. Primarily this standard has a direct connection and
+interdependence with the distance between the partitions (or between the
+slots) in coagulating tanks. The distance found most practicable is 1-1/2
+inches. This thickness of coagulum, when prepared from latex not exceeding
+a standard of 1-1/2 lbs. dry rubber per gallon, is found to yield a very
+satisfactory sheet in all respects.
+
+It will be seen that we have two possible main factors of variation:
+
+     (_a_) Distance between partitions, causing visible differences in
+     thickness of coagulum.
+
+     (_b_) Dry rubber content of latex, causing differences in the density
+     (_e.g._, hardness or softness) of the coagulum.
+
+The effect of variation in (_a_) will be clear. Even when latex of a
+standard of 1-1/2 lbs. per gallon is employed the resulting sheet may be
+either too thin or too thick.
+
+Similarly, as already argued, the use of too low or too high a standard of
+dilution (when the factor of distance between partitions is not allowed to
+vary) is capable of causing much difficulty. While this is correct,
+broadly, it is found in the experience of some estates that their
+requirements are satisfied by a slightly lower standard than 1-1/2 lbs. per
+gallon. Thus it is not uncommon to note the adoption of a standard
+equivalent to 1 lb. 4 ozs. or 1 lb. 6 ozs. dry rubber per gallon.
+Experience dictates, however, that for the recognised standard measurements
+of modern tanks the practical limits of satisfactory density of latex lie
+between 1-1/4 lbs. and 1-1/2 lbs. per gallon.
+
+STANDARDISING INSTRUMENTS.--For standardising latex by dilution all that is
+required is an instrument which will preserve a perpendicular position
+while floating in latex, will be sufficiently sensitive to indicate fairly
+small differences in density of latex, and has one mark on its aerial
+portion accurately indicating a density corresponding to the required
+standard. On scientific grounds it can be demonstrated that such an
+instrument as employed in common practice would not be strictly
+accurate.[6] It is not proposed, in this section of the book, to discuss
+such considerations.
+
+[6] De Vries, "Archief voor de Rubbercultuur."
+
+Instruments of this nature are represented by the "Metrolac" (originating
+from the Rubber Growers' Association) and other similar recorders. They
+generally consist of a submersible bulb with a projecting stem which is
+graduated. The "Metrolac" differs from others in that the bulb is of
+torpedo form (thus reducing "skin friction"), and the graduations on the
+stem indicate actual weight of dry rubber per gallon instead of the
+ordinary specific gravity figures.
+
+Theoretical considerations to the contrary, it is found in actual practice
+in Malaya and Ceylon that, although such instruments are naturally delicate
+and require careful manipulation, they are of considerable practical value
+and satisfy a definite requirement. Until an instrument of greater accuracy
+and equal simplicity can be discovered all estates should regard the
+possession of a few "Metrolacs" as essential.
+
+The nature of their construction and the average conditions under which
+they are used (and abused) make it impossible to rely upon their accuracy
+indefinitely or for any long period. It is always recommended, therefore,
+that there should be at least two instruments available, one of which may
+be in daily use, while the other is kept in safe custody and only employed,
+say, once a week for purposes of checking the accuracy or degree of
+inaccuracy of the other. This can be done with reasonable approximity by
+placing both instruments in a tall vessel containing well-mixed and diluted
+latex. Instruments showing a marked degree of inaccuracy should not be
+preserved; but in cases of necessity "Metrolacs" from estates belonging to
+company members of the Rubber Growers' Association may be sent to the
+laboratories for repair and adjustment.[7]
+
+[7] This applies to the gilt brass instruments. As the result of experiment
+the Rubber Growers' Association are now introducing glass instruments.
+These are necessarily more fragile, but while unbroken can be relied on to
+give correct readings.
+
+Where field coagulating stations have been instituted on estates, it is
+strictly necessary that instruments should be provided in all cases; and it
+should be a rule that these are tested and corrected weekly by a standard
+instrument employed for that purpose only. This need was well recognised by
+many estates when, during the War and the consequent shortage of supply of
+"Metrolacs," a demand arose which was met in some degree by crude
+instruments of local manufacture, such as that commonly known as the
+"Castlefield bobber," contrived and made by the enterprising manager of the
+estate of that name. The demand for the more accurate instruments can now
+be met.
+
+METHODS OF USING THE INSTRUMENTS.--The "Metrolac" was devised and
+introduced by the writers on behalf of the Rubber Growers' Association, and
+directions for its use were given. Tables were prepared by means of which
+simple calculations for the dilution of any given latex could be made.
+These did not find an extended application, inasmuch as in the majority of
+cases native workers only were in charge of the processes of rubber
+preparation. In point of fact, such calculations are not strictly
+necessary, as the operation of standardising the latex can be done quite
+simply and skilfully by a trained native. Latex as it reaches the store in
+average weather from any particular division or field does not vary greatly
+in density. The trained coolie or foreman, basing his practice on
+experience, adds to the latex a quantity of water, and then makes a first
+test with the standardising instrument. Several additions of water (with
+thorough stirring) may have to be made before a test indicates that the
+correct density has been obtained, but it is surprising how quickly a
+skilled worker will arrive at the desired standard. Extreme or absolute
+accuracy is not insisted upon or desired, as avoidable delay is to be
+deprecated, and the result in any case is sufficiently exact for practical
+purposes.
+
+SKIMMING.--During the gravitation of the latex from the reception vessels
+(in which the standardising of the latex is effected) to the coagulating
+tanks, much surface froth is usually caused. This is best removed by means
+of a thin board of a width slightly less than the breadth of the tank. The
+skimmings are sometimes placed in pans and subsequently made into a second
+grade of sheet rubber, or they receive treatment with a small proportion of
+sodium bisulphite and eventually appear as fine pale crepe. The practice
+varies usually according to the form in which the general No. 1 grade is
+prepared.
+
+On some estates a great deal of the frothing is avoided by placing in
+position at the receiving end of the tank a perforated partition. This
+partition may be made of wood, or of stout zinc (or aluminium) carrying ten
+circular holes to the inch. Through this the latex percolates, while the
+froth is retained on a small area. The froth is removed prior to the
+addition of the acid. After stirring in the acid solution most estates
+again skim the surface of the latex; but if the stirring has been performed
+properly there should be little froth. This, when it collapses, in any case
+will appear only on the upper edge of the strip of coagulum, and after
+rolling should not be visible. It would appear, therefore, that the second
+skimming is not necessary.
+
+STYLE OF SHEET.--Within the last few years the custom of making plain
+sheet--_i.e._, sheet having a plain surface--has gradually given place to
+the preparation of ribbed sheet--_i.e._, sheet having a pattern marked on
+the surface. It would probably be correct to say that plain (smooth) sheet
+is now only prepared by natives or by some estates just come into bearing.
+Even in the latter case there is no reason why smooth sheet should be made,
+as hand machines are sold which will do all the work required. It will be
+evident to anyone acquainted with rubber preparation that in the matter of
+actual quality of rubber the question of smoothness or a pattern can have
+no bearing on the result. One advantage claimed for ribbed sheet which may
+entirely justify the preference exhibited by consumers, relates to the
+question of packing. When rubber arrives at home it is frequently found to
+be in an almost solid block, due to the pressure of the sheets superimposed
+in the case. The smoother the surfaces of the rubber in contact the greater
+the adhesion and the denser will be the mass, and consequently the greater
+the difficulty in separating individual pieces. Under such circumstances it
+is plain that the difficulty is diminished if the sheets have a raised
+pattern on them. It is noted also that the liability to mildew-growth is
+greater the smoother the surfaces of the rubber.
+
+On these grounds the "marking" of sheet rubber is to be commended. These
+reasons apart, it is really astonishing the difference made in the
+appearance of the sheets by impressing upon them a ribbed pattern, and it
+is highly probable that the market value of the rubber is slightly
+increased. It is not our duty to attempt to reason why this simple
+operation should increase the market value of sheet rubber; it is
+sufficient to recognise that it is so, and that money may be thrown away by
+neglecting to cater for the taste of the market. Of the patterns impressed
+upon sheet rubber there is a variety, but the general style is that known
+as the "spirally close-cut ribbing."
+
+STANDARD SHEET.--Leaving for the present the question of pattern of mark,
+one cannot do better by way of introduction than to reproduce the
+instructions[8] given generally to estates.
+
+[8] "Handbook on Preparation of Rubber," Rubber Growers' Association, May,
+1917, p. 28.
+
+ROLLING AND MARKING OF SHEET RUBBER.--Working with standard latex it is
+found that strips of coagulum 1-1/2 inches in thickness require little
+rolling to produce sheets of desirable thickness.
+
+     (1) The sheets or strips are first given a preliminary rolling with a
+     heavy hand-roller made of hard wood. The roller is passed once in one
+     direction, and once in the reverse direction.
+
+     (2) The coagulum is then passed through smooth machines twice, once
+     with the rolls fairly open, and once with a narrower space. It is not
+     found advisable to close the smooth rolls so tightly that the rubber
+     is made too hard.
+
+     (3) The sheets or strips are then passed once through a pair of
+     marking rollers. Various types of patterns are used, but the one which
+     appears to give the most satisfactory results is that known as the
+     "close-cut spiral." This produces the semblance of a small diamond
+     pattern on the rubber. The surface of the sheet is raised in
+     well-defined ridges, which appear to present the maximum drying
+     surface exposed to the atmosphere of the smoke-house. Thus, not only
+     is the appearance of the sheet rendered attractive, but also the
+     period of drying is reduced. Starting with standard latex and
+     following the procedure here described for rolling and marking, sheets
+     should be ready for packing in ten or eleven days. If the period is
+     longer, it is possible that the design or structure of the smoke-house
+     is at fault.
+
+WHEN TO WORK THE COAGULUM.--Before proceeding to discuss other points the
+question remains to be settled as to how long it may be necessary or
+advisable to allow the coagulum to remain in the serum before rolling it.
+For reasons of practical economy in factory working, it is usual to allow
+sheet rubber to remain over night, and the coagulum receives attention
+early next morning. During the interval (averaging about eighteen hours),
+the coagulum consolidates, leaving an almost clear serum if the correct
+quantity of acid has been added to the latex. Any but the very slightest
+trace of milkiness in the serum indicates an insufficiency of coagulant. If
+the serum is always definitely clear, there may be grounds for believing
+that an excess is being used. If the quantity of coagulant has been
+calculated to an average nicety, the serum should be just dubiously free
+from milkiness.
+
+The firmness gained by the coagulum on standing in the serum overnight
+should enable it to be handled next morning without any marked stretching,
+and in some estates the rubber is put direct through the first pair of
+smooth rolls without a preliminary consolidation by means of hand-rolling.
+
+Some estates prefer to handle the coagulum while rather softer, as it is
+claimed:
+
+     (_a_) That the coagulum is easier to work, and sheets of improved
+     appearance can be made.
+
+     (_b_) That there is greater freedom from "bubbles."
+
+     (_c_) That the incidence of "rust" is lessened.
+
+     These claims are substantiated in practice; but in the case of the
+     third, it only holds provided that the rubber can be finished and
+     placed in the smoke-house almost as soon as the last sheet has been
+     machined.
+
+In such cases all latex must reach the store comparatively early in the
+day--_e.g._, before noon. Three hours is allowed for coagulation, and the
+working of the rubber is then commenced. As a general rule this means that
+the operations of rolling and marking must be completed, a short interval
+given for dripping, weighing must be done, and the rubber placed in the
+smoke-house before night falls (as a rule about 6.30 p.m.).
+
+Unless factories dealing with a large crop are well equipped with
+artificial light, such a course is not open to them; in any case it remains
+true that night work should be avoided if possible. If, however, it can be
+arranged without increasing the cost of production, there would appear to
+be no objection to the early working of the coagulum as described above.
+
+HAND-ROLLING.--As already indicated, some few estates do not give the
+strips of coagulum any preliminary hand-rolling, as the rubber is
+considered to be sufficiently firm to be handled into the first machine.
+
+On most estates hand-rolling is found necessary, owing to the tendency of
+the long strips to stretch unduly, giving badly shaped sheets. This
+hand-rolling should be done carefully, and is best effected on a specially
+constructed table. This consists essentially of an inch-thick hard-wood
+plank about 2 inches wider, and 4 or 5 feet longer, than the strip of
+coagulum. Along the edges of the plank, and at right angles to its upper
+flat surface, may be fastened strips of wood about 1/2 inch square in
+section, thus forming a shallow tray open at either end. These strips serve
+two purposes:
+
+     (_a_) As the wooden roller is wider than the plank, they prevent the
+     coagulum being rolled too thin and too firm.
+
+     (_b_) They prevent the coagulum being squashed too wide, and tend to
+     keep the edges straight.
+
+To avoid "thick ends" it is sometimes considered advisable to insert, at
+either end of the rolling table, shallow wedges about 6 inches long, of the
+same width as the table (between the edge-strips), and with the sharp end
+of the wedge pointing in the direction of the length of the table. The ends
+of the coagulum are drawn up and finished on these inclined planes.
+
+These points may appear to be extreme refinements, but as long as rubber is
+valued on such grounds we must endeavour to meet the system imposed upon
+us.
+
+SMOOTH-ROLLING.--It is advised that, after hand-rolling, the coagulum
+should be passed through at least two machines having smooth-rolls. On some
+estates three such machines are employed. The purpose of this procedure is
+to reduce the thickness of the coagulum gradually. The same could be
+effected, of course, on one machine; but obviously the distance between the
+rolls would have to be readjusted at each operation and for each piece of
+coagulum. Apart from the time thus wasted, there is the certainty, in view
+of the rough adjustment of the machines, that the chances of obtaining
+uniformly thick sheets would be slight.
+
+The machines should be arranged as a battery, with the marking rolls at one
+end, so that the operations are consecutive. It is erroneous to imagine
+that heavy machines (such as those used in crepe preparation) are required.
+Light machinery only is necessary for sheet-making; but any available heavy
+smooth-roll machines in a crepeing battery may serve admirably for the
+purpose.
+
+MARKING.--Heavy machines are unnecessary for the purpose of putting a
+pattern on sheet rubber. If the rubber has been properly prepared a light
+pair of rolls is capable of exerting sufficient pressure to cause a good
+upstanding pattern.
+
+Rolls are cut in various designs: some with "diamond" grooves on both
+rolls; some with grooves of varying width and depth encircling the
+circumference of the rolls, thus creating a "stripe" effect on the rubber;
+and some with diagonally-cut spiral grooves placed closely together. The
+last has the greatest vogue at present, while the first has almost gone out
+of favour. An objection lodged against the second design is that the edges
+of the grooves sometimes cut through the rubber, so that the dried sheet
+divides in strips. It would appear in such instances that either the
+coagulum was too thin and soft, or that the grooves had been cut too deeply
+and sharply. In any case the choice of a design is an arbitrary matter, and
+should depend upon the effect produced on the rate of drying and the
+general appearance.
+
+The popular "close-cut spiral" roll is machined with varying measurements,
+but the usual design has grooves 1/8 inch wide by 1/8 inch deep and 3/16
+inch apart.
+
+Many estates have a particular "brand" cut in the middle of the rolls for
+purposes of identification. If this is done it is advised that the main
+grooving of the rolls be carried into the "branding" strip; otherwise grip
+will be lacking on this portion, and a certain amount of "cockling" of the
+sheets will result.
+
+Sheets are often seen in which the potential effect of the grooving is
+reduced to a comparatively flat pattern in place of the desired ridges. The
+fault is generally attributed to the shortcomings of the marking rolls.
+While it is true that the grooving often deteriorates by friction-wear when
+the rolls are running "free," experience generally decides that the
+deficiency in the appearance of the rubber should be attributed to faulty
+previous preparation rather than to the marking rolls. Sets of rolls have
+been changed often without justification or an improved result. It would
+always be well to be certain first that the trouble did not emanate from
+the fact that the coagulum had been previously rolled so thin and hard that
+the rubber could not be squeezed so as to fill the grooves. This has been
+found to be a common fault, and the general effect is to delay drying in
+spite of the thinness of the rubber.
+
+Again, the trouble may have been due to an incorrect standardisation of the
+latex, generally in the direction of too heavy a density (too rich a latex)
+being employed. The original thickness of the coagulum would be normal, but
+owing to the abnormal rubber-content the effect of passing through the
+smooth rolls would be the production of a strip thicker and firmer than
+ordinary. If this firmness is appreciable the resistance of the rubber to
+the squeezing action of the marking rolls will result in a flat
+pattern--_i.e._, the grooves cannot be filled, and the ridges are low.
+
+It is advised that all rolls used in the preparation of sheet rubber should
+be at least 18 inches wide, in order to avoid the appearance of thickened
+edges which delay drying.
+
+Working with the correct standard of dilution of latex, and following the
+procedure indicated in the foregoing paragraphs, the dry sheet should not
+exceed an average thickness (over ridges and depressions) of 1/8 inch.
+
+PREPARATION FOR SMOKE-CURING.--It used to be the custom to allow sheet
+rubber to air-dry first for periods varying from one to several days.
+Naturally moulds were soon formed, and when the sheets were quite
+smoke-cured a mass of the dead moulds could be seen, if not over the whole
+sheet, at least in the corners of each diamond mark. It has been
+demonstrated in practice that there is no advantage in allowing sheets to
+air-dry partially before smoking. In fact, to obtain the greatest benefit
+from smoke-curing, sheet rubber should be placed in the smoke-house as soon
+as possible. The same effect of mould-growth may be noted if the wet sheets
+are placed in a smoke-house insufficiently heated.
+
+Other defects may arise which can be traced to faulty treatment of the
+marked coagulum prior to hanging in the smoke-house and subsequent to
+rolling. These will be enlarged upon in a subsequent section of the book,
+and at present it will suffice to indicate the procedure which experience
+directs as likely to give the best results.
+
+When the lengths of coagulum leave the marking machine they are usually
+laid in piles containing two dozen or more strips. The piles are then cut
+into the required lengths, the exact length generally being determined by
+the available perpendicular distance between the supports in the
+smoke-house. It is necessary to remark that the piles of sheets should not
+be allowed to accumulate, but should be dealt with in subsequent treatment
+progressively. If for some reason this is not possible, then all piles of
+sheets should be turned on edge so as to assist the draining away of the
+serum or "mother-liquor," which continues to ooze from the rubber for some
+time after the squeezing in the machines.
+
+Where hot water is available the freshly cut sheets should be passed into
+it as soon as possible, and given a thoroughly good swilling. The caution
+must be given that the hot water should be changed very frequently and, if
+possible, after every batch, say, of a hundred sheets.
+
+The sheets should then be carried immediately to racks on which they are
+hung to drip. Generally these racks are situated under cover, but there is
+no reason why they should not be placed in the open air without cover or
+shade. From continued experience of this practice over a period of years it
+is found advantageous and to be preferred to the usual method of allowing
+sheets to drip under cover.
+
+While the sheets are fresh and loaded with internal moisture, the effect of
+sun-heat upon the surface, when exposed for, say, two hours, is nil; and
+the safety of the process can be guaranteed, provided the stated limit is
+not exceeded to an appreciable extent.
+
+[Illustration: THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN
+THE FACTORY.]
+
+After dripping for an hour or so, the sheets should be placed in the
+smoke-house. If it is a bright sunny day, no extra precautions need be
+taken; but on cool, dull days it would be advisable to light the fires
+earlier than usual, consistent with the work required to be done in the
+house--_e.g._, in the removal of dry rubber. There would appear to be no
+reason why the dry sheets should not be first removed, so that on dull or
+wet days smoking can be commenced as soon as the wet rubber has been hung.
+
+On a few estates where the smoke-houses are worked continuously, except for
+a few hours in the morning, a portion of the building is separated by a
+partition for the reception of the wet rubber. The sheets are taken
+directly from the marking rolls and placed in the chamber, beneath which a
+fire is started. The sheets thus drip in a warm and smoke-laden atmosphere
+until next morning, when they are weighed and removed to the smoke-house
+proper. It is claimed that freedom from "rust" is thus obtained.
+
+It will be clear that in the treatment of the rubber preparatory to smoking
+the whole process should be continuous, and delay should be avoided if the
+best results are to be obtained.
+
+[Illustration: THE NEWER METHOD OF HANGING IN THE OPEN AIR.]
+
+SMOKING OF RUBBER.--The assumption may have been noted above that the sheet
+is to be smoked. As far as our knowledge extends, none but small native
+estates now prepare sheet rubber of any other type, with the exception of
+certain patent processes. Air-dried sheets are generally made on
+small-holdings, and are bought in the market chiefly for the purpose of
+macerating and making into blanket crepe. We have no intention, therefore,
+of discussing the possibilities or qualities of air-dried sheets, as the
+output of sheet-rubber from our estates is always in smoked form. The
+drying (or, properly, smoking) stage will be discussed in Chapter XI.
+
+
+
+
+CHAPTER X
+
+_PREPARATION OF CREPE RUBBER_
+
+
+NO. 1, OR FINE PALE CREPE.--Considering first the preparation of the
+highest grade, fine pale crepe, it must be stated that the difficulties
+attached to the process are generally not sufficiently appreciated. In this
+pale rubber minor blemishes are so plainly apparent that their importance
+is highly exaggerated, and what would worthily escape notice in smoked
+rubber assumes disproportionate prominence in pale crepes. The very fact
+that such a delicate material as colourless coagulum has to be manipulated
+in coarse iron rollers, with the attendant oil and grease worries, should
+be sufficient to deter one from criticising too harshly the occasional
+lapses of an estate struggling to give of its best to the market. At the
+same time there can be no doubt that if precautions are taken to attend to
+all likely sources of contamination, defects in pale crepe may be avoided
+to a wonderful extent; and on some estates the observance of elementary
+rules enables the preparation of the finest pale crepe to be made almost
+mechanically.
+
+STANDARDISATION OF LATEX.--The question of the standardisation of latex has
+been dealt with in a general way in Chapter VII., and the reader is now
+familiar with the trend of the argument in its favour. It will be
+recognised that the necessity for standardisation exists to the same degree
+in the correct preparation of pale crepe as in the case of smoked sheet.
+Unless the dry rubber content is invariable, and the quantities of
+chemicals fixed, the colour of the crepe may vary appreciably.
+
+It may be pointed out that it is not _essential_ to adopt the same standard
+of dilution as for sheet preparation. Given that latices from all fields or
+divisions are fairly uniform, and of high rubber content, the standard may
+be taken at a figure equivalent, for example, to 2 lbs., or 2-1/2 lbs., or
+even 3 lbs. per gallon. It is wise, nevertheless, to take a lower standard
+for several reasons. For instance:
+
+     (_a_) The average dry rubber content varies with climatic conditions,
+     position of the cut on the tree, general health of the tree, etc. On a
+     rainy day the dry rubber content may be lowered too greatly by
+     adventitious circumstances.
+
+     (_b_) Recording instruments often fail to give even approximately
+     correct readings in rich latex. Errors may thus be made easily.
+
+     (_c_) A fairly soft coagulum means easier working on the machines,
+     less labour, and proportionately cheaper costs.
+
+[Illustration: THREE GRADES OF CREPE RUBBER.
+
+Left to right: fine pale crepe; second quality pale crepe; compound crepe.]
+
+It is advised, therefore, that for general purposes the same standard as
+that found suitable for sheet rubber should be taken--viz., 1-1/2 lbs. dry
+rubber per gallon. At all events the standard should not exceed 2 lbs. per
+gallon.
+
+COAGULATION AND COAGULANT.--Coagulation may be undertaken without any
+special arrangement of tanks, and is usually effected in the ordinary
+"Shanghai" glazed earthenware jars containing about 45 gallons. Given
+reasonable care, and a fairly fool-proof system of calculation for the
+quantities of chemicals required, no difficulty need be experienced.
+
+[Illustration: A WASHING SHED.
+
+Sheets are soaked in hot water in tanks in the background, and then
+scrubbed under a spray of cold water.]
+
+On a larger scale it is advised that proper reception tanks, in which
+standardisation can be effected, should be installed. Where both sheet
+rubber and fine crepe are being prepared, the whole system of
+sheet-coagulating tanks may be employed with considerable advantage, even
+to the insertion of the partitions.
+
+If ordinary jars are used, and the coagulum is left until the following
+morning, the mass of rubber has to be cut up into pieces of a size suitable
+for the machines. The knives or saws are sometimes rusty, and the colour of
+the coagulum is affected. The coolies often feed into the machines lumps
+which are too large, with the result that portions are thrust under the
+cheek-blocks and become stained.
+
+When a sheet-coagulating tank is used all labour of cutting the coagulum is
+obviated. The long strips are handled and fed into the rolls easily. It may
+be seen, likewise, that actual work is thus saved in machining.
+
+QUANTITY OF COAGULANT.--For a general discussion on the coagulant and
+quantities employed, the reader is referred to Chapter VIII. It is there
+recommended that for latex standardised to a level of 1-1/2 lbs. per
+gallon, the proportion of pure acetic acid should be in the ratio of
+1:1,200. Directions are there given for the making of the solution, and the
+calculation of the quantity required for any given volume of latex.
+
+It is pointed out that for average _undiluted_ latex the basis of
+calculation, for quantities of acetic acid required, should be taken on the
+ratio 1:1,000. Where latex exceeds a dry rubber content of 3 lbs. per
+gallon, it may be necessary to increase the quantity of acid to 1:800.
+
+If a standard of 2 lbs. per gallon is adopted, the formula given for the
+1-1/2 lbs. standard will not give full satisfaction, and the quantity of
+acid solution must be increased slightly in order to obtain complete
+coagulation. Assuming that the original solution is prepared in 1 per cent.
+strength, the following difference would be noted:
+
+     (_a_) One part pure acetic acid to 100 parts water (theoretically 99
+     parts).
+
+     (_b_)  _1-1/2 lbs. per gallon._    |      _2 lbs. per gallon._
+                                        |
+     Of the above solution use 1 gallon | Of the above solution use 1
+     to every 12 gallons of standardised| gallon to every 10 or 11
+     latex.                             | gallons of standardised latex.
+
+It is not possible to lay down an exact figure governing all cases, as so
+much depends upon the treatment undergone by the latex before it reaches
+the store.
+
+Some estates continue to use solutions of greater strength, generally 5 per
+cent., in crepe preparation. While such solutions may be effectively
+stirred in when the latex is dilute, it is advised that for intimate
+mixture the solution need not be stronger than 1 per cent.
+
+In estimating the quantities of acetic acid required much depends upon the
+interval which is to elapse between the addition of acid and the time of
+working of the coagulum. If the rubber is to remain until next morning, the
+average formulæ will be found suitable; but if it is required to work the
+coagulum with an interval of less than three hours, an excess of acid must
+be employed. The excess need be comparatively small, unless the interval is
+much reduced. For instance, it is the practice on some few estates to begin
+the machining of the coagulum about half an hour after coagulation
+commences; in which case it is usual to add from a quarter to a half of the
+normal quantity in excess. It need scarcely be pointed out that unless this
+procedure is strictly unavoidable it should be discouraged on account of
+the waste of coagulant involved. Incidentally, the use of strong solutions
+of acid under such circumstances may lead to increased deterioration of the
+rolls.
+
+COLOUR OF FINE CREPE.--We are sometimes assured that manufacturers do not
+pay the attention to the question of colour which sale conditions would
+lead one to believe. As far as we are concerned, and as long as there is no
+direct traffic between producer and consumer, it must be recognised that in
+the vast majority of cases we are forced to concern ourselves only with the
+standards set up in the markets. This, in spite of the knowledge that, all
+other things being equal, the arbitrary distinctions in colour afford no
+indication of the intrinsic value of the rubber. Under present
+circumstances it is plain that if paleness is demanded it has to be
+supplied.
+
+Probably without exception all estates employ sodium bisulphite as the
+agent for the prevention of that darkening (oxidation) which is natural in
+drying rubber.
+
+SODIUM BISULPHITE.--A formula for use of this chemical is given in Chapter
+VIII., and is applicable to latex standardised to 1-1/2 lbs. dry rubber per
+gallon. If a higher standard is chosen the quantity calculated as in (_b_)
+of that formula may be increased slightly, and the exact requirements found
+by experience. The caution must again be given that the employment of an
+excess of sodium bisulphite will lead to the production of an over-pale
+rubber, and a prolongation of the drying period. If thick crepes are made,
+an excess of the chemical is sometimes made visible by a greyish powder
+deposited on the edges of the strips of dry rubber.
+
+It must be emphasised that the formula in Chapter VIII. indicates the
+_maximum_ quantities required for use with standard latex. Many estates
+will find it expedient to use less of the chemical; and if it is found that
+the desired result is not obtained from normal proportions, attention
+should be directed to the points discussed in the following paragraph.
+
+EVALUATION AND DETERIORATION OF SODIUM BISULPHITE AND SODIUM
+SULPHITE.--Sodium bisulphite and sodium sulphite are both bought for our
+purpose in the form of a fine crystalline powder, and on analysis good
+specimens should contain over 90 per cent. pure substance, when packed in
+well-sealed vessels.
+
+It has often happened that shippers or local sellers, by inadvertence, have
+supplied the one chemical in place of the other--to the detriment of the
+rubber and the discomfiture of managers of estates. The error, as a rule,
+has not been detected for some time, and then perhaps only as a result of
+complaints or enquiries reaching the laboratories. To the layman, and
+certainly to the native who usually has charge of these substances, it is
+not a simple matter to distinguish between them without special knowledge.
+There are certain elementary tests, however, which can be applied on all
+estates serving to make the distinction, but affording no information
+regarding the actual quality of the chemicals. They are given in a
+comparative form on page 116. Samples of doubtful specimens may be sent to
+the laboratories for analysis, but the bulk of the chemical should not be
+used.
+
+During the War some very poor shipments were received, and much trouble was
+caused. Under normal conditions there can be no question that it is to the
+interests of chemical manufacturers to supply the best article; and it is
+anticipated that in future there should be no difficulty in procuring
+shipments of a high degree of purity.
+
+      _Sodium Bisulphite._           |     _Sodium Sulphite._
+                                     |
+  1. If in good condition it         | 1. It has no perceptible
+  has a powerful odour of            |    odour.
+  sulphur dioxide.[9]                |
+                                     |
+  2. In solution it should turn      | 2. In solution it should turn
+  a blue litmus-paper red.           |    a red litmus-paper blue.
+                                     |
+  3. It exhibits a marked tendency   | 3. The tendency to "cake"
+  to "cake" if the                   |    is less marked than in
+  drum is allowed to                 |    the case of the bisulphite.
+  remain open.                       |
+
+[9] High-grade sodium bisulphite has very little odour, but by the time it
+reaches the estate, and as a result of short exposure to the moist
+atmosphere of the tropics, a little decomposition sets in and a strong
+odour of sulphur dioxide gas is noticeable.
+
+It will be evident that, as sodium bisulphite under normal conditions gives
+off a gas when exposed to the atmosphere, it deteriorates in quality
+continuously. It is the potential presence of this gas which makes the
+powder effective as an anti-oxidant and disinfectant. It is within the
+experience of all accustomed to the handling of this chemical, that in
+addition to the loss of gas, the powder cakes into a hard mass on exposure.
+If only the top layer is caked, the remainder may be in fair condition; but
+no caked portions should be used, as they cannot be of good quality. They
+may, however, be used for the treatment of scrap rubber, to be discussed
+later.
+
+CARE OF SODIUM BISULPHITE.--The ready tendency of sodium bisulphite to
+deteriorate on exposure should give sufficient indication regarding its
+treatment in storage. It should be bought only in drums (or other air-tight
+containers), and should be stored in a dry place. No drum should be opened
+until required, and the common practice of keeping an open drum on the
+floor of the factory should be avoided.
+
+Drums are of two sizes, generally containing 1/4 or 1/2 cwt. respectively.
+It will be obvious that, although the prime cost may be cheaper with the
+larger quantity, it would always be preferable to secure the smaller
+drums, as the loss on exposure will be less.
+
+Most commonly the 56 lb. drum is purchased. It should not be difficult to
+calculate the period during which the contents will be consumed, on the
+basis of a maximum of 1 lb. per 100 gallons of latex. A 56 lb. drum,
+assuming no loss or waste, should be sufficient to treat _at least_ 5,600
+gallons of latex (say, 8,500 lbs. of rubber)--if the bisulphite is of
+first-class quality, and the use is applied only to the preparation of fine
+pale crepe.
+
+Where the quantity used per diem is small, it is advised that precautions
+should be taken to preserve the quality of the chemical when a drum is
+opened. It might be of advantage to place the contents of the drum in
+smaller sealed tins, or to have made a special container (with a closely
+fitting lid) into which the powder can be placed as soon as the drum has
+been opened.
+
+MIXING SOLUTION WITH LATEX.--Emphasis has been laid, in Chapter VIII., upon
+the necessity for care in the preparation of the solution. Equal regard
+must be given to the mixture of the solution with the latex.
+
+On a few estates it used to be the practice to add the powder to the
+solution of acid, with stirring. Obviously this led at least to a great
+loss of efficiency, owing to the rapid escape of the gas which was evolved.
+
+The solution of sodium bisulphite should be poured into the latex in as
+uniform a distribution as possible. The mixture of solution and latex
+should be thoroughly stirred, and if only natives are in charge a minimum
+period of five minutes should be prescribed before the addition of the
+coagulant. A thorough stirring should again follow the advent of the acid.
+
+If these elementary rules are not observed faithfully, the deficiency will
+most probably be manifested in the dry rubber in the shape of streaks of
+varying shades of colour.
+
+Finally it may be insisted upon that deteriorated sodium bisulphite should
+not be used. In order to obtain an effect double the quantity may be
+required, and the residual salts left in the rubber on evaporation of the
+moisture will be responsible for prolonged drying, surface deposits, and
+possibly "spot disease."
+
+FORMER METHODS OF MAKING PALE RUBBER.--Merely as a matter of historic
+interest it may be mentioned that previous to the introduction of sodium
+bisulphite pale crepes were made in comparatively small quantity by various
+devices, among which the following might be quoted:
+
+     (_a_) Use of excessive quantities of strong acetic acid.
+
+     (_b_) Extreme dilution of latex in conjunction with excessive
+     quantities of acid.
+
+     (_c_) Extreme dilution in conjunction with steaming and excess of
+     acid.
+
+     (_d_) Extreme dilution of latex in conjunction with excess of acid and
+     subsequent heating of the coagulum in hot water.
+
+     (_e_) The use of excess of a mineral acid such as sulphuric acid.
+
+     (_f_) The skimmings and very dilute latex, coagulated with excess of
+     acid.
+
+WORKING THE COAGULUM.--Description of the details of necessary machinery
+for crepe-making is relegated to Section III. of this book. Here we shall
+treat only of the matter in general.
+
+In the preparation of crepe rubber heavy machinery is necessary, and ample
+engine-power must be available. The machines should comprise three types:
+
+     (_a_) With rolls cut in such fashion, and run at such different
+     speeds, as to have a macerating effect upon the coagulum. Such
+     machines or rolls will be referred to as "macerators."
+
+     (_b_) Intermediate rolls, grooved in varying designs and geared
+     differentially. These reduce the thick rough crepe obtained from the
+     macerators into a form suitable for passing to the rolls described in
+     (_c_). They are sometimes called "crepers," but as this term may be
+     applied equally to the macerating rolls, they will be termed the
+     "intermediate" rolls.
+
+     (_c_) Smooth rolls usually run at approximately even speeds and, as
+     their name denotes, devoid of any grooving. They are called "smooth"
+     rolls or "finishers."
+
+Without such equipment it is not possible to prepare the grade which is
+known as "fine pale crepe." In the common acceptation of this term crepe of
+No. 1 quality generally connotes fineness and paleness with a thin crepe
+which has a good, smooth, and fairly well-knit texture.
+
+It is, of course, possible to make a thick pale crepe, using only the
+macerators and intermediates, but the "finish" will be that typical of the
+particular grooving of the intermediate rolls. For the preparation of crepe
+ordinarily, the possession of smooth rolls is a _sine qua non_.
+
+For reasons which will be explained more fully in the chapter dealing with
+the defects of crepe rubber, the practice of preparing thick crepes direct
+from the coagulum is now very uncommon. Thick crepes are generally made by
+reworking dry rubber, either in the form of thin crepes or from air-dried
+sheets. The market for the latter in Malaya is confined almost entirely to
+Singapore, where factories buy native rubber and re-work it into thick
+crepe.
+
+The bulk of the output of No. 1 crepe from estates is in the form of thin
+"fine pale crepe." The artificial standard set up by buyers and brokers
+necessitates this thin crepe being of even texture and fairly free from
+small holes ("looseness"). What difference the small holes are to make in
+the vulcanising properties of the rubber is beyond our knowledge; but such
+being the standard, it must be attained if the full price is to be
+obtained.
+
+In order to secure the desired effect the coagulum must be passed
+consecutively through the three types of rolls, and undergoes a varying
+degree of working in each.
+
+Given the necessary equipment of machines, it is possible to make a good
+specimen of thin pale crepe if the coagulum passes through all the rolls a
+total of twelve times (or even less in exceptional cases). There is no
+intention of suggesting that this is possible on all estates. Clearly the
+number of times the rubber passes through the rolls will depend upon the
+total efficiency of the machines. This in turn involves such factors as
+(_a_) the size of the rolls, (_b_) the number of machines of each type,
+(_c_) the gearing of the pinions, (_d_) the speed of the drive, etc. Again,
+much depends upon the nature of the coagulum worked. A fairly soft coagulum
+will offer less resistance, and conversely a dense coagulum will require
+more machining.
+
+It has been shown by the writers in previous publications that over-working
+of the coagulum has an effect on the vulcanisation of the rubber; and this
+has been confirmed by others.[10] Apart from this point, it should be
+recognised that over-working, beyond that necessary to produce a thin crepe
+of even texture, is to be deprecated, on the ground of economy, in working.
+
+[10] Bulletin No. 27, Department of Agriculture F.M.S., April, 1918,
+"Preparation and Vulcanisation of Plantation Para Rubber," Eaton, Grantham
+and Day.
+
+Owing to the existing differences in equipment and speed of drive, etc.,
+the regular practice of any one estate may be unsuitable for another. It
+remains, therefore, a matter of study for each estate to discover the
+minimum number of times which rubber should pass through the machines,
+consistent with the factors indicated above. In any case it may be assumed
+that if any factory cannot prepare a good crepe by passing the rubber, say,
+twelve times through the rolls, there is some deficiency in the machines,
+or of speed; the coagulum may be too hard, or the rolls may be badly worn.
+
+LOWER GRADES OF CREPE RUBBER.--Even a few years ago it was plain that the
+lower grades of crepe (_i.e._, all grades lower than first latex rubber)
+were not sufficiently appreciated in the market. There was often a marked
+difference in price between a first-grade crepe and crepe made from
+naturally coagulated lump. This arose chiefly from lack of knowledge. It
+has since been recognised in some measure that no reason exists for such a
+wide difference in price, and more recently the margin between even the
+first-grade rubber and the lowest grade of scrap rubber has been a
+gradually diminishing one. Providing sufficient care is exercised in the
+preparation of the lower grades, one would expect to see but very small
+difference in prices between any two grades. It is true that adequate
+attention has been given to the preparation of the scrap grades only in
+comparatively recent years, and it is acknowledged that when high prices
+were ruling for first-grade rubbers sufficient attention was not generally
+given to the subject of the preparation of the lower grades.
+
+NATURALLY COAGULATED LUMP RUBBER.--The grade of rubber made from the
+naturally coagulated lump which forms in buckets and carts is usually of a
+mixed colour, due to the fact that the lumps oxidise very quickly. When
+they are allowed to remain overnight before being machined, it can be
+imagined that the colour of the dry crepe would be very dark, or would
+contain very dark streaks. Such is ordinarily the case, unless special
+precautions are taken.
+
+Providing that the coagulated lump is free from bark, leaves, and
+leaf-stems, and certain other precautions taken, the difference in price
+between coagulated-lump crepes and first-grade crepes should be very
+slight. Too often, however, not sufficient supervision is given to the
+coagulated-lump rubber, and it is common to see it come into the factory
+containing leaves and bark. These should be picked out before the latex is
+strained, but obviously it would be better to ensure that they did not
+enter the buckets in the first place.
+
+It would seem reasonable to suppose that if some means could be employed
+for preventing or checking the surface oxidation of naturally-coagulated
+lump rubber, there would be a corresponding improvement in the colour of
+the dry crepe. That such a method is practicable has been demonstrated on
+many estates. The lump when lifted out of the latex is allowed to drain for
+a few minutes, and is then (without squeezing) placed in a dilute solution
+of sodium bisulphite. A 1 per cent. solution is sufficiently powerful. It
+is not to be thought for a moment that by the use of sodium bisulphite any
+previous oxidation will be counteracted; all that is claimed for the
+treatment is that any further surface oxidation will be checked, and the
+rubber may be allowed to remain until the next day, for working, if it is
+so desired. It will probably be found that quite a quantity of latex has
+been expressed from the lumps by contraction, and acid may be added to
+obtain the rubber from this. On other estates the lump rubber is worked on
+the machines as it is received, and the resulting crepe is submerged in a
+weak solution of sodium bisulphite over-night. It is then rinsed in water
+and hung to drip before weighing and placing in the drying house. Under
+certain conditions some of the lump rubber darkens rapidly during transport
+to the store, and any such oxidised portions must be rejected if a uniform
+colour is to be expected in the crepe.
+
+Following the procedure indicated above, some estates find it possible to
+prepare from naturally coagulated lump rubber a crepe which can be classed
+as No. 1 grade.
+
+SKIMMINGS AND WASHINGS.--The skimmings of tanks, as already shown, may be
+prepared sometimes as a second quality of smoked sheet; but generally they
+are amalgamated with the rinsings of cups and buckets, treated with sodium
+bisulphite and acid, and made into crepe form.
+
+The cup-washings, as they arrive at the store, represent a very dilute
+latex, the rubber from which is generally of a greyish colour.
+
+Bucket-washings should yield a good type of pale rubber if they are
+obtained properly. To obtain the maximum quantity of good rubber the
+buckets should first be rinsed. A gang should be taken, a small quantity
+(say a quart) of water poured into the first bucket, and this dilute latex
+used progressively in all the buckets of that gang of tappers. The result
+is a fair latex which can be added to the bulk of No. 1 latex, provided it
+is free from dirt. Where sheet rubber is being prepared, carefully strained
+cup-washings or bucket-washings may be utilised in the dilution of the
+latex to the required standard, thus increasing slightly the percentage of
+first-grade rubber.
+
+TREE-SCRAP.--As tree-scrap is a naturally coagulated rubber, it should be
+expected to show up well in quality. This is usually the case; but from
+what has been said of the effect of sun-heat it will be understood that if
+trees are not regularly "scrapped," there is a danger that the crepes may
+be found to contain tacky streaks due to the inclusion of old scrap which
+has been sun-baked. In hot dry weather, on widely planted areas tapped on
+alternate days, it has been noticed that scrap remaining for two days often
+exhibits a resinous appearance, and feels sticky to the touch.
+
+If tree-scrap is to be made as a separate grade, as used to be the general
+custom, care should be taken to see that it is free from bark and dirt. On
+some estates where scrap-rubber is paid for per pound collected, it is
+usually the rule to insist that scrap shall be washed free from dirt and
+picked free of bark. This course is to be commended, but might probably
+prove impracticable to the majority of estates. Theoretically, of course,
+the operation of machining should rid the scrap of all traces of bark; but
+in practice it does not do so.
+
+Some proportion of the tree-scrap is usually found to be heavily oxidised,
+and naturally if a crepe of uniform colour is to be obtained these dark
+scraps must be rejected, otherwise dark streaks will be formed. Coolies
+should be instructed to sort out the dark pieces before arriving at the
+store.
+
+BARK-SHAVINGS.--It has been intimated in a previous section that the method
+of obtaining and collecting bark-shavings varies with the type of labour
+employed.
+
+Where the scrap is removed from the edge of the bark on each occasion
+before tapping, the amount of rubber to be extracted from the dry shavings
+is very small--so small, in fact, that when the price of rubber is low, it
+is doubtful whether it pays to collect and work the material.
+
+On the other hand, where trees are not "scrapped" before tapping, the
+bark-shavings and tree-scrap are collected together, and the amount of
+rubber derived from the mixture may be 30 to 40 per cent. upon the gross
+weight--depending chiefly upon the quality of the tapping (_i.e._, in this
+case, the thickness of the paring). Another factor influencing this figure
+would be the effect of using an anti-coagulant on the cuts.
+
+Bark-shavings entail such wear upon the ordinary machines during working,
+especially if fairly free from rubber, that unless the factory is equipped
+with a special "scrap-washer" it is advised that this material should be
+sent for working to a factory having the necessary equipment. Whenever
+possible, bark-shavings should receive treatment on the day of collection.
+
+It used to be quite common to see heaps of bark-shavings accumulating on
+the floor of a factory, and generating excessive heat. Yet these heaps were
+allowed to stand about for a day or days. Is it any wonder then that
+tackiness was found to develop when the rubber was dry? It is here
+definitely laid down that no heaps of bark-shavings should be accumulated
+even for half a day. Tanks should be provided in which the shavings should
+be submerged in water.
+
+EARTH-SCRAP.--Of all grades of crepe this is the one most liable to become
+tacky in transit. This tackiness to a large extent cannot be avoided, as
+old pieces of earth-scrap may be brought in amongst the bulk. Probably
+these old pieces have been exposed to the sun for days, and have become
+quite resinous. It would be practically impossible to go through all
+earth-scrap in order to find these odd pieces, but unless this were done
+one could not guarantee that the earth-rubber would always be free from
+tackiness. The difficulty does not appear, however, on estates where
+earth-rubber is collected systematically at very frequent intervals.
+
+FIBROUS MATTER IN LOW-GRADE RUBBERS.--It is sometimes found in this and
+other lower grade rubbers that pieces of cloth or cotton-waste are
+concealed. Coolies may have used them for cleaning cups, or the store
+coolies may have been at fault. Earth-scraps especially should be examined,
+before working, for such extraneous matter.
+
+SCRAP-WASHERS.--These are heavy machines specially devised for the
+treatment of lower grade rubbers. In these the raw rubber is well
+masticated and freed from impurities, if the machine functions efficiently.
+
+There are several types of these machines, all of which are efficient. That
+best known is the "Universal" washer, made by Joseph Baker, Sons, and
+Perkins, Ltd. (formerly Perkins Engineering Company). Coming into local
+favour during the War, the "U.E." scrap-washer, made by the United
+Engineering Company (Singapore), gives very good service. The "C.C.C."
+washer, made by the Colombo Commercial Company, is suitable for the
+purposes of an average estate. There are others, less well known. Most of
+these machines are made in varying sizes to meet the requirements of small,
+medium, or large estates; and if funds are available, a scrap-washer should
+be regarded as an essential item in the machinery of any estate employing
+engine power.
+
+The rate of output of scrap-washers will depend mainly upon the speed at
+which they are driven, and when ordering the equipment it would be
+advisable to state the ordinary speed of the back-shaft, length of drive,
+etc. It does not follow that the larger the rate of output, the greater is
+the efficiency of the washer. The point is not as to what quantity of
+rubber can be taken out per hour, but what quantity is actually freed from
+impurities.
+
+It is advisable for the superintendent to obtain a thorough knowledge of
+the general construction and principles of the particular scrap-washer
+employed. In the past it was not uncommon to find superintendents innocent
+of the fact that a certain type of washer possessed movable parts upon
+which the efficiency of the cleansing largely depended. It was often found
+that these parts, which were intended to be removed and cleaned at
+intervals, had become firmly fixed and could not be removed for inspection.
+
+It must be recognised also that the machines are liable to considerable
+damage if extraneous substances are allowed to enter--for example,
+tapping-knives, stones, pieces of iron, spouts, etc., which are sometimes
+present in the loose scraps of rubber or shavings, owing to the
+carelessness of coolies. Under the best regulated-system, such accidents
+occasionally occur, but a great deal of trouble could be avoided by having
+it understood that each charge must be sorted over before entering the
+washer.
+
+Again a deal of extra work, and much wear and tear, is caused by the
+_abuse_ of the scrap-washer--_e.g._, in the cleansing of earth-scrap. As
+this reaches the factory it often contains a quantity of internal or
+adhering earth. Before entering the washer a good proportion of the
+external soil could be removed if the scraps were thrown into a tank and
+given a thorough soaking and stirring. In a similar manner dry
+bark-shavings, which have been allowed to accumulate, could be softened.
+
+In the actual working of scrap-washers instructions are generally given by
+the makers. These sometimes advise the introduction of warm water (or of
+steam into the cold water supply) for an interval during the working of
+each charge. Where possible, such instructions should be followed, as by
+this means the individual pieces of rubber are massed together, in the
+final stage, into a "sausage" form which is easy to transport and to
+manipulate in the ordinary crepeing battery.
+
+COMPOUND CREPES.--The attitude of both buyers and sellers with regard to
+the types of lower grade rubbers appears to be changing. In the past, from
+any one estate there might be obtained as many as six grades of crepe below
+No. I. These comprised:
+
+     (1) A pale rubber (often streaked) obtained from coagulation of cup
+     washings and bucket rinsings.
+
+     (2) A pale rubber (often streaked) obtained by coagulation of the
+     skimmings from the surface of the No. 1 latex.
+
+     (3) A streaked and dull rubber prepared from naturally-coagulated
+     clots found in cups, buckets, and latex carts.
+
+     (4) A streaked rubber prepared from scrap which had coagulated upon
+     the face of the cut bark.
+
+     (5) A brownish and streaked rubber made by maceration of bark-shavings
+     to which pieces of tree-scrap adhered.
+
+     (6) A dark rubber, often tacky, prepared from scrap found in or on the
+     ground near the base of the trees. As it is often a matter of weeks
+     between any two regular collections, it is easy to understand why the
+     dry rubber was more liable to be "tacky" than any other grade of
+     crepe.
+
+It will have been evident to all who have acquaintance with these grades,
+as shipped from many different estates, that the diversity in the various
+shipments must have been rather bewildering. There appeared to be a
+regrettable lack of uniformity, even in the appearance of, say, a bark
+scrap rubber from any two estates. When, in addition to these variations,
+the further complication of condition of cleanliness is introduced, one may
+realise the difficulty attaching to the evaluation of these rubbers as they
+appeared upon the market.
+
+Although the foregoing paragraph is written in the past tense, it should be
+pointed out that within certain limits the trouble continues to exist with
+respect to the output of a great number of estates.
+
+In the case of many, it has been realised that the manufacturer does not
+want to buy a large number of "parcels," all differing in some respect. It
+is probably correct to state that what a manufacturer requires is a big
+"parcel" uniform in appearance and treatment, even though the colour may
+not be so light as that of many smaller lots. This statement is modified
+with the proviso that the rubber, no matter what its colour or appearance
+may be, must be free from dirt, grit, and bark.
+
+The difficulty of making a uniform product from several types of lower
+grade rubbers has been successfully solved on several estates by the
+preparation of a "compound" crepe composed of a mixture of the best lower
+grades in approximately definite proportions daily. Naturally the shade of
+colour of this compound crepe will depend largely upon the types of rubber
+employed, but as a rule it is somewhat darker than the highest of the types
+employed in the mixture. To the writers this seems immaterial as long as
+the manufacturer is offered a larger and more uniform lot which can be
+given uniform treatment in vulcanisation processes. Neither would it appear
+that the seller suffers any monetary loss. In point of fact it will be
+found probably that the reverse is the case. For instance, supposing it
+were decided to mix for a compound crepe--
+
+     (_a_) Naturally coagulated lump rubber.
+
+     (_b_) Tree-scrap.
+
+     (_c_) Bark-shavings scrap.
+
+The product would be darker in colour than (_a_) and slightly better than
+(_b_). Let it be granted that there might be a monetary loss on (_a_), it
+is probable that there would be a slight gain in comparison with the usual
+prices obtained for (_b_) and (_c_). Now, as a general rule, the actual
+percentage of crop made into (_b_) is appreciably less than that made into
+(_c_) and still less than (_b_) and (_c_) together. Apparently, therefore,
+there would be a margin of profit on the whole by making a compound crepe.
+It may be pointed out, on the other hand, that there might be expended on
+the manufacture of this crepe more time and labour, but as against this the
+labour of sorting and grading would be simplified.
+
+Unfortunately this process is not open to estates which do not possess a
+scrap-washer. _It is essential that the rubber should be free from grit,
+sand, and bark particles._ In the absence of a scrap-washer for the
+cleansing of the bark-shavings, it would be futile to attempt to make a
+compound crepe containing that type of rubber, as one would run the risk of
+spoiling the whole. It seems certain that in course of time a scrap-washer
+will be considered as necessary a piece of machinery as an ordinary
+crepeing machine in the factories of estates having sufficient means. Until
+that time the preparation of compound crepes must be the privilege only of
+well-equipped estates, unless other estates can send their lower grade
+rubbers for treatment in a scrap-washer to their more fortunate neighbours.
+
+In previous publications a diminution in the number of grades of crepe
+rubber has been advocated, and it is gratifying to find that in many cases
+the amending grades suggested have been improved upon. Many estates now
+make only three grades of crepe--viz.:
+
+     (_a_) No. 1. From latex coagulated in the store.
+
+     (_b_) No. 2. Compound.
+
+     (_c_) No. 3. Earth-rubber.
+
+It will be seen that the compound crepe includes all types between fine
+pale crepe and earth-rubber. Naturally one could not safely recommend the
+inclusion of earth-rubber in any compound crepe, as the risk of possible
+"tackiness" in the whole would be serious. In the case of the bark-shavings
+rubber to be incorporated, it is first cleaned alone in the scrap-washer.
+Then all types are mixed together again in the scrap-washer in proportions
+ruled by the experience of the usual average percentages of each grade of
+the crop.
+
+Besides the estates having only three grades, there are others which make
+four--viz.:
+
+     (_a_) No. 1. From latex coagulated in the store.
+
+     (_b_) No. 2. Compound, from cup washings, etc., skimmings, and
+     naturally coagulated lump.
+
+     (_c_) No. 3. Compound, from tree-scrap and bark-shavings rubber.
+
+     (_d_) No. 4. Earth-scrap.
+
+     Other variations are possible, but their number is limited, and they
+     all conduce to simplification of working, and a supply to the market
+     of rubber having greater uniformity.
+
+NEED FOR INCREASED CARE WITH LOWER GRADE RUBBER.--In the ordinary procedure
+of estate-working there appears to be an undesirable variety in the style
+of lower grade crepes. On some estates an examination of these rubbers
+would appear to suggest that there need be no expenditure of care in the
+preparation or the form in which it is made. This is a great mistake. With
+the exception of the lowest grade (earth-rubber), it would not be unfair to
+state that the quality of the rubbers on testing should be very little
+inferior to the No. 1 product. Often, as in the case of naturally
+coagulated rubbers, they are superior in some respects to ordinary fine
+pale crepe. Doubtless manufacturers are aware of these facts, but what
+course is open to them if they find the rubber spoiled for their purpose by
+the presence of particles of sand, grit, or bark? The possible injury
+caused by these ingredients cannot be insisted upon too strongly, and it
+must be evident that great care should be exercised in the preparation of
+the lower grades of crepe.
+
+As to the particular form of the lower grade crepe rubber, one may apply
+the remarks made under the section dealing with the best grades. It is
+common to find thin crepes, medium crepes, and "blanket" crepes. More often
+than otherwise, the medium and thicker crepes are prepared direct in those
+forms. It follows that they are liable to attacks of "spot" disease, which,
+however, is not easily visible in the lowest grades, owing to the dark
+colour of the rubber. Furthermore, it is not possible to cleanse the rubber
+so thoroughly if thick crepes are made.
+
+BLOCK RUBBER.--Few estates now prepare block rubber, which is essentially
+crepe rubber pressed into blocks. In the ordinary process the fresh
+coagulum is lightly rolled into thin crepe, which is then vacuum-dried.
+There are slight variations in the subsequent procedure. Sometimes the
+rubber as it comes from the vacuum drier is merely allowed to remain on
+racks overnight before blocking. In other instances, the sticky rubber from
+the vacuum drier is passed once or twice through wet, smooth rolls and hung
+to dry for some days. The dry crepe is then folded into the pressing box or
+cut to suit the size of the box. Pressure is applied for some time, and
+finally the rubber is taken out in one homogeneous mass. Naturally the
+appearance of the block depends upon the quality of the parent crepe. Some
+block rubber is made up thick; other is made in slabs about 3 inches or 4
+inches in thickness. With the latter, it should be possible, when held up
+to the light, to see the shape of a hand held between it and the source of
+light.
+
+It is possible that an erroneous idea of the strength of block rubber has
+been formed. It should only be necessary to point out that essentially
+block rubber is merely pressed crepe rubber. It is inconceivable that the
+mere action of pressing layers of crepe together would increase the
+physical quality of the rubber.
+
+The advantages which block rubber possesses are the compactness of the
+output, its ease of packing, and a saving in freight; but there is the
+disadvantage, from the consumer's point of view, that extra labour is
+involved in the preparatory work of cutting up the blocks.
+
+SMOKED CREPE AND SHEET CLIPPINGS.--There appears to be no certain demand
+for any grade of smoked crepe, and probably all which is put into the
+market is really comprised of (1) clippings obtained from the ends of
+sheets, (2) sheets which have been malformed in machining, or (3) sheets
+showing the presence of many "bubbles."
+
+As to the first class it might be explained that through defective rolling,
+thick ends or edges may be caused. These show signs of contained moisture
+when the bulk of the sheet is perfectly dry, and as undue delay would
+otherwise result these moist strips are trimmed and either returned to the
+smoke-house, or machined to form crepe.
+
+Similarly a torn or otherwise badly formed sheet, when brought from the
+smoke-house, may be made into crepe, rather than it should prejudice the
+selling price of the bulk under ruling conditions.
+
+In the same manner, although "bubbles" have no influence upon the quality
+of the rubber on vulcanisation, sheets thus affected are generally made
+into crepe.
+
+It cannot possibly be argued that rubber of this description would be in
+any way inferior to the best smoked sheet for manufacturing purposes, but
+owing to the prevailing system of evaluation for market purposes, it is
+necessary to resort to the expedients indicated above.
+
+On some estates the rubber specified in the three classes mentioned is not
+made into crepe, but cut up into small pieces and shipped as "sheet
+clippings" or "sheet trimmings"--a procedure which would appear to be
+justified by a steady demand. In point of fact, the buyers are really
+obtaining a first-class article (except in superficial appearance) at a
+reduced price.
+
+
+
+
+CHAPTER XI
+
+_DRYING OF RUBBER_
+
+
+AIR-DRYING OF CREPE.--It is still the prevailing custom to air-dry crepe
+rubbers. A few estates, it is true, have artificial driers installed, and
+in some necessary cases others will be erected. But in the majority of
+cases where money has been expended in building air-drying sheds, as long
+as it is only possible to ship rubber regularly air-drying is likely to
+remain in favour.
+
+The great drawback to air-drying is that one is so dependent upon the
+weather conditions. In favourable weather the rubber dries well, but in a
+long period of wet weather rubber may accumulate at an alarming rate, and
+the accommodation is sometimes severely taxed. Of course, the rate of
+drying under the best conditions is mainly dependent on the thickness of
+the crepe, and every endeavour should be made to maintain a thin style of
+preparation. If this precaution is not taken, the rubber is liable to
+recurrent attacks of "spot" disease, and one's troubles are very much
+augmented. This is a disability to which rubber treated in artificial
+driers is not liable. Still, air-dried rubber can be made equal, if not
+superior, in appearance to pale rubbers prepared by other processes.
+
+For the lowest grades of crepe air-drying is always likely to remain the
+only method, as it would be extremely unsafe to submit them to heat.
+
+It is noted in ordinary practice that the rate of drying on different
+estates, for the same type of rubber, may vary widely. Naturally the
+construction of the house has a great effect, and this subject will receive
+attention in a subsequent chapter.
+
+Similarly the position of the drying-shed exerts an important influence,
+and the erection of the building in low-lying surroundings is always
+calculated to prolong the drying period appreciably. Incidentally this
+means that the building must be larger than a normal rate of drying would
+otherwise demand.
+
+The combination of a poor type of drying-house, a low-lying situation, and
+a prolonged wet season, might render it advisable to abandon the air-drying
+of high grade crepes in favour of artificial drying.
+
+ARTIFICIAL DRIERS FOR CREPE.--It is more common to find artificial driers
+in use in Ceylon than in Malaya, possibly because these driers have been in
+use in Ceylon for other products. Some time ago the question of installing
+artificial driers received the serious attention of a number of estates in
+this country, chiefly on account of the incidence of fungoid and bacterial
+diseases in crepe rubber. The simple treatment for the prevention of these
+diseases is to get the rubber dry in the shortest possible space of time.
+In most cases it is found sufficient to roll crepe thin for air-drying in
+order to prevent the appearance of coloured spots. It is found, however,
+that some drying-houses are so badly planned and constructed, that quick
+drying under even the best of conditions is a practical impossibility.
+Cases have been known in which the disease may disappear almost entirely
+during a period of freedom from rain, only to recur as soon as wet weather
+sets in again. There can be no doubt that, on the whole, the number of
+cases of "spot" disease is on the decline; but equally it is certain that a
+very few estates will always be liable to outbreaks as long as drying is
+attempted in existing houses. For these reasons it is a poor policy to
+temporise, and the only sound policy in extreme cases would be to give up
+ordinary air-drying in favour of some method of artificial drying. As
+regards the majority of estates preparing pale crepe for various reasons,
+it is not expected that any will instal artificial driers. Money has been
+expended in elaborate buildings which certainly do the work for which they
+were designed. As long, therefore, as the accommodation is sufficient, and
+regular shipments are the rule, it is expected that ordinary air-drying
+will still remain the general practice.
+
+Of the better-known artificial driers, there are only three which merit
+serious consideration in these pages. They are the vacuum driers, the
+Colombo Commercial Company's hot-air drier, and the Michie-Golledge
+process.
+
+VACUUM DRIERS.--The vacuum drier is so well known that only a brief
+description need be given. It consists of a chamber heated by steam pipes
+and capable of having the contained air and moisture withdrawn by a pump.
+This description sounds very simple, and in practice the operation of
+vacuum drying is really a simple one, and can well be entrusted to an
+intelligent coolie under efficient supervision. Indicators are fitted which
+show the vacuum pressure and the pressure of steam in the heating pipes
+which travel underneath horizontal slabs upon which trays may be placed.
+Still, in spite of the apparent simplicity of the process, there would
+appear to be a number of little details which, if overlooked, prove to be
+factors influencing the result to a considerable degree. Thus it is not
+uncommon to find complaints that the rubber is not dry when packed. The
+writers have seen rubber taken from a vacuum drier still containing a
+visible quantity of moisture. One would have imagined that continuous
+working of the drier would give the experience necessary to obtain dry
+rubber, but, apparently, such is not the case in a number of instances.
+Elaborate instructions are given by the makers, but often they are more
+honoured in the breach than in the observance. Really, there are only two
+points to bear in mind:
+
+     (1) That the rubber must be fairly thin.
+
+     (2) That the temperature be not allowed to rise too high. Some makers
+     advise 140° F. as a maximum, but no harm results from a temperature of
+     150° to 160° as long as the interval is not prolonged.[11]
+
+[11] These figures refer to temperatures recorded by thermometers placed in
+the folds of the rubber.
+
+These two points presume that the vacuum drier is true to its name, and
+that one can obtain a maximum steady pressure. The machines are so well
+made now that no drier should be taken over from those responsible for its
+erection unless it can show a vacuum pressure of 28 inches within fifteen
+minutes of starting the pump; and with the pump stopped, there should not
+be a greater fall in pressure than 1 inch within ten minutes after stopping
+the pump.
+
+One of the most frequent sources of error is the control of steam pressure
+which is responsible for the temperature of the drier. It is quite
+unnecessary and unwise to maintain any steam pressure once the drying is
+well under way. All that is necessary is to heat the chamber well, with a
+steam pressure of 5 lbs., before inserting the rubber. As soon as the
+maximum vacuum pressure has been obtained, steam should be shut off from
+the heating pipes, and it will be found that the temperature is well
+maintained throughout the operation with a rise of ten to twenty degrees at
+the end. If the drier is working at a vacuum pressure of 28 inches, and if
+the crepe has been prepared thin enough, the rubber should be quite dry
+within two hours. Should the operation have to be extended to two and a
+half hours at 28 inches vacuum pressure, it is a sign that the crepe is too
+thick. On such occasions it is often noticed that these thicker crepes are
+not thoroughly dry, having moist spots enclosed in them. On re-rolling,
+these moist patches become easily visible, and are a source of great
+annoyance, inasmuch as they take quite a long time to dry out.
+
+As mentioned before, the crepe for vacuum drying should be thin. There is
+no necessity to give it a superfine finish, and the presence of small holes
+is quite permissible, as they disappear on subsequent re-rolling. The thin
+crepe may be folded loosely to the length (or breadth) of the tray several
+times, but in no other way can the drier be expected to perform its work
+satisfactorily. A case was noted in which thin crepe was excellently
+prepared, and four or five layers were rolled together for vacuum drying.
+Naturally this mode of procedure does not give the drier a fair chance, and
+it would be ridiculous to judge vacuum drying on the results. After two and
+a half hours at a temperature of 145° F. the rubber appeared to be only
+about three parts dry, and the subsequent air-drying extended well into a
+fortnight.
+
+It is the common practice to screw up the door of the chamber as tightly as
+possible. As a rule it is found in course of time that the obtainable
+maximum vacuum pressure decreases. This may be attributed solely to the
+forcible screwing up of the door. Around the inside edges of the door are
+strips of rubber compound, the function of which is to form a tight joint.
+Should the door be screwed up too tightly, these strips become deformed in
+course of time, and slight leaks occur. It should be pointed out that it is
+only necessary to screw up the door at the beginning of the operation. When
+the vacuum has been obtained, the screw pressure may be released, as the
+atmospheric pressure outside the chamber is more than ample to keep the
+door in a close fitting position. This will be obvious from the fact that
+the difference in pressure between the inside and the outside of the door
+amounts to, say, 28 inches atmospheric pressure--_i.e._, nearly 14 lbs. per
+square foot. By slackening the screw handles, therefore, as soon as the
+indicator shows the maximum working vacuum pressure, the life of the door
+joints may be prolonged, and the drier will remain efficient for a longer
+time.
+
+A careful consideration of the question of temperature leads one to the
+conclusion that the practice of placing a thermometer through the roof of
+the chamber does not enable one to determine the temperature correctly. In
+the same way a thermometer suspended behind the observation window cannot
+indicate the temperature of the rubber, as in both of these positions the
+thermometer must be influenced by radiation from the walls of the chamber.
+The only position in which the correct temperature could be indicated is
+between the folds of crepe. This can be arranged easily so as to enable one
+to read the temperature from the observation window.
+
+COLOMBO COMMERCIAL COMPANY'S DRIER.--The drier of the Colombo Commercial
+Company consists in principle of a number of small chambers or units in
+which crepe rubber is placed, and through which hot air is passed. As in
+the case of vacuum drying, a great deal depends upon the preliminary
+treatment of the rubber. If the crepe is not rolled thin enough drying will
+be unduly prolonged, with a possibility that the rubber will become tacky.
+The temperature usually obtained is about 150° F., and if the rubber is
+thin the production of an installation of two chambers should be at the
+rate of 1 lb. of dry rubber per minute. The usual period of drying is
+under two hours. One advantage which this drier has over the vacuum drier
+is that the chamber can be opened at any time for a short period to
+withdraw or insert trays. The thin crepe is folded several times, as in the
+case of vacuum-drying.
+
+Figures obtained from the actual working of a drier in Ceylon are given
+below:
+
+  -------------------------------------------------+-----------------------
+         CHAMBER 1.--TEMPERATURE 160°-180°F.       |
+  -------------------------------------------------|CHAMBER 2.--TEMPERATURE
+  _NO. OF | _DRYING  |  _WEIGHT OF  |  _WEIGHT OF  |      150°-165°F.
+   Tray._ | Period._ | Wet Rubber._ | Dry Rubber._ |
+  --------+----------+--------------+--------------+-----------------------
+          |Hrs. Mins.|     Lbs.     |     Lbs.     |
+     1    | 1    22  |     7-1/2    |      6       |Worked similarly
+     2    | 1    42  |     7-1/2    |      6       |to No. 1. Yielded
+     3    | 1    57  |     7-1/2    |      6       |in 2 hrs. 23 mins.
+     4    | 1    57  |     7-1/2    |      6       |70-3/4 lbs. dry rubber,
+     5    | 1    57  |     7        |      5-3/4   |from 87-1/2 lbs. wet
+     6    | 1    57  |     7-1/2    |      6       |rubber.
+     7    | 2     0  |     7-1/2    |      6       |
+     8    | 2     0  |     7-1/2    |      6       |
+     9    | 2    11  |     6-1/2    |      5       |
+    10    | 2    11  |     7-1/2    |      6       |
+    11    | 2    11  |     7-1/2    |      6       |
+    12    | 2    18  |     7-1/2    |      6       |
+  --------+----------+--------------+--------------+-----------------------
+          |          |    88-1/2    |     70-3/4   |
+  --------+----------+--------------+--------------+-----------------------
+
+It will be seen, therefore, that the drier had an output in 2 hrs. 23 mins.
+of 141-1/2 lbs., which is at the rate of 1 lb. per minute approximately.
+
+As the rubber leaves the driers it resembles vacuum-dried rubber in being
+surface-sticky. This stickiness is only temporary, and is got rid of by
+passing the crepe through wet rolls. Opinions differ as to when this
+rolling should be given. On some estates the rubber is only allowed to cool
+a little before passing through the rolls; on others it is given a day or
+so before rolling. The methods of rolling also differ. In some factories
+the rubber has been cut to lengths before drying, and these lengths are
+merely rolled together by simple pressure. Other estates prefer to
+re-macerate the crepe while still fairly warm and soft. It is probable that
+little harm, if any, results from this re-maceration while the rubber is
+soft, as it is more easily worked in this condition. The thick rubber is
+then generally hung for a few days to air-dry before packing. As most of
+the moisture taken up by the dry rubber is surface moisture, three or four
+days is usually found ample for air-drying.
+
+MICHIE-GOLLEDGE SYSTEM.--The Michie-Golledge system comprises a process of
+preparation and drying. The latex is diluted with two, three, or four
+volumes of water and coagulated with acid in a vessel which is rotated with
+a churning motion. In this cylinder there are curved and fixed blades. The
+revolving cylinder and its ribs force the latex against the curved blades
+so as to cause an eddy in the middle of the machine. Here the rubber
+coagulates and accumulates, the remaining liquor whirling round outside the
+blades. It can be imagined that with such dilute latex, the coagulum is
+very soft and spongy. This soft mass is passed through a machine which cuts
+it into "worms" about 3/16 inch in section. These are placed upon wire
+trays and dried by means of hot air. The "worms" when dry are re-macerated
+and built up into medium and thick crepes. The colour of the rubber
+prepared by this process is usually very good. When treated in a Colombo
+drier the "worms" usually require about two hours to dry, so that crepe
+rubber may be packed at latest on the fourth or fifth day, as in the case
+of vacuum-dried rubber.
+
+RATE OF AIR-DRYING OF CREPE RUBBER.--In spite of the facts that some
+estates have been making thin pale crepes for years, and that so much has
+been written concerning the preparation of this grade of rubber, one
+occasionally meets with a case in which an estate seems to be unable to
+prepare thin pale crepe, or if it does the period of drying is much longer
+than obtains on most estates.
+
+Again, when cases of infection by spot disease in fairly thin crepes are
+submitted, it is usually found that the particular crepes are of that type
+which, though fairly thin, show whitish spots of moisture when the bulk of
+the rubber is nearly dry. This type of crepe is to be noted for the
+excessive period of drying in comparison with other crepes of equal
+thinness. It has been advanced elsewhere[12] that a factor of the most
+considerable importance in the rate of drying of crepe rubber is the type
+of drying-house and its situation. This accounts very largely for observed
+differences in the rate of drying of thin crepes on different estates. Yet
+even where two drying-houses may be of the same type, and the situations
+may be comparable, one still observes that one thin crepe dries more
+quickly than another. It has been remarked also that a thin crepe in one
+old drying-house dries in a shorter period than a similar crepe in another
+more modern house, although the methods of coagulation and preparation
+exhibit no apparent diversity. In all these conflicting cases allowance is
+made for the weather conditions, and the observed differences seem to be
+inexplicable. It has always been the opinion of the writers that the actual
+rolling of the rubber plays an important part in determining the rate of
+drying of crepe, apart from the question of thinness; and it seemed
+possible that this factor would account for the discrepancies noted above,
+either partially or wholly.
+
+[12] "Preparation of Plantation Rubber," Morgan, 1913, chapters xii. and
+xiii.
+
+With a view to determining to what degree the drying of crepe rubber was
+hastened by the extent to which the rubber was rolled, experiments were
+made. It was hoped, also, that some idea would be gained of the particular
+stage in crepe rolling which had the greatest effect upon the rate of
+drying. In preparing crepe in the estate in the ordinary way the coagulum
+is passed through three sets of rollers, and the stages may be described
+as:
+
+     (1) Rough rolling.
+
+     (2) Medium rolling.
+
+     (3) Smooth rolling.
+
+In the first the coagulum is broken down by passing through the machines
+until a thick rough crepe is formed. This passes to the intermediate
+rollers, where it is worked down to a medium crepe. The rubber finally goes
+to the smooth running at approximately even speeds. Passing through these a
+number of times it emerges as a thin uniform crepe, free from "lumpiness"
+and free from holes, which should dry in from ten to twelve days.
+
+In the experiment the rubber was passed through the machines with varying
+frequency, the number of times in each machine being progressively
+increased, while the working on the other machines remained constant.
+
+It was determined that the rate of drying was affected only by the extent
+to which the crepe was worked in the smooth rolls. The less often the
+rubber passed through these rolls, the slower the rate of drying. Beyond a
+limit in the other direction, increased rolling did not reduce the period
+of drying. It follows, therefore, that crepes which have a good thin finish
+should dry in a minimum period.
+
+[Illustration: DRYING GRAPH. PALE CREPE (THIN).]
+
+WHEN DOES AIR-DRYING TAKE PLACE?--Experiments[13] were conducted with a
+view to discovering, if possible, the rate at which crepe rubber dries, and
+the extent of drying during the night under weather conditions such as
+prevail ordinarily in Malaya. It is to be remembered that, during the day,
+most drying-houses are fairly open and that the temperature ranges from
+about 88° F. in the lower rooms to over 100° in the upper rooms (near the
+roof) when the sun shines. At night, however, there is usually a decided
+drop in the temperature, and unless it is a very clear night the air is
+generally saturated with moisture. In addition the drying-house is closed
+as thoroughly as possible, and we should expect the atmosphere of the house
+to be laden with moisture from the wet and drying rubber. It would be a
+just inference, therefore, that the rate of drying during the night would
+be much less than the rate of drying during the day, and the results of
+experiments confirm this very fully. One was hardly prepared, however, to
+find that, under certain circumstances and at a certain stage, the amount
+of drying is nil; not only so, but it was found under certain conditions
+that the amount of drying which took place was negative--_i.e._, the rubber
+weighed slightly more when taken out in the morning than it had weighed the
+previous afternoon.
+
+[13] Rubber Growers' Association, Malaya Local Report, No. 2, 1914.
+
+CREPE MAY INCREASE IN WEIGHT.--As an instance of the kind of result
+obtained a graph is here given of the rate of drying of a batch of pale
+crepe. This was hung to dry in the top room of a drying-house in which
+rubber ordinarily dries quickly. The rubber was hung in a good position,
+with the bulk of output, near a window which was open for some time during
+the day. In order to restrict the day interval of drying to the actual
+period in which the sun was likely to be in evidence, the day was taken to
+begin at 8 a.m. and end at 4 p.m., the night interval covering the
+remaining sixteen hours. Thus the night interval was twice as long as the
+period of day drying. The lengths of crepe were weighed carefully at 8 a.m.
+and 4 a.m., and the average of the several weights was plotted in a graph.
+
+The weights are placed vertically and the duration of drying horizontally.
+It will be seen that the rubber was quite dry and fit for packing on the
+sixth day, as far as could be judged in the usual way by casual inspection.
+Peculiarly enough at this time it weighed slightly more than had been
+registered on the fourth and fifth days, but the difference did not amount
+to more than about 0·4 per cent. In examining the graph it should be borne
+in mind that the steeper the slope of the curve downwards the quicker the
+rate of drying, and that when the curve takes an upward direction there is
+an addition of moisture instead of abstraction. It will be noted that when
+drying takes place the slopes more nearly approximating the vertical
+represent the extent of day drying, and that often the night drying is
+represented either by a very flat curve or even by an upward curve which
+shows the addition of moisture. A striking feature of the experiment is
+shown by the rapidity with which drying takes place during the first few
+days and the comparative slowness with which the remaining moisture is got
+rid of. Thus, from the graph, it may be calculated that about 80 per cent.
+of the total moisture content was lost in the first two days, and over 93
+per cent. in two and a half days. Yet three days had to elapse before the
+remaining 7 per cent. of total moisture was lost--_i.e._, before the rubber
+was judged to be ready for packing. It will be seen that after this stage
+had been reached the rubber alternately lost and gained in weight, with a
+tendency to increase. This increase was attributed to the presence of
+surface moisture after hanging overnight, when the rains had become
+frequent. Some light is thus shed upon a subject which has puzzled both
+shippers and receivers of crepe rubber.
+
+DIFFERENCES IN WEIGHT.--It will be obvious that if rubber is allowed to
+hang after becoming dry, and is taken down, packed, and weighed in the
+early morning, it will weigh more than when it reaches a drier climate. The
+loss in weight under such circumstances might amount to even 1 per cent. It
+may seem to some an unnecessary refinement to introduce, but it would
+appear from the graph that rubber should be packed for preference in the
+afternoon if the weights are to be more nearly correct.
+
+It is extremely singular to note how quickly the curve changes its slope
+after the major portion of the moisture has evaporated, and it will be very
+plain that in the last stages any decrease in weight during the day would
+appear to be counterbalanced, or more than counterbalanced, by the addition
+of moisture during the night. It may be pointed out, however, that this
+increase in weight during the later stages of drying of pale crepe is
+mainly, if not altogether, due to surface moisture. The chief point of
+interest is the fact that in the case of thin pale crepe, quite 80 per
+cent. of the total moisture content is lost during the first two or three
+days, and that, owing to the negative influence of the night atmosphere,
+the final drying is delayed. It will be understood that the foregoing
+results applied to thin pale crepe. Thin lower-grade crepes appeared to dry
+at more uniform rates, but the differences between the rates of drying at
+night and during the day were similarly notable.
+
+AIDS TO NORMAL AIR-DRYING.--These experiments were undertaken in a
+drying-house, favourably situated for rapid drying, in which the average
+period of drying for thin crepes is nine days. It is easy to imagine that
+the condition of affairs as revealed would be much exaggerated in a
+drying-house situated on low-lying ground and surrounded by trees. In
+extreme cases of this nature the use of large fans and heating pipes has
+been advocated. It is believed that in some cases these installations have
+given satisfaction, but that in others the degree of improvement obtained
+has not been in economic proportion to the outlay incurred.
+
+SMOKE-CURING OF SHEET RUBBER.--It will have been evident that one of the
+disadvantages of air-drying sheet is the incidence of moulds. Now it is
+found that moulds should not develop in smoke-curing; and if they do, then
+the smoke-curing has been insufficient or inefficient. The difference in
+the drying period also is a strong argument in favour of smoke-curing, so
+that all-round it is seen that there are many valuable advantages to be
+gained by smoke-curing sheet in comparison with air-drying, and no
+disadvantages.
+
+The manipulation of the rubber, after it leaves the marking rolls and
+preparatory to smoke-curing, has been discussed in Chapter IX. It is
+sufficient only to allow adequate time for furnace water to drip from the
+sheets before transferring them to the smoke-house. As it is the general
+rule to roll sheet rubber in the morning, this arrangement fits in very
+well. The furnaces of the smoke-house are usually extinguished as soon as
+the sun is well risen, and the rest of the day is occupied in sorting dry
+sheets, etc. Towards noon the day's wet sheets should have been admitted,
+and smoking may be commenced as soon as the sun is well in the west--say,
+at half-past four o'clock or earlier.
+
+It used to be the custom on a few estates to smoke during the daytime and
+to discontinue smoking at night. As the night-air in Malaya is usually
+heavily laden with moisture, it will be plain that such a policy was a
+topsy-turvy one. It is vastly more reasonable to smoke-cure at night;
+usually the heat of the sun during the day is quite sufficient in itself to
+promote the drying of rubber; but there is no reason why smoking should not
+be carried on in the daytime in wet weather, should it be found expedient
+to do so.
+
+RECORDING INSTRUMENTS.--During the night the care of the smoke-houses is
+usually in the hands of natives, except for occasional surprise visits from
+a European superintendent. To all acquainted with the ways of the native it
+must be plain that means must be provided for the checking of the
+temperatures attained in the smoke-house. Ordinary thermometers are quite
+unsuitable, and even thermometers registering maximum and minimum
+temperatures are of little avail, inasmuch as they record only the degree
+of heat attained at a particular moment, and do not indicate any period
+during which a particular temperature was maintained.
+
+It is evident that something more informative is required. There are many
+types of suitable recording instruments or "pyrometers," some of which can
+be electrically connected, so as to cause the ringing of a bell, placed in
+the superintendent's office or house, on the attainment of a certain
+temperature. The type best known in estate practice is that named the
+"Thermograph," in which a pen traces a curve or graph on a plotted piece of
+paper carried by a rotating cylinder which is actuated by clockwork. Such
+instruments can be purchased through most of the local firms dealing in
+estate supplies. From experience it can be asserted that, given intelligent
+attention, these instruments yield very satisfactory results. The apparatus
+should not be placed always in one position in the smoke-house, but should
+be moved frequently so as to obtain information regarding the distribution
+of heat.
+
+TEMPERATURE OF SMOKE-CURING.--In the question of temperature of drying, it
+is well to be as strict as possible; not that any great harm will result
+from a rise of 10° above that recommended, but because the higher the
+temperature recorded the larger the fires must have been, and consequently
+the more real danger there was of the store becoming ignited. It has been
+shown[14] that the temperature giving the maximum benefit of drying and
+quality was found experimentally to be rather above the temperature usually
+prescribed for smoke-houses, but in the experimental work there was no
+danger from fire.
+
+[14] "Preparation of Plantation Rubber," Morgan, 1913, chapter x.
+
+The figure given in previous publications as a maximum working temperature
+for smoke-houses was 110° F., but certainly the temperature may be as high
+as 130° if it is considered safe to allow fires to be so arranged. One or
+two estates are known to work at temperatures of 130° F. and over, in spite
+of the recommendations of the writers. If those estates care to risk it
+they may do so, with increased rapidity of drying; but no responsibility
+can be taken for whatever may happen in smoke-houses where the temperature
+is allowed to remain, as in one case, at 160° F. Naturally the range of
+temperature is strictly limited by the properties of the substance to be
+treated, and with a substance such as rubber it would be far better to err
+on the side of caution than to risk damage to such a commodity, apart from
+the consideration of the possible destruction of the building.
+
+PERIOD OF DRYING.--Considerable differences are noted in the periods of
+drying on various estates; but, as there is more than one factor
+influencing the results, it is not easy at first to find why these
+differences should exist. Really there are three factors:
+
+     (1) Relative thickness of rubber.
+
+     (2) Extent and quality of rolling.
+
+     (3) Temperature of drying.
+
+It is presumed that the smoke-houses are identical in type and efficiency,
+and that smoking is in force for the same length of time each day. There
+need be no discussion of these points; the effect of each is so obvious.
+The thinner the sheet, the quicker the rate of drying; the better the sheet
+has been rolled, the shorter the period of drying; the higher the
+temperature, the more rapid the drying.
+
+It has been shown in Chapter IX. that the condition of the sheet after
+rolling depends primarily upon the standard of dilution of the latex and
+the original thickness of the coagulum. If these factors are correctly
+controlled, the rolling should give a sheet which is fairly soft and
+porous--_i.e._, it should not have been subjected to such pressure as to
+make it both thin and hard. An average sheet of rubber which has been well
+rolled should be smoke-dried at a temperature of 120° F. in about ten days.
+If sheets take appreciably longer to dry, then the three foregoing factors
+must be examined.
+
+On the other hand, it is often found that thin sheets made from very dilute
+latex dry so quickly that they are considered to be fully smoke-cured in
+from five to seven days. It frequently happens in such cases, however, that
+the smoking is insufficient, and by the time the rubber reaches home it has
+begun to show signs of surface moulds. It is evident, therefore, from this
+discussion that:
+
+     (1) If smoked sheet develops surface moulds within a short period
+     after smoking, the duration of curing has been insufficient, or the
+     quality of the smoking is at fault.
+
+     (2) The actual time taken to smoke-dry rubber may be insufficient to
+     smoke-cure it.
+
+     (3) The rate of drying of smoked sheet depends upon--
+
+          (_a_) The relative thickness of the rubber.
+
+          (_b_) The preliminary treatment of rolling.
+
+          (_c_) The temperature of the smoke-house, and
+
+          (_d_) The type of smoke-house used. This point will be treated
+          in a subsequent chapter.
+
+FUELS FOR SMOKING.--The general idea formerly held was that the beneficial
+effects of smoking were to be attributed to the constituents of the smoke,
+and chiefly the creosotic substances. This is not now the opinion of the
+writers, who attribute the effect largely to the temperature of drying and
+constituents of the smoke other than creosotic substances. There can be no
+doubt that the presence of creosotic bodies is responsible largely for the
+absence of moulds and the existence of the typical odour, but it is
+becoming increasingly known that the employment of substances rich in
+creosote is not required or desirable.
+
+Estates used to be put to considerable expense in the purchase of "bakau"
+(a mangrove timber rich in creosote and creating much heat), under the idea
+that it was the best material and almost indispensable. Most estates now
+restrict themselves to the consumption of timber obtained from their own
+areas. Thinning-out programmes are largely responsible for the supply, but
+the local authorities are much concerned regarding future supplies; and
+consideration has been given in some quarters to the question of the
+development of quick-growing trees on estates with a view to safeguarding
+the future. This seems to be desirable, as it is difficult to imagine that
+the place of timber can be taken by any other material in the smoke-curing
+of rubber. Unless some such precautions are taken it is not difficult to
+predict that, in course of time, some estates will be able to continue the
+preparation of smoked sheets only at considerable expense in obtaining
+suitable fuel from a distance.
+
+It is not true that _any kind of timber_ is suitable as a fuel to be used
+in a smoke-house. All timbers are suitable, either alone or in mixture with
+others, provided that the wood is not too green.
+
+Naturally an absolutely dead and crumbling wood will smoulder, but does not
+develop sufficient smoke. A green timber will give an acrid and moist
+smoke, but demands the consumption of a certain amount of dry timber in
+addition if it is to be used.
+
+Rubber-tree prunings and sawn rubber trees obtained by thinning-out may be
+used in mixture with dead wood, provided the logs are stacked to dry in the
+sun for some weeks before use. If the timber is too green, steam is formed
+as well as smoke, and the sheets of rubber may have a moist surface glaze.
+
+SUN-DRYING SHEET RUBBER.--Among the first curious sights which impress the
+visitor or newcomer to this country is the spectacle of sheet rubber
+hanging in the sun on native holdings. From what one has learned of the
+extraordinary care which must be exercised in all the processes of rubber
+preparation, one fails to understand how such rubber reaches the market
+without becoming tacky. That some of it does become slightly tacky is
+certain, but on the whole native rubber, though crudely prepared, is
+usually sound. The native idea of giving sheet rubber a preliminary drying
+in the sun is to hasten the total period of drying. That the period is
+curtailed would seem to be the case, but it is open to doubt, as the effect
+of sun-drying, if unduly prolonged, is to create a thin surface film of dry
+rubber which retards the drying of the rubber below the surface. Working
+with wet crepe rubber, the writer found that, to all external appearances,
+there was no effect upon the rubber when it was allowed to sun-dry for four
+or five hours. With periods of from six to ten hours the crepe becomes
+slightly sticky, chiefly on that portion across the support. When removed
+to the air-drying house this tackiness developed further, and the rubber,
+on the line of support, became so weak that it stretched and broke.
+
+Reasoning by analogy, it would appear that no apparent harm would result to
+sheet rubber from sun-drying for periods up to four or five hours. From
+experience (see Chapter IX.), not the slightest ill-effect is found to
+result from the short interval of preliminary drying or dripping practised
+on many estates preparatory to smoke-curing.
+
+ARTIFICIAL DRIERS FOR SHEET RUBBER.--It is understood that when vacuum
+driers were first applied to the drying of rubber it was thought possible
+to dry sheet rubber in this way. The practice was found to be impossible,
+as the length of time required and the temperature were responsible for the
+destruction of the form of the rubber; it became tacky and semi-liquid.
+
+THE "CHULA" DRIER.--Although several suggestions of devices for
+artificially drying sheet have been made, only one is known to be in use at
+the present time. In the original form this was used for drying other
+tropical products. It consists of a large iron chamber, in which are
+several compartments divided by means of baffle-plates. At one end there is
+a small furnace and, by means of a fan, smoke and hot air are drawn
+through the compartments. Owing to the temperature attained (140° to 160°
+F.) sheet rubber cannot be completely dried in the chambers, and is, as a
+rule, only treated in this manner for one or two days. Drying is then
+completed in an ordinary air-drying house. It is claimed that drying is
+expedited, and that the rubber can be packed in ten days.
+
+In the more recent modification, the smoke and hot air which leave the
+Chula drier pass through a large room in which may be hung either sheet or
+crepe rubber. It would seem that all sources of danger have not been
+eliminated from the process, as on one estate a wooden room containing
+rubber was ignited by a spark which passed through the drier.
+
+Yet another form exists in which the furnace is outside the main building,
+and in the ordinary course of working only heats a series of open pipes
+through which air is drawn by a powerful fan. By means of a valve it is
+possible to allow smoke from the furnace to pass into the room with the hot
+air for the preparation of smoked rubber. The hot air or smoke is
+distributed in the lower room by means of main and branch pipes, and passes
+through an open floor to the room above. With such an arrangement it is
+possible, therefore, to prepare either air-dried or smoke-cured rubber. If
+the method could be successfully applied to the drying of crepe it would be
+of great assistance on some estates. There would seem to be a difficulty in
+working it for the drying of sheer rubber and crepe together, as the
+temperature suitable for the one is excessive for the other. Given an
+efficient control over the temperature of the hot air, the house should be
+successful in the drying of crepe, provided the rubber is not hung in folds
+of too great length. For smoke-curing sheet rubber the period is said to be
+reduced by several days in comparison with the time occupied in an ordinary
+smoke-house, but it is not clear that such a system would have any
+advantage over a modern smoke-house, in types of which rubber can be fully
+cured in periods ranging from five to ten days.
+
+
+
+
+CHAPTER XII
+
+_SORTING, GRADING, AND PACKING_
+
+
+The question of standardising the output of our plantations is one which
+has occupied attention for some years, with a not inconsiderable degree of
+success.
+
+Meanwhile opinion is growing in favour of proceeding along the line of
+reducing the number of plantation grades to a minimum. At present some
+confusion exists. Some estates make up tree-scrap and bark-shavings
+together; one estate puts tree-scrap, earth-scrap, and bark-shavings into
+one uniform crepe; other estates have three or more separate scrap
+grades--_e.g._, lump-rubber and "washings," tree-scrap, earth-scrap, and
+bark-shavings scrap. There is a movement on foot at present to try to
+restrict plantation rubber to three grades:
+
+CREPES--1. _First Quality Latex._--_I.e._, crepe made from the true
+coagulum obtained from the regulated coagulation of strained latex. This is
+a pale rubber, and may be prepared satisfactorily if the directions given
+in preceding chapters are followed. Naturally there must be, in all
+factories, some defective rubber of this grade. For various reasons the
+crepe may be of inferior colour, or is slightly contaminated with dirt or
+traces of oil and grease, etc. This defective rubber should be placed aside
+most rigorously and plainly marked as "off-quality."
+
+If a proper scheme of standardisation of latex and chemicals is followed,
+there should not be any such variety in shades of colour, such as was
+common in No. 1 crepe in the past.
+
+Comparatively few estates in Malaya now prepare thick (or blanket) crepes
+in the No. 1 grade, but in such cases the same rules must be applied as
+govern the sorting of thin fine pale crepes.
+
+2. _Compound Crepe, No. 1._--In this it is proposed to include
+cup-coagulated lumps, coagulated lumps from transport vessels, skimmings,
+bucket rinsings, cup-washings, and tree-scrap. It has been shown in Chapter
+X. that strict care is necessary to eliminate all oxidised (dark) scraps.
+These are relegated to a lower grade. The possession of a "scrap-washer" is
+necessary if the best results are to be obtained.
+
+On some estates the ingredients of this compound crepe, while fresh, are
+placed in a common jar or tank to which a quantity of sodium bisulphite (1
+per cent. solution) and acid are added. The resulting conglomerate mass is
+cut up for working.
+
+3. _Compound Crepe, No. 2._--This grade would include the remaining lower
+grades--viz., bark-shavings, scrap, and earth-rubber scrap.
+
+REDUCTION CARRIED TOO FAR.--However desirable it may be to diminish the
+number of grades, it must be pointed out that diminution and simplification
+are not necessarily synonymous terms in this matter. It is well known that
+on estates where the earth-rubber is only brought in at lengthy intervals,
+say of a week, the resulting crepe is sometimes very tacky. This is only
+natural, and is due to the prolonged exposure to the sun's rays. With the
+improved machinery now at our disposal, and with the increasing attention
+which will be given to the lower grades in the future, it is possible to
+prepare from average bark-shavings crepe free from bark, and of quite a
+good colour. Where trees are not "scrapped" before tapping, there would
+seem to be no objection to amalgamating the rubber obtained from the
+bark-shavings with the No. 1 Compound crepe; and it would be a distinct
+danger and possible loss if this good rubber were to be mixed with earth
+rubber. The liability of the latter to become tacky is well recognised; and
+if possible it should be maintained as a separate grade, in which it would
+be permissible to mix only rubber obtained from actually dry shavings from
+"scrapped" trees, or heavily-oxidised scraps which have been rejected from
+other grades.
+
+SHEETS.--Broadly there are no fine distinctions to be made at present in
+the grading of smoked-sheet rubber; it is either No. 1, or if any
+so-called defect is visible the sheets must be rejected and plainly marked
+as "off-quality."
+
+Clippings (trimmings) may either be made into crepe or shipped under their
+own description.
+
+RUBBER GROWERS' ASSOCIATION'S RECOMMENDATIONS.--Taking the foregoing
+arguments into full consideration, it would seem that, strictly speaking,
+the number of grades cannot be reduced to less than four at present without
+producing some amount of confusion.
+
+In its handbook,[15] the Rubber Growers' Association remarks:
+
+[15] "Preparation of Plantation Rubber," 1917.
+
+     "The fewer grades the better, and regularity of each grade is most
+     important.
+
+     "The grading should be as follows:
+
+          "(No. 1) Fine crepe (or No. 1 sheet), made from the free or
+          liquid latex.
+
+          "(No. 2) Clean light brown crepe, made from lumps and skimmings.
+
+          "(No. 3) Scrap crepe, made from tree-scrap.
+
+          "(No. 4) Dark crepe, made from bark-shavings, earth rubber, and
+          the lower quality of scrap.
+
+          "Tacky rubber should be packed separately.
+
+"_Compound Scrap Crepe._--Estates using scrap-washers should make a
+compound crepe of grades Nos. 2 and 3, which will make one compound free
+from bark and specks. All rubber intended for No. 4 should be most
+thoroughly washed."
+
+Concerning these recommendations the remarks in preceding paragraphs should
+be studied.
+
+CARE IN SORTING.--Whether dealing with smoked-sheet, pale crepe, or lower
+grades, the strictest care is necessary in sorting and grading. This work
+must of necessity be relegated to coolies, and they should be trained men.
+Instructions must be definite, and doubtful specimens of rubber should
+always be placed aside for the decision of the European superintendent. Any
+pieces showing unmistakable signs of what are regarded as defects should be
+stringently rejected. In the case of pale crepe, when the defect is
+confined only to a small area it is permissible to cut out the affected
+portion. Similarly there can be no objection, in the case of smoked sheets,
+to an occasional sheet being treated in this manner. On the majority of
+estates these rules are observed carefully, but some estates yet have to
+learn that defective pieces of rubber may not be concealed in a bulk of
+otherwise good quality. Samplers have often an uncanny knack of hitting
+upon the defective specimens, and it is entirely the fault of the estate's
+sorters if these pieces are submitted as being representative of the mass.
+
+CHOICE OF CASES.--Consumers complain justly of the presence of chips,
+splinters, and wood-dust. It will be evident, therefore, that whatever the
+type of case employed the interior surfaces should be smooth, there should
+be no cracks or gaps in the timber, and the cases should be cleaned out
+before using. There remains great room for improvement in the means and
+method of packing, and in spite of suggested alternatives we are at present
+restricted to the use of wooden cases.
+
+From comparisons of actual quality and fulfilment of the requirements
+indicated above, there can be no question that cases made of three-ply
+wood, such as the "Venesta," are in every respect superior to the ordinary
+wooden cases of "Momi" type. The consideration of cost and available
+supplies, of course, enters largely into the question, and three-ply cases
+are not at present so largely employed as they deserve to be.
+
+A new type of case was recently exhibited in Singapore. It emanates from
+the U.S.A. and is made of a fibrous material, resembling in appearance a
+very stout cardboard. The complete case when assembled consists really of
+two boxes, one of which is inverted and slides down over the other. Packing
+is completed by means of stout wire, which is strained by a simple ratchet
+arrangement. It is claimed that from 225 to 250 lbs. of rubber can be
+contained. Other claims made amount to the statement that the case is
+practically indestructible under normal conditions of handling and
+shipping. A demonstration given certainly appeared to substantiate the
+statement fully. Rubber packed in cases of various and average type was
+allowed to fall from a height of about twenty feet. In all instances the
+wooden cases of every type were either smashed or badly burst, whereas the
+fibre cases were merely dented. These cases are obtained in flat sections,
+which, in assembling, are folded and clamped by means of copper rivets in
+a special but simple machine. It was pointed out that objection might be
+lodged against the use of copper for this purpose.
+
+More recently there is announced a new packing case which is stated to be
+made from low-grade rubbers, but information is rather vague.
+
+BAGS.--There are in local use stout canvas bags which have the advantage of
+being used many times, as long as they are waterproof and kept in good dry
+condition. Their employment for the conveyance of smoked-sheets would
+appear to be permitted, but crepe rubbers sent in them are often reported
+upon as being "massed" at the edges, and hence difficult to "sample."
+
+BALES.--Attempts to bale rubber for the market have been frequent, but no
+success seems to have attended the efforts. In some quarters the failure
+has been ascribed to prejudice on the part of buyers, but it is the opinion
+of the writers that the objections to baling are, or could be,
+well-founded. Massed rubber often cannot be inspected properly, and hence
+is always open to suspicion that internally there may be unsuitable
+portions.
+
+There have been several schemes put forward for winding crepe rubber on
+spindles so as to form a cylindrical package complete in itself. We have
+seen the process, and certainly the method had much which appeared
+commendable. Apart from other objections which might be raised, there is
+always the one prominent objection mentioned in the preceding paragraph.
+
+While baling of rubber is thus not likely to suit the general market, there
+is no reason why, as in one or two instances, it should not be practised by
+agreement between producer and consumer. It is believed that "slab" rubber
+is shipped in bales from Sumatra to the U.S.A.
+
+Quite recently a proposal has been put forward to revert to a simple form
+of baling for ordinary plantation rubber. Under this scheme wooden cases
+are discarded, the packing material being composed of scrap-grade crepe
+rubber which, it is claimed, could be put to use by the manufacturer. An
+obvious drawback would be evident if these bales happened to be exposed to
+direct sunlight or a continuous high temperature. The tackiness which might
+supervene would make the handling of such bales unpleasant, even if it did
+not affect the internal rubber.
+
+FOLDING FOR PACKING.--In the packing of smoked sheets it would appear to be
+advisable to avoid, if possible, the folding of any pieces, as the
+objection is made that such rubber is difficult to "sample" on arrival,
+especially in cold weather. Sheets should be prepared or cut to such length
+that they occupy the full superficial area of the box, either singly or
+side by side.
+
+[Illustration: A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT.]
+
+The same remark applies to the packing of crepe rubbers, except that here
+we deal with units of folded rubber. Crepes are generally folded by hand,
+and coolies usually work to a certain dimension by means of a standard
+stick. The work is slow, but often gives employment, at a cheap rate of
+pay, to women and weak coolies.
+
+Several machines have been invented to replace this labour. The best of
+these yet seen has a simple device by means of which the length of the fold
+is adjustable to suit the size of any packing case. It is called the
+"Senang" folder, and is made by the General Engineering Company (Radcliffe)
+Ltd., Radcliffe, near Manchester.
+
+CARE IN ASSEMBLING.--Whatever the type of case employed, great care must be
+given to the assembling of parts and the final fastening. It is not
+uncommon to find in the operation of putting on the "strapping" that nails
+have been driven into the rubber. Extra bands of strapping are sometimes
+advised, and where these bands pass over the sides (not edges) of the case
+only specially short nails should be used.
+
+All wood should be planed, and in cases other than three-ply should be of
+stout wood, not less than 5/8 inch in thickness. All timber used should be
+of uniform type and thickness.
+
+METHODS OF PACKING.--The usual method of packing crepe is to fold the
+lengths to some measure of the dimensions of the case. This is done in a
+haphazard fashion on some estates, with the result that either space is
+lost or the packing is badly arranged.
+
+Some ingenuity can be displayed in the packing of sheet rubber in order to
+avoid folding the sheets, which, besides increasing the difficulty of
+sampling, leads to loss of space. Endeavours are being continually made on
+estates to prepare sheet of such a size as to obtain the maximum benefit of
+space both in smoke-house accommodation and in packing. A few estates
+employ tanks of such calculated dimensions as will yield uniform sheets
+which pack flat and fill the superficial area of the case.
+
+In view of the contamination which sometimes characterises the employment
+of wooden cases it is sometimes advised that the interior should be lined
+with sheets, or pieces of crepe, the ends of which are later folded over
+the top of the mass. In this manner it is stated that contamination is
+confined only to the exterior of the contents of the case.
+
+WEIGHT OF CONTENTS.--The dimensions of average cases are 19 inches by 19
+inches by 24 inches, giving a capacity of 5 cubic feet.
+
+In these it is possible to pack 150 lbs. of crepe rubber and 200 lbs. of
+sheet rubber (about 5 per cent. more in cases of three-ply wood). It may
+be noted that boxes arrive in better condition when fully packed. The
+foregoing figures are not adhered to strictly. For example, some estates
+find it expedient to ship rubber in actual ton lots, and for this purpose
+pack only 140 lbs. of crepe per case, giving sixteen cases to the ton.
+Other estates, using presses, pack more per case than the quantities noted
+above. At present there does not appear to be any definite regularity in
+practice.
+
+[Illustration: ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT.]
+
+In all instances it should be the invariable rule that the rubber should be
+weighed before packing, and that all cases should contain uniform nett
+quantities of any particular type of rubber. Invoicing, etc., will thus be
+greatly facilitated. If these practices are followed, and the rubber always
+weighed on the same scales (assuming it to be perfectly dry when packed)
+complaints of "short-weight" should be infrequent.
+
+"SHORT" WEIGHTS.--In some cases the occurrence of "short" weights on
+arrival at ports would appear to be inexplicable. It often happens that the
+constituent parts of wooden cases have been in stock for a considerable
+period. If for no other reason than that indicated below, all cases,
+either before or after assembling, should be thoroughly dried in the sun.
+"Short" weight could be accounted for to some degree by a lack of
+observance of this elementary rule, as it is most probable that there would
+be a perceptible difference in weight of the wooden case in a drier
+atmosphere.
+
+     (_a_) If rubber is weighed in the box, and the average tare of the
+     case deducted from the gross weight (in order to obtain the nett
+     weight), any loss in the weight of the timber would appear as a
+     deficiency of rubber at the distant port.
+
+     (_b_) Whether the same effect would be produced eventually in the case
+     of rubber which is weighed before packing will depend upon the method
+     of weighing at the warehouse. If the rubber is weighed in the box, any
+     observed deficiency would be attributed to a loss of weight in the
+     rubber.
+
+
+
+
+PART III
+
+MACHINERY AND BUILDINGS
+
+
+
+
+CHAPTER XIII
+
+_MACHINES_
+
+
+The number of manufacturers of machines for preparing rubber would seem to
+be on the increase, and there can be little doubt that this competition
+will result in a continued improvement in the design of machines. It cannot
+be denied that there has been room for such improvement, and it is believed
+that manufacturers will display judgment in putting only their best quality
+into the work. While design and finish are very excellent in their way, it
+is to be regretted that in a number of cases in the past the material of
+rolls has been found to be of inferior quality. Generally, the complaint
+seemed to be that the rolls were too soft, and that the "grinding" effect
+was far too great. The damage to pale rubber in such cases is considerable,
+as it is impossible to keep the rolls free from fine dark powder. The
+effect is generally noticed more in the smooth rolls with which a finish is
+put upon the crepe.
+
+Cases have occurred frequently in which rolls have been returned, because
+of the injury caused to pale rubber, and there can be little doubt that the
+life of quite a large number of rolls is even now far too short in
+comparison with the expense involved.
+
+It is a moot point, however, in many instances how far the quality of the
+rolls is actually responsible for the damage done to the rubber. In the
+experience of the writers it is certain that complaints regarding the rolls
+were unjustifiable, and that the injury had been caused by carelessness in
+the "feeding" of the machine. Especially in the case of smooth finishing
+rolls, it is clear that if the rolls are allowed to run idle for more than
+the briefest possible interval grinding must take place.
+
+The complaints apply not only to the rolls themselves, but also to the
+brass linings for shaft-bearings. Cases are known in which a brass "liner"
+was so worn within a few weeks as to be quite useless. If the matter ended
+there it would not be so bad; but there is always the possibility of
+particles of brass finding their way into trays, and so into the rubber.
+The damage which ensues to the rubber is quite irreparable. This particular
+defect arising from the presence of brass will be dealt with in a later
+chapter. But here again it is necessary to point out that such wear on
+brass liners may be caused by the standards (ends) of the rolls being
+eccentric; and the case may be analogous to the placing of "new wine in old
+bottles."
+
+_En passant_ it may be remarked that in any case brass liners are not
+strictly necessary. White-metal alloys are in use on rubber machines, and
+cast-iron bearings have been employed satisfactorily for years.
+
+It would be well for managers to remember, therefore, that when machines
+have to be ordered, nothing but the best is good enough, and that the
+difference between good machinery and passable machinery is probably
+immensely greater in effect than any saving in expenditure would warrant.
+
+ADEQUACY OF MACHINES.--In general, the factories which prepare sheet rubber
+are usually equipped with adequate machinery. This arises from the fact
+that machines are necessary for preparing all grades below the first, even
+if they are not necessary for the making of sheet. Thus all the necessary
+macerators and finishing machines are installed, but the major part of the
+output is in sheet form. For the preparation of sheet, no heavy machinery
+is required; all that is necessary are light machines for rolling the
+sheets and expressing as much moisture as possible. To obtain a pattern on
+the sheet, another light machine may be used. It may be imagined, then,
+that the work of rolling sheet rubber by power machines is small, and that
+a large quantity of rubber can be worked off in a comparatively short time.
+It follows, therefore, that the preparation of the lower crepe grades can
+be proceeded with at once, and that the whole work of the factory is
+expedited.
+
+The case of factories which have to prepare all first-grade rubber in crepe
+form is quite different, especially when thin rubber has to be made. The
+care which has to be exercised in preparing pale crepe rubber is very great
+in comparison with what is demanded by sheet rubber. The rubber has to go
+first through the uneven-speed macerators, from there to the intermediate
+rollers, thence to the finishing rollers. Considerable ingenuity has to be
+displayed in the arrangement of the machines, so that one section will not
+work faster or slower than another. More often than not, the attempt to
+arrive at such a desirable arrangement fails, owing to an insufficiency of
+machines. Such a statement will probably read strangely to the uninitiated;
+but an example will make it plain. A factory may have a battery of six
+machines, one only of which is a finishing machine (smooth rolls). With
+five macerators and intermediate machines working continuously, it will be
+more than the work of one finishing pair of rolls to keep pace, especially
+as so much more care has to be exercised in finishing than in rough
+crepe-making. The obvious course to adopt is to substitute a pair of smooth
+rolls, with suitable gear ratio, for a pair of macerators or
+"intermediates."
+
+If, however, the macerators and intermediates are already fully occupied
+the whole of the time, any such change would be of small benefit. What is
+really needed in this case is more machinery.
+
+It might be pertinently asked what constitutes an adequate equipment of
+machines for crepe-making. The writers cannot give a number, but have no
+hesitation in stating that if a factory cannot complete its whole day's
+work before dark, it is inadequately equipped. No work should be done after
+dark, if possible, as it cannot receive the supervision which crepe-making
+demands. To make comparison between the number of machines in any two
+factories and their respective outputs is not sound argument, as the
+out-turn of two similar machines will depend upon the speed at which the
+rolls travel--_i.e._, the gearing between the machines and the engines.
+Thus, while one machine will out-turn 40 lbs. of crepe per hour, another
+may only have an output of 30 lbs., although the machines may be identical
+in pattern. To make calculations based on a rate per hour for any known
+make of machine, and to apply those calculations to the existing machinery
+in any factory, in an attempt to judge whether there is a sufficient number
+of machines, would be a mistake, unless one were also supplied with the
+relative speeds at which the rolls work.
+
+Finally, on the question of adequacy of machines, it must be pointed out
+that an insufficient number of machines must result in a poor product,
+since all rolls have to be used for all grades. Even with the greatest
+possible care it happens that pale crepe is sometimes spoiled because it is
+contaminated with foreign matter, resulting from the working of lower
+grades on the same machines. This is one of the great arguments in another
+direction for the installation of a scrap-washer.
+
+In conclusion, the writers can only give their opinion that one must not
+decide the question of adequacy by the number of existing machines, but by
+the time taken each day in working off the rubber, providing one can be
+satisfied that the best arrangement of the existing machines has been made.
+
+IDEAL ARRANGEMENT.--As to what this best arrangement may be, guidance can
+be obtained from the results of experience here given. It must be premised
+that the output of any factory preparing fine pale crepe is limited by the
+output of the smooth finishing rolls. Broadly, it will be recognised that
+if there is any excess of capacity in a battery it should be found in the
+smooth-roll machines. This sufficiency, or excess of capacity, may
+sometimes be attained by an alteration in the gearing of the drive of the
+rolls from the back-shaft, or by an addition to the number of machines. In
+the former case, there are practicable limits of speed, beyond which the
+second alternative measure must be adopted.
+
+SPEED.--The usual speed at which the back-shaft travels ranges from 60 to
+70 revolutions per minute. Taking first the macerating machines, the
+intermediate gearing between the shaft and the rolls should give a driving
+speed of about 20 revolutions per minute on the faster-travelling roll.
+This is equivalent, with a 15-inch diameter roll, to a peripheral speed of
+about 60 to 65 feet per minute.
+
+The intermediate and smooth rolls can be arranged to travel more quickly,
+but the maximum comfortable speed for proper feeding and control appears to
+be about 25 revolutions per minute on even-speed rolls. In view of the fact
+that the rubber at each successive machine becomes longer and thinner, it
+will be seen that a smooth-roll machine could not cope with the output of a
+macerator in the same period of time. If, therefore, the macerator is fully
+occupied for the greater part of the time, an additional smooth-roll
+machine must be installed, even though the existing one has been "speeded
+up" to practicable limits.
+
+For the information of the uninitiated it might be explained that in the
+macerating and intermediate machines the cog-wheels driving the two rolls
+are of different sizes (_i.e._, differentially geared), as opposed to the
+smooth rolls on which the cog-wheels are usually of the same size (_i.e._,
+even speed). The idea in the one case is to exert a "working" influence
+upon the rubber while it is being washed by the stream of water coming from
+above; in the smooth rolls a squeezing action only is effected.
+
+To give an idea of the ratio of the speeds of the rolls in each machine in
+a typical working battery, the following particulars may be noted:
+
+GEAR RATIOS.--
+
+               _Machine._            _Differential Ratio._
+
+  1. Macerator                              32-17
+  2. Intermediate (coarse grooved)          32-17
+  3.      "       (fine grooved)            30-19
+  4. Smooth (uneven speed)                  30-19
+  5.  "     (finishing)                     25-24
+  6.  "     ( "  )                          25-24
+
+It will be seen that the so-called "even-speed" smooth rolls run at
+approximately the same rate.
+
+It is advised that in all cases the gear wheels should be cut helically.
+Those who have experience of the noise of some batteries after they are
+slightly worn will appreciate such a remark.
+
+GROOVING OF ROLLS.--Concerning the choice of grooving, there is divergence
+of opinion, some managers preferring one type, which others reject in
+favour of another type. Provided any particular type can be shown to be as
+effective as required, no necessity for laying down hard-and-fast rules
+seems to exist.
+
+The following particulars serve to describe a battery well known to the
+writers, and accustomed to produce the finest quality of thin pale crepe
+and lower grades:
+
+  -----------------+-----------------------------------+-------------
+                   |                                   |_No. of Times
+     _Machine._    |         _Grooving._               |Rubber passes
+                   |                                   |  through._
+  -----------------+-----------------------------------+-------------
+  1. Macerator     | Deep horizontal grooves;          |
+                   | square-cut, 5/16 inch × 5/16 inch |
+                   | × 5/8 inch spaces                 |      3
+  2. Intermediate  | Horizontal grooves; 3/16 inch     |
+                   | × 3/16 inch × 3/8 inch spaces     |      2
+  3.     "         | Fine spiral grooves; 1/8 inch     |
+                   | × 1/8 inch × 1/4 inch spaces      |      2
+  4. Geared smooth | Nil                               |      1
+  5. "Even" smooth |  "                                |      1
+  6.    "     "    |  "                                |      1
+  -----------------+-----------------------------------+-------------
+                   |        Total                      |   10 times
+  -----------------+-----------------------------------+-------------
+
+The actual rate of output of this installation is the capacity of the last
+smooth machine. This is about 180 lbs. per hour, while the output of the
+macerator is approximately double this amount. Thus the macerator only
+works for about half the time. This applies also to the two intermediate
+machines. After a study of the preliminary remarks, it would not be
+difficult to suggest methods for improving the condition of affairs. It
+would appear that, in order to obtain a uniform rate of working in such a
+battery, the relative peripheral speeds of the several machines should
+be--(1), (2), and (3) 100; (4) 150; (5) and (6) 200. The remarks on the
+practical limits of speed should be borne in mind. In this case the smooth
+rolls travelled at 23 revolutions per minute.
+
+As already stated, it is not intended to lay down definitely that, _e.g._,
+horizontal grooving alone should be cut on macerating rolls. Some estates
+employ with satisfaction a deep square-cut spiral 1/4 inch by 1/4 inch by
+1/4 inch or 1/2 inch spacing; others use a large diamond pattern. Similarly
+various types of grooving are cut in the intermediate rolls.
+
+[Illustration: A BATTERY OF MACHINES.
+
+On the left, light marking rolls for sheet rubber; on the right, heavy
+machines for crepe preparation. In the middle background, "scrap-washing"
+machines outside the main building.]
+
+It has been remarked in the chapter dealing with crepe preparation that
+much depends upon the condition of the coagulum. There is no necessity, or
+desirability, for having a standard higher than 2 lbs. dry rubber per
+gallon, and it has been argued that it would be better to select a standard
+of 1-1/2 lbs. The tougher the coagulum, the more the power required, and
+the slower the rate of output of the leading machines.
+
+In ordering machines for crepe-making, only large rolls should be
+considered--_e.g._, rolls having a diameter of 12 inches to 18 inches and
+from 15 inches to 18 inches face.
+
+ROLLS RUNNING HOT OR "FREE."--If the rolls are found to become hot, work on
+that machine should be stopped, and an examination made, otherwise there
+is the possibility of the crepe becoming sticky and "tacky" when dry.
+
+Although comparatively cold water may be flowing upon the rubber and the
+rolls, little alleviation may be noticed, inasmuch as the source of heat
+lies generally at the bearing ends of the rolls. This may be tested by
+placing the hand on the top of the "standard" of the machine. The
+development of the heat may be due to lack of lubrication, worn bearings,
+or sometimes faulty setting-up of the machines.
+
+Allusion has been made to the necessity for avoiding the running "free" of
+rolls--_i.e._, in the absence of rubber. The grinding of the rolls, when
+working close together, produces a fine powder, which causes a more or less
+pronounced deposit on pale crepe. When the rolls have been in action for
+some time and become slightly worn, this deposit may be confined only to
+the edges of the rubber.
+
+SHEETING MACHINES.--The foregoing paragraphs have dealt entirely with
+machines for crepe preparation. Concerning machines for use in
+sheet-making, the ground has been mainly covered in Chapter IX.
+
+Where both crepe and sheet are made, it is permissible and advantageous to
+use the heavy smooth rolls for the rolling of the sheets, and it is only
+necessary to instal one or two light machines for placing a pattern on the
+rubber.
+
+Where a heavy battery does not exist, light machines with smooth rolls may
+be employed satisfactorily. Even engine-power is not necessary for the
+preparation of excellent sheets, but the output is limited where hand-power
+only is employed. Estates are known on which upwards of 1,000 lbs of sheet
+rubber are made daily with hand-power machinery in one station. Beyond this
+figure, it is deemed advisable to instal a small engine, say of 7-9
+horse-power. This is ample to drive a battery of three smooth-roll machines
+and two markers, and yet have sufficient reserve to actuate a small pump
+for the water supply.
+
+LUBRICATION OF MACHINES.--It must always appear to those inexperienced in
+engineering matters that existing methods for lubricating rubber machinery
+are distinctly crude, when one considers the delicacy of the material to
+be prepared. Many existing machines are still lubricated with oil, which
+has to be administered in generous quantities. Generally, such machines
+have been so designed that the excess of oil may find an easy passage into
+the tray which receives the rubber. If not, it drops just outside the tray
+to the floor, and is washed away in great gouts. Even where grease-cap
+lubricators are fitted it is common to find that the excess can often be
+transferred from the bearings to the trays and so to the rubber. One would
+have expected from the attention which is being given to machinery for
+rubber estates that some improvement in lubrication methods would have been
+devised.
+
+It is probable, however, that a great deal of the disabilities attaching to
+present methods of lubrication might be obviated if closer attention were
+given to the actual operation of the lubricators. Coolies should not be
+allowed to handle them, and the responsibility should be placed upon a
+foreman or the engine-driver.
+
+TRAYS.--The most unsuitable and damage-causing part of the vast majority of
+machines, without doubt, is the tray. On nearly all machines the tray is
+wider than the effective portion of the rolls, so that any excess of
+lubricant may drop into it. On others, not only is the tray wider than the
+rolls, but its edge either is in contact with the shaft of a roll or just a
+small distance away. The edge of the tray is thus favourably situated for
+acting as a "wipe," and the lubricant is transferred to the inside of the
+tray. Considering that the effective portion of rolls is about two-thirds
+of their length, it must be unnecessary to have trays wider than the length
+of the rolls. For the preparation of fine crepe trays are quite
+superfluous, and their place can be taken by a narrow piece of board if
+required. If the bed of the machines has been covered with glazed tiles,
+even a piece of board is not necessary. Where trays have been removed from
+the fine-crepe rolls on a number of estates, a marked decrease in the
+number of spoiled pieces of rubber has resulted.
+
+It must be recorded that the foregoing paragraph appeared in our 1913
+publication. After a lapse of over seven years, the remarks remain as true
+as when originally written. One of us is continually meeting with cases in
+which the defects are plainly attributable to the cause indicated above,
+and the fault often lies with the management of estates. On most machines
+the trays are not fixtures, and could be removed if desired.
+
+ARRANGEMENT OF MACHINES.--In considering the future arrangement of
+machines, the first care should be to see that machines and windows are to
+be found together.[16] Of all the factory operations, rolling of rubber
+should be given the maximum light. At the same time it would not be
+advisable always to choose a southern aspect, unless outside shades were
+supplied. The best position for setting up machines, therefore, is along a
+wall having a number of windows. This is extremely convenient also from the
+view of power transmission, and gives the maximum free floor space to the
+factory. In setting up machines, foresight must be displayed, otherwise one
+may find, when future extensions are made, that the extra machines may
+obstruct an entry or exit.
+
+[16] Windows imply the existence of walls. Such is the conventional design
+of factories. It may be pointed out that walls are not necessary. The roof
+may be supported on pillars between which expanded metal of large size may
+be placed. This fulfils all requirements and gives the maximum of light and
+air. Many new factories have been erected to such a design.
+
+For the actual erection of machines, no labour should be accepted without
+European supervision. At present there are machines which are practically
+useless owing to faulty workmanship, and on many machines bearings run hot
+for no apparent or explicable reason. Whether the fault lies with the
+turning of the rolls or the setting of the machine cannot be decided; but
+at any rate too much care cannot be expended on the supervision of setting
+up machines.
+
+There is no reason why everything in a factory should not be made as easy
+to clean as possible. For this desirable condition all machines should have
+the beds faced with tiles. A word of caution should be given against using
+marble slabs under the machines, as they would be eroded in time by the
+slight amount of acid washed out of the rubber. There would be no such
+objection against the use of white glazed tiles, if they are well set.
+
+ACCESS TO BACK OF MACHINE.--In a few factories it has been noticed that the
+drainage of water from the machines runs to the front of them. This means
+that the coolies are put to unnecessary inconvenience and discomfort, and
+they often suffer from sore feet. All water should drain to the back of the
+machines. The necessity for seeing that these drains are kept clear might
+then induce those in charge to examine the back of the machines. It is
+often the case that, while the front of the rolls and tray are kept clean,
+little attempt is made to cleanse those parts which are not visible or
+accessible from the front. There should be no need to point out that any
+labour expended in such "front-window" work is rendered useless by the
+contamination from accumulations of old rubber and grease at the back of
+the machines. In the course of visiting factories one of us has many times
+seen great surprise exhibited by the manager or assistants on being shown
+the state of affairs at the back of the machines. There should have been no
+occasion for such surprise, for the back of the machines is quite as
+accessible to them as to the visitor.
+
+In conclusion it might be said that the manager needing advice as to the
+best machines cannot go far wrong in purchasing any of the better-known
+makes, such as Shaw's, Bridge's, Robinson's, Bertram's, Walker's, Carter's,
+Iddon's, etc. This list does not include local manufacturers such as the
+"United Engineers." It must not be imagined that their machines are not
+recommended. As a matter of fact, their machines compare well with those
+made at Home. It would be well to judge in the final decision upon--
+
+     1. Cost.
+
+     2. The experience of those already using the machines.
+
+     3. Simplicity of parts.
+
+     4. Lubrication system.
+
+     5. Mode of adjusting rolls.
+
+     6. Fitting of trays.
+
+ENGINES.--It is not intended here to discuss particular makes of engines,
+or even to attempt to lay down definite statements with regard to the type
+of engine. Without a full knowledge of local circumstances, it is not
+possible to recommend whether the engine shall be oil-driven, gas-driven,
+or steam-driven.
+
+Assuming a copious supply of very cheap timber, there could be no objection
+to the employment of a steam-engine; but for most estates such a choice is
+out of the question.
+
+Again, in deciding between oil and gas, local economic factors must be
+considered. Suction-gas plants are now made, in which a wonderful variety
+of refuse can be consumed in the production of gas, whereas ordinarily
+estates are restricted to the use of either charcoal or anthracite coal.
+Both oil and gas driven engines are eminently suitable for the purpose of a
+rubber factory, and the results obtained on different estates with either
+are often discussed in favour of one or the other. The selection ultimately
+narrows itself down to one of cost of running, in which availability of
+supplies becomes an essential feature.
+
+POWER.--No matter what type is selected, there should be made an ample
+allowance for margin of power. The general experience of estates has been
+that when the first portion of the estate comes into bearing, there is a
+desire to avoid great outlay, which should really have been secured in the
+original capital. The result has been that as later the estate expands, the
+original power unit is found to be inadequate, and a larger engine has to
+be purchased. In a short while the original engine is found to be
+unsuitable even as a "stand-by," inasmuch as it is incapable of doing more
+than a portion of the work required. This means eventually that another
+large engine is required. Had sufficient margin of power been allowed
+originally, only two engines would have been bought, as against the three
+indicated above. Without going into finer details, it is usual to allow a
+rate of 10 horse-power per heavy machine used for crepe preparation. In
+actual practice, when a battery is working under full load, the power
+demanded is about 6 horse-power per machine. Thus a 50 horse-power engine
+running six machines and a scrap-washer is really running with only a small
+margin of power, and if large pieces of hard coagulum are placed in the
+washer or the macerator there may be a sudden stoppage. Assuming an average
+estate commences with only three machines for crepe-making, on an expanding
+programme, allowance of power should be made for six machines and a
+scrap-washer, if the purchase of larger power units is to be avoided
+later.
+
+
+
+
+CHAPTER XIV
+
+_FACTORIES_
+
+
+GENERAL CONSTRUCTION.--On the question of general construction there is
+little to be said, except that buildings are now being properly designed in
+more permanent form than were some of the earlier buildings. On the whole
+there is little fault to be found with factories in general, except in so
+far as the output has outgrown the accommodation.
+
+Most factories are now erected in iron, but there are a few which are built
+of bricks. It should be premised that a factory in which rubber is to be
+prepared should be as light and airy as possible. In this respect quite a
+number of the older factories are lacking, and they seem to have been
+designed to exclude as much air and light as possible. Under these
+circumstances, the building is always dark, there is always an air of
+dampness, dirt may accumulate, and there is usually a bad smell. Rubber
+prepared under these conditions is always liable to be below the high
+standard which should be attained, and the general tone of the factory is
+depressing.
+
+PLENTY OF LIGHT.--The old idea that light must be excluded is now known to
+be erroneous; so that in designing a factory, provision should be made for
+ample light and air. It should not be forgotten that in tropical climates,
+iron buildings may become uncomfortably hot, as most of our older factories
+are. Usually it will be found that the ventilation is imperfect. There is a
+lack of window space, and the roof is imperfectly ventilated. The ridge of
+the roof should be opened up by means of a "jack-roof," so that the warm
+air rising naturally may escape at the highest point of the building. These
+are defects which should be remedied in old buildings.
+
+As a rule no rubber remains in the factory at night-time, except in the
+form of coagulum, the loss of any of which would be noted with ease. The
+conventional idea of enclosing the factory with walls of galvanised
+sheeting, wood, or brick, is not strictly necessary. In modern buildings
+these walls are replaced by large-mesh expanded metal, thus making the
+machine-room perfectly light and plentifully ventilated. Under such
+conditions, dirt cannot accumulate unseen, and the general tone of the work
+is raised.
+
+THE FLOOR.--The floor should be of thick concrete, and have a good surface
+layer of cement. Preparations are now advertised for which claims are made
+that their employment renders the surface of such floors waterproof and
+dustproof. If these claims can be substantiated when the use is applied to
+the floors of rubber factories, the employment of a preparation of this
+nature should result in a considerable saving of expense and trouble.
+Preferably the floor should not be flat, but should slope slightly from the
+longitudinal middle of the building to the sides on either hand. If the
+floor is level it usually results in accumulation of water, the cement
+breaks in patches, and the factory always appears to be dirty.
+
+POSITION OF MACHINES.--All machines should be arranged adjacent to and
+parallel with one of the long sides of the building, and should be raised
+about 6 inches above the floor, so that water may escape easily. Tanks for
+the reception of latex, scrap rubber, etc., should be placed along the
+opposite wall to the machines, and the intermediate length of the building
+should be entirely free from fixtures. It was not uncommon in older
+factories to find the engine situated in the middle of the floor, so that
+what with the space occupied by the engine, and the space rendered
+unavailable by the belt-drive, the real accommodation of the factory was
+sadly diminished. In no modern factory should the engines be brought into
+the main room. They should always be accommodated in a special compartment,
+situated outside the wall, along the inside of which machines are placed.
+In this way considerable floor space is left available, and the machines
+may be worked by direct drive. Not only so; but if a suction-gas plant is
+worked, there can then be no excuse for particles of coal or charcoal dust
+being found in the factory.
+
+POSITION OF ENGINES.--It scarcely need be pointed out that if the engines
+are placed outside the wall which is opposite the machines, a long
+belt-drive would be necessitated, and that the presence of the belt would
+prevent the use of end doors. It is presumed in these arguments that two
+engines are to be installed. One can hardly imagine a modern factory in
+full working being equipped with only one engine, which might possibly have
+an excess of power necessary to drive all the machines. In the case of
+breakdown, which sometimes happens in the best supervised factories, it
+would be small consolation to know that this excess of power was present
+theoretically.
+
+HOW MANY STOREYS.--There can be no doubt that, taking all things into
+consideration, the best type of factory is that consisting only of one
+floor. The factory should be quite separate from all other buildings, and
+if attempts are made to conserve ground space by putting a drying-room over
+the factory, much trouble will ensue, especially if pale crepes are to be
+made. In the first place, the factory is made very much darker, and hence
+more difficult to keep clean; secondly, the ventilation of the factory is
+seriously interfered with; and thirdly, it is manifestly prejudicing the
+drying of rubber to place it directly over a room which is always more or
+less awash with water. At night such a building would reek with a
+moisture-laden atmosphere, and little drying could be expected to take
+place in that interval. From actual experience it has been shown that
+rubber hung to dry in such a room, situated over a damp factory, is very
+liable to attacks of "spot" diseases, since the presence of perpetual
+moisture is favourable to the development of these diseases. If a
+double-storey building has to be worked, it will be readily seen that no
+first-grade rubber should be allowed to dry in it. The accommodation over
+the factory may be restricted to the purpose of receiving lower grade
+rubber which is not so liable to "spot" diseases, and possibly does not
+take so long to dry as first-grade rubbers of equal thickness. It is
+evident, therefore, that the erection of double-storey factories is false
+economy, as separate drying-houses have to be built eventually. This
+conclusion does not apply with the same force to factories worked in
+conjunction with smoke-houses for preparing sheet rubber, but,
+nevertheless, such a factory should not have another floor above the
+work-room.
+
+VERANDAHS.--One of the worst features in many factories is the necessity
+for coolies to bring latex into the factory. As already mentioned, the
+floors of factories are usually running with water (or should be), and it
+can be imagined that the passage to and fro of scores of coolies must bring
+in a great quantity of dirt. Not only so; the very presence of the coolies
+is a hindrance to the efficient working of the factory, and considerable
+floor-space and time are wasted.
+
+This feature in factory working is all the more annoying because the
+necessity for it could so easily be obviated. All that is necessary is the
+erection of a wide, open verandah outside the wall of the factory. Here all
+latex could be received and strained, scrap-rubbers could be received and
+passed through an opening into tanks placed in convenient position. Water
+could be laid on in this verandah so that coolies might wash their buckets,
+and the whole verandah might be enclosed only with expanded metal so as to
+avoid interference with the lighting of the factory. In this way it would
+be quite unnecessary for any field coolie to enter the factory proper, and
+this would facilitate cleanliness. Such an arrangement has been discussed
+by the writers many times during the last few years, but the number of
+estates which have made such provision is still in the minority, and the
+same slipshod and dirt-making procession of coolies continues to walk
+through the factories, and the same piles of bark-shavings and scrap-rubber
+continue to accumulate and ferment in a few instances.
+
+An indication of types of verandahs is given in Chapters VII. and IX. These
+are not intended to be representative of a universal design, but may be
+suggestive in the planning of others according to local conditions.
+
+SITUATION OF TANKS.--It will be noted that these verandahs are raised from
+the ground-level to a height of about 3 feet in order that latex may be
+gravitated, with a slight fall, into the coagulating tanks which are within
+the factory. There exists a real necessity for this practice, inasmuch as
+otherwise to obtain gravitation of latex (which is quicker and cheaper
+than handling) the coagulating tanks would have to be either placed on the
+floor or sunk beneath the level. The risk of contamination of latex or
+coagulum under such circumstances would be appreciable. Apart from this, it
+is advisable to have the coagulating tanks raised to a height of between 2
+and 3 feet, to secure the advantage of ease of working in the processes of
+coagulation and the handling of coagulum--a not inconsiderable factor.
+
+In some modern designs it is proposed to place the coagulating tanks in a
+separate building. This would seem to be an unnecessary refinement in a new
+building, if observance is given to the suggestions made in previous
+paragraphs.
+
+DESIGNS AND "LAY-OUT."--In a previous publication[17] comment was made upon
+grievous errors in designs prepared by those inexperienced in the
+requirements of the tropics. There is little ground now for complaint, and
+local engineering firms are fully capable of advising upon, and
+constructing, suitable buildings.
+
+[17] "Preparation of Plantation Rubber," Morgan, 1913.
+
+In considering the first installation of a factory and equipment one always
+has to weigh the question of prime cost against the probability of future
+expansion of crop. If it should be decided at first merely to cater for
+contemporary requirements, the fullest consideration should be given in
+discussing design of building and lay-out of machinery to the
+practicability of later extension. The site should be large enough for the
+eventual group of buildings, the building should be easily capable of
+extension with the least cost, and the same forethought should govern the
+lay-out of the machinery.
+
+DRAINS.--Lastly, there is the question of drains. Generally speaking, all
+factories are well provided with drains, and the only difficulty is that of
+getting an adequate fall for efficient drainage. But there is a certain
+amount of laxity exhibited in the matter of providing sieves in drains. To
+anyone acquainted with factory working, it must be apparent that quite a
+lot of small pieces of rubber are washed into the drains. This rubber
+should be collected at intervals during the day; but in many instances
+that collected is only a fraction of what escapes. Wherever possible the
+drainings of a factory should be carried as far as is practicable from the
+buildings by means of cement drains. Too often these are short, and lead
+into earthen drains. Even if no pieces of rubber are present, the serum
+from the coagulum is subject to decomposition, the effluvium from which is
+objectionable.
+
+WATER SUPPLY.--It is essential that a good supply of water should be
+available. This should be distributed by pipes all round the building, so
+that a hose may be used in every part for the thorough cleansing of the
+factory at intervals during the hours of working.
+
+Summing up, it might be said that a good factory, therefore, should have
+the following features:
+
+     1. Plenty of windows, or walls of expanded metal.
+
+     2. A jack-roof in the ridge, and hence a good system of ventilation.
+
+     3. Engines in compartments outside the walls of the factory.
+
+     4. Machines close to and parallel with the wall outside of which the
+     engines are placed.
+
+     5. Latex tanks and other fixtures along the wall opposite the
+     machines.
+
+     6. A long middle free space, at either end of which a large double
+     door should be placed in the end walls.
+
+     7. A good concrete and cement floor sloping slightly from the middle
+     towards each long wall.
+
+     8. An abundant water supply, and several lengths of hose.
+
+     9. The building should be of only one floor, and have ample head room.
+
+     10. There should be an outside, open verandah upon which latex may be
+     received, etc.; preferably outside the wall which is opposite to the
+     machines.
+
+     11. The system of drainage should be thorough, and the drains should
+     be adequately screened, so that all particles of rubber may be
+     collected.
+
+
+
+
+CHAPTER XV
+
+_OTHER BUILDINGS_
+
+
+DRYING-HOUSES FOR CREPE.--It has already been shown in the previous chapter
+that one type of drying-houses--viz., that over a factory--stands
+condemned, except for the drying of low-grade rubbers. Generally speaking,
+a great advance has been made in the design of crepe drying-houses during
+recent years, and it has been possible even to improve older ones so as to
+bring them into line with the more modern buildings. Houses for drying
+crepe rubber may be of one floor, two floors, or even three floors.
+Doubtless those built with three floors were designed with a view to
+economising the available site for factory buildings, and as long as the
+ventilation is good there can be no very great objection to them. It might
+be pointed out, however, that even with the best of ventilation the air
+passing successively through three layers of rubber must be fairly
+saturated with moisture by the time it leaves the building. The effect of
+this upon the rate of drying in the uppermost chamber will not be so marked
+as it will be in the middle floor, as the temperature of the top floor must
+be many degrees higher than that of the other two rooms. It would be
+expected, therefore, that the rate of drying in the middle storey would be
+slower than that in either of the other two.
+
+In houses of two floors this objection would not have to be met, and
+drying-houses of this type are successful and common.
+
+HOW MANY STOREYS?--Again nothing could be urged against a building of two
+or three storeys in which the ground floor was occupied as a packing-room,
+except that, by negligence in not allowing wet crepe a preliminary dripping
+period, water might fall upon the packed rubber below.
+
+As a matter of experience, such a house is, taking all into consideration,
+the cheapest and most suitable type for any estate with an increase in
+output. Even at the outset there should be a separate room in which sorting
+and packing is undertaken. This is conveniently the lower room of a
+drying-house. The only stipulation to be made for a house with two storeys
+is that the floor of the upper room should be of an open pattern, so that
+the air may circulate right through the building. This is usually and very
+successfully attained by laying down wide slats of wood, with spaces of an
+inch or more between them. It is not advisable to have spaces wider than
+1-1/2 inches, otherwise there is a certain amount of danger to the limbs of
+individuals who have to work or supervise in the building. In any case, it
+is very convenient to have pathways of planks running the whole length of
+the floor, so that the supervision is made more convenient. If this is
+done, there can be no objection to the custom of suspending the rubber of a
+lower chamber from the slats of the floor of the upper room. At present, in
+some drying-houses, this means of suspension is used, but no planks are
+laid down, and it becomes necessary to walk over the drying rubber. This is
+a detail, but it is one which does not make for the improvement of rubber,
+and the expenditure of a small sum would be sufficient to rectify the
+matter.
+
+From every point of view, it would be desirable to have the floor of the
+packing-shed (or the packing-room in a combined house) raised from the
+ground, to a height of, say, 3 feet; or the height of a bullock-cart or
+motor-lorry. Not only is ventilation improved, but there would be a great
+saving in labour. Packed cases could be wheeled directly on a level with
+the cart or lorry.
+
+A great many estates favour drying-houses of one storey. These are
+eminently suitable, provided that the site is suitable, and that the
+relative dimensions of the house are favourable to efficient ventilation.
+It is a common mistake to find buildings of which the breadth is out of
+proportion to the height. Obviously, if the height is not considerably in
+excess of the breadth, ventilation will be defective. For a single-storey
+drying-house, the maximum height should bear the ratio to the breadth of
+3:2, and in a house of this type specially long pieces of crepe can be
+utilised. Naturally, in a house of two storeys, this factor is not likely
+to be neglected, and if the lower room is used for packing purposes the
+rate of drying should be rapid. Again, when a single-storey building is
+contemplated, it is well to make strict examination of local conditions. If
+the site is low-lying and surrounded by trees it will be clear that tall
+buildings are required, and that a house of more than one floor is to be
+preferred. Considerations of this nature would have prevented the erection
+of some dry-sheds which do not give a satisfactory rate of drying.
+
+VENTILATION.--No matter how many floors there may be in a drying-house, the
+greatest attention should be given to the question of ventilation. It is an
+elementary point in the study of ventilation problems that the best system
+of natural ventilation is obtained by admitting cool air near or through
+the floor and providing an exit for the warmer air at the highest point in
+the building. It is not often that such a rule is infringed in the
+ventilation of rubber drying-houses, but several of the older buildings
+erred in this respect. In a good modern house there is a space (about 2
+feet in height) all round the base of the walls merely closed with expanded
+metal; this admits cool air. An exit for warm air is provided in the ridge
+of the roof by either ventilation chimneys or by a jack-roof. The latter is
+preferable, as it provides for a more free and uniform escape.
+
+In some drying-houses, besides the ridge openings, the space along the
+eaves is left open. This would seem to be undesirable, as it provides for
+the entrance of outer air, which might combat the ascending warm air and so
+interfere with the natural upward currents. Provided that a jack-roof or
+other suitable openings have been installed, there is, therefore, no
+necessity for the existence of open spaces at the eaves, and they probably
+do more harm than good.
+
+In the tropics, on days of sunshine, there must always be an upward current
+of air in well-designed houses. Temperatures of 105° F. are easily recorded
+in the ridge space of a building, while the temperature in the lower part
+of the house may be at least 15° F. lower. On the floor of an upper room a
+temperature of 90° F. is commonly noted, and in buildings with three
+storeys the usual day temperature of the top room is about or over 100° F.
+Even, therefore, when there is no trace of a breeze, there must be a
+displacement of air in an upward direction, though it may not be detected
+without tests being applied.
+
+It is often asked whether a temperature of 100° F., such as is obtained in
+the upper room, is calculated to injure the quality of the rubber. There
+need be no fear on this ground; the experience of many estates goes to show
+not only that no harm results, but also that the drying of the rubber is
+expedited. There would seem to be no reason why crepe rubber should not be
+dried at a temperature of 100° F. It must be understood, however, that
+higher temperatures for crepe rubber are not recommended, as it has been
+proved that the rubber is affected. The fact becomes obvious with continued
+treatment at temperatures much above 100° F., for the rubber stretches and
+breaks across the support.
+
+WINDOWS.--Concerning the subject of window space in a drying-house, there
+has been much discussion at various times. Years ago it was common to find
+windows widely open with the sunshine streaming in. Naturally, tackiness
+developed in some of the rubber, and care was then taken to keep the
+windows closed. Thus the rooms were darkened and air excluded. There
+followed a period in which windows were fitted with ruby-coloured glass to
+keep out the actinic rays of the sun, which were responsible for tackiness,
+and excess of light, which was supposed to be responsible for the rapid
+oxidation of rubber. Unless special precautions were observed in the
+processes of coagulation and preparation, it was not proved that the
+exclusion of light prevented or lessened the natural oxidation of crepe
+rubber. Since the introduction of sodium bisulphite for the prevention of
+oxidation, there has been no cause to worry as to the possible effect of
+light, as no perceptible darkening of the rubber takes place. It follows,
+therefore, that no trouble need be taken to exclude light, although the
+necessity for excluding direct sunshine still exists. Windows may be left
+open as long as the sun does not reach them. This can usually be arranged
+in a drying-house by manipulating the windows at intervals during the day,
+so that those in the shady side of a building are always open, while those
+on the sunny side are always closed. If it is thought that this
+manipulation cannot be entrusted with success to the store coolies, the
+case may be met by having all windows constructed on the louvre pattern, so
+that, although the windows are closed all day, air and light are not
+excluded. Should it be desired to retain the existing type of windows,
+which open outwards, and to keep them open all day, a simple arrangement of
+ruby-coloured cloth on an outstanding wooden frame may be placed within the
+walls of the building, or the shutters of the windows may be hinged at the
+top to open outwards. Unless there is a pronounced breeze, or it is
+required to examine the rubber closely, there is no necessity to have
+windows open, except in the case of a house in which the bottom floor is
+used as a packing-room. The windows of this chamber may remain open during
+the day, to advantage in sorting and packing, and also to the proper
+ventilation of the building. Thus the direct rays of the sun are rendered
+harmless, while air and light are allowed to enter.
+
+HOT-AIR DRYING-HOUSES.--Mention has already been made of the existence of a
+system of drying in which hot air is forced into a drying-house by means of
+a powerful fan. Provided that the temperature of the hot air could be so
+regulated as not to exceed 100° F., there would be merit in the system.
+Such matter of regulation could be solved by having a duct in the main air
+passage, through which cool air could be admitted in such proportion as to
+modify the temperature of the hot air. As the process is worked at present,
+the temperature attained is often well above 100° F., and there is a danger
+of thin crepe placed in this house over-night being found upon the floor in
+the morning. Unless the crepe is prepared thick and cut into fairly short
+lengths, it will not bear its own weight at higher temperatures; and if it
+is made thick, drying is impracticably prolonged. It is probable that, with
+a temperature of 100° F., and a steady current of air, average thin crepe
+would dry in such a drying-house within six or seven days. This would be
+an improvement upon the usual rate of drying in most factories, although
+several ordinary drying-houses are known in which thin crepe will dry
+naturally in that period.
+
+SMOKE-HOUSES.--No discussion of theoretical considerations regarding the
+process of smoke-curing will be attempted here. We are concerned only with
+the necessity for supplying a demand for smoke-cured sheet rubber. Broadly,
+the process is akin to the smoke-curing of herrings, and the objects are
+much the same--viz., (1) drying, (2) preservation--except that while
+herrings are only dried partially, rubber should be dried perfectly.
+
+On a small scale a primitive smoke-house could be built easily and cheaply,
+and such a building might be fully as efficacious as the most elaborate and
+expensive installation. In the early days of estates it was not uncommon to
+see temporary smoke-houses constructed of wood, and roofed with "attaps"
+(palm leaves). Some of the best rubber in the market has come from wooden
+buildings, but naturally the risk of destruction by fire is considerable.
+
+For imperative reasons it may be sometimes found necessary to smoke rubber
+when the only available building is a single-storey one. As a temporary
+measure, the building may be converted into a smoke-house by placing the
+fires in pits sunk deeply into the ground, and effectively screened above
+by iron baffle plates. But it is not advisable that smoking be continued in
+such a single-storey building, as the best effects are not obtained, and
+the risk of fire is far too great.
+
+USUAL TYPES.--At first sight it would appear that the best type of
+smoke-house would be one consisting of a tall building, covering a
+comparatively small superficial area, and having a number of superimposed
+chambers in which the rubber could be hung to dry. In practice there are
+several solid objections which limit the height and the number of floors.
+Chief among these is the question of temperature. If smoke-curing is to be
+effective, a certain temperature must be attained and maintained. To obtain
+such results in a house of excessive height would be difficult, if not
+impossible, under normal conditions. It would be found that the chamber
+immediately above the furnace-room would be overheated if the temperature
+in the upper rooms was within the desired range, etc.
+
+Until recent years smoke-houses could be classed as belonging to one of two
+types:
+
+     (1) Those having external furnaces.
+
+     (2) Those having internal furnaces.
+
+The number of the former existing at the present time must be very small,
+as it has been shown that the arrangement of the furnace outside the house
+is unsatisfactory in comparison with the other type of house. In discussing
+the question of smoke-houses, therefore, it will be understood that the
+standard type accepted is that having an internal furnace. In its original
+form it was known as a "Kent" drier, and consisted of a tall two-storey
+wooden building. The walls of the lower chamber had the form of an inverted
+and truncated pyramid. By this arrangement it was possible to obtain from a
+comparatively small fire sufficient smoke and heat to cure the product
+placed in the room above. This is the principle upon which many
+smoke-houses in Malaya are designed. On a very large scale it is not
+claimed that the sloping sides of the lower chamber lead to economy in the
+number of fires, but merely divert the smoke in an upward direction. It is
+acknowledged that vertical lower walls are quite effective, and it is an
+easier matter to fit in doors.
+
+It may be noted that the usual type of smoke-house now in general use
+consists of a building of two storeys, in the lower of which are situated
+the furnaces, while rubber is hung on racks in the upper room. Sometimes
+there may be a third storey, also used as a drying (curing) chamber. As a
+rule the drying-room is one long unit, as also is the furnace chamber; but
+in some cases they are subdivided by vertical partitions into smaller
+chambers, for ease of working and better control. This applies with some
+force in the case of very long houses standing in an open space. It is
+sometimes found in such cases that at certain seasons the prevailing winds
+have the effect of making drying and curing uneven in parts of the
+building.
+
+With these exceptions, the ordinary type of smoke-house functions very
+efficiently, and is capable of drying average sheet (from standardised
+latex) in a period ranging from seven to eleven days. Should the building
+not be capable of such performance, in spite of the strict observance of
+all rules laid down for the processes of preparation, then there is some
+defect in ventilation or in the distribution of heat.
+
+GENERAL VENTILATION.--The ordinary rules of ventilation in drying-houses
+apply equally to a smoke-house. There should be a slow current of air and
+smoke from the lowest point to the highest point in the building.
+
+In spite of all that has been written on this subject, it is by no means
+uncommon to encounter the idea that a smoke-house should be perfectly
+closed in order to get good results. As to what must become of the (say) 25
+per cent. of moisture which the rubber contains there is no knowledge. In
+dozens of cases, when complaints regarding slowness of drying have been
+investigated, it has been necessary to point out the need for providing a
+rational system of ventilation.
+
+Naturally only a slow current of air and smoke is required. The creation of
+an appreciable draught would have the effect of increasing the fuel
+consumption of the furnaces, raising dust from the ash, and of causing a
+temperature higher than that which is known to be desirable. It will be
+clear, therefore, that if there are to be any openings at the base of the
+walls they should be small in area, and should have some device by means of
+which the current of air can be efficiently regulated. In the usual case
+the construction of the building is not calculated to render it air-tight,
+and the necessity for providing special air inlets does not arise.
+
+WINDOWS.--Windows are not strictly necessary, and are only intended to be
+of service during the time in which coolies are at work within the
+building. The operations of examining rubber, turning sheets, removing dry
+rubber, cleaning racks and floors, and putting wet rubber into position,
+usually occupy some hours daily. During this interval the windows should be
+widely opened if the weather is favourable, and should remain so until the
+fires have been lighted. It should not be forgotten that during the heat
+of the day quite an appreciable degree of drying is possible. Advantage can
+be taken of this; but there is no necessity to extend the interval unduly,
+and it is of greater advantage to proceed with smoke-curing when the work
+in the drying-chambers has ceased.
+
+RACKS OF SUPPORTS.--Still referring to the usual type of smoke-house, it
+may be remarked that in the upper room bays of racks run at right angles to
+a central passage down the length of the building. Narrower passages run
+between the bays of the racks to facilitate ease in handling and
+inspection. The wooden supports may be placed about 3 inches apart
+horizontally, and 15 or 18 inches apart vertically. A full bay of racks
+should contain nine or more lines of support in each of the planes which
+are 15 or 18 inches apart vertically. The number of these planes is
+governed only by the height of the room, measured from the floor to eaves.
+The supports should be of smooth timber, and need not exceed 1-1/2 inches
+square in section.
+
+It is usual and advisable to smooth off the rectangular edges of the
+supports or bars, to avoid the incidence of splinters of wood adhering to
+the rubber. The bars should not be fixtures, but may either be accommodated
+in slots, or may rest _between_ two nails, so that it is possible to give
+them a rotary motion by turning the projecting ends. This practice is
+followed in smoke-houses, the idea being to move the drying sheets slightly
+each day, with a view to the prevention of a pronounced mark across the
+sheets.
+
+Care should be taken to see that the vacant racks are thoroughly cleaned
+before fresh rubber is placed upon them, otherwise a distinct dirty mark is
+caused across the middle of the sheet. This mark usually cannot be removed,
+even by scrubbing with water. Where this mark occurs regularly in all
+sheets, attention should be turned to the openings beneath the bays of
+racks, if open fire furnaces are employed. It will generally be found that
+gauze of too wide mesh has been fitted. This should be removed or covered
+with a finer gauze.
+
+A more effective way of dealing with the trouble, provided other
+precautions have been taken, is to have plenty of spare wooden bars. It
+should be a rule stringently enforced that, as soon as racks are emptied,
+the bars should be removed to the factory to be cleansed thoroughly. A
+spare set should enter the smoke-house with each batch of fresh rubber. The
+actual number of spare sets required could be limited to a two days'
+supply, and the extra cost would be recouped easily.
+
+FLOOR OF DRYING-CHAMBER.--The floor of the chamber is usually of planks,
+except that the space under each bay of racks should be filled with
+expanded metal. With the use of wood fires there is always a large amount
+of light ash formed, which may find its way into the upper chamber. To
+counteract this, screens of fine mesh gauze are laid over the expanded
+metal. This gauze may be fitted into a movable wooden frame, so that when
+it becomes necessary to clean it the whole may be removed.
+
+The difficulty is that with furnaces of the "open-fire" type the rise of
+dust is so great that the gauze screens soon become clogged, especially as
+the slight tarry matter in the smoke condenses on the gauze, causing the
+dust to adhere. With the better types of furnaces, the employment of gauze
+screens is not necessary, as there should be very little rise of dust. It
+is sufficient to use only expanded metal, to prevent any displaced pieces
+of rubber falling into the furnace chamber.
+
+FURNACES GENERALLY.--The crudest and dirtiest method of fuel consumption in
+the preparation of smoked-sheet rubber is that of making a fire on the
+ground. This is still a common practice, and should be condemned as being
+both wasteful and harmful. Under prevailing conditions coolies will, in
+spite of instructions, heap up a pile of logs in order to save themselves
+the trouble of stoking the fire in small quantity and at regular intervals.
+A small supply of water is kept at hand with which to quench the fire
+somewhat if it threatens to cause trouble. Naturally a large quantity of
+fine ash is thus thrown up, and the rubber above receives the deposit. If
+the coolie does not happen to be sufficiently awake, of course a house
+burns occasionally.
+
+From this primitive type of furnace, others have been evolved. These
+usually take the form of more or less shallow trucks, the majority of
+which are similar in principle to the fire on the ground, except that the
+container can be withdrawn from the house for the purpose of removing the
+ash. Sometimes they are even more objectionable than the ground fire,
+inasmuch as, being raised above the ground level, an under-draught through
+fire-bars is caused, and consumption of fuel is so much the more rapid.
+
+PITS.--It is clear that large fires are not desirable, and that combustion
+should be slow, provided that the necessary temperature can be maintained.
+The lines along which the development of furnaces needed to extend are
+therefore plain. The simplest device adopted was the digging of pits in the
+ground. Sometimes these pits received the addition of an iron truncated
+cone which was movable. Naturally the combustion was slow, but sufficient
+heat was obtained if the pits were large enough or in sufficient number. An
+objection was that the ash had to be cleared _in situ_, and in the process
+the earthen pits gradually increased in size. In all cases it was necessary
+to suspend an iron baffle-plate above the furnaces to distribute smoke and
+arrest any sparks.
+
+"POT" FURNACES.--The next development was the employment of "pot-furnaces."
+These consist of iron drums, sometimes merely resting on the ground, and
+sometimes mounted on trucks for easy withdrawal. These drums radiate
+sufficient heat if present in sufficient numbers, and the fuel consumption
+is low. They are usually manipulated by starting a fire in the bottom and
+packing in logs cut to the necessary length. Some have no lids, while
+others are fitted with perforated caps.
+
+It was considered necessary in some instances to punch a few small holes
+near the base of the drum in order to ensure a very slight upward draught.
+In a few cases this perforation has been exaggerated to the form of a
+hinged door. Unless this can be closed with ease, and is closed according
+to instructions, part of the object of this type of furnace is defeated;
+fuel consumption is rapid, and the temperature is too high. In the original
+form "pot-furnaces" have been found to be effective on many estates, and
+are still employed with satisfaction.
+
+IRON STOVES.--Working on exactly the same principle, on some estates one
+finds small iron stoves in use. Sometimes broad pipes are attached for the
+better distribution of the smoke; if this is the case it should be noted
+that the pipes should have a slight downward slope, and that the "bend" at
+the end should be turned downwards. In this way condensed moisture and
+creosotic matter falls to the ground, and does not lodge in the pipe. The
+life of the conduit is thus prolonged. Usually such stoves are in use where
+the "head-room" of a smoking chamber is insufficient for other types, or
+where the nature of the site does not permit of sunken furnaces being
+installed. They are of value likewise on occasions where the fuel supply is
+limited to a rich timber such as mangrove-logs ("bakau"), when it is
+necessary to ensure a low combustion with low cost of fuel.
+
+HORIZONTAL DRUM-FURNACES.--To overcome difficulties inherent to drums or
+"pot-furnaces," the next development was that in which the drum was made to
+assume a horizontal position, and adapted ingeniously to a simple system of
+working from the outside of the building. Reference to the drawings given
+will explain how this is effected. In the first illustration (No. 2) it
+will be noted that the drum is supported upon brick pillars, with one end
+projecting through the wall of the building. At the other end a short
+chimney is mounted, having within it a "damper" which is adjustable from
+the outside. Over this chimney is suspended a simple baffle-plate, made
+from a Chinese iron cooking-pan. The outer end of the drum is furnished
+with a hinged and latched door, in which a small air-regulator is
+accommodated.
+
+In the second set of drawings (No. 1) the drum is increased in size and
+fitted in a special manner for incorporation with a distinct type of
+building. Such a scheme was first put into effect by Mr. R. C. Sherar, the
+manager of Third Mile Estate, Seremban, F.M.S., and for ease of reference
+the house and furnace will hereafter be mentioned when necessary as the
+"Third Mile" type.
+
+[Illustration: "THIRD MILE" TYPE; HORIZONTAL DRUM.
+
+This type of furnace is suitable for adapting to existing buildings with
+perpendicular lower walls.]
+
+[Illustration: "THIRD MILE" TYPE OF FURNACE, USED IN CONJUNCTION WITH
+"THIRD MILE" SMOKE-HOUSE.]
+
+It will be seen that the furnace has at the farther end a door for the
+removal of ash. As this, if badly fitting, may result in too great a
+draught, it is well to insist upon good workmanship. Other adjustable
+air-inlets are provided, and the drum is enclosed in a brick chamber.
+
+RATE OF COMBUSTION.--However successful this furnace may have proved in the
+hands of trained coolies, one must feel that with such a number of
+air-inlets (whether accidental or designed) there would always be present
+the possibility of obtaining too rapid a combustion. In the original forms
+of drums or pot-furnaces of various kinds, a very slow rate of combustion
+was attained. Naturally a relatively larger proportion of carbon remained
+unconsumed, and there was a small proportion of ash. In these respects the
+furnaces resembled charcoal-burners. In point of fact, some estates used
+this principle for the dual purpose of smoke-curing the rubber, and at the
+same time obtaining a supply of charcoal to provide fuel for their
+suction-gas engines. This is a consideration in times when managers are
+desirous of discovering any devices which tend towards reduction of costs.
+
+It will be clear that, under ordinary circumstances, the condition of what
+remains after the combustion of the fuel gives an indication of the rate at
+which the wood has burned, and this test should apply to all furnaces. That
+in which there is the most ash and the least charcoal is the one least to
+be desired. In direct connection with this consideration, one must
+recognise that a fire which is sunk below the level of the ground exposes
+the least surface from which heat may radiate; and hence, in order to
+obtain the maximum benefit of heat from a slow-combustion furnace, it
+should be above ground-level, or should have a superstructure from which
+the heat may be dissipated.
+
+Simple drum furnaces, with slow combustion, have the further advantages
+that a "charge" of fuel will need no attention for possibly eight to ten
+hours, and practically no ash is found to be ejected. These advantages have
+great practical importance. The first minimises any disabilities arising
+from neglect on the part of coolies, and the second makes for increased
+cleanliness in the drying-chamber. While these advantages would appeal to
+most estates, there would appear to be a further advantage to small
+estates which have only temporary timber smoke-houses. With a slow rate of
+combustion in a furnace of this type, danger from fire is diminished
+considerably.
+
+Bearing in mind the slow rate of combustion, and hence the comparatively
+low temperature obtained, it will be plain that drum furnaces should be
+employed in larger number than ordinary open-hearth fires; and the drums
+can be so placed as to ensure the best possible uniform distribution of
+heat and smoke.
+
+Large furnaces are sometimes seen, with flues of brickwork. In view of the
+foregoing remarks, it will be obvious that these tend to large fires and a
+rapid combustion, and hence must be classed as undesirable.
+
+BRICK STOVES.--Developing from "drum" furnaces, another type comes into
+existence. In principle it consists of an enclosed brick furnace, with
+feeding door, and a low conical dome surmounted by an adjustable cap or
+spark-arrester. The rate of combustion can be influenced by a suitable
+movement of the cap, which is operated by a screw. This type of furnace has
+been installed on several estates by the engineering department of Messrs.
+Harrisons and Crosfield, and is understood to give satisfaction.
+
+PATALING TYPE.--With the exception of the "Third Mile" type already
+mentioned, all the furnaces described are open to a strong objection, in
+that the coolies have to enter a room, usually filled with hot smoke, in
+order to attend to the fires. The mere opening of the door of the building
+is sufficient to fan most fires into a blaze and to raise sparks. Apart
+from these points, it is natural for coolies to avoid entering too often,
+with the result that they generally stoke with the maximum load of timber.
+Even should they not sleep the danger is clearly great.
+
+[Illustration: SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE).]
+
+[Illustration: PATALING TYPE OF FURNACE.]
+
+To obviate these drawbacks, furnaces which are fed from the outside of the
+building were designed. There have been various forms, but as they were
+first installed on Pataling Estate, in the present form, they may be known
+under the description of the Pataling type of furnace. They are eminently
+satisfactory, and have a low rate of fuel consumption. They are very
+safe, and in fact, if worked with average intelligence in supervision, can
+be regarded as being fool-proof. There is practically no ejection of fine
+ash, and no fine-mesh screens need be employed. They can be adapted to any
+building having either vertical or sloping walls of galvanised iron.
+
+[Illustration: LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED
+VENTILATORS PERMANENTLY OPEN.
+
+In foreground, movable folding racks on which sheets "drip" in the open
+air. This smoke-house is equipped with brick furnaces fed from the outside
+(Pataling Estate).]
+
+In essential the furnace consists of a shallow pit below ground-level,
+lined with brick, and having a square brick superstructure rising 4 feet
+above the floor of the building. On top of the brick walls rests a sheet of
+boiler-plate perforated with small holes. The hearth being below
+ground-level, and with the extra 4 feet of height above the floor, it
+follows that if ash is disturbed it is confined.
+
+From the drawings it may be seen that the pit is prolonged to the side wall
+of the building, with steps leading up to the ground-level. The top and
+sides of the opening are made with galvanised sheeting, forming a kind of
+short tunnel in which the coolie may stand upright. The outer face of the
+brick furnace forms the inner end of the tunnel, and accommodates the door
+of the furnace. The bottom of the pit is filled up with clay and stones
+almost to the level of the bottom of the door. This ensures a very shallow
+hearth, and guards against an unduly large fire. Obviously it is not
+desirable or necessary to make the hearth of fire-bars, as was done in one
+instance, with the provision of a door below for removing the ash. This
+would lead only to a strong draught being created, with a high rate of fuel
+consumption.
+
+[Illustration: BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE
+BUILDING, BUT FED FROM OUTSIDE.
+
+On the top of the superstructure rests a sheet of perforated boiler-plate.
+The actual fire-pit is below ground-level, and to the left may be seen
+parts of the sides and top of the downward approach, from the outside, to
+the door of the fire-pit.]
+
+The openings can be screened by a narrow sloping lean-to, which serves to
+keep out rain, and provides shelter for the stock of fuel and the coolie.
+The iron furnace-door should be well made, with an easily worked latch; but
+it is not necessary that it should be perfectly fitting. Any slight
+aperture will serve to provide the necessary air-inlet, but in any case it
+should not be more than slight.
+
+CONSUMPTION OF FUEL.--Regarding this furnace, it may be said in conclusion
+that it is more satisfactory in general working than any other furnaces yet
+encountered. Obtaining information from over sixty estates, on the question
+of fuel consumption compared with output of rubber, it was found that, as
+far as ordinary smoke-houses were concerned, the Pataling type of furnace
+showed the lowest unit consumption of fuel.
+
+[Illustration: GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES.]
+
+This was at the rate of slightly less than 1 lb of fuel per 1 lb of
+thoroughly cured sheet rubber. The figure on some estates mounted as high
+as 4-1/2 lbs. of fuel per lb. of rubber. Naturally this factor may have
+been affected by failure to utilise the drying space to its fullest
+capacity, but in the main the high rate of consumption could be attributed
+solely to the deficiencies of the furnaces.
+
+FLOOR OF FURNACE-ROOM.--As a rule no attempt is made to improve the natural
+earthen floor. Whether open-hearth fires, truck furnaces, or drums are
+employed, it is usual to find a floor with an inch or two of dust upon it.
+Where all endeavours are directed in other directions towards cleanliness,
+it appears strange that this should be overlooked. In contrast, houses
+employing the Pataling type of furnace (or others) have concrete and cement
+floors, which can be kept quite clean. Cleanliness should be as zealously
+attempted in the smoke-house as in other departments.
+
+[Illustration: NEAR VIEW OF SHELTER.
+
+Steps lead downwards where the wall of the smoke-house has been removed.]
+
+ROOF.--In any type of smoke-house, the roof should fit tightly at the
+eaves, and the only vent should be in or near the roof-ridge.
+
+In an ordinary smoke-house, the opening should take the form either of a
+low jack-roof or of squat chimneys protected against rain. If a jack-roof
+is chosen, it may be so low as to need no scheme of adjustment, or
+otherwise adjustable swing shutters must be provided. The chimneys may be
+made with such low fitting between the cap and the body that no interior
+swinging flaps are required.
+
+During the operation of smoke-curing the smoke vents must remain open to a
+degree which is arrived at by experience. Failure to provide a
+comparatively free egress for smoke and moisture will bring trouble in its
+train. After a house has been in use for some time, it will be noted that
+the timber becomes covered with a shiny tarry coating deposited by the
+smoke. If the rubber remained in the house for an equal period, it would
+take on the same appearance. During the interval between the entry and the
+exit of the rubber some amount of deposit does take place, and it is this
+mixture of creosotic substances which plays a part in fitting the rubber to
+withstand growths of mildew which would otherwise form.
+
+If proper smoke-vents are not provided, the moisture evaporating from the
+sheets is unable to escape quickly enough, with the result that a great
+deal condenses at night-time upon the inner surface of the comparatively
+cool roof, and falls back upon the rubber in unsightly black "drips," which
+leave a distinct mark on the sheet. Even if vents are open, this may happen
+during seasons of rain. The temperature of the moist smoke in the
+roof-ridge may be as high as 130° to 140° F., while the outer atmosphere
+may have been cooled by rain to 70° F. Such a difference on the two
+surfaces of the roof must lead to condensation within the house, with
+consequent "dripping." It used to be the custom to drape sacking material
+above the bays of racks in order to prevent the drops of liquid falling
+upon the rubber; but often for want of renewal the last state was worse
+than the first. Modern houses have often an inner lining, a few inches
+below the roof. This is made of soft wood which receives any product of
+condensation and absorbs it.
+
+OTHER TYPES OF SMOKE-HOUSE.--So far we have confined the arguments to
+smoke-houses of the usual type. There are others which vary in either
+design and method of working, or in the material of the structure. Mention
+may be made of the most prominent of these.
+
+BRICK HOUSES.--Some houses are constructed of brick, and may have one or
+two storeys above the furnace chamber. The floors are sometimes made of
+ferro-concrete, and the furnaces may also be of this material. These brick
+houses give satisfaction, but there would seem to be some difficulty in
+obtaining and maintaining the desired temperature, although it is not quite
+plain why this should be so. The principle of these buildings is the same
+as that of the ordinary iron house, and the suggestions made in previous
+paragraphs apply with equal force.
+
+"THIRD MILE" TYPE.--Reference has been made to the "Third Mile" type of
+furnace. This is an integral part of a smoke-house, which for clearness of
+distinction may be known as the "Third Mile" type of smoke-house, the
+original of which was erected on the Third Mile Estate, Seremban, F.M.S.
+
+[Illustration: "THIRD MILE" TYPE OF SMOKE-HOUSE.]
+
+In essence the design consists of a building, having two storeys for
+rubber-drying, and a shallow inverted pyramidal base, ending on the ground
+in "Third Mile" furnace, already described and illustrated.
+
+It will be seen that the principles of ventilation employed are those
+indicated for an ordinary house--viz., air-inlet near the ground (with
+little draught), and smoke-vent at the roof-ridge. The windows shown in the
+drawing are only for purposes of inspection of the rubber during the day,
+and form no part of the scheme of ventilation during the hours of smoking.
+
+It is claimed that the efficiency of the house is high. Certainly the work
+of attending to the furnaces is simplified, and there should be small
+ground for excuse if negligence is displayed.
+
+JACKSON HOUSE.--This was brought into notice under the description of the
+"Jackson Cabinet," and it was claimed that average sheets could be dried in
+a few days. It consisted of a small house of one storey, having several
+tiers of racks. Smoke and heat were generated in a small stove placed
+outside the wall. A smoke vent was provided in the roof. These cabinets had
+a certain vogue as part of a small unit installation, with a fair degree of
+success. It is not clear, however, that such speed in drying is required.
+(This point will receive further attention in a subsequent chapter.)
+
+"DEVON" TYPE.--In its full original design this type owes its origin to Mr.
+H. E. Nixon, General Manager of the Devon Estates, Malacca, where it forms
+part of unit divisional installations worked under a scheme of
+decentralisation.
+
+The original units consisted of a building erected with an iron framework
+covered with sheets of asbestos-slate, and a roof of galvanised iron.
+
+The novelty in design lies in the utilisation of external platforms upon
+which the racks of bars supporting the sheets of rubber may be drawn out of
+the smoking chambers, and on which the racks are loaded and unloaded. By
+this device it is possible to remove the contents of any compartment bodily
+without interfering with the continuity of curing in the other
+compartments. That is to say, smoking in such a house can proceed day and
+night if necessary, and yet the rubber in any part of the house can be
+examined, can be removed, or can be replaced without cessation of smoking.
+
+It will be seen from the illustrations that the house is more or less of
+the same general design as the "Third Mile" type, with the addition of
+external platforms. It has two storeys for the reception of rubber; and a
+basal furnace-room with sloping sides converging downwards into a pit
+containing a large drum-furnace. This is mounted on a low truck, and
+travels on a short length of railway.
+
+[Illustration: GENERAL VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE.
+
+The platforms are common to both units. Building of brick with iron roof
+(Batu Caves Estate).]
+
+Each of the curing-rooms is divided into four compartments (making eight
+compartments in all). These are closed by swing doors, each of which is the
+full width of a compartment, and has a slight overlapping edge. Through
+these doors light railways run into the house and out upon the platforms.
+On the rails "bays" of racks run, and when fully loaded they are easily
+moved. The racks were designed with a frame of stout hard wood, but light
+angle-iron could be utilised.
+
+[Illustration: GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND FACTORY
+BUILDINGS.
+
+Timber in foreground cut to length for stoking. Note water-tower and engine
+cooling-tanks adjacent to factory.]
+
+The chimney style of smoke-vent has an internal butterfly flap, which is
+controlled by means of a wire from the outside. In the ordinary course of
+smoke-curing, it is advised that this flap should be permanently open so as
+to reduce the possibility of internal condensation of moisture and
+creosotic matter. The exact degree to which it should be open must be found
+by experience.
+
+[Illustration: VIEW OF PLATFORM OF "DEVON" SMOKE-HOUSE; DOORS OF
+COMPARTMENTS OPEN, AND ONE RACK PARTIALLY WITHDRAWN.
+
+Note below each rack opening through which smoke rises, covered with wire
+netting.]
+
+Although reference has been made several times to compartments, it should
+be understood that the chambers are not subdivided internally by means of
+partitions. There exists only the external effect of compartments in the
+form of the eight swinging doors which allow for the withdrawal of, or
+insertion of, any one unit of racks at any time without interference with
+the bulk of the rubber.
+
+[Illustration: DOUBLE "DEVON" SMOKE-HOUSE OF BRICK, WITH ROOF OF CHINESE
+TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM SMOKING
+CHAMBERS.
+
+Federated Engineering Co., Ltd., Kuala Lumpur.]
+
+[Illustration: SIDE VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL
+ARRANGEMENT FOR STOKING FURNACES.
+
+Federated Engineering Co., Ltd., Kuala Lumpur.]
+
+DETAILED DESCRIPTION.--As enquiries are often received it is permissible to
+reproduce the following detailed description of the original house. This
+appeared in the Fourth Local Report (Malaya) 1916, issued to subscribers by
+the Rubber Growers' Association.
+
+     "The house has a steel frame-work, 22 feet long, 16 feet wide, and 22
+     feet high. Of the length, 14 feet is occupied by the platforms, and 8
+     feet by the chambers. These measurements can be varied. The whole of
+     the width (16 feet) is occupied by compartments of which one series is
+     placed above the other.
+
+     [Illustration: FRONT VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE.
+
+     Glenmarie Estate: Batu Tiga Co.]
+
+     "_Platforms._--The loading verandahs or platforms are of ordinary
+     'seriah' timber.
+
+     "_Compartments and Furnace Chamber._--These are enclosed with Bell's
+     'Poilite' sheets, each of which measures 8 feet by 4 feet by 3/16
+     inch. The sheets are affixed to the steel stanchions, doors, etc., by
+     galvanised bolts (1 inch by 1/4 inch) which pass through iron flats
+     measuring 8 feet by 2 inches by 3/8 inch (about). These iron flats
+     hold the sheets at the edges. The dimensions of the compartments are 8
+     feet by 8 feet by 4 feet.
+
+     "_Racks._--These are eight in number, and measure just under 8 feet by
+     8 feet by 4 feet. The capacity of each is roughly about 450 lbs., of
+     dry sheet rubber. The racks are mounted on 6-inch iron wheels, running
+     on rails of stock size, 'T' iron (1-3/4 inches by 1-3/4 inches by 1/4
+     inch).
+
+     "The sheets are hung on split bamboos. To prevent these projecting
+     over the edge of the rack and catching in the doors when the rack is
+     moved in or out, a thin strip of wood, about 1/2 inch high, is nailed
+     along the sides of the rack.
+
+     [Illustration: SIDE VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE.
+
+     Building constructed of galvanised iron. Shows door to furnace
+     chamber, and ventilator.]
+
+     "_Furnace._--This is of the type that aims at slow combustion. It
+     consists of a cast-iron cylinder, 3 feet in diameter and 4 feet high,
+     carried on a truck made of a sheet of boiler-plate, and mounted on
+     small wheels, so that the whole can be moved easily out of, and into,
+     the furnace chamber for easy cleaning and stoking.
+
+     "The furnace chamber is a pit lined with concrete, just wide enough
+     to take the trolley, and about 12 feet long. The top of the furnace,
+     which is almost flush with the ground-level, consists of a sheet of
+     zinc or galvanised iron with numerous holes about 3 inches in
+     diameter. Over these holes are strips of mosquito gauze, as flame and
+     dust arresters (see note below). There are no holes in the sides or
+     bottom of the cylinder.
+
+     "Over the furnace is hung a baffle-plate, measuring 4 feet by 4 feet.
+     Above this, on the first floor-level, the bottom of the compartments
+     is covered with wire netting, to prevent any rubber dropping
+     accidentally into the furnace chamber. The furnace chamber is fitted
+     with an iron-frame door, swinging on perpendicular hinges.
+
+     "_Method of Stoking._--The timber used is a mixture of jungle wood and
+     rubber-tree wood, cut to lengths of about 1-1/2 feet. In the ordinary
+     way the furnace is charged at 6 p.m., and at six-hour intervals a
+     little more fuel is added, but a new charge is not necessary. During
+     the daytime, when the heat of the sun is sufficient to raise the
+     temperature appreciably, a smaller fire is maintained.
+
+     "_Temperature._--There is no difficulty in maintaining a temperature
+     of 120° F. By continuous smoking, average sheets prepared from
+     standardised latex can be fully cured in five days. This represents
+     110 hours of smoke-curing, which is at least equal to ten days'
+     intermittent smoking in an ordinary house.
+
+     "_Capacity._--There are eight racks, each accommodating 450 lbs. of
+     standardised sheet rubber. The loading capacity of the house,
+     therefore, is 3,600 lbs. As each charge is cured in five days, the
+     monthly output may be 21,000 lbs.
+
+     "The cubic capacity is 2,048 cubic feet. As there are no gangways,
+     etc., this is fully utilised. This gives a rate of monthly output
+     capacity to over 10-1/4 lbs. dry rubber per cubic foot of drying
+     space; an excellent figure much in advance of values obtained in the
+     great majority of ordinary smoke-houses."[18]
+
+[18] Since the above was written, it has been found possible to eliminate
+the gauze. A mild steel top has been made, perforated with 2-inch holes.
+Practically no dust is ejected from the furnace, and there are no flames.
+
+Owing to shortage of supplies during the War, similar buildings have been
+erected with frames of well-seasoned hard wood, which was protected by
+strips of asbestos-slate or galvanised iron. The latter material was also
+substituted in the covering walls. Later, houses were erected of brick,
+with other minor modifications. As a natural development, the latest
+buildings consist of two of the original houses face to face, under a
+common roof, and served by common platforms.
+
+As originally designed, the house was intended to meet the needs of a small
+estate, or a division of an estate, having a maximum output of about 20,000
+lbs. of sheet rubber per month. The possibility of an extension of this
+idea has been shown to be great.
+
+The furnace has been described as situated in a pit. Situated on a bank or
+on sloping ground, it was easy to arrange for withdrawal of the furnace. In
+some cases this has not been possible, and various modifications have been
+effected. The most satisfactory yet encountered is that in which a shallow
+brick pit is surmounted by an iron cone, about 4 feet in height. This is
+fitted with a cap having small perforations. The fire burns in the pit, and
+the heat is radiated by the cone. It would have been more effective to have
+allowed greater height in the furnace chamber, and to have employed the
+travelling drum-furnace as in the original design.
+
+In order to avoid interference in draught by a space between the bottom of
+the doors of the compartments and the platform (due to the presence of
+rails), the floor of the platform is laid level with the top of the rails;
+or to the bottom of the doors is attached a swinging flap, notched for
+accommodating the rails when in position.
+
+       *       *       *       *       *
+
+There are in use houses of other designs, which all more or less vary only
+in some modifications from the types described. Hence they do not call for
+special comment. Recently a rather distinct departure has been noted in a
+structure designated the "Barker" smoke-house.
+
+BARKER PATENT.--In essential this consists of a long narrow structure
+erected with an appreciable slope from one end to the other. At the lower
+end is a small furnace enclosed in a brick compartment. The smoke from this
+furnace travels up the slope to the other end, at which the rubber enters.
+The sheets are hung on bars which are attached to a unit framework. This
+frame slides, by its own weight, upon timber side supports. A sufficient
+number of these units occupies the full effective length of the structure.
+The removal of "stops" at the lower end enables the foremost frame to be
+removed, and the succeeding frames slide into a new position. Thus the
+freshly prepared sheets, entering at the higher end, gradually and
+automatically move towards the furnace as the frames of dry rubber are
+removed from the lower end.
+
+[Illustration: THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT.
+
+The racks slide automatically from top to bottom on withdrawal of the lower
+frames through door at front. The furnace is contained in the brick
+compartment at the lower (front) end.]
+
+Thus far only small units have been seen. It is claimed that, properly
+prepared, sheet rubber can be smoke-cured in about five or six days, and it
+is stated that installations have been in successful working for
+sufficiently long periods to prove their efficacy. The device is better
+known in Java and Sumatra than in Malaya. The capacity of a unit building
+is stated to be 7,000 lbs. per month, calculating on a six days' cycle of
+working. In a more recent design provision is made at the lower end for a
+water tank, into which all rubber can be discharged in case of fire.
+
+
+
+
+CHAPTER XVI
+
+_OTHER BUILDINGS (continued) AND SITUATION OF BUILDINGS_
+
+
+SORTING-ROOM AND PACKING-ROOM.--It is in these departments that most
+factory installations are lacking. More often than one cares to
+acknowledge, sorting and packing are done under conditions which place a
+premium upon poor work. As a consequence, consignments of rubber are often
+marred by the inclusion of defective specimens. The result is that
+shipments may be rejected when tendered against contracts, or that
+allowances in price have to be made. In many instances it would not be fair
+to lay the blame upon the manager or an assistant, as it is obviously
+impossible for an individual to inspect every piece of rubber. Neither
+would it be strictly fair in some cases to ascribe the fault to pure
+carelessness on the part of the coolies.
+
+Often the only provision made for this important work is the lower room of
+a drying-shed, which may also contain hanging rubber. Under these
+circumstances, space is cramped, and the light often poor. Small defects
+may pass unnoticed, and the general surroundings do not conduce to keen
+work.
+
+Where, for economic reasons, the sorting and packing operations are
+conducted in the drying-shed, there should be ample space free from hanging
+rubber, and it should not be possible for wet rubber placed in the upper
+room to drip upon the dry rubber below or upon packed cases. There should
+be plenty of light, and for this reason windows should be ample. Usually
+the window-frames are fitted with wooden shutters, which are preferably
+hung on horizontal hinges from the top of the frame. By this device it is
+not necessary to close all windows during a shower of rain, and rubber may
+be stacked near a window with reasonable chance that direct sunlight will
+not be allowed to fall upon it.
+
+In dealing with smoked sheet, it is advised that the rubber to be examined
+should be placed upon tables facing the windows, so that each piece may be
+scrutinised in a strong light.
+
+Crepe rubber also is best examined in a strong light, but preferably with
+one's back towards the source of light or at an angle to it. For this work
+coolies usually are most efficient when sitting on the floor.
+
+It will be clear from the foregoing remarks that the best conditions would
+be secured in a separate building especially constructed. A single room
+would be all that is required; at one end sorting could be undertaken,
+while packing could be done at the other end. No hanging rubber should be
+allowed in the room.
+
+The floor should be of hard timber, and raised from the ground, to the
+height approximately of a bullock-cart or motor-lorry, as the case may be.
+The boxes of rubber could thus be transported by small hand-trucks on a
+level with the transport vehicle, reducing labour to the minimum.
+
+The ventilation of the building should be good, especially if cases of
+rubber are to be stored therein; and the entire structure should be
+weather-proof.
+
+STORE-ROOMS FOR RUBBER AND STORAGE.--The question of storage of rubber in
+factory buildings has always possessed importance, but has demanded
+increased consideration recently.
+
+From experience in this country, it is clear that cement floors for
+store-rooms or packing-sheds are the least suitable. They are often visibly
+damp, especially in the early morning. To allow rubber, packed or unpacked,
+to remain upon a cement floor in the tropics, is to court trouble from
+moulds, external or internal. If the employment of a cement floor is
+unavoidable, the rubber and boxes should be raised on wooden supports,
+giving a clearance of at least 3 or 4 inches, and there should be clear
+ventilation space between tiers of boxes.
+
+Experience indicates that the best type of floor is that already advised
+for sorting and packing rooms--_i.e._, a good hard timber floor raised at
+least 3 feet above ground-level. Apart from the advantage in labour
+specified in the previous paragraphs, this provision of ample ventilation
+space below the floor is a great consideration in the preservation of the
+timber. Raised store-rooms become essential in low-lying districts which
+are at all subject to flooding, yet the writer has seen many boxes of
+rubber damaged by flood-water entering a packing-room situated on the
+level.
+
+The question has often been raised recently as to the length of the period
+during which rubber may be safely stored in this country. The answer can be
+only supplied by experience, of which up to the present we have none
+possible of being classed as reliable. Whatever storage may have been done
+in the past has been influenced greatly by the unsuitability of the storage
+accommodation, and the fact that often the rubber was not prepared with a
+view to prolonged storage.
+
+While the market demand was strong, rubber was being shipped and passed
+into circulation, at a rate which did not demand investigation of the
+subject of local storage. In the year 1918 conditions were such as to bring
+the matter into prominence, and we were able to tender advice on the lines
+given in this chapter. The necessity passed, but has again arisen.
+
+Our experience goes to prove that if rubber is properly prepared and
+thoroughly dried before packing, it will remain in good condition for a
+period of a year or more in this country. How much beyond a year it may be
+kept remains to be determined. The assumption of "proper preparation"
+leaves great room for reservations.
+
+In the case of crepe rubbers, there is no great difficulty, provided that
+the recognised methods and formulæ are employed, and that the rubber is
+packed only when perfectly dry. Under those conditions, the higher grades
+of crepe remain apparently unaffected on storing. Any appreciable
+deterioration may be attributed to defective preparation or external
+causes, such as accidental damage by water.
+
+The prolonged storage of lower grade rubbers is attended by more risk,
+especially in the case of the lowest grade (earth-scrap) from estates which
+neglect the practice of regular and frequent collection of the raw product.
+The same reservation applies to crepes made from tree-scrap which is not
+collected daily. In these types of crepe rubber "tackiness" may be
+initially present only in small degree, but the final damage may be
+immensely greater by close contact of the folded rubber during prolonged
+storage.
+
+When we come to discuss the possibility of storage of smoked sheets, the
+difficulties become immensely greater. We have yet no reliable experience
+as to the keeping properties of this grade when properly prepared, fully
+cured, correctly packed, and stored under the best of local conditions. It
+is understood, of course, that in the qualification by the term "local"
+conditions, we assume it to be more difficult to store rubber generally in
+Malaya than in a temperate climate. The average temperature and humidity of
+the atmosphere are here much more favourable to the development of mould
+growths than would be the case, say, in Great Britain.
+
+In discussing this question, as far as it refers to the preservation by
+storing of smoked sheet rubber, it is not fair to draw conclusions as to
+the likely behaviour of packed rubber from data based upon observation of
+loose specimens. We have samples of smoked sheets prepared in 1910, and
+these, superficially, appear to have remained unchanged. No mould is
+present and, as far as intermittent observation enables us to judge, moulds
+have never been incident. Whether such rubber would have been preserved in
+this condition had it formed part of a packed case, is a point upon which
+we have no experience; neither can we give any opinion. It seems true,
+however, that loose specimens "keep" better than bulk samples of the same
+preparation.
+
+It cannot be argued that the present good condition of these old specimens
+may be due to correct preparation. In those days methods and formulæ were
+rather haphazard, especially in view of the fact that the daily variability
+of dry rubber content of latices was not then recognised.
+
+One would rather submit the factor of adequate smoke-curing as the chief
+influence in the superficial preservation of smoked sheets. Ten or eleven
+years ago it was considered advisable to allow the rubber to remain in the
+smoke-house for a period extending well beyond that necessary for ordinary
+drying. As a result, very dark rubber was produced, which was thoroughly
+impregnated with the products of wood combustion. There would seem to be
+little doubt that this procedure was responsible for the prolonged freedom
+from mould growths.
+
+Market standards have varied to some degree since, with a tendency to
+prefer a paler product than that in vogue, say, six or seven years ago.
+Moreover, standardised methods of preparation have been introduced, with
+the result that sheets of a desirably high standard can be produced in from
+ten to fourteen days, when smoke-curing is conducted only during night
+hours. Some estates are equipped with smoke-houses which, by continuity of
+working day and night, provide smoke-dried rubber in from five to six days;
+but the actual hours of smoke-curing are approximately equal to those of
+the ordinary type of house.
+
+This tendency towards the production of sheets paler in colour than the old
+standard is probably largely responsible in the present for the commonly
+observed incidence of surface moulds on stored smoked sheets, and also for
+some complaints of "under-curing," where the term specifically refers to a
+failure to dry and cure the rubber thoroughly. Boxes of smoked sheets,
+which had been stored for varying periods up to five months, were recently
+inspected, and, in the majority of instances, surface moulds were found to
+be plentiful. In all cases it was observed that the trouble was intensified
+where boxes of rubber were stored in contact with cement floors.
+
+This "under-curing" is not a question solely of the duration of
+smoke-drying, although probably the modern practice of curtailing the
+period has exerted a great influence. To make this clear, it may be stated
+that, given two batches of uniformly prepared wet sheets, it would be
+possible to smoke-cure them for equal periods in different houses, so as to
+produce one batch very much paler in colour than the other, although the
+total hours of actual smoke-curing would be identical. In order to produce
+such effects, all that is necessary is to employ different timbers for fuel
+or different types of furnaces. In the one case there would be produced
+heat and very little smoke, while in the other the necessary heat would be
+obtained plus plenty of smoke. The best results naturally are obtained by
+the employment of the happy medium, and if smoked sheets have to be stored,
+the ordinary period of smoke-curing should be prolonged to an interval
+consistent with the capacity of the smoke-house.
+
+All precautions taken in preparation and curing can be nullified, as
+already indicated, by unsuitable storage conditions.
+
+TOOL-SHEDS AND STORE-ROOMS.--In some factories it is the rule to see lime,
+cement, spare rolls, sieves, and a general heterogeneous assortment
+occupying part of the rubber-drying rooms. The inconvenience is often
+great; and it certainly seems that these stores and tools are of sufficient
+value to be accommodated in suitable buildings.
+
+SITUATION OF FACTORY BUILDINGS.--There can be no doubt that a great deal of
+the "spot" disease trouble, and the general slowness of drying, can be
+attributed in many factories to the unsuitability of the site chosen.
+Probably the idea which actuated those responsible for the choice of site
+generally was proximity to a water supply. This would account for the fact
+that a number of factories are situated in valleys or near swamps. More
+often than not, also, the actual clear space is very limited, and rubber
+trees grow close up to the walls of the buildings. Under such
+circumstances, it is difficult to see how these buildings can be anything
+but dark and damp, and it is not difficult to understand the slow rate of
+drying. In a few cases the sites chosen proved to be so unsuitable that the
+estates were confronted with a very serious problem, the solution to which
+was, either the erection of another complete set of buildings in a more
+suitable spot or the installation of artificial driers.
+
+It must be laid down as an axiom that the first essential in a suitable
+site is that water may be brought to it easily, but, as already indicated,
+this does not mean that the buildings need be placed in actual proximity to
+the water-supply. The mistakes made by pioneers in this work are not likely
+to be repeated, and it is common now to note well-designed and
+comprehensive schemes in which the water is pumped to a reservoir placed at
+a suitable elevation, whence the supply is gravitated to bungalows, coolie
+lines, and the factory. The importance of securing a plentiful supply of
+good water for factory purposes cannot be exaggerated, and it is a point
+which is only thoroughly appreciated on estates where smoke-sheet rubber
+has to be prepared.
+
+The second essential, but of equal importance, is that there shall be an
+ample open space on which the sun may shine all day. There must be no trees
+too near the buildings, and there should be no adjacent swamps. Preferably,
+the site should be on a raised position, so that it will be impossible for
+surrounding trees to cut off sunshine, even when they are fully grown. From
+such an arrangement it will follow that the factory will be light and airy,
+and the drying-houses will receive the maximum of benefit to drying from
+direct sunshine on the roof and walls. There can be little doubt that these
+considerations play a most important part in determining the rate of drying
+of the rubber, and where comparisons are made between the rates of drying
+in various drying-houses all these factors enter into the question and
+contribute to the total result. Presuming that the thin crepes made in two
+factories are equal in thickness, it is not uncommon to find that in a
+drying-house, situated in a wide open space, the period of drying may be as
+low as six or seven days; while in another drying-house, situated near a
+swamp and surrounded by trees, the period may be as high as eighteen days
+to twenty-one days. The figures quoted are not fictitious, but are facts
+actually noted in the course of the writers' experience.
+
+A great deal also depends upon the exact position of buildings. Thus, to
+obtain the maximum of light in a factory, it will be obviously beneficial
+to erect it with the long sides running east and west, so that the windows
+face the north and south, and the large end doors face the east and west
+respectively. At first sight it would appear that the best position for the
+machines would be on the north side of the building where no sun can enter;
+but a moment's consideration shows that the south side would give the best
+results. By the time the sun has come round to the south, it is usually
+high in the heavens, and the direct sunshine does not fall very far into
+the room. Even should it play upon the machines for an hour or two during
+the day, no harm could result to the rubber which was being worked, as no
+piece would remain there a sufficiently long time to be injured in the
+slightest degree. Placed in this position, the maximum benefit of light
+would be obtained, whereas if the length of the building ran east and west,
+the machines would have only either the morning or afternoon light.
+
+[Illustration: SUGGESTED ARRANGEMENT OF BUILDING.]
+
+While it is advisable to erect a factory running east and west, the
+drying-houses should run north and south. In this position the maximum wall
+area will be exposed to the sun during the day, and it will be possible to
+manipulate the windows of the drying-rooms so that those along one side are
+open, and it will never be necessary to close all the windows at any time
+of the day. Thus the windows facing east will be closed, and those facing
+west will be open until after midday; then _vice versa_. With such an
+arrangement a more uniform temperature may be obtained than by any other
+arrangement of the buildings. If the building ran east and west, the
+windows on the north side could remain open all day, while those facing
+south would have to remain closed practically all day. The south side of
+the house would be heated by the sun, while the north side would remain
+cool, and the rates of drying would be correspondingly unequal. The total
+wall area heated by the sun at any time of the day would be less in this
+position than if the house ran north and south.
+
+Similarly, to obtain the best drying effect during the daytime in a
+smoke-house the building should run north and south. By this means the
+temperature will be maintained to the maximum possible by sun heat, and the
+rate of drying will correspond.
+
+
+_References to Sketch Plan._
+
+Drying-house No. 2 should be of two storeys, and unless a separate sorting
+and packing room is to be built, No. 1 should also have two floors (see
+previous notes on packing-rooms).
+
+In the factory--
+
+     _V_ shows the position of the verandah, which may be quite open and
+     only divided from the inner room by
+
+     _S_, a wall composed of very strong expanded metal, which allows light
+     and air to enter the factory.
+
+     _T,T_ are the glazed tile tanks for the reception of latex, scrap
+     rubbers, and bark-shavings.
+
+     _M_ shows the position of the machines on the south side of the
+     factory, with the direction of extensions, and
+
+     _E,E_ the compartments in which the engines are bedded. In these
+     positions it is possible to obtain direct drive to the machines.
+
+     _D,D_ are large double swing or sliding doors (the latter for
+     preference always). These, while suiting transport of rubber, provide
+     also for a free draught of air.
+
+If possible the scrap-washing machine should be placed outside the wall of
+the factory, and tanks for the reception of scrap rubbers may then be
+situated in convenient proximity.
+
+Economy of labour is obtained by grouping all factory buildings as closely
+as possible, but it should be borne in mind that smoke-houses should be
+regarded as a possible source of danger from fire. This point has a
+practical bearing upon rates of insurance, and it is essential that the
+smoke-house should be situated at a minimum of 50 feet from any other
+building or group of buildings. In this connection, also, it may be noted,
+as being of further practical interest, that, in the insurance of
+smoke-houses, preferential rates are given to those having a good type of
+slow-combustion furnace.
+
+CHOOSING A FACTORY SITE.--Sufficient has been written to make it clear that
+the choice of a site for factory buildings is a matter demanding weighty
+consideration. Much, of course, depends upon the planted area, and the rate
+at which it comes into bearing. Under certain circumstances which will be
+obvious, it is permissible to instal first a group of buildings of a
+temporary nature only, the future site and permanent buildings to be chosen
+later when the main portion of the estate comes into bearing. Often,
+however, one finds that, from lack of forethought, the estate has been
+committed to considerable expense in the establishment of equipment, which
+later is proved to be unfavourably situated with regard to the majority of
+the area in ultimate bearing. In such case, transport of latex is fraught
+with difficulties and may be expensive.
+
+In the instance of an estate which will gradually come into bearing, it is
+not easy to decide whether a temporary installation shall first be
+provided, or whether, in anticipation of future demands, a complete
+equipment shall be erected. So much depends upon the financial aspect of
+the question, and upon the rate at which areas will come into bearing. As
+far as is possible, the best policy would be that of a compromise under
+which the site would suit later requirements, and the factory would be so
+planned as to be capable of future easy extensions both of buildings and
+machinery.
+
+It is not possible to lay down any definite data as regards requirements
+based on acreage, or to make comparisons between any two estates of similar
+acreage. The important factors determining such requirements are:
+
+     (_a_) Area.
+
+     (_b_) Shape of the estate.
+
+     (_c_) Topography of the estate.
+
+     (_d_) Available supplies of water.
+
+Naturally the ideal site for factory buildings would lie in a central
+position, given other favourable conditions.
+
+CENTRALISATION OR DECENTRALISATION.--It is the experience of a number of
+estates that, all other conditions being favourable, there is a limit
+beyond which the centralisation of factory work leads to an unwieldy
+position. We are not here concerned with the few extremely large estates
+running into tens of thousands of acres. In those cases the total area
+would be divided into economic sections. The argument there would resolve
+itself into a discussion on the size of an economic section. This, in turn,
+would be dependent upon the type of main product, involving the question of
+transport of latex or coagulum, and the possible provision of batteries of
+heavy machinery.
+
+The differentiation between the transport of latex and coagulum,
+respectively, is a most important one, and has a powerful influence in
+determination of the maximum of centralisation possible. Whereas properly
+prepared coagulum may be safely transported by bullock-cart, light-railway,
+or motor vehicle for many miles, latex, on the other hand, demands very
+careful treatment. Anti-coagulants may be employed to preserve fluidity,
+but only within certain limits. Even under these conditions, other factors
+(chiefly climatic) exert an influence which renders the transport of latex
+for any distance a matter of anxiety.
+
+It will be plain, therefore, that the limits of centralisation of factory
+work are much narrower for the preparation of sheet rubber than is the case
+when crepe rubber is to be made. In actual experience the preparation of a
+high standard and a high percentage of smoked sheet is attended with
+considerable difficulty in those cases where the factory processes have
+been ultra-centralised. Apart from the difficulties inherent to the
+transport of latex in a state of good preservation, there is the added
+difficulty of dealing quickly with large volumes of latex brought from
+various quarters. None of these should be allowed to remain standing if the
+best results are to be secured; but obviously there must at times be some
+congestion. Even on a small scale it is often found that the latest batches
+of latex are unfit for the preparation of good sheet rubber, and the
+trouble may be easily exaggerated when working on a large scale.
+
+The centralisation of work on crepe preparation, therefore, is limited only
+to a comparatively slight degree by distance of transport, and in the main
+only by the size of the necessary equipment of machinery and drying
+accommodation.
+
+The successful preparation of sheet rubber is, on the contrary, governed
+chiefly by the factor of transport. With this consideration in view,
+several large estates, preparing sheet rubber as the chief grade, have
+found it necessary to decentralise the factory work, with very satisfactory
+results. Outlying sections are given uniform and complete equipments of
+necessary buildings on a small scale, and hand-driven light machines.
+Uniform coagulating tanks are installed, and the methods and quantities of
+chemicals employed are carefully standardised. Experience has shown that
+often the best sheet rubber coming to the market has been prepared on small
+estates; and the same applies to the product of these decentralised
+stations on large estates. There is no _a priori_ reason why the product
+from one station should differ in the smallest particular from that of
+another, apart from minor fluctuations which are due to variable weather
+conditions affecting the latex. If the contrary is found to be the case, it
+indicates failure on the part of the person responsible to follow the
+regular rules and methods.
+
+In the natural scheme of development of a large estate, it would be
+necessary, of course, to have a comparatively small centrally situated
+factory, equipped with power and heavy machinery for working scrap rubbers
+in the preparation of crepe grades below No. 1 in quality. As the yield per
+acre increases, or the area in bearing expands, it would be advisable later
+to increase the size of the central factory and buildings so as to permit
+of the preparation of a proportion of the crop in the form of No. 1 crepe
+rubber, in order to be able to comply with prevailing market demands under
+which preferential rates fluctuate between pale crepe and smoked sheet.
+
+
+
+
+PART IV
+
+THE FINISHED RUBBER
+
+
+
+
+CHAPTER XVII
+
+_DEFECTS IN CREPE RUBBERS_
+
+
+GENERAL STYLE OF FINISH.--Broadly, there is no single and definite style of
+finish, but on the whole it may be stated that the greater proportion of
+crepe rubbers are prepared in a thin form and with a close-knit texture or
+finish.
+
+Very little thick or blanket crepe is now made on estates in Malaya, so
+that beyond the mention of that type little need be written. A fair amount
+of blanket crepe is sold in the Singapore market, but it should generally
+be regarded as re-made rubber--_i.e._, it may have been prepared from thin
+crepes, or from native pale sheets, in local rubber-washing factories. In
+appearance these crepes have a rough finish, and vary in colour according
+to the crude material employed.
+
+The general preference of the market at present is for a thin,
+smooth-finished crepe, with a close-knitted surface--_i.e._, free from what
+is described as "laciness." What effect this looseness of finish can
+possibly have upon the quality of the rubber is not understood, but the
+standard type set up by the market must be comparatively free from small
+holes.
+
+Under existing conditions governing the sale and purchase of rubber,
+various "standards" are set up. These really have no bearing upon the
+intrinsic qualities of the rubber, and are concerned almost entirely with
+superficial attributes. They are necessary in the absence of any proper
+scheme of evaluation for the establishment of certain standards of
+comparison, which imply that the rubber is apparently clean, free from
+certain recognised defects, and has been carefully prepared--as far as can
+be determined by a superficial examination. Thus the question of "finish"
+has attained disproportionate importance, but must be respected when
+preparing rubber for sale.
+
+Under ordinary conditions, thin crepe rubber, as it leaves the finishing
+machines, has what may be termed "deckled" edges. On many estates, in order
+to comply with market conditions, the edges of the wet crepe are trimmed,
+and the trimmings re-made into lengths of crepe. This is done under the
+impression that the market price is influenced by the evenness of the edges
+of crepe rubbers.
+
+Again, it sometimes happens that, owing to "wear" of the rolls, the
+finished dry crepe may show a faint but distinct pattern of mark--a diamond
+or a horizontal bar. Since these are not accepted under the "standard"
+comparisons, rubber exhibiting these characteristics does not obtain the
+top market price. In other words, these innocent and innocuous marks are
+regarded as defects and penalised accordingly.
+
+Enough has been written to show how very important becomes the question of
+finish. It will be acknowledged that the superficial qualities demanded in
+the "standard" market type can be reproduced by any estate having adequate
+machinery and ample facilities for drying and handling the rubber.
+
+Methods of preparation and formulæ for the employment of chemicals are so
+well laid down that, up to the stage of machining, no difficulty need be
+encountered. But the standard type of finish in the dry crepes cannot be
+obtained unless the estate factory is fully equipped with the three types
+of rolls necessary--_i.e._, macerators, intermediate crepers, and smooth
+finishing-rolls. This subject has received full discussion in Chapter
+XIII., and is here only mentioned with the view of emphasising the point
+that no estate can be blamed for a lack of "finish" in crepe rubbers if the
+equipment of machinery is inadequate or in poor condition.
+
+If, on the other hand, the factory has ample machinery for requirements,
+and a good finish cannot be obtained on the thin crepe, then it is time the
+rolls were attended to and changed, or that the ratios of the driving
+pinions were altered.
+
+DIRTY EDGES.--It seems to be almost impossible to keep old machines clean,
+and it is equally difficult to keep the edges of crepe free from oil and
+dirt. Usually these dark edges are to be found on crepe which is rather
+wide, and it will be noticed that where wide crepe is made, unless special
+precautions are taken, the edges of the rubber often pass under the edges
+of the hopper and so pick up dirt and oil. On most machines it is a great
+mistake to attempt the preparation of wide crepe; nothing but narrow crepe
+must be made. To obtain this it is necessary to decrease the width of the
+hopper placed above the rolls. This can easily be effected by blocks of
+heavy hard wood, cut to shape and fastened in position.
+
+Sometimes the dark edges of crepe are due to another cause. Rolls may be
+gradually worn in the middle, so that to obtain a good finish it becomes
+increasingly necessary to tighten up the screws which regulate the distance
+between the rolls. It thus happens that just at, and beyond, the edges of
+the rubber the rolls grind upon each other, and fine particles of iron and
+graphite are transferred to the rubber. In such a case it is evident that
+either the rolls must be "turned" or that a new pair of rolls must be
+substituted.
+
+IRON-STAINS.--One of the causes of iron-stain on rubber has been mentioned
+in the preceding paragraph. This particular kind of iron-stain must not be
+confounded with rust-stain, and gives a dark dirty colour. It results from
+the grinding together of the rolls, and is usually noticed in the finishing
+of fine pale crepe. For this operation it is necessary to screw up the
+rolls tightly, and it will be plain that, whenever the rolls are vacant of
+rubber, there is a tendency for them to grind upon each other, thus setting
+free fine particles of iron and graphite. In order to avoid this, one must
+be careful to see that between the working of each length of fine crepe the
+rolls should be occupied with another piece of rubber, which may be kept
+for the purpose. In some factories this trouble apparently does not exist,
+while in others the amount of wear on the rolls is surprisingly great, and
+the damage done to the rubber is excessive. The only way in which this
+difference can be accounted for is that there must be a great difference
+in the quality of the roll material. Some rolls seem to be excessively
+soft, and from these contamination by iron-stain is great. For this reason
+rolls are sometimes rejected, and there would appear to be an objection to
+any but chilled steel rolls for the final stage of finishing crepe rubbers.
+
+RUST-STAINS.--Rust-stains, on the other hand, throw the responsibility
+entirely upon the labour and supervision of the factory. Rust is formed
+upon the rolls when they are at rest, and any one passing pale rubber
+between the rolls before they have been thoroughly cleaned is guilty of
+culpable negligence. Even when apparently clean, a piece of lower grade
+rubber should be passed through the rolls several times so as to remove any
+slight trace of rust remaining.
+
+Rust-stains have also been caused in a few cases by the large knives which
+are used to cut up lumps of coagulum, or by allowing freshly coagulated
+rubber to come into contact with iron vessels in the factory.
+
+A similar appearance has been traced in a few instances to contamination of
+the coagulum in transit by the dust of the reddish rock (laterite) employed
+in localities for road-making.
+
+OIL-MARKS.--The origin of oil-marks in crepe has already been described in
+Chapter XIII. The whole question resolves itself into one of cleanliness,
+moderation in lubrication, and supervision. The machines should be
+inspected every day, and once a week rolls may be swabbed down with a 10
+per cent. solution of caustic soda applied by means of a piece of cloth
+fastened round the end of a stick. Immediately after this operation water
+should be turned on and the rolls set in motion, so that all traces of
+caustic soda are thoroughly removed. If possible, lubrication by oil should
+be substituted by grease lubrication through screw caps.
+
+Particular attention should be paid to the back of the machines. None but
+the individual in charge of engines should be allowed to lubricate the
+machines, and he should be held responsible for any excess of lubricant.
+
+As a rule oil-marks are restricted to the edges or the proximity of the
+edges of crepe, but sometimes the streak is to be found in the middle of
+the length. In such a case it is almost certain that the oil or grease has
+been picked up by the rubber in the tray. It sometimes happens, if the
+"liners" of the bearings are eccentrically worn, that a few drops of dirty
+oil or a particle of grease are squirted out to some distance. These
+usually find a resting-place in the tray, and the contamination may then
+appear in any part of the rubber.
+
+It will be clear, therefore, that all trays beneath machines should be
+examined as the probable source of danger from contamination by oil and
+dirt. If the trays are as wide as or wider than the effective portion of
+the rolls, they should be discarded. In their place (except sometimes in
+the case of the macerating machine) all that is necessary is a movable
+piece of board, in width not less than from 4 to 6 inches shorter than the
+width of the rolls. Any oil or grease ejected from the bearings will thus
+be allowed to fall clear of the board; and defects due to oil streaks,
+etc., will be very much diminished, if not entirely obviated.
+
+This point in connection with the damage possible by the existence of wide
+trays is commended to the notice of manufacturers of machines for
+plantations, as it is common to find that trays are made which contravene
+the rule prescribed by experience. In fact, trays on some machines have
+been so designed as to act as "traps" for all dirty matter exuding from the
+bearings. Not only so; they are sometimes made of such a shape and height
+that oil or grease lodging upon the edges act as a "wipe" to the rolls,
+thus increasing the possibility of contamination. Until this defect was
+investigated, it was common to note continued contamination of pale crepes
+in spite of all precautions taken in cleaning the rolls at frequent
+intervals. The trouble due to this cause is intensified when the same
+machines are employed for the preparation of scrap-rubber crepes and No. 1
+crepe. Small pieces of scrap find their way towards the bearings and lodge
+on the edges of the trays. Unless a thorough inspection is made before
+proceeding with the working of the No. 1 (pale) grade, contamination may be
+continuous.
+
+DIRT.--Streaks due to the presence of dirt (as apart from oil or grease
+contamination, or that due to pieces of oxidised scrap) are unusual, and
+when they do appear their origin seems to be somewhat of a mystery. It
+could scarcely be advanced that the dirt was picked up on the machines, as
+it is difficult to imagine where such dirt could come from. In one or two
+instances there has been fairly clear evidence that the dirt was contained
+in the coagulum, and the only explanation fitting the case is that it fell
+into the latex after straining and during the course of coagulation. On
+cutting open lumps of coagulum brought in from the field division, it has
+sometimes been noticed that dirt is included, and the foregoing explanation
+is the only reasonable one. How it was possible for dirt to get into the
+latex must be left for explanation to those better acquainted with the
+conditions under which the latex was coagulated.
+
+HOLES.--On some estates it would seem impossible, with the existing
+machines, to make really good crepe. The complaint is that, if thin crepe
+is attempted, it is invariably found to be "full of holes"; and as,
+apparently, the presence or absence of small holes in crepe rubber is a
+factor which influences buyers, this defect must be avoided at all costs.
+Why this matter of small holes in thin crepe should weigh so heavily with
+buyers is a matter which the writers are not in a position to explain. As a
+matter of fact, the presence of small holes is most generally an indication
+that the rubber has received the minimum amount of working on the rolls
+consistent with good washing. Further working would only be undertaken with
+the idea of so consolidating the rubber as to get rid of holes in order to
+meet the market scheme of valuation.
+
+This is usually achieved by making a very thin crepe and rolling together
+two lengths when wet. The resulting crepe may be slightly thicker than
+ordinary, and the method employed may be usually detected by the appearance
+of the edges unless these are trimmed.
+
+GREENISH AND TACKY STREAKS.--Occasionally one meets cases in which pale
+crepe exhibits streaks varying in colour from a decided green to an almost
+black in which the greenish tinge is scarcely perceptible. Experience
+indicates that these streaks are much more dangerous than they appear
+superficially, inasmuch as they contain traces of brass from the "liners"
+of the bearings. The presence of the copper in brass is responsible for a
+gradual disintegration of the rubber, commonly recognised as "tackiness."
+In fact, copper may be said to be a "poison" to rubber, and every effort
+should be made to avoid possible sources of contamination. The effect may
+be proved easily and perceptibly by fastening together several pieces of
+crepe rubber by means of a brass "paper-fastener." In course of time a salt
+of copper, green in colour, will be formed, and it will be found that the
+portions of rubber in contact with the fastener have "perished" and become
+tacky.
+
+This contamination of crepe rubber may take place in two ways:
+
+     (1) By the ejection of actual particles of brass from the bearings of
+     machines, due to eccentric grinding of the "standards" of the rolls
+     upon the brass "bushes." These particles are carried by exuded oil or
+     grease into trays, and thence to the rubber.
+
+     (2) By the action of an acid lubricant upon the brass, with the
+     formation of a metallic soap which has a decided green colour, unless
+     obscured by the dark colour of the oil or grease. It is transferred to
+     the crepe rubber in the manner indicated above.
+
+The inevitable effect, apart from the superficial defect, is incipient
+tackiness. The extent to which this may develop will depend upon the amount
+of the copper compound present, but it should be remembered that an
+exceedingly small trace is capable of causing a disproportionately large
+amount of damage. This effect is further magnified if the "tacky" piece of
+rubber is packed in close contact with previously unaffected rubber.
+
+When the defect is discovered, the affected portions should be cut out, and
+the cuttings should be burned. To mix them with the lowest scrap grades, as
+may be done thoughtlessly, is only inviting further trouble.
+
+Besides the source of danger already indicated, it may be found, but far
+less frequently, that contamination may arise from the presence in the
+rubber of small pieces of the brass mesh which is generally used for
+straining latex.
+
+The view appears to be held in some quarters that these tacky streaks and
+patches in crepe rubber may arise from contamination with oil or grease
+alone. This does not agree with our experience. An experiment was made to
+test the point using fresh oil and grease drawn from drums in stock,
+specimens of the same lubricants to which traces of a copper salt were
+added, and samples of lubricants taken from the bearings of several
+machines. The treated pieces of rubber were placed in contact with
+untreated pieces of crepe which served as "blanks."
+
+Notes were made at intervals extending over a period of two years. The
+conclusions arrived at were:
+
+     (1) Although there was surface discoloration, no tackiness had been
+     caused by fresh (unadulterated) lubricant; neither were the "blanks"
+     affected.
+
+     (2) In the majority of specimens upon which had been smeared a small
+     streak of lubricant taken from the bearings of machines, tackiness had
+     supervened, and had developed likewise in the contact "blanks."
+
+     (3) In all cases where a trace of copper salt had been used to
+     adulterate the fresh lubricant, tackiness was to be noted in the
+     course of a short period (a week upwards) after the rubber was dry.
+     Development was slow, but progressive, over the full period of
+     experiment, and the "blanks" in contact were affected. The degree of
+     affection was determined by the proportion of copper salt employed. In
+     the worst cases the affected strip of rubber had deteriorated and
+     disintegrated to such a degree as to cause a distinct longitudinal
+     gap, the edges of which appeared to consist of a moist gummy substance
+     of a deep syrup colour. The adjacent blanks in some cases exhibited a
+     similar appearance in lesser degree, or were merely affected by a
+     characteristic brownish stain.
+
+These observations regarding the possibility of damage to crepe rubbers
+from the existence of brass "liners" or "bushes" in the bearings of the
+machines lead to the natural query as to whether the use of brass is
+necessary. Experience shows that it is not necessary. Machines in use for
+years have been running with plain bearings of iron or other metallic
+substances. Satisfaction is obtained without the use of brass.
+
+COTTON AND OTHER FIBRE.--One of the most frequent complaints made against
+low grade crepes is the presence of fibre--generally classed in a wholesale
+fashion as "cotton-waste."
+
+It is true that some years ago most of the complaints were genuine in
+referring the cause to cotton-waste. The defect arose chiefly owing to the
+careless use of this material in the factory. Lumps of waste when discarded
+were often thrown to the ground, and became mixed with the heaps of scrap
+rubber and bark-shavings awaiting attention. The fault was one of sheer
+negligence, and nothing can be advanced in extenuation. Even when the
+soiled waste was thrown into the external drains, it often returned to the
+factory mixed up with the scraps of rubber recovered by means of the
+drain-screens.
+
+As far as the complaint concerns itself with cotton-waste only, the remedy
+is plain, and lies in the power of the management by reason of the ability
+to restrict the use of "waste" only to the engine-drivers and mechanics.
+
+In the vast majority of cases, however, the defect arises from
+circumstances beyond the direct control of the factory, and under
+conditions which make it difficult to check the evil. Although against
+instructions, and for the purpose of fulfilling other orders, some coolies
+persist in using pieces of cloth for cleaning cups. In course of time,
+unless the practice is detected, this cloth becomes coated with rubber.
+Careless coolies throw it away, when it may be collected by the individuals
+who gather earth-scrap; or it may be brought into the factory in the
+tappers' scrap-bag.
+
+Cases have been known in which the fibrous matter observed in the dry crepe
+rubber was of such a nature as to indicate that the source might be
+attributed to leaf-stalks which had passed through the scrap-washer. It is
+an easy matter to condemn the sorting as being careless, but it is another
+matter to instil into the mind of factory coolies such a respect for easy
+and sane precautions that the practice of them will be continued when the
+eye of the supervisor is not fixed upon the workers.
+
+It will be clear that contamination by fibrous matter should be limited
+practically to the lowest grades of rubber.
+
+The appearance of cotton-waste in high-grade crepes must be most unusual,
+and the writers have not yet seen a case in a drying-house. That it does
+occur, however, seems to be evident from brokers' reports. It is extremely
+difficult to imagine how the waste enters the rubber. One possible
+explanation is that a coolie may have been cleaning the rolls
+surreptitiously with waste, which may have passed later into the rolls
+together with rubber. Another explanation was offered in one factory by the
+observed fact that coolies engaged in cutting up coagulum, ready for
+passing into the machines, kept a wad of waste for the purpose of keeping
+the knife-blade clean. This may have found its way into the rolls. It must
+be recorded that in the course of many years of experience no case has been
+seen in any drying-house of contamination of the higher grades of crepe by
+fibrous matter.
+
+BARK AND GRIT.--With ordinary machines and the usual process of working, it
+would seem impossible to wash and macerate some of the scrap rubbers
+sufficiently to free them entirely from bark. This applies specially to the
+grade of rubber prepared from bark-shavings. Specimens have been handled in
+which it was practically impossible to detect bark, but in such instances
+the amount of working necessary would be such as to interfere seriously
+with the regular working of the factory. Even with the employment of
+special scrap-washing machines, complaints of the presence of bark in dry
+crepe have been received, but it is certain that this mode of operation
+reduces the quantity of bark to a minimum. While fully realising that the
+amount of working it is possible to give in proportion to the existing
+machinery and the output per day is limited, it must be recognised that the
+working of lower grades of rubber is usually insufficient, and that where
+possible it is the duty of estates to pay more attention to these lower
+grades. A considerable improvement in this direction has been noticed of
+recent years. It is not uncommon to encounter managers who fail to
+appreciate that complaints regarding the presence of bark in the lower
+grades are founded on legitimate grounds, and that they are not frivolous
+objections put forward for the purpose of depressing the price of the
+article. The sooner such an idea is jettisoned the better. There would
+appear to be a good future demand for the lower grades, and it is only
+natural that consumers will be willing to pay the best price only for an
+article which is clean.
+
+The same arguments apply to the complaints regarding the presence of sand
+and grit. The quantity of the latter found in low-grade crepes from some
+estates is surprisingly high. Its presence can often be shown by the simple
+device of spreading a piece of crepe over the upturned and hollowed palm of
+one hand, while striking the rubber with the other hand.
+
+The incidence of bark in higher grades of crepe may be due to inadvertence
+or to gross negligence. In the former class one might put those occasions
+on which pieces of bark are embedded in lumps of naturally coagulated
+rubber. A piece of bark-shaving may fall unnoticed into latex and be
+partially responsible for the coagulation which takes place. This piece of
+coagulated lump may be massed with others, and hence, unless each small
+piece is cut up, the bark is not perceived. Or again, by some unknown
+means, a piece of shaving may drop into a jar of latex, and so become
+embedded in the coagulum. Sometimes this becomes evident on cutting up the
+rubber, but it is quite as likely to pass unseen. On the whole, the
+presence of bark in first-grade rubber is most unusual, and should be seen
+before the rubber is packed.
+
+In the class due to negligence may be included cases in which careless
+coolies place the cup upon the ground before tapping. Pieces of shavings
+fall into the cup, and coolies are too lazy to pick them out. More often
+than not coagulation in the cup is caused. As it is impossible for the
+European staff to supervise each individual tree tapped, some cases must
+continue to pass unheeded. Sometimes bark-shavings are brought in with the
+latex, and if a broken sieve is being used, these, with other impurities,
+pass into the jar, and are embedded in the coagulated rubber. This must be
+classified as negligence, for no manager would willingly allow the use of a
+broken sieve. Again, naturally coagulated lump rubber on arrival at the
+factory sometimes contains evident pieces of bark, leaves, and stems of
+leaves. For lack of supervision the average coolie would not think of
+picking out these obvious impurities, and would pass the whole mass into
+the machines.
+
+OXIDATION STREAKS.--Since the introduction of sodium bisulphite defects due
+to streaks, caused by portions of the coagulum becoming oxidised, have
+practically ceased to exist. In the usual course, and without the use of an
+antiseptic agent, the freshly coagulated rubber has a surface darkened by
+oxidation. Unless this dark surface were carefully cut off, there would
+result a crepe containing dark streaks caused by the mixture of the
+oxidised surface portion with the bulk of the paler coagulum. The presence
+of oxidation streaks in No. 1 crepes, now being made, would imply either
+that no anti-oxidant substance was in use, or that the quantity necessary
+to prevent this surface oxidation is exceedingly small. Although the price
+obtained would appear to be influenced by the presence of oxidation
+streaks, no evidence can be obtained that the actual quality of the rubber
+suffers to the same degree as does the appearance--_i.e._, there is no
+evidence to show that a pale rubber, in which surface oxidation has been
+inhibited, is intrinsically superior to one in which slight natural
+oxidation has been incident.
+
+"YELLOW LATEX" STREAKS.--This appearance of "yellow-latex" streaks in not
+common, and may be accounted for by incomplete mixture of two different
+latices. It is a fact of common observation that, when a new portion of
+bark is being tapped for the first time, there is a distinct yellow tinge
+in the latex excluded. As tapping progresses, this colour vanishes; usually
+it may persist for a period varying from two weeks to more than a month.
+Should this latex be poured into ordinary latex without thorough mixing, it
+is sometimes found that, when the crepe rubber is dry, there are distinct
+yellow streaks. It should be remembered that, as the rubber content of the
+latex from first tappings is high, this latex is lighter than latex which
+is more dilute, so that the mixed latices must be well stirred with a broad
+paddle to obtain intimate mixture. It would be much better to keep yellow
+latex apart, and coagulate it separately, if at all possible. In such case
+the resultant crepe may be of a distinct canary yellow in tint.
+
+In scrap-crepes of the higher grade this distinct yellow colour is often
+visible in streaks which indicate the presence of tree-scrap, etc.,
+obtained from recently opened tapping areas.
+
+BISULPHITE STREAKS.--These, again, arise from defective mixing. In the dry
+rubber it is seen that there are streaks of colourless rubber in a general
+mass, which may be of varying shades of yellow; or, a length of exceedingly
+pale rubber is apparently streaked in patches with a darker shade of
+colour. A solution of sodium bisulphite is heavier than latex, and there
+would be a tendency, therefore, for the chemical to sink in the large
+mixing jar. Unless stirring is thorough it is possible that portions of the
+latex would not be in contact with sodium bisulphite while others receive
+more than a fair share. Especially would this effect be seen where
+coagulation takes place quickly, and experience bears out the truth of the
+suggestion. Another factor which has some bearing on the point is the
+strength of solution in which sodium bisulphite is used. In the ordinary
+course of working, the acid coagulant is added immediately after sodium
+bisulphite has been stirred in. Should a strong solution of the bisulphite
+be used, and if coagulation takes place quickly, it is easy to see that the
+possibilities of obtaining a uniform and intimate mixture are small.
+Probably in no factory is the sodium bisulphite now added to latex in
+powder form, but it has been found that if care is not taken to see that
+all the bisulphite has dissolved before the solution is added to latex
+streaks may result in the dry rubber. The undissolved particles sink to the
+bottom of the coagulating jar or tank, and there slowly dissolve, forming
+local strong solutions. The effect upon the rubber in the vicinity of these
+strong solutions is much more marked than in the bulk of the coagulum, and
+hence lighter streaks or patches appear in the dry rubber. In spite of
+apparently complete mixture by good stirring, it will be seen that it is
+possible, therefore, to have failed in this direction if any undissolved
+powder remains in the solution of sodium bisulphite.
+
+"SPOT" DISEASE.--Few managers of estates preparing pale crepe rubbers are
+unacquainted with this defect. It is manifested by the appearance of small
+coloured spots varying in density (_i.e._, number to a unit area) and
+differing in hue. The most common colours are black and orange, but "spots"
+of brick-red, yellow, violet and ruby and green tints have been noted, the
+last named very seldom. Sometimes in place of definite "spots," or
+colonies, the colour is spread over practically the whole surface of the
+rubber as a "flush."
+
+These coloured spots, or "flushes," indicate infection by minute fungi,
+which are present in the latex prior to coagulation. The infection of the
+latex takes place in the field by means of spores, which are only visible
+with a microscope.
+
+It is not feasible to discuss any method of preventing this infection of
+latex by air-borne spores, as the eventual preventive measures are so
+simple. But it may be believed that under ordinary weather conditions most
+latices are infected before reaching the factory. It is likewise true that
+even fine pale crepes shipped in perfect condition may contain
+possibilities of trouble in the form of "dormant" spores, the development
+of which may commence and continue if favourable conditions arise.
+
+The subject of "'Spot' Diseases" has been treated fully in previous
+publications,[19] and it is not proposed here to enter into any lengthy
+discussion.
+
+[19] "Preparation of Plantation Rubber," Sidney Morgan, 1913. "Spotting of
+Plantation Rubber," Keith Bancroft, 1913; Bulletin No. 16, F.M.S.
+Department of Agriculture. "Spotting of Prepared Plantation Rubber," A.
+Sharpies, 1914; Bulletin No. 19, F.M.S. Department of Agriculture.
+
+If any reader is desirous of producing the defect experimentally, all that
+is necessary is to prepare a piece of crepe rubber of rather more than
+ordinary thickness, roll it up while wet, and place aside for some days.
+
+This experiment reproduces the conditions favourable for the development of
+the spores, and spots of various colours may result. It will be clear that
+the chief factor influencing the result is the continued presence of plenty
+of moisture.
+
+This condition may be created inadvertently in the course of factory
+practice, if piles of crepe rubber are allowed to remain for any
+appreciable period before hanging to dry. For this reason batches of wet
+crepe should always be placed on edge, to allow free drainage of surface
+moisture, if the rubber cannot be taken at once to the drying-sheds.
+
+[Illustration: THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM "SPOT"
+DISEASE.]
+
+The condition also is provided if the thickness of the crepe is
+excessive. In some factories, having no smooth-roll finishing machines, the
+crepes may have a distinct raised pattern upon them. It is usual to note
+that if "spot" disease appears in such crepes, it is incident to much
+greater degree in the thicker portions of the rubber--_i.e._, upon the
+raised pattern.
+
+The direct connection between the rate of drying and the appearance of
+coloured spots or flushes is thus established, and it only remains to adopt
+precautionary measures which will lead to an avoidance of delay (1) between
+machining and hanging, (2) in drying.
+
+It is indicated, therefore, that, if spot disease is to be avoided, the
+prime consideration is the preparation of a thin crepe which will dry
+quickly under average conditions. It may sometimes happen that even very
+thin crepes will sometimes be found affected on some estates. In such
+instances, it will be found that the design or situation of the
+drying-house is at fault, and that specially favourable conditions for the
+development of the fungi have been created by excessively wet weather.
+Should the trouble persist in spite of the preparation of the thinnest
+crepe, it would be advisable either to abandon this form of No. 1 product
+or to consider the installation of artificial aids to drying.
+
+We have not yet encountered any case in which it was found necessary to
+treat the latex with an antiseptic or disinfectant substance for the
+prevention of "spot" disease. There appears to be an idea held in some
+quarters that sodium bisulphite may be so employed as a fungicide. This
+does not agree with our experience, which is confirmed by Sharpies
+(Bulletin No. 19, F.M.S. Department of Agriculture).
+
+In 1913 experiments with chinosol were undertaken at the Pataling
+Laboratory of the Rubber Growers' Association, and an account of the method
+of treatment was given in a printed report issued to subscribers. Dr. P.
+Arens,[20] of the Malang Experimental Station (Java), has also recommended
+the use of chinosol. The substance is expensive, but is effective in very
+small quantity. On the whole, given average conditions in factory practice,
+such aids should not be necessary, and where keen supervision is not
+available may lead to other difficulties.
+
+[20] "Guide to the Preparation of Rubber," Arens, 1918; Communications from
+the Experimental Station (Malang, Java).
+
+It has already been remarked that it is possible for "spot" disease to
+develop in dry rubber which previously gave no evidence of the presence of
+fungi. The condition necessary to such an occurrence is supplied by the
+presence of moisture. Thus, to state instances which are by no means
+uncommon, if a box of rubber is allowed to remain exposed to rain, or is
+damaged by flood-water, or by sea-water during transit, or (sometimes) if
+the rubber is packed in a damp case, the crepe on arrival at its
+destination may be found to be affected to a degree dependent upon the
+extent of wetting and the duration of the wetting period.
+
+No means are known by which these coloured spots, due to the growth of
+chromogenic organisms, can be removed from the rubber. Naturally, although
+they may be present in the darker lower grades of crepe, they are not so
+easily visible as in pale crepe. It follows, therefore, that every possible
+precautionary measure must be taken when pale crepe has to be prepared.
+
+We are often asked whether it is possible for an infected piece of rubber
+to affect sound rubber hanging in the same building; and whether, in case
+of "spot" disease appearing, it is necessary to disinfect the drying-house.
+
+In a general sense, the answer to both queries is in the negative. It has
+not been proved possible to transmit the disease from one piece of crepe to
+another, except by the closest possible contact and in the presence of an
+abundance of moisture.
+
+A dry crepe, even when in close contact with an infected dry specimen, has
+not been found to be affected.
+
+Unless, therefore, pieces of rubber are pressed together, under favourable
+conditions as to moisture, there has been observed no transfer of disease.
+
+Similarly it has not been found that the presence of spotted rubber in one
+part of the drying-house has been responsible for an outbreak of disease
+in another part of the same building. Furthermore, after the removal of
+diseased rubber from the drying-shed, freshly prepared rubber may be hung
+on the same supports without becoming affected, and without any
+intermediate treatment of the wooden bars, providing the crepe is thin and
+weather conditions are good. In our experience, no case has been observed
+in which the disease has been communicated to freshly prepared rubber by
+reason of the previous presence of affected rubber. In our opinion,
+therefore, any scheme for disinfecting the interior of a drying-house, as a
+preventive measure against the spread of "spot" disease, is unnecessary.
+
+All other things being equal, it is plain that much will depend, as to the
+incidence of coloured spots, upon the design and situation of the
+drying-house. Sufficient has been written in previous chapters to indicate
+the importance of these points as affecting the rate of drying, upon which
+hinges the possibility of the appearance of "spot" disease.
+
+In conclusion, the chief points in any discussion of this subject may be
+summarised thus:
+
+     1. No coagulum should be left without working for longer than the
+     ordinary period. Otherwise, the prevailing conditions are very
+     favourable for the development of the disease.
+
+     2. Thin crepe only should be made. The quicker the rate of drying the
+     less possibility is there of the coloured spots appearing.
+
+     3. Crepe should never be allowed to remain folded overnight, and
+     batches of folded wet crepe should be placed on edge to drain off
+     surface moisture. The rubber should be hung to dry as soon as
+     possible.
+
+     4. Several species of fungi causing coloured spots have been
+     recognised, and it has been proved conclusively that it is possible to
+     infect latex and also fresh coagulum.
+
+     5. As far as our present knowledge goes, it appears that infection
+     takes place chiefly, if not entirely, by means of the latex in the
+     field-vessels. It may take place during transport also, or even during
+     coagulation.
+
+     6. While it is certain that infection can be caused by contact, it has
+     not yet been shown that infection of the finished wet rubber takes
+     place in the drying-houses by means of air-borne spores--at least,
+     under ordinary drying conditions.
+
+     7. There is reason to believe that no further infection takes place
+     once the rubber is well into the drying stage, and that dry rubber is
+     not infected even by contact. From this one might infer that, as long
+     as rubber remains dry, infection cannot take place during the voyage
+     to the port of consignment.
+
+     8. Coloured spots do not appear until the rubber is about half dry,
+     because that period is necessary for the development of the fungus to
+     that stage in its life-history when it excretes colouring matter. The
+     fungus in its earlier and colourless stage may have been present from
+     the time the latex entered the cup.
+
+     9. The natural habitat of the fungi would appear to be decaying
+     vegetable matter in the field.
+
+     10. Finally, if it is found impossible to be rid of fungoid-spot
+     disease after having exercised all care and observed all known
+     precautions, nothing remains but to supersede the ordinary drying
+     process by some system of quick drying, such as the vacuum-drying
+     process or a hot-air draught system, in which the rubber dries so
+     quickly that any possibility of appearance of "spots" is entirely
+     removed.
+
+SURFACE MOULDS OR MILDEWS ON CREPE RUBBER.--Defects of this nature are most
+uncommon in the higher grades of crepe rubber, but cases of affection in
+the lower grades are not rare.
+
+It will be evident from all previous discussions that the incidence of
+these moulds must be due to an extremely slow rate of drying. The necessary
+conditions would be supplied by one or more of the following causes:
+
+     (_a_) Making the crepe too thick.
+
+     (_b_) Hanging the crepe in a badly ventilated or badly situated
+     building.
+
+     (_c_) Occasionally by abnormally wet weather.
+
+     (_d_) Allowing piles of crepe to remain too long before hanging.
+
+     (_e_) Using excessive quantities of deteriorated sodium bisulphite. In
+     short, any factor contributing towards a retarded rate of drying may
+     be responsible for the appearance of surface mildews. The last
+     mentioned cause is of not infrequent occurrence. Knowing the chemical
+     to be of poor quality, relatively more is used to produce the desired
+     anti-oxidant effect. Unless the rubber is particularly well washed on
+     the rolls, there remains within it a residue of sodium _bisulphate_,
+     an oxidation product of the bisulphite. This is hygroscopic to some
+     degree--_i.e._, it takes up moisture from the atmosphere. Hence
+     drying is delayed, and even should mildews not develop the chemical
+     may sometimes be seen on the surface of the rubber as a whitish
+     "bloom."
+
+The enumeration of the possible causes of mildews on crepe rubber is
+sufficient to indicate the necessary precautions to be taken, and the
+discussion will not be extended further.
+
+TACKINESS IN RUBBER.--"Tackiness" is a term used to denote a deterioration
+of rubber which renders it sticky, and, beyond this, implies that some
+physical and chemical change in the nature of the substance has taken
+place. In fact, it is no longer "rubber," but an oxidation product
+containing much resinous matter. It does not behave as rubber, and hence
+its value is much depreciated.
+
+With modern ideas of erection of factories to guard against the
+introduction of direct sunlight, it was hoped that this defect had
+practically ceased to exist. In one grade of rubber it would be expected
+that tackiness would continue to appear. Earth-rubber, often exposed to
+direct sunlight for a week, would naturally become tacky, and this
+tackiness cannot be avoided unless the earth-scrap is to be collected more
+frequently. But in many cases even the higher grades of rubber show signs
+of tackiness. Experiments have been carried out at various times and in
+various places to determine the cause of tackiness. For some time the
+theory of bacterial origin was in favour, but none of the experimental
+results was convincing. Bacteria may be present in tacky rubber; but, on
+the other hand, many cases of bacteria in rubber have been observed in
+which there was no tackiness. Experiments were made by one of us some years
+ago with a view to testing the bacterial theory by inoculating latex with
+small pieces of tacky rubber. In opposition to the results which were
+stated to have been obtained, there was no spread of tackiness. Other
+investigators have obtained similar results. One writer proposed to explain
+tackiness as caused by excess of moisture. This perfectly simple
+explanation unfortunately displays only a profound ignorance of the
+subject, and does not take into account the fact that tackiness is incident
+in rubber after dryness has been reached. It need not be pointed out to
+planters in Malaya that wet sheets of rubber are often exposed to direct
+sunlight by workers of native holdings, with no resulting harm as long as
+plenty of moisture is present in the rubber.
+
+TACKINESS THE RESULT OF A SLOW PROCESS OF CHANGE.--As stated above,
+tackiness does not appear until the rubber is dry, and even then it is to
+be noted that it is possible for tackiness to appear in rubber arriving in
+London, which showed no indications of tackiness when packed for shipment.
+
+TACKINESS CAUSED BY TRACES OF COPPER SALTS.--Spence, as the result of
+investigations, has pointed out that none of the various theories put
+forward to account for tackiness--viz., the action of bacteria, premature
+putrefaction, oxidation, excess of moisture, the action of enzymes,
+etc.--have any basis in scientific proof, and believes that the cause of
+tackiness cannot be directly attributed to bacteria. It has been stated
+that the only known way of causing rubber to become tacky is to expose it
+to sunlight or heat. While agreeing that in the ordinary way this statement
+is correct as far as one rules out the employment of chemical substances,
+it must be pointed out that tackiness of the worst degree may be caused by
+the presence of traces of copper or copper salts. This point has already
+been touched upon in a preceding paragraph dealing with the defect of
+"green streaks" in pale crepe rubber.
+
+In the course of laboratory experiments tackiness has often been induced by
+the use of traces of copper salts. The rate at which tackiness is induced
+appears to be dependent upon the amount of copper salt used, but once it
+begins, the rubber molecule is very rapidly broken down, and resins are
+formed. As the formation of resins is accompanied by the inclusion of
+oxygen in the chemical constitution, it would be expected that dry rubber
+becoming tacky should increase in weight. This is found to be the case, and
+to give an idea of how this weight increases with the progress of
+tackiness, the results below may be studied.
+
+It will be seen that the maximum quantity of copper sulphate used amounted
+to 0·025 per cent, (approx.) upon the weight of latex taken. Now it is
+highly probable that only a fraction of this quantity was retained in the
+rubber on coagulation, the remainder being in solution in the serum.
+Furthermore, as the rubber was well washed and worked down to thin crepe,
+_the total quantity of copper salt remaining in the dry crepe must have
+been exceedingly small_. Yet the effect is most marked and should impress
+upon all managers the necessity for guarding against any possible
+contamination caused by brass or copper.
+
+  ----------+-----------------+--------------------------------------------
+  _Sample._ |                 |             _Weight of Rubber._
+     +------+                 +------+--------+--------+--------+----------
+     |                        |      | After  |Further |Further | Percent-
+     |_Amount of Copper Salt._| When |Interval|Interval|Interval|age in In-
+     |                        | Dry. |of Four |of Seven|of Three|crease in
+     |                        |      | Weeks. | Weeks. | Weeks. | Weight.
+  ---+------------------------+------+--------+--------+--------+----------
+     |                        | Grms.| Grms.  | Grms.  |  Grms. |
+   1 |0·02 grms. copper       |      |        |        |        |
+     |sulphate per 100 c.c.   | 430  |  441   |  482   |  488   |   13·5
+     |latex                   |      |        |        |        |
+   2 | Ditto                  | 428  |  439   |  481   |  486   |   13·55
+   3 |0·01 grms. copper     } |      |        |        |        |
+     |sulphate, per 100 c.c.} |      |        |        |        |
+     |latex                 } | 962  |  987   | 1035   | 1036   |    7·7
+     |0·01 grms. copper     } |      |        |        |        |
+     |acetate, per 100 c.c. } |      |        |        |        |
+     |latex                 } |      |        |        |        |
+   4 |0·025 grms. copper      |      |        |        |        |
+     |sulphate, per 100 c.c.  | 502  |  513   |  558   |  560   |   11·5
+     |latex                   |      |        |        |        |
+  ---+------------------------+------+--------+--------+--------+----------
+
+In view of the effect thus produced by the addition of traces to latex of a
+copper salt, and the observed effect on rubber of contact with copper
+salts, one may imagine the result produced some years ago when on an estate
+smoked sheets were washed with a solution of copper sulphate as a remedy
+for surface moulds!
+
+With the exception of this chemical action we know of no other means by
+which tackiness is produced, beyond those of direct sunshine and heat.
+Cases governed by these two causes are common on estates. They are confined
+chiefly to the lowest grades of scrap rubber, when the component raw
+materials have been exposed to the sun for a period before being brought to
+the factory.
+
+It is now comparatively rare to find cases of tackiness in the higher
+grades of crepe, and when they occur, one may look for evidence of gross
+carelessness in the admission of direct sunshine. Usually this means the
+failure of some individual to regulate window shutters according to the
+position of the sun in the sky. More rarely does it happen that tackiness
+may have been induced by placing thin crepe rubber too near the iron roof
+of the drying-shed.
+
+Regarding the question as to whether tackiness may be communicated by
+direct contact, opinion appears to be divided. It has been stated that
+sound rubber left in contact with tacky specimens was found to be
+unaffected after two years. On the other hand, it is claimed that tackiness
+has been induced in a sound rubber by infecting it with small pieces which
+were tacky. In a preliminary article on the effect of copper and copper
+salts upon pieces of dried and sound crepe[21] it was noted, after one
+year, that tackiness had been communicated from the treated portion to the
+"blank" in contact. There is sufficient evidence to warrant the injunction
+that tacky rubber should be excluded from contact with sound rubber. If
+shipped it should be packed separately.
+
+[21] Report I., 1916 (Sidney Morgan), Rubber Growers' Association (Malaya).
+
+Compounds have been put upon the market which assumedly claim to be cures
+for tackiness. These are merely palliatives, consisting of starch, talc, or
+chalk powders, which counteract stickiness.
+
+NO CURE FOR TACKINESS.--At the present stage of our knowledge, there
+appears to be no cure for tackiness. Neither do we see the necessity for a
+cure when the phenomenon may be avoided by taking simple precautions, which
+may be briefly summarised thus:
+
+     (1) Any permanent openings through which it is possible for direct
+     sunlight to enter, whether large or small, should either be totally
+     closed or provided with some substance which cuts off the direct
+     effect of the sunlight--_e.g._, ruby glass or ruby glazed cloth.
+
+     (2) Rubber should under no circumstances be placed near any source of
+     heat.
+
+     (3) No rubber should be hung in a drying-room in such a position
+     adjacent to a window or door that it is possible for sunshine to reach
+     it, even should coolies neglect to obey rules.
+
+     (4) Instruments or vessels of copper or brass should not be used where
+     acids are employed.
+
+LACK OF UNIFORMITY IN COLOUR.--The complaint is far less real than it was
+a few years ago. The introduction by the Rubber Growers' Association of the
+"Metrolac" led to uniform dilution of latices varying in rubber content.
+Previously the only known method of obtaining uniformity in colour and
+appearance was that by which latices from all fields were mixed together in
+bulk. Even so the uniformity applied only to the one bulking operation, and
+any other day's results might show considerable variation from the first
+standard.
+
+This does not take into account any observed differences in shade of colour
+attributable to natural oxidation which might vary in intensity from day to
+day. The introduction of sodium bisulphite as an anti-oxidant exerted a
+great influence upon the colour of pale crepes generally; but considerable
+variation would still have been notable but for the adoption of the scheme
+for uniform dilution, in addition to the use of small quantities of
+anti-oxidant.
+
+On most estates it is now possible, with slight exceptions due to abnormal
+conditions, so to treat the latex that the pale crepes prepared on any one
+day differ in no perceptible degree from the product of any other day.
+Where this is not the case it must be suspected that there has been some
+carelessness in manipulating the latex or the chemicals. Attention has been
+drawn to the fact that there may be exceptional cases, when the determining
+factors lie beyond the control of factory processes--_e.g._, heavy rains
+causing over-dilution of latex, the yielding of "yellow" latex from newly
+opened areas, etc. But on the whole there is now no reason why the general
+average product from any estate should not be uniform in colour and
+appearance. Furthermore, it should be possible for large groups of estates,
+by the adoption of uniform methods, to produce similar rubber from all the
+plantations. Moreover, apart from some differences caused by factors which
+still need determination, the total product in a general sense should not
+only be uniform in appearance but uniform in physical and chemical
+properties.
+
+BLOCK RUBBER.--This mode of preparation is employed only in comparatively
+few instances. The block is prepared from crepe rubber, which has been
+dried either in a hot-air drier or in a vacuum chamber.
+
+There is another type of block which is made by placing layers of dry crepe
+under considerable pressure. This is not the true type of block, and the
+layers are quite distinct--_i.e._, they do not amalgamate. Usually this
+pressed rubber consists of lower grades of crepe, and it should not be
+popular, inasmuch as it leaves too wide an opportunity for the inclusion of
+dirt, bark particles, and other impurities, which cannot be seen generally
+on account of the protective colour of the rubber.
+
+In the true type of block, the layers are in a plastic condition, due to
+heat, when they leave the drying-chamber; and being immediately submitted
+to great pressure the result is a homogeneous mass in which the layers
+disappear by amalgamation. Only the best grade of crepe is employed, and
+given the absence of defects in the layers there should be no complaint
+regarding the final block.
+
+Prepared in slabs which are three or four inches in thickness, the product
+is easily handled, and should be sufficiently translucent to make it
+possible to distinguish the shape of the hand when held between the block
+and the light. This is not possible when blocks are made of greater
+thickness.
+
+The only complaints which it should be possible to lodge against block
+rubbers are:
+
+     (_a_) The inclusion of dirt and other matter.
+
+     (_b_) The use of layers of crepe which have some defect.
+
+     (_c_) The inclusion of air-bubbles.
+
+The remedy for (_a_) and (_b_) lies in the hands of the factory
+superintendent. The last ground of complaint is dependent upon the style of
+preparation of the original layers of crepe.
+
+When layers of crepe are placed one upon the other, and submitted to great
+pressure, it is natural to suppose that air would be contained in spaces,
+and would be unable to escape. To guard against this, it would seem
+necessary to prepare the crepe thin and with a fairly good surface finish.
+
+It must be obvious to all acquainted with the processes involved in the
+preparation of block rubber, that no possibility exists for the presence
+of air-bells actually enclosed _in_ thin crepe. When the vacuum-dried crepe
+is folded preparatory to the blocking process it is apparent that between
+the layers there must always be a considerable volume of air, a small
+proportion of which is bound to be retained owing to the nature of the
+surface of crepe rubber.
+
+That this has always been true of the preparation of block rubber cannot be
+denied. It is possible, of course, for one type of block to show the
+presence of air-bells more than another type, the proportion of air
+enclosed in blocking depending upon the nature of the crepe of which the
+block is composed. A block built up of layers of smooth, fine crepe would
+be expected to contain less air-bells than a block composed of layers of a
+rough crepe.
+
+Block rubber has been seen which was free from air-bells, but this was the
+thin variety of block prepared for show purposes with far greater care,
+probably, than would be expended in commercial preparations.
+
+
+
+
+CHAPTER XVIII
+
+_DEFECTS IN SHEET RUBBER_
+
+
+Before proceeding to deal with defects in the rubber as it is put upon the
+market a brief account will be given of faults which may be noted in the
+preparatory stages.
+
+MILKY RESIDUE OR SERUM.--If the serum is not clear after the ordinary
+period allowed for coagulation, it indicates one of the following possible
+causes:
+
+     (_a_) Failure to obtain complete mixture by thorough stirring.
+
+     (_b_) Insufficiency of acid solution. This may be real or indirectly
+     due to the presence of an excess of anti-coagulant such as formalin or
+     sodium sulphite.
+
+     (_c_) In cases where other coagulants than acetic or formic acids have
+     been employed the failure may be due to an excess of, or an
+     unsuitable, coagulant--_e.g._, hydrochloric acid.
+
+COLOURED SURFACE BLOTCHES AND UNPLEASANT ODOUR.--Sometimes the surface of
+the coagulum exhibits yellowish or bluish streaks and patches. It will be
+found generally that the yellowish colour is possessed by a slimy
+substance, of offensive odour, which may be scraped from the surface.
+Either insufficient acid has been used, or the mixing of latex and
+coagulant has been at fault.
+
+DARK DISCOLORATION OF THE RUBBER.--This may be stated to be a natural
+process when fresh rubber is exposed to the atmosphere. It is usually
+described as "oxidation," and it will be noted to be absent, or to occur to
+less degree, on those portions of the rubber which are protected from the
+atmosphere by being below the surface of the remaining liquid. This surface
+change may be prevented (see Chapters VIII. and IX.) by the use of small
+quantities of sodium sulphite (for preference) or bisulphite.
+
+SOFT COAGULUM, SPONGY UNDER-SURFACE, TEARING OF COAGULUM.--If the whole
+mass of coagulum is too soft, while coagulation appears to be complete,
+over-dilution of the latex has occurred. This may apply also to the case in
+which the under-surface only is spongy and soft. If coagulating-tanks are
+employed, the upper edge may be comparatively hard, while the lower is soft
+and weak. Often the spongy portion may adhere to the partitions. This
+prevents the natural rise of the coagulum, due to retraction, as the mass
+"sets." The pull between the free upper portion and the adhering lower edge
+causes splitting and tearing of the coagulum, with marked porosity (spongy
+appearance). The two factors to receive attention are the standard of
+dilution and the condition of the surfaces of the partitions. If these have
+minute cracks into which latex can penetrate, and in which coagulation
+takes place, the boards should be discarded. Given the conditions indicated
+above, the tearing and splitting of rubber in coagulating tanks is
+sometimes augmented by the practice of flooding the tanks when coagulation
+is judged to be complete. The surface water finds its way downwards between
+strips of coagulum and the partitions, thus increasing the upward tension
+between the free and adhering portions. The main idea governing the
+practice of flooding the tanks is to prevent "oxidation" (darkening) of the
+upper edges. If a small quantity of sodium sulphite is employed as an
+anti-oxidant and to retard coagulation, it is not necessary to flood tanks.
+
+"PITTING" OF SURFACES.--In pan coagulation this "pitted" appearance is
+usually limited to the under-surface, while coagulum prepared in tanks may
+exhibit the defect on both faces. The existence of these numerous "pits,"
+or small depressions, points to the presence of bubbles of gas which have
+been unable to escape freely. As the formation and retention of gas-bubbles
+is not a normal occurrence in coagulation, we are led to infer that some
+special conditions must have arisen. These may be supplied by one or more
+of the following contributory causes:
+
+     (_a_) The latex had begun to "sour" before arrival at the factory or
+     while waiting to be treated. This premature coagulation is usually
+     checked or diminished by the employment of anti-coagulants (see
+     Chapters VIII. and IX.). It is generally accompanied by the
+     appearance of enclosed gas-bubbles in the dry rubber.
+
+     (_b_) There may have been a slight insufficiency of coagulant, or the
+     admixture was not thorough, thus allowing a slow putrefactive change
+     to take place in the incompletely coagulated areas.
+
+     (_c_) The wooden partitions may not have been effectively cleansed.
+     The existence of a thin slime, of bacterial origin, is sometimes
+     noted. This is accountable for putrefactive effects in the surfaces of
+     the coagulum, or in the serum, giving rise to the formation of gases.
+     If these cannot escape freely, by reason of adhesion between the
+     coagulum and the partitions, "pitting" occurs.
+
+THICKENED ENDS OR EDGES, AFTER ROLLING.--As a rule these defects may be
+ascribed to the employment of too rich a latex, or faulty manipulation.
+Even if the standard of dilution should be correct it sometimes happens
+that, in the preliminary rolling of a long strip of rubber, coolies begin
+in the middle, rolling with a forward pressure and tension towards the ends
+of the strip. This is generally not so much the fault of the coolie as
+being due to the lack of proper facilities for preliminary rolling. The
+table should be about 3 feet in height, so that ease of working is obtained
+merely by natural pressure due to the position in which the worker stands.
+The use of a heavy wooden roller would contribute towards this result,
+inasmuch as it obviates the use of force, and the pressure is almost
+entirely in a vertical direction.
+
+MIS-SHAPEN SHEETS.--It is sometimes noted that sheets may be wider and
+thicker at the ends than in the middle. Manipulation alone, as indicated
+above, is not solely responsible. The primary cause is to be traced to
+over-dilution of latex, giving a very soft coagulum which responds too
+readily to tension and pressure. Faulty treatment in rolling exaggerates
+the tendency for the strip of sheet to become narrow and thin in the
+middle, wider and thicker at the ends.
+
+THICKENED PATCHES, TORN SHEETS, "DOG-EARS," CREASES.--These elementary
+defects are all due to careless working. While occasional errors cannot be
+avoided, there is no real excuse for the continuance of trouble to any
+degree, under average supervision.
+
+Thickened patches are often caused in conjunction with torn sheets, and
+the trouble may be ascribed to faulty practice in allowing too heavy a pile
+of wet strips to accumulate before machining. Or a comparatively small pile
+may have been transported some distance. It is difficult to separate the
+strip, and occasionally the separation is only effected at the expense of
+two sheets, one of which is torn and the other has a portion of the first
+strip adhering to it.
+
+"Dog-ears" due to the folding over of corners of the sheets, and creases
+due to the rumpling of the coagulum, are generally the result of haste and
+lack of average care. Machine coolies, more often than not, will not be at
+any pains to straighten out folds before passing the coagulum through the
+rolls.
+
+GREASINESS BEFORE SMOKING.--Under ordinary methods of working this should
+never be encountered. It may be taken to show that the machined rubber has
+been allowed to remain, either hanging or in piles, far too long before
+entering the smoke-house. The appearance is most marked if the rubber has
+remained in a cool and moist atmosphere--_e.g._, if it has been hanging
+over-night in a closed and badly-ventilated factory. In a marked degree
+this is to be observed in the preparation of air-dried sheets, unless they
+are exposed, when freshly prepared, to the action of the sun for a period.
+This period, in the case of rubber prepared on native small-holdings,
+generally extends over several days--until the sheets are more than half
+dry.
+
+In the preparation of smoked sheet, the greasy appearance and the cause
+outlined contribute to a defect which is eventually described as
+"stretching rusty."
+
+SURFACE BLEMISHES.--The coagulum, during coagulation and subsequently, can
+be contaminated in various ways. In most cases a little intelligence or
+increased care would prevent the occurrence of these defects.
+
+When the coagulum remains over-night, in the absence of a cover, it is not
+uncommon to note the presence of dirt (from the roof above, or blown in
+from the outside), the droppings of mice and rats, flies and small insects.
+In theory these should be seen and removed by the factory hands. In
+practice, except while under immediate supervision, the extraneous matter
+is often rolled into the soft coagulum.
+
+A fairly common cause of this surface contamination is the exhaust from the
+power-unit; generally the worst offender is a steam-engine. Grit and smuts
+continually find their way into the factory, alighting on the tables, in
+the latex, in the water, and on the freshly prepared rubber. They are
+rolled into the soft rubber and lead to marked depreciation in the selling
+value. The radical remedy seems obvious, but is often beset with many
+difficulties not unconnected with financial considerations.
+
+Other superficial blemishes, such as those due to the presence of rust
+marks, oil or grease patches, etc., are self-explanatory, if a little
+thought is brought to bear upon them; and it is not proposed here to
+discuss such defects more fully.
+
+       *       *       *       *       *
+
+Having now dealt with certain defects which are visible in wet rubber, we
+come to the discussion of others which are only perceptible either during
+or after the drying period. As far as is known no plantations of any size
+now prepare sheets other than in the form of smoke-dried rubber, with the
+exception of a few which make a special form of thick and partially
+air-dried product known as "slab" rubber.
+
+It is not proposed, therefore, to treat in any detail with air-dried sheet
+rubber. Certain obvious defects are common to both air-dried and
+smoke-cured sheets, and these will be first discussed.
+
+UNEVENNESS OF APPEARANCE.--This lack of uniformity may refer either to size
+or colour, or to both. Apart from any other contributory causes, this
+variation is due, in pan sheet, to a neglect to standardise the dilution of
+all latices, or to lack of uniformity in the quantity of standardised latex
+placed in each receptacle.
+
+Where tanks are employed all sheets from the same tank should be of the
+same size before rolling, and any subsequent disparity in thickness and
+length must be attributed to some alteration in the width of the gap
+between the rolls of the machines.
+
+Unless all latices are standardised by means of an instrument, it is of
+course probable that the content of one tank may be found to differ from
+that of another.
+
+In a general sense, whether air-dried or smoke-cured sheets are considered,
+a thin strip will dry more quickly than a thick one, and should be paler in
+colour when viewed by transmitted light--_i.e._, when the rubber is held
+between the eye and the source of light.
+
+It is necessary, therefore, to guard against the possibility of variations
+in thickness caused by faulty manipulation. The distance between the
+squeezing rolls (smooth) and between the marking rolls (patterned) should
+be adjusted and should remain set until the conclusion of work. In a
+factory having nothing beyond average requirements in equipment of machines
+it should not be necessary to have to interrupt the work of the smooth
+rolls or "markers" by having to make adjustments. This is, however,
+inevitable if there is only one smooth-roll machine, as it is always
+desirable to reduce the thickness of the coagulum by at least two stages
+through even-speed smooth rolls. In some factories there are three light
+power-driven smooth-roll machines, the gaps between pairs of rolls being
+set so as to obtain a gradual thinning effect upon the fresh coagulum,
+which is then passed once between patterned rolls. With such equipment it
+is found possible, in some cases, to omit the preliminary hand-rolling, and
+the strips of coagulum from the tank are passed direct through rolls set
+with a wide gap. This work demands much care, as it is necessary to avoid
+any distortion of the coagulum which may be caused by its own weight and
+length.
+
+VARIATION DUE TO OXIDATION.--The subject of oxidation has been mentioned in
+the opening paragraphs of this chapter. It will have been learned that
+oxidation is a natural process, and that it may be prevented by the
+employment of anti-oxidants such as the sulphite or bisulphite of soda. In
+earlier days it was sometimes prevented by steeping the thin rubber in very
+hot water.
+
+In the absence of an anti-oxidant the degree of oxidation may vary daily
+and in different batches of latex on any one day, so that there is always
+the possibility of a lack of uniformity due to oxidation effects. This
+would be more evident in air-dried sheets than in smoke-cured rubber, as in
+the latter case the darkening of the surface would be masked by the colour
+induced by the smoke-drying process.
+
+To obviate this variation anti-oxidants are used on most estates, but the
+accidental or misinformed abuse of these chemicals may lead to further lack
+of uniformity. Hence it is necessary to follow carefully the formulæ
+prescribed by experience.
+
+COLOUR OF SMOKED SHEETS.--It may be of interest to note that the effect
+known as oxidation is attributed to the presence of micro-organisms called
+enzymes (ferments) in the latex. It can also be produced artificially in
+various ways--_e.g._, by the use of the crude product of wood-distillation
+(pyroligneous acid) as a coagulant, or by the addition to the latex of
+small quantities of a phenol such as carbolic acid. It is thus possible to
+prepare in sheet form a rubber which has the appearance of having been
+smoke-cured, although it may never have been in a smoke-house.
+
+It will be clear, therefore, that apart from other causes, the colour of
+the cured sheets may be influenced by oxidation of the fresh coagulation,
+and by the constituents of the smoke. It follows that the smoke from
+timbers which are richer than others in certain chemical bodies set free by
+combustion will produce a rubber darker in colour.
+
+There is thus no real connection between colour and period of cure,
+although in a general sense the longer the interval the darker the colour.
+
+Similarly it is now plain that when anti-oxidants are employed in excess
+the paleness of the rubber is in no degree truly indicative of the period
+during which the rubber has been smoke-cured.
+
+The influence of the effect of the hypsical condition of the wet rubber
+upon the final colour must be thoroughly grasped. One may take two sheets
+of apparently the same thickness, and smoke-cure them in juxtaposition
+within the same house, only to find that one dries much more rapidly than
+the other. As a consequence, the first, when fully cured, will be of a
+medium golden brown colour; while the other, owing to protracted smoking,
+will be dark. Evidently there must be some distinct difference between the
+two in physical condition prior to the smoking. Here the factor involved is
+the rubber-content of the latex. Given two pieces of coagulum of identical
+thickness, but prepared from latices of different dry rubber content, it
+will be obvious that to reduce them to similar thickness, more pressure
+will be necessary in one case--_i.e._, that piece of coagulum will be much
+more dense (more consolidated)--while the other will be comparatively soft
+and porous. Into the latter warm smoke can penetrate much more easily, and
+the internal moisture can escape more rapidly. The full cure may be made,
+say, within twelve days, while the tougher sheet may demand up to twenty
+days.
+
+To attain uniformity in colour, therefore, the following points must be
+studied and controlled as far as is possible:
+
+     (_a_) Uniform dilution of all latices.
+
+     (_b_) Uniform dimensions of coagulating receptacles.
+
+     (_c_) Uniform volumes of standardised latex.
+
+     (_d_) Uniform quality and quantities of chemicals.
+
+     (_e_) Uniform methods of manipulating the coagulum.
+
+     (_f_) Uniform conditions of fuel and accommodation during
+     smoke-curing.
+
+SURFACE GLOSS.--In the choice of fuel there is room for control if one has
+good timber available. This point opens up a discussion on the vexed
+question of "over-smoking," as the term is sometimes applied to a
+pronounced dry glossy appearance of the surface of sheets.
+
+Three main factors are involved:
+
+     (1) The nature of the fuel.
+
+     (2) The ratio between furnace capacity and the capacity of the
+     smoke-house.
+
+     (3) The rate of combustion.
+
+     Obviously any fuel which yields an excessive quantity of tarry matter
+     or creosotic substance would conduce to the formation of a heavy glaze
+     on the rubber. Such fuel, therefore, should at most only be employed
+     as the smaller portion in a mixture with "dead" timber.
+
+It is impossible to lay down any general rules for the guidance of estates,
+as the timber available varies so widely in nature. Experience must be the
+only guide, and it should not be difficult to obviate the defect. Even so,
+there must be minor differences between the results obtained on estates, so
+that it is not possible to make strict estimations of the smoke-curing
+period by an examination of the surface appearance of rubber, even under
+the best of conditions. Some estates find that the rubber has a distinct
+gloss in ten days, while others may smoke-cure for twice that period
+without difficulty. Evidently, therefore, the question of available fuel is
+of prime importance. It may be remarked that very satisfactory results are
+always obtained from the use of fairly dry timber obtained from thinned
+rubber trees, mixed with the "dead" timber of old logs and stumps found on
+the estates.
+
+Obviously if a smoke-house has a superabundance of furnaces, producing more
+heat and smoke than is required, glazing will result. The point is tested
+by the average temperature maintained and the average rate of drying. The
+result of a high temperature would be the possibility of volatile tarry
+matter being driven in excess to the upper chamber. That this effect is
+eventually produced even at optimal temperatures is evident from an
+examination of the wood-work within the upper room.
+
+It is clear, also, that the rate of combustion exerts an influence. In a
+general sense a rapid consumption of fuel would augment the quantity of
+tarry matter passing into the upper chamber over any given period, and the
+possibility of glazing would be increased.
+
+On the other hand, it is possible that a surface glaze might be formed if
+the temperature were uniformly too low, especially if the rubber were
+rather thick. The rate of drying would be so slow, that if a timber rich in
+tarry matter were employed, the rubber might be exceedingly glossy.
+
+In order to guard against the appearance of a heavy glaze, then, the
+following points must be observed:
+
+     1. The fuel must be carefully selected by experience.
+
+     2. The sheets must not be thick. No sheets should be thicker than 1/8
+     inch measured in average section across the ribs.
+
+     3. The temperature must not be too high. An average working
+     temperature of 120° to 125° F. should be ample.
+
+     4. If the sheets are fairly thick, a low average temperature should be
+     avoided. No lower average than 110° F. should be allowed.
+
+DULL, BLACK SURFACE.--This is the opposite of the previous case, and
+generally is accompanied by a fairly heavy darkening of the surface due to
+"oxidation" effects. The fuel used is too "dead," and needs the addition of
+some substance containing a fair amount of creosotic matter. The appearance
+of the rubber does not justify the assumption that it has been over-smoked.
+As a matter of fact, this type of rubber often becomes affected by mildew
+fairly rapidly, thus showing that the smoking has been inefficient.
+
+It may happen that an estate is in the habit of using a fuel which gives
+even to a thin sheet a heavy glaze in a comparatively brief period. The
+general custom is to soak such sheets in cold water, and then to scrub the
+surfaces, sometimes using soap, in order to cleanse the rubber and free it
+from the glaze. This operation may be done too well, in which case the
+rubber will have a dull appearance, and may be rather more liable to
+develop surface mildew after a time.
+
+MOIST GLAZE, GREASINESS OF SURFACE.--This describes the condition of sheet
+rubber when taken from the smoke-house. Sometimes the greasiness does not
+develop until the rubber has been out of the smoke-house for a day or two.
+
+As far as experience shows at present it may be due to two causes:
+
+     (_a_) The use of an excess of sodium bisulphite or sodium sulphite.
+     The use of sodium bisulphite is not recommended generally for
+     sheet-making. It may cause the rubber to be too pale in colour, and
+     the abuse of it may delay the drying unduly. In the latter case, a
+     trace of the salt may remain within the rubber or upon the surface. If
+     so, as the substance remaining is fairly hygroscopic, it will take up
+     moisture from the atmosphere and may cause the surface of the sheets
+     to have a moist and shiny appearance. The moist surface deposit comes
+     away upon the hand when the sheets are touched, and is difficult to
+     remove entirely. On some estates a very small quantity of the
+     bisulphite is employed, as it is found to be of service in the
+     prevention of bubbles, but in unskilled hands the method is open to
+     abuse, and is, therefore, not recommended for general use.
+
+     A large number of estates now use sodium sulphite in very small
+     quantities as an anti-coagulant and a preservative for latex in the
+     field. The abuse of this very useful substance carries its own
+     penalty. The substance is hygroscopic; and if an excess is present the
+     drying period will be protracted, and the sheets will have a very
+     moist surface film.
+
+     It may be found sometimes that only some of the sheets are affected.
+     This indicates that, whereas uniform quantities of a solution of
+     sodium sulphite have been served out in all fields, the proportion may
+     have been excessive in the case of fields giving a latex of
+     comparatively low rubber content. What suits the latex from old trees
+     may be excessive probably for the latex of younger trees. This is not
+     an infallible rule, as in the case of older fields in which immature
+     bark is being tapped, it is to be noted that the dry rubber content of
+     latex may be less than that of latex obtained from younger trees.
+
+     This type of moist glaze is not easy to remove. Ordinary surface
+     washing had but a temporary effect, and the trouble recurs. The only
+     way of dealing with the difficulty is to soak the sheets for days in
+     running water (or in successive changes of water) and to re-smoke
+     until dry.
+
+     (_b_) The second type of moist glaze is not so difficult to deal with,
+     and may be removed as a rule by washing the sheets when the rubber is
+     otherwise apparently dry.
+
+     It appears to be mainly a matter of unsuitable fuel for smoking and of
+     failure to provide adequate ventilation. A large number of estates
+     have been "thinning-out" or are doing so systematically. The logs thus
+     obtained are often used as fuel in the very green stage. The smoke
+     thus generated must be moist, and if the building is entirely closed,
+     this moisture must be deposited eventually upon the rubber and racks.
+     Some estates have surmounted the difficulty by opening up the
+     roof-ridge slightly so as to allow the moisture to escape with some of
+     the smoke; but if the logs from rubber-trees are to be used, they
+     should be stacked in the sun for some time. Even then, preferably,
+     they should not be used alone. A judicious admixture of dead and
+     rotting jungle-timber appears to give very satisfactory results.
+
+VIRGIN SPOTS AND PATCHES.--If the description really indicates the defect
+it simply means that portions of the sheets are not dry. When cut they
+exhibit the typical whitish, opaque appearance described as "virgin." It is
+doubtful whether any rubber put upon the market as No. 1 product nowadays
+can have this complaint levelled at it. In the extreme case it points to
+gross negligence on the part of the packer.
+
+Sometimes what are taken to be small spots of "virgin" are really patches
+of tiny air or gas bubbles. The point can be easily determined by cutting
+through the patch and examining the cut edges.
+
+SURFACE MOULDS OR MILDEW.--During the last two years, complaints regarding
+the incidence of "mouldy rubber" (_i.e._, relating chiefly to the presence
+of mildews on the surface) have become increasingly common.
+
+To judge by the comments of producers, who as a rule never again see their
+rubber after it leaves the estate, one would infer that the defect is
+imaginary, and that the complaints are made solely with a view to
+repudiation of contracts or the general cheapening of an article of
+commerce. They can often point out, with a certain amount of truth, that
+there has been no change in the methods of preparation or curing, and that
+previously there were no complaints.
+
+It is forgotten, however, that in former years the smaller output of rubber
+was taken into consumption more rapidly than of recent years. That is to
+say, the interval between smoke-curing and the employment of the rubber in
+the manufacture of goods did not demand such a long period of storage.
+Hence the effects of smoke-curing are now more likely to vanish.
+
+Going still further back in the history of plantation rubber, we can point
+to the time when smoked sheets were allowed, or had, to remain in the
+curing-sheds for very extended periods. Loose specimens of rubber prepared
+during that decade still exhibit no signs of mildew growth.
+
+In later years a demand arose for sheets paler in colour than the old type,
+and in order to meet that demand, a change had to be made in methods. This
+led to a system of working whereby it was possible to smoke-dry sheets
+thoroughly in from twelve to fourteen days. This interval was further
+reduced on many estates, until some were producing rubber which appeared to
+satisfy all requirements after only five or six days' curing. This does not
+refer to the case of estates having smoke-houses of "continuous-working"
+type, but to those on which smoking was confined practically to the hours
+of night. Under former conditions of rate of production and consumption,
+this short period of smoke-curing would possibly have been ample; but even
+this is very doubtful, as often the rubber would not stand the relatively
+short journey from the estate to Singapore without mildew-growth being
+incipient. We have often received specimens of rubber sent from estates for
+criticism, and have noted that within a comparatively brief period mildew
+was to be seen.
+
+The whole matter resolves itself into a question of thorough efficiency of
+smoking. This is not dependent on duration of smoking alone, but involves
+other factors, such as the kind of fuel employed, the rate of combustion of
+fuel, the average temperature sustained, the ventilation of the
+smoke-house, and the situation of the building. Other occasional
+contributory factors are contemporary adverse climatic conditions and the
+possible abuse of an anti-coagulant such as sodium sulphite.
+
+It has been shown that after a time, given suitable conditions involving
+the presence of moisture, moulds may appear on sheets which were apparently
+fully smoke-cured, and that under the same conditions other and older
+samples were unaffected. It is argued that the latter sheets had evidently
+been smoked more efficiently than the others. Hence it is fair to assume
+that, except under very special conditions, which do not apply to the
+ordinary procedure in the shipping, storage, and sale of rubber, moulds
+will not develop upon sheets which have been properly smoked. The term
+"properly smoked" signifies efficient smoking for all practical purposes
+under ordinary procedure, and implies or includes all the advantageous
+factors which have been discussed or alluded to in preceding paragraphs.
+
+Without discussing in wearisome detail conditions which may give rise to
+the incidence of mildew on properly smoked rubber, it may be pointed out
+that the following are favourable to the growth of moulds:
+
+     (_a_) Storing sheets in a damp place before packing.
+
+     (_b_) Packing sheets in wooden cases which are not thoroughly dry.
+
+     (_c_) Piling up cases of rubber in a badly ventilated store-room.
+
+     (_d_) Placing the cases on a cement floor.
+
+     (_e_) Wetting of cases by sea-water or by rain during transport, etc.
+
+BLACK STREAKS, SPOTS OR PATCHES.--The origin of these is not difficult to
+trace. They are caused by drippings from the roof, and contain condensation
+products from smoke plus moisture. The ventilation of the roof-ridge should
+receive attention, and if the trouble persists it will be necessary to
+place some absorbent screen below the sloping roof. Sackcloth is sometimes
+used, but leads to a worse state of affairs unless changed frequently. In
+most modern smoke-houses having an iron roof there is an inner lining of
+soft timber.
+
+There scarcely seems a necessity to discuss the case in which an iron roof
+has become perforated by the action of smoke. The remedy is too obvious to
+describe.
+
+WHITISH OR GREY STREAKS.--This is a very uncommon defect, and is generally
+to be traced to a building in which fairly new galvanised sheets have been
+employed. The zinc surface becomes oxidised, and the whitish powder which
+is formed "flakes," or is carried away by drops of moisture condensing on
+the surface of the iron sheets.
+
+RUST.--Sometimes if a sheet is stretched forcibly and allowed to retract
+quickly, the hitherto clear surface will be seen to be marred by a "rusty"
+deposit. The rubber is then described as "stretching rusty," and its value
+is depreciated.
+
+This defect has caused more trouble during recent years than any other. It
+is not proposed here to argue the question as to whether the presence of
+this film, which appears when some rubbers are stretched, is detrimental to
+the physical qualities of the product on vulcanisation. With the mere
+statement of opinion that it could do no apparent harm, we may pass to the
+aspect of the case as it affects the buyer and consumer. If one were to
+judge by the attention drawn to the appearance of smoke sheet-rubber after
+it has been stretched and allowed to retract, one would imagine the defect
+to be of comparatively sudden and recent incidence. This is not so. The
+peculiarity must have existed for years, and perhaps became more marked as
+so many estates abandoned the former common practice of allowing varying
+quantities of water to be placed in the collecting cups. As the substances
+which cause the defect to be visible are partially soluble in water, it
+would follow that when working with the very dilute latices which were
+characteristic of the earlier years of the plantation industry, the
+remaining liquid in the pan after coagulation would contain an appreciable
+quantity of soluble substances which would otherwise have been retained in
+the coagulum.
+
+Conversely, the richer the latex, the greater the percentage of protein
+matter retained in the coagulum. In the case of very rich latex, it must be
+within the knowledge of every manager that the quantity of remaining liquid
+in the pans would be almost nil. We may assume that the greater part of
+these soluble proteins would be enclosed in the structure of the rubber,
+but as the fresh coagulum must retain a quantity of liquid amounting to
+from 60 to 70 per cent. by weight (we are now referring to rich latices),
+it follows that some of the soluble protein matter must be removed when the
+coagulum is placed under pressure. Even after the pressure is released more
+of the contained liquid will exude from the surface of the rubber; and from
+experience it is easy to imagine that this exudation, becoming
+progressively feebler, will continue until the rubber begins to dry. Then,
+with the evaporation of the surface moisture, the protein matter, either in
+original form or as a degradation product, remains on the surface of the
+rubber as a thin, solid film or crust. As drying continues, the interior
+moisture escaping through the pores of the rubber evaporates, leaving
+behind the substances hitherto held in solution. Should, however, the sheet
+be thick and/or the temperature of drying low, the rubber may dry first on
+the outside, forming a thin skin of dry rubber, which delays further drying
+indefinitely.
+
+It will be seen, therefore, that sheets which have been prepared from rich
+latex or from too deep a layer of comparatively dilute latex will have a
+surface film of dry protein matter. Moreover, these sheets will be slow in
+drying, and in all probability will have a surface gloss and a dark colour.
+Hence it is not difficult to understand that some brokers regarded the
+presence of the so-called "rust" as an indication of over-smoking.
+
+To show that this is not so, and further that the presence of rust has
+nothing whatever to do with smoke-curing, it may be stated that _the
+presence of this protein film may be seen on unsmoked sheets_ which have
+been prepared from rich latex, from too deep a layer of more dilute latex,
+or from some thick sheets which have been rolled only very lightly. In
+fact, the presence of the protein film was noted on unsmoked sheet in 1910,
+when it was seen to resemble a thin yellowish glaze which could be scraped
+off with a pen-knife. Later, sufficient of this substance was removed from
+some very thick air-dried sheets, or thin slabs, to fill a small test-tube.
+
+When the sheets were bent or twisted, the apparent surface of the rubber
+(_i.e._, the protein glaze) cracked in all directions. In the case of
+sheets prepared from less rich latex, the surface film naturally is
+extremely thin, and no cracking is observed.
+
+If the fresh sheets are placed in a smoke-house, the drying film will take
+up colour from the constituents of the smoke, and it will be invisible.
+Somewhat analogous to the instance of a transparent glass giving a visible
+and opaque powder when crushed, so the transparent film on stretching
+breaks up into a visible powder which is lighter in colour than the rubber
+on which it is superimposed.
+
+It will be noted that since the introduction of standard methods of
+preparation, involving uniform dilution of latex, say, to a content of
+1-1/4 or 1-1/2 lbs. dry rubber per gallon, complaints as to "rust" have
+decreased considerably.
+
+It is to be further noted as a peculiar fact that while two estates may be
+apparently working on identical lines, both as regards manipulation of
+latex and subsequent treatment of the coagulum, the rubber of the one may
+always be free from rust, while that of the other is often, if not always,
+condemned for the alleged defect. Obviously, in such a case, there must be
+an initial difference between the two latices as regards the percentage of
+proteins present; or there must be some small unrecognised difference at
+some stage of working.
+
+It will now be clear that "rust" is caused by a film of matter which is
+formed on the surface of the pressed coagulum, being there deposited by the
+exudations from within the rubber and through the pores. It is, therefore,
+necessary to avoid any conditions which will favour the formation of this
+deposit--_e.g._, allowing sheets to remain too long in a moist atmosphere
+before placing in the smoke-house.
+
+At present there would seem to be only two methods which are successful in
+the prevention of a "rusty" appearance in the dry rubber. Singularly
+enough, the two methods appear to be directly opposed in principle. They
+are:
+
+     A. THE HOT-WATER TREATMENT.--This method has been in constant use on
+     estates which have old trees giving rich latices. These latices are
+     always diluted to a uniform standard daily. Some estates which
+     formerly suffered from the defect now experience no difficulty, and in
+     other instances, where no complaint has yet been received, the
+     treatment has been followed consistently.
+
+     (1) After the sheets have been through the marking rolls, it is the
+     general custom to allow them to drip for about three hours. This
+     interval is really excessive for the mere draining away of the surface
+     water, but as a rule it is just sufficient to allow a portion of the
+     liquid retained in the rubber to exude. It has been shown that this
+     liquid may contain some protein matter in solution. Sometimes in the
+     case of thick sheets which have been subjected to pressure so much of
+     this matter is exuded as to form a thin surface slime which is
+     distinctly evident to the touch. If the sheets are allowed to hang
+     overnight, the presence of the exuded matter may be detected also by
+     its odour.
+
+     (2) Obviously, any method which will remove this surface film should
+     be of great benefit. It is found that the best results are obtained by
+     allowing sheets to drip for about two hours, and then placing them in
+     hot water for five or ten minutes. The water should be hot as the hand
+     can conveniently bear, and it need hardly be pointed out that the same
+     water should not be used for the whole day's output. For preference
+     there should be three or four vessels, each capable of holding a fair
+     proportion of the total number of sheets, and frequent changes of hot
+     water.
+
+     (3) After remaining in the hot water for the period mentioned, the
+     sheets are removed singly, each one being surface washed or swilled as
+     it is taken out.
+
+     (4) _It is important to see that the sheets are now well washed or
+     scrubbed under running cold water, or in frequent changes of water._
+     The reason for this procedure is plain. If the sheets are merely hung
+     again to drip after removing from the hot water, some moisture is
+     bound to remain on the surface of the sheet. As this surface moisture
+     contains some protein matter in solution, it is evident that, as the
+     water evaporates, the solid protein is again deposited on the surface
+     of the rubber. This would explain why some estates were unsuccessful
+     with the hot-water treatment. It is not essential that the running
+     water should be cold; it may be conveniently lukewarm if drawn from
+     the cooling tanks of the engines. But it is essential for the best
+     results that there should be running water, so that the substance in
+     solution is carried away. If the sheets are merely washed in a large
+     vessel, which has been filled with clean water, it must be obvious
+     that, by the time some scores of sheets have been washed, the protein
+     matter in solution on the surface of the sheets has been transferred
+     to the washing water, so that the later sheets of the batch are liable
+     to show the defect again on drying.
+
+     B. The second method is much more simple, and entails no extra labour
+     such as is demanded by the first method. A successful issue, however,
+     is rather more uncertain, and the method appears to give the best
+     results with sheet-rubber prepared on young estates or from more
+     dilute latex.
+
+     In this method, the sheets after rolling are allowed to drip for a
+     very short interval, so that the surface water is mainly removed. The
+     sheets are then placed in the smoke-house, and smoking is commenced at
+     once. In some cases where the defect had appeared continuously for a
+     long period, it was found to vanish entirely as soon as the method was
+     adopted; but when tried on some of the older estates, the results were
+     very doubtful, and a return was made to the hot-water treatment.
+
+     The explanation of the action which takes place is rather obscure, but
+     two theories may be advanced.
+
+     (_a_) It may be assumed that the interval given for dripping is too
+     brief to allow for the exudation of the internal moisture containing
+     dissolved protein matter.
+
+     In such case, the rubber is still in a highly porous condition, and it
+     might be advanced that the heat of the smoke may help to maintain that
+     condition. Thus the contained liquid might evaporate so quickly as to
+     leave behind the dissolved substances in the minute cellular structure
+     of the rubber. In other words, instead of the internal moisture
+     exuding slowly to the surface in liquid form, it may leave the
+     rubber, even in the first stages, in an evaporated condition, just as
+     it does in the subsequent stages of drying. Thus no dissolved protein
+     matter would be brought to the surface of the sheet and be deposited
+     there.
+
+     (_b_) The other theory also demands the first assumption propounded in
+     the preceding theory, but subsequently perhaps is less feasible as it
+     assumes a chemical action of which we have no definite knowledge.
+
+     The idea is that as the rubber is in a porous condition, and is placed
+     quickly in an atmosphere of smoke, the heat may maintain that
+     condition to such a degree, that some constituents of the smoke may
+     enter the rubber and cause the precipitation _in situ_ of the protein
+     matter held in solution by the contained water or other liquid. The
+     contained liquid would be water which has in solution possibly a very
+     slight trace of the coagulant employed, of sugars, of protein matter,
+     and of inorganic salts. Of these the substances which would evaporate
+     would be probably the water and the coagulant in most cases. If a salt
+     had been used as a coagulant, the dissolved trace would be deposited
+     within the rubber in this case, whereas if a rich latex had been
+     employed or a thicker sheet made from more dilute latex, some of the
+     salt would be brought to the surface and there deposited together with
+     the protein matter. This has actually been experienced in practice,
+     and it has been possible to remove minute crystals from the edges of
+     the rubber so prepared.
+
+It will be evident that in order for either theory to contain an element of
+probability, the rubber must be soft (porous) when placed in the
+smoke-house, and must also be fairly thin. It is observed in all cases
+where the method has been successfully employed that both these conditions
+are generally fulfilled--at all events the rubber is fairly thin. When
+thicker sheets are made, either from rich latex or from a deeper layer of
+comparatively dilute latex, the method is not uniformly successful.
+
+OTHER VIEWS ON "RUST" CAUSATION.--Later experimental work on "rust"
+formation by Hellendoorn[22] leads to the observation that "rustiness" is
+caused, not actually by the deposition of original serum-substances, but by
+the decomposition thereof, under the action of aerobic micro-organisms.
+
+[22] "The Cause of Rustiness in Sheet-Rubber," H. J. Hellendoorn, Archief
+voor de Rubbercultuur, October, 1919 (Communication from the Central Rubber
+Station, Buitenzorg, Java).
+
+Without going into a full discussion of the subject, the following points
+noted in the experimental work may be quoted:
+
+     1. Rustiness could apparently be produced at any time merely by
+     keeping freshly rolled sheets for periods varying from twenty-four to
+     forty-eight hours in a moist atmosphere.
+
+     2. Sheets placed immediately in a temperature of, say, 110° to 130° F.
+     never showed "rust"; but if air-dried at ordinary room temperature,
+     "rust" might appear.
+
+     3. "Rust" can be prevented by soaking freshly prepared sheets in
+     dilute solutions of disinfectants--_e.g._, formalin, sodium
+     bisulphite, or chinosol.
+
+     If subsequently the sheets are hung for any length of time in a moist
+     atmosphere, the protective effect of the disinfectant gradually
+     vanishes and "rustiness" may be produced.
+
+     The same disinfecting effect may be obtained by the use of steam or
+     hot water. It was found that there was less liability to the formation
+     of "rust" when sheets were immersed in water at a temperature of 95°
+     to 120° F., whilst steeping at 140° F. gave complete freedom.
+
+     4. It was shown that the micro-organisms which cause decomposition of
+     the serum-products flourish only in the presence of air--_i.e._, they
+     are aerobic in character. It is not uncommon to find, therefore, that
+     "rust" may be incident only on those parts of a sheet which have been
+     exposed for some time to air and moisture before being placed in a
+     warm smoke-room.
+
+     5. The optimal temperature for development of the particular organisms
+     appeared to be about 100° F., in a moist atmosphere.
+
+     6. Soaking the sheets in water (except the short immersion in hot
+     water, which we recommend), even for a period extending over a week,
+     does not hinder the formation of "rust."
+
+     7. Rustiness may be prevented by placing the sheets in a sufficiently
+     warmed smoke-house as long as there is adequate ventilation and a
+     moist atmosphere does not persist.
+
+     The simplest means of prevention is to soak the sheets first for a
+     short period in water, and then to hang them to drip for a few hours
+     in a well-ventilated place, outside the factory and under cover.[23]
+
+[23] We advise and practise hanging sheets in the open, without shade or
+cover.
+
+It will be gathered that, although there may be a slight difference between
+our previous views and those advanced by Hellendoorn as to the exact cause
+of formation of the "rusty" film, the general conclusions are identical
+with those given by us in preceding paragraphs and previously advised in
+the Malayan reports of the Rubber Growers' Association.
+
+BUBBLES.--The presence of bubbles in sheet-rubber has for years been the
+bane of some managers' existence, and the bone of contention between
+sellers and buyers. Taking the argument down to bed-rock, producers urge
+that the presence of bubbles has no influence upon the ultimate quality of
+the rubber on vulcanisation. They assert that the alleged defect is merely
+a peg upon which to hang an unreal grievance, serving the purpose of the
+buyer under the existing conditions of sale. All this may be true, but as
+long as the present system continues, it must be recognised that "kicking
+against the pricks" is a futile recreation.
+
+The sympathy of the writers is certainly on the side of the producers,
+inasmuch as they realise how extremely difficult, and even impossible at
+times, it is for the most careful individual to prepare sheet-rubber free
+from this blemish.
+
+Much has been written, and many have been the discussions, on this vexed
+subject; and it is recognised that sometimes, in spite of all precautions,
+there may suddenly be an incidence of bubbles in rubber which is ordinarily
+free from them. It must be allowed that climatic conditions and
+physiological variations affecting the metabolic functions of the trees
+exert an influence which is difficult at times to combat, and often beyond
+human control.
+
+The contributory causes are many and varied. It should be premised that,
+although the defect is described as "air-bubbles," it is seldom that the
+appellation is strictly correct. Rarely do the bubbles contain air. In the
+vast majority of cases they contain gases in minute quantity. These gases
+may be considered to arise, broadly, from some decomposition of substances
+(other than rubber), contained either in the coagulum or in the serum. In a
+general way, if this decomposition is evidenced by an unpleasant odour, it
+is described under the term of "putrefaction." We are not concerned here
+with the question as to how far such decomposition may be ascribed to a
+purely chemical action, or to the indirect result of the presence of
+certain bacteria or other micro-organisms. Suffice it to state that, at
+least as far as field operations influence the result, the decomposition is
+generally to be attributed to the work of micro-organisms. Conditions
+favourable to the incidence and development of these are to be found when
+absolute cleanliness in all details is not aimed at.
+
+With this preamble we may proceed to classify possible causes of the
+formation of bubbles into two groups:
+
+     (_a_) Those originating in field operations.
+
+     (_b_) Others which may arise after the arrival of the latex at the
+     factory.
+
+IN THE FIELD.--Decomposition may be caused by:
+
+     (1) Spouts, buckets, and cups being dirty. Regular cleaning is
+     necessary. If the buckets are allowed to be taken to the lines by
+     tappers, trouble may ensue. Within the writers' experience it has been
+     shown that an otherwise baffling case of premature flocculation of
+     latex was traced to the presence of acid substances in the buckets,
+     which had been used by coolies for preparing their food.
+
+     (2) Delay in commencing work. This means similar delay in collecting
+     the latex which is exposed to greater heat than under ordinary
+     circumstances.
+
+     (3) Exposure to the sun's rays. The heating of the latex may provide
+     improved conditions favourable to the development and action of
+     micro-organisms.
+
+     (4) Allowing latex to stand too long before collection. This usually
+     is the result of giving tappers too great a task.
+
+     (5) The addition of water to the latex, either purposely or
+     accidentally, in the form of rain. The water may be slightly acid in
+     character, or it may carry micro-organisms from the bark into the
+     latex.
+
+     (6) Tapping trees at too great a height. The latex generally has an
+     abnormal distance to travel before reaching the cup.
+
+     (7) Sometimes the latex from old trees, or from trees after wintering
+     (just prior to full renewal of leaf), contains more than the usual
+     proportion of substances (_e.g._, sugars), which are capable of
+     effecting flocculation or coagulation.
+
+     (8) Too great a distance for transport. The trouble arising from this
+     cause is likely to be much increased if the journey has to be made
+     over bad roads. In such case the physical action augments the effect
+     likely to be produced by long standing.
+
+The foregoing do not include all possible causes, but serve to indicate the
+directions from which trouble may be mainly anticipated. It will be plain
+that any latex which exhibits symptoms of premature coagulation (or minute
+flocculation) should be regarded as a potential source of bubbles in
+sheet-rubber.
+
+It will be equally obvious that the employment in the field of any harmless
+substance of an anti-coagulant nature is to be encouraged. This point is
+discussed in detail in Chapter V.
+
+IN THE FACTORY.--As a general rule it may be understood that the mischief
+has been done before the latex is handled at the factory. Sometimes it is
+perceptible from the peculiar appearance of the latex, and in such case the
+batch should not be used for the preparation of sheet-rubber. Often it is
+found that only the last to arrive at the store is visibly affected. This
+should not be mixed with other apparently normal latex, as it is capable of
+acting as a "leaven" to the bulk.
+
+Contributory factors in the store are:
+
+     (1) Lack of cleanliness of utensils, particularly of coagulating
+     dishes or tanks.
+
+     The trouble becomes acute sometimes where wooden tanks are employed.
+     Unless the tank and the partitions are thoroughly and regularly
+     cleansed, the wood may become coated with a bacterial slime, which is
+     capable of causing what may be termed "fermentation" of the latex
+     layers in contact.
+
+     The tank should be thoroughly cleaned occasionally with a weak (5 per
+     cent.) solution of sodium bisulphite. The partitions should be
+     scrubbed and placed in the sun twice or three times a week.
+
+     (2) Allowing latex to stand too long before treatment. This point
+     needs no further expansion.
+
+     (3) The use of a latex of too high a rubber content. Such latices are
+     difficult to handle in order to secure uniform mixture with the
+     coagulant.
+
+     (4) The use of too concentrated a solution of coagulant. In
+     conjunction with (3) there may be a rapid and irregular coagulation,
+     giving rise not only to decomposition in parts (and subsequent
+     formation of gas), but also to the formation of true "air-bubbles" by
+     inclusion of air during stirring.
+
+     (5) The use of insufficient coagulant. Coagulation is slow and
+     incomplete.
+
+     (6) Defective straining and skimming. Small flocculated particles of
+     rubber may pass, or be rubbed through, the strainer. If allowed to
+     remain, they act as local points of danger.
+
+     (7) The proximity of the coagulating latex to some source of heat, or
+     exposure to sunlight.
+
+     (8) Any delay of drying in the preliminary stages, either before or
+     after the rubber enters the smoke-house.
+
+BLISTERS.--This description aptly fits the case in which sheet-rubber in
+the smoke-house exhibits large bubbles of gas which distend the surface of
+the rubber. When subjected to pressure, small "balloons" are formed, which
+burst with a perceptible report. It was formerly the belief that this
+defect was occasioned solely by an abnormally high temperature. That such
+is not the case can be shown by the experience of estates which have had
+only the rubber of a particular day or short period affected under normal
+factory conditions.
+
+At the same time it is not disputed that the heat of the smoke-house exerts
+an influence (causing expansion and distension), but it is advanced that
+the gases had begun to form before the rubber entered the house.
+
+The view held is that decomposition had supervened or was taking
+place--probably from one or more of the causes enumerated in the preceding
+paragraphs. The heat of the smoke-house only serves to exaggerate the
+effect. It is acknowledged that the degree of decomposition must be
+initially greater than in the ordinary incidence of "bubbles."
+
+Beyond this point we are not in a position to put forward any definite
+supposition as to the apparently haphazard occurrence of the phenomenon.
+
+It is to be noted, fortunately, that the defect is comparatively rare, and
+seldom appears on estates which employ an anti-coagulant in the field.
+While we have examined persistent cases, one of which led to a temporary
+discontinuance of the preparation of smoked sheet rubber, we have not yet
+been able to arrive at any satisfactory idea of the exact conditions
+governing the incidence of "blisters." Our investigations only lead us to
+two observations:
+
+     (_a_) That blisters have appeared on the rubber of some estates after
+     wintering, and during the period of new leaf-development.
+
+     (_b_) That the defect has been noted on other estates during a period
+     when there were frequent but not heavy rains, and when there was a
+     comparatively low average temperature.
+
+In either case, as the factors are beyond human control, it would be
+expected that without any change being made in estate procedure, the
+trouble would vanish as mysteriously as it appeared. This is our
+experience; but as showing the possible intensive effect of a high
+temperature in the smoke-house, it may be remarked that very infrequently,
+in a batch of sheets exhibiting ordinary bubbles, a few hanging directly
+above the furnaces show signs of a slight blistering effect.
+
+"SPOT" DISEASE IN SHEET RUBBER.--That "spot" disease may appear in
+air-dried sheets was evident at the beginning of the outbreak in the spring
+of 1911. The first cases noticed took the form of pink and bluish "blushes"
+spreading over the whole of the sheets. Later, fungoid spots began to
+appear. These mainly took the form of red or black blotches, and were very
+unsightly. As "spot" disease cannot develop in smoked rubber, the obvious
+and simple course to adopt was to smoke-cure the sheets. When it is stated
+that "spots" do not develop in smoke-cured rubber, it is understood that
+the smoke-curing must be efficient and must commence as soon as the rubber
+has been rolled, and the surface water has drained away. If the sheets are
+allowed to air-dry for a few days, the disease may develop, and then
+smoke-curing will not get rid of the coloured patches. The operation of
+smoke-curing will not get rid of the coloured patches. The operation of
+smoke-curing may tone down the colour, but the spots would still remain
+evident.
+
+SUPPORT MARKS.--It frequently occurs that one sees across the middle of
+smoked sheets a wide mark. This is where the wooden support in the
+smoking-chamber has been. As a rule, even in the most careful cases a faint
+mark may always be seen, but in many instances this mark is exaggerated to
+such an extent as to point to lack of care on the part of the store
+supervision. If bays of racks remain empty over-night, they may possibly
+become covered with a light sprinkling of fine wood-ash and tarry deposit.
+Wet rubber placed upon these racks will pick up and retain the impurities,
+and more often than not they cannot be washed out. It is incumbent upon the
+manager to see that empty racks are thoroughly cleansed before placing wet
+rubber upon them. The better plan is to arrange that the bars can be
+removed easily from sockets. There should be in stock sufficient "spares"
+for, say, two days' rubber. When the dry rubber is removed, the bars should
+likewise be taken away, to be cleansed and kept in the factory until again
+required. This will ensure that fresh rubber always rests upon a clean
+support.
+
+On some estates, in order to guard against a pronounced "bar-mark," sheets
+are moved and turned daily.
+
+In other smoke-houses the upper surface of the bar is chiselled in concave
+form, so as to admit of the passage of smoke below the surface resting on
+the bar.
+
+STICKINESS.--This is not to be confounded with "tackiness," from which the
+rubber does not recover. Stickiness is only temporary, and may be remedied.
+As a general rule, it is due to packing sheets, which have not a good
+raised "ribbing," and which may have been coated with light tarry deposits
+(see Glaze). This surface film may be removed by washing the sheets, or
+scrubbing them, with cold water. Usually a further two days' air-drying
+will make the rubber fit for packing; and if the smoke-curing has been
+efficient, there should be no need to anticipate trouble from mildew. Some
+estates adopt this practice daily with success, as a form of insurance
+against complaints of surface deposits.
+
+RIBBING, SURFACE PATTERN.--While we know that the passing of sheets of
+rubber between rolls, causing a particular raised pattern to appear, has no
+effect upon the actual quality of the rubber, there is a great deal of
+practical advantage gained.
+
+The practice ensures an increase of superficial area which is an aid in
+drying, improves the appearance of the rubber for selling purposes, and is
+of distinct advantage in enabling the rubber when packed to travel in
+better condition. Sheets do not become so closely packed; sampling and
+general handling are easier on delivery.
+
+As long as the plane surfaces are sufficiently and regularly distorted,
+there would seem to be no limits to the type of pattern or "mark" which may
+be placed upon the rubber. But in actual practice the variety is small. The
+most popular type of "ribbing" is that best described as a small diamond
+effect, produced by a pair of rolls cut with closely placed narrow grooves
+running spirally. The spirals travel in the same direction on both rolls,
+producing close-cut ribbing running in opposite directions on the surfaces
+of the sheet. On sheets of standard thickness, the result approaches a
+diamond effect.
+
+A few other patterns are employed, notably that producing longitudinal
+stripes of varying thickness. On the whole, the type of pattern would seem
+to be immaterial, if the points already indicated are achieved.
+
+It is seldom one encounters a case nowadays in which the "marking" is
+unsuitable, but a few estates may be using an old type of patterned roll on
+which the full diamond grooving is cut. As this appears on both sides of
+the sheet of rubber, and as the ribbing does not coincide, a blurred effect
+is seen when the sheet is viewed against the light.
+
+THICK ENDS, "SHEET CLIPPINGS."--It rarely happens, even with good equipment
+and average supervision, that the preparation of smoked sheet is
+unaccompanied by slight defects. For instance, in spite of rules and
+regulations regarding manipulation of the coagulum, it is not uncommon to
+find that some sheets, after rolling, have slightly thickened ends. In the
+ordinary course of events these might delay drying considerably. It is the
+practice on some estates to cut off these thickened ends while the rubber
+is still wet. The pieces are then machined into crepe form, but as no
+sodium bisulphite may have been used, the resulting rubber cannot be
+classed as No. 1 Standard Crepe.
+
+The other alternative is to trim the ends when the bulk of the rubber is
+thoroughly smoke-dried. The moisture containing portions are then returned
+to the smoke-house until dry, and are subsequently packed without further
+treatment as "smoked-sheet clippings." It will be plain that, except in the
+particularity of form, these clippings differ in no degree from the
+original sheets; and, owing to extra smoke-curing, may arrive in even
+better condition. One must be prepared, however, to find that a slightly
+lower price is offered. Whether the price obtained would be comparable with
+that commanded by the crepe made from wet sheet slipping would depend upon
+general ruling market conditions, and the degree of care exercised in
+guarding against the inclusion of any inferior pieces of rubber. In
+ordinary factory practice, there could be no room for abuse under the
+latter clause.
+
+OTHER INFREQUENT DEFECTS.--This chapter will be closed with a reference to
+other small defects which, although infrequent, cannot be classed as minor
+complaints. In point of fact, when they occur, they assume an importance,
+in the eyes of the consumer, which is not, perhaps, sufficiently
+appreciated by producers.
+
+DIRT.--Trouble from this source should be absent, but carelessness on the
+part of packing coolies may be responsible for occasional complaints. How
+the dirt is incident may remain a mystery, but it has been noted that
+sheets have at times been thrown upon a cement floor. A certain amount of
+loose dust may thus adhere to the rubber.
+
+ASH.--The source of this surface deposit scarcely needs indication. Where
+open-hearth furnaces are employed, and the wire-mesh floor screens are not
+perfectly sound, fine ash may find its way into the upper chamber. If this
+trouble is persistent in spite of precautions, the sheets should be
+surface-washed and air-dried before packing.
+
+BARK.--Complaints of the presence of particles of bark in sheet rubber used
+to be fairly frequent, but are now less common. The trouble may be traced
+to the use of defective straining sieves when the latex is being handled.
+
+SPLINTERS.--The use of packing-cases of unplaned soft timber is responsible
+for complaints of this nature on delivery. Without here discussing the
+larger question of the ideal packing case, it is sufficient to emphasise
+that the interior surfaces of wooden chests should be planed. The cases are
+often so damaged in transit, that splinters of wood may be found throughout
+the contents. The device adopted on some estates may go far to prevent
+this. The cases are first lined with loose sheets, and finally other sheets
+are arranged to overlap at the top of the case. The bulk is thus enclosed
+in a wrapping of sheets, and any splinters or other deleterious substances
+are confined to the surface of the mass.
+
+
+
+
+PART V
+
+GENERAL
+
+
+
+
+CHAPTER XIX
+
+_CHOICE OF COAGULANT_
+
+
+Almost without exception, the agent employed in the coagulation of
+plantation (_Hevea_) rubber is acetic acid, or in some cases formic acid.
+Under ordinary trade conditions supplies are always obtainable at
+reasonable prices, but during the recent War the question of possible
+substitutes was brought greatly to the fore. Fortunately the subject of
+coagulation and coagulants had been previously studied to such effect in
+laboratory practice, that there would have been small difficulty in
+prescribing agents other than acetic acid in cases of expediency. As far as
+our knowledge extends, all the possible substances which have the power of
+coagulating latex have been tested. They include mineral acids, organic
+acids, compounds known chemically under the general term of "salts,"
+alcohols, sugars, etc.
+
+The heading of this chapter must be seen to "beg the question," inasmuch as
+it leads to the assumption that a coagulant (in the popular sense) is
+necessary to secure coagulation. In point of fact, methods are sometimes
+employed which depend upon no artificial coagulant to produce the desired
+effect. To these methods reference will be made later.
+
+In this section it is proposed to describe briefly the more important
+agents which are used, or might be used, in effecting coagulation. In the
+class of those which are not in common use some could be used as
+expedients, while others are only of scientific interest.
+
+ACETIC ACID.--There is no need to enter into a discussion of the merits of
+this agent. In practice it remains the cheapest and safest coagulant known
+at present.
+
+FORMIC ACID.--This agent is equally as safe to use as acetic acid, and as
+easy to handle. Bulk for bulk its coagulative power is higher than that of
+acetic acid. Its pre-war shipping price, when taken in conjunction with its
+coagulative power, was slightly below that of acetic acid, but local prices
+put the balance in favour of the latter. If prevailing costs put it on
+terms of parity with acetic acid, there would appear to be no reason why
+formic acid should not have a widely-extended use on plantations.
+
+CITRIC ACID, TARTARIC ACID.--The acids of the extracted juices of most
+tropical fruits consist, to a large degree, of citric or tartaric acids.
+These can be used in place of acetic acid as satisfactory coagulants in
+case of emergency; but the questions of availability of supplies and of
+costs preclude their more general adoption.
+
+OXALIC ACID.--This is a satisfactory coagulant as far as observed effect is
+concerned. It produces a rubber paler than ordinary coagulants (without the
+use of sodium bisulphite), as it has the nature of an anti-oxidant.
+
+It would not be a safe agent in the hands of coolies, as it is classed as a
+poison.
+
+SULPHURIC ACID.--During the War, in a period of shortage of acetic acid and
+of high prices, this agent was used with success on some estates.
+
+It scarcely need be remarked that it is a dangerous substance to handle,
+and that its employment must be accompanied by close European supervision.
+
+At prevailing prices during the War it was very much cheaper than acetic
+acid, and even at the present reduced cost of the latter the advantage
+still lies with sulphuric acid.
+
+It must be emphasised, however, that the abuse of this agent to any but the
+slightest degree is harmful to the resultant rubber. Hence its use would be
+sanctioned _only in the absence of the commoner, and much safer,
+coagulants_.
+
+In view of the possible incidence of such an emergency, the following
+notes are given. It is impressed that strict adherence to the rules must be
+given.
+
+HANDLING SULPHURIC ACID.--(_a_) Always use glass or glazed earthenware
+vessels.
+
+(_b_) Pour slowly and avoid splashing. Drops finding their way to clothing
+or other fibrous material will destroy it locally; and if thrown upon any
+part of the body may cause painful burns.
+
+(_c_) When diluting this agent always remember to pour the acid into the
+water (_i.e._, the lesser into the greater), and never _vice versa_. Pour
+the acid carefully and slowly down the side of the vessel, and stir well.
+
+(_d_) Should strong acid be spilled, do not throw water upon it. A supply
+of sand or dry earth should be kept close at hand. Throw this upon the
+acid.
+
+STORING SULPHURIC ACID.--(_a_) Jars or cases should be handled as seldom,
+and as carefully, as possible. If the acid is contained in a case, the top
+should be plainly indicated.
+
+(_b_) Stocks should be stored in a detached building which should not be
+damp. Jars or cases should not stand on a wooden floor if possible.
+
+(_c_) See (_d_) above.
+
+BUYING SULPHURIC ACID.--(_a_) Commercial acid of specific gravity 1·84 is
+the best of its kind. It contains impurities which are non-injurious to
+rubber preparation.
+
+(_b_) It is always advisable, if possible, to buy the acid in small jars
+containing not more than 100 lbs. each. Smaller jars, with a content not
+exceeding 50 lbs., would be preferable.
+
+(_c_) If the acid is bought in jars, it should be stipulated that the
+stoppers be covered with a plaster head, and that the containing crate or
+case should have prominent labels or marks indicating the top of the case.
+
+FORMULA FOR USE OF SULPHURIC ACID.--It will be understood that as this
+formula has been calculated for working with latex, having a consistency of
+1-1/2 lbs. dry rubber per gallon, it applies in a strict degree only to
+such latex. In other cases, where the dilution of the latex is not known,
+the formula will serve as a basis for experiment until the correct quantity
+has been discovered.
+
+(Sulphuric acid of specific gravity 1·84.)
+
+     NOTE.--The directions must be followed carefully, and glass measuring
+     vessels should be used if procurable.
+
+     (_a_) Measure out 1 pint of strong acid, and pour it carefully and
+     slowly _down the inner surface_ of a jar containing 20 gallons of
+     water. Do not pour it directly into the water.
+
+     The heavy acid will sink to the bottom of the jar, and a good mixture
+     must be obtained by stirring well.
+
+     (_b_) Of this solution (which is approximately 1 per cent. by weight),
+     use 1 gallon to 20 gallons of latex.
+
+Readers are doubtless now well aware of the corrosive action of strong
+sulphuric acid, and we scarcely need point out that even the dilute acid
+should not be kept in contact with the usual iron vessels found in
+factories. The mixing of solutions should be done in one of the glazed
+earthenware jars commonly in use.
+
+The formula given above works out at approximately 1 part strong acid to
+2,000 parts of latex (of dry rubber content 1-1/2 lbs. per gallon). The
+formula for using acetic acid with the same latex works out at about 1:
+1,200. It will be apparent, therefore, that relatively sulphuric acid is a
+more powerful coagulant than acetic acid. In terms of dry rubber obtained
+from latex of the consistency indicated above--
+
+     1 lb. sulphuric acid will produce 300 lbs. dry rubber. 1 lb. acetic
+     acid will produce 180 lbs. dry rubber.
+
+With both acids selling at the same rate, sulphuric acid would be more
+economical in use; when its cost is less than that of acetic acid, which is
+the normal condition, the economic advantage in favour of sulphuric acid is
+augmented still further.
+
+It may be found that the standard formula for sulphuric acid will not
+always give a perfectly clear remaining serum, even though an attempt is
+made daily to work to a uniform consistency for all latices. It is
+inevitable that the manipulation of the latices should be slightly in error
+on occasions, or that a small mistake might occur in preparing the solution
+of acid. Hence a clear remaining serum after coagulation may be secured
+less often than a slightly turbid serum. This is as it should be. The
+minimum quantity of acid may be adjusted so closely as to give such
+results. If a clear serum is obtained always, that should be an indication
+of continual excess of coagulant. Naturally, if a milky serum is always
+obtained, the reverse is the case.
+
+As a last word on the subject, it may again be emphasised that the use of
+sulphuric acid is not advised, except in an emergency; and that the
+greatest possible care must be exercised in the observance of the strict
+formula for use.
+
+HYDROCHLORIC ACID, NITRIC ACID.--These mineral acids would prove more
+expensive than sulphuric acid. In addition they are much more uncertain in
+action. For example, the use of a certain excess of hydrochloric acid would
+not hasten coagulation, but would prevent it. Above all their effect, in
+excess, is deleterious to the rubber.
+
+HYDROFLUORIC ACID.--This has a strong corrosive action on porcelain or
+glass. Hence it has to be contained in bottles of gutta-percha or lead. It
+is mentioned here merely because some years ago it found a use as a
+coagulant, chiefly in Ceylon. It was sold in the form of a 10 per cent.
+solution under the name of "Purub," and was the subject of a patent.
+
+It is effective as a coagulant, and has also an anti-oxidant action, which
+was its chief recommendation when cheap and harmless anti-oxidants were not
+commonly known. It is comparatively expensive, and, as indicated above,
+difficult to handle and store. In short, it has nothing to commend it, in
+comparison with acetic or formic acids.
+
+ALUM.--This substance has been used for years by native rubber producers as
+a coagulant. It fulfils the desired purpose, and its popularity was
+maintained because of the ease with which it could be stored and handled.
+Unfortunately, this facility often led to the use of an excess, and native
+sheets were often criticised as being brittle. Investigations have shown
+that alum, even in minimum proportions, has an appreciably harmful effect
+upon the quality of the rubber prepared by its use as a coagulating agent.
+Its employment by native rubber producers has now been largely superseded
+by acetic acid in some form.
+
+PYROLIGNEOUS ACID.--This is otherwise known under the names of "crude
+acetic acid" and "crude wood vinegar." Owing to the shortage of acetic acid
+during the War, attention was directed towards the possibility of making an
+effective coagulant locally by what is termed the "dry distillation of
+wood"--_i.e._, the wood is not burned but heated in a retort. The enquiries
+could be placed in two classes:
+
+     1. Those which aimed at making the pure, strong acid of commerce.
+
+     2. Those which sought information concerning a crude coagulant
+     (pyroligneous acid) on estates.
+
+Regarding the first class, we can do no better than reproduce our remarks
+published in the April local report of the Rubber Growers' Association for
+1916--with the reservation that, on account of a threatened shortage of
+timber, a local scheme might not now be feasible:
+
+     "Probably the most common enquiry encountered since the rise in the
+     price of acetic acid is concerned with the possibility of making
+     acetic acid in this country. It may be stated that the proposition is
+     a feasible one, even on a fairly large scale. We have the essentials
+     necessary for such a scheme in:
+
+          "1. A good supply of suitable timbers, the most valuable of
+          which, possibly, is mangrove timber, locally known as 'bakau.'
+          Other suitable timbers are known, but as far as preliminary
+          experiments show mangrove timber gives the best yield. At present
+          this timber is in great demand as a fuel for steam plants, but
+          with the extension of the local coal industry the timber may
+          become cheaper.
+
+          "2. There would appear to be less valuable timber which would be
+          suitable for heating the retorts. Or, local coal might be used.
+
+          "3. Supplies of lime at reasonable rates are available, as the
+          limestone formation in the peninsula is quite considerable in
+          extent.
+
+          "4. Supplies of sulphuric acid are available from Japan,
+          Australia, Burma, etc., even at the present time, although
+          naturally rates are higher than normal. Under ordinary
+          conditions, supplies from England and parts of Europe would be
+          much cheaper than at current rates.
+
+          "For the benefit of many readers perhaps a brief and nontechnical
+          description of the preparation of acetic acid would not be amiss,
+          and would explain the necessity for the essentials indicated
+          above. In brief, the process is as follows:
+
+          "(_a_) A suitable timber is heated in a closed retort. This is
+          termed 'dry distillation,' and results eventually in the
+          carbonisation of the wood--_i.e._, charcoal is obtained in the
+          retort.
+
+          "(_b_) Tar, vapours and gases are distilled over during the
+          carbonisation of the wood. These liquors and gases pass through
+          condensers. The gases pass away, while the condensed liquors
+          separate out into (1) wood tar, (2) a watery liquor called
+          pyroligneous acid or crude wood vinegar.
+
+          "(_c_) The pyroligneous acid is separated from the tar, and again
+          distilled to obtain the acetic acid present.
+
+          "(_d_) This crude acid is steam-heated with milk of lime, which
+          fixes the acid, forming calcium acetate (or acetate of lime).
+
+          "(_e_) Eventually the calcium acetate is taken out in the form of
+          a thick paste, which is spread to dry. When dry this 'grey
+          acetate' is the main source of all glacial acetic acid now made.
+
+          "(_f_) The acetic acid is released from the 'acetate of lime' by
+          the action of sulphuric acid. It is then distilled several times,
+          and under various conditions, in order to increase its strength.
+          In the past copper tubes were used for this purpose, but owing to
+          the fact that traces of copper were found to be injurious to
+          rubber, some works instal tubes of glazed earthenware for the
+          distillation.
+
+     "Such is the process in outline, and it will be seen that no proposal
+     to manufacture _glacial acetic acid_ on an estate could be considered
+     feasible, although it would not present any great difficulty on a
+     large scale and under skilled direction. Furthermore, the cost of the
+     plant would be far too great for any estate."
+
+Although it is clear that pure acetic acid is beyond the scope of an
+estate, crude pyroligneous acid has been produced on a varying scale in
+this country and in Ceylon. In the latter country some success was obtained
+by the distillation of coconut shells with comparatively inexpensive plant.
+In this country, wood-distillation was practised on a few estates, but
+improved facilities for obtaining pure acetic led to a termination of the
+experiments, although sufficient crude acid could then be made at a
+reasonable cost.
+
+The pyroligneous acid obtained, is generally clear, after nitration, and of
+a dark brown colour. It has a peculiar odour reminiscent of smoked
+sheet-rubber, or of creosotic substances in general.
+
+Its acid content depends chiefly upon:
+
+     (_a_) The kind of timber heated in the retort.
+
+     (_b_) The efficiency of the apparatus.
+
+     (_c_) Condition of the timber as to moisture.
+
+     (_d_) The temperature employed, and rate of working.
+
+     (_e_) The point at which distillation ceases (_i.e._, the duration of
+     interval between commencement of heating and cessation of collection).
+
+Samples received from estates for testing purposes were found to contain
+equivalents varying from 2 per cent. to 10 per cent. of acetic acid.
+
+They were all suitable coagulants when used in quantity calculated from the
+discovered acidity, but produced rubber darker than ordinary when
+air-dried. This effect was not of much importance in the preparation of
+smoked sheets, but to produce a pale crepe it was necessary to employ
+sodium bisulphite as an anti-oxidant.
+
+This darkening in colour is to be ascribed to the presence of traces of
+phenols,[24] which are stated to exert an effect upon the rubber during and
+after vulcanisation.[25] This subject will be discussed in another section.
+
+[24] Whitby, _Journal Soc. Chem. Industry_, vol. xxxv., No. 9, 1916.
+
+[25] See also "Preparation and Vulcanisation of Plantation Rubber" (Eaton,
+Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture,
+April, 1918.
+
+With this provision the crude pyroligneous acid which can be produced on
+estates, could be employed as a coagulant until such time as the price of
+glacial acetic acid was so low as to make the production of the crude acid
+non-profitable. This point would be determined from a knowledge of the cost
+of production per gallon, and the percentage of acetic acid per unit. For
+example, if the cost of production (including cost of timber for
+distillation, cost of fuel for heating the retort, cost of labour, etc.)
+was 60 cents per gallon of crude acid containing 9 per cent. of acetic
+acid, that would be equivalent approximately to buying glacial acetic acid
+at $30 per demijohn of 44 lbs.
+
+SMOKED WATER.--A weak solution of pyroligneous acid may also be obtained
+by passing smoke through water. With this object in view, a machine was
+designed by the Federated Engineering Company of Kuala Lumpur. In this the
+principle of retorting was not employed. Smoke was produced by ordinary
+combustion in a compartment of the apparatus, and was drawn through water
+by the action of a high-speed fan worked by hand. A solution, equivalent in
+effect to a 2 per cent. solution of acetic acid, could be obtained at a
+comparatively cheaper cost than crude pyroligneous acid produced by dry
+distillation as it was then being practised. This was chiefly because of
+the wasteful methods of fuel combustion, in the latter process, in the
+heating of the retort.
+
+CHINESE VINEGAR.--This agent was found to be a satisfactory coagulant, and,
+_a priori_, there is no reason why it should not be suitable, as it is
+essentially a dilute solution of acetic acid.
+
+The qualities sold were generally colourless, and were probably the result
+of acetic fermentation of rice.
+
+Samples tested showed a varying content of acetic acid, ranging roughly
+from 3 per cent. to 8 per cent.; but on this basis of valuation it was
+found generally that the price bore no relation to the degree of
+efficiency.
+
+It was advanced not only that the vinegar was an efficient substitute for
+glacial acetic acid, but that it was also cheaper. This latter claim was
+proved to have no foundation in fact, even at the high price of acetic acid
+prevailing during the period of stress. It is not likely, therefore, that
+vinegar can displace acetic acid, except as an expedient.
+
+SULPHUROUS ACID.--The anti-oxidant effect of sodium bisulphite and sodium
+sulphite is due to the liberation of the gas, sulphur dioxide. This gas
+dissolves easily in water, forming an acid solution called sulphurous acid.
+
+This acid solution is an effective coagulant in fairly small quantity. Not
+only so, but it produces, in addition, the anti-oxidant effect noted in the
+employment of sodium bisulphite. It is thus possible to produce rubber
+varying in shade of paleness by means of a single solution.
+
+In the event of sulphurous acid being used, it would be necessary to
+import cylinders of sulphur dioxide from which the solution could be
+prepared in factories each day. There would be no insurmountable difficulty
+in this, as it is only necessary to pass the gas through a series of closed
+vessels containing water. Enough solution could be prepared at one time for
+three or four days, but preferably the solutions should be as fresh as
+possible. Altogether there would seem to be possibilities in the use of
+sulphurous acid for preparing pale crepe rubbers, providing the cost is
+within comparable limits with the commoner coagulants at present in use,
+and that no adverse effect on the rubber can be shown to result. If the
+cost did not exceed the combined cost of acetic acid and sodium bisulphite,
+the employment of sulphurous acid solution might be worthy of
+consideration. There is one drawback to the use of sulphurous acid
+solution, and that lies in the proximity of the limits of the quantities
+necessary for coagulation and that which is in excess, and prevents
+coagulation. Thus, with ordinary field latex having about 20 per cent. dry
+rubber content, the minimum necessary for coagulation per 100 c.c. of latex
+is about 8 c.c. of a 1 per cent. solution. The maximum quantity possible
+for use is about 15 c.c. of a 1 per cent, solution, so that great care
+would have to be exercised in avoiding an excess of coagulant, otherwise
+coagulation would be effectually prevented.
+
+It is believed that the preparation of rubber by this method is the subject
+of a patent secured by Messrs. Boake, Roberts, and Co., London.
+
+SUGARS.--Coagulation may be effected by the addition of small quantities of
+sugars.[26] These are assumed to be effective by fermentative conversion
+into lactic and acetic acids. The presence of lactic acid is supposed to
+have a twofold effect:
+
+[26] "Preparation and Vulcanisation of Plantation Para Rubber" (Eaton,
+Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture;
+Gorter and Swart, Bulletin No. 6, West Java Expt. Station.
+
+     (_a_) As a direct coagulant.
+
+     (_b_) In its action upon certain organisms which, in the ordinary
+     course of events, would delay or prevent coagulation. Although work on
+     an experimental scale has been done, as far as we know no practical
+     application has been made of the employment of sugars as coagulating
+     agents.
+
+VARIOUS SALTS.--Of experimental interest only it may be recorded that
+coagulation has been effected by means of various chemical "salts"--_e.g._,
+calcium chloride, barium chloride, magnesium chloride, sodium chloride,
+aluminium sulphate, magnesium sulphate, sodium sulphate, etc. None of these
+has been found to have any practical application, except, perhaps, calcium
+chloride, which is used in small quantity as an accelerating agent in a
+special process of anaerobic coagulation, which will receive mention in the
+following chapter.
+
+At one period during the War and the dearth of acetic acid, it was found
+that there were available in England large supplies of the acid sulphate of
+sodium (sodium hydrogen sulphate), which proved to be an effective
+coagulant. Experimental work gave satisfactory results, but no practical
+application resulted when supplies of acetic acid were again obtainable.
+
+VARIOUS PROPRIETARY COMPOUNDS.--We have seen many proprietary coagulants
+advertised and pass into the limbo of forgotten things. They can generally
+be divided into two classes. The first embraces those founded upon a
+woefully incomplete knowledge of requirements. The second covers those
+which meet requirements, but for which exaggerated claims are made and
+excessive prices charged.
+
+As as instance of a substance which fell under both classifications might
+be mentioned the case of "Coagulatex." Pretentious claims were made, and it
+was emphasised that the liquid contained no _vegetable acids_. Acetic and
+formic acids might be quoted as examples of vegetable acids, and as these
+have been shown to be the most satisfactory coagulants now employed one
+fails to imagine where lay the value of the guarantee given by the
+advertisers of "Coagulatex."
+
+On analysis the liquid was found to consist mainly of sulphuric acid,
+against the indiscriminate use of which warnings have been given. Thus it
+was a dangerous substance for common use.
+
+Furthermore, comparing the value with its sulphuric acid content, it was
+found that the price required for "Coagulatex" was roughly four times the
+contemporary cost of commercial sulphuric acid in the Federated Malay
+States.
+
+Those in charge of estates should realise, therefore, that no proprietary
+coagulants should be adopted until a proper report of tests, and a
+comparative valuation, has been obtained from one of the research
+laboratories.
+
+CARBONIC ACID GAS, CARBON DIOXIDE.--Now of only scientific interest, it may
+be noted that some years ago great claims were made for the use of carbon
+dioxide gas as a coagulant. In actual practice we were unable to effect
+coagulation by passing the dry gas into latex. It was suggested that the
+original investigators were misled by failure to secure a dry and clean
+gas. It would appear that probably the gas was prepared by the action of
+hydrochloric acid upon marble or limestone. Unless intervening "washers"
+and "driers" were used, the liberated gas, when passed into latex, would
+carry with it traces of hydrochloric acid, which would effect coagulation.
+
+ALCOHOL.--In the cheap form of methylated spirit, alcohol has been employed
+by us as a speedy coagulant for many years. Latex run slowly into alcohol
+coagulates instantaneously. The method has been in common laboratory use.
+
+The employment of alcohol has also been made the part-subject of a patent
+process of coagulation, to which reference will be made in the succeeding
+chapter.
+
+VEGETABLE EXTRACTS.--At various times experimental work has been directed
+towards the use of liquids of purely vegetable origin, such as the juices
+of tropical fruits, and of a waste product of tropical industry--the
+so-called "milk" (or water) of ripe coconuts.
+
+In the former class there is usually a natural acidity, but in coconut
+water the acidity is chiefly the result of fermentation of the carbohydrate
+(sugar) constituents.
+
+These substances were all found to effect a more or less satisfactory
+coagulation, but it is unlikely that they would be suitable for practical
+application on a large scale.
+
+As being more directly related to the subject of coagulation in general
+than to coagulants in particular, a discussion of several special processes
+will be relegated to the ensuing chapter.
+
+
+
+
+CHAPTER XX
+
+_SPECIAL METHODS OF PREPARATION_
+
+
+Every year appears to bring forth some new ideas in the mode of rubber
+preparation. Some of them are based in principle upon the oldest known
+method--_i.e._, the native Brazilian process of making "Hard Para." Others
+strike a new note, and in a few cases the claims put forward are
+substantially confirmed by results. In other instances the claims are too
+pretentious, and discredit may be brought upon schemes which, although
+lacking in comparative success, are yet commendable for the ingenuity
+manifested.
+
+To the present not one of these new methods has been able to compete to any
+marked degree in general practice with the established methods of ordinary
+preparation. A few continue to find local application, but most have either
+been abandoned or are gradually falling into desuetude.
+
+We do not propose to discuss in fine detail all the various claims made on
+behalf of these special processes, or to enter into controversies. The aim
+is to present to the reader an outline embodying the main principles and
+advantages claimed.
+
+DA COSTA PROCESS.--Briefly, this was a method by which coagulation was
+effected with smoke. The smoke was generated by the combustion of wood in a
+special compartment, and was forced into latex by means of a jet of steam.
+It was really only applied to the preparation of coagulum intended for
+crepe form. The exact degree of coagulation effected was uncertain, and the
+final colour of the rubber precluded it from being classed as a modern No.
+1 product.
+
+"BYRNE CURING" PROCESS.--This is a process for treating coagulum obtained
+by ordinary methods.
+
+It was the subject of a patent obtained by Messrs. E. J. and F. A. Byrne,
+and at one time had a considerable vogue on estates. The chief claim
+advanced was that the rubber produced was in all respects equal to Fine
+Hard Para, and could be shipped while still moist without detriment to the
+physical qualities.
+
+The principle of the process was the treatment of coagulum, in either sheet
+or thick crepe form, with vapours produced by the volatilisation of two
+special fluids. This treatment was undertaken in comparatively small wooden
+sheds, in which the coagulum was placed. The "smoke" was conducted into the
+curing sheds from furnaces outside the building. The sheds were covered
+externally with "felt" material to prevent leakage of the vapours, and a
+very dense smoke was obtained.
+
+The furnaces were specially designed, and consisted essentially of a
+"hot-plate" heated by a powerful kerosene blast-flame. On top of the
+machine were two reservoirs controlled by taps. In these were placed the
+special fluids which were released in definite proportion. The composition
+of the fluids was not divulged, but it is assumed that the principal
+ingredients were (_a_) wood tar products, (_b_) crude pyroligneous or
+acetic acid. The mixture of these, dropping on the hot plate at the correct
+temperature, spontaneously volatilised, to form dense whitish fumes, having
+an intense and not disagreeable odour of wood combustion. A duct led from
+the back of the machine into the curing-shed, where the vapours were
+distributed through perforations in the pipe.
+
+The coagulum usually remained under treatment in the shed for three to four
+hours, and then was removed for ordinary air-drying. When taken from the
+curing-shed it had a pinkish colour, which later developed into a dark
+brown by a natural process of oxidation. The exterior of the rubber, on
+shipment, resembled the appearance of smoked sheets; while the interior, on
+cutting, was seen to be still white. As packed for shipping, the rubber
+contained from 10 to 15 per cent. of original moisture, for the usual sheet
+form, and even more when "slab" rubber was prepared.
+
+Originally either crepe or sheet rubber was made, but later the preparation
+of the crepe form was displaced largely by "slab" rubber. These "slabs"
+were really very thick sheets, which had been subject to only slight
+pressure.
+
+Still later the preparation of the "slab" form was displaced by "loaf"
+rubber. This form was built up by winding together ordinary thin sheets
+which had been subject to the "cure." Only slight tension was needed,
+during the operation of winding, to cause close adhesion of the component
+wet layers, and the final result was a "loaf" or roll dark in colour, and
+apparently dry when examined superficially. On being cut, even after an
+interval of months, the middle portion was still so moist as to be quite
+white.
+
+In course of time it was discovered that all the claims made for the
+process could not be substantiated, and for various reasons (which need not
+be detailed) most of the estates which had adopted the scheme reverted to
+ordinary methods of preparation. At the time of writing few, if any,
+continue to work the process. It appears to be agreed, as the result of
+investigations, that in no degree does the process yield advantage over
+ordinary methods.
+
+FREEZING PROCESS.--A patent was secured a few years ago to cover a process
+whereby coagulation was effected by refrigeration.
+
+Latex remained for several hours in the refrigerating chambers of an
+ordinary ice-making plant. The resulting solid mass, on being thawed,
+yielded a coagulum appearing in no way to differ from that obtained by
+ordinary methods of coagulation.
+
+Provided the process exerted no influence for good or evil upon the quality
+of the resulting dry rubber, the value of it would appear to depend upon
+the relative cost of working, plus considerations of capital expenditure
+and depreciation on the plant. At the present time it would be difficult to
+imagine that the cost of preparation alone would compare favourably with
+that sustained by ordinary coagulative methods.
+
+Furthermore, beyond the expensive refrigerating plant, the usual machinery
+of a factory would still be required if the ordinary market demands are to
+be met.
+
+Finally, it has not been found[27] that any advantage in the final physical
+qualities of the rubber is obtained by the employment of this process.
+
+[27] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture.
+
+WICKHAM PROCESS.--This process, invented by Sir Henry Wickham, aimed at the
+production of a rubber resembling Fine Hard Para. The principle employed
+was that underlying the preparation of the best rubber in Brazil--viz.,
+coagulation of superimposed thin layers of latex by the action of smoke and
+heat.
+
+In essential the machine employed consisted of a rotating drum into which
+latex and smoke entered. The result was the formation of thin "skins" of
+rubber which, coagulating _in situ_, formed a mass corresponding to "Fine
+Hard."
+
+That the rubber was fully satisfactory as to quality is acknowledged, but
+economically and in practical utility the process was unsuccessful, the
+rate of output being so low.
+
+DERRY PROCESS.--The invention of Mr. R. Derry, late of the Singapore
+Botanic Gardens, this in principle resembled the Wickham and other
+processes. It aimed at a mechanical imitation of the native method of
+producing Fine Hard Para.
+
+In place of the rotating drum, an endless belt was used. This travelled
+over pulleys, more or less horizontally placed. The upper of these could be
+raised to varying height above the level of the other, and likewise could
+be so adjusted as to tighten the belt.
+
+The under layer of the belt impinged, in its travel, upon the surface of a
+layer of latex contained in a shallow tray. The belt was operated by
+hand-power, and the height of the latex trays was adjustable.
+
+The trays of latex were situated at the lower end of the machine which lay
+outside the smoking-chamber. It will be understood that the vastly major
+part of the total length of belt was always within the chamber.
+
+Smoke was generated by combustion of wood in an external structure, was
+brought into the chamber by a wide duct, and was then distributed below
+the belt by means of perforated pipes.
+
+The thin film of latex picked up by the belt was coagulated partly by the
+action of smoke constituents by evaporation due to heat. Assuming (1) that
+the belt was of adequate length, (2) that the rate of travel was not
+excessive, (3) that the latex was not too dilute, (4) that the temperature
+of the smoke was sufficiently high, (5) that the smoke was sufficiently
+dense and not too damp--then the process should be a continuous one.
+
+It will be clear that success could only be obtained by a careful
+adjustment of all these factors. The latex must, necessarily, be of a
+fairly rich consistency (at least 2-1/2 lbs. dry rubber per gallon), but
+unfortunately there is considerable difficulty in maintaining such latex in
+a state of fluidity for the period demanded by this process, without loss
+of latex. Naturally, the addition of an anti-coagulant would retard the
+rate of output of the machine to a marked degree.
+
+The layer of rubber thus formed on the belt was stripped off, and hung for
+further air-drying, as it still contained a fair percentage of moisture.
+
+As a really practicable method for treating plantation latex, the process
+failed by reason of its low rate of output over a given interval. This
+alone was sufficient to condemn it, apart from the facts (1) that it was
+not shown to be a cheaper method than coagulation by acetic acid, (2) that
+the resulting rubber was not proved to be of superior intrinsic value to
+rubber prepared by ordinary methods.
+
+SPONTANEOUS COAGULATION.--All readers will be aware of the phenomenon of
+the curdling or souring of milk. The behaviour of _Hevea_ latex, under
+certain conditions, may be taken to be analogous. Difficulty is experienced
+in maintaining fluidity--a difficulty which appears to vary in great degree
+according to locality, nature of soil, age of trees, the relative demand
+made upon the trees by the system of tapping employed, etc.
+
+It is sometimes found, before the latex reaches the store, that it may
+exhibit one of various stages of premature (spontaneous) coagulation:
+
+     (_a_) To all appearances it may be quite fluid, but a close
+     examination shows it to consist mainly of a serum containing very
+     minute particles of rubber in suspension (microscopic coagulation).
+
+     (_b_) In a later stage these particles coalesce to form larger
+     "flocks" (macroscopic coagulation).
+
+     (_c_) The whole, or practically the whole, of the latex may have
+     coagulated, forming one mass of rubber with a milky residual serum.
+
+Passing from this aspect of the question, it may be noted as peculiar facts
+that:
+
+     (1) A shallow layer of latex is less likely to coagulate spontaneously
+     (_i.e._, without the addition of a coagulant) than a deeper volume.
+
+     (2) The shallow layer, and also the surface of the deeper volume
+     (where exposed to air), on standing will be found to develop a
+     superficial film of finely coagulated particles, yellowish in colour,
+     and having an offensive odour due to decomposition of protein matter.
+
+     (3) While this partial coagulation is confined only to the surface of
+     a shallow layer of latex, it will be found that below the surface film
+     of the deeper volume a much more definite coagulation has taken place.
+     The coagulation will be practically complete, and the coagulum, apart
+     from a spongy appearance, is normal in character. This coagulum is
+     free from the offensive odour noted above.
+
+     (4) On testing the surface film of both the shallow layer and the
+     deeper volume, it will be found to be _alkaline_ in character; whilst
+     the lower liquid surrounding the main portion of the coagulum in the
+     deeper volume of latex is of an _acid_ nature.
+
+These observed facts are sufficient to indicate that there are apparently
+_two distinct types of spontaneous coagulation_, and that the latter takes
+place particularly where the latex is more or less out of contact with the
+atmosphere. We may, therefore, differentiate thus:
+
+     (_a_) _In contact with air (aerobic)_: incomplete spontaneous
+     coagulation, accompanied by yellowish slime, offensive in odour and
+     alkaline in character.
+
+     (_b_) _Out of contact with air (Anaerobic)_: Practically or wholly
+     complete. There is no offensive odour under normal conditions and the
+     serum is acid in character.
+
+It is concluded[28] that there are present in latex, on collection in the
+field, two types of organisms. Those which work in contact with air
+(aerobic) show a tendency to _prevent_ coagulation and to form an alkaline
+yellow slime on the surface of the latex. The others, which work in the
+absence of air (anaerobic), may, under favourable conditions, cause
+complete coagulation unaccompanied by any decomposition or offensive odour
+within a normal period. If air is rigidly excluded, the coagulum obtained
+is quite satisfactory for all purposes.
+
+[28] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918; "De la
+Coagulation naturelle du Latex d'Hevea Brasiliensis" (Denier and Vernet),
+_Comptes Rendus l'Académie des Sciences_, No. 3, July, 1917.
+
+This type of coagulation, without the employment of a chemical coagulant,
+and under anaerobic conditions, was the subject of a patent granted in 1914
+to Messrs. Maude, Crosse and others. The process has been in use on Cicely
+Estate (Perak) for some years. With subsequent slight modifications the
+apparatus consisted in essential of a tank with a loose cover. The flanges
+of the cover were sufficiently long to dip into a water-seal surrounding
+the tank. Thus the cover may rise and fall without an inrush of air.
+
+Coagulation, in fact, can be effected thus in any kind of air-tight
+receptacle; and experimentally the reader can obtain a satisfactory result
+by filling completely with latex the bottle which has a loose stopper.
+
+Under the patent held the coagulum may be prepared either for crepe-making,
+or for sheets by a modification of the tank.
+
+The crepe when dry does not have the bright appearance of the ordinary
+"Fine Pale" standard prepared with the aid of the anti-oxidant sodium
+bisulphite.
+
+Unfortunately the addition of this substance to the latex in normal
+proportions is not possible under anaerobic conditions, as it is found to
+prevent coagulation, probably owing to its sterilising effect upon the
+anaerobic organisms.
+
+To prevent the oxidation of the rubber in actual practice, the freshly
+prepared crepe is soaked in a solution of sodium bisulphite before hanging
+to dry. The resulting colour of the rubber is quite good.
+
+It was shown by Eaton and Grantham that anaerobic coagulation is slightly
+uncertain in action. Owing probably to variations in the composition of the
+latices, or to the extent of infection by organisms, coagulation may one
+day be complete and on other days less satisfactory.
+
+They found further that, by the addition of small quantities of sugars,
+coagulation under both aerobic and anaerobic conditions was improved. The
+conclusion formed was that the addition of sugars created a medium
+favourable to the development of anaerobic organisms and unfavourable to
+those which cause decomposition of the natural nitrogenous constituents of
+latex.
+
+This work was confirmed by Gorter and Swart,[29] who attributed the action
+to the conversion of sugar to lactic, acetic, and succinic acids by
+fermentation.
+
+[29] Gorter and Swart, Bulletin No. 6, West Java Station.
+
+Denier and Vernet, whose work has already been mentioned, studied the
+presence of the organisms in latex, and succeeded in isolating one which,
+under anaerobic conditions, effects coagulation within twenty-four hours.
+Sometimes to produce complete coagulation it was found necessary to employ
+small quantities of sugars--_e.g._, 1 gramme per litre of latex (1:1,000).
+
+It is to be noted also that the addition of small quantities of soluble
+calcium (lime) salts to latex has much the same effect as the employment of
+sugars. Recent investigations[30] showed that the addition of 0·5 to 1
+gramme of calcium chloride per litre of latex caused complete coagulation
+in closed vessels within twenty-four hours, a result agreeing with the
+findings of Barrowcliff.
+
+[30] "Archief voor de Rubbercultuur," Nederlands Indies, 1920, 4, 273.
+
+On page 308 of the same publication, experiments on the effect of sugars
+are described, in connection with _aerobic_ coagulation. Observations from
+a further set of experiments tended to indicate a direct connection between
+the effects of tapping and spontaneous coagulation. It is suggested that
+heavy tapping causes a diminution in the latex of those substances which
+act in some way as accelerating agents in coagulation--_e.g._, sugars. The
+smaller the proportion of these substances, the slower and less complete is
+natural (spontaneous) coagulation.
+
+ILCKEN-DOWN PROCESS.--This process is the subject of patents granted in
+1915 to Messrs. Ilcken and Down. It has been in fair prominence, and has
+been tried experimentally on several estates and in public demonstration.
+
+It is a coagulating process, and, in the original specification, employed
+as agents a mixture of alcohol (in the form of methylated spirit) and
+benzene (petrol), or alcohol with petrol and coal-tar naphtha. The mixture
+was injected in the form of a fine spray into the latex, contained in a
+tank specially fitted with paddles.
+
+Later modifications covered the addition of a small quantity of glycerine;
+or, failing supplies of that substance, coconut oil.
+
+Many advantages are claimed for the process, but most of them cannot be
+substantiated. The two chief claims are:
+
+     1. The production of a uniform standard of rubber.
+
+     2. The obtainment from a unit volume of latex of a greater weight of
+     rubber than can be obtained from an equal volume of the same latex by
+     ordinary coagulation with acetic acid. It is to be inferred that the
+     agents employed have the power of adding to the coagulum some of the
+     substances which usually remain in solution in the clear serum.
+
+Regarding the first of these claims, it has been shown[31] that the rubber
+is not uniform in its behaviour on vulcanisation, and that its variability
+is similar to that of rubber prepared by other processes.
+
+[31] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918.
+
+The second claim has been the subject of much controversy. Experiments made
+on estates under the supervision of, or in the absence of, the patentees
+have given conflicting results. When varying factors have been eliminated,
+the general conclusion was that no increase in weight of rubber was
+obtained.
+
+Private laboratory investigations led to a similar verdict, and Eaton[32]
+records a confirmatory finding. More recently the claims made for the
+process were investigated in Java[33] under varying conditions. Three
+series of experiments were made:
+
+[32] _Ibid._
+
+[33] "Archief voor de Rubbercultuur" (De Vries and Spoon), Central Rubber
+Station, Java, May, 1921.
+
+     (1) During the rainy monsoon and at a height of 1,800 feet.
+
+     (2) During the dry monsoon on a low-country estate.
+
+     (3) In the experimental gardens at Buitenzorg during bright sunny
+     weather and the most favourable conditions.
+
+The agents used were (_a_) a mixture of alcohol and fusel oil, (_b_)
+alcohol and petrol (benzene).
+
+In these experiments no advantage in weight of rubber was obtained by the
+Ilcken-Down process, and it would thus appear that the principal claim
+fails to be substantiated.
+
+The general composition of the rubber was approximately the same as
+ordinary crepe obtained from undiluted latex. The rubber on vulcanisation
+was found to be normal in behaviour, and was similar to the controls.
+
+The coagulum ordinarily is affected by oxidation, and does not produce a
+fine pale crepe. To remedy this defect the freshly prepared crepe is soaked
+in a solution of sodium bisulphite and sulphuric acid.
+
+It may be noted that in the recent experiments coagulation was effected in
+vacuum in a specially designed wooden tank. From a study of the previous
+section on "Spontaneous Coagulation," the reader will perceive that results
+equal to those obtained by the Ilcken-Down process can be obtained
+_without_ the necessity of using such agents as alcohol, petrol, or fusel
+oil.
+
+SLAB RUBBER.--This type of preparation has been the subject of much
+discussion of recent years. There is nothing really special in the mode of
+preparation, and in its original form "slab" rubber is only a thick sheet
+which may be obtained by coagulation with acetic acid or other agents.
+
+The coagulum, when removed from the serum, is subjected to comparatively
+slight pressure, and the "slab" thus made is either placed to air-dry at
+once, or may be subject to treatment in other liquids before drying.
+
+The rubber is not allowed to remain until wholly dry, but is shipped while
+still containing an appreciable percentage of enclosed moisture.
+
+It is claimed[34] that the production of "slab" rubber by standardised
+methods eliminates to a great degree the variability which at present
+characterises plantation rubber, and that a fast-curing medium is obtained.
+These claims will be discussed in later chapters dealing with the
+vulcanisation of rubber, and demand no notice in this section.
+
+[34] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918.
+
+From the producers' point of view, it may be noted that the preparation of
+slab rubber is a simple process, but not altogether as pleasant probably as
+might be desired, when undertaken in crude form.
+
+The appearance of the partially dry slabs is unattractive, but that does
+not signify if the quality of the vulcanised product satisfies
+requirements.
+
+For the average producer, the difficulty lies in having to meet the demands
+of the general market. Even, therefore, if one assumes that the intrinsic
+qualities of slab rubber are all that the claims advance, it would be
+necessary for the producer to be assured of definite and regular sales.
+
+At present it would probably be fair to state that practically all the
+"slab" rubber being prepared is produced by those who are also consumers.
+They are thus in the enviable position of being able to satisfy their
+requirements as to the mode of preparation. Until such time, therefore, as
+there exists a regular demand for "slab" rubber in the general market, the
+vast majority of estates must proceed on ordinary lines of preparation.
+
+
+
+
+PART VI
+
+VULCANISATION
+
+(BY DR. H. P. STEVENS)
+
+
+
+
+CHAPTER XXI
+
+_INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION_
+
+
+In the foregoing chapters the methods of treating latex, coagulating,
+rolling and curing, or drying, have been described in great detail. These
+details will give the reader some idea of the precautions taken, and
+procedure necessary to produce rubber which will be acceptable to the
+market. The expressions "inferior rubber," "defective crepe," "poor quality
+sheets," etc., are frequently met with, but these expressions must not be
+taken to indicate any defect in the rubber for manufacturing purposes, but
+merely that the rubber is defective for selling purposes--that is to say,
+being unsightly, it will not fetch the full market price.
+
+Raw rubber, as produced on the plantations, is almost invariably subjected
+to the process of vulcanisation in the production of manufactured rubber
+articles as we know them. Previous to the advent of plantation rubber, the
+raw material was purchased by the manufacturer in a moist and impure
+condition; frequently the rubber was adulterated with sand, dirt, and even
+small stones. Consequently it was the invariable practice of the rubber
+manufacturer to wash the raw rubber and convert it into crepe, which was
+then hung and air-dried before use. The effect on the rubber, if of high
+grade, was more severe than the washing and crepeing process on the
+plantation, because the rubber was not a soft coagulum but generally dried
+on the surface and semi-hard. The power required was considerable, and the
+resulting crepe was consequently softer and more susceptible to heat than
+plantation first latex crepe. Much of the "wild" rubber was soft and tacky
+and inferior to "earth-scrap."
+
+Vulcanising in its simplest aspect consists in mixing the rubber with
+sulphur and heating the product under regulated conditions. The effect of
+heat on the inferior grades of "wild" rubber is very marked. A soft,
+sticky, and resinous material is transformed into a relatively tough and
+elastic product. The effect of vulcanising on the better grades is less
+marked, but immediately apparent. On the other hand, the effect of
+vulcanising is least apparent on first latex plantation grades, because in
+these we have a raw rubber prepared in a manner best suited to retain its
+natural characteristics.
+
+The need of vulcanising in the process of manufacturing rubber goods became
+an axiom in pre-plantation days, and it is only quite recently that
+attempts have been made to utilise raw rubber directly, without
+vulcanisation, particularly for shoe soles. For this purpose a thick dense
+crepe has been found satisfactory. Smoked sheet rubber is not generally
+suitable, apparently owing to its microphysical structure. It is possible
+that the process of rolling in the making of dense crepe compacts the
+rubber particles, yielding a harder and more resilient product. The rolling
+must not be carried too far, or the "working" of the rubber will
+approximate to a preliminary mastication, and the product will be weakened.
+
+The utilisation of crepe rubber directly has not yet been sufficiently
+tested to enable a definite conclusion to be reached as to its future
+scope, but it is obvious that for use in a raw state some modification in
+preparation may be advantageous. The present method--_e.g._, coagulation
+with acetic acid--does not yield the hardest and toughest rubber.
+
+Hardness and toughness are actual drawbacks in the utilisation of rubber
+which is required for vulcanising. When the output of plantation rubber
+began to increase and to displace the inferior wild sorts, manufacturers
+complained of the increased power consumption of their machines. The power
+was required mainly to "break down" or "mill" the rubber preliminary to the
+mixing with sulphur and other ingredients. It is obvious that a material
+such as raw rubber cannot be mixed with powders such as sulphur with a
+pestle and mortar, or in any simple form of mixing machine. This difficulty
+was overcome by the earlier experimenters by immersing the rubber in a bath
+of molten sulphur. The latter was gradually absorbed and "dissolved" in the
+rubber, and the heat of the bath caused the dissolved sulphur to combine
+with the rubber to produce vulcanised rubber. The limitations of such a
+process are apparent. Thus the vulcanised rubber retains the form in which
+it was originally shaped. Moreover, other ingredients, such as mineral
+matters, cannot be dissolved or absorbed by the rubber in this manner. The
+method eventually adopted consisted in "breaking down," "milling," or
+"masticating" the rubber by passing it continuously between differentially
+geared steam-heated rollers. By this means a high-grade rubber is converted
+into a soft, plastic mass, which will "take up" sulphur, mineral matter,
+and other ingredients as desired. The mixing operation may be carried
+through on the same roller machine as was used for breaking down the
+rubber, or separate machines of other designs may be adopted. Details of
+the process will be found in books dealing with rubber manufacturing.[35]
+It will suffice here to explain that when rubber is kneaded between two hot
+rollers moving at different speeds the rubber forms a continuous band
+around the slower moving roller, and if the distance between the rollers be
+adjusted the excess of rubber held back by the nip of the rollers will form
+a "bank" or moving wedge-shaped mass on the top of the nip. This closes the
+space between the rollers, so that sulphur and powder placed on the rubber
+pass round towards the nip, and are there driven into the rubber. In this
+manner it is easy to mix, say, 10 per cent. of sulphur into the rubber
+without a single particle falling through. In technical mixes where large
+quantities of powders require to be mixed there is always some caking, and
+part of the powder falls between the rollers into a tray underneath. This
+is swept up with a broom and put back on to the rollers, the process being
+repeated until the whole of the ingredients have been incorporated.
+
+[35] For instance, "India-Rubber and its Manufacture," by H. L. Terry.
+
+From this description it follows that, preliminary to mixing, it is
+necessary to thoroughly masticate or "plasticise" the raw rubber. Much of
+the "wild" rubber was of so inferior a quality that it very readily broke
+down, and but little mastication was necessary. It was soft and resinous,
+and readily took up the powders which were to be mixed with it. The better
+grades of wild rubber, such as Fine Para, were more difficult to break
+down, but not so difficult as most plantation rubber, because they had
+already received a preliminary "working" in the process of washing and
+crepeing, and we have already explained that such treatment takes more
+power than the crepeing of the soft moist coagulum on the plantations. The
+amount of "working" or "plasticising" produced in the rubber is connected
+with the power expended; the greater the expenditure of power, _caeteris
+paribus_, the greater the working effect on the rubber. Although the
+manufacturers possessed a relatively soft rubber in the form of washed Fine
+Para, it was customary in most cases to employ this rubber in conjunction
+with washed lower grades to produce a soft plastic material for further
+treatment. Now, however, the manufacturer has little else but plantation to
+deal with, and most of it more difficult to break down than washed Para
+crepe. This is the reason why a hard, tough rubber is no longer a
+desideratum with manufacturers, although originally taken as an indication
+of good quality. For the majority of purposes they want something which
+will break down easily. Hence if a rubber could be produced answering to
+these requirements, without loss of vulcanising quality, it would be
+preferred.
+
+Having incorporated sulphur and other ingredients, the plastic mass is
+sheeted and run between layers of calico to prevent the superimposed sheets
+from adhering. From this "calendered sheet" the article, whatever it may
+be, is built up. The calender rollers are heated so as to keep the rubber
+compound plastic. There is a limit to the thickness of the sheet which can
+be produced. It is a difficult operation to perform satisfactorily so as
+to yield a smooth surface and a sheet free from enclosed air. When cool the
+rubber hardens and is readily handled. The object to be manufactured is
+then built up from the calendered sheet. Thus in the manufacture of a motor
+tyre the tread is built up on the casing or carcase by laying the sheets on
+the canvas and rolling these with a hand or power operated roller, so that
+they adhere firmly, the first layer to the canvas of the casing and
+subsequent layers to one another. This rough description will suffice to
+illustrate how important it is that the rubber when mixed should be plastic
+enough to give a smooth sheet, and to allow the sheet to be manipulated in
+building up the article in process of manufacture. The testing of rubber in
+regard to its plasticity and power to absorb finely divided mineral matter
+will be discussed in a later chapter. We may, however, point out here, that
+the mineral matter is not generally added as an adulterant, but because of
+certain specific properties it confers on the product.
+
+To proceed with our outline of vulcanisation, we have now arrived at the
+stage at which the goods are built up and ready for vulcanising. For this
+purpose they are generally enclosed in some manner, either in metal moulds
+bolted together, or tightly wrapped in cloth, as, _e.g._, in the
+manufacture of inner tubes, hose, etc. In the latter case, you can detect
+the cloth mark on the finished product. Sometimes the rubber is
+spewed--that is, driven out of a barrel by means of an endless screw
+revolving in it. In this way rubber tubing, perambulator tyres, and such
+articles, may be made. More recently even tyre treads and the shaped rubber
+for band tyres (heavy solid tyres) have been extruded in this manner, for
+the process is much cheaper than building up a tyre from calendered sheet,
+and then cutting the mass to shape by hand. But for spewing the rubber mass
+must be very soft and plastic; this condition is not obtainable unless the
+raw rubber originally used can be made thoroughly plastic without damage.
+Nor can it be effected with a rubber mass containing much finely divided
+mineral matter, as this hardens the mixture.
+
+For other purposes the rubber is swollen in a solvent, such as coal-tar
+naphtha, and subsequently masticated; the soft dough is then shaped or
+spread on cloth, and vulcanised after allowing the solvent to evaporate.
+Here, again, the properties of the raw rubber are of immense importance.
+Thus, the more plastic the dough, the less solvent required, and the less
+there is to drive off before vulcanising. The plasticity of the dough will
+depend on the plasticity of the raw rubber, and so forth. It is evident
+that the physical properties of the raw rubber are of great importance.
+They directly affect the manufacturing operations up to the vulcanising
+stage, and indirectly affect the results obtained on vulcanising.
+
+The actual vulcanising consists of heating the mass of mixed rubber for
+a definite time and at a definite temperature, each "heat" being chosen
+to suit the particular mixture. These data are arrived at
+empirically--that is, by trying a number of "heats" and choosing that
+which appears the most suitable. The suitability will depend on the
+nature of the article, the service to which it is to be put, and the
+time it is intended to last. All vulcanised rubber goods, whatever the
+process, have a limited life or period during which they can be relied
+on to give useful service. After a time, vulcanised rubber tends to
+harden, cracks appear on the surface when the article is bent or
+stretched, and eventually the rubber becomes rotten and "perished." This
+tendency varies with the quality of the original raw rubber and the
+conditions of vulcanising. Before plantation rubber was available, the
+manufacturers were dependent on inferior wild grades for a great part of
+their output, and, consequently, the goods made from these inferior
+rubbers never showed very good mechanical properties and soon
+deteriorated. The severest critics of plantation rubber have admitted
+the advantages to the manufacturers of the replacement of the lower wild
+grades by plantation rubber.[36] But even the best grades give a
+vulcanised product which rapidly deteriorates if the vulcanisation is
+carried too far. This results from too long heating, or too high a
+temperature, and the product is termed "overvulcanised" or
+"overcured."[37] The appearance of the product is deceptive, as the
+physical properties are remarkably good if the overvulcanising is not
+more than 50 to 100 per cent. in excess of the normal cure. Only in the
+case of very much overvulcanised rubber do we obtain a product which is
+brittle from the beginning.
+
+[36] See Williams, "The Rubber Industry," 1914, p. 284. It must also be
+remembered that the inferior wild grades were derived from latices often
+containing a large proportion of "resinous" matter, and which could not
+yield a really high grade of vulcanised rubber whatever the care and skill
+employed in preparation.
+
+[37] The terms "curing" and "vulcanising" are generally employed as if
+synonymous. Twiss has suggested that the former be applied in regard to a
+change in physical properties, and the latter to the chemical change
+whereby sulphur is combined with the rubber. The term "curing" is also
+applied to the process of preparation of raw rubber. This must be kept in
+mind so as to avoid confusion.
+
+The degree of vulcanising will vary with the type of article to be
+produced, and where a long life is desired, the tendency will be to
+"undervulcanise"; but if the best mechanical properties are desired, the
+tendency will be towards "overvulcanising," or, more correctly, "fully"
+vulcanising. These considerations are aptly illustrated by reference to
+pneumatic tyres. The inner tube need not possess high tensile strength,
+provided that it is easily distensible, for the reason that, during use, it
+is protected by the casing of the tyre proper, which confines and supports
+it against the air-pressure applied. Inner tubes are therefore cured to
+give a long life without developing the maximal physical properties. On the
+other hand, the casing and tread of the tyre are required to withstand
+severe mechanical conditions--particularly the constant flexing of the
+cover, and the abrasion of the road surface. Tyres are not stored for any
+long period, and, when put into service, have a limited period of useful
+life. Consequently it is needful to develop maximal mechanical properties,
+and vulcanisation is therefore carried further than in the manufacture of
+inner tubes.
+
+The rate of cure is controlled by a number of factors in addition to the
+period and temperature of vulcanisation, in particular by the proportion
+and nature of the other ingredients, especially sulphur and accelerators,
+and also by the rubber itself. The main complaint as regards plantation
+rubber is that it varies excessively in this respect. This matter will not
+be discussed here, but is only introduced in order to explain the
+importance of a constant rate of vulcanising to the manufacturer.
+Plantation rubber should, therefore, be prepared so as to be as uniform as
+possible in this respect, and the earlier part of this book gives full
+details of the precautions advised, and in many cases adopted on the
+plantations. Unfortunately, it is impossible to secure uniformity of
+methods among all producers, even when they are Europeans, to say nothing
+of the native producers, who account for perhaps one-third of the output.
+Hence the importance of branding the rubber whenever possible, so that the
+manufacturer may identify the rubber he purchases. If found satisfactory,
+he can then secure further supplies from the same estate.
+
+
+
+
+CHAPTER XXII
+
+_TESTING OF PLANTATION RUBBER_
+
+
+This subject may be subdivided into (_a_) Tests on the raw rubber; (_b_)
+tests on the vulcanised rubber.
+
+The tests on the raw rubber may be carried out (1) on the sample of sheet
+and crepe as received. For this purpose the rubber is cut into a strip,
+which is clamped between grips and gradually stretched to breaking-point.
+The ring testing machine can be adapted for this purpose by replacing the
+rollers with clamps. As the thickness of the samples to be tested will
+vary, it is advisable to cut the strips of such a width that the
+cross-sectional area of all test pieces is the same--say, 40 sq. mm. The
+method is applicable to both sheet and crepe rubber. (2) Tests may be made
+as to the behaviour of the rubber during milling or mastication. Small
+batches are milled under uniform conditions, preferably in an enclosed
+masticator such as Baker and Perkins supply. The power taken (as measured
+by the current taken to drive the motor actuating the machine) and the time
+are recorded. A further test may be applied to the milled or masticated
+rubber, to ascertain the amount and the time taken to incorporate a finely
+divided mineral matter, such as carbon black, zinc oxide, or one of the
+refined clays.[38] The results are not very exact, and the difference in
+plasticity and dryness noted are usually less than found when working with
+full-sized machines in the factory. (3) The rubber, either raw or
+masticated, may be "dissolved" in a "solvent," such as benzene, and the
+viscosity of the "solution" measured. Generally speaking, the less viscous
+the solution, the more plastic the rubber.
+
+[38] Bulletin Rubber Growers' Association, January, 1921, p. 43; August,
+1921, p. 340.
+
+The testing of vulcanised rubber has been treated in such detail in the
+recent works of Whitby[39] and De Vries[40] that a few special points only
+will be dealt with here. The preparation of samples for testing involves
+first the sheeting of the mixture of rubber, sulphur, and other
+ingredients, if any. The sheets may be 1 to 2 mm. thick. They are soft and
+adherent, and must be kept between layers of calico to prevent adhesion. A
+sheet of rubber is then built up by laying three or four sheets evenly upon
+one another, and pressing together to form a sheet 5 mm. thick. The thick
+sheet is then roughly cut to shape and vulcanised in a mould by heating in
+steam under pressure. From the vulcanised sheet so obtained the rings for
+testing are cut (45 mm. internal diameter. 5 mm. face, and 4 mm. thick).
+Rings obtained in this manner will not vary in diameter or thickness
+(reckoned as sections of a tube), as these are controlled by the size of
+the punch, but will vary a little in the face, as this is controlled by the
+thickness of the sheet, which depends on the completeness with which the
+mould is closed. More recently smaller moulds have been adopted, one mould
+for each ring, and an annular space for moisture to develop a pressure
+during vulcanising and prevent porosity. The moulds are vulcanised in an
+oil bath, or oven of some description, in which a constant temperature is
+maintained. I have adopted for some years a third method. The principle is
+that used in the factory for making annular-shaped rubber articles, such as
+washers, rings, elastic bands, etc. An aluminium mandrel, 45 mm. external
+diameter, is taken, and the thin rubber sheet is wrapped round this, so as
+to build up a tube about 4 mm. thick, the surplus rubber is cut off, and
+the edge bevelled with a wet knife. The manipulation will vary somewhat
+with the type of compound to be treated; thus, in some cases, it is
+sufficient to well roll the tube with a hand roller to secure adhesion. In
+other cases it is better to wipe the sheet of compound with a rubber
+solvent previous to rolling. In the latter case time must be given for the
+solvent to evaporate before vulcanising. The tube is next tightly wrapped
+in wet cloth, and is then ready for the vulcaniser. Or the tube may be
+enclosed in moulds which form an outer circular shell and take the place of
+the cloth, but for most purposes, and in particular for the rubber-sulphur
+mixing usually employed, it is sufficient to use cloth to obtain even and
+regular tubes. The tube, after vulcanising, is slipped on to a wooden
+mandrel and cut into rings on a lathe. Of these rings the internal diameter
+is constant, for this is formed on the mandrel, also the face, which can be
+cut accurately in the lathe, but the external diameter, and consequently
+the thickness, may vary a little.
+
+[39] "Plantation Rubber and the Testing of Rubber."
+
+[40] "Estate Rubber."
+
+It appears, therefore, that all methods result in rings of approximately
+the correct size, and it is usual to check, and, if necessary, make an
+allowance for variation in dimensions. It is not possible to do this, even
+approximately, with soft rubbers, as the rubber gives under the pressure of
+the micrometer. No doubt a photographic method would give more accurate
+results, but would take too long. I have found that a very close
+approximation is obtainable by weighing the rings as the specific gravity
+of the standard rubber mix is known. It is not necessary to weigh each
+ring, but the whole five or ten taken for testing may be weighed together.
+
+The next point that arises is the choice of a formula for the test mix.
+Practically all the work to date has been carried out on mixtures of rubber
+with 7 to 10 per cent. of sulphur. For some purposes--_e.g._, detecting
+variation in rate of cure--this mixing is satisfactory, but for other
+purposes it is not. Nor is the behaviour of a rubber-sulphur mixing a sure
+guide to the behaviour of one containing other ingredients, such as
+litharge. Thus, two samples vulcanised satisfactorily when mixed with
+sulphur only, but one of them gave unsatisfactory results in the presence
+of litharge. It has long been recognised that mineral ingredients may
+modify the product when vulcanised, but the modification is not necessarily
+uniform. Consequently, tests should also be made, when practicable, with
+vulcanised rubber containing other ingredients in addition to sulphur.
+
+As regards physical tests on the vulcanised products, these usually involve
+determination of breaking load and elongation at rupture (usually recorded
+as final length--that is, including the original length reckoned either as
+unity or as 100 units). Simultaneously a load-stretch curve is recorded on
+an autographic attachment. The type of curve varies with (1) state of cure,
+or degree to which the rubber is vulcanised; (2) proportion of sulphur
+and/or other ingredients; (3) specific nature of the rubber used. The last
+factor is almost negligible compared with the two former--at any rate for
+average quality rubber. As (2) is kept constant for any batch of tests, or
+even for every test, it follows that the load-stretch curve is mainly
+dependent on the state of cure, and the degree of vulcanising may be
+measured by comparing either the elongation produced at a given load or the
+load produced at a given elongation. Either set of figures is readily
+determined by measuring up the load-stretch diagram.
+
+The peculiar type of the curves has long been a subject of comment and
+speculation. Special properties have been attributed to the "slope" or
+inclination of the upper and approximately straight portion of the curve.
+According to the writer's investigations, the "slope" is largely dependent
+on the degree of vulcanisation, so that it is difficult to "place" as an
+index of the specific nature of a rubber.[41] Moreover, it has recently
+been shown that the peculiar type of curve given by vulcanised rubber is
+the result of plotting the load against the sectional area of the
+unstretched test piece, whereas this area decreases progressively as the
+test piece stretches. If this decrease be allowed for, the curve obtained
+is an equilateral hyperbola.[42] Preliminary experiments with rubber
+compounded with large proportions of finely divided mineral matter, such as
+carbon black, show that the load-stretch curves obtained autographically
+are likewise reducible to equilateral hyperbolæ.
+
+[41] Bulletin R.G.A., October, 1921, p. 397.
+
+[42] _Hatschek Journal Soc. Chem. Ind._ 1921; _Trans._, p. 251.
+
+
+
+
+CHAPTER XXIII
+
+_THE PROPERTIES OF RUBBER_
+
+
+This section, like the last, is divisible into two subsections. The first
+deals with raw rubber, the second with vulcanised rubber.
+
+We have already explained that, until recently, rubber was not used in the
+unvulcanised condition, but that the excellent physical properties of
+plantation rubber have made this possible. It is interesting to compare the
+physical properties of raw rubber with that vulcanised with sulphur. A
+compact sample of crepe as received from the East will give breaking strain
+of over 30 kilos per sq. cm. and over 300 per cent. elongation. When mixed
+with sulphur and vulcanised, a breaking strain of 150 kilos and elongation
+of 1,000 per cent. are not unusual. It is possible that crepe rubber would
+give higher figures if it could be prepared in the form of a compact ring,
+as used for tests on vulcanised rubber. In any case, the figures for
+vulcanised rubber are much in excess of those for raw crepe rubber. It must
+also be remembered that a breaking strain of 150 kilos is not permanent
+with vulcanised rubber, for reasons which will be explained later.[43] To
+obtain a reasonably permanent vulcanised product, the vulcanisation would
+not be carried further than to give a figure of 100 kilos. On the other
+hand, raw rubber is remarkable on account of its great permanency, although
+subject to some physical changes at ordinary atmospheric temperatures.
+Tensile tests, although valuable, do not tell us all about the physical
+properties of a sample of rubber. Abrasion tests, or tests designed to
+measure resistance to wear and tear, would be more valuable, but,
+unfortunately, these properties do not lend themselves to simple tests.
+There are grounds for believing that raw rubber is superior in some
+respects to fully vulcanised rubber, if prepared without the addition of
+finely divided mineral substances which exert a toughening effect.
+
+[43] _Journal Soc. Chem. Ind._, 1916, p. 872.
+
+Sheet rubber gives results in some ways inferior to compact crepe rubber
+when subjected to physical tests. Tensile strength seldom exceeds 15 kilos,
+but the elongation is usually higher--up to 600 or 700 per cent. That is to
+say, it stretches more, but breaks more easily. If, however, we take into
+consideration the diminution in sectional area of the test piece during
+stretching, it will be seen that crepe and sheet rubber have compensating
+properties.
+
+As this matter of sectional area reduction during stretching is important,
+both for raw and vulcanised rubber, it may be briefly referred to here.
+When rubber is stretched, the volume does not appreciably alter--at any
+rate, as regards uncompounded rubber. Hence the reduction of sectional area
+on stretching bears a simple relationship to the amount of stretching. If
+we double the length of the test piece, we halve the sectional area; if we
+treble the length, we reduce it to one-third, and so forth. Hence, if we
+multiply the breaking strain by the final length (_i.e._, length at break,
+taking the original length = 1), we obtain a figure, the "tensile product,"
+which embodies both breaking strain and stretching capacity. In effect it
+gives us the breaking strain calculated on the sectional area at the
+_moment of rupture_ of the test piece. Adopting this formula, we obtain for
+crepe--
+
+   _Tensile    _Final Length--i.e.,    _Tensile
+  Strength._     Elongation + 1._      Product._
+     30      ×        4            =     120
+
+and for smoked sheet
+
+     15      ×        8            =     120
+
+The difference in properties between crepe and sheet may probably be
+attributed to the heavier rolling of the crepe; which compacts the rubber.
+But if the crepe is rolled too much, the tensile strength falls, and there
+is no increased elongation to compensate. For the same reason, crepe which
+has been rerolled in this country is inferior to crepe as received direct
+from the plantation. At the most it is permissible to unite two or three
+layers of thin crepe to a thicker one by a single passage through even
+speed rollers, if the physical properties of the original rubber are to be
+conserved.[44]
+
+[44] Bulletin R.G.A., February, 1922, p. 64.
+
+Attempts to prepare crepe for use in a raw state, by rerolling uneven or
+irregular surfaced crepe in this country, only result in a rubber with
+inferior physical properties. Nor can sheet be rerolled to give crepe of
+good physical properties. The power required to break down the sheet and
+the heat developed, even on cold rollers, are an indication of physical
+properties destroyed. For subsequent vulcanisation this is not a matter of
+importance, because the vulcanising process restores to the rubber the
+properties which are lost in the process of rolling and milling or
+mastication.
+
+Raw rubber has been used to some extent for proofing purposes, as for the
+manufacture of material for hoods of motor-cars. In this case no attempt is
+made to preserve the physical properties. The rubber is masticated, mixed,
+taken up with solvent and spread on the cloth exactly as if it were to be
+vulcanised.
+
+VULCANISED RUBBER.--We have already explained that the properties of
+vulcanised rubber are dependent, to some extent, on the specific nature of
+the raw rubber, or what De Vries terms the "inner qualities." That is to
+say, differences appear on vulcanising which are not apparent from the
+tests made on the raw rubber. Indeed, no investigation or analysis of the
+raw rubber can enable one to foresee exactly how the rubber will behave on
+vulcanisation. This illustrates the deficiency in our knowledge of
+vulcanisation. When dealing with soft, resinous, or decomposed rubbers, it
+is safe to anticipate a weak vulcanised product; but when we come to deal
+with a number of samples of "standard" crepe or sheet--_i.e._, sheet or
+crepe passing a certain standard of appearance--it is found that
+differences in vulcanising properties cannot be foreseen. This matter is,
+however, not so great a drawback as might be imagined, for reasonably well
+prepared consignments of standard crepe or sheet differ but little from
+one another, and the difference is mainly in the ease with which they break
+down, or the rate or speed with which they vulcanise, and not with the
+properties of the vulcanised product. Many of the plantation scrap grades
+are equal to or nearly equal to "standard"; but some of these, as also the
+rubber produced by native holders, show appreciable variation, and are the
+source of most of the complaints which emanate from manufacturers. We shall
+consider in turn the different grades and the effect of the usual surface
+defects, such as mould, spots, etc.
+
+CREPE RUBBER.--Oil marks and tackiness are the most serious defects from
+the manufacturing standpoint. In the first part of this book we have shown
+that damage caused by the so-called oil marks is not due to the oil, but to
+traces of copper from the bearings of the machines. There are several
+metallic compounds which cause deterioration of rubber both raw and
+vulcanised, but copper is the most deadly, and rubber showing signs of
+deterioration is rightly rejected by the manufacturers.
+
+The only other defect of crepe rubber which has any bearing on its use in
+manufacture is mould. Crepe rubber very seldom shows the ordinary surface
+moulds not uncommon in sheet-rubber. There are, however, microscopic
+growths which cause the development of coloured spots referred to in detail
+in the earlier part of this book. The rubber hydrocarbon itself does not
+appear to be affected by the moulds, but some of the serum constituents are
+altered, with the result that the rubber vulcanises more slowly than it
+otherwise would do. For this reason, crepe rubber with coloured spots may
+give rise to trouble in the factory.
+
+SHEET RUBBER.--The commonest defect is mould.[45] This is usually of a
+light surface type, easily brushed off, and numbers of vulcanising tests
+failed to trace any reduction in rate of vulcanising or other defect due to
+this. In spite, however, of the harmlessness of light surface moulds, they
+are looked upon with suspicion by the manufacturer. Occasionally samples of
+smoked sheet are offered contaminated with a "heavy" type of mould. The
+sheet feels damp and "heavy" or flabby, and contains an excess of moisture;
+sometimes a moist exudation is noticeable on the surface, and "virgin"
+patches are present. Such sheet vulcanises more slowly than F.A.Q. samples,
+but does not necessarily show other defects after washing and drying.
+
+[45] Bulletin R.G.A., February, 1921, p. 97; April, 1921, p. 190; June,
+1921, p. 243; November, 1921, p. 472.
+
+"Stretching rusty," as already explained, is due to a dry film on the
+surface of the sheet, and according to a recent investigation, this film
+consists, not of serum substances, but of a microscopic mould growth, which
+presumably grows on the serum substances. A sample of sheet which stretches
+rusty gives the rubber a "dry" appearance, and for a long time
+manufacturers mistook the surface film for resin. On the assumption that
+such rubber was "resinous" they rejected it, and to this day it is regarded
+as a defect, although it has no influence on the vulcanising properties of
+the rubber.
+
+It is hardly necessary to point out that defective appearance, such as is
+due to thickened edges, faint markings, bubbles, and so forth, have no
+effect on the vulcanising properties of the rubber. They only point to some
+irregularity or carelessness in preparation. The only justification for
+distinguishing between rubber of good and bad appearance is that the former
+bears the impress of careful preparation, and is therefore more likely to
+be uniform in rate of vulcanising.
+
+Similar considerations apply to the colour of smoked sheet, which may vary
+from a pale yellow-brown, through various shades of red-brown to dark
+brown. There are various factors affecting the colour, but the buyer can
+see but one--viz., the "degree" of smoking--and the rubber, from his point
+of view, may be undersmoked or oversmoked. No doubt the degree of smoking
+affects the vulcanising properties, but to a less extent than was at one
+time imagined. In a recent paper[46] it has been shown that the average
+breaking strain and rate of cure of a number of samples of smoked sheets
+were practically the same for light as for dark sheets.
+
+[46] Bulletin R.G.A., December, 1921, p. 521.
+
+VARIATION IN PHYSICAL PROPERTIES.--A very large number of tests on
+vulcanised specimens of plantation rubber have been carried out. The
+rubber was almost invariably mixed with 7 to 10 per cent. of sulphur, and
+no other ingredient, and vulcanised to give the maximal breaking load.
+Unfortunately, this determination is subject to a very appreciable
+experimental error, so that a large number of determinations are necessary
+to give a reliable figure. It is quite impracticable to make a large number
+of determinations in routine testing, on account of the labour involved. It
+is usual to make five, or possibly ten, determinations, although some
+investigators have been content with two. It is generally conceded that any
+exceptionally low figures should be ignored, as probably caused by some
+flaw or irregularity in the test piece. On the other hand, a study of
+actual determinations shows an occasional excessively high figure, and it
+is questioned whether this also should be left out of account. Others
+ignore all except the highest figure, and take this to represent the true
+breaking strain. As a consequence, the figures published by different
+workers show considerable variation. De Vries has analysed a large number
+of the figures obtained in systematic examination of estate samples, and
+has constructed curves to illustrate the results.[47] It is open to
+question how far the variations shown are attributable to experimental
+error. The figures show, however, that the variation in breaking strain is
+relatively small, and not very different for crepe and sheet rubber. In our
+opinion, undue importance should not be attached to very high or
+exceptionally high figures for breaking strain, which are occasionally met
+with. Provided the figure does not fall much below the average, the sample
+may be regarded as satisfactory. It is very seldom that any sample of first
+latex estate rubber does not show satisfactory figures.
+
+[47] "Estate Rubber," p. 466.
+
+THE RATE OF CURE OR RATE OF VULCANISATION is subject to more exact
+measurement, whether this be based on the physical or the chemical
+properties of the rubber. If the testing machine be provided, as is usual,
+with an autographic attachment, the position of the curves traced on the
+recording paper gives a measurement of the rate of cure. These load-stretch
+curves, to which reference has already been made, take up a definite
+position in accordance with the physical properties; it is only the length
+of the curve, or the point where it terminates (which gives the breaking
+strain and elongation at break), which is largely fortuitous.
+
+As a measure of rate of cure we may take the actual measurements made on
+the record.[48] It is convenient to measure the elongation produced by a
+load of 130 kilos per sq. cm., as all fully vulcanised rings of soft rubber
+should give higher breaking load figures. For less cured or weaker samples
+a lower figure may be taken, such as 60 kilos. We have found that when
+fully vulcanised to give the maximal breaking strain, the elongation at a
+load of 130 kilos is in the neighbourhood of 850 per cent. (final length
+950 per cent.). This applies to ordinary samples of estate rubber under the
+conditions of testing indicated above. If, however, the proportion of
+sulphur be considerably reduced, or mineral ingredients in a fine state of
+division be added to the mixing, or accelerators, whether organic or
+inorganic, be employed, the above relationship no longer holds. Nor does it
+hold with regard to plantation rubber prepared in an exceptional manner,
+as, for instance, matured coagulum or "slab."
+
+[48] Bulletin R.G.A., June, 1921, p. 246.
+
+There is a second method of determining the rate of cure--namely, by
+analysing a vulcanisate produced under standard conditions, and determining
+the amount of sulphur which has entered into chemical combination with the
+rubber. For this purpose the weighed sample is cut thin or creped thin, and
+exhaustively extracted with acetone to remove any "free" sulphur--that is,
+sulphur not in combination with the rubber. The sulphur remaining is then
+determined and calculated as a percentage of the raw rubber contained in
+the sample taken. This gives the so-called coefficient of vulcanisation.
+
+If we compare the coefficient with the time of cure at a constant
+temperature for an ordinary sample of plantation rubber, they are found to
+be approximately proportional, so long as the sulphur is in sufficient
+excess. The amount of combined sulphur is, therefore, an index of the time
+vulcanisation has been in progress (under standard conditions of
+temperature, etc.), and, therefore, the coefficient is a measure of the
+rate of cure.
+
+The change in position of the load-stretch curve is not directly
+proportional to the time of heating, and it therefore follows that it is
+also not directly proportional to the coefficient. For ordinary samples of
+crepe and sheet the relationship is, however, not very far removed from
+proportionality. This applies particularly to sheet rubber. The
+relationship is readily seen on plotting one against the other and tracing
+the curves. For sheet we get an almost straight line; for crepe there is
+some curvature.[49] For ordinary estate samples of sheet and crepe rubber
+the maximal breaking strain is obtained when the coefficient reaches
+approximately five units, so that this corresponds to the elongation of 850
+per cent. at a load of 130 kilos.
+
+[49] Bulletin R.G.A., June, 1921, p. 246, October, 1921, p. 398.
+
+Either physical or chemical methods may, therefore, be used for determining
+the rate of cure of ordinary sheet or crepe rubber, but great care must be
+taken when interpreting the results obtained with rubber prepared in an
+unusual manner. The rate of cure may be expressed in terms of the time
+taken to vulcanise the rubber at a constant temperature (in our case 138°
+C.), so as to give an elongation of 850 per cent. at a load of 130 kilos,
+or to give a coefficient of five units. The higher the figure so obtained,
+the slower curing the rubber. To express the results more directly as rate
+of cure, we have adopted the plan of taking an average crepe rubber,
+calling the rate of cure 100 units, and expressing the rate of cure of
+other samples in these terms. Thus, a sample which gave a coefficient of
+four only, in the time taken by the standard to give a coefficient of five,
+would have a rate of cure four-fifths of the standard, that is, 80; or if a
+sample takes only two hours to give an elongation of 850 per cent., whereas
+the standard takes three hours, the rate of cure of the sample will be 3/2
+of standard or 150.[50]
+
+[50] _Journal Soc. Chem. Ind._, 1918, p. 280.
+
+As stated, the coefficient is approximately directly proportional to the
+time of cure; it is also independent of the proportion of sulphur, if in
+fair excess, and in the presence of inert ingredients. It is also
+independent of the amount of mastication given to the original raw rubber,
+however great. On the other hand, the position of the load-stretch curve is
+variously modified by these factors--in some respects, therefore, the
+coefficient is a more reliable index. However, the coefficient is
+influenced by accelerators, so that here also great care must be exercised
+when interpreting results. For the purpose of detecting variations in rate
+of cure, it is best to choose a mixing which is particularly sensitive. In
+the first place, there must be an ample excess of sulphur; and in the
+second place, no ingredient should be added which will complicate the
+load-stretch curves, and no accelerators should be present which may
+possibly tend to obscure the vulcanising properties of the rubber itself.
+It has been found, therefore, that the best mixing to use consists of
+rubber with an excess of sulphur--say, in the proportion 9:1 without other
+ingredients. The rate of cure of a specimen of plantation rubber is
+attributed to the presence of certain natural vulcanising catalysts,
+because it is found that carefully purified raw rubber (that is, with the
+resinous and nitrogenous constituents removed) vulcanises very slowly or
+hardly at all, but that on replacing the extracted matter the rate of
+vulcanising is restored. The natural catalysts contained in the extracted
+matter are influenced to a varying degree by some of the common ingredients
+of manufactured rubber articles. This applies particularly to litharge
+(oxide of lead), to which reference has already been made. Thus, acetone
+extraction of raw rubber to remove resinous matter has but little effect on
+the vulcanising properties of a mixture of rubber and sulphur. But if
+litharge be a constituent, it is found that acetone-extracted rubber will
+hardly vulcanise at all. From this, it follows that a rubber giving a low
+acetone extract may be found to vulcanise exceptionally slowly in a mixing
+containing litharge, whereas it shows no such defect when compounded with
+sulphur only.[51] Litharge is used to a very large extent, as it has a
+balancing effect in a rubber compound--that is to say, it allows of
+appreciable variation in vulcanising conditions, without corresponding
+alteration in the state of cure.[52]
+
+[51] _Journal Soc. Chem. Ind._, 1916, p. 874.
+
+[52] _Ibid._, 1915, p. 524.
+
+INFLUENCE OF VARIOUS FACTORS IN RAW RUBBER PREPARATION ON THE "RATE OF
+CURE," OR "RATE OF VULCANISATION."--As the capacity of a rubber for
+vulcanisation depends on the presence of small quantities of accessory
+substances in the serum which act as catalysts, the rate of vulcanisation
+(or curing) will depend on the nature and quantity of such substances
+present in the rubber. A very small quantity of these substances has a
+considerable influence on rate of vulcanising, and as the substances are
+difficult to isolate and identify, our knowledge of their formation and
+chemical nature is not as definite as is desirable. Substances have been
+isolated having the characteristics of "simpler bases." Bodies of this
+class are formed by putrefaction of organic matter, and can be separated in
+much larger quantity from coagulated latex, which has been allowed to
+putrefy before working up than from such which has been worked up without
+giving time for an appreciable amount of putrefaction to take place.
+Further, rubber from putrefied coagulum vulcanised much faster than that
+ordinarily prepared, so that we are justified in connecting the
+putrefaction bases with the rate of vulcanisation. Moreover, it has been
+shown that any treatment of the latex or coagulum which inhibits the
+development of putrefactive organisms also prevents the rubber vulcanising
+as fast as would otherwise have been the case.[53] Also, the crude bases
+isolated from fast vulcanising rubber have the power of increasing the rate
+of vulcanisation when added to ordinary slow vulcanising rubber.[54]
+
+[53] Eaton and Co-workers: See Bulletin No. 27, F.M.S. Department of
+Agriculture.
+
+[54] _Journal Soc. Chem. Ind._, 1917, p. 365.
+
+On the other hand, there are one or two facts which are difficult although
+not impossible to fit in with theory. Thus, although the putrefaction bases
+are very easily soluble in water and acetone, they cannot be removed by
+washing on the creping rollers, or by acetone extraction. This may be due
+to the power of colloidal substances to retain other crystalloidal
+substances, such as the bases, which, in consequence, cannot be washed out.
+A parallel case is the retention of small quantities of water soluble
+substances in the soil. Also, the theory does not explain why rubber
+obtained by evaporation of latex at relatively high temperatures is fast
+vulcanising, although the possibility of putrefaction is excluded.
+
+As regards practical results, it follows that the rate of vulcanisation (or
+cure) of a sample of rubber will depend on the time allowed to elapse
+between the collection of the latex and treatment till the rubber is dry,
+as also on atmospheric conditions. Thus, slow drying will result in an
+increased rate of cure, for it gives an opportunity for putrefactive
+organisms to play a part. The results will, however, be influenced by the
+extent to which the rubber was washed previous to hanging, and so forth.
+Smoking is an antiseptic process and will, therefore, tend to inhibit the
+action of micro-organisms and produce a slower vulcanising rubber. On the
+other hand, sheet contains more serum than crepe, so that there is more
+food material for growth of micro-organisms. The net result is to give a
+rubber (sheet) which usually vulcanises a little faster than crepe.
+
+Among other factors controlling the rate of cure, special mention should be
+made of the nature and amount of coagulants. Weak "organic" acids, such as
+acetic, lactic, tartaric, etc., used in the minimal proportions (1 to 1,200
+of standardised latex in the case of acetic acid), give the fastest
+vulcanising rubber; "strong" mineral acids, such as sulphuric acid, even
+when used in the minimal proportions (1 to 2,000), yield slower vulcanising
+rubber. Acid salts, such as alum, are intermediate in effect. Increased
+proportions of coagulant cause a reduction in rate of vulcanising with all
+coagulants, and the effect is least noticeable in crepe rubber,
+intermediate in sheet rubber, and most pronounced in "slab" rubber
+(discussed below).[55]
+
+[55] Bulletin R.G.A., July, 1919, p. 39; September, 1920, p. 343; November,
+1920, p. 433; October, 1921, p. 393; March, 1922, p. 134.
+
+OTHER TYPES OF PLANTATION RUBBER.--We have up to now confined our attention
+to ordinary thin air-dried crepe and smoked sheet, as almost all plantation
+rubber is now marketed in one or other of these two forms. There are,
+however, other types, to which reference has been made. Of these, the most
+important is the thick blanket crepe, made chiefly in Ceylon by rolling
+together thin crepe, which has been artificially dried (Colombo drier or
+vacuum drier). The heat of the driers causes a surface stickiness, which is
+got rid of by rolling several thin layers together to give one thick one.
+This rubber vulcanises at about the same rate as ordinary thin crepe, for
+the relatively high temperature of drying does not appear to influence the
+rate of cure. The rubber is generally softer than air-dried crepe, and is
+easily "let down" in naphtha; it is, therefore, suitable for some solution
+work. Generally speaking, the properties of blanket crepe do not differ
+materially from ordinary thin crepe. Another type of rubber seldom met with
+is matured slab or crepe, prepared from it. This type of rubber is being
+made in small quantities on one or two estates, who supply direct to the
+manufacturer. The method of preparation has already been described. It is
+unsuitable for sale in the open market, as it contains a variable amount of
+moisture, has the various surface defects such as slime, mould, and "rust,"
+and there is the additional disadvantage that it is not easy to judge of
+its cleanliness or freedom from coarse impurities by inspection. If the
+slab rubber be creped and air-dried on the spot, the product is of
+satisfactory appearance, except that it is of low colour and may be
+streaked. As the crepe so produced vulcanises almost as fast as the
+original slab, the crepe embodies all the advantages of a fast curing
+rubber with few of the disadvantages of the slab itself. We have made
+experiments from time to time, and found that by a judicious use of sodium
+bisulphite it is possible to produce a fast vulcanising crepe rubber
+sufficiently even and light in colour to satisfy the Standards Committee.
+
+A fast curing raw rubber is not necessarily a desirable type for all
+manufacturing purposes. In the vulcanising of large masses of rubber, a
+slower rather than a faster vulcanising rubber may be desirable, so as to
+give ample time for the heat to penetrate and spread evenly throughout the
+mass. But for many purposes a fast curing rubber enables a larger output to
+be obtained, so that artificial organic accelerators are coming more and
+more into use. The addition of such accelerators might be obviated, if a
+suitable fast curing rubber were available, but it is essential that such
+rubber should be uniform. It is just in this respect that slab rubber or
+crepe made therefrom is found to be deficient.[56] The rate of cure depends
+on the functions of wild bacteria, which are naturally sensitive to changes
+of conditions, such as temperature, etc. The coagulated rubber depends on
+chance circumstances for infection, and, as a natural result, the activity
+of the bacteria and the nature and amounts of active vulcanising agent
+produced will vary and be difficult to control. Consequently, the rate of
+cure of slab rubber shows considerably greater variation than ordinary
+crepe or sheet.[57] This, in our opinion, is the main difficulty of
+utilising "slab," or crepe prepared from it. Experience in other
+industries, using micro-organisms, has shown that the only method of
+control has been to replace the wild growths by cultures of some particular
+strain, as, for instance, in yeasts for brewing. To control the rate of
+cure of slab, it might be possible to use a special culture for the
+purpose.
+
+[56] Bulletin R.G.A., January, 1920, p. 6; January, 1921, p. 47.
+
+[57] _Ibid._, January, 1920, p. 68.
+
+Other less usual methods of preparation, referred to in the earlier part of
+this book, do not call for particular mention, as the properties of the
+rubber do not differ much from ordinary sheet or crepe. It is mainly a
+matter of variation in rate of cure.
+
+This short account of the vulcanising properties of plantation rubber would
+not be complete without a reference to Fine Hard Para, the premier rubber
+of the Amazon. This rubber has come to be regarded as the standard
+high-grade product with which plantation rubber may be compared, and many
+manufacturers are still of the opinion that it is unsurpassed by any
+plantation product. Yet, when subjected to the ordinary vulcanising tests,
+we find that samples of Fine Hard Para give figures very similar to average
+plantation rubber; indeed, it is not difficult to find specimens of
+plantation rubber which give appreciably higher figures on testing. It is
+claimed, however, that Fine Para is more uniform than plantation rubber,
+and can be relied on always to give the same results. Yet tests on a series
+of Fine Hard Para specimens gave variations in rate of cure similar to
+those found for plantation. Some figures were published, which tended to
+show that the variation was smaller for Fine Para, but it turned out that
+each of the samples taken for examination consisted actually of a number of
+slices cut from different balls, so that greater uniformity was not
+unexpected.[58] The superiority of Fine Para is, therefore, somewhat of a
+mystery. It is probable that some manufacturers prefer to use it because
+they feel safer with it, and know actually how it will behave from long
+experience. In one respect Fine Para is possibly superior to most
+plantation rubber--that is, for the preparation of raw rubber solution for
+sticking the seams of waterproof garments, and for similar purposes. The
+method of preparation may well influence the strength of the raw rubber
+when used for this purpose. Plantation rubber has been prepared in the same
+manner as Brazilian Para, in particular on an estate in Java. The product
+resembles Brazilian Para in appearance. Vulcanising tests gave satisfactory
+figures, but, as already stated, this would not serve to show that the
+rubber was equal to Brazilian Para from the manufacturer's standpoint.
+
+[58] Bulletin R.G.A., September, 1920, p. 347.
+
+
+
+
+INDEX
+
+
+  Acetic acid, 74, 279
+
+  Acid, acetic, 74, 279
+  --, carbonic, gas, 289
+  --, formic, 279
+  --, hydrochloric, 282
+  --, hydrofluoric, 282
+  --, mixing, with latex, 79
+  --, nitric, 282
+  --, oxalic, 279
+  --, pyroligneous, 282
+  --, quantity of, 76
+  --, sulphuric, 279, 286
+
+  Acids for coagulation, effect of, on rate of cure, 323
+  --, quantities necessary for modern requirements, 78
+
+  Air-drying, aids to normal, 143
+  --, of crepe, rate of, 138
+  --, progress of, 140
+
+  Alcohol, coagulation with, 289
+
+  Alum, coagulation with, 282
+
+  Anti-coagulant for transport, 61
+
+  Anti-coagulants, 46
+
+  Artificial driers, 133, 148
+
+  Ash on sheet, 276
+
+  Assembling cases for shipment, 156
+
+
+  Bags for packing, 154
+
+  Bakau, 147
+
+  Bales for packing, 154
+
+  Bark in crepe, 232
+  -- -- shavings, 56, 123
+  -- -- sheet, 276
+
+  Bases in vulcanised rubber, 322
+
+  Basket plants, 10
+
+  Blanket crepe, properties of, 324
+
+  Blemishes of surface, 252
+
+  Blister in sheet, 272
+
+  Block rubber, 129, 246
+
+  Breaking down of rubber, 304
+  -- load of test piece, 311
+
+  Bubbles in sheet, 269
+
+  Buildings, 159
+
+  Bulking latex, 69
+
+  Byrne curing process, 270
+
+
+  Calendered sheet, 304
+
+  Carbon dioxide, 289
+
+  Carbonic acid gas, 289
+
+  Cases, choice of, for packing, 153
+
+  Catalysts, natural, in rubber, 312
+  --, vulcanising, 312
+
+  Centralisation of factories, 221
+
+  Chinese vinegar, 286
+
+  Chinosol, 238
+
+  "Chula" drier, 148
+
+  Clippings, sheet, 275
+
+  Coagulant, 111
+  --, choice of, 74, 278
+  --, quantity of, 113
+
+  Coagulation, 74, 111
+  -- centres, 62
+  --, premature, 46
+  --, spontaneous, 294
+  -- with alcohol, 289
+  -- -- sugars, 287
+  -- -- various salts, 288
+
+  Coagulum, soft, 249
+  --, spongy undersurface of, 249
+  --, tearing of, 249
+  --, transport of, 59, 63
+  --, working of, 103
+
+  Coefficient of vulcanisation, 319
+
+  Collecting latex, 38
+  -- pails, 48
+
+  Collection, advantages of early, 60
+
+  Combustion, rate of, in smoke house, 191
+
+  Compound crepes, 126
+  -- -- No. 1, 151
+  -- -- No. 2, 151
+
+  Contents of cases, weight of, 156
+
+  Copper salts, cause of tackiness, 243
+
+  Cotton fibre in crepe, 230
+
+  Creosotic substances, 146
+
+  Crepe, air-drying of, 132
+  --, bark in, 232
+  --, bearing of defects in, on manufacture, 316
+  --, bisulphite streaks in, 235
+  --, colour of fine, 114
+  --, dirt in, 227
+  --, dirty edges of, 225
+  --, drying houses for, 178
+  --, fibre in, 230
+  --, general style of finish, 223
+  --, grades of, 150
+  --, greenish, tacky streaks in, 228
+  --, iron stains on, 225
+
+  Crepe, No. 1 fine pale, 110
+  --, oil marks on, 226
+  --, oxidation streaks in, 234
+  --, rate of air-drying of, 138
+  --, rust stains on, 226
+  --, smoked, 130
+  --, surface moulds on, 241
+  --, weight increased in drying house, 141
+  --, yellow latex streaks in, 234
+  -- rubber, defects in, 223
+  -- --, lower grades of, 120
+  -- --, preparation of, 110
+  -- --, tensile strength of, 313
+
+  Cups, cleaning, 40
+  --, water in, 44
+
+  Cure, rate of, 318
+
+  Curing, 307
+
+
+  Da Costa process, 290
+
+  Decentralisation of factories, 221
+
+  Defects of sheet, infrequent, 276
+
+  Derry process, 293
+
+  Designs and "layout" of tanks, 176
+
+  Dirt in sheet, 276
+
+  Discoloration of rubber, dark, 249
+
+  Drains for tanks, 176
+
+  Drier, Colombo Commercial Company's, 136
+
+  Driers, artificial--for crepe rubber, 133
+  -- --, for sheet rubber, 148
+  --, "Chula," 148
+  --, vacuum, 134
+
+  Drum furnaces, horizontal, 189
+
+  Drying chamber, floor of, 187
+  -- --, arrangements of, 186
+  -- houses for crepe, 178
+  -- --, hot air, 182
+  -- --, ventilation of, 185
+  -- --, windows of, 185
+  -- of rubber, 132
+  --, period of, 145
+  --, rate of, effect on rate of cure, 323
+
+
+  Earth scrap, 124
+  -- --, collection of, 58
+
+  Edges, thickened, after rolling, 251
+
+  Elongation of test piece, 311
+
+  Ends, thickened, after rolling, 251
+
+  Engines, 170
+  --, position of, 174
+
+
+  Factories, 172
+  --, centralisation of, 221
+  --, decentralisation of, 221
+  --, number of floors, 174, 178
+  --, ventilation of, 180
+  --, windows of, 181
+
+  Factory buildings, situation of, 216
+  --, choosing site for, 220
+  --, ideal arrangement of, 162
+  -- operation, 65
+
+  Fibre cotton, in crepe, 230
+
+  Field maintenance, 13
+
+  Fine hard Para properties of, 325
+
+  First latex and other grades, percentage of, 59
+
+  Floor of drying chamber, 187
+  -- factories, 173
+  -- furnace room, 196
+
+  Formalin, 87
+
+  Formic acid, 74, 279
+
+  Formula for test mix, 311
+
+  Freezing (coagulation) process, 293
+
+  Fuel, consumption of, 196
+
+  Fuels for smoking, 146
+
+  Furnace room, floor of, 196
+  -- --, Petaling type of, 192
+
+  Furnaces, horizontal drum, 189
+  --, "pot," 188
+
+
+  Germination, 6
+
+  Grades, number of, 151
+
+  Grading, 150
+
+  Grafting, 8
+
+  Grass squares, 14
+
+  Greasiness before smoking, 252
+  -- of surface, 258
+
+  Grit in crepe, 232
+
+
+  Hand rolling sheets, 104
+
+  Hevea Brasiliensis, 1
+
+  Hot air drying houses, 182
+
+  Hydrochloric acid, 282
+
+  Hydrofluoric acid, 282
+
+
+  Ilcken-Down process, 298
+
+  Instruments, method of using, 100
+  --, recording, 144
+  --, standardising, 98
+
+
+  Lallang, eradication of, 15
+
+  Latex, bulking, 69
+  -- cups, choice of, 40
+  --, decomposition of, in the field, 270
+  --, first and other grades, percentage of, 59
+  --, first quality, 150
+  --, mixing acid with, 79
+  --, mixing sodium bisulphite solution with, 117
+  --, preliminary treatment of, 65
+  --, reception of, at the store, 65
+  --, standard, 96
+  --, standardisation of, 69, 110
+  --, straining, 67
+  --, transport of, 59
+
+  Light, importance of, in factories, 172
+
+  Litharge, 312
+
+  Load stretch curve, 312, 319, 320, 321
+
+  Low grade rubbers, fibrous matter in, 124
+
+  Lower grade rubber, care in manufacture, 129
+
+  Lubrication of machines, 166
+
+  Lump rubber, naturally coagulated, 120
+
+
+  Machinery, 159
+
+  Machines, access to, 169
+  --, adequacy of, 160
+  --, arrangement of, 168
+  --, lubrication of, 166
+  --, position of, 173
+  --, sheeting, 166
+  --, speed of, 162
+
+  Mangrove, 147
+
+  Marking sheets, 105
+
+  Metrolac, 98, 100
+
+  Michie-Golledge system, 138
+
+  Mildew on surface, 260
+
+  Milky residue on serum, 249
+
+  Mixing acid with latex, 79
+
+  Moist glaze of surface, 258
+
+  Mould on surface, 260
+
+  Moulds, surface, on crepe, 241
+
+
+  Natural catalysts, 312
+
+  Nitric acid, 282
+
+  Nurseries, 9
+
+
+  Overcured, 307
+
+  Overvulcanised, 306
+
+  Oxalic acid, 279
+
+  Oxidation, prevention of, 56
+  --, variation due to, 254
+
+
+  Packing, 150
+  --, bags for, 154
+  --, bales for, 154
+  --, cases, choice of, 153
+  --, folding for, 155
+  --, methods of, 156
+  --, rooms, 211
+
+  Pale crepe, No. 1 fine, 110
+  --, rubber, former methods of making, 118
+  --, sheet, 89
+
+  Patches, 259, 260
+  --, virgin, 259
+
+  Payment by result, 53
+
+  Perished rubber, 306
+
+  Physical properties of rubber, variation of, 317
+
+  Pits for smoke houses, 188
+
+  Pitting of surface, 250
+
+  Plantation rubber, testing of, 309
+
+  Planting, 1
+
+  Plasticising of rubber, 304
+
+  Plasticity of plantation rubber, 309
+
+  "Pot" furnaces, 188
+
+  Power units, 170
+
+  Premature coagulation, 46
+
+  Preparation, special methods of, 290
+
+  Pyroligneous acid, 282
+
+
+  Racks, 186
+
+  Rate of cure, 307
+
+  Raw rubber, physical properties of, 313
+  -- --, tests on, 309
+  -- --, uses of, 315
+
+  Recommendations, Rubber Growers' Association, 152
+
+  Recording instruments, 144
+
+  Ribbing of sheet, 274
+
+  Rolling, 251
+
+  Rolls, grooving of, 164
+  -- running hot, 165
+  -- -- "free," 165
+
+  Roof of smoke house, 197
+
+  Rubber, drying of, 132
+
+  Rubber Growers' Association, Recommendations, 152
+
+  Rubber, properties of, 313
+  --, smoking, 109
+
+  Rust, cause of, 267
+  -- on sheet, 262
+  --, treatment to prevent, 265
+
+
+  Scrap washers, 57, 124
+
+  Screw plug, unsatisfactory, 73
+
+  Seed at stake, 10
+
+  Seeds, 2
+
+  Selection, 5
+
+  Senang folder, 156
+
+  Serum, milky residue on, 249
+
+  Sheet, ash on, 276
+  --, bark in, 276
+  --, bearing of defects on, in manufacture, 316
+  --, blisters in, 272
+  --, bubbles in, 269
+  --, clippings, 130, 275
+  --, creases in, 251
+  --, dirt in, 276
+  --, "dog ears," 251
+  --, grades of, 151
+  --, infrequent defects of, 276
+  --, pale, 89
+  --, ribbing of, 274
+  -- rubber, artificial driers for, 148
+  -- --, defects in, 249
+  -- --, preparation of, 89
+
+  Sheet rubber, rolling and marking of, 102
+  -- --, tensile strength of, 313
+  --, rust on, 262
+  --, splinters in, 276
+  --, stickiness in, 274
+  --, style of, 101
+  --, support marks on, 273
+  --, surface pattern of, 274
+  --, thick ends of, 275
+
+  Sheeting machines, 166
+
+  Sheets, mis-shapen, 251
+  --, thickened patches in, 251
+  --, torn, 251
+  --, unevenness of appearance, 253
+
+  Short weights, 157
+
+  Skimming, 100
+
+  Skimmings, 122
+
+  Slab rubber, 299
+  -- --, properties of, 324
+
+  Slope, 312
+
+  Smoke curing of sheet rubber, 143
+  -- --, temperature of, 144
+  --, houses, 183
+  -- --, Barker patent, 209
+  -- --, Devon type, 200
+  -- --, iron stoves for, 189
+  -- --, Jackson type, 200
+  -- -- of brick, 198
+  -- -- rate of combustion in, 192
+  -- --, roof of, 197
+  -- --, "Third Mile" type, 199
+  -- --, types of, 198
+
+  Smoked crepe, 130
+  -- sheets, colour of, 255
+  -- water for coagulation, 286
+
+  Smoking, effect on rate of cure, 323
+  --, greasiness before, 252
+  -- rubber, 109
+
+  Smooth rolling of sheets, 104
+
+  Sodium bisulphite, 80, 114
+  -- --, abuse of, 85
+  -- --, care of, 116
+  -- --, deterioration of, 115
+  -- --, evaluation of, 115
+  -- --, making a solution of, 85
+  -- --, quantity of, 84
+  -- --, residual traces of, 86
+  -- -- solution, mixing, with latex, 117
+  -- sulphite, 86
+  -- --, deterioration of, 115
+  -- --, evaluation of, 115
+
+  Sorting, 150, 152
+  -- rooms, 211
+
+  Spewing, 305
+
+  Splinters in sheet, 276
+
+  Spontaneous coagulation, 294
+
+  Spot disease, 235
+  -- -- in sheet rubber, 273
+
+  Spots, 259, 262
+  --, virgin, 259
+
+  Standard latex, 96
+  -- sheet, 102
+
+  Standardising instruments, 98
+
+  Stickiness in sheet, 274
+
+  Stock solution, method of making, 75
+
+  Storage of rubber, 212, 216
+
+  Stoves, iron, for smoke houses, 189
+
+  Straining latex, 67
+
+  Streaks, 262
+
+  Stumps, 9
+
+  Sugars, coagulation with, 287
+
+  Sulphuric acid, 280, 286
+  -- --, buying, 280
+  -- --, formula for use of, 280
+  -- --, storing, 280
+
+  Sun-drying sheet rubber, 147
+
+  Support marks on sheet, 273
+
+  Surface blotches, coloured, 249
+  --, dull or black, 258
+  -- pattern of sheet, 274
+
+
+  Tackiness, cause of, 243
+  --, copper salts cause of, 243
+  -- in rubber, 242
+
+  Tanks, 90
+  --, care of, 94
+  --, designs and "layout," 176
+  --, drains for, 176
+  --, installation of, 93
+  --, situation of, 175
+  --, water-supply for, 177
+
+  Tapping, 38
+  --, former systems of, 29
+  -- knives, 38
+  -- systems, 38
+
+  Tartaric acid, 279
+
+  Tensile product, 314
+
+  Test mix, formula for, 311
+  -- pieces, making of, 310
+
+  Testing of plantation rubber, 307
+
+  Thick ends of sheet, 275
+
+  Thinning, 19
+
+  Timber for smoking, 147
+
+  Tool sheds, 216
+
+  Transport, 60
+  -- by coolie, 62
+  -- of coagulum, 59, 63
+  -- of latex, 59
+
+  Trays, 167
+
+  Treatment of rubber in the factory, 301
+  -- to prevent rust, 265
+
+  Tree scrap, 55, 122
+  -- --, care of, 56
+  -- --, oxidation of, 56
+
+  Trees per acre, 26
+
+  Trenches, silt catchment, 11
+
+
+  Uniformity, 90
+  -- in colour, lack of, 246
+
+
+  Vacuum driers, 134
+
+  Variation due to oxidation, 254
+
+  Vegetable extracts, 289
+
+  Ventilation of drying houses, 185
+  -- factories, 180
+
+  Verandas, 175
+
+  Virgin spots, 258
+
+  Viscosity of rubber solution, 309
+
+  Vulcanisation, 301
+  --, rate of, 318
+
+  Vulcanised rubber, 318
+  -- --, tests on, 309
+
+  Vulcanising, 307
+  -- catalysts, 312
+  --, "heat," 306
+
+
+  Washers, scrap, 57, 124
+
+  Washings, 122
+
+  Water-supply for tanks, 177
+
+  Weeding, clean, 13
+
+  Weights, "short," 157
+
+  Wickham process, 293
+
+  Windows of drying houses, 185
+  -- factories, 181
+
+  Working of rubber, 304
+
+
+  Yields, 23, 25
+
+
+
+
+
+End of the Project Gutenberg EBook of The Preparation of Plantation Rubber, by 
+Sidney Morgan
+
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+    <meta http-equiv="content-type" content="text/html; charset=iso-8859-1" />
+    <title>
+      The Project Gutenberg eBook of The Preparation of Plantation Rubber, by Sidney Morgan, A.R.C.S.
+    </title>
+    <style type="text/css">
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+Project Gutenberg's The Preparation of Plantation Rubber, by Sidney Morgan
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Preparation of Plantation Rubber
+
+Author: Sidney Morgan
+
+Contributor: Henry P. Stevens
+
+Release Date: March 7, 2011 [EBook #35510]
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+Language: English
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+
+
+<h2>THE PREPARATION OF PLANTATION<br />
+RUBBER</h2>
+
+<hr class="c25" />
+
+
+<h1>THE PREPARATION</h1>
+<h3>OF</h3>
+<h1>PLANTATION RUBBER</h1>
+<h4>BY</h4>
+<h3>SIDNEY MORGAN, A.R.C.S.</h3>
+
+<p class="center">VISITING AGENT FOR ESTATES IN THE EAST; FORMERLY SENIOR SCIENTIFIC OFFICER<br />
+AND NOW HONORARY ADVISER TO THE RUBBER GROWERS&#8217; ASSOCIATION<br />
+IN MALAYA</p>
+
+<h3>WITH A PREFACE AND A CHAPTER ON VULCANIZATION</h3>
+<h4>BY</h4>
+<h3>HENRY P. STEVENS, M.A. (<span class="smcap">Oxon.</span>,) <span class="smcap">Ph.D.</span>, F.I.C.</h3>
+<p class="center">CONSULTING CHEMIST TO THE RUBBER GROWERS&#8217; ASSOCIATION IN LONDON</p>
+
+
+<h4>CONSTABLE &amp; CO. LTD.<br />
+LONDON : BOMBAY : SYDNEY<br />
+1922</h4>
+
+<hr class="c25" />
+
+<p class="center">PRINTED IN GREAT BRITAIN BY<br />
+BILLING AND SONS, LTD., GUILDFORD AND ESHER</p>
+
+<hr class="c25" />
+
+<p class='pagenum'><a name="Page_v" id="Page_v">[v]</a></p>
+
+
+<h2><a name="Ch0" id="Ch0"></a>PREFACE</h2>
+
+
+<p>Mr. Sidney Morgan&#8217;s work on Plantation Rubber in the
+East is so well known that he hardly needs introduction.</p>
+
+<p>An earlier book, published in 1914, by the Rubber Growers&#8217;
+Association, entitled &#8220;The Preparation of Plantation Rubber,&#8221;
+was well received and widely read. This book dealt in a very
+practical manner with problems with which the industry had
+to contend. A second edition was subsequently published.
+Both editions are now out of print. The present opportunity
+was therefore taken to revise the original work, with the result
+that it has been enlarged and practically rewritten. The
+information given is brought up-to-date, and covers the whole
+process of production, commencing with the planting of the
+tree, passing on to the collection, coagulation, and curing of
+the rubber, and concluding with the packing for export. In
+the course of his work for the Association, Mr. Morgan carried
+out a great deal of industrial research in rubber production,
+including lengthy experiments on tapping, the use of different
+coagulants and different conditions of coagulation, and also on
+varying modes of rolling, drying, and smoking rubber. He
+also went very fully into the types of construction and details
+of the machinery and buildings employed on estates.</p>
+
+<p>Much of this valuable work has escaped notice, owing to its
+having been published in reports with limited circulation.
+Also a great deal of information was supplied to planters in a
+quiet and unobtrusive fashion, in interviews, visits to estates,
+and on other similar occasions. The knowledge and experience
+thus accumulated has been embodied in the present volume.
+The subject-matter should interest not only those actually
+engaged in rubber planting, but those otherwise directly or
+<span class='pagenum'><a name="Page_vi" id="Page_vi">[vi]</a></span>indirectly connected with the industry, such as importers,
+brokers, and particularly the rubber manufacturers in this
+country and in America. My experience has been that manufacturers
+as a whole have but a vague idea as to the methods
+employed in the preparation of plantation rubber, and this
+work provides them with the opportunity of obtaining an
+insight into the actual operations on the estates. It is most
+desirable that a closer bond should unite the plantation and
+manufacturing rubber industries. Such a result is best promoted
+by a better understanding of the problems with which
+each is confronted. Perhaps I may go so far as to suggest
+that some leading scientific officer in the employment of one of
+the large manufacturing concerns may take in hand a book
+which will give the planters the equivalent of information in
+regard to the manufacturing industry which the planters are
+now offering to the manufacturers.</p>
+
+<p>The photographs in the earlier part of the book will give the
+layman some conception of the enormous amount of labour
+that must be expended in the opening up, planting, trenching,
+and weeding the plantations which have replaced the virgin
+jungle. The authors are indebted for most of these photographs
+to Mr. H. Sutcliffe, one of the mycologists of the
+Rubber Growers&#8217; Association. The pictures of spotless
+coagulating tanks and tiled verandahs regularly hosed down
+will indicate the cleanliness necessary for the preparation of
+the beautifully clean sheet and crepe rubber which became
+available with the advent of plantation rubber. These results
+are largely due to the work of Sidney Morgan and his colleagues,
+on whom the planters have relied for technical
+guidance and advice.</p>
+
+<p>As regards my own contribution this is confined to a general
+outline of the subject. I have, therefore, omitted reference
+to a number of matters which would have been dealt with in
+detail had space permitted. The information given is based
+on researches on vulcanisation carried out for the Rubber
+Growers&#8217; Association by the writer over a period of nine or
+ten years. It was not found practicable to give detailed
+references in all cases. The reports on which the conclusions
+are based will, however, be found among the regular quarterly<span class='pagenum'><a name="Page_vii" id="Page_vii">[vii]</a></span>
+reports made by the writer for the Association up to June, 1919.
+Subsequent reports have been published in the Monthly
+Bulletin of the Rubber Growers&#8217; Association. We are indebted
+to the Association for permission to publish details
+from these reports, and also for the use made of numerous
+earlier reports published both in London and in the East.</p>
+
+<hr class="c25" />
+<p class='pagenum'><a name="Page_ix" id="Page_ix">[ix]</a></p>
+
+<h2>CONTENTS</h2>
+
+<table class="toc" summary="ToC">
+
+<tr>
+<td colspan="2" class="center fsize125"><a href="#Part1">PART I</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Part1"><i>FIELD OPERATIONS</i></a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch1">CHAPTER I</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch1">PLANTING</a></td>
+</tr>
+
+<tr>
+<td>&nbsp;</td>
+<td class="right fsize80">PAGE</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec1_1">Seeds</a>&mdash;<a href="#Sec1_2">Seed selection</a>&mdash;<a href="#Sec1_3">Strain improvement
+by bad propagation</a>&mdash;<a href="#Sec1_4">Nurseries</a>&mdash;<a href="#Sec1_5">Stumps</a>&mdash;<a href="#Sec1_6">Seed at
+stake</a>&mdash;<a href="#Sec1_7">Basket plants</a>&mdash;<a href="#Sec1_8">Preparation of land</a>&mdash;<a href="#Sec1_9">Danger of
+disease</a>&mdash;<a href="#Sec1_10">Clean clearing</a>&mdash;<a href="#Sec1_11">Loss of top-soil</a>&mdash;<a href="#Sec1_12">Silt-trenches
+on slopes</a></td>
+<td class="rightbot"><a href="#Page_1">1</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch2">CHAPTER II</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch2">FIELD MAINTENANCE</a></td>
+</tr>
+
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec2_1">Clean weeding</a>&mdash;<a href="#Sec2_2">Selective weeding</a>&mdash;<a href="#Sec2_3">Loss of
+top-soil</a>&mdash;<a href="#Sec2_4">Grass ridges</a>&mdash;<a href="#Sec2_5">Lallang eradication</a>&mdash;<a href="#Sec2_6"><i>Mimosa
+gigantea</i> (<i>M. invisa</i>)</a>&mdash;<a href="#Sec2_7">Green cover-plants</a>&mdash;<a href="#Sec2_8">Connection between weeding,
+soil conservation, and soil improvement</a></td>
+<td class="rightbot"><a href="#Page_13">13</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch3">CHAPTER III</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch3">THINNING OF AREAS</a></td>
+</tr>
+
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec3_1">Original planting per acre</a>&mdash;<a href="#Sec3_2">Ultimate stand per acre</a>&mdash;<a
+href="#Sec3_3">Close-planting <i>versus</i> wide-planting</a>&mdash;<a href="#Sec3_4">When to commence thinning operations</a>&mdash;<a
+href="#Sec3_5">How to select in preliminary rounds</a>&mdash;<a href="#Sec3_6">Later selections based on yields of
+individuals</a>&mdash;<a href="#Sec3_7">Yields per tree, present and future</a>&mdash;<a href="#Sec3_8">Trees per acre</a></td>
+<td class="rightbot"><a href="#Page_19">19</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch4">CHAPTER IV</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch4">TAPPING SYSTEMS</a></td>
+</tr>
+
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec4_1">Former methods</a>&mdash;<a href="#Sec4_2">Former systems</a>&mdash;<a href="#Sec4_3">Tendency
+to reduce number of tapping cuts and frequency of tapping</a>&mdash;<a href="#Sec4_4">Period allowed for bark-renewal</a>&mdash;<a
+href="#Sec4_5">Modern systems</a>&mdash;<a href="#Sec4_6">Superimposed cuts</a>&mdash;<a href="#Sec4_7">Single cuts,
+etc.</a>&mdash;<a href="#Sec4_8">Tapping experiments</a>&mdash;<a href="#Sec4_9">R.G.A. experiment</a>&mdash;<a
+href="#Sec4_10">Alternate-daily <i>versus</i> daily tapping</a></td>
+<td class="rightbot"><a href="#Page_28">28</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;<span class='pagenum'><a name="Page_x" id="Page_x">[x]</a></span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch5">CHAPTER V</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch5">TAPPING AND COLLECTING</a></td>
+</tr>
+
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec5_1">Tapping knives</a>&mdash;<a href="#Sec5_2">Personal equation in use of knives</a>&mdash;<a
+href="#Sec5_3">Choice of latex cups</a>&mdash;<a href="#Sec5_4">Cleaning of cups</a>&mdash;<a href="#Sec5_5">Water in cups</a>&mdash;<a
+href="#Sec5_6">Premature (spontaneous) coagulation</a>&mdash;<a href="#Sec5_7">Prevention of spontaneous coagulation</a>&mdash;<a
+href="#Sec5_8">The use of anti-coagulants in the field</a>&mdash;<a href="#Sec5_9">Collecting pails</a>&mdash;<a href="#Sec5_10">Payment
+by result</a>&mdash;<a href="#Sec5_11">Methods for calculation of yields per coolie</a>&mdash;<a href="#Sec5_12">Tree-scrap, oxidation
+of</a>&mdash;<a href="#Sec5_13">Prevention of oxidation</a>&mdash;<a href="#Sec5_15">Bark-shavings</a>&mdash;<a href="#Sec5_16">Collection
+and storage of shavings</a>&mdash;<a href="#Sec5_17">Treatment of shavings</a>&mdash;<a href="#Sec5_18">Collection of earth-scrap</a></td>
+<td class="rightbot"><a href="#Page_38">38</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch6">CHAPTER VI</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch6">TRANSPORT OF LATEX AND COAGULUM</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec6_1">Percentages of &#8220;first&#8221; latex and other grades</a>&mdash;<a href="#Sec6_2">Early
+collection of latex</a>&mdash;<a href="#Sec6_3">Transport, nature of</a>&mdash;<a href="#Sec6_4">Light railways</a>&mdash;<a
+href="#Sec6_5">Motor-lorries</a>&mdash;<a href="#Sec6_6">Bullock-carts</a>&mdash;<a href="#Sec6_7">Care of transport vessels</a>&mdash;<a
+href="#Sec6_8">Use of an anti-coagulant during transport</a>&mdash;<a href="#Sec6_9">Transport by coolie</a>&mdash;<a
+href="#Sec6_10">Coagulation centres (stations)</a>&mdash;<a href="#Sec6_11">Transport of coagulum</a></td>
+<td class="rightbot"><a href="#Page_59">59</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize125"><a href="#Part2">PART II</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Part2"><i>FACTORY OPERATIONS</i></a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch7">CHAPTER VII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch7">PRELIMINARY TREATMENT OF LATEX</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec7_1">Reception at store</a>&mdash;<a href="#Sec7_2">Receptacles</a>&mdash;<a
+href="#Sec7_3">Jars</a>&mdash;<a href="#Sec7_4">Tanks</a>&mdash;<a href="#Sec7_5">Necessity for close supervision</a>&mdash;<a
+href="#Sec7_6">Need for utmost cleanliness</a>&mdash;<a href="#Sec7_7">Straining of latex</a>&mdash;<a
+href="#Sec7_8">Strainers</a>&mdash;<a href="#Sec7_9">Facilitation of straining</a>&mdash;<a href="#Sec7_10">Bulking of latex</a>&mdash;<a
+href="#Sec7_11">Standardised dilution of latex</a>&mdash;<a href="#Sec7_12">Facilities for receiving and handling latex</a>&mdash;<a
+href="#Sec7_13">Reception verandahs</a>&mdash;<a href="#Sec7_14">Receiving vessels</a>&mdash;<a href="#Sec7_15">Types of
+installations</a></td>
+<td class="rightbot"><a href="#Page_65">65</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch8">CHAPTER VIII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch8">COAGULATION</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec8_1">Choice of coagulant</a>&mdash;<a href="#Sec8_2">Strength of acid solution</a>&mdash;<a
+href="#Sec8_3">Making stock solution</a>&mdash;<a href="#Sec8_4">Quantity for use</a>&mdash;<a href="#Sec8_5">Quantities under modern
+requirements</a>&mdash;<a href="#Sec8_6">Care in mixing</a>&mdash;<a href="#Sec8_7">Method of mixing with latex</a>&mdash;<a
+href="#Sec8_8">Use of sodium bisulphite as an anti-oxidant</a>&mdash;<a href="#Sec8_9">Quantities for use</a>&mdash;
+<a href="#Sec8_10">Formul&aelig;</a>&mdash;<a href="#Sec8_11">Abuse of the chemical</a>&mdash;<a href="#Sec8_12">Residual traces in the
+dry rubber</a>&mdash;<a href="#Sec8_13">Use of sodium sulphite as an anti-coagulant, quantities for use</a>&mdash;<a
+href="#Sec8_14">Formul&aelig;</a>&mdash;<a href="#Sec8_15">Use of Formalin as anti-coagulant</a>&mdash;<a href="#Sec8_16">Formul&aelig;
+for use</a></td>
+<td class="rightbot"><a href="#Page_74">74</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;<span class='pagenum'><a name="Page_xi" id="Page_xi">[xi]</a></span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch9">CHAPTER IX</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch9">PREPARATION OF SHEET RUBBER</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec9_1">Pale (air-dried) sheets</a>&mdash;<a href="#Sec9_2">Uniformity of product</a>&mdash;<a
+href="#Sec9_3">Pans <i>versus</i> tanks</a>&mdash;<a href="#Sec9_4">The ideal tank</a>&mdash;<a href="#Sec9_5">Modern
+installations</a>&mdash;<a href="#Sec9_6">Care of tanks</a>&mdash;<a href="#Sec9_7">Standardised dilution of latex</a>&mdash;<a
+href="#Sec9_8">Variation in dimensions and density of coagulum</a>&mdash;<a href="#Sec9_9">Standardising instruments</a>&mdash;<a
+href="#Sec9_10">Method of using</a>&mdash;<a href="#Sec9_11">Skimming latex</a>&mdash;<a href="#Sec9_12">Style of sheets</a>&mdash;<a
+href="#Sec9_13">Standard sheets</a>&mdash;<a href="#Sec9_14">Rolling and marking</a>&mdash;<a href="#Sec9_15">When to work the
+coagulum</a>&mdash;<a href="#Sec9_16">Hand-rolling</a>&mdash;<a href="#Sec9_17">Power smooth-rolling</a>&mdash;<a href="#Sec9_18">Marking
+rolls</a>&mdash;<a href="#Sec9_19">Preparation for smoke-curing</a>&mdash;<a href="#Sec9_20">Caution against accumulation of wet
+sheets</a>&mdash;<a href="#Sec9_21">Hot-water treatment</a>&mdash;<a href="#Sec9_22">Dripping in the open air</a>&mdash;<a
+href="#Sec9_23">When to place in smoke-house</a></td>
+<td class="rightbot"><a href="#Page_89">89</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch10">CHAPTER X</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch10">PREPARATION OF CREPE RUBBER</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec10_1">First consideration, fine pale crepe</a>&mdash;<a href="#Sec10_2">Standardised dilution of
+latex</a>&mdash;<a href="#Sec10_3">Coagulation and coagulant</a>&mdash;<a href="#Sec10_4">Quantities of coagulant</a>&mdash;<a
+href="#Sec10_5">Colour of rubber</a>&mdash;<a href="#Sec10_6">Sodium bisulphite (use of)</a>&mdash;<a href="#Sec10_7">Evaluation and
+deterioration of the bisulphite and sulphite of sodium</a>&mdash;<a href="#Sec10_8">To distinguish between these two
+chemicals</a>&mdash;<a href="#Sec10_9">Care of sodium bisulphite</a>&mdash;<a href="#Sec10_10">Mixing solution with latex</a>&mdash;<a
+href="#Sec10_11">Former methods of making pale rubber</a>&mdash;<a href="#Sec10_12">Working the coagulum</a>&mdash;<a
+href="#Sec10_13">Lower grades of crepe</a>&mdash;<a href="#Sec10_14">Naturally coagulated lump</a>&mdash;<a href="#Sec10_15">Skimmings
+and washings</a>&mdash;<a href="#Sec10_16">Tree-scrap</a>&mdash;<a href="#Sec10_17">Bark-shavings</a>&mdash;<a
+href="#Sec10_18">Earth-scrap</a>&mdash;<a href="#Sec10_19">Fibrous matter in low-grade rubbers</a>&mdash;<a
+href="#Sec10_20">Scrap-washers</a>&mdash;<a href="#Sec10_21">Compound crepes</a>&mdash;<a href="#Sec10_22">Increased care with lower
+grades</a>&mdash;<a href="#Sec10_23">Block rubber from crepe</a>&mdash;<a href="#Sec10_24">Smoked crepe <i>versus</i> sheet
+clippings</a></td>
+<td class="rightbot"><a href="#Page_110">110</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch11">CHAPTER XI</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch11">DRYING OF RUBBER</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec11_1">Air-drying of crepes</a>&mdash;<a href="#Sec11_2">Artificial driers for crepes</a>&mdash;<a
+href="#Sec11_3">Vacuum drying</a>&mdash;<a href="#Sec11_4">Hot-air driers</a>&mdash;<a href="#Sec11_5">Michie-Golledge system</a>&mdash;<a
+href="#Sec11_6">Rate of air-drying</a>&mdash;<a href="#Sec11_7">When drying takes place</a>&mdash;<a href="#Sec11_8">Increase in weight of
+drying crepe</a>&mdash;<a href="#Sec11_9">Differences in weight</a>&mdash;<a href="#Sec11_10">Aids to normal drying</a>&mdash;<a
+href="#Sec11_11">Smoke-curing of sheet rubber</a>&mdash;<a href="#Sec11_12">Instruments for recording temperature</a>&mdash;<a
+href="#Sec11_13">Temperatures of smoke-house</a>&mdash;<a href="#Sec11_14">Period of drying</a>&mdash;<a href="#Sec11_15">Fuels for
+smoking</a>&mdash;<a href="#Sec11_16">Sun-drying of sheet rubber</a>&mdash;<a href="#Sec11_17">Artificial driers for sheet rubber</a></td>
+<td class="rightbot"><a href="#Page_132">132</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;<span class='pagenum'><a name="Page_xii" id="Page_xii">[xii]</a></span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch12">CHAPTER XII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch12">SORTING, GRADING, AND PACKING</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec12_1">Reducing number of grades</a>&mdash;<a href="#Sec12_2">Reduction carried too far</a>&mdash;<a
+href="#Sec12_3">R.G.A. recommendations</a>&mdash;<a href="#Sec12_4">Care in sorting</a>&mdash;<a href="#Sec12_5">Choice of packing
+cases</a>&mdash;<a href="#Sec12_7">Bags</a>&mdash;<a href="#Sec12_8">Bales</a>&mdash;<a href="#Sec12_9">Folding of crepe</a>&mdash;<a
+href="#Sec12_10">Mechanical folders</a>&mdash;<a href="#Sec12_6">Care in assembling</a>&mdash;<a href="#Sec12_11">Methods of
+packing</a>&mdash;<a href="#Sec12_12">Weight of contents</a>&mdash;<a href="#Sec12_13">Short weights</a></td>
+<td class="rightbot"><a href="#Page_150">150</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize125"><a href="#Part3">PART III</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Part3"><i>MACHINERY AND BUILDINGS</i></a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch13">CHAPTER XIII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch13">MACHINES</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec13_1">Quality of metal in rolls</a>&mdash;<a href="#Sec13_2">Nature of roll-bearings</a>&mdash;<a
+href="#Sec13_3">Brass liners</a>&mdash;<a href="#Sec13_4">Liners of alloy or of cast-iron</a>&mdash;<a href="#Sec13_5">Adequacy of
+machines</a>&mdash;<a href="#Sec13_6">Arrangement of battery</a>&mdash;<a href="#Sec13_7">Speed of machines</a>&mdash;<a
+href="#Sec13_8">Gear ratios</a>&mdash;<a href="#Sec13_9">Grooving of rolls</a>&mdash;<a href="#Sec13_10">Heating of rolls</a>&mdash;<a
+href="#Sec13_11">Sheeting machines</a>&mdash;<a href="#Sec13_12">Lubrication</a>&mdash;<a href="#Sec13_13">Trays</a>&mdash;<a
+href="#Sec13_14">Position of battery</a>&mdash;<a href="#Sec13_15">Drainage of battery</a>&mdash;<a href="#Sec13_16">Access to back of
+machines</a>&mdash;<a href="#Sec13_17">Engines</a>&mdash;<a href="#Sec13_18">Power</a></td>
+<td class="rightbot"><a href="#Page_159">159</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch14">CHAPTER XIV</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch14">FACTORIES</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec14_1">General construction</a>&mdash;<a href="#Sec14_2">Plenty of light</a>&mdash;<a
+href="#Sec14_3">Floors</a>&mdash;<a href="#Sec14_4">Drainage of</a>&mdash;<a href="#Sec14_5">How many storeys</a>&mdash;<a
+href="#Sec14_6">Verandahs</a>&mdash;<a href="#Sec14_7">Tanks, situation of</a>&mdash;<a href="#Sec14_8">Designs and lay-out</a>&mdash;<a
+href="#Sec14_9">Drains</a>&mdash;<a href="#Sec14_10">Water supply</a></td>
+<td class="rightbot"><a href="#Page_172">172</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch15">CHAPTER XV</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch15">OTHER BUILDINGS</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec15_1">Drying-houses for crepe rubber</a>&mdash;<a href="#Sec15_2">How many storeys</a>&mdash;<a
+href="#Sec15_3">Ventilation</a>&mdash;<a href="#Sec15_4">Windows</a>&mdash;<a href="#Sec15_5">Effect of light</a>&mdash;<a
+href="#Sec15_6">Effect of direct sun-rays</a>&mdash;<a href="#Sec15_7">Hot-air houses</a>&mdash;<a
+href="#Sec15_8">Smoke-houses</a>&mdash;<a href="#Sec15_9">Various types</a>&mdash;<a href="#Sec15_10">Ordinary smoke-houses</a>&mdash;<a
+href="#Sec15_11">General ventilation</a>&mdash;<a href="#Sec15_12">Windows</a>&mdash;<a href="#Sec15_13">Racks of supports</a>&mdash;<a
+href="#Sec15_14">Floors</a>&mdash;<a href="#Sec15_15">Furnaces in general</a>&mdash;<a href="#Sec15_16">Pit-fires</a>&mdash;<a
+href="#Sec15_17">Pot-fires</a>&mdash;<a href="#Sec15_18">Iron stoves</a>&mdash;<a href="#Sec15_19">Horizontal drum-furnaces</a>&mdash;<a
+href="#Sec15_20">Rate of combustion</a>&mdash;<a href="#Sec15_21">Brick stoves</a>&mdash;<a href="#Sec15_22">Pataling type
+of</a>&mdash;<a href="#Sec15_23">Consumption of fuel</a>&mdash;<a href="#Sec15_24">Floor of furnace room</a>&mdash;<a
+href="#Sec15_25">Roof</a>&mdash;<a href="#Sec15_25a">Brick built houses</a>&mdash;<a href="#Sec15_26">&#8220;Third Mile&#8221;
+type</a>&mdash;<a href="#Sec15_27">Jackson cabinet</a>&mdash;<a href="#Sec15_28">Devon type</a>&mdash;<a href="#Sec15_29">Detailed
+description of</a>&mdash;<a href="#Sec15_30">Barker patent design</a></td>
+<td class="rightbot"><a href="#Page_178">178</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;<span class='pagenum'><a name="Page_xiii" id="Page_xiii">[xiii]</a></span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch16">CHAPTER XVI</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch16">OTHER BUILDINGS (<i>continued</i>), AND SITUATION OF BUILDINGS</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec16_1">Sorting-room</a>&mdash;<a href="#Sec16_2">Packing room</a>&mdash;<a href="#Sec16_3">Store
+rooms</a>&mdash;<a href="#Sec16_4">Storage of rubber</a>&mdash;<a href="#Sec16_5">Need for special accommodation</a>&mdash;<a
+href="#Sec16_6">Floor of store room</a>&mdash;<a href="#Sec16_7">Local conditions</a>&mdash;<a href="#Sec16_8">Temperature and
+humidity</a>&mdash;<a href="#Sec16_9">Incidence of moulds</a>&mdash;<a href="#Sec16_10">Effect upon smoked sheets</a>&mdash;<a
+href="#Sec16_11">Tool-sheds and stores</a>&mdash;<a href="#Sec16_12">Situation of buildings</a>&mdash;<a href="#Sec16_13">Position with
+respect to points of the compass</a>&mdash;<a href="#Sec16_14">Choosing a factory site</a>&mdash;<a
+href="#Sec16_15">Centralisation</a>&mdash;<a href="#Sec16_16">Decentralisation</a></td>
+<td class="rightbot"><a href="#Page_211">211</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize125"><a href="#Part4">PART IV</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Part4"><i>THE FINISHED RUBBER</i></a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch17">CHAPTER XVII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch17">DEFECTS IN CREPE RUBBERS</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec17_1">General style of finish</a>&mdash;<a href="#Sec17_2">Dirty edges</a>&mdash;<a
+href="#Sec17_3">Iron-stains</a>&mdash;<a href="#Sec17_4">Rust-stains</a>&mdash;<a href="#Sec17_5">Oil-marks</a>&mdash;<a
+href="#Sec17_6">Trays</a>&mdash;<a href="#Sec17_7">Dirt</a>&mdash;<a href="#Sec17_8">Holes</a>&mdash;<a href="#Sec17_9">Greenish and
+tacky streaks</a>&mdash;<a href="#Sec17_10">Not due to oil <i>per se</i></a>&mdash;<a href="#Sec17_11">Tackiness and copper</a>&mdash;<a
+href="#Sec17_12">Cotton and other fibre</a>&mdash;<a href="#Sec17_13">Bark and grit</a>&mdash;<a href="#Sec17_14">Sand</a>&mdash;<a
+href="#Sec17_15">Oxidation streaks</a>&mdash;<a href="#Sec17_16">Yellow streaks</a>&mdash;<a href="#Sec17_17">Bisulphite
+streaks</a>&mdash;<a href="#Sec17_18">Spot disease</a>&mdash;<a href="#Sec17_19">Cause of</a>&mdash;<a href="#Sec17_20">Influence of rate
+of drying</a>&mdash;<a href="#Sec17_21">Percentage of moisture</a>&mdash;<a href="#Sec17_22">Humidity of atmosphere</a>&mdash;<a
+href="#Sec17_23">Prevention of disease</a>&mdash;<a href="#Sec17_24">Infection by contact</a>&mdash;<a href="#Sec17_25">Outbreak of
+dormant spores</a>&mdash;<a href="#Sec17_26">Rules to be observed</a>&mdash;<a href="#Sec17_27">Surface moulds or mildew</a>&mdash;<a
+href="#Sec17_28">Tackiness in general</a>&mdash;<a href="#Sec17_29">Full discussion of</a>&mdash;<a href="#Sec17_30">Experimental
+reproduction</a>&mdash;<a href="#Sec17_31">Lack of uniformity in colour</a>&mdash;<a href="#Sec17_32">Defects in block rubber</a></td>
+<td class="rightbot"><a href="#Page_223">223</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch18">CHAPTER XVIII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch18">DEFECTS IN SHEET RUBBER</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec18_1">Defective coagulation</a>&mdash;<a href="#Sec18_2">Coloured surface blotches</a>&mdash;<a
+href="#Sec18_3">General darkening of surface</a>&mdash;<a href="#Sec18_4">Soft coagulum</a>&mdash;<a href="#Sec18_5">Spongy
+underface</a>&mdash;<a href="#Sec18_6">Tearing</a>&mdash;<a href="#Sec18_7">&#8220;Pitting&#8221; of surface</a>&mdash;<a
+href="#Sec18_8">Thick ends or edges</a>&mdash;<a href="#Sec18_9">Mis-shapen sheets</a>&mdash;<a href="#Sec18_10">Thick patches</a>&mdash;<a
+href="#Sec18_11">Torn sheets</a>&mdash;<a href="#Sec18_12">&#8220;Dog-ears&#8221;</a>&mdash;<a href="#Sec18_13">Creases</a>&mdash;<a
+href="#Sec18_14">Greasiness of surface before smoking</a>&mdash;<a href="#Sec18_15">Surface blemishes</a>&mdash;<a href="#Sec18_16">Uneven
+appearance</a>&mdash;<a href="#Sec18_17">Variation due to oxidation</a>&mdash;<a href="#Sec18_18">Colour when dry</a>&mdash;<a
+href="#Sec18_19">Surface gloss</a>&mdash;<a href="#Sec18_20">Dull surface</a>&mdash;<a href="#Sec18_21">Moist glaze and
+greasiness</a>&mdash;<a href="#Sec18_22">Virgin spots</a>&mdash;<a href="#Sec18_23">Surface moulds or mildew</a>&mdash;<a
+href="#Sec18_24">Black streaks or spots</a>&mdash;<a href="#Sec18_25">White or grey streaks</a>&mdash;<a href="#Sec18_26">Rust</a>&mdash;<a
+href="#Sec18_27">Theories on formation of</a>&mdash;<a href="#Sec18_28">Prevention of</a>&mdash;<a href="#Sec18_29">Two
+methods</a>&mdash;<a href="#Sec18_30">Other views on causation</a>&mdash;<a href="#Sec18_31">Bubbles</a>&mdash;<a href="#Sec18_32">Causes
+of formation</a>&mdash;<a href="#Sec18_33">In the field</a>&mdash;<a href="#Sec18_34">In the factory</a>&mdash;<a
+href="#Sec18_35">Blisters</a>&mdash;<a href="#Sec18_36">&#8220;Spot&#8221; disease in sheet rubber</a>&mdash;<a href="#Sec18_37">Support
+marks</a>&mdash;<a href="#Sec18_38">Stickiness</a>&mdash;<a href="#Sec18_39">Surface pattern</a>&mdash;<a href="#Sec18_40">Sheet
+clippings</a>&mdash;<a href="#Sec18_41">Other infrequent defects</a>&mdash;<a href="#Sec18_42">Dirt</a>&mdash;<a
+href="#Sec18_43">Ash</a>&mdash;<a href="#Sec18_44">Bark</a>&mdash;<a href="#Sec18_45">Splinters</a></td>
+<td class="rightbot"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;<span class='pagenum'><a name="Page_xiv" id="Page_xiv">[xiv]</a></span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize125"><a href="#Part5">PART V</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Part5"><i>GENERAL</i></a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch19">CHAPTER XIX</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch19">CHOICE OF COAGULANT</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec19_1">Acetic acid in general use</a>&mdash;<a href="#Sec19_2">Is a coagulant necessary?</a>&mdash;<a
+href="#Sec19_3">Acetic acid</a>&mdash;<a href="#Sec19_4">Formic acid</a>&mdash;<a href="#Sec19_5">Citric acid</a>&mdash;<a
+href="#Sec19_6">Tartaric acid</a>&mdash;<a href="#Sec19_7">Oxalic acid</a>&mdash;<a href="#Sec19_8">Sulphuric acid</a>&mdash;<a
+href="#Sec19_9">Hydrochloric and nitric acids</a>&mdash;<a href="#Sec19_10">Hydrofluoric acid</a>&mdash;<a
+href="#Sec19_11">Alum</a>&mdash;<a href="#Sec19_12">Pyroligneous acid</a>&mdash;<a href="#Sec19_13">Smoked water</a>&mdash;<a
+href="#Sec19_14">Chinese vinegar</a>&mdash;<a href="#Sec19_15">Sulphurous acid</a>&mdash;<a href="#Sec19_16">Sugars</a>&mdash;<a
+href="#Sec19_17">Various salts</a>&mdash;<a href="#Sec19_18">Proprietary compounds</a>&mdash;<a href="#Sec19_19">Carbonic acid
+gas</a>&mdash;<a href="#Sec19_20">Alcohol</a>&mdash;<a href="#Sec19_21">Vegetable extracts</a></td>
+<td class="rightbot"><a href="#Page_278">278</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch20">CHAPTER XX</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch20">SPECIAL METHODS OF PREPARATION</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec20_1">Da Costa process</a>&mdash;<a href="#Sec20_2">Byrne curing process</a>&mdash;<a
+href="#Sec20_3">Freezing process</a>&mdash;<a href="#Sec20_4">Wickham process</a>&mdash;<a href="#Sec20_5">Derry process</a>&mdash;<a
+href="#Sec20_6">Spontaneous coagulation</a>&mdash;<a href="#Sec20_7">Definition of</a>&mdash;<a href="#Sec20_8">Discussion of
+types</a>&mdash;<a href="#Sec20_9">&AElig;robic</a>&mdash;<a href="#Sec20_10">An&aelig;robic</a>&mdash;<a
+href="#Sec20_11">Organisms</a>&mdash;<a href="#Sec20_12">Maude-Crosse patent</a>&mdash;<a href="#Sec20_13">Method of operation</a>&mdash;<a
+href="#Sec20_14">Accelerating action of sugars</a>&mdash;<a href="#Sec20_15">Accelerating action of soluble calcium salts</a>&mdash;<a
+href="#Sec20_16">Ilcken-Down process</a>&mdash;<a href="#Sec20_17">Slab rubber</a></td>
+<td class="rightbot"><a href="#Page_290">290</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize125"><a href="#Part6">PART VI</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Part6"><i>VULCANISATION</i></a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch21">CHAPTER XXI</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch21">INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec21_1">Wild rubber contrasted with plantation rubber</a>&mdash;<a href="#Sec21_2">Milling and
+mixing</a>&mdash;<a href="#Sec21_3">Preparation for vulcanising</a>&mdash;<a href="#Sec21_4">Vulcanising</a></td>
+<td class="rightbot"><a href="#Page_301">301</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch22">CHAPTER XXII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch22">TESTING OF PLANTATION RUBBER</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec22_1">Tests on raw rubber</a>&mdash;<a href="#Sec22_2">Breaking strain</a>&mdash;<a
+href="#Sec22_3">Behaviour of rubber during milling, etc.</a>&mdash;<a href="#Sec22_5">Preparation for testing</a>&mdash;<a
+href="#Sec22_4">Tests on vulcanised rubber</a>&mdash;<a href="#Sec22_6">Choice of a formula</a>&mdash;<a href="#Sec22_7">Physical
+tests</a></td>
+<td class="rightbot"><a href="#Page_309">309</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch23">CHAPTER XXIII</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="center fsize110"><a href="#Ch23">THE PROPERTIES OF RUBBER</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><a href="#Sec23_1">Raw rubber</a>&mdash;<a href="#Sec23_2">Physical tests</a>&mdash;<a href="#Sec23_3">Vulcanised
+rubber</a>&mdash;<a href="#Sec23_4">&#8220;Inner qualities&#8221; of raw rubber</a>&mdash;<a href="#Sec23_5">Defects of crepe and
+sheet</a>&mdash;<a href="#Sec23_6">Variation in physical properties</a>&mdash;<a href="#Sec23_7">Rate of cure</a>&mdash;<a
+href="#Sec23_8">Influence of various factors in raw rubber on rate of cure</a>&mdash;<a href="#Sec23_9">Other types of plantation
+rubber</a>&mdash;<a href="#Sec23_10">Fine para</a></td>
+<td class="rightbot"><a href="#Page_313">313</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="just ind"><span class="smcap"><a href="#INDEX">Index</a></span></td>
+<td class="rightbot"><a href="#Page_327">327</a></td>
+</tr>
+
+</table>
+
+<p class='pagenum'><a name="Page_xv" id="Page_xv">[xv]</a></p>
+
+<hr class="c25" />
+<h2>LIST OF ILLUSTRATIONS</h2>
+
+<table class="loi" summary="List of Illustrations">
+
+<tr>
+<td colspan="2" class="right fsize80">PAGE</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig1">SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING</a></td>
+<td class="rightbot">2</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig2">FELLING LIGHT (SECONDARY) JUNGLE</a></td>
+<td class="rightbot">3</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig3">SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED</a></td>
+<td class="rightbot">4</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig4">NEW CLEARING</a></td>
+<td class="rightbot">5</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig5">TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING</a></td>
+<td class="rightbot">6</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig6">LIGHT JUNGLE</a></td>
+<td class="rightbot">7</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig7">DENSE JUNGLE</a></td>
+<td class="rightbot">8</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig8">CLEARING READY FOR PLANTING</a></td>
+<td class="rightbot">9</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig9">NEW CLEARING: SLOPES &#8220;HOLED&#8221; FOR PLANTING; FLAT AREA BEING DRAINED</a></td>
+<td class="rightbot">11</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig10">TYPICAL YOUNG CLEARING, WITH TIMBER</a></td>
+<td class="rightbot">15</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig11">TYPICAL YOUNG CLEARING, WITH TIMBER</a></td>
+<td class="rightbot">17</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig12">TYPICAL YOUNG PLANTED AREA</a></td>
+<td class="rightbot">20</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig13">ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA</a></td>
+<td class="rightbot">21</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig14">WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO TAPPING</a></td>
+<td class="rightbot">24</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig15">FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED TOO LONG</a></td>
+<td class="rightbot">25</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig16">TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE</a></td>
+<td class="rightbot">31</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig17">THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE AND ON RENEWED BARK</a></td>
+<td class="rightbot">33</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig18">SINGLE CUT ON HALF CIRCUMFERENCE (HALF-SPIRAL)</a></td>
+<td class="rightbot">35</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig19">A <span class="ssfont">V</span>-CUT ON HALF THE CIRCUMFERENCE</a></td>
+<td class="rightbot">37</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig20">SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE</a></td>
+<td class="rightbot">41</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig21">EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING</a></td>
+<td class="rightbot">44</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig22">ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING</a></td>
+<td class="rightbot">45</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig23">1. SHOWING EFFECT OF &#8220;WINTERING&#8221;</a></td>
+<td class="rightbot">48</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig24">2. NEW GROWTH OF YOUNG LEAF ON SAME TREE</a></td>
+<td class="rightbot">49</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig25">EFFECTS OF DISEASE&mdash;&#8220;MOULDY ROT&#8221;</a></td>
+<td class="rightbot">50</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig26">EFFECTS OF DISEASE&mdash;&#8220;MOULDY ROT&#8221;</a></td>
+<td class="rightbot">51</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig27">EFFECTS OF DISEASE&mdash;&#8220;MOULDY ROT&#8221;</a></td>
+<td class="rightbot">52</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig28">EFFECTS OF DISEASE&mdash;&#8220;MOULDY ROT&#8221;</a></td>
+<td class="rightbot">53</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig29">RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED WITH FACILITIES FOR CALCULATING INDIVIDUAL
+DAILY &#8220;YIELD PER COOLIE&#8220;BY SAMPLING OF LATEX</a></td>
+<td class="rightbot">66</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig30">END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD FOR
+RECEIVING LATEX AND FILLING TANK</a></td>
+<td class="rightbot">70</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig31">RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX</a></td>
+<td class="rightbot">71</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig32">ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH</a></td>
+<td class="rightbot">72</td>
+</tr>
+
+<tr>
+<td class="left ind"><span class='pagenum'><a name="Page_xvi" id="Page_xvi">[xvi]</a></span><a href="#Fig33">TWO VIEWS OF
+DILUTION AND MIXING TANKS</a></td>
+<td class="rightbot">81</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig34">UNIT MODERN COAGULATING TANK (TWO VIEWS)</a></td>
+<td class="rightbot">91</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig35">ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON THE RIGHT</a></td>
+<td class="rightbot">92</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig36">CLOSER VIEW OF FOREGOING</a></td>
+<td class="rightbot">93</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig37">ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF GRAVITATING LATEX</a></td>
+<td class="rightbot">95</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig38">A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION</a></td>
+<td class="rightbot">96</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig39">A &#8220;BATTERY&#8221; OF SHEETING TANKS (PATALING ESTATE).
+DILUTION TANKS, RAISED, ON THE LEFT</a></td>
+<td class="rightbot">97</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig40">THE OLD METHOD OF &#8220;DRIPPING&#8221; FRESHLY ROLLED SHEETS WITHIN THE FACTORY</a></td>
+<td class="rightbot">108</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig41">THE NEWER METHOD OF HANGING IN THE OPEN AIR</a></td>
+<td class="rightbot">109</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig42">THREE GRADES OF CREPE RUBBER</a></td>
+<td class="rightbot">111</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig43">A WASHING SHED</a></td>
+<td class="rightbot">112</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig44">DRYING GRAPH. PALE CREPE (THIN)</a></td>
+<td class="rightbot">140</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig45">A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT</a></td>
+<td class="rightbot">155</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig46">ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT</a></td>
+<td class="rightbot">157</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig47">A BATTERY OF MACHINES</a></td>
+<td class="rightbot">165</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig48">&#8220;THIRD MILE&#8221; TYPE; HORIZONTAL DRUM</a></td>
+<td class="rightbot">190</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig49">&#8220;THIRD MILE&#8221; TYPE OF FURNACE, USED IN CONJUNCTION WITH &#8220;THIRD MILE&#8221;
+SMOKE-HOUSE</a></td>
+<td class="rightbot">190</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig50">SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE)</a></td>
+<td class="rightbot">193</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig51">PATALING TYPE OF FURNACE</a></td>
+<td class="rightbot">193</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig52">LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED VENTILATORS PERMANENTLY OPEN</a></td>
+<td class="rightbot">194</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig53">BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE BUILDING, BUT FED FROM OUTSIDE</a></td>
+<td class="rightbot">195</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig54">GENERAL VIEW OF SHELTERS COVERING APPROACHES  TO FURNACES</a></td>
+<td class="rightbot">196</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig55">NEAR VIEW OF SHELTER</a></td>
+<td class="rightbot">197</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig56">&#8220;THIRD MILE&#8221; TYPE OF SMOKE-HOUSE</a></td>
+<td class="rightbot">199</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig57">GENERAL VIEW OF DOUBLE &#8220;DEVON&#8221; TYPE OF SMOKE-HOUSE</a></td>
+<td class="rightbot">201</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig58">GENERAL VIEW OF DOUBLE &#8220;DEVON&#8221; SMOKE-HOUSE AND FACTORY BUILDINGS</a></td>
+<td class="rightbot">202</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig59">VIEW OF PLATFORM OF &#8220;DEVON&#8221; SMOKE-HOUSE;
+DOORS OF COMPARTMENTS OPEN, AND ONE RACK PARTIALLY WITHDRAWN</a></td>
+<td class="rightbot">203</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig60">DOUBLE &#8220;DEVON&#8221; SMOKE-HOUSE OF BRICK,
+WITH ROOF OF CHINESE TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM SMOKING CHAMBERS</a></td>
+<td class="rightbot">204</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig61">SIDE-VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL ARRANGEMENT FOR STOKING FURNACES</a></td>
+<td class="rightbot">205</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig62">FRONT VIEW OF DOUBLE &#8220;DEVON&#8221; TYPE OF SMOKE-HOUSE</a></td>
+<td class="rightbot">206</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig63">SIDE-VIEW OF DOUBLE &#8220;DEVON&#8221; TYPE OF SMOKE-HOUSE</a></td>
+<td class="rightbot">207</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig64">THE NEW &#8220;BARKER&#8221; TYPE OF SMOKE-HOUSE: A SMALL UNIT</a></td>
+<td class="rightbot">210</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig65">SUGGESTED ARRANGEMENT OF BUILDING</a></td>
+<td class="rightbot">218</td>
+</tr>
+
+<tr>
+<td class="left ind"><a href="#Fig66">THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM &#8220;SPOT&#8221; DISEASE</a></td>
+<td class="rightbot">237</td>
+</tr>
+
+</table>
+
+<p class='pagenum'><a name="Page_1" id="Page_1">[1]</a></p>
+
+<hr class="c25" />
+<h1>THE PREPARATION<br />
+OF PLANTATION RUBBER</h1>
+
+<h2><a name="Part1" id="Part1"></a>PART I</h2>
+
+<h3>FIELD OPERATIONS</h3>
+
+<h2><a name="Ch1" id="Ch1"></a>CHAPTER I</h2>
+
+<h3><i>PLANTING</i></h3>
+
+
+<p>To criticise the methods of the pioneer planters of <i>Hevea
+Brasiliensis</i> presents no difficulty in the light of present comparative
+knowledge, and to be &#8220;wise after the event&#8221; is a failing
+which is not confined to those interested in modern planting
+methods. Looking at the matter broadly, however, it must
+be acknowledged that the pioneers, wrong though they may have
+been on some points, did remarkably well, considering that
+there existed no real knowledge on the subject and that the
+methods employed were perforce of an empirical nature.
+Although we know a little more concerning the scientific
+aspects of rubber planting, the sum total of that knowledge
+does not justify any drastic criticism of the methods employed
+by our predecessors. In fact, although we may be of opinion
+that on general lines there is little now to be learned regarding
+the planting of <i>Hevea Brasiliensis</i>, our present knowledge
+does not preclude the possibility that future investigations
+may bring against us charges similar to those sometimes
+levelled at the earlier planters.</p>
+
+<p>The main theme of the present volume is that of the preparation
+of rubber for the market. Hence it is not proposed to
+deal in detail with the work attaching to the opening and
+development of rubber estates. For this the reader is referred
+to the literature dealing specifically with rubber planting.
+Certain points in connection with planting may advantageously<span class='pagenum'><a name="Page_2" id="Page_2">[2]</a></span>
+be treated in a general way according to modern knowledge,
+and of these it is proposed to discuss a few in the following
+pages.</p>
+
+<div class="figcenter"><a name="Fig1" id="Fig1"></a><img src="images/illo019.jpg" alt="Seeds, showing Variable Size, Shape, and Marking" />
+<p class="caption"><span class="smcap">Seeds, showing Variable Size, Shape, and Marking.</span></p></div>
+
+<p><span class="smcap"><a name="Sec1_1" id="Sec1_1"></a>Seeds.</span>&mdash;The view is now generally held that many areas
+were planted from seed which was not collected in a discriminate
+manner; and that probably the comparatively low yields
+obtained on areas of some estates may be due to the employment
+of seed from a poor strain. To be able to decide whether
+such explanation fits the case demands a full knowledge of
+all the possible factors governing the question of yields. It
+may, or may not, be a fact that seed from a poor strain is wholly<span class='pagenum'><a name="Page_3" id="Page_3">[3]</a></span>
+or partially accountable for low yields; but whatever the degree
+in which the seed influences the result, it is an axiom that to
+obtain the best results in all planting industries a most judicious
+selection of seed should be made. In short, seed obtained
+from good-yielding specimens by selective treatment will
+eventually produce progeny of good-yielding strain.</p>
+
+<div class="figcenter"><a name="Fig2" id="Fig2"></a><img src="images/illo020.jpg" alt="Felling Light (Secondary) Jungle" />
+<p class="caption"><span class="smcap">Felling Light (Secondary) Jungle.</span></p></div>
+
+<p>The recognition of these principles as applied to the planting
+of <i>H. Brasiliensis</i> has focussed recent attention upon the
+desirability of planting nurseries with seeds obtained from those
+trees which are known to be good producers of latex of normal
+consistency. It does not follow that the tree of most rapid
+growth and development is necessarily the best yielder; such
+is often not the case. In the matter of selection, therefore, one
+has to take other standards than that of size; and the issue is
+narrowed chiefly to a consideration of the yields of latex given
+by individual trees. It has been found by various experimenters
+that there is no necessity to proceed to such a refinement
+as the determination of the actual weight of rubber yielded.
+The dry rubber content of latices from the same trees is found<span class='pagenum'><a name="Page_4" id="Page_4">[4]</a></span>
+to be so comparatively regular, allowing for climatic changes,
+that it is sufficient for the purposes of selection to measure the
+volumes of latex yielded by individual trees.</p>
+
+<div class="figcenter"><a name="Fig3" id="Fig3"></a><img src="images/illo021.jpg" alt="Seedling, showing Root-System with Seed
+still Attached" />
+<p class="caption"><span class="smcap">Seedling, showing Root-System with Seed<br />still Attached.</span></p></div>
+
+<p>Unfortunately the industry is so young that the question of
+seed selection yet awaits study. The task presents certain
+practical difficulties, and would be by no means so easy to
+control as in the case of seed selection from other plants. It
+will be obvious that several generations of trees raised from
+selected seed would have to be under observation before any
+sound deductions could be made from statistics obtained in
+the course of the work. Thus the problem of seed-selection<span class='pagenum'><a name="Page_5" id="Page_5">[5]</a></span>
+as it concerns the establishment of a high-yielding strain would
+involve many years of observation on the part of a trained
+man. Unfortunately neither the man nor the facilities for
+such experimental work exist at the present moment in the
+Federated Malay States. On the scientific side the industry
+is incommensurably staffed, and most of the workers&#8217; time is
+occupied with routine work connected with estate practice.</p>
+
+<div class="figcenter"><a name="Fig4" id="Fig4"></a><img src="images/illo022.jpg" alt="New Clearing" />
+<p class="caption"><span class="smcap">New Clearing.</span></p>
+<p class="capt500">In the middle distance, felled trees awaiting burning; in the
+foreground, a flat and wet area with main drainage outlined.
+(<i>By courtesy of the manager of Membakut Estate, British North
+Borneo.</i>)</p></div>
+
+<div class="figcenter"><a name="Fig5" id="Fig5"></a><img src="images/illo023.jpg" alt="Typical Young Clearing, Aged about Three Years, planted on
+Virgin Soil" />
+<p class="caption"><span class="smcap">Typical Young Clearing, Aged about Three Years, planted on Virgin Soil.<br />
+Original Jungle Timber slowly Rotting.</span></p></div>
+
+<p><span class="smcap"><a name="Sec1_2" id="Sec1_2"></a><a name="Sec1_3" id="Sec1_3"></a>Selection.</span>&mdash;It
+is possible, however, that the question of
+strain improvement will be solved in another manner than
+that of successive breeding from the seeds of high-yielding
+trees. Such investigatory work is now occupying the attention
+of scientific organisations in the East, and credit is due to the
+stations in Java which have begun experimental work in this
+direction. In brief, the scheme may be outlined as follows.
+Trees known to be uniformly good yielders are kept under<span class='pagenum'><a name="Page_6" id="Page_6">[6]</a></span>
+observation, and the seeds gathered carefully. These seeds
+are germinated in a special nursery, and the best-grown seedlings
+are selected for further operations. At a certain stage a bud
+is taken from a high-yielding parent tree and grafted upon the
+stem of the seedling. When this has &#8220;struck&#8221; the original
+head of the seedling is removed. This ensures that one has
+in the seedling both the stem and future branch system of the<span class='pagenum'><a name="Page_7" id="Page_7">[7]</a></span>
+same strain as the parent high-yielding trees. It is possible to
+go a step farther, and by certain processes induce a new root
+system to grow above the existing roots, which are then removed.
+One is then able to guarantee that the roots, stem, and branches
+will be of the original high-yielding strain. An objection
+sometimes made against the third operation of inducing
+a new root system is that the original tap-root is removed and
+that the subsequent system consists only of laterals. Against
+this argument may be quoted the observed fact that in actual
+development any one of the laterals may under such circumstances
+function eventually as a tap-root.</p>
+
+<div class="figcenter"><a name="Fig6" id="Fig6"></a><img src="images/illo024.jpg" alt="Light Jungle" />
+<p class="caption"><span class="smcap">Light Jungle.</span></p></div>
+
+<p>On the whole, this system of propagation receives the approval<span class='pagenum'><a name="Page_8" id="Page_8">[8]</a></span>
+of investigators, and removes the objections which may be
+advanced against the development of a scheme entirely founded
+upon successive breedings from selected seed. The course of
+the investigations, also, are thereby shortened considerably.
+Care must be exercised in the work of obtaining and grafting
+the buds, but it has now been proved that by exercising reasonable
+precautions which are not beyond the intelligence and
+ability of subordinates, an extremely high percentage of
+success can be attained.</p>
+
+<div class="figcenter"><a name="Fig7" id="Fig7"></a><img src="images/illo025.jpg" alt="Dense Jungle" />
+<p class="caption"><span class="smcap">Dense Jungle.</span></p></div>
+
+<p>Until such time as this process becomes practicable the
+inception of a planted area must follow the lines usually
+adopted.</p>
+
+<p><span class='pagenum'><a name="Page_9" id="Page_9">[9]</a></span><span class="smcap"><a
+name="Sec1_4" id="Sec1_4"></a>Nurseries.</span>&mdash;The usual
+practice is to obtain seeds from some estate which has a reputation for good yields and for exercising
+care in the gathering and shipping of seeds. The seed is planted
+in specially prepared beds, and the percentage of germination
+noted for future reference. The plants should be tended
+carefully, and close observation made for the detection of disease
+or pests. It is not uncommon to find that owing to lack of
+care in the preparation of the seed-bed, the young plants are
+attacked by disease.</p>
+
+<div class="figcenter"><a name="Fig8" id="Fig8"></a><img src="images/illo026.jpg" alt="Clearing Ready for Planting" />
+<p class="caption"><span class="smcap">Clearing Ready for Planting.</span></p>
+<p class="center">Surface timber removed, but stumps remaining.</p></div>
+
+<p><a name="Sec1_5" id="Sec1_5"></a><span class="smcap">Stumps.</span>&mdash;At a stage, varying according to the requirements
+of the estate, when the plants are from twelve to
+eighteen months old, they are lifted from the earth. The
+roots and head are cut off, and the &#8220;stump&#8221; is ready for
+immediate planting in the field. Naturally any appreciable
+delay in planting, or unfavourable weather conditions, will
+militate against the chances of successful &#8220;striking&#8221;; and it
+is not uncommon to find that a certain number of &#8220;supplies&#8221;
+will be necessary.</p>
+
+<p><span class='pagenum'><a name="Page_10" id="Page_10">[10]</a></span><a name="Sec1_6" id="Sec1_6"></a><span class="smcap">Seed
+at Stake.</span>&mdash;A method sometimes adopted is to put out
+seed in the field, in prepared holes which indicate the exact
+position of the future trees. Usually three seeds are placed
+in each hole, and if two or three germinate, the plant having
+the healthiest appearance is retained, and the others removed.
+The possible objections to this method of planting are obvious
+to those acquainted with field conditions, but in actual practice
+planting seed &#8220;at stake&#8221; has often proved highly successful.
+Naturally the results obtained must depend upon the selection
+of good seeds, the care exercised in the preparation of the
+&#8220;holes,&#8221; weather conditions, and the discrimination exercised
+in the selection of the plants to be retained&mdash;apart from such
+disabilities as the depredations of rats and other pests.</p>
+
+<p><a name="Sec1_7" id="Sec1_7"></a><span class="smcap">Basket Plants.</span>&mdash;Yet another and perhaps the most popular
+method at present is the germination and growth of seedlings
+in baskets specially constructed for the purpose. These plants
+are kept under observation until of the required age and
+growth. They are then conveyed to the field, and the baskets
+are planted in prepared holes. The baskets, being of vegetable
+material, are liable to be attacked by various diseases while
+in the nursery or after planting. It is considered advisable,
+therefore, to treat them by dipping into some disinfectant such
+as tar, or a mixture of tar and one of the common proprietary
+disinfectants. Otherwise a disease may be conveyed from the
+basket to the seedling.</p>
+
+<p><a name="Sec1_8" id="Sec1_8"></a><a name="Sec1_9" id="Sec1_9"></a><span class="smcap">Preparation
+for Planting.</span>&mdash;There can be no other
+opinion than that ideally all land required for planting should
+be perfectly clear of timber of every description. After
+felling and burning, under ordinary conditions a certain
+amount of clearing is effected, but in actual practice this
+amounts to comparatively little. Big logs and stumps are left
+because the cost of clean clearing is judged to be prohibitive
+and non-economic. Surface timber is gradually cleared in
+the course of development, and usually large stumps are the
+last to be tackled. The objection to this procedure is really
+not strong, but unfortunately an important point is generally
+overlooked. Granted that most of the dreaded diseases travel
+beneath the surface of the ground by means of buried timber,<span class='pagenum'><a name="Page_11" id="Page_11">[11]</a></span>
+it is plain that as far as stumps are concerned, the chief source
+of danger lies in the existence of the roots. If these were
+carefully exposed and removed, the isolated stumps would then
+not be such potential infection points. It follows from this
+argument that the importance of removing buried timber
+cannot be too strongly insisted upon. It is not uncommon to
+find that some years after the opening of an estate, and after
+surface timber has been removed, a large number of trees
+are affected with <i>Fomes lignosus</i> (formerly known as <i>Fomes
+semitostus</i>). Such cases are directly attributable to the existence
+of buried timber, and no local treatment will be successful
+unless the whole of the area is dug over carefully, and all
+pieces of timber removed.</p>
+
+<div class="figcenter"><a name="Fig9" id="Fig9"></a><img src="images/illo028.jpg" alt="New Clearing; Slopes &#8220;Holed&#8221;
+for Planting; Flat Area being Drained" />
+<p class="caption"><span class="smcap">New Clearing; Slopes &#8220;Holed&#8221; for Planting; Flat Area
+being Drained.</span><br />(<i>By courtesy of manager, Membakut Estate, British North Borneo.</i>)</p></div>
+
+<p><a name="Sec1_10" id="Sec1_10"></a><a name="Sec1_11" id="Sec1_11"></a><a name="Sec1_12" id="Sec1_12"></a><span class="smcap">Silt
+Catchment Trenches.</span>&mdash;Granted the ultimate necessity
+of clean clearing, it becomes necessary to take some precautions
+to prevent loss of soil by &#8220;wash&#8221; in young areas<span class='pagenum'><a name="Page_12" id="Page_12">[12]</a></span>
+planted on sloping land. An argument often used in extenuation
+of the practice of allowing large surface timber to remain
+until it becomes rotten is that it is an aid in preventing loss of
+soil by wash. Its removal necessitates the institution of some
+method of preventing &#8220;wash.&#8221; The establishment of terraces
+on steep slopes tends to the achievement of the desired result,
+but this method is not extended to more moderate slopes where
+loss by wash is still considerable. It is the opinion of the
+writers and others that the general case calls for the institution
+of silt catchment trenches, which, as the name denotes, fulfil
+the duty of catching any surface soil and of retaining rainwater.
+These trenches are usually laid out on contour, and
+do not exceed a length of 20 feet. They are usually from
+18 inches to 2 feet wide and deep, and are so arranged on the
+slope that they occupy overlapping positions. The actual
+number of trenches required will depend upon the angle of
+slope; the steeper the slope the greater the number required&mdash;<i>i.e.</i>,
+the shorter will be the length of slope between any two
+trenches. Given a clean area, it is obvious that the momentum
+acquired by running water (and hence the amount of soil
+removed) on any one slope will depend upon the distance
+travelled. It is advisable, therefore, to place a larger proportion
+of the trenches on the upper part of the slope than on the
+lower, so as to guard against the breaking down of the trench
+system under an abnormal downpour of rain.</p>
+
+<p>On land thus prepared the writer has seen areas successfully
+planted, which, under ordinary conditions, were condemned as
+being too steep for planting. It is true that these trenches
+necessitate continual upkeep until the soil becomes well shaded
+by trees, but the actual amount of work demanded in cleaning
+and maintaining the trenches will depend largely upon the
+thoroughness with which the original work was planned and
+executed. Whatever may be the weaknesses exposed as a result
+of providing an insufficient number of trenches of inadequate
+dimensions, there can be no question that they are a necessity.</p>
+
+
+<p class='pagenum'><a name="Page_13" id="Page_13">[13]</a></p>
+<hr class="c25" />
+<h2><a name="Ch2" id="Ch2"></a>CHAPTER II</h2>
+
+<h3><i>FIELD MAINTENANCE</i></h3>
+
+
+<p><a name="Sec2_1" id="Sec2_1"></a><span class="smcap">Clean Weeding.</span>&mdash;Intimately connected with the growth
+and development of the rubber tree one has to consider the
+conditions under which it is allowed to mature. The argument
+has been used that, since the habitat of <i>Hevea Brasiliensis</i>
+is in the jungle, we should be proceeding against nature
+by introducing conditions unlike those under which the
+&#8220;wild&#8221; rubber tree grows. It is difficult to treat such an
+argument seriously, as by quoting parallel instances in arboriculture
+it could be shown that growth, development, and
+yields are improved by cultivation of &#8220;wild&#8221; plants.</p>
+
+<p>It needs small experience with rubber-tree plantations to be
+convinced of the necessity for dealing with other growths,
+which would otherwise soon surround and overshadow young
+rubber trees.</p>
+
+<p>Apart from checking and preventing woody undergrowths
+it is considered advisable to keep the ground more or less free
+from light vegetable growths, which are roughly grouped under
+the heading of &#8220;weeds.&#8221;</p>
+
+<p>Naturally, if these weeds are allowed to flourish and seed,
+their eventual eradication may be a matter of extreme difficulty
+and expense. It is the aim, therefore, of properly conducted
+estates generally to institute such a system of work that
+the weeding-gangs cover the whole estate at regular intervals;
+and, as a general rule, it may be accepted that the shorter the
+interval between successive visits by the gang to any particular
+area, the easier it is to keep weeds in check, and the cheaper
+the work will eventually be done. This procedure defines
+roughly what is implied by the term &#8220;clean weeding,&#8221; and it
+is the policy adopted by most estates.<span class='pagenum'><a name="Page_14" id="Page_14">[14]</a></span></p>
+
+<p>Strict adherence to this practice in rubber cultivation has
+been inculcated by the older school of planters who obtained
+their experience in the cultivation of other crops such as tea,
+coffee, tobacco, etc.</p>
+
+<p><a name="Sec2_2" id="Sec2_2"></a><a name="Sec2_3" id="Sec2_3"></a>In latter years the wisdom of scrupulous clean weeding
+under all conditions has been questioned; and there can be no
+doubt that under certain special conditions a continuation of the
+policy of clean weeding is calculated to produce, in course of
+time, more harm than benefit. As an instance, the case might
+be cited of steep slopes on poor land. Continual clean weeding
+on such areas will lead eventually to a great loss of the surface
+soil, unless some precautions are adopted for catching and
+retaining the fine silt particles. It is to be noted that such a
+type of soil and slope, when the shade is appreciable, often
+produces no weeds heavier in growth than a very light grass.
+It is urged that the necessity for strict clean weeding on such
+soils does not exist, and, in fact, that it would be an injurious
+policy. Such arguments appear to be well founded in experience,
+and the writers are in thorough agreement that such
+special cases deserve special consideration. Rigid adherence
+to a policy of clean weeding, without regard to special conditions,
+would be most inadvisable.</p>
+
+<p>Nevertheless, such exceptional cases do not detract from the
+wisdom of clean weeding in general. Every planter of experience
+realises how easily fields become infested with weeds if
+the regular work is suspended or delayed. It is probably
+quite true that the harm due to the presence of some weeds
+on an occasion is negligible; but apart from this debatable
+point, there is the solid fact that if once an area is allowed to
+become weedy it may soon demand a much greater expenditure
+to bring it back to normal condition than if it had been regularly
+weeded. This is common experience, and for that reason
+alone a general policy of clean weeding is thoroughly sound;
+especially if combined with some system of silt-retention.</p>
+
+<p><a name="Sec2_4" id="Sec2_4"></a><span class="smcap">Grass Squares.</span>&mdash;On some estates the practice of clean
+weeding is undertaken in combination with a system of silt-retention,
+which depends upon the development and maintenance
+of ridges. These are built up from the d&eacute;bris of<span class='pagenum'><a name="Page_15" id="Page_15">[15]</a></span>
+weeding in the form of hollow squares. Grass is allowed to
+sprout and grow in these ridges, and when it attains a certain
+height it is trimmed down so as to keep it within bounds. The
+soil within the hollow square is clean weeded; and it is maintained
+that loss of soil by wash is avoided. Under certain
+conditions there is a great deal to be said in favour of the
+method, but in the opinion of the writers it should be regarded
+only as a method of expediency. It is not to be preferred to
+the more thorough practice of soil-retention by means of silt-trenches,
+although the latter method may be slightly more
+expensive in the end.</p>
+
+<div class="figcenter"><a name="Fig10" id="Fig10"></a><img src="images/illo032.jpg" alt="Typical Young Clearing, with Timber" />
+<p class="caption"><span class="smcap">Typical Young Clearing, with Timber.</span></p>
+<p class="center">Planted &#8220;rubber-stump&#8221; in foreground.</p></div>
+
+<p><a name="Sec2_5" id="Sec2_5"></a><span class="smcap">&#8220;Lallang&#8221; Eradication.</span>&mdash;The greatest bugbear of the
+planter in connection with weeding is the incidence of
+lallang. Many proposals have been put forward at various
+times for the complete eradication of this pest; but at present,
+under ordinary circumstances, there would seem to be no better
+method than by heavy and deep digging, followed by regular
+attention. The method is acknowledged to be expensive, but<span class='pagenum'><a name="Page_16" id="Page_16">[16]</a></span>
+any half-hearted measure otherwise taken will eventually prove
+to be even more costly.</p>
+
+<p>One has to differentiate, of course, between the incidence of
+lallang attributable to negligence on the estate itself, and the
+occasional outbreaks near boundaries, due to seeds having been
+wind-borne from patches of lallang outside the boundaries
+But, in general, it would be safe to remark that the appearance
+of lallang could be taken as evidence of a failure to cover the
+area at sufficiently short intervals.</p>
+
+<p>As already intimated, the usual method of eradication of
+areas of lallang is by thorough digging, and the exposure of
+the strong root system to the sun. As a matter of interest it
+may be noted that recently some success has been obtained by
+another method<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1"
+class="fnanchor">[1]</a> on areas which one may have in view for
+planting at some future date.</p>
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span
+class="label">[1]</span></a> &#8220;Eradication of Lallang,&#8221; W. P. Handover, <i>The Planter</i>, Vol. I.,
+No. 1, August, 1920.</p></div>
+
+<p><a name="Sec2_6" id="Sec2_6"></a>It consists in the employment of <i>Mimosa gigantea</i>, which
+eventually smothers the growth of lallang.</p>
+
+<p>The seeds are sown broadcast, in drills, or in pockets,
+amongst the lallang. In the course of about three months it
+overtops the grass and proceeds to travel. At this stage the
+whole mass is pressed down, and the pressing is repeated at
+regular intervals. Under favourable conditions, in about
+twelve months, an impenetrable mat has been formed, which
+gradually forms a good mulch. When it is desired to
+remove the Mimosa, the mass (pressed down) is cut and rolled
+up like a carpet. Cleared in this manner, the area then needs
+regular weeding, in order to check the development of any
+stray lallang shoots. In actual practice it was found that the
+cost of this method was approximately two-thirds that of the
+usual digging method.</p>
+
+<p><a name="Sec2_7" id="Sec2_7"></a><span class="smcap">Green Cover Plants.</span>&mdash;Some years ago it was quite common
+to find green cover-plants employed on estates with the primary
+idea of minimising weeding costs. With most of these it
+was found later that their value was not real, and that they
+harboured diseases, and pests. Moreover, when they were<span class='pagenum'><a name="Page_17" id="Page_17">[17]</a></span>
+removed, it was often found that an abundant crop of lallang
+and weeds resulted.</p>
+
+<p><a name="Sec2_8" id="Sec2_8"></a>There can be no question that certain plants can be employed
+with advantage, not only in the control of weeds, but also by
+reason of benefit to the soil in which they are established.
+These plants are leguminous, and their use is restricted almost
+entirely to young areas, inasmuch as they will not continue to
+grow when shade becomes marked. Of those best known in
+modern practice might be mentioned <i>Tephrosia candida</i>
+(Boga bean), <i>Centrosema Plumerii</i>, and <i>Dolichos Hoseii</i>
+(Sarawak bean).</p>
+
+<div class="figcenter"><a name="Fig11" id="Fig11"></a><img src="images/illo034.jpg" alt="Typical Young Clearing, with Timber" />
+<p class="caption"><span class="smcap">Typical Young Clearing, with Timber.</span></p>
+<p class="capt500">Young rubber plants in foreground. Two of these are easily
+distinguishable, both with small crowns of leaves.</p></div>
+
+<p>It is wrong to imagine, however, that the establishment of
+such leguminous cover-plants obviates weeding. So far is this
+from being the case, that in practice it is found that the weeding
+&#8220;rounds&#8221; must be conducted at first with the same regularity
+as in ordinary working, but that naturally there is much less
+work to be done.</p>
+
+<p><span class='pagenum'><a name="Page_18" id="Page_18">[18]</a></span>As the plants develop, they can be pruned or dug into the
+soil, as the case may be. The addition of the green material
+to the soil, either by digging or by burying in open trenches, is
+calculated to cause improvement in the condition of the soil.
+There may thus be a close connection between weeding, soil
+conservation, and soil improvement.</p>
+
+<p class='pagenum'><a name="Page_19" id="Page_19">[19]</a></p>
+<hr class="c25" />
+<h2><a name="Ch3" id="Ch3"></a>CHAPTER III</h2>
+
+<h3><i>THINNING OF AREAS</i></h3>
+
+
+<p><a name="Sec3_1" id="Sec3_1"></a><a name="Sec3_2" id="Sec3_2"></a>On this subject there is unanimity regarding the necessity for
+the operation. Divergence of opinion exists only as to a
+matter of degree.</p>
+
+<p><a name="Sec3_3" id="Sec3_3"></a>On the one hand there is the school of planters who would
+advocate the advisability of planting up to, say, 200 trees per
+acre, with subsequent thinning out by selection. At the other
+extreme there is the opinion that we should plant only a few
+more trees per acre than it is intended eventually to maintain,
+the argument being that by this method the growth and
+development of individual trees will be so much greater than
+in close planting that the necessity for drastic thinning out
+will not arise.</p>
+
+<p>Unfortunately for the latter school, a very important point
+is overlooked&mdash;viz., that size and general development are not
+criteria of yielding capacity. It might thus follow that a
+stand of ninety well-grown trees per acre might give very
+disappointing yields per acre. In a few instances this has
+been noted with 30 by 30 feet planting, but it is doubtful
+whether the factor influencing such results has been appreciated.</p>
+
+<p>The apostles of close-planting have this in their favour:
+that if the trees to be removed are selected on proper lines, it is
+possible to have all remaining trees of comparatively high-yielding
+strain. This is a very sound argument, but its
+practicability is limited very largely by the question of early
+growth and development. It would seem the sane course
+in any event not to plant more trees per acre than may grow
+normally, and without branch or root interference up to the
+fifth year (the normal first year of tapping).</p>
+
+<p><a name="Sec3_4" id="Sec3_4"></a>Before this stage has been reached, stunted or deformed trees
+will have been noted and removed, so that in the first year of
+tapping thinning proper can be commenced. In the past<span class='pagenum'><a name="Page_20" id="Page_20">[20]</a></span>
+this has been effected wholly by selection of trees according to
+their general appearance and situation; but it is now safe to
+predict that future operations will be based upon sounder and
+more scientific lines.</p>
+
+<p><a name="Sec3_5" id="Sec3_5"></a>Trees will be selected for removal according to their individual
+yields, a standard which we have been advocating for years
+without much practical success. In Java and Sumatra much
+good work has been done in this direction, and recently a
+commencement has been made in the F.M.S.</p>
+
+<div class="figcenter"><a name="Fig12" id="Fig12"></a><img src="images/illo037.jpg" alt="Typical Young Planted Area" />
+<p class="caption"><span class="smcap">Typical Young Planted Area.</span></p>
+<p class="center">Heavy original jungle timber.</p></div>
+
+<p>It is within the daily observation of all planters that certain
+trees regularly give greater yields than others, and that such
+trees are not to be distinguished by size or general development.
+Moreover, with slight variations, it has been found that a good
+yielding tree is consistently a good yielder, and the converse
+holds true.</p>
+
+<p><a name="Sec3_6" id="Sec3_6"></a>If, therefore, measurements of individual yields are taken at
+intervals, and the results recorded during the first year of
+tapping of an area, an excellent guide is obtained for the first<span class='pagenum'><a name="Page_21" id="Page_21">[21]</a></span>
+round of thinning. It is found in actual practice that five,
+or even three, readings during the year are sufficient to give the
+indication required. It is not essential that simultaneous
+readings should be taken over a large area; in fact, such a step
+is really impracticable at first. The simplest method is to
+employ either&mdash;</p>
+
+<div class="blockquot"><p>(<i>a</i>) A small uniform vessel in which the latex is measured
+by means of a thin slip of bamboo upon which graduations
+are marked.</p>
+
+<p>(<i>b</i>) A glass measure graduated regularly.</p></div>
+
+<div class="figcenter"><a name="Fig13" id="Fig13"></a><img src="images/illo038.jpg" alt="Another example of a Recently Planted Area" />
+<p class="caption"><span class="smcap">Another example of a Recently Planted Area.</span></p></div>
+
+<p>In both cases it is immaterial what units are represented by
+the graduations&mdash;whether cubic centimetres, quarter ounces,
+half-ounces, or ounces, as long as the unit is not too large.
+It is preferable to employ a fairly small unit, so that in taking
+readings from young trees a wider range may be obtained
+between poor yields and good yields. In the case of older
+trees a larger unit may be taken.</p>
+
+<p>The first stage in the operations is to number all trees in<span class='pagenum'><a name="Page_22" id="Page_22">[22]</a></span>
+the field to be tested, and to prepare a rough register, with three
+or five vacant columns opposite each tree number.</p>
+
+<p>It is not advisable to commence the record of yields until the
+panel of bark has been under tapping for a month or two. It
+is found that an intelligent coolie can be taught the method of
+measuring and rough recording. The latter is accomplished
+by means of marks made upon the virgin bark of the tree above
+the tapped area. The marks may be made with a tapping
+knife, by means of paint, or with a lead pencil. The simplest
+form of record consists in putting one mark for each graduation
+of reading.</p>
+
+<p>In practice it is found that, commencing about an hour after
+the first tree has been tapped (in the case of young trees) and
+following the course taken by the tapper, the measurer of yields
+is able to do about 2 full tasks (650 to 750 trees) per diem.
+Each day progress is made through the field.</p>
+
+<p>Obviously on such a small scale and utilising only one
+measuring coolie the comparison is restricted very much; but
+in any case this is immaterial as, owing to the personal equation
+of the tapper, comparison strictly should be limited and internal&mdash;<i>i.e.</i>,
+it should really be confined to one task only at a time.
+In this way the worst trees in any task are indicated.</p>
+
+<p>The keeping of the records may be entrusted to a field clerk,
+but is better placed in the hands of a European. The register
+is taken into the field and the rough records found on the trees
+are noted in the columns against the tree number.</p>
+
+<p>Most planters are aware in a general way of the disparity
+between the yields of individual trees, but they would probably
+be surprised if they undertook the institution of such records.</p>
+
+<p>The following figures must not be taken as typical. They
+represent the average results from several tasks in a young
+field from which all ill-grown and deformed trees had been
+removed. It is immaterial what the units represent, as they
+are purely arbitrary and were selected for the purpose of
+obtaining a fairly wide range.</p>
+
+<p>Any trees which failed to yield sufficient latex to reach the
+first mark were registered at zero. The following percentages
+were obtained:</p>
+
+<p class='pagenum'><a name="Page_23" id="Page_23">[23]</a></p>
+
+<table summary="Table p23">
+
+<tr>
+<td colspan="3" class="left">Zero</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">3</td>
+<td class="center">per cent.</td>
+</tr>
+
+<tr>
+<td class="left">Above</td>
+<td class="center">mark</td>
+<td class="right">1</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">6</td>
+<td class="center">&#8222;</td>
+</tr>
+
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">2</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">16</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">3</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">42</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">4</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">12</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">5</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">14</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">6</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">6</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">7</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">0</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">8</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">1</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">9</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right bb">0</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="center">&nbsp;</td>
+<td class="center">&nbsp;</td>
+<td class="right">&nbsp;</td>
+<td class="center padr padl">&nbsp;</td>
+<td class="right">100</td>
+<td class="center">&#8222;</td>
+</tr>
+
+</table>
+
+<p>It may be remarked that, judging by ordinary standards, it
+was impossible to discriminate between good yielders and others,
+and if thinning were to be done on the usual lines it is quite
+possible that some of the best yielding trees would be removed.</p>
+
+<p>Taking the mark No. 5 as the datum line, it will be noted that
+79 per cent. of the trees come below and 21 per cent. above.
+In the latter proportion the majority lie close to the datum
+line. It will be seen that there are outstanding yielders even
+amongst these young trees, and that it would be possible to
+mark about 10 per cent. of the stand per acre at once for
+removal in the first round of thinning.</p>
+
+<p>In the case of old trees it is possible that one would encounter
+greater extremes of yields than those shown in the foregoing
+table, especially if a certain amount of thinning had been done
+previously on empirical lines. Sufficient has been written to
+show that the only reasonable basis for selection of trees in
+thinning is that of yields; and it is obvious that if the method
+be adopted the future yield per acre of any area is bound to be
+in excess of the same area as thinned on rule-of-thumb lines.</p>
+
+<p><a name="Sec3_7" id="Sec3_7"></a><span class="smcap">Yields per Tree.</span>&mdash;A great feature is made in estate reports
+of the figure showing the average yield per tree per annum.
+Assuming an area to be yielding at the average high rate of
+540 lbs. per acre per annum, with an average stand of ninety
+trees per acre, the yield per tree per annum averaged over
+all trees is 6 lbs. Keeping in mind the test-figures on a previous
+page, it will be obvious that some of these trees may have given
+very much more than 6 lbs. during the year, and some less.<span class='pagenum'><a name="Page_24" id="Page_24">[24]</a></span>
+In view of present information it would not be surprising to
+find that a few might have been yielding upwards of 15 lbs.
+per annum. Unfortunately this information is only to be
+obtained by individual tests, and under normal estate conditions
+the facts escape notice. Cases are known in which
+out-standing individual trees have been known to yield at the
+rate of 25 lbs. and more per annum.</p>
+
+<div class="figcenter"><a name="Fig14" id="Fig14"></a><img src="images/illo041.jpg" alt="Widely Planted
+Young Area, just ready to be brought into Tapping" />
+<p class="caption"><span class="smcap">Widely Planted Young Area, just ready to be brought<br />
+into Tapping.</span></p></div>
+
+<p><span class='pagenum'><a name="Page_25" id="Page_25">[25]</a></span><span class="smcap">Future
+Yields per Tree.</span>&mdash;It has been shown that by selective
+methods based on yields, poor trees can be eliminated.
+Whether by a process of seed-selection or by means of propagation
+based on bud-grafting and marcotting, it needs no
+great stretch of imagination to forecast future conditions under
+which trees may be bred which will be capable eventually of<span class='pagenum'><a name="Page_26" id="Page_26">[26]</a></span>
+giving an average yield of 25 lbs. per annum over any given
+area. Yields of 1,000 lbs. per acre per annum should be
+obtained easily.</p>
+
+<div class="figcenter"><a name="Fig15" id="Fig15"></a><img src="images/illo042.jpg" alt="Field of
+Old Rubber Trees in which Thinning had been delayed too long" />
+<p class="caption"><span class="smcap">Field of Old Rubber Trees in which Thinning had been<br />
+delayed too long.</span></p>
+<p class="center">Note height and comparative lack of girth.</p></div>
+
+<p><a name="Sec3_8" id="Sec3_8"></a><span class="smcap">Trees per Acre.</span>&mdash;This brings us to the question as to how
+many trees one should leave to the acre after thinning operations.
+Figures have been given by various authorities, but it
+appears to the writer at the present time to be impossible to
+lay down a general rule. So much depends upon conditions.
+In certain cases where the soil is admittedly poor, the average
+growth below normal, and thinning has been postponed too
+long, the writer has been forced to the conclusion that it would
+be most inadvisable, and commercially unsound, to reduce
+the stand of trees below 120 per acre. In such instances the
+average yield per tree equalled only 3 lbs. per annum, and
+although the trees were upwards of nine or ten years old the
+crowns were small and sparse. It is doubtful whether such
+trees will ever exhibit any further development, and to thin
+them further would probably lead only to a diminution in the
+crop per acre.</p>
+
+<p>Under normal conditions of growth an arbitrary figure of
+eighty trees per acre has been selected as a standard by many
+estates. In these cases it would probably be correct to state
+that thinning was undertaken on almost purely empirical lines&mdash;<i>i.e.</i>,
+that trees were not selected by tests of individual yields.
+As far as such a method retained the apparently most vigorous
+trees it was successful; but in view of what has been written it
+might explain some of the disappointing results which have
+followed upon such a system of thinning.</p>
+
+<p>It will be clear that any decision regarding the number of
+trees to be retained must be derived from a study of the detailed
+results of individual tests. If the large majority of the trees
+appear to be fairly uniform in yields the first thinning must be
+confined to comparatively few trees. Where there is, on the
+other hand, a good percentage of high-yielding trees the final
+stand per acre may be appreciably less. Unless and until such
+information is available, one cannot give any definite opinion
+as to the requisite number of trees to be retained per acre.</p>
+
+<p>Similarly, intelligence must be displayed in deciding which<span class='pagenum'><a name="Page_27" id="Page_27">[27]</a></span>
+of several uniformly-yielding trees should be removed. In
+the average sense of this consideration one must pay no attention
+to symmetry of spacing, but when dealing with trees of
+fairly uniform yields one needs to study the characteristic
+development of the trees individually, in order to retain those
+which would appear to be most favourably situated with regard
+to surrounding trees.</p>
+
+
+<p class='pagenum'><a name="Page_28" id="Page_28">[28]</a></p>
+<hr class="c25" />
+<h2><a name="Ch4" id="Ch4"></a>CHAPTER IV</h2>
+
+<h3><i>TAPPING SYSTEMS</i></h3>
+
+
+<p><a name="Sec4_1" id="Sec4_1"></a>Broadly there are only two methods employed in obtaining
+the latex from <i>Hevea Brasiliensis</i>. The first is that employed
+in South America, where incisions are made by means of a
+light axe. The other is the system of excision, or paring, of
+the bark practised on plantations in the East.</p>
+
+<p>In the early days of the plantation industry, the South
+American method seems to have been employed, and the writer
+has knowledge of trees on one of our best-known estates in
+Malaya which still exhibit the outward and visible signs of that
+method. At a comparatively early stage, however, the method
+of excision was introduced. Curiously enough there appears
+to be no record of its inception or of the individual who was
+responsible for the substitution of this method. We have
+been so accustomed to regard it as one of the ordinary facts of
+estate procedure, that this point seems to have escaped notice
+and enquiry.</p>
+
+<p>As a variant of these two main methods, a slight vogue was for
+a short while obtained by the operation known as &#8220;pricking.&#8221;
+This was generally combined with excision of bark, and was
+then known as the &#8220;paring and pricking&#8221; method; but the
+simple operation of pricking alone had its adherents, and various
+forms of instruments were designed to achieve the object.
+As a means for obtaining a flow of latex, pricking may have
+been effective, but the general difficulties attaching to the
+collection of the latex was such as to put the method out of
+favour.</p>
+
+<p>In the employment of &#8220;paring and pricking,&#8221; a thin shaving
+of bark was excised on one occasion. At the next tapping no
+bark was excised, but a pricking instrument was used along
+the previously cut surface. It was not proved that any
+advantage was gained by this method, which was more commonly<span class='pagenum'><a name="Page_29" id="Page_29">[29]</a></span>
+employed in Ceylon than elsewhere, and it would be
+surprising to find it in use at the present day.</p>
+
+<p>In the ordinary way the method of excision is practised in
+such a manner that the &#8220;cut&#8221; gradually descends to the base
+of the tree.</p>
+
+<p>Planters with original views, and of an enquiring nature,
+often query the common practice; and it has been suggested
+that &#8220;as the latex descends by the force of gravity,&#8221; one&#8217;s
+paring should be done in an upward direction, thus obtaining
+a greater pressure of latex&mdash;and hence a greater flow. It will
+be obvious that it would be no simple matter to collect effectively
+the latex thus obtained from the under edge of a sloping
+cut, but apart from this the argument would appear to be
+founded upon what is now accepted to be a fallacy&mdash;viz., that
+the latex <i>per se</i> is manufactured in the leaves and gravitates
+down the tree.</p>
+
+<p><a name="Sec4_2" id="Sec4_2"></a><span class="smcap">Former Systems of Tapping.</span>&mdash;To hark back ten years in
+the plantation rubber industry is equivalent to delving into
+history, since development has been so rapid. It was then
+thought necessary to place upon the trees a number of simultaneous
+cuts which the modern planter would judge to be
+inconceivably excessive. Were it not for evidence in the
+shape of photographs extant, it would be difficult to convince
+a young planter that such systems were employed.</p>
+
+<p>It was not uncommon for trees to have from six to ten cuts,
+sometimes all placed on one half of the tree in a herring-bone
+fashion, and sometimes divided into two portions, each of which
+tapped the opposite quarter panel of the tree&#8217;s circumference.
+Such superimposed cuts were spaced from 1 foot to 18 inches
+apart.</p>
+
+<p>On other occasions, a spiral cut was employed, commencing
+at a height of, say, 5 feet, and gradually descending to the cup
+at the base of the tree.</p>
+
+<p>Later systems varied from several cuts on a half-circumference,
+or on a quarter of the tree, tapped either daily, or on
+alternate days, to cases in which one-third or one-fifth of the
+tree was employed. Also popular were the systems of the
+<span class="ssfont">V</span> and half-spiral cuts on half the circumference.</p>
+
+<p><a name="Sec4_3" id="Sec4_3"></a><span class='pagenum'><a name="Page_30" id="Page_30">[30]</a></span>It
+did not take long to be recognised that with all these
+systems demanding a number of simultaneous parings from
+the same panel of bark, the rate of excision was so heavy that
+the period available for the renewal of bark was insufficient
+for continuous tapping.</p>
+
+<p><a name="Sec4_4" id="Sec4_4"></a>As a result most of the systems specified have fallen into
+desuetude, and the tendency has since been to reduce the
+number of cuts, or the periodicity of tapping, so as to allow
+for increasing periods of bark renewal.</p>
+
+<p>In the earlier days, a period of four years was thought to
+be an extremely generous allowance, whereas six years is now
+becoming recognised as a minimum necessity. Eight years
+is not regarded as extravagant, while with older bark on some
+estates periods of ten and twelve years have to be allowed for
+full renewal. Even so no finality has been reached, and no
+general rule can be laid down. Local conditions of planting
+and growth exercise great influence, and the writers have in
+mind instances in which a period of eight years has proved
+to be insufficient even for a first renewal after the excision of
+virgin bark.</p>
+
+<p><a name="Sec4_5" id="Sec4_5"></a>In the main the most popular systems of tapping are:</p>
+
+<div class="blockquot"><p>(<i>a</i>) One cut on a quarter of the tree, tapped daily.</p>
+
+<p>(<i>b</i>) One cut on a third of the tree, tapped daily.</p>
+
+<p>(<i>c</i>) One cut on half the circumference, tapped on alternate days.</p>
+
+<p>(<i>d</i>) A <span class="ssfont">V</span> cut on half the circumference, tapped on alternate
+days.</p></div>
+
+<p>Variants and extremes are:</p>
+
+<div class="blockquot"><p>(1) One cut on a quarter, tapped on alternate days.</p>
+
+<p>(2) One cut on a half, tapped daily.</p></div>
+
+<p>Superficially viewed the latter is four times as strenuous as the
+former, and the relative position seems to be inexplicable. It
+may be explained that as a rule the former system is practised
+on old trees with poorly renewed bark, in order to allow for
+adequate bark renewal; and the latter is employed in opening
+young trees just brought into tapping, when the rate of bark
+renewal is at a maximum.</p>
+
+<div class="figcenter"><a name="Fig16" id="Fig16"></a><img src="images/illo048.jpg" alt="Two
+Cuts on a Quarter Circumference, on an Old Tree" />
+<p class="caption"><span class="smcap">Two Cuts on a Quarter Circumference, on an Old Tree.</span></p></div>
+
+<p><a name="Sec4_6" id="Sec4_6"></a>A few estates in
+this country still continue to tap trees by<span class='pagenum'><a name="Page_31" id="Page_31">[31]</a></span>
+means of two superimposed cuts on a quarter of the tree.
+This was a very popular system some four or five years ago,
+but it has come to be recognised by practical experience that
+any system employing superimposed cuts leads to a high
+consumption of bark without proportionate increase in yield.
+For instance, if one compares the system of two cuts on a
+quarter tapped daily with a similar system employing only one
+cut, one finds that the major quantity of latex is yielded by the<span class='pagenum'><a name="Page_32" id="Page_32">[32]</a></span>
+lower cut, and that the single-cut system which excises approximately
+half the amount of bark gives about 80 per cent.
+of the yield obtained by the tapping of two superimposed cuts.</p>
+
+<p>Of experiments to test the relative values of different systems
+of tapping there have been many. Most of them suffered
+from the initial handicap that they dealt with systems which
+were then popular. In order to obtain any valid result they
+had to be undertaken over a long period. Meantime there
+was a progressive movement in actual estate practice towards
+a greater conservatism in bark removal, and hence the experiments
+as originally planned lost value.</p>
+
+<p>Moreover, in Malaya it was difficult for experimenters to
+obtain practical support in the form of areas of trees suitable
+for experiment. As a result experiments were often confined
+to small blocks of trees, and a small number of blocks, from
+which any conclusions derived were subject to considerable
+errors of experiment. Often comparisons were made between
+only two blocks, and no allowance was made for varying factors,
+such as initial differences in yielding capacities of the trees,
+soil conditions, or the personal equation of the tappers. As a
+general rule, therefore, the results were vitiated to a very
+appreciable extent.</p>
+
+<p>All these factors were later taken into consideration in an
+experiment undertaken on behalf of the Rubber Growers&#8217;
+Association. In this instance unique facilities were provided
+by the London Asiatic Rubber Company on their property
+at Semenyih Estate, and it is only fitting that the company
+should receive the recognition which its enterprise deserves.</p>
+
+<p>It would have been a great advantage to have included in that
+experiment other features which have since come into prominence,
+but the original scope of the experiment had to be
+confined to the point of comparing yields obtained in making
+comparative tests based on one system of tapping with different
+frequencies. Such data were required as a check upon a
+Ceylon tapping experiment which had attracted much attention.
+In that experiment trees were tapped at intervals ranging from
+one day to seven days; and it was concluded that after a period
+of three and a half years trees tapped with greater intervals<span class='pagenum'><a name="Page_33" id="Page_33">[33]</a></span>
+gave yields equalling or exceeding those obtained from trees
+tapped with shorter intervals.</p>
+
+<div class="figcenter"><a name="Fig17" id="Fig17"></a><img src="images/illo050.jpg" alt="The Single Cut on a
+Quarter Circumference, on an Old Tree and on Renewed Bark" />
+<p class="caption"><span class="smcap">The Single Cut on a Quarter Circumference, on an Old Tree<br />
+and on Renewed Bark.</span></p></div>
+
+<p>In the Semenyih experiment the system chosen was that
+which had the greatest contemporary vogue&mdash;viz., two superimposed
+cuts on a quarter of the tree. The various blocks
+were tapped respectively every day, every second day, and
+every third day.</p>
+
+<p><span class='pagenum'><a name="Page_34" id="Page_34">[34]</a></span>It was found that the conclusions drawn from the Ceylon
+experiment were not confirmed. After a period of three and
+a half years&#8217; continuous tapping neither the alternate-day
+system nor the third-day system gave results in any way
+approximating to the yield of the daily system.</p>
+
+<p>The actual average yields from these systems over the whole
+period were in the order of&mdash;</p>
+
+<table summary="Table p34">
+
+<tr>
+<td class="center"><i>Daily.</i></td>
+<td>&nbsp;</td>
+<td class="center"><i>Two Days.</i></td>
+<td>&nbsp;</td>
+<td class="center"><i>Three Days.</i></td>
+</tr>
+
+<tr>
+<td class="center">100 per cent.</td>
+<td class="padr padl">&nbsp;</td>
+<td class="center">60 per cent.</td>
+<td class="padr padl">&nbsp;</td>
+<td class="center">45 per cent.</td>
+</tr>
+
+</table>
+
+<p>and throughout the course of the experiment neither of the
+other sections showed any appreciable improvement in position
+relative to the daily section.</p>
+
+<p>In actual yields &#8220;per tapping&#8221; over the whole period the
+alternate-day and the third-day divisions showed advantages
+of 20 and 35 per cent. respectively over the daily portion.</p>
+
+<p><a name="Sec4_7" id="Sec4_7"></a>At the beginning of the second year of experiment another
+section of blocks was opened with a single cut on a quarter,
+tapped daily. This enabled direct comparison between the
+values of one cut and two cuts on a quarter in daily tappings
+and between a daily single cut and two cuts tapped alternate
+daily.</p>
+
+<p><a name="Sec4_8" id="Sec4_8"></a><a name="Sec4_9" id="Sec4_9"></a>It appeared that the daily single cut yielded over the period
+of experiment 80 per cent. of that obtained by tapping two cuts
+daily; and that in the comparison between two cuts tapped
+alternate-daily and a single cut tapped daily the latter had an
+advantage of about 40 per cent. in yield.</p>
+
+<p>This result has been used by advocates of daily tapping
+generally, but it does not constitute a fair argument, inasmuch
+as the single cut was tapped twice as often, and its position was
+always relatively low on the hole of the tree. It has been
+shown in the comparison between the daily single cut and the
+two cuts daily that the influence on yields of the superimposed
+cut is relatively small. A fairer comparison would have been
+obtained if the two cuts tapped alternate-daily had been either
+amalgamated to form one long cut on half the tree or to form
+a <span class="ssfont">V</span> on half the tree, thus placing the cuts in the opposing
+sections on the same level. With the knowledge that the yield<span class='pagenum'><a name="Page_35" id="Page_35">[35]</a></span>
+obtained from cuts is <i>always greater per tapping</i> by using the
+alternate-daily system, it would appear to be plain that the
+one long cut on half the tree would at least equal the yield of
+the single short cut tapped daily on a quarter tree.</p>
+
+<div class="figcenter"><a name="Fig18" id="Fig18"></a><img src="images/illo052.jpg" alt="Single Cut on Half Circumference (Half Spiral)" />
+<p class="caption"><span class="smcap">Single Cut on Half Circumference (Half Spiral).</span></p>
+<p class="capt350"><i>Note.</i>&mdash;In this particular instance the cut is changed to the
+opposite half of the tree every half-year.</p></div>
+
+<p>Unfortunately no opportunity has been afforded up to the
+present of definitely proving this point by prolonged experiment<span class='pagenum'><a name="Page_36" id="Page_36">[36]</a></span>
+under strict conditions. It is true that the view is held
+strongly in some quarters as a result of the experience of
+managers, chiefly on their own estates, that alternate-daily
+tapping generally gives better yields than daily tapping.</p>
+
+<p>In a number of instances this view is probably correct, and
+the writers are in agreement; but it is necessary to clear away
+some misconceptions which confuse the issue. In the main
+there are two schools, one of which plumps for alternate-daily
+tapping, while the other adheres strongly to daily excision.
+Great confusion exists, inasmuch as in many instances the
+disciples of these schools are really discussing different matters.
+In the case of managers who argue for alternate-daily tapping
+their experience is gained, with very few exceptions, from
+systems in which the excision covers half the circumference of
+the tree; whereas in almost all cases daily tapping is confined to
+a single cut on a quarter of the girth. Bearing on such a comparison
+there are, as far as the writers are aware, no reliable
+published experimental results. To compare the results
+obtained from one system practised on one estate with the
+results of the other system established on another estate is not
+strictly permissible, as we know that conditions generally may
+vary to an enormous degree.</p>
+
+<p>The controversy has raged, however, to such an extent that
+many who are not directly engaged in estate practice have
+obtained confused impressions. For instance, it appears to be
+the belief in some quarters that alternate-daily tapping, when
+applied to a single cut on a quarter of the tree, will yield more
+than an exactly similar cut tapped daily. In support of such
+a statement there does not appear to be any confirmation under
+normal conditions; although such a result might be obtained
+in the case of old trees which have been heavily over-tapped
+in the past, and on which the rate of bark renewal has been
+appreciably retarded. It might also be the case eventually
+when trees with the opposing frequencies have been tapped
+for a period extending into many years; but it is the opinion
+of the writers that under normal conditions such a result would
+be extremely doubtful.</p>
+
+<p><a name="Sec4_10" id="Sec4_10"></a>When we come, however, to a comparison
+of daily tapping<span class='pagenum'><a name="Page_37" id="Page_37">[37]</a></span>
+on a single cut on a quarter with double the length of that cut
+on half the circumference, at the same height, tapped alternate-daily&mdash;whether
+in the form of one long cut or in the form of a
+<span class="ssfont">V</span>&mdash;we arrive at a contrast which gives a clear issue. As already
+stated, facts and figures of reliable experiment are wanting;
+but it is the opinion and experience of the writers that the
+alternate-daily system at least suffers no disadvantage on the
+point of yields, and in other respects, such as conservation of
+labour and costs, is superior to the daily system.</p>
+
+<div class="figcenter"><a name="Fig19" id="Fig19"></a><img src="images/illo054.jpg" alt="A V-Cut on Half the Circumference" />
+<p class="caption"><span class="smcap">A <span class="ssfont">V</span>-Cut on Half the Circumference.</span></p></div>
+
+
+<p class='pagenum'><a name="Page_38" id="Page_38">[38]</a></p>
+<hr class="c25" />
+<h2><a name="Ch5" id="Ch5"></a>CHAPTER V</h2>
+
+<h3><i>TAPPING AND COLLECTING</i></h3>
+
+
+<p><a name="Sec5_1" id="Sec5_1"></a><span class="smcap">Tapping Knives.</span>&mdash;The choice of a tapping knife is a subject
+upon which there is much divergence of opinion. This must
+be so because no known knife has such apparent outstanding
+superior features or claims as would enable one to settle the
+point. Moreover, the personal factor is so large that, as far
+as the knives in common use are concerned, it appears to exert
+the greatest influence. The possibility of obtaining the ideal
+knife, which will go to sufficient depth into barks of varying
+thickness to yield the maximum quantity of latex without
+wounding, is quite as remote at the present time as it was some
+years ago. Meanwhile the search for that ideal knife continues,
+and occasionally one learns of the alleged merits of some
+new instrument which, it is said, fulfils all requirements. It is
+only to be regretted, both for the sake of the inventor and for
+the expectant buyers, that the claims always fail in some one
+or more particulars.</p>
+
+<p>In Malaya probably the number of different types of tapping
+knives may amount to a half-dozen, but those most commonly
+in use are:</p>
+
+<div class="blockquot"><p>(1) The gouge&mdash;straight or bent.</p>
+
+<p>(2) The ordinary farrier&#8217;s knife.</p>
+
+<p>(3) Modifications of the farrier&#8217;s knife, such as the &#8220;Jebong.&#8221;</p></div>
+
+<p>Argument on the respective merits of knives is popular, and
+discussion seems endless. It is claimed for the bent gouge
+that it is superior to the straight instrument, because, the
+leverage being downwards on the handle, the tendency is to lift
+the cutting edge upwards and out of the bark, whereas with a
+straight gouge the tendency is to push the knife downwards
+into the bark. It is claimed, therefore, that the average<span class='pagenum'><a name="Page_39" id="Page_39">[39]</a></span>
+shavings taken off by the bent gouge should be thinner than
+those obtained by the use of the straight instrument.</p>
+
+<p>For similar reasons it is asserted that the &#8220;Jebong&#8221; and
+other modifications are superior to the original form of the
+farrier&#8217;s knife. These points are generally accepted without
+great argument, but when comparisons are made between the
+gouge and the farrier&#8217;s knife (with its modifications) the opinions
+of planters are so varied and conflicting as to be almost irreconcilable.
+Two opinions based on experience with both
+types of knives are often wholly contradictory.</p>
+
+<p><a name="Sec5_2" id="Sec5_2"></a>There can be no doubt that the likes and dislikes of operative
+coolies have a considerable influence in determining the measure
+of success obtained with any one knife. Should coolies have
+been accustomed to the use of a particular form of instrument
+they become quite expert, and any proposed change creates
+in the minds of coolies a prejudice which is considerable in
+effect on the quality of the handicraft. Such prejudice may
+be overcome in course of time, but in the interval not a little
+damage may have been done in the shape of tapping wounds.
+So considerable is this question of personal favour that
+even on estates where a standard pattern of knife is issued
+coolies often modify that knife slightly on their own accord.
+Such alteration is ignored by the superintendents as long as
+the quality of the tapper&#8217;s work is maintained at a high
+standard.</p>
+
+<p>Naturally there is a limit to such leniency, and this limit is
+soon reached in the case of knives having adjustable parts controlled
+by screws, or nuts and bolts, etc. Some knives of this
+description really merit a much wider use than is afforded them
+at present; but in view of the potential damage which might
+be done as a result of adjustments made by the coolies these
+knives do not become popular.</p>
+
+<p>It is not proposed here to enter into a description of even
+recent instruments for which strong claims are being made by
+their inventors or vendors. If they possess the merits attributed
+to them they will soon find favour, as managers are always
+keen on studying the points of any new knife which will lead
+to a conservation of bark and a reduction in the number of<span class='pagenum'><a name="Page_40" id="Page_40">[40]</a></span>
+wounds. On the whole, it may be advanced that the best
+general results are obtained by the adoption of a simple non-adjustable
+knife and the retention of its use.</p>
+
+<p><a name="Sec5_3" id="Sec5_3"></a><span class="smcap">The Choice of Latex Cups.</span>&mdash;It has come to be recognised
+that the maximum possible cleanliness is essential in all details
+of estate work, and the younger generation of planters could
+scarcely be aware that a few years ago it was deemed sufficient
+to use coco-nut shells for the reception of latex on individual
+trees.</p>
+
+<p>Terne-plate cups ousted the coco-nut shell, and they had
+the merit of being cheap. The interior coating of tin did not
+last long if the cups were properly cleaned. The iron being
+exposed, with a minutely roughened surface, each microscopic
+projection served as a point around which latex coagulated.
+Scrapping the film of interior rubber became more and more
+difficult, and often the cups were burnt in order to get rid of
+the accumulation of rubber. The last state of such cups was
+worse than the preceding one. On some estates fairly successful
+attempts were made to keep these cups clean by making
+the coolies bring them into the store each day. Terne-plate
+cups are not now in common use.</p>
+
+<p>Aluminium cups have their advocates, but much the same
+argument applies to the difficulty of keeping them clean as was
+used in the foregoing paragraph. On many estates, however,
+they are used with success, the usual method of treatment
+being to make the coolies bring them into the store and clean
+them there. Owing to the comparative lightness of the
+material such a scheme is more feasible than was the case
+with terne-plate cups.</p>
+
+<p>The cups now most in general use are either of glass or
+white-ware, and probably those of glass are the most extensively
+employed. There are many details to be studied in the choice
+between these two types of cups&mdash;<i>e.g.</i>, percentage of breakage
+in transport and in the field, price when breakage is taken into
+account, etc.; but these apart the glass cups have one advantage&mdash;namely,
+the ability of the superintendents to see whether
+the cups have been properly cleaned. In the case of white-ware
+cups this means an inspection and handling of individual<span class='pagenum'><a name="Page_41" id="Page_41">[41]</a></span>
+cups, whereas in the case of glass the point is settled by visual
+examination at a comparative distance.</p>
+
+<div class="figcenter"><a name="Fig20" id="Fig20"></a><img src="images/illo058.jpg" alt="Single Cut on Two-Fifths of Circumference" />
+<p class="caption"><span class="smcap">Single Cut on Two-Fifths of Circumference.</span></p>
+<p class="capt350">The opening cut covers two-fifths. Subsequent cuts occupy
+one-fifth of circumference.</p></div>
+
+<p>Glass cups are made in two patterns, one having a flat
+bottom and the other a conical base. The latter is convenient
+for use when wire supports are employed, the cup fitting into a
+loop placed beneath the spout. Used on the ground its shape<span class='pagenum'><a name="Page_42" id="Page_42">[42]</a></span>
+is an obvious disadvantage, as, unless a hole is scooped for its
+reception, it has to be propped up with sticks or stones. Often
+a touch is sufficient to upset the balance, and latex is lost.</p>
+
+<p>The flat-bottomed cup, on the other hand, may be used with
+success equally on a wire support or on the ground. It is
+sometimes said that owing to its shape the ease of cleaning,
+as compared with the half-spherical cup, is diminished, and
+that if the cups when not in use are kept inverted upon sticks
+placed near the foot of the tree the breakage is apt to be high.
+This latter objection is being rapidly removed as the practice
+of using these sticks is losing vogue for various reasons, and
+wire cup-holders will be in general use as soon as the cost of
+material becomes normal.</p>
+
+<p>There are on the market, and in fairly wide use, cups of
+Chinese and Japanese manufacture. These generally consist
+of brown earthenware with an interior glass finish. These are
+cheap in comparison with glass and white-ware cups, but it is
+a pity that the glass does not extend over the whole of the cup.
+The outer surface has a tendency to collect rubber and dirt.
+On some few estates small china bowls or saucers are still used
+and are quite satisfactory, except for the favour with which
+they are regarded by natives on the outskirts of the estates.</p>
+
+<p><a name="Sec5_4" id="Sec5_4"></a><span class="smcap">Cleaning Cups.</span>&mdash;The question of cup-cleaning would
+appear to be a very simple one; but in practice it is quite a
+source of worry to managers, especially where a mixed labour
+force is employed. Tamil coolies can be made to clean their
+cups in the day&#8217;s task and at odd times. Chinese coolies, more
+often than not, either refuse to give the necessary attention or
+else demand extra pay for the work.</p>
+
+<p>The method of cup-cleaning employed more popularly
+within recent years was that of daily washing. The tapper
+carried two buckets, one for receiving the latex and the other
+containing water. Pouring the latex in the bucket the coolie
+then added a little water to the cup and added these rinsings to
+the latex collected. The cup was next washed hastily in the
+bucket of water and replaced. By the time the coolie has
+emptied and washed some 200 cups (about half the task
+generally) the water has the consistency of dilute latex, and the<span class='pagenum'><a name="Page_43" id="Page_43">[43]</a></span>
+wet cup when replaced becomes coated with a thin film of
+rubber. If the latex is always collected in one direction it will
+be clear that, while the cups at one end of the task are comparatively
+clean, those at the other end have the chance of being
+correspondingly dirty.</p>
+
+<p>Controversy has raged respecting this question of cup-washing,
+and many estates have abandoned it as a daily practice.
+Coolies have not to carry an extra bucket of water. The
+contents of the cups are poured into the latex-bucket, and the
+bulk of the latex film remaining is also removed by the aid of
+a finger. The cup is then replaced, a thin skin of rubber
+forming on the interior surface. As a general rule this is
+easily removed on the next occasion, except perhaps in dry
+weather. It is the custom on most estates employing this
+practice to have all cups receive special attention at regular
+intervals.</p>
+
+<p>There are certain economic factors entering into the difference
+of opinion regarding the two broad methods employed. In
+some cases&mdash;<i>e.g.</i>, on old areas&mdash;it would be practically impossible
+to follow the older method of daily cup-washing, as the
+tappers have to employ two buckets for the collection of the
+latex. The employment of special coolies for cup-washing
+would be necessitated, such as may be seen sometimes on
+estates working Chinese &#8220;squatter&#8221; labour&mdash;where the man
+taps, a child assists in collecting, and another child, or the
+mother, washes the cups. It may be pointed out that in
+such instances the helpers are not paid by the estate. Their
+services merely mean a saving in time which is spent in the
+squatter&#8217;s garden, and perhaps the permission to the tapper
+to work a larger number of trees than would be allotted
+ordinarily to a task.</p>
+
+<p>Again, on some estates, the tappers, while not being required
+to carry a bucket of water for cup-washing, are given an increased
+number of trees to tap. Furthermore, on hilly areas
+under tapping, it is often manifestly unfair to expect the
+tapper to be able to carry two buckets during collection, when
+the slope is such, as to make the manipulation of even one
+bucket a matter of difficulty.</p>
+
+<p><span class='pagenum'><a name="Page_44" id="Page_44">[44]</a></span>It will be seen, therefore, that there is no clear issue for
+argument concerning the two methods, and that the point
+must be decided on the economic factors peculiar to each
+estate or district.</p>
+
+<div class="figcenter"><a name="Fig21" id="Fig21"></a><img src="images/illo061.jpg" alt="Effects upon Renewed Bark of Previous Tapping" />
+<p class="caption"><span class="smcap">Effects upon Renewed Bark of Previous Tapping.</span></p>
+<p class="center">Note uneven surface and callosities.</p></div>
+
+<p><a name="Sec5_5" id="Sec5_5"></a><span class="smcap">Water in Cups.</span>&mdash;Much discussion used to take place
+regarding the necessity or otherwise for placing a small quantity
+of water in the cups when tapping. It was recognised that<span class='pagenum'><a name="Page_45" id="Page_45">[45]</a></span>
+the permission to use water (with the idea of preventing
+coagulation) led to much abuse, apart from the question as
+to the utility of the method. Dirty water was often used,
+although clean water may have been placed in the buckets when
+coolies left the muster-ground. The small quantity of water
+often exceeded the actual yield of pure latex by hundreds per<span class='pagenum'><a name="Page_46" id="Page_46">[46]</a></span>
+cent., with the result that on arrival at the factory the diluted
+latex was below the standard desirable for the preparation of a
+good sheet-rubber.</p>
+
+<div class="figcenter"><a name="Fig22" id="Fig22"></a><img src="images/illo062.jpg" alt="Another Example Showing the Effects of Previous
+Tapping" />
+<p class="caption"><span class="smcap">Another Example Showing the Effects of Previous<br />
+Tapping.</span></p></div>
+
+<p><a name="Sec5_6" id="Sec5_6"></a><span class="smcap">Premature Coagulation.</span>&mdash;Other opinion to the contrary it
+is now generally acknowledged that the possibility of premature
+coagulation in the cup or bucket is at least not diminished by
+the addition of even clean water. The use of water often
+obtained from estate drains clearly led to increased trouble.
+The extent to which such premature coagulation takes place
+varies greatly under the influence of many factors&mdash;<i>e.g.</i>:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Cleanliness of cups and spouts (the latter an important
+item often overlooked, and involving the presence of certain
+organisms which effect coagulation).</p>
+
+<p>(<i>b</i>) Climatic conditions.</p>
+
+<p>(<i>c</i>) Rate and volume of flow of latex.</p>
+
+<p>(<i>d</i>) Size of tappers&#8217; tasks (involving the length of interval
+between tapping, and the collection of latex).</p>
+
+<p>(<i>e</i>) Distance to be traversed between the site of the task and
+the store.</p>
+
+<p>(<i>f</i>) Care in collecting, to exclude extraneous matter.</p>
+
+<p>(<i>g</i>) Nature of transport; agitation of the latex to be reduced
+to a minimum.</p>
+
+<p>(<i>h</i>) Nature of the soil, and situation of the estate.</p></div>
+
+<p>The last mentioned factor is of great importance. As a
+general rule it is noted that premature coagulation is less
+marked on estates situated on comparatively hilly land. The
+greatest effect is remarked on estates situated on the flat lands
+of the coastal area where peaty soils are a feature. On many
+such estates, in spite of the observance of all ordinary precautions,
+it is not possible to receive the latex at the factory
+without a large percentage of prematurely coagulated rubber
+being found in the transport vessels.</p>
+
+<p><a name="Sec5_7" id="Sec5_7"></a><span class="smcap">Anti-Coagulants.</span>&mdash;For this reason on these (and other)
+estates, the use of small quantities of anti-coagulants is common.
+The effect of these is to keep the latex liquid and thus render
+possible the preparation of a higher percentage of first-grade
+rubber than would be otherwise obtained.</p>
+
+<p><a name="Sec5_8" id="Sec5_8"></a>Among the better known agents which have such an effect
+upon latex, formalin and sodium sulphite (not bisulphite) are<span class='pagenum'><a name="Page_47" id="Page_47">[47]</a></span>
+the chief. The latter is the more popular as it is slightly
+cheaper and much more stable. As now used, it is in the form
+of an easily soluble powder (anhydrous sodium sulphite).
+The ordinary crystalline form of sodium sulphite as used in
+photography is not recommended, on account of its comparative
+lack of power and its poor keeping qualities.</p>
+
+<p>It will be obvious that, given two equal quantities of different
+latices, different amounts of an anti-coagulant may be required
+to produce the same effect. Hence it should be remembered
+that a formula which suits the needs of one field or one estate
+will not necessarily prove suitable in the case of another field or
+estate. Unless this point is appreciated trouble may ensue.
+On some estates it has been the custom to give equal quantities
+of sodium sulphite solution to all coolies irrespective of the
+ages of the trees in the fields to be tapped. Thus it happened
+that the latex from one field was found to have insufficient
+anti-coagulant present, while that from another field could only
+be coagulated by the addition of an excess of acid. In this
+matter the experience of the preliminary trials should have
+caused some discrimination to be exercised as to the quantities
+of solution to be issued in each field or division. It has been
+found sometimes that a moist glossiness in the smoked sheet
+could be attributed to the use of an excess of sodium sulphite.
+Traces of the salt remained in the rubber, and as the substance
+is hygroscopic, moisture was being absorbed from the air, to
+cause a surface deposit which often returned even after the
+sheets were surface-washed and re-dried.</p>
+
+<p>If sodium sulphite is to be used in the field, the following
+formula, which is in wide use, may serve as a basis for trials.</p>
+
+<p class="center"><i>Formula for Use of Sodium Sulphite in the Field.</i></p>
+
+<div class="blockquot"><p>(<i>a</i>) Dissolve anhydrous sodium sulphite in water at the rate
+of 1 pound to 3 gallons.</p>
+
+<p>(<i>b</i>) Of this solution each coolie is given about <span class="enum">3</span>&#8260;<span class="denom">4</span> pint. This
+is usually sufficient for a task of 350 trees. The solution is
+used by shaking a few drops into the cup or, diluted with an
+equal volume of water, it is run down the main channel when
+the latex flows.</p></div>
+
+<div class="figcenter"><a name="Fig23" id="Fig23"></a><img src="images/illo065.jpg" alt="Showing Effect of 'Wintering'" />
+<p class="caption">1. <span class="smcap">Showing Effect of &#8220;Wintering.&#8221;</span></p></div>
+
+<p><span class='pagenum'><a name="Page_48" id="Page_48">[48]</a></span>On some estates it is found either unnecessary or impracticable
+to use the solution in this manner. Instead the anti-coagulant
+is placed in the bottom of the bucket prior to the commencement
+of collection. The solution is made as in (<i>a</i>) above,
+and roughly half an ordinary latex-cupful is placed in
+each bucket.</p>
+
+<div class="figcenter"><a name="Fig24" id="Fig24"></a><img src="images/illo066.jpg" alt="New Growth of Young Leaf on Same Tree" />
+<p class="caption">2. <span class="smcap">New Growth of Young Leaf on Same Tree.</span></p></div>
+
+<p><a name="Sec5_9" id="Sec5_9"></a><span class="smcap">Collecting Pails.</span>&mdash;All vessels intended for the transport
+of latex should have a smooth and curved interior, so that<span class='pagenum'><a name="Page_49" id="Page_49">[49]</a></span>
+cleansing may be easy. Preferably the interior and exterior
+surfaces should be glazed, but it is often found that the enamel
+chips easily, and that the handles are too frail in construction.
+The shoulder-pieces, to which the handles are joined, are
+often too lightly attached to the bucket. Something stouter
+in the shape of enamelled ware is required, without an appreciable
+increase in weight. Until such a utensil is available,
+the heavily galvanised and brass-bound milk-pails used on some<span class='pagenum'><a name="Page_50" id="Page_50">[50]</a></span>
+estates are as good as anything at present in vogue, providing
+they are kept scrupulously clean.</p>
+
+<table summary="Mouldy Rot">
+
+<tr>
+<td class="figcenter"><a name="Fig25" id="Fig25"></a><img src="images/illo067.jpg" alt="Mouldy Rot 1"  /></td>
+<td class="padr padl">&nbsp;</td>
+<td class="figcenter"><a name="Fig26" id="Fig26"></a><img src="images/illo068.jpg" alt="Mouldy Rot 2"  /></td>
+</tr>
+
+<tr>
+<td class="caption"><span class="smcap">Effects of Disease&mdash;&#8220;Mouldy Rot.&#8221;</span></td>
+<td class="padr padl">&nbsp;</td>
+<td class="caption"><span class="smcap">Effects of Disease&mdash;&#8220;Mouldy Rot.&#8221;</span></td>
+</tr>
+
+<tr>
+<td style="text-align: justify; width: 350px;">(<i>a</i>) Note on right hand the panel next in order for tapping; a hopeless position.</td>
+<td class="padr padl">&nbsp;</td>
+<td style="text-align: justify; width: 350px;">(<i>b</i>) The present cut badly infected; above there is no renewal of bark.</td>
+</tr>
+
+<tr>
+<td class="figcenter"><a name="Fig27" id="Fig27"></a><img src="images/illo069.jpg" alt="Mouldy Rot 3"  /></td>
+<td class="padr padl">&nbsp;</td>
+<td class="figcenter"><a name="Fig28" id="Fig28"></a><img src="images/illo070.jpg" alt="Mouldy Rot 4"  /></td>
+</tr>
+
+<tr>
+<td class="caption"><span class="smcap">Effects of Disease&mdash;&#8220;Mouldy Rot.&#8221;</span></td>
+<td class="padr padl">&nbsp;</td>
+<td class="caption"><span class="smcap">Effects of Disease&mdash;&#8220;Mouldy Rot.&#8221;</span></td>
+</tr>
+
+<tr>
+<td style="text-align: justify; width: 350px;">(<i>c</i>) As in (<i>b</i>); another tree.</td>
+<td class="padr padl">&nbsp;</td>
+<td style="text-align: justify; width: 350px;">(<i>d</i>) At close quarters. Note wounds due, apparently, to bad
+tapping, but really caused by the disease.</td>
+</tr>
+
+</table>
+
+<p>The collecting pails should be kept under cover, when not in
+use, either at the muster grounds or at the factory. On some
+estates coolies are allowed to take them to their quarters, where
+they are used for various purposes. Curious effects of this<span class='pagenum'><a name="Page_51" id="Page_51">[51]</a></span>
+practice have sometimes been noticed. As an example might
+be quoted an instance in which premature coagulation was
+found to take place to a surprising degree. It was discovered
+eventually that the coolies (Javanese in this case) were in the
+habit of utilising the buckets for the preparation of their food.
+A liquid extract of a popular fruit was often made. This extract<span class='pagenum'><a name="Page_52" id="Page_52">[52]</a></span>
+was very markedly acid in character, and as the buckets were
+not afterwards thoroughly cleansed, the latex of the following
+day suffered.</p>
+
+<p>Preferably all buckets should have a lid of slightly funnel
+shape. This is inverted during collection, and thus prevents
+much dirt falling into the latex.</p>
+
+<p><a name="Sec5_10" id="Sec5_10"></a><span class='pagenum'><a name="Page_53" id="Page_53">[53]</a></span><span class="smcap">Payment
+by Result.</span>&mdash;The arguments for and against the
+institution of this practice are many. In actual result there
+can be no question that a higher yield is obtained by the
+adoption of a scheme under which the coolie is either given a
+bonus based on result or is paid at a definite rate per pound.
+It is fully recognised, both by advocates and opponents of
+payment by result, that the personal equation of the tapper
+is a very important factor. A good skilled tapper will always<span class='pagenum'><a name="Page_54" id="Page_54">[54]</a></span>
+obtain a higher yield than an ordinary individual from the
+same task of trees, and without any more injury to the trees.
+It is argued, therefore, that such an operative should be given
+the benefit of his skill. Apart from this, it is claimed that
+even the average tapper does not do his best work if he knows
+that he will get his daily wage, no matter what his yield may
+be, as long as he does not injure the trees by wounding. It is
+claimed that this sense of security leads to shallow tapping
+which, while it has an agreeable appearance, does not produce
+the available amount of rubber.</p>
+
+<p>On the other hand, it is advanced in opposition that under
+a scheme of payment by result the tappers&#8217; only consideration
+is the matter of obtaining rubber, and that considerable damage
+in the form of wounds is done by over-deep tapping. That
+there is a great deal of truth in these statements is not to be
+doubted. Much, of course, depends upon the amount and
+quality of the supervision possible, and upon the standard
+demanded. It is a notable fact, however, that on estates which
+first introduced the system some years ago the quality of the
+tapping compares favourably with that of average estates, and
+in a few instances within the experience of the writer the tapping
+is of a high standard. Possibly these are exceptional instances,
+and there can be no doubt that the opposition of many managers
+of considerable experience is founded upon the deterioration
+in the standard of tapping which often follows the institution
+of payment of tappers by result.</p>
+
+<p><a name="Sec5_11" id="Sec5_11"></a>It will be recognised by planters that apart from the personal
+factor in tapping, the worker might be so unfortunate as to be
+placed in an area from which the yield is naturally low, either
+by reason of its youth or from other natural causes. Obviously
+such individuals are entitled to special consideration in respect
+of the rate per pound paid for the rubber obtained. Again, on
+very hilly land it may be not humanly possible for a worker to
+tap the usual number of trees. Hence to place him on a
+parity with other tappers, as far as wage-earning capacity is
+concerned, a higher rate than ordinary must be given. It will
+be plain, therefore, that on any one estate it is generally impossible
+to set a standard rate per pound for payment by result;<span class='pagenum'><a name="Page_55" id="Page_55">[55]</a></span>
+the rate may vary, for example, from, say, 3 cents per pound
+in old and high-yielding tasks to 12 cents or more per pound
+on young areas of the same estate.</p>
+
+<p>Naturally the actual rates paid will primarily depend upon
+the average yield per tree or yield per acre, and the lower the
+average yield the higher the rates to be paid per pound. Thus,
+on low-yielding properties where the natural conditions render
+a high yield impossible the rate per pound may reach a figure
+of 22 cents (approximately 6d.).</p>
+
+<p>The methods of arriving at the yield of rubber brought in by
+individual tappers vary, but broadly they fall into two classes:</p>
+
+<div class="blockquot"><p>(<i>a</i>) That in which the volume of latex is ascertained (either
+by measuring or by weighing), a sample is drawn, and the
+final calculation made from the weight of the more or less
+dry sample.</p>
+
+<p>(<i>b</i>) That in which, after noting the volume, the calculation is
+based upon a reading of the dry rubber content of the latex,
+obtained by means of an instrument such as the &#8220;Metrolac,&#8221;
+or any other instrument working on the same principle.</p></div>
+
+<p>Quite a number of estates which have not adopted the full
+system of payment by result yet employed some such method
+of checking the yields of individual coolies, as the observed
+results act as a great deterrent against various malpractices,
+such as neglecting to tap trees, adulteration of the latex, etc.</p>
+
+<p><span class="smcap">Tree-Scrap.</span>&mdash;The thin film of latex which coagulates
+naturally upon the surface of the tapping cut after the latex
+has ceased to flow is known as &#8220;tree-scrap.&#8221; Normally it is
+collected on all estates, but the method of collection varies
+according to the class of labour employed. On most estates,
+where the labour is Tamil or Javanese, it is supposed to be
+removed as fully as possible before the tapping cut is reopened.
+The narrow strips are then placed in a bag or basket carried
+by the tapper. Chinese tappers usually decline to follow this
+practice of first peeling off the scrap, and remove it by the
+operation of tapping, with the result that the scrap when
+brought into the store has adhering to it various shavings of
+bark. Unless these can be thoroughly cleaned off the scrap
+cannot truly be classed as &#8220;tree-scrap.&#8221;</p>
+
+<p><span class='pagenum'><a name="Page_56" id="Page_56">[56]</a></span><a name="Sec5_12" id="Sec5_12"></a><span class="smcap">Oxidation
+of Tree-Scrap.</span>&mdash;It is often noted that some
+scrap is dark in colour, and in this condition it is generally
+spoken of as &#8220;oxidised&#8221; scrap. The oxidation is probably
+due to an enzyme, and also to the presence of chemical substances
+of a phenolic nature. In the course of laboratory
+experiments with normal latex, it was found possible to reproduce
+this darkening due to oxidation by the addition of very
+small quantities of various phenols used in general chemical
+processes, and the rapidity with which the darkening was
+effected depended upon the quantity of the phenol added.
+If this rapidly oxidising latex be mixed with normal latex, it
+would seem that the whole bulk of the latex is affected by this
+tendency to rapid oxidation. It is observed that this condition
+under which any tree may yield rapidly oxidising latex is not
+a permanent one.</p>
+
+<p><span class="smcap">Care of Tree-Scrap.</span>&mdash;As these scraps eventually give a
+grade of rubber which compares well with other and better-looking
+grades care should be exercised in collection and
+treatment so that its quality is not impaired in any way.</p>
+
+<p><a name="Sec5_13" id="Sec5_13"></a><span class="smcap">To Prevent Oxidation.</span>&mdash;As a rule the scraps are picked
+over, and heavily oxidised pieces are sorted out; otherwise the
+crepe rubber prepared exhibits black streaks. The scraps
+should not be allowed to remain in the sun (which induces
+&#8220;tackiness&#8221;), and if they have to be kept over night they may
+be placed in a weak solution (1 per cent.) of sodium bisulphite
+to arrest oxidation. It should be recognised that such a
+solution will not &#8220;bleach&#8221; already darkened scrap-rubber, and
+the nature of its action is only anti-oxidant.</p>
+
+<p><a name="Sec5_15" id="Sec5_15"></a><span class="smcap">Bark
+Shavings.</span>&mdash;In the matter of collecting bark-shavings
+much depends upon the organisation and nature of the labour
+force. Probably, on the majority of estates bark-shavings are
+collected systematically, but on quite a number considerable
+laxity in this respect has been noted. This may arise from
+lack of adequate supervision or from the peculiar systems of
+working which seem to pertain to Chinese labour. Granted
+that the trees are well &#8220;scrapped,&#8221; and that the percentage of
+rubber obtained from shavings under such circumstances
+would be extremely small (say 2 per cent. by weight on the<span class='pagenum'><a name="Page_57" id="Page_57">[57]</a></span>
+total output), it does not need much calculation to see that
+annually the loss of rubber to the estate must be considerable.
+It would also seem to follow that, if the adult labour declines
+to pick up bark-shavings carefully, it might pay to employ
+children for the purpose. Or, as is done in some places, the
+adult labour might find it advantageous to collect bark-shavings
+at low rates per pound.</p>
+
+<p><a name="Sec5_16" id="Sec5_16"></a>It is a well-known fact that if bark-shavings be allowed to
+accumulate in a heap for any but a short period, a fermentative
+and heating action is set up. The heat developed in these piles
+of shavings is so considerable that it is impossible to keep the
+hand in a heap for more than a second or two. Should this
+be allowed to persist, as would happen in the case of a breakdown
+of engine or machines, it usually results in the final
+crepe rubber becoming tacky when approaching dryness.</p>
+
+<p>To avoid this heating effect it is necessary to have spare jars
+or proper tanks in which the shavings may be soaked in water.
+In this condition bark-shavings may be kept for many days.</p>
+
+<p>For the same reason (<i>i.e.</i>, the heating effect and consequent
+tackiness) the custom followed on some estates of allowing
+coolies to keep bark-shavings in their &#8220;lines&#8221; until they
+have accumulated a fair quantity cannot be commended, quite
+apart from the possibility of actual loss by theft, which is thus
+rendered easy.</p>
+
+<p>It will be clear that where the trees are scrapped efficiently
+before tapping, the amount of rubber to be obtained from the
+treatment of pure dry shavings would be almost nil, and would
+scarcely repay the cost of collection and working. In actual
+practice, however, it is not possible to guarantee that the
+shavings are free from some scrap-rubber. Shavings brought
+in by Tamils and Javanese carry only a small amount of
+rubber, whereas where Chinese tappers are employed the yield
+of rubber may be as high as 35 to 40 per cent. upon the total
+weight of the material treated.</p>
+
+<p><a name="Sec5_17" id="Sec5_17"></a>Few estates now are not equipped with &#8220;scrap-washers&#8220;&mdash;machines
+specially designed for removing the bark from the
+rubber&mdash;and if they function efficiently the resulting crepe
+should be free from bark-particles.</p>
+
+<p><a name="Sec5_18" id="Sec5_18"></a><span class='pagenum'><a name="Page_58" id="Page_58">[58]</a></span><span class="smcap">Collection
+of Earth-Scrap.</span>&mdash;This, the lowest grade of
+rubber, is found at the base of the tree. Theoretically, if
+proper precautions are observed, the amount should be comparatively
+small, but in actual practice it may be very appreciable.
+The usual contributory causes are:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Failure to replace cups beneath the spouts of trees which
+continue to drip latex after collection.</p>
+
+<p>(<i>b</i>) Collection of latex at too early a stage.</p>
+
+<p>(<i>c</i>) Failure on the part of the tapper to ensure the flow of
+latex, by means of the spout, into the cup.</p>
+
+<p>(<i>d</i>) Flowing of latex over the edge of the cut before it reaches
+the vertical channel.</p>
+
+<p>(<i>e</i>) &#8220;Wash-cuts&#8221; on wet days, when the volume of rainwater
+down the tree is sufficient to wash the latex out of the
+cup.</p></div>
+
+<p>The amount of earth-scrap collected on any estate will
+depend, all other things being equal, upon the labour expended
+in its collection. Certainly on well-organised estates, having
+ample labour, the amounts collected are huge in comparison
+with other estates. The ground at the base of the tree below
+the latex-spout is systematically turned over with pointed
+sticks and large clots of rubber are often picked up. Here,
+again, it is advised that the collected earth-scrap should not
+be allowed to remain in heaps upon the floor of the factory.
+It should be placed in suitable tanks containing water, and
+quite a considerable portion of the cleansing work is thus
+taken from the machines.</p>
+
+
+<p class='pagenum'><a name="Page_59" id="Page_59">[59]</a></p>
+<hr class="c25" />
+<h2><a name="Ch6" id="Ch6"></a>CHAPTER VI</h2>
+
+<h3><i>TRANSPORT OF LATEX AND COAGULUM</i></h3>
+
+
+<p><a name="Sec6_1" id="Sec6_1"></a><span class="smcap">Percentage of First Latex and Other Grades.</span>&mdash;One of the
+problems confronting any manager is the question of the
+percentage of first-grade rubber calculated upon the whole
+output. Inquiries are constantly being received for advice as
+to what the various percentages of each grade of rubber should
+be. This is a question to which no definite list of figures can
+apply. There are so many little factors influencing the result.
+Some estates are not particularly careful in collecting tree-scrap.
+Hence quite a quantity of tree-scrap finds its way into
+the crepe made from bark-shavings. On the other hand,
+bark-shavings are not collected systematically on some estates,
+and the total output is thereby diminished. In consequence
+the first-grade rubber shows a higher percentage than it would
+otherwise. Again, if the earth-rubber is not regularly collected
+the percentages of the best grades are higher than they should
+be. In comparing the percentages of each grade of rubber
+from any two estates, therefore, one should have all the information
+possible as to the various working details of the estates.
+Without wishing to lay down any definite proportions which
+can be applied to all estates it might be said that, taking
+averages over a large number of estates, the percentages to
+be aimed at are:</p>
+
+<table summary="Table p59">
+
+<tr>
+<td class="left" style="padding-right: .5em;">First-grade latex</td>
+<td class="right">75</td>
+<td class="left">per cent.</td>
+<td class="left" style="padding-right: .5em;">to</td>
+<td class="right">80</td>
+<td class="left">per cent.</td>
+</tr>
+
+<tr>
+<td class="left">Other grades</td>
+<td class="right">20</td>
+<td class="center">&#8222;</td>
+<td class="center">&#8222;</td>
+<td class="right">25</td>
+<td class="center">&#8222;</td>
+</tr>
+
+</table>
+
+<p>For these figures one promises that all lower grades are
+collected and accounted for carefully and regularly. The
+distribution of the lower grades will depend upon the field
+practices of the particular estate, but the following list might<span class='pagenum'><a name="Page_60" id="Page_60">[60]</a></span>
+be given for an estate keeping all lower grades distinctly
+separate:</p>
+
+<table summary="Table p60">
+
+<tr>
+<td class="left">First-grade latex</td>
+<td class="left">&nbsp;</td>
+<td class="right">75</td>
+<td class="left">per cent.</td>
+</tr>
+
+<tr>
+<td class="left">Cup-washings</td>
+<td rowspan="2" class="left" style="font-size: 1.75em; vertical-align: middle;">}</td>
+<td rowspan="2" class="right" style="vertical-align: middle;">10</td>
+<td rowspan="2" class="center" style="vertical-align: middle;">&#8222;</td>
+</tr>
+
+<tr>
+<td class="left">Coagulated lump, etc.</td>
+</tr>
+
+<tr>
+<td class="left">Tree-scrap</td>
+<td class="left">&nbsp;</td>
+<td class="right">9</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="left">Bark-shavings</td>
+<td class="left">&nbsp;</td>
+<td class="right">4</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td class="left">Earth rubber</td>
+<td class="left">&nbsp;</td>
+<td class="right bb">2</td>
+<td class="center">&#8222;</td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+<td class="right">100</td>
+<td class="center">&#8222;</td>
+</tr>
+
+</table>
+
+<p>Emphasis is again laid on the statement that these figures
+must not be accepted as a standard. Nevertheless, they may
+prove of some service to managers in giving an idea of what the
+general line of percentages may be. There are special circumstances,
+such as distance of transport and the nature of the land,
+which at present would render the attainment of more than
+75 per cent. first-grade rubber impossible on some estates.
+Still the fact remains that if the percentage is low through
+distance of transport, etc., some method will have to be discovered
+by means of which the difficulty maybe overcome.
+On a few estates the percentage of first-grade rubber obtained
+sometimes reaches 85, but these results are rather out of the
+ordinary. An estate which collects all lower grades properly
+is doing well if the percentage of first-grade rubber is 75 or
+over.</p>
+
+<p><a name="Sec6_2" id="Sec6_2"></a><span class="smcap">Early Collection.</span>&mdash;As already noted in the <a href="#Ch5">preceding
+chapter</a>, one of the factors influencing premature coagulation
+is that of the interval elapsing between the commencement of
+tapping and the collection of latex. It will be seen that this
+ordinarily would depend, in turn, upon such considerations as
+the size of the tappers&#8217; tasks, the spacing of the trees, and the
+natural conformation of the land over which the tappers have
+to perform their tasks. In general it need only be remarked
+that every possible consideration should be given to this
+question, and that any delay should be avoided.</p>
+
+<p><a name="Sec6_3" id="Sec6_3"></a><a name="Sec6_4" id="Sec6_4"></a><a name="Sec6_5" id="Sec6_5"></a><a
+name="Sec6_6" id="Sec6_6"></a><span class="smcap">Transport.</span>&mdash;Wherever possible it is endeavoured to convey
+latex from field to factory by man-power. Tamil coolies, as a
+rule, place the bucket on the head; Chinese and Javanese
+coolies like to use a balanced carrying-pole. Where distance<span class='pagenum'><a name="Page_61" id="Page_61">[61]</a></span>
+renders these methods too costly in time and labour, it is
+usual to have field centres where the latex is collected and
+dispatched to the factory generally (<i>a</i>) by means of vessels
+conveyed on light railways; (<i>b</i>) in large cans placed on motor-lorries;
+(<i>c</i>) in cylindrical galvanised drums supported on two
+wheels and drawn by bullocks. There may be variants, but
+these are the chief means of transport in bulk over a distance.</p>
+
+<p>Where possible, the best system is that employing a trolley-line,
+as great agitation of the latex is avoided, and the time in
+transit is much reduced.</p>
+
+<p>The usual method of transport by bullock power is slow,
+and as estate roads (and even Government roads) are often
+below the standard expected in this country, the jolting undergone
+by the latex is, to say the least, not calculated to afford a
+high yield of first-grade rubber. The late Mr. F. W. F. Day
+advocated the use of a circular perforated wooden grid, to be
+floated on the latex, in order to moderate the wave effect
+produced by jolting.</p>
+
+<p><a name="Sec6_7" id="Sec6_7"></a>Whatever the means of bulk-transport employed, it should
+be the care of those in charge to see that vessels are not
+allowed to remain in the sun longer than is necessary. Even
+during the journey they should be shaded in the best possible
+manner.</p>
+
+<p>These large transport vessels usually receive what is really
+only perfunctory attention in the matter of cleaning. They
+should receive the same care as would be exercised in dealing
+with milk cans in other countries. Ordinary sluicing with
+water is not sufficient, and if they cannot be sterilised by
+means of boiling water, they should be treated, after ordinary
+washing, with a 5 per cent. solution of sodium bisulphite
+every day.</p>
+
+<p><a name="Sec6_8" id="Sec6_8"></a><span class="smcap">Anti-Coagulant for Transport.</span>&mdash;When anti-coagulants
+are not used in the cups or buckets, it is advisable to use them
+in the bulk-transport vessels. Either formalin or sodium
+sulphite is of service, but the great objection advanced against
+the former is its loss due to evaporation while the carts are
+going to the fields or waiting at the centres. For this reason
+sodium sulphite is now generally employed.</p>
+
+
+<p class='pagenum'><a name="Page_62" id="Page_62">[62]</a></p>
+<p class="center"><i>Formula for Use of Sodium Sulphite in Transport.</i></p>
+
+<div class="blockquot"><p>(<i>a</i>) Dissolve 1 pound of powder in 3 gallons of water.</p>
+
+<p>(<i>b</i>) Of this solution, place half a gallon in the vessel for
+every 30 to 40 gallons of latex.</p></div>
+
+<p><a name="Sec6_9" id="Sec6_9"></a><span class="smcap">Transport by Coolie.</span>&mdash;As already pointed out, the extent
+to which man-power can be used in transport of latex is generally
+limited. On small estates it is an easy matter for coolies to
+carry the latex to the factory, but on larger estates many
+difficulties may arise, which may also militate against the
+successful use of other means of transport. It is not uncommon
+to find, therefore, that a policy of decentralisation
+has been adopted.</p>
+
+<p><a name="Sec6_10" id="Sec6_10"></a><span class="smcap">Coagulation Centres.</span>&mdash;Divisions of the estate have their
+own small stations at which latex is received and coagulated.
+In this way it is possible to receive latex without much delay,
+and with benefit to the resultant rubber, especially if prepared
+in sheet form. Much controversy has arisen regarding these
+decentralised establishments, but the fact remains that on large
+estates, which are efficiently controlled, the scheme has been
+highly successful from all points of view. On the other hand,
+it is alleged that this method of working increases costs, and
+often gives an unsatisfactory quality of rubber. Concerning
+the latter point it seems to be reasonable to expect that the
+European in charge of any division should be conversant with
+the method of preparation required, and should be capable of
+seeing that no mistakes are made. Given uniform equipment
+in all stations, and uniform rules for treatment of the latex,
+there does not appear to be any valid reason why the product of
+one station should be inferior to that of the others. Neither is
+it so in the case of several estates which might be quoted.</p>
+
+<p>In the matter of costs of working the writer has had to
+investigate several cases regarding which there was dissatisfaction.
+In some instances it was found that the stations
+had not been placed advantageously with respect to a water-supply;
+and instead of one or two coolies pumping for an
+hour or two, a larger number had to be employed for hours in
+the carriage of water from the nearest available source. This<span class='pagenum'><a name="Page_63" id="Page_63">[63]</a></span>
+meant that, as the coolies were on daily wage, the force appeared
+to be much bigger than that usually required. In other cases
+there were too many store coolies, when often the place of
+some could have been taken for the necessary period by tappers
+arriving early from the nearer fields. Sometimes costs were
+increased by reason of the use of an excess of chemicals, owing
+to the lack of uniform rules throughout the several stations.
+In spite of all that has been written, and the verbal instructions
+that have been given, it was not uncommon to find unstable
+chemicals such as sodium bisulphite exposed to the moist air.
+In this way not only was there waste of material, but also the
+probability of inferior rubber being made.</p>
+
+<p><a name="Sec6_11" id="Sec6_11"></a><span class="smcap">Transport of Coagulum.</span>&mdash;On the whole if it is a question
+between the transport of latex and the transport of coagulum,
+the writer would always favour the latter, for reasons which
+have possibly been made clear in the preceding paragraphs.
+In effect, it should be recognised that the less handling and
+transport the latex receives the better the general result.</p>
+
+<p>If proper precautions are taken, the transport of coagulum
+intended for the preparation of crepe should present no difficulty,
+and should have no injurious effect upon the quality of
+the resultant rubber. It is only too common, nevertheless,
+to note defects, in the finished crepes, which can only be attributed
+to a failure to observe reasonable care in the transport
+of the coagulum. For example, it has been observed that a
+mass of coagulum from a coagulation station has been conveyed
+on the floor of a bullock-cart, or motor-lorry, previously used
+in the carriage of other materials. Unless the boards have
+been most scrupulously cleansed, the coagulum is found to be
+contaminated, often to a marked degree. Again, although the
+cart may be clean, it may have to travel some distance on roads
+carrying a fair amount of motor traffic. Even should the cart
+have a canopy, road-dust is often whirled through the open sides
+of the cart; and in the districts where red laterite roads are
+common, the stain of such dust often persists in the finished
+crepe. It scarcely need be remarked that coagulum should be
+transported in closed wooden boxes or in galvanised iron drums
+fitted with lids; and that preferably sufficient water should be<span class='pagenum'><a name="Page_64" id="Page_64">[64]</a></span>
+present in these receptacles to allow the coagulum to float. All
+such containers should receive the same scrupulous attention
+as the vessels employed in the transport of latex.</p>
+
+<p>The successful transport of coagulum for sheet-making is
+fraught with much greater disabilities, and it is usual to note
+on most estates that the resulting sheets from out-stations are
+always inferior, in final result, to those coagulated and prepared
+at the central factory. If the flat pieces of coagulum are
+placed in piles of any height it is common to find, on arrival
+at the factory, that much adhesion has been caused. There is
+great difficulty in separating the pieces, and often the successful
+operation is impossible. It is usual to hand-roll the coagulum
+before transport, but it is often found that by the time
+the rubber reaches the factory it has become too hard for
+subsequent good results.</p>
+
+<p>One of the strong arguments in favour of the establishment
+of divisional stations is to be found in the preceding paragraph.
+Sheet-making, as it necessitates the employment of only light
+machines suitable for hand-power, is a feasible proposition in
+a field station. There is no reason for sheets made thus to be
+in any way inferior to those made at a central factory; in fact,
+they are often better, as the latex has the chance of being treated
+when comparatively fresh.</p>
+
+<p>If it is found necessary to transport sheet-coagulum, every
+possible precaution should be taken against piling the pieces.</p>
+
+<p>After hand-rolling some estates bring the rubber from the
+field-stations to the central factory in drums of water, others in
+shallow boxes containing not more than half a dozen sheets
+in a pile. A method proposed long ago, but not in practice,
+was to have a number of shallow trays subdivided so that each
+compartment held one sheet only. If these trays were properly
+made and carefully fitted there appeared to be no reason why
+they should not form sliding parts of a large box, in which
+squeezing and adhesion of the pieces of coagulum would be
+avoided. Naturally any such device would increase appreciably
+the weight to be transported, and on this ground would
+not find popular favour except where motor-power is used
+for road transport.</p>
+
+
+<p class='pagenum'><a name="Page_65" id="Page_65">[65]</a></p>
+<hr class="c25" />
+<h2><a name="Part2" id="Part2"></a>PART II</h2>
+
+<h3>FACTORY OPERATIONS</h3>
+
+
+<hr class="c25" />
+<h2><a name="Ch7" id="Ch7"></a>CHAPTER VII</h2>
+
+<h3><i>PRELIMINARY TREATMENT OF LATEX</i></h3>
+
+
+<p><a name="Sec7_1" id="Sec7_1"></a><a name="Sec7_2" id="Sec7_2"></a><span class="smcap"><a name="Sec7_3" id="Sec7_3"></a><a
+name="Sec7_4" id="Sec7_4"></a>Reception
+of Latex at the Store.</span>&mdash;Bearing in mind the
+remarks in <a href="#Sec6_3">Chapter VI.</a> on the conditions under which latex
+is transported, it follows that nothing but the very best and
+most suitable vessels should be used in the store. A point to
+which adequate attention is not given in many factories might
+be mentioned here. Considering the importance attached to
+colour in the dry rubber by brokers and consumers, and knowing
+how extremely trivial are the causes which may mar the colour,
+it is rather surprising that better provision is not made for
+the reception and handling of latex in factories. Too often the
+receiving vessels are placed on the floor of the store close to the
+entrance. Coolies bringing in latex cannot avoid bringing
+with them quite a considerable amount of dirt. Presuming
+that a hose-pipe has been installed, and that the floor is constantly
+being sluiced down with water, no great harm will
+result. But would it not be ever so much better if the dirt
+were kept out? In how many factories is provision made for
+this? Such an arrangement is not difficult to make, and is
+already in practice on a few estates. A verandah is built outside
+the wall of the factory and all latex is received there. In
+another place open chutes are provided which terminate in the
+straining sieves. The coolie thus stands on the verandah
+where he removes coagulated lump and impurities from the
+latex, which is then poured down the chute, passing through
+the sieve into large coagulating jars or tanks.</p>
+
+<p><a name="Sec7_5" id="Sec7_5"></a>Too often it would appear, from the writers&#8217; observation,
+there is a lack of adequate supervision on the arrival of latex<span class='pagenum'><a name="Page_66" id="Page_66">[66]</a></span>
+at the store. Much can be learned from an inspection of the
+coolies&#8217; buckets, and the cause of small defects in the finished
+rubber can often be thus traced. Leaves, stems, bark-shavings,
+and dirt appear in the buckets, and it is a source of constant
+surprise to imagine how even unintelligent coolies can allow
+such things to happen. These objects are removed before or
+during straining, but still they ought not to be there in the
+first place, and the fact that such a state of things exists is
+evidence of neglect on the part of the coolies or lack of supervision.
+Efforts are made in a large number of cases to cope
+with these troubles, but on some estates things are allowed
+to proceed in the same slipshod way, and too much responsibility
+is thrown on the straining process.</p>
+
+<div class="figcenter"><a name="Fig29" id="Fig29"></a><img src="images/illo083.jpg" alt="Raised Verandah for Reception of Latex" />
+<p class="caption"><span class="smcap">Raised Verandah for Reception of Latex; likewise equipped<br />
+with Facilities for calculating Individual Daily<br />
+&#8220;Yield per Coolie&#8221; by Sampling of Latex.</span></p></div>
+
+<p>It is suggested that it should be the business of a European
+to supervise the reception of latex every day. This is at
+present quite impossible on some estates, but it does not alter
+the fact that this supervision should be provided, and is
+extremely necessary.</p>
+
+<p><a name="Sec7_6" id="Sec7_6"></a><span class='pagenum'><a name="Page_67" id="Page_67">[67]</a></span>It
+is surprising how the point is overlooked in many factories&mdash;not
+that they are in a dirty state, but they fall short of being
+classed as clean factories for want of the little that makes the
+difference. Possibly those in charge do not believe that all
+this fuss need be made, but the writers can assure them, from
+a practical knowledge of a very large number of factories, that
+cleanliness does pay.</p>
+
+<p>It might not be credited to Tamil coolies, but yet it is
+probably true, that the moral effect of working under the
+cleanest and best conditions has an influence upon the store
+coolies, and that their work is better in consequence. Everything
+which will tend to simplify the cleansing of the factory
+should therefore be installed. Hose-pipes, glazed tiles, clean
+floors, plenty of light and air are not fads or fancies, but considerable
+factors in determining the final quality of the rubber.
+There is considerable truth in the suggestion that the coagulating
+room and machine room should be as &#8220;spick and span&#8221;
+as a modern home dairy.</p>
+
+<p><a name="Sec7_7" id="Sec7_7"></a><span class="smcap">Straining of Latex.</span>&mdash;This is a most necessary process,
+and one which usually entails much trouble and time which
+one could wish avoided. It will be admitted that the trouble
+could be reduced greatly if the regulation of field processes
+could be made more stringent. In spite of knowledge that
+impurities must not be allowed to enter the cups, coolies will
+ignore the rule that the cup must not be placed in position until
+the bark shaving has been cut. The result is that pieces of
+bark fall into the cups, and coolies are generally too careless
+or too hurried to remove them.</p>
+
+<p>Again, when cups are placed on the ground, it is easy to see
+that dirt may adhere to them. In the collection of latex some
+of this dirt may fall into the bucket. Since the introduction of
+cup-holders on many estates the trouble from this source has
+decreased considerably, but, nevertheless, it may be taken for
+granted that even under the best of conditions all latex requires
+straining.</p>
+
+<p><a name="Sec7_8" id="Sec7_8"></a>The best type of strainer has yet to be evolved. Usually it
+consists in principle of a piece of fine brass mesh contained in
+some form of holder. Theoretically such a strainer should<span class='pagenum'><a name="Page_68" id="Page_68">[68]</a></span>
+work well, but in actual practice nearly all strainers are a
+source of continual worry. Undiluted latex, as received at the
+factory, is of a rich consistency, containing very fine particles
+of dirt and often minute particles of prematurely coagulated
+rubber. The latter soon clog a fine mesh strainer, while the
+former may pass through. When the flow through the strainer
+becomes slow, the coolie in charge generally rubs the top
+surface of the sieve with a piece of coagulum, thus forcing
+material through the mesh. He then rubs the under-surface,
+with the result that undesirable matter falls into the strained
+latex. In theory it seems a simple matter to have a number of
+sieves ready so that a clean one may be substituted for a clogged
+one, which should be cleansed at once with water. In practice
+the factory coolie will probably only carry out instructions
+when the eye of the superintendent is alert. As a result of the
+rubbing and consequent strain, the brass mesh usually breaks
+away from its support and the fracture may not be detected for
+some time, during which irreparable damage may have been
+done to the resultant rubber.</p>
+
+<p>In view of the presence of the fine particles of dirt, to which
+allusion has been made, fine sieving of the latex appears to be
+essential, especially when sheet-rubber is to be prepared. The
+fine sieves are generally of the type known as &#8220;60 mesh,&#8221; and
+they do not usually give thoroughly satisfactory results even
+when the gauze is supported and strengthened by means of
+cross-wires placed underneath. The general fault with these
+strainers is that a sufficiently wide &#8220;selvage&#8221; is not allowed
+in the clamped edges of the gauze, or that the edges of the
+support are so sharp and abrupt that the strands of the gauze
+are soon severed by the strain imposed in vigorous cleaning.</p>
+
+<p><a name="Sec7_9" id="Sec7_9"></a>Many estates use two strainers; the first a more robust one
+containing &#8220;30 mesh&#8221; gauze, and the second the fine &#8220;60
+mesh.&#8221; Even this device does not bring about the desired
+immunity from trouble. Relief could be obtained if the latex
+were always in a more freely fluid form. Estates employing
+anti-coagulants in the field benefit in this respect. Other
+estates, although finally using the finest of mesh, experience
+far less trouble than most estates by reason of a difference in<span class='pagenum'><a name="Page_69" id="Page_69">[69]</a></span>
+method of working. This can be explained by an outline of
+the system adopted on a particular estate:</p>
+
+<div class="blockquot"><p>(<i>a</i>) On arrival of the rich latex at the store, all visible coagulated
+lumps and other extraneous matter are removed by
+the tapper.</p>
+
+<p>(<i>b</i>) Each tapper&#8217;s latex is diluted with a quantity of water.</p>
+
+<p>(<i>c</i>) The diluted latex passes through two sieves, one above
+the other. The top sieve is of stout perforated zinc sheet,
+with 10 circular holes to the inch. This removes all large
+particles. The lower is of &#8220;30 mesh&#8221; brass gauze, and
+practically no rubbing is required. The latex is now in
+glazed-tile tanks, in which it is further diluted to the required
+standard by means of a recording instrument.</p>
+
+<p>(<i>d</i>) The latex flows by means of a chute into the coagulating
+tanks, passing through a large &#8220;60 mesh&#8221; sieve.</p></div>
+
+<p>It is not guaranteed that this method will furnish a complete
+absence of very fine particles of dirt in sheet rubber, as the
+human element enters so largely into the question; but it can
+be stated that no complaints have been received on the point
+of &#8220;specks of dirt&#8221; since this system was inaugurated.</p>
+
+<p>On the same estate fine sieving in the preparation of pale
+crepe has been abandoned as an unnecessary refinement. The
+two coarse sieves mentioned above are employed only,
+and it is to be acknowledged that the results justify the
+procedure.</p>
+
+<p><a name="Sec7_10" id="Sec7_10"></a><span class="smcap">Bulking of Latex.</span>&mdash;Not long ago advanced estates used
+to combine all latex before coagulation, in order to obtain
+uniformity of product. Previously it had been the custom
+to deal only with comparatively small separate volumes of
+latex, with obviously great disadvantage.</p>
+
+<p>Since the introduction of instruments such as the &#8220;Metrolac,&#8221;
+by means of which any volume and all volumes of latex may
+be reduced to a common standard of dry rubber content, the
+necessity for &#8220;bulking&#8221; has passed. It is not now necessary
+to keep latex standing, perhaps for two hours, awaiting the
+arrival of other latex from distant fields.</p>
+
+<p><a name="Sec7_11" id="Sec7_11"></a><span class="smcap">Standardisation of Latex.</span>&mdash;In modern practice, as
+already pointed out, it is possible now to handle any volume of
+latex with a view to its reduction to any required standard of<span class='pagenum'><a name="Page_70" id="Page_70">[70]</a></span>
+dilution for the purpose of obtaining a uniform product.
+For the reception and subsequent handling of the latex various
+schemes have been devised, and they are usually planned in
+connection with coagulating tanks used in the preparation
+chiefly of sheet rubber.</p>
+
+<div class="figcenter"><a name="Fig30" id="Fig30"></a><img src="images/illo087.png" alt="End-Section Sketch of Verandah, etc." />
+<p class="caption"><span class="smcap">End-Section Sketch of Verandah, etc., showing a Good<br />
+Method for receiving Latex and filling Tank.</span></p>
+<p class="capt500">T, Sheet coagulation tank; C, cylinder for reception and dilution
+of latex; GG, gutter; PP, raised platform on verandah;
+SS, steps leading to platform; W, dwarf wall; EE, expanded
+metal partition; OO, open.</p></div>
+
+<p><a name="Sec7_12" id="Sec7_12"></a><a name="Sec7_13" id="Sec7_13"></a>In the successful working of a tank it is necessary, in order
+to obtain the best results, to standardise all latex. This cannot
+be effected properly in the tank itself, and hence it is the
+practice to dilute each lot of latex to standard before it is run
+into the tank. In the ordinary way this would entail a great
+deal of labour in handling the diluted latex. To obviate
+this, the scheme outlined in the accompanying <a href="#Fig30">sketch</a> has been
+suggested on several occasions and in various quarters. Such
+a scheme or modification of it has been put into successful
+practice on several estates. Although the drawing was made
+some considerable time ago when estates were not then prepared
+to go so far in this direction, subsequent modifications show
+only minor differences which, while leaving the original principle
+intact, testify to a fertility of resource in adapting the idea
+to existing circumstances and buildings. The drawing is <i>in
+toto</i> almost a replica of the original installation now in successful<span class='pagenum'><a name="Page_71" id="Page_71">[71]</a></span>
+use on the Kinrara Estate of the Ledbury Rubber Company.
+On this company&#8217;s Ledbury Estate likewise a similar system
+is employed, except that the reception verandah is part of a
+natural formation and needed no such direct raising. Several
+other estates have now adopted the scheme, which has been
+proved to be of practical value. The writers make no claim to
+originality in the idea, which might have occurred to many
+independently on the introduction of coagulating tanks.</p>
+
+<div class="figcenter"><a name="Fig31" id="Fig31"></a><img src="images/illo088.jpg" alt="Raised
+Verandah for Reception and Handling of Latex" />
+<p class="caption"><span class="smcap">Raised Verandah for Reception and Handling of Latex.</span></p></div>
+
+<p><a name="Sec7_14" id="Sec7_14"></a><span class="smcap">Verandah.</span>&mdash;In reproducing the drawing it is believed that
+the sketch will convey practically all the information required.
+It may be explained that the coolies are allowed to enter
+only the outer part of the verandah. The buckets are
+handed across the low wall into the care of factory coolies,
+who strain the latex through gauze sieves into the latex
+cylinders.</p>
+
+<p><a name="Sec7_15" id="Sec7_15"></a><span class="smcap">Latex Reception Vessels.</span>&mdash;These cylinders may be similar
+to the tanks commonly used for transport of latex from distant
+fields to the factory. An 80-gallon cylinder is easily mounted<span class='pagenum'><a name="Page_72" id="Page_72">[72]</a></span>
+by its trunnions on a suitable iron framework which is superimposed
+on a skeleton truck.</p>
+
+<div class="figcenter"><a name="Fig32" id="Fig32"></a><img src="images/illo089.jpg" alt="Another
+Set of Dilution Tanks on Raised Verandah" />
+<p class="caption"><span class="smcap">Another Set of Dilution Tanks on Raised Verandah.</span></p></div>
+
+<p>The latex is diluted down to standard in the cylinders, the
+truck is moved opposite the compartment to be filled, and a
+light movable gutter is placed beneath the vent of the outlet
+pipe. This pipe is fixed in the bottom of the cylinder, and is
+provided with a large stop-cock which is operated by a spanner
+key. The stop-cock should be of the simplest type, capable
+of being taken apart and assembled in a minute or so. The
+orifices should be large enough for a coolie to insert at least two
+or three fingers so as to facilitate cleaning, and the pipe should
+have no right-angle bends.</p>
+
+<p><span class='pagenum'><a name="Page_73" id="Page_73">[73]</a></span>On the inside of the cylinder a scale of gallons may be
+painted, so that one may possess a knowledge of the quantities
+run into, or required for the completion of, any compartment.</p>
+
+<p><span class="smcap">A Screw Plug Unsatisfactory.</span>&mdash;It may be of benefit to
+managers who contemplate such an installation to know that
+the adoption of a stop-cock in the vent pipe of the cylinder
+is the outcome of experience. In one instance the vent pipe
+as designed was fitted with a screw plug at the end. Unfortunately
+with this arrangement the flow could not be regulated,
+and owing to the &#8220;head&#8221; of the latex it dashed violently
+down the gutter, struck the bottom of the coagulating tank,
+and thence was scattered over the factory.</p>
+
+<p><span class="smcap">Another Installation.</span>&mdash;In another type of installation,
+in place of the vessels travelling upon a raised verandah platform,
+the standardised latex is conveyed to the coagulating
+tanks by means of drums supported by hooks to a chain-block
+and pulley which travels on an overhead gantry. This method
+is practicable, but may be regarded as less satisfactory in general
+working than the verandah method of treatment.</p>
+
+<p><span class="smcap">A Modern Installation.</span>&mdash;In the most recent scheme for
+dealing with the reception of latex, its standardisation, and
+conveyance to the coagulating tank, the main principle of the
+first system outlined is retained; but the receptacles are not
+mobile. Glazed-tile tanks are employed, the capacity of each
+being approximately equivalent to that of each unit coagulating
+tank.</p>
+
+<p>The accompanying illustrations show the general arrangement
+and some details of the system of reception tanks employed
+on the well-known Pataling Estate.</p>
+
+
+<p class='pagenum'><a name="Page_74" id="Page_74">[74]</a></p>
+<hr class="c25" />
+<h2><a name="Ch8" id="Ch8"></a>CHAPTER VIII</h2>
+
+<h3><i>COAGULATION</i></h3>
+
+
+<p>Whether it is necessary to employ any coagulant, or whether
+latex should be allowed to coagulate naturally, will not be discussed
+at this stage. Neither will mention be made of any
+patent processes of coagulation which employ other than acid
+mediums. These subjects will be treated in a <a href="#Ch20">subsequent
+section</a> of the book.</p>
+
+<p><a name="Sec8_1" id="Sec8_1"></a><span class="smcap">Choice of Coagulants.</span>&mdash;It is not proposed here to enter
+into a discussion as to the merits of the dozens of known
+coagulants. Suffice it to state that acetic acid, although the
+oldest general coagulant, still remains the best and safest
+at the present time. There is a deal to be said in favour of the
+use of another organic acid, formic acid. It is equally as safe as
+acetic acid, and quite efficacious; the only drawback is that,
+taking all things into consideration, it is very slightly more
+expensive. Acetic acid, therefore, will always be implied in
+this chapter when the word &#8220;acid&#8221; is used.</p>
+
+<p><a name="Sec8_2" id="Sec8_2"></a><span class="smcap">Strength of Acid Solution.</span>&mdash;In the old days it was the
+rule rather than the exception to find pure, undiluted acid used
+in coagulation. In many cases no harm resulted, for the simple
+reason that, owing to the large proportion of water in the latex,
+the acid was thereby very much diluted. The estates had to
+thank the over-dilution of the latex for the non-injury of the
+resulting rubber.</p>
+
+<p>Some estates make up a stock solution of 1 part acid to 20
+of water, and use this with success because of the fair amount
+of added water present in the latex.</p>
+
+<p>It must be understood that what is being referred to now is
+not the absolute quantity necessary for coagulation, but the
+proportions&mdash;<i>i.e.</i>, the respective volumes of acid and water<span class='pagenum'><a name="Page_75" id="Page_75">[75]</a></span>
+in the solution of acid made up every day. That the strength
+of the acid solution, as well as the quantity used, has an effect
+upon coagulation can be easily demonstrated in the following
+way:</p>
+
+<p>Take separate and equal lots of the same latex, and to each
+add the same quantity of pure acid, but in each case diluted
+with varying quantities of water. It will be found that coagulation
+is quickest where pure acid is employed, and slowest
+where the acid is most dilute. It will also be found that, providing
+the quantity of acid employed was sufficient for coagulation,
+the best and most uniform coagulation is obtained from
+the use of the most dilute acid, within limits. It will often
+be found that where pure acid has been employed coagulation
+is local&mdash;<i>i.e.</i>, we have lumpy coagulation, and often a very
+milky remaining liquor. This is due to the fact that, as coagulation
+is immediate upon the spot which is first touched by
+the pure acid, a deal of the acid is enclosed within the rubber at
+that spot, and hence other portions of the latex are deprived of
+acid. It is in such cases that most air-bubbles are enclosed.</p>
+
+<p>As the dilution of the acid solution is increased the mixing
+is more thorough and uniform. Coagulation is slower, and air-bubbles
+can escape to the surface.</p>
+
+<p><a name="Sec8_3" id="Sec8_3"></a><span class="smcap">Method of Making Stock Solution.</span>&mdash;Experiments have
+been repeatedly made in the laboratory with acid solutions of
+varying dilution, from pure acid down to 1 part of acid in 500
+parts of water. While it has been found that a 1 in 5 solution
+can be used where the latex is very dilute (say, 1 part of latex
+to 5 parts of water), and a 1 in 20 solution may be used in
+fairly dilute latex (for crepe-making), it is undoubtedly a fact
+that for latex as generally &#8220;standardised&#8221; on estates a much
+more dilute solution of acid should be used&mdash;<i>e.g.</i>, 1 in 100, or
+even 1 in 200, of water. It must be borne in mind that the
+quantity of acid necessary for coagulation is not changed, but
+merely the dilution. Let us take a concrete case to illustrate
+the point:</p>
+
+<div class="blockquot"><p>On an estate at present the stock solution is made up by
+diluting 1 pint of acid with 20 pints of water, and 1 gallon of
+this is necessary to coagulate 50 gallons of pure latex.</p>
+
+<p><span class='pagenum'><a name="Page_76" id="Page_76">[76]</a></span>It is desired to use a stock solution of 1 pint of acid to 100
+pints of water. Evidently, therefore, 5 gallons of this stock
+solution contain only the same quantity of pure acid as 1 gallon
+of the old solution contained, and it will be necessary to add
+5 gallons for every 50 gallons of pure latex. Thus:</p>
+
+<div class="blockquot"><p>1 to 20; 1 gallon necessary for 50 gallons pure latex.<br />
+1 to 100; 5 gallons necessary for 50 gallons pure latex.</p></div></div>
+
+<p>It may be pointed out that the quantities worked out in the
+foregoing examples are not absolutely and mathematically
+correct, but they are quite close enough for all practical
+purposes.</p>
+
+<p>It may be advanced by someone that if a dilute solution of
+acid, such as 1 in 100, is used the bulk of this stock solution
+(5 gallons to 50 gallons of latex) is very great, and might be
+injurious to the quality of the resulting rubber. A moment&#8217;s
+consideration will show that, after all, the volume of acid
+solution is only one-tenth that of the volume of latex. This
+can have no effect upon the quality of the rubber. Even
+dilution of the pure latex with half its bulk of water in the
+factory will have no effect upon the quality of the resulting
+rubber. It is to be remembered that, except in cases where
+the proportion of added water to latex is absurdly large, the
+main argument against putting water into the latex-cups is
+against the possible poor quality of the water rather than
+against the actual small quantity theoretically added. It is
+acknowledged that, where the water to be put into the cups
+can be guaranteed to be of good quality, no great objection
+would be raised against placing the smallest possible quantity
+of such water in the cups. But how many estates have such
+good water easily available to the coolies, and how many
+estates can be sure that only that smallest possible quantity
+would be used? It is a notorious fact that, even on estates
+where the quantity of water used was supposed to be a minimum,
+the proportion of water to latex in some cups often exceeded
+even three or four to one. In any case it may be stated as
+an elementary truism that the absence of water is more to be
+desired than water of doubtful quality.</p>
+
+<p><a name="Sec8_4" id="Sec8_4"></a><span class="smcap">Quantity of
+Acid.</span>&mdash;As a result of repeated experimental<span class='pagenum'><a name="Page_77" id="Page_77">[77]</a></span>
+work it has been found that, for pure average latex, the quantity
+of acid necessary for complete coagulation, reckoned in parts
+of pure acid to parts of latex, is:</p>
+
+<div class="blockquot"><p>1 part pure acid; 1,000 parts average latex.</p></div>
+
+<p>Where the latex is rather richer than average (above 30 per
+cent. dry rubber) probably a little more acid would be required,
+and similarly if the dry rubber content is lower the quantity
+of acid must be less.</p>
+
+<p>It used to be a common belief that the more dilute the latex
+the greater the quantity of acid necessary, but this would only
+apply to cases of extreme dilution of latex.</p>
+
+<p>As a matter of fact, up to certain limits of added water, the
+reverse is actually the case&mdash;<i>i.e.</i>, the more water in the latex the
+less acid must be added, assuming that for pure latex the proportion
+of pure acid to latex is taken as 1 part to 1,000 parts.
+This was found to be the case up to dilutions of three or four
+times the volume of latex. To take concrete examples which
+will perhaps make the truth more clear:</p>
+
+<div class="blockquot"><p>Assuming we commence by making up our stock solution of
+acid by adding 100 parts of water to 1 part of pure acid, this
+gives us a mixture of 1 to 100. For 1 gallon of pure latex it
+would be necessary to add one-tenth of its volume of the above
+mixture&mdash;<i>i.e.</i>, 16 ozs.</p>
+
+<p>Suppose we take a gallon of pure latex and add a gallon of
+water, we now have 2 gallons of so-called latex. But we still
+have only 1 gallon of real latex present in the diluted latex,
+and it is only necessary to add sufficient acid to coagulate this
+gallon&mdash;<i>i.e.</i>, 16 ozs.</p>
+
+<p>Further, if 1 gallon of latex be diluted with 2, 3, or even
+4 gallons of water it is still only necessary to add 16 ozs. of the
+acid mixture.</p>
+
+<p>At dilutions beyond this limit, however, it is necessary to
+add a little more acid to obtain complete coagulation.</p></div>
+
+<p>In the process of preparing sheet rubber it is very necessary
+to see that the minimum quantity of acid is used, otherwise
+visible defects are caused. But in coagulating latex intended
+for preparing crepe, where the rubber undergoes protracted
+washing on the machines, the presence of a slight excess of
+acid in coagulation is not calculated to cause any deterioration<span class='pagenum'><a name="Page_78" id="Page_78">[78]</a></span>
+in the quality of the rubber. Advantage must not be taken
+of this statement to argue that more than a slight excess may
+be used without injury to the rubber, as it can be shown that
+the use of a large excess of acid results in an inferior rubber.</p>
+
+<p><a name="Sec8_5" id="Sec8_5"></a><span class="smcap">Quantities Necessary for Modern Requirements.</span>&mdash;It
+may be commended to the notice of the beginner that any
+further experimental work as to the quantity of acetic acid
+necessary for complete coagulation would only involve a
+waste of time and energy.</p>
+
+<p>The general figure given in a preceding paragraph (1 part
+pure acid to 1,000 parts of latex) may be accepted as the
+rough basis for working. In modern practice, however,
+undiluted latex is usually diluted to a standard which may
+vary on different estates from 1<span class="enum">1</span>&#8260;<span
+class="denom">4</span> lbs. to 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber per
+gallon.</p>
+
+<p>Latices of these strengths can be coagulated at a ratio of
+1 part pure acid to 1,200 parts of standardised latex; and this
+quantity need not be exceeded, except in cases where an appreciable
+amount of some anti-coagulant is present in the latex.
+The proportion may then be raised to 1 in 1,000.</p>
+
+<p>If considered advisable the acid may be used in a <span class="enum">1</span>&#8260;<span class="denom">2</span> per cent.
+solution for sheet preparation; but in any case it is advised
+for the sake of uniformity that a 1 per cent. solution should be
+employed in the preparation of both sheet rubber and crepe
+rubber. In most modern factories, measuring vessels of
+various capacities are to be found, and it is always more satisfactory
+to have the solution made up in approximately correct
+strength at the rate of 1 oz. of pure acid to 5 pints of water.
+Often, however, on some estates European supervision of this
+work is not possible, and the preparation of the acid solution
+has to be left in the hands of a (more or less) skilled coolie.
+It is thus necessary to find some less fine, but still approximately
+correct, method of procedure. In the East the kerosene tin is
+in universal favour for the carriage of water, and there is no
+reason why it should not be utilised as a standard measure for
+preparing the dilute acid solution, <i>providing it is not allowed to
+become rusty</i>. The capacity of the tin is 4 gallons (640 fluid ozs.),
+so that a one-hundredth part would be approximately
+6<span class="enum">1</span>&#8260;<span class="denom">2</span> ozs.<span class='pagenum'><a name="Page_79" id="Page_79">[79]</a></span>
+It is suggested that this quantity should be measured out by
+means of a glass graduated vessel, and then that an aluminium
+cup should be cut down so as to hold the exact quantity.</p>
+
+<p>This would reduce the making of a solution, sufficiently
+approximate to 1 per cent. strength for all practical purposes,
+into a simple operation of mixing pure acid and water in the
+ratio of one cupful of acid to 1 kerosene tin of water.</p>
+
+<p>The actual quantity of solution required for the coagulation
+of any volume of standardised latex can be calculated easily
+from the ratio 1:1,200. As the strength of solution is 1:100
+it will be seen that the quantity to be taken is <i>always one-twelfth</i>
+that of the volume of latex&mdash;<i>e.g.</i>:</p>
+
+<div class="blockquot"><p>(<i>a</i>) If the latex tank holds 90 gallons of standardised latex,
+7<span class="enum">1</span>&#8260;<span class="denom">2</span> gallons of dilute acid solution are required.</p>
+
+<p>(<i>b</i>) A tank containing 120 gallons of latex would need 10
+gallons of the 1 per cent. acid solution.</p></div>
+
+<p>It is assumed that all estates, not only in the preparation of
+sheet rubber, but also in the making of crepe rubber, always
+employ the system of standardising latex in order to obtain
+uniformity. They are ill-advised if they do not follow this
+practice; but in case average undiluted latex is treated in
+coagulation, the quantity of acetic acid to be used should be
+calculated from the ratio 1:1,000.</p>
+
+<p>If the acid solution is to be employed in 1 per cent. strength,
+<i>one-tenth</i> of the volume of latex to be treated will indicate the
+required quantity of solution necessary for complete coagulation
+unless anti-coagulants have been used, when the quantity must
+be increased as experience directs. It will be recognised, of
+course, that undiluted latex may only be used in any case for the
+preparation of crepe rubber; or in some exceptional case, such
+as the special preparation of &#8220;slab&#8221; rubber.</p>
+
+<p><a name="Sec8_6" id="Sec8_6"></a><span class="smcap">Care in Mixing.</span>&mdash;It is essential that the mixture of dilute
+acid and latex should be thoroughly intimate. This can only be
+attained by careful manipulation, especially in the case of sheet
+preparation. Where crepe rubber is to be made it may be
+permissible to employ a solution stronger than 1 per cent.,
+but it is not advised. The acid should be poured into the<span class='pagenum'><a name="Page_80" id="Page_80">[80]</a></span>
+latex while stirring, and the agitation should continue for such
+a period as to ensure thorough mixing in all parts.</p>
+
+<p><a name="Sec8_7" id="Sec8_7"></a>It will be appreciated that in the preparation of sheet rubber
+this period may not be unduly prolonged, otherwise the latex
+will have begun to coagulate before skimming and the placing
+of the partitions in their respective slots can be effected.
+Furthermore, while in the preliminary treatment for crepe
+rubber, the formation of enclosed bubbles and surface froth
+is immaterial. For sheet preparation it is essential that the
+stirring shall be done so carefully as to try to avoid internal
+bubbles and to reduce surface froth to a minimum. For
+crepe-making a perforated board, with handle attached at
+right angles to the face of the board, may be used; but in shallow
+sheet-coagulating tanks, broad paddles (which may or may not
+be perforated) give good results as long as there is a sufficient
+number used to cover the area of the tank in reasonable time.
+Obviously also, where the area of any tank or compartment
+is of any appreciable size, the dilute acid solution should be
+poured in from various points so as to obtain a good even
+distribution. In some cases the acid is distributed from a
+sprinkling can, but this is a refinement which experience shows
+to be unnecessary. In actual practice, working on a tank
+measuring 12 ft. by 4 ft., no difficulty is found if coolies pour
+in acid solution from four points. The degree of success depends
+entirely upon experience and efficient supervision. This remark
+applies equally to the use of various devices, such as rakes
+with broad teeth, used as stirring implements. There is room
+for display of ingenuity in this direction, and it is found often
+that, while they are used successfully on one estate, they may
+be condemned on another.</p>
+
+<p class='pagenum'><a name="Page_81" id="Page_81">[81]</a></p>
+
+<div class="figcenter"><a name="Fig33" id="Fig33"></a><img src="images/illo098.jpg" alt="Two Views of Dilution and Mixing Tanks" />
+<p class="caption"><span class="smcap">Two Views of Dilution and Mixing Tanks.</span></p>
+<p class="capt350">Below, on the right, coagulating tanks. At the far end strainers.
+Each dilution tank is of equal capacity to the corresponding coagulating
+tank.</p></div>
+
+<p><a name="Sec8_8" id="Sec8_8"></a><span class="smcap">Use of Sodium Bisulphite</span>.&mdash;Some few years ago a demand
+for pale crepe rubbers sprang up, and this demand has been
+maintained. The total quantity of pale rubber put on the
+market previously could only have amounted to very little,
+and that little was obtained by luck and various tricks in manipulation.
+It must be premised that if coagulation is allowed to
+take place, either naturally or with the aid of acetic acid, the
+resulting rubber will almost inevitably oxidise on the
+surface,<span class='pagenum'><a name="Page_82" id="Page_82">[82]</a></span>
+except in the cases of very dilute or young latices. Even
+supposing that this darkening of the surface does not take
+place in the wet stage, it is often found that a rubber expected
+to dry to a pale colour does not fulfil expectations, and a dull
+neutral shade results. This darkening of crepe rubber may
+be attributed to a slow process of oxidation, which continues
+until the rubber is dry. From these remarks it will be seen
+that the process of oxidation is a natural one, and that any
+pale rubber formerly shipped was the outcome of circumstances
+outside the control of the estate, except in such cases
+where boiling of the coagulum, etc., was resorted to. The
+fact that one rubber happened to be a shade darker than another
+was absolutely no criterion as to the value of the rubber, but
+apparently the market thought, and still thinks, otherwise,
+although the actual necessities of manufacturers for a pale crepe
+to be employed in special processes must be comparatively
+small.</p>
+
+<p>The prevention of this natural oxidation was a problem
+which exercised the minds of all responsible for the preparation
+of pale rubbers, and much time and thought were expended
+upon it. Various theories were propounded, and the chief
+conclusion arrived at was that the darkening of rubber was to
+be prevented by excluding all the light possible from the
+drying houses. To this end windows were to be kept shut,
+or else they were provided with ruby-coloured glass, which
+incidentally kept out the air. In spite of these precautions,
+little success attended the expenditure of so much energy
+and thought. It was absolutely necessary that some chemical
+agent should be discovered which would make the preparation
+of pale crepe possible for any estate. This chemical would
+have to fulfil several requirements before it could become
+popular:</p>
+
+<div class="blockquot"><p>1. It must be a simple substance capable of being easily
+handled.</p>
+
+<p>2. It must be very soluble, so that solutions could easily be
+made up by inexpert workers.</p>
+
+<p>3. It must be cheap.</p>
+
+<p>4. It must be quite innocent of any harmful effect upon the
+quality of the rubber.</p></div><p><span class='pagenum'><a name="Page_83" id="Page_83">[83]</a></span></p>
+
+<p>After months of investigation into the properties of other
+chemicals the writers decided that the only one which satisfactorily
+answered all requirements was sodium bisulphite.
+The writers make no pretension to any claim of having discovered
+the properties of this substance, which was a common
+chemical, and widely known. Even its action on latex was
+suspected before they engaged upon the work. These matters
+are only mentioned because the credit, if any, should be given
+to the laboratories of the Rubber Growers&#8217; Association.</p>
+
+<p>As soon as it began to be known on the market that sodium
+bisulphite was being used in the preparation of pale crepe, a
+great outcry was made, and estates were warned that no more
+rubber prepared in this way would be accepted. It was said
+that the chemical would destroy the &#8220;nerve&#8221; of the rubber,<a name="FNanchor_2_2"
+id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a>
+and it was definitely stated that rubber prepared with this
+chemical was brittle. It must be remembered that brokers
+had some legitimate excuse in raising objections to the introduction
+of new and strange chemicals for preparing rubber,
+as they were quite without means of judging whether the rubber
+had suffered harm or not. Still, on the other hand, private
+tests had been made in conjunction with Messrs. Beadle and
+Stevens for fully eight months before the name of the chemical
+was mentioned in reports, and they had decided from the
+results of vulcanisation tests that the chemical was quite
+innocuous. Then, and only then, did we consider it advisable
+to recommend the use of sodium bisulphite in general estate
+practice. Owing to the initial prejudice against rubber prepared
+with sodium bisulphite, the results of our preliminary
+work were published by permission of the Rubber Growers&#8217;
+Association.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3"
+class="fnanchor">[3]</a> The original instructions to estates regarding
+the proper employment of this chemical were given in the
+private reports issued by the Rubber Growers&#8217; Association in
+1911. At the present time it is probably accurate to state that
+it is now used by all estates preparing fine crepes. Representatives<span class='pagenum'><a name="Page_84" id="Page_84">[84]</a></span>
+of manufacturers have sometimes given us to understand
+that the question of paleness of colour in such rubber is
+of no such importance as is impressed upon us as producers.
+While we are prepared to believe, we can only plead that from
+our point of view the supply arises from the demand. Such
+are the conditions governing the sale of rubber that, irrespective
+of the requirements of the ultimate user, we have to market
+rubber which is valued almost completely upon its appearance
+at the time of sale.</p>
+
+<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span
+class="label">[2]</span></a> Williams, International Rubber and Allied Congress, London,
+1914.</p></div>
+
+<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span
+class="label">[3]</span></a> &#8220;The Employment of Sodium Bisulphite in the Preparation of
+Plantation Rubber,&#8221; Beadle, Stevens, and Morgan, <i>India-rubber
+Journal</i>, August 2, 1913.</p></div>
+
+<p>As long as such conditions prevail estates must continue to
+adopt any device of proved harmlessness, in order to obtain
+the best possible price for their product, and not because we
+desire to continue a practice which some assure us to be unnecessary,
+and which, moreover, adds somewhat to the cost
+of production.</p>
+
+<p><a name="Sec8_9" id="Sec8_9"></a><span class="smcap">Quantities of Sodium Bisulphite.</span>&mdash;It must be premised
+that, although sodium bisulphite is employed on some few
+estates in the preparation of sheet rubber, we do not advise
+the practice. It is unnecessary, and may lead to some little
+trouble and delay in drying. In any case, sodium sulphite
+gives the results desired for sheet rubber (see <a href="#Sec8_13">following</a>). It
+must be understood, therefore, that we are concerned here, in
+the case of sodium bisulphite, with its employment in the
+preparation of fine pale crepe only.</p>
+
+<p>As the dry rubber contents of latices vary with the age of the
+trees, the general health of the trees, the seasons and general
+climatic conditions, the relative strain imposed by depletion of
+reserves through tapping, etc., it will be clear that the effect
+produced by a definite quantity of sodium bisulphite in any
+given volume of latex will also vary&mdash;<i>i.e.</i>, the effect depends
+upon the potential amount of rubber present. A dilute latex
+needs less sodium bisulphite than a richer latex to produce
+the same effect in colour.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a></p>
+
+<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span
+class="label">[4]</span></a> Incidentally there are certain occasions, as in the opening of
+areas of bark rested for long periods, when the latex is of a rich
+yellow colour. Sodium bisulphite will not &#8220;bleach&#8221; this colour,
+and it is well to remark again at this stage that the action of the
+chemical is only to avoid or arrest oxidation (darkening).</p></div>
+
+<p>Hence it follows that if in any factory uniform quantities of<span class='pagenum'><a name="Page_85" id="Page_85">[85]</a></span>
+the solution are used for any given volume of undiluted latices
+from different areas of the estate, the effect upon the dry
+rubbers will vary. This explains why some estates obtain
+different shades of rubber in their fine pale crepes.</p>
+
+<p>The remedy obviously is to reduce the variation in latices
+by diluting them all to a standard rubber content as is done
+in sheet preparation. One is thus assured that the prescribed
+quantities of sodium bisulphite will meet requirements in
+every case, and that waste will be avoided.</p>
+
+<p><a name="Sec8_10" id="Sec8_10"></a>Working with a standard of 1<span class="enum">1</span>&#8260;<span
+class="denom">2</span> lbs. dry rubber per gallon
+the following formula should serve as a <i>maximum</i>:</p>
+
+
+<p class="center"><i>Formula for Use of Sodium Bisulphite.</i></p>
+
+<div class="blockquot"><p>(<i>a</i>) Dissolve sodium bisulphite in water at the rate of 1 lb.
+to 10 gallons.</p>
+
+<p>(<i>b</i>) Of this solution use 1 gallon to every 10 gallons of latex.</p></div>
+
+<p><span class="smcap">Making a Solution.</span>&mdash;The making of a solution of the
+chemical would seem to be a simple matter, but to judge by
+the ill-effects sometimes observed in the dry rubber the simplicity
+of the operation appears to have been overrated. Great
+care must be exercised in preparing the solution, and the work
+should not be left to the few minutes preceding its actual
+requirement; such has been found to be the case in several
+factories, so that it is not surprising if the rubber is defective.</p>
+
+<p>The powder should be added gradually to water with
+thorough stirring, which should be continued for five minutes
+at least. Even then there may often be seen at the bottom
+undissolved particles, sand, and other impurity. It is necessary,
+therefore, in such cases to decant the solution through a
+piece of cotton cloth before using. No solid particles should
+be allowed to enter the latex.</p>
+
+<p><a name="Sec8_11" id="Sec8_11"></a><span class="smcap">Abuse of Sodium Bisulphite.</span>&mdash;It is now generally recognised
+that the abuse of sodium bisulphite, in the form of an
+excess, leads mainly to delay in the period of drying and the
+production of an overpale rubber.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5"
+class="fnanchor">[5]</a> It is probable that few
+estates, if any, now experience trouble due to this non-observance
+of the rules and quantities laid down for use.</p>
+
+<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span
+class="label">[5]</span></a> &#8220;The Preparation of Plantation Rubber,&#8221; Morgan, 1913, p. 74.</p></div>
+
+<p><a name="Sec8_12" id="Sec8_12"></a><span class='pagenum'><a name="Page_86" id="Page_86">[86]</a></span><span
+class="smcap">Residual Traces of Sodium Bisulphite.</span>&mdash;The prolongation
+of the drying period was attributed to the fact that traces
+of substances caused by the decomposition of sodium bisulphite
+remained in the rubber if the rubber were not sufficiently
+worked and washed on the rolls. These traces must have
+been very minute, but they were sufficient to retard the progress
+of drying. That much depended on the care exercised in
+washing is evident from the fact that samples prepared with
+varying quantities of the chemical show varying results on
+extraction. These samples were tested for the presence of
+sulphates. Of the series tested that sample prepared with
+bisulphite in the proportion of 1 part to 600 parts latex showed
+only a trace of sulphate present; while the one prepared
+1:2,400 gave an equal quantity. Intermediate samples contained
+no trace of sulphate. On the whole, therefore, the
+presence of sulphate in crepe rubber is adventitious, and
+properly washed crepe prepared with moderate quantities of
+bisulphite may be taken as free from any residual quantities.
+Meanwhile there cannot possibly be any doubt of the advantages
+gained by the use of sodium bisulphite, and it would not
+be very wide of the mark if the statement were made that, in
+the event of this chemical being discarded, most contracts for
+pale crepe could not be fulfilled.</p>
+
+<p><a name="Sec8_13" id="Sec8_13"></a><span class="smcap">Sodium Sulphite.</span>&mdash;It would not be amiss to insist upon
+the point that while the nature of sodium <i>bisulphite</i>, as employed
+in the preparation of rubber, is anti-oxidant, sodium sulphite
+is employed chiefly for its anti-coagulant property. It is not
+used, therefore, in the making of crepe rubber, but is of service
+in the preparation of sheet rubber, where the aim is to keep the
+latex in good fluid condition as long as is necessary, and to
+retard coagulation slightly so that enclosed bubbles of gas or
+air may escape. Formul&aelig; have been given for its use in the
+field when required. On some estates this practice is not
+found necessary, but a quantity of solution is always placed in
+the bottom of the reception vessels prior to the straining of
+latex into them. Only a small quantity is used, and as a
+working basis the following formula may be adopted:</p>
+
+
+<p class="center"><span class='pagenum'><a name="Page_87" id="Page_87">[87]</a></span><i>Sodium Sulphite: For Use in the Factory.</i>
+<a name="Sec8_14" id="Sec8_14"></a></p>
+
+<div class="blockquot"><p>(<i>a</i>) Dissolve 2 ozs. of anhydrous sodium sulphite in a
+gallon of water.</p>
+
+<p>(<i>b</i>) The gallon of solution, placed in the bottom of the
+reception jar or tank, is sufficient for the treatment of 40 gallons
+of standardised latex (1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber per gallon).</p></div>
+
+<p>The warning previously given regarding the necessity for
+thoroughness in the preparation of solutions is here reiterated.
+Stirring should be thorough, say for five minutes, and if there
+is any sediment or undissolved matter the solution should be
+strained through cloth before using.</p>
+
+<p>Where uniform jars or tanks are in use, the majority of which
+will contain uniform quantities of latex daily, the practice of
+using the chemical can be made almost fool-proof even in the
+hands of coolies. A calculation is made of the quantity of
+powder required for each vessel daily. The necessary number
+of lots is weighed out each morning and each placed in an
+envelope. The process is thus simplified by the fact that the
+contents of an envelope, neither more nor less, are required
+for each unit reception vessel. Even the weighing can be done
+by a coolie if he is given a counterpoise (of lead, for example)
+equivalent to the required weight.</p>
+
+<p>It will not be found necessary to do any vigorous stirring of
+the solution with the latex, as the latter is strained into the
+solution and the continued addition of successive quantities
+is sufficient to give a good mixture.</p>
+
+<p><a name="Sec8_15" id="Sec8_15"></a><span class="smcap">Use of Formalin.</span>&mdash;Few estates now use formalin (formaldehyde)
+as an anti-coagulant. It must be acknowledged
+that when not abused there are points in favour of its employment
+in preference to sodium sulphite, but these are outbalanced
+by certain disadvantages. The argument may be
+stated thus:</p>
+
+<div class="blockquot"><p><i>Points for</i>: (1) If made up freshly it is an effective anti-coagulant.</p>
+
+<p>(2) Formalin being the solution of a gas in water, there is no
+residual substance left in the rubber to delay drying.</p>
+
+<p>(3) Its use gives a bright clear rubber.</p></div>
+
+<div class="blockquot"><p><span class='pagenum'><a name="Page_88" id="Page_88">[88]</a></span><i>Points
+against</i>: (1) Its cost at all times is greater than that
+of sodium sulphite.</p>
+
+<p>(2) If the jar is not sealed there is loss by evaporation, thus
+increasing the cost.</p>
+
+<p>(3) Its effect upon the rubber is uncertain. Even in normal
+quantity it is said to cause &#8220;brittleness&#8221; or &#8220;shortness.&#8221;</p></div>
+
+<p>Certain few estates, however, have continued its use, and
+no trouble is claimed to ensue. The following formula is
+stated to give satisfactory results in the preparation of sheet
+rubber, when applied as in the preceding paragraphs bearing
+on the employment of sodium sulphite:</p>
+
+
+<p class="center"><a name="Sec8_16" id="Sec8_16"></a><i>Formula for Use of Formalin (Formaldehyde).</i></p>
+
+<div class="blockquot"><p>(<i>a</i>) 1 pint of formalin is diluted with 5 gallons of water.</p>
+
+<p>(<i>b</i>) Of this solution 1 gallon is required for 50 gallons of
+standardised latex.</p></div>
+
+<p>In noting this formula the writer gives no recommendation
+regarding its use. Whatever may be the actual facts regarding
+the effect of formalin upon the vulcanisation of rubber, when
+used in minimum proportions, there can be no question concerning
+its injurious effect if used in excess. Beyond this the
+factors of cost and loss militate against its wider employment.</p>
+
+
+<p class='pagenum'><a name="Page_89" id="Page_89">[89]</a></p>
+<hr class="c25" />
+<h2><a name="Ch9" id="Ch9"></a>CHAPTER IX</h2>
+
+<h3><i>PREPARATION OF SHEET RUBBER</i></h3>
+
+
+<p><a name="Sec9_1" id="Sec9_1"></a><span class="smcap">Pale Sheet.</span>&mdash;The first form in which plantation rubber was
+prepared was as &#8220;biscuits&#8221; or sheets. This form remained
+in favour for some years. The first biscuits or sheets were
+rather dark in colour owing to the natural oxidation which
+followed. Then it was discovered that by diluting the latex
+the degree of oxidation was diminished, and later it was found
+that if the soft coagulum were placed in almost boiling water
+for a short time the resulting rubber was pale. Thus there
+arose gradually a demand for pale sheet. With our present
+knowledge we are in a position to state that the pale biscuits
+were not in any way superior to the darker ones, and they were
+in most cases actually inferior.</p>
+
+<p>It was found also as time progressed that sheet rubber, on
+air-drying, became covered with external surface moulds, and
+that, more often than not, the smell of the drying rubber was
+the reverse of pleasant. Even when dry the sheets had to be
+continually brushed free from moulds, and by the time the
+rubber reached the market it was again usually mouldy. Such
+are, even now, the handicaps under which those who prepare
+pale sheets have to labour. Few, however, are the estates
+making pale sheets, and they are confined almost entirely to
+native holdings.</p>
+
+<p>To those accustomed only to the preparation of crepe rubber,
+where coagulation can be effected in large batches, the preparation
+of sheet rubber always seems to demand much more
+labour. As a matter of fact, although the preliminary operations
+certainly do demand more care and labour than in crepe-making,
+there are compensating advantages in the machining
+stage. For the preparation of sheet of the highest quality on
+any but the largest scale, elaborate installations of machinery<span class='pagenum'><a name="Page_90" id="Page_90">[90]</a></span>
+are quite superfluous, as equal results can be obtained with
+pairs of rolls worked by hand.</p>
+
+<p><a name="Sec9_2" id="Sec9_2"></a><span class="smcap">Uniformity of Product.</span>&mdash;There will be no need to enter
+again into a discussion of the preliminary operations of receiving
+and straining latex for sheet-making. They have been fully
+dealt with in <a href="#Ch7">Chapter VII</a>. It used to be the general custom
+to mix the acid and latex in each individual dish, and in some
+small or non-progressive factories that is still the procedure.
+Quite apart from the question of labour entailed, the process is
+quite unnecessary. Even if comparatively small volumes of
+latex are handled, standardisation by dilution should be the
+rule, and the acid solution should be added to the bulk. It is
+possible to stir in the acid and to ladle out uniform quantities
+in each pan or dish from a bulk volume of up to 40 gallons if
+the organisation is efficient.</p>
+
+<p><a name="Sec9_3" id="Sec9_3"></a>On any but a small scale the labour entailed in the handling
+and cleaning of pans is excessive, and shallow tanks are now
+employed on most estates. The reception and standardisation
+of latex by dilution has already been discussed in
+<a href="#Ch7">Chapter VII</a>. The combination of this practice with the
+employment of shallow coagulating tanks has simplified working
+and reduced the cost of labour. It is not intended to enter
+into any lengthy discussion relative to the merits of sheets
+made in pans as against those made in tanks. It is granted
+that it is possible to make a &#8220;pan&#8221; sheet superior in appearance
+to the general average of &#8220;tank&#8221; sheets; but from an economic
+standpoint the introduction of the use of tanks into all but the
+smallest factories is only a matter of time, if the demand for
+this class of rubber persists.</p>
+
+<p><a name="Sec9_4" id="Sec9_4"></a><span class="smcap">The Ideal Tank.</span>&mdash;Even the most modern installations of
+sheet-coagulating tanks must be regarded as merely temporary
+devices, as, given facilities, the room for improvement is so
+wide.</p>
+
+<p>The first tanks made erred in being too large, and as the
+result of experience the size of units has now been reduced
+to a maximum of 12 feet by 4 feet by 1 foot deep.</p>
+
+<p class='pagenum'><a name="Page_91" id="Page_91">[91]</a></p>
+
+<table summary="Fig 34">
+
+<tr>
+<td class="figcenter"><a name="Fig34" id="Fig34"></a><img src="images/illo108a.jpg" alt="Top Figure" /></td>
+<td class="padr">&nbsp;</td>
+<td class="figcenter"><img src="images/illo108b.jpg" alt="Bottom Figure" /></td>
+</tr>
+
+<tr>
+<td colspan="3" class="caption"><span class="smcap">Unit Modern Coagulating Tank (Two Views).</span><br />
+Construction of brick and cement with lining of glazed tiles. Note
+slots incorporated in side tiles. Partition boards in piles in the
+background.</td>
+</tr>
+
+</table>
+
+<p>Tanks are at present constructed either of hard timber or of
+brick and cement faced with glazed tiles; both types have<span
+class='pagenum'><a name="Page_92" id="Page_92">[92]</a></span>
+inherent drawbacks. The wooden tanks are difficult to keep
+clean and in &#8220;sweet&#8221; condition. The glazed tiles, unless
+extremely well laid, allow the acid serum (from which the
+rubber is removed) to percolate between the interstices.
+Thus &#8220;pockets&#8221; of liquid collect beneath the tiles, and in
+process of the decomposition of certain constituents dissolved
+in the serum evil-smelling gases are set free.</p>
+
+<div class="figcenter"><a name="Fig35" id="Fig35"></a><img src="images/illo109.jpg" alt="Another Battery of Tanks" />
+<p class="caption"><span class="smcap">Another Battery of Tanks, with Dilution Tanks, Raised,<br />
+on the Right.</span></p>
+<p class="center">Note drainage cocks, chute, and sieve in position.</p></div>
+
+<p>It should not be a matter of difficulty for manufacturers to
+make sheets of thick glass sufficiently large to form the bed-plate
+and side-pieces necessary in the lining of a tank. If such
+adjuncts could be secured, the disabilities indicated above
+would be perhaps wholly removed. Unless there is a demand
+from estates, however, it is idle to expect a supply to be forthcoming.</p>
+
+<p>An even greater improvement would take the form of unit
+tanks cast in glazed white-ware with the necessary slots<span class='pagenum'><a name="Page_93" id="Page_93">[93]</a></span>
+incorporated in the sides. At present no known firm makes
+such tanks of sufficient size. A unit could measure (internally)
+6 feet by 4 feet by 1 foot deep, with slots 1<span class="enum">1</span>&#8260;<span class="denom">2</span> inches apart, and
+<span class="enum">3</span>&#8260;<span class="denom">8</span> inch in width. The tanks might be reinforced with iron
+bars, so that they could either be used alone or embedded in
+the usual brick structure. The junctions of the bed-plate and
+side-pieces could be finely rounded so as to facilitate cleaning,
+and at one end a draining-hole could be made, say, 1 inch in
+diameter.</p>
+
+<div class="figcenter"><a name="Fig36" id="Fig36"></a><img src="images/illo110.jpg" alt="Closer View of Foregoing" />
+<p class="caption"><span class="smcap">Closer View of Foregoing.</span></p>
+<p class="center">Note partitions in position and coagulum being removed.</p></div>
+
+<p>Meantime both the hard-wood tanks and those of glazed tiles
+find their particular applications. The former is generally
+employed in smaller factories, or where future large increases of
+crop preclude the present installation of a fixed system. The
+latter find use in large factories, or where no new areas remain
+to come into bearing.</p>
+
+<p><a name="Sec9_5" id="Sec9_5"></a><span class="smcap">Modern Installation.</span>&mdash;As an example of a modern
+installation of coagulating tanks, we can do no better than<span class='pagenum'><a name="Page_94" id="Page_94">[94]</a></span>
+offer reproductions of the system now in use on Pataling
+Estate.</p>
+
+<p>A warning must be given against employing all tanks of
+stone-ware or cement unless well glazed. Almost without
+exception, irrespective of the material used in the construction
+of coagulating tanks, wooden partitions are employed.
+In the few exceptional cases the partitions are either of
+glass or of aluminium. The former would appear to be
+the ideal substance, were it not for initial cost and loss by
+breakage. These disabilities may possibly be overcome in
+course of time.</p>
+
+<p><a name="Sec9_6" id="Sec9_6"></a><span class="smcap">Care of Tanks.</span>&mdash;The use of aluminium would have been
+wider had it not been for lack of supplies and the question of
+cost during the War. A novel method of employing aluminium
+partitions was introduced in the factory of Tremelbye Estate.
+There were no slots in the sides of the glazed-tile tanks, but the
+necessary slots were very ingeniously created by means of
+aluminium &#8220;distance-pieces,&#8221; the two long edges of which
+were turned at right angles to the face of each piece to a depth
+of about <span class="enum">1</span>&#8260;<span class="denom">4</span> inch. The ends of the thin aluminium partition
+moved in the slot thus formed between two adjacent &#8220;distance-pieces.&#8221;
+The friction between the surfaces was sufficient
+to allow all the partitions, when in position, to be raised well
+above the floor of the tank, so that a uniform level of latex was
+obtained. Slight hand-pressure only was then required to
+push the partitions down.</p>
+
+<p>Naturally the cleansing of glass or aluminium partitions
+presents no difficulty, but in the case of wood failure to ensure
+thorough cleanliness leads to possible defects in the finished
+dry rubber. Provided the wood could be made waterproof,
+no trouble would ensue, and hence various measures have been
+tried with that object in view. When new the boards have been
+surface-waxed or varnished, and the treatment has been repeated
+on occasions. But in course of time the surface film of waterproof
+material has disappeared, partially or wholly, and the
+trouble recurs. When partitions become sodden with serum, the
+surfaces are liable to be coated with a slime, consisting largely
+of organic growths which have an effect upon the latex, causing<span class='pagenum'><a name="Page_95" id="Page_95">[95]</a></span>
+&#8220;pitting&#8221; on the surface of the coagulum and enclosed bubbles
+within.</p>
+
+<div class="figcenter"><a name="Fig37" id="Fig37"></a><img src="images/illo112.jpg" alt="Another Battery of Tanks,
+without Dilution Tanks or Means of Gravitating Latex" />
+<p class="caption"><span class="smcap">Another Battery of Tanks, without Dilution Tanks or Means<br />
+of Gravitating Latex.</span></p></div>
+
+<p>It is recommended, therefore, that wooden tanks, after
+ordinary cleansing daily, should be swabbed out with a
+5 per cent. solution of sodium bisulphite. Wooden partitions
+should receive the same treatment, and once a week at least
+(or every day if possible) they should be placed in the sun for
+an hour or two, care being taken that both sides of a partition
+are exposed in turn. Before being placed in the latex, all
+wooden partitions should be made wet on the surfaces.</p>
+
+<p>Some years ago the writers had made a partition of vulcanite,<span class='pagenum'><a name="Page_96" id="Page_96">[96]</a></span>
+which apparently would have proved of great service but for
+the initial cost. The advent of the War put the matter out
+of the question, but it is possible now that such a material
+would be worthy of extended trial. Except in the matter of
+cost, it would appear to have advantages over any substance
+yet tried; and if it were possible for estates to supply their
+own lower grade rubbers direct, the cost might be reduced
+considerably.</p>
+
+<div class="figcenter"><a name="Fig38" id="Fig38"></a><img src="images/illo113.jpg" alt="Sheeting Tank containing Coagulum for Crepe
+Preparation" />
+<p class="caption"><span class="smcap">A Sheeting Tank containing Coagulum for Crepe<br />
+Preparation.</span></p>
+<p class="capt500">Behind wall in background are the tanks in which latex is standardized.
+Note vent, to the left, through which latex flows and
+wooden &#8220;stopper&#8221; on edge of tank.</p></div>
+
+<p><a name="Sec9_7" id="Sec9_7"></a><span class="smcap">Standard Latex.</span>&mdash;Enough has been written (see <a href="#Ch7">Chapter
+VII.</a>) to familiarise the reader with the use of this term for
+the description of latex diluted daily to a level of dry rubber
+content. Whatever may be the practice elsewhere, it is now
+fairly general on estates in Malaya to reduce all latices to a
+uniform &#8220;strength&#8221; for the preparation of sheet rubber.
+It is claimed that only in this manner can uniformity of product
+be achieved.</p>
+
+<p><span class='pagenum'><a name="Page_97" id="Page_97">[97]</a></span>The selection of a standard has been the outcome of general
+experience. It has been found that if too high a standard is
+taken difficulties arise, such as (1) unsatisfactory and uneven
+coagulation, (2) too thick a coagulum for easy working in
+general, (3) too extended a period of drying and smoke-curing,
+and hence too dark a colour in the finished rubber.</p>
+
+<div class="figcenter"><a name="Fig39" id="Fig39"></a><img src="images/illo114.jpg" alt="A
+'Battery' of Sheeting Tanks (Pataling Estate)" />
+<p class="caption"><span class="smcap">A &#8220;Battery&#8221; of Sheeting Tanks (Pataling Estate).<br />
+Dilution Tanks, Raised, on the Left.</span></p></div>
+
+<p>On the other hand, too low a standard also brings trouble
+in its train. The coagulum is too porous, will not stand handling,
+and the resultant sheet is too thin unless an abnormal
+thickness of coagulum is prepared. Furthermore, over-dilution
+means an increase in the number of tanks required for any
+original volume of latex. This involves an increase in floor
+area, and perhaps in the size of the building. The soft sheets,
+when rolled, may spread to such a width as to cause the edges
+to be squeezed under the cheek-blocks of the machines, etc.</p>
+
+<p><a name="Sec9_8" id="Sec9_8"></a>For all practical purposes, whether sheets are prepared in
+pans or in tanks, it has been found that the optimum results
+are obtained by the adoption of a standard approximating and
+not exceeding 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber per gallon. Primarily this
+standard has a direct connection and interdependence with<span class='pagenum'><a name="Page_98" id="Page_98">[98]</a></span>
+the distance between the partitions (or between the slots) in
+coagulating tanks. The distance found most practicable is
+1<span class="enum">1</span>&#8260;<span class="denom">2</span> inches. This thickness of coagulum, when prepared from
+latex not exceeding a standard of 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber per gallon,
+is found to yield a very satisfactory sheet in all respects.</p>
+
+<p>It will be seen that we have two possible main factors of
+variation:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Distance between partitions, causing visible differences
+in thickness of coagulum.</p>
+
+<p>(<i>b</i>) Dry rubber content of latex, causing differences in the
+density (<i>e.g.</i>, hardness or softness) of the coagulum.</p></div>
+
+<p>The effect of variation in (<i>a</i>) will be clear. Even when latex
+of a standard of 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. per gallon is employed the resulting
+sheet may be either too thin or too thick.</p>
+
+<p>Similarly, as already argued, the use of too low or too high
+a standard of dilution (when the factor of distance between
+partitions is not allowed to vary) is capable of causing much
+difficulty. While this is correct, broadly, it is found in the
+experience of some estates that their requirements are satisfied
+by a slightly lower standard than 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. per gallon. Thus it
+is not uncommon to note the adoption of a standard equivalent
+to 1 lb. 4 ozs. or 1 lb. 6 ozs. dry rubber per gallon. Experience
+dictates, however, that for the recognised standard measurements
+of modern tanks the practical limits of satisfactory
+density of latex lie between 1<span class="enum">1</span>&#8260;<span
+class="denom">4</span> lbs. and 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. per gallon.</p>
+
+<p><a name="Sec9_9" id="Sec9_9"></a><span class="smcap">Standardising Instruments.</span>&mdash;For standardising latex by
+dilution all that is required is an instrument which will preserve
+a perpendicular position while floating in latex, will be sufficiently
+sensitive to indicate fairly small differences in density
+of latex, and has one mark on its aerial portion accurately
+indicating a density corresponding to the required standard.
+On scientific grounds it can be demonstrated that such an
+instrument as employed in common practice would not be
+strictly accurate.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a
+href="#Footnote_6_6" class="fnanchor">[6]</a> It is not proposed, in this section of the
+book, to discuss such considerations.</p>
+
+<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span
+class="label">[6]</span></a> De Vries, &#8220;Archief voor de Rubbercultuur.&#8221;</p></div>
+
+<p>Instruments of this nature are represented by the &#8220;Metrolac&#8221;<span
+class='pagenum'><a name="Page_99" id="Page_99">[99]</a></span>
+(originating from the Rubber Growers&#8217; Association) and
+other similar recorders. They generally consist of a submersible
+bulb with a projecting stem which is graduated. The
+&#8220;Metrolac&#8221; differs from others in that the bulb is of torpedo
+form (thus reducing &#8220;skin friction&#8221;), and the graduations on
+the stem indicate actual weight of dry rubber per gallon instead
+of the ordinary specific gravity figures.</p>
+
+<p>Theoretical considerations to the contrary, it is found in
+actual practice in Malaya and Ceylon that, although such
+instruments are naturally delicate and require careful manipulation,
+they are of considerable practical value and satisfy
+a definite requirement. Until an instrument of greater
+accuracy and equal simplicity can be discovered all estates
+should regard the possession of a few &#8220;Metrolacs&#8221; as essential.</p>
+
+<p>The nature of their construction and the average conditions
+under which they are used (and abused) make it impossible
+to rely upon their accuracy indefinitely or for any long period.
+It is always recommended, therefore, that there should be at
+least two instruments available, one of which may be in daily
+use, while the other is kept in safe custody and only employed,
+say, once a week for purposes of checking the accuracy or degree
+of inaccuracy of the other. This can be done with reasonable
+approximity by placing both instruments in a tall vessel containing
+well-mixed and diluted latex. Instruments showing a
+marked degree of inaccuracy should not be preserved; but in
+cases of necessity &#8220;Metrolacs&#8221; from estates belonging to
+company members of the Rubber Growers&#8217; Association may
+be sent to the laboratories for repair and adjustment.<a name="FNanchor_7_7"
+id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a></p>
+
+<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a
+href="#FNanchor_7_7"><span class="label">[7]</span></a> This applies to the gilt brass instruments. As the result of
+experiment the Rubber Growers&#8217; Association are now introducing
+glass instruments. These are necessarily more fragile, but while
+unbroken can be relied on to give correct readings.</p></div>
+
+<p>Where field coagulating stations have been instituted on
+estates, it is strictly necessary that instruments should be provided
+in all cases; and it should be a rule that these are tested
+and corrected weekly by a standard instrument employed for
+that purpose only. This need was well recognised by many
+estates when, during the War and the consequent shortage of<span class='pagenum'><a name="Page_100" id="Page_100">[100]</a></span>
+supply of &#8220;Metrolacs,&#8221; a demand arose which was met in
+some degree by crude instruments of local manufacture, such
+as that commonly known as the &#8220;Castlefield bobber,&#8221; contrived
+and made by the enterprising manager of the estate of
+that name. The demand for the more accurate instruments
+can now be met.</p>
+
+<p><a name="Sec9_10" id="Sec9_10"></a><span class="smcap">Methods of Using the Instruments.</span>&mdash;The &#8220;Metrolac&#8221;
+was devised and introduced by the writers on behalf of the
+Rubber Growers&#8217; Association, and directions for its use were
+given. Tables were prepared by means of which simple
+calculations for the dilution of any given latex could be made.
+These did not find an extended application, inasmuch as in
+the majority of cases native workers only were in charge of
+the processes of rubber preparation. In point of fact, such
+calculations are not strictly necessary, as the operation of
+standardising the latex can be done quite simply and skilfully
+by a trained native. Latex as it reaches the store in average
+weather from any particular division or field does not vary
+greatly in density. The trained coolie or foreman, basing his
+practice on experience, adds to the latex a quantity of water,
+and then makes a first test with the standardising instrument.
+Several additions of water (with thorough stirring) may have
+to be made before a test indicates that the correct density has
+been obtained, but it is surprising how quickly a skilled worker
+will arrive at the desired standard. Extreme or absolute
+accuracy is not insisted upon or desired, as avoidable delay is
+to be deprecated, and the result in any case is sufficiently exact
+for practical purposes.</p>
+
+<p><a name="Sec9_11" id="Sec9_11"></a><span class="smcap">Skimming.</span>&mdash;During the gravitation of the latex from the
+reception vessels (in which the standardising of the latex is
+effected) to the coagulating tanks, much surface froth is usually
+caused. This is best removed by means of a thin board of a
+width slightly less than the breadth of the tank. The skimmings
+are sometimes placed in pans and subsequently made
+into a second grade of sheet rubber, or they receive treatment
+with a small proportion of sodium bisulphite and eventually
+appear as fine pale crepe. The practice varies usually according
+to the form in which the general No. 1 grade is prepared.</p>
+
+<p><span class='pagenum'><a name="Page_101" id="Page_101">[101]</a></span>On some estates a great deal of the frothing is avoided by
+placing in position at the receiving end of the tank a perforated
+partition. This partition may be made of wood, or of stout
+zinc (or aluminium) carrying ten circular holes to the inch.
+Through this the latex percolates, while the froth is retained on
+a small area. The froth is removed prior to the addition of the
+acid. After stirring in the acid solution most estates again
+skim the surface of the latex; but if the stirring has been performed
+properly there should be little froth. This, when it
+collapses, in any case will appear only on the upper edge of the
+strip of coagulum, and after rolling should not be visible. It
+would appear, therefore, that the second skimming is not
+necessary.</p>
+
+<p><a name="Sec9_12" id="Sec9_12"></a><span class="smcap">Style of Sheet.</span>&mdash;Within the last few years the custom of
+making plain sheet&mdash;<i>i.e.</i>, sheet having a plain surface&mdash;has
+gradually given place to the preparation of ribbed sheet&mdash;<i>i.e.</i>,
+sheet having a pattern marked on the surface. It would
+probably be correct to say that plain (smooth) sheet is now only
+prepared by natives or by some estates just come into bearing.
+Even in the latter case there is no reason why smooth sheet
+should be made, as hand machines are sold which will do all
+the work required. It will be evident to anyone acquainted
+with rubber preparation that in the matter of actual quality
+of rubber the question of smoothness or a pattern can have
+no bearing on the result. One advantage claimed for ribbed
+sheet which may entirely justify the preference exhibited by
+consumers, relates to the question of packing. When rubber
+arrives at home it is frequently found to be in an almost solid
+block, due to the pressure of the sheets superimposed in the
+case. The smoother the surfaces of the rubber in contact the
+greater the adhesion and the denser will be the mass, and
+consequently the greater the difficulty in separating individual
+pieces. Under such circumstances it is plain that the difficulty
+is diminished if the sheets have a raised pattern on them. It is
+noted also that the liability to mildew-growth is greater the
+smoother the surfaces of the rubber.</p>
+
+<p>On these grounds the &#8220;marking&#8221; of sheet rubber is to be
+commended. These reasons apart, it is really astonishing the<span class='pagenum'><a name="Page_102" id="Page_102">[102]</a></span>
+difference made in the appearance of the sheets by impressing
+upon them a ribbed pattern, and it is highly probable that the
+market value of the rubber is slightly increased. It is not our
+duty to attempt to reason why this simple operation should
+increase the market value of sheet rubber; it is sufficient to
+recognise that it is so, and that money may be thrown away
+by neglecting to cater for the taste of the market. Of the
+patterns impressed upon sheet rubber there is a variety, but
+the general style is that known as the &#8220;spirally close-cut
+ribbing.&#8221;</p>
+
+<p><a name="Sec9_13" id="Sec9_13"></a><span class="smcap">Standard Sheet.</span>&mdash;Leaving for the present the question of
+pattern of mark, one cannot do better by way of introduction
+than to reproduce the instructions<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a
+href="#Footnote_8_8" class="fnanchor">[8]</a> given generally to estates.</p>
+
+<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a
+href="#FNanchor_8_8"><span class="label">[8]</span></a> &#8220;Handbook on Preparation of Rubber,&#8221; Rubber Growers&#8217;
+Association, May, 1917, p. 28.</p></div>
+
+<p><a name="Sec9_14" id="Sec9_14"></a><span class="smcap">Rolling and Marking of Sheet Rubber.</span>&mdash;Working with
+standard latex it is found that strips of coagulum 1<span class="enum">1</span>&#8260;<span class="denom">2</span> inches in
+thickness require little rolling to produce sheets of desirable
+thickness.</p>
+
+<div class="blockquot"><p>(1) The sheets or strips are first given a preliminary rolling
+with a heavy hand-roller made of hard wood. The roller is
+passed once in one direction, and once in the reverse direction.</p>
+
+<p>(2) The coagulum is then passed through smooth machines
+twice, once with the rolls fairly open, and once with a narrower
+space. It is not found advisable to close the smooth rolls so
+tightly that the rubber is made too hard.</p>
+
+<p>(3) The sheets or strips are then passed once through a
+pair of marking rollers. Various types of patterns are used,
+but the one which appears to give the most satisfactory results
+is that known as the &#8220;close-cut spiral.&#8221; This produces the
+semblance of a small diamond pattern on the rubber. The
+surface of the sheet is raised in well-defined ridges, which appear
+to present the maximum drying surface exposed to the atmosphere
+of the smoke-house. Thus, not only is the appearance
+of the sheet rendered attractive, but also the period of drying
+is reduced. Starting with standard latex and following the
+procedure here described for rolling and marking, sheets
+should be ready for packing in ten or eleven days. If the
+period is longer, it is possible that the design or structure of
+the smoke-house is at fault.</p></div>
+
+<p><a name="Sec9_15" id="Sec9_15"></a><span class='pagenum'><a
+name="Page_103" id="Page_103">[103]</a></span></p><p><span class="smcap">When
+to Work the Coagulum.</span>&mdash;Before proceeding to
+discuss other points the question remains to be settled as to
+how long it may be necessary or advisable to allow the coagulum
+to remain in the serum before rolling it. For reasons
+of practical economy in factory working, it is usual to allow
+sheet rubber to remain over night, and the coagulum receives
+attention early next morning. During the interval (averaging
+about eighteen hours), the coagulum consolidates, leaving an
+almost clear serum if the correct quantity of acid has been added
+to the latex. Any but the very slightest trace of milkiness in the
+serum indicates an insufficiency of coagulant. If the serum is
+always definitely clear, there may be grounds for believing
+that an excess is being used. If the quantity of coagulant
+has been calculated to an average nicety, the serum should be
+just dubiously free from milkiness.</p>
+
+<p>The firmness gained by the coagulum on standing in the
+serum overnight should enable it to be handled next morning
+without any marked stretching, and in some estates the rubber
+is put direct through the first pair of smooth rolls without a
+preliminary consolidation by means of hand-rolling.</p>
+
+<p>Some estates prefer to handle the coagulum while rather
+softer, as it is claimed:</p>
+
+<div class="blockquot"><p>(<i>a</i>) That the coagulum is easier to work, and sheets of
+improved appearance can be made.</p>
+
+<p>(<i>b</i>) That there is greater freedom from &#8220;bubbles.&#8221;</p>
+
+<p>(<i>c</i>) That the incidence of &#8220;rust&#8221; is lessened.</p>
+
+<p>These claims are substantiated in practice; but in the case of
+the third, it only holds provided that the rubber can be finished
+and placed in the smoke-house almost as soon as the last sheet
+has been machined.</p></div>
+
+<p>In such cases all latex must reach the store comparatively
+early in the day&mdash;<i>e.g.</i>, before noon. Three hours is allowed
+for coagulation, and the working of the rubber is then commenced.
+As a general rule this means that the operations of
+rolling and marking must be completed, a short interval given
+for dripping, weighing must be done, and the rubber placed in
+the smoke-house before night falls (as a rule about 6.30 p.m.).</p>
+
+<p>Unless factories dealing with a large crop are well equipped<span class='pagenum'><a name="Page_104" id="Page_104">[104]</a></span>
+with artificial light, such a course is not open to them; in any
+case it remains true that night work should be avoided if
+possible. If, however, it can be arranged without increasing
+the cost of production, there would appear to be no objection
+to the early working of the coagulum as described above.</p>
+
+<p><a name="Sec9_16" id="Sec9_16"></a><span class="smcap">Hand-Rolling.</span>&mdash;As already indicated, some few estates
+do not give the strips of coagulum any preliminary hand-rolling,
+as the rubber is considered to be sufficiently firm to be
+handled into the first machine.</p>
+
+<p>On most estates hand-rolling is found necessary, owing to the
+tendency of the long strips to stretch unduly, giving badly
+shaped sheets. This hand-rolling should be done carefully,
+and is best effected on a specially constructed table. This
+consists essentially of an inch-thick hard-wood plank about
+2 inches wider, and 4 or 5 feet longer, than the strip of coagulum.
+Along the edges of the plank, and at right angles to its
+upper flat surface, may be fastened strips of wood about <span class="enum">1</span>&#8260;<span class="denom">2</span> inch square
+in section, thus forming a shallow tray open at either end.
+These strips serve two purposes:</p>
+
+<div class="blockquot"><p>(<i>a</i>) As the wooden roller is wider than the plank, they prevent
+the coagulum being rolled too thin and too firm.</p>
+
+<p>(<i>b</i>) They prevent the coagulum being squashed too wide,
+and tend to keep the edges straight.</p></div>
+
+<p>To avoid &#8220;thick ends&#8221; it is sometimes considered advisable
+to insert, at either end of the rolling table, shallow wedges
+about 6 inches long, of the same width as the table (between
+the edge-strips), and with the sharp end of the wedge pointing
+in the direction of the length of the table. The ends of the
+coagulum are drawn up and finished on these inclined planes.</p>
+
+<p>These points may appear to be extreme refinements, but
+as long as rubber is valued on such grounds we must endeavour
+to meet the system imposed upon us.</p>
+
+<p><a name="Sec9_17" id="Sec9_17"></a><span class="smcap">Smooth-Rolling.</span>&mdash;It is advised that, after hand-rolling,
+the coagulum should be passed through at least two machines
+having smooth-rolls. On some estates three such machines
+are employed. The purpose of this procedure is to reduce
+the thickness of the coagulum gradually. The same could be<span class='pagenum'><a name="Page_105" id="Page_105">[105]</a></span>
+effected, of course, on one machine; but obviously the distance
+between the rolls would have to be readjusted at each operation
+and for each piece of coagulum. Apart from the time
+thus wasted, there is the certainty, in view of the rough adjustment
+of the machines, that the chances of obtaining uniformly
+thick sheets would be slight.</p>
+
+<p>The machines should be arranged as a battery, with the
+marking rolls at one end, so that the operations are consecutive.
+It is erroneous to imagine that heavy machines (such as those
+used in crepe preparation) are required. Light machinery only
+is necessary for sheet-making; but any available heavy smooth-roll
+machines in a crepeing battery may serve admirably for the
+purpose.</p>
+
+<p><a name="Sec9_18" id="Sec9_18"></a><span class="smcap">Marking.</span>&mdash;Heavy machines are unnecessary for the purpose
+of putting a pattern on sheet rubber. If the rubber has been
+properly prepared a light pair of rolls is capable of exerting
+sufficient pressure to cause a good upstanding pattern.</p>
+
+<p>Rolls are cut in various designs: some with &#8220;diamond&#8221;
+grooves on both rolls; some with grooves of varying width and
+depth encircling the circumference of the rolls, thus creating
+a &#8220;stripe&#8221; effect on the rubber; and some with diagonally-cut
+spiral grooves placed closely together. The last has the
+greatest vogue at present, while the first has almost gone out
+of favour. An objection lodged against the second design
+is that the edges of the grooves sometimes cut through the
+rubber, so that the dried sheet divides in strips. It would
+appear in such instances that either the coagulum was too
+thin and soft, or that the grooves had been cut too deeply
+and sharply. In any case the choice of a design is an arbitrary
+matter, and should depend upon the effect produced on
+the rate of drying and the general appearance.</p>
+
+<p>The popular &#8220;close-cut spiral&#8221; roll is machined with
+varying measurements, but the usual design has grooves
+<span class="enum">1</span>&#8260;<span class="denom">8</span>
+inch wide by <span class="enum">1</span>&#8260;<span class="denom">8</span>
+inch deep and <span class="enum">3</span>&#8260;<span class="denom">16</span> inch apart.</p>
+
+<p>Many estates have a particular &#8220;brand&#8221; cut in the middle
+of the rolls for purposes of identification. If this is done it is
+advised that the main grooving of the rolls be carried into
+the &#8220;branding&#8221; strip; otherwise grip will be lacking on this<span
+class='pagenum'><a name="Page_106" id="Page_106">[106]</a></span>
+portion, and a certain amount of &#8220;cockling&#8221; of the sheets
+will result.</p>
+
+<p>Sheets are often seen in which the potential effect of the
+grooving is reduced to a comparatively flat pattern in place
+of the desired ridges. The fault is generally attributed to
+the shortcomings of the marking rolls. While it is true that
+the grooving often deteriorates by friction-wear when the
+rolls are running &#8220;free,&#8221; experience generally decides that
+the deficiency in the appearance of the rubber should be
+attributed to faulty previous preparation rather than to the
+marking rolls. Sets of rolls have been changed often without
+justification or an improved result. It would always be well to
+be certain first that the trouble did not emanate from the fact
+that the coagulum had been previously rolled so thin and hard
+that the rubber could not be squeezed so as to fill the grooves.
+This has been found to be a common fault, and the general
+effect is to delay drying in spite of the thinness of the rubber.</p>
+
+<p>Again, the trouble may have been due to an incorrect
+standardisation of the latex, generally in the direction of too
+heavy a density (too rich a latex) being employed. The original
+thickness of the coagulum would be normal, but owing to the
+abnormal rubber-content the effect of passing through the
+smooth rolls would be the production of a strip thicker and
+firmer than ordinary. If this firmness is appreciable the
+resistance of the rubber to the squeezing action of the marking
+rolls will result in a flat pattern&mdash;<i>i.e.</i>, the grooves cannot be
+filled, and the ridges are low.</p>
+
+<p>It is advised that all rolls used in the preparation of sheet
+rubber should be at least 18 inches wide, in order to avoid
+the appearance of thickened edges which delay drying.</p>
+
+<p>Working with the correct standard of dilution of latex, and
+following the procedure indicated in the foregoing paragraphs,
+the dry sheet should not exceed an average thickness (over
+ridges and depressions) of <span class="enum">1</span>&#8260;<span class="denom">8</span> inch.</p>
+
+<p><a name="Sec9_19" id="Sec9_19"></a><span class="smcap">Preparation for Smoke-Curing.</span>&mdash;It used to be the custom
+to allow sheet rubber to air-dry first for periods varying from
+one to several days. Naturally moulds were soon formed, and
+when the sheets were quite smoke-cured a mass of the dead<span class='pagenum'><a name="Page_107" id="Page_107">[107]</a></span>
+moulds could be seen, if not over the whole sheet, at least in
+the corners of each diamond mark. It has been demonstrated
+in practice that there is no advantage in allowing sheets to
+air-dry partially before smoking. In fact, to obtain the greatest
+benefit from smoke-curing, sheet rubber should be placed in
+the smoke-house as soon as possible. The same effect of
+mould-growth may be noted if the wet sheets are placed in a
+smoke-house insufficiently heated.</p>
+
+<p>Other defects may arise which can be traced to faulty treatment
+of the marked coagulum prior to hanging in the smoke-house
+and subsequent to rolling. These will be enlarged upon
+in a <a href="#Ch11">subsequent section</a> of the book, and at present it will
+suffice to indicate the procedure which experience directs as
+likely to give the best results.</p>
+
+<p><a name="Sec9_20" id="Sec9_20"></a>When the lengths of coagulum leave the marking machine
+they are usually laid in piles containing two dozen or more
+strips. The piles are then cut into the required lengths, the
+exact length generally being determined by the available perpendicular
+distance between the supports in the smoke-house.
+It is necessary to remark that the piles of sheets should not be
+allowed to accumulate, but should be dealt with in subsequent
+treatment progressively. If for some reason this is not possible,
+then all piles of sheets should be turned on edge so as to assist
+the draining away of the serum or &#8220;mother-liquor,&#8221; which
+continues to ooze from the rubber for some time after the
+squeezing in the machines.</p>
+
+<p><a name="Sec9_21" id="Sec9_21"></a>Where hot water is available the freshly cut sheets should be
+passed into it as soon as possible, and given a thoroughly good
+swilling. The caution must be given that the hot water should
+be changed very frequently and, if possible, after every batch,
+say, of a hundred sheets.</p>
+
+<p><a name="Sec9_22" id="Sec9_22"></a>The sheets should then be carried immediately to racks on
+which they are hung to drip. Generally these racks are situated
+under cover, but there is no reason why they should not be
+placed in the open air without cover or shade. From continued
+experience of this practice over a period of years it is found
+advantageous and to be preferred to the usual method of
+allowing sheets to drip under cover.</p>
+
+<p><span class='pagenum'><a name="Page_108" id="Page_108">[108]</a></span>While the sheets are fresh and loaded with internal moisture,
+the effect of sun-heat upon the surface, when exposed for, say,
+two hours, is nil; and the safety of the process can be guaranteed,
+provided the stated limit is not exceeded to an appreciable
+extent.</p>
+
+<div class="figcenter"><a name="Fig40" id="Fig40"></a><img src="images/illo125.jpg" alt="The Old Method
+of 'Dripping' Freshly Rolled Sheets within the Factory" />
+<p class="caption"><span class="smcap">The Old Method of &#8220;Dripping&#8221; Freshly Rolled Sheets<br />
+within the Factory.</span></p></div>
+
+<p>After dripping for an hour or so, the sheets should be placed
+in the smoke-house. If it is a bright sunny day, no extra
+precautions need be taken; but on cool, dull days it would be
+advisable to light the fires earlier than usual, consistent with
+the work required to be done in the house&mdash;<i>e.g.</i>, in the removal
+of dry rubber. There would appear to be no reason why the
+dry sheets should not be first removed, so that on dull or wet
+days smoking can be commenced as soon as the wet rubber has
+been hung.</p>
+
+<p>On a few estates where the smoke-houses are worked continuously,
+except for a few hours in the morning, a portion
+of the building is separated by a partition for the reception
+of the wet rubber. The sheets are taken directly from the
+marking rolls and placed in the chamber, beneath which a<span class='pagenum'><a name="Page_109" id="Page_109">[109]</a></span>
+fire is started. The sheets thus drip in a warm and smoke-laden
+atmosphere until next morning, when they are weighed
+and removed to the smoke-house proper. It is claimed that
+freedom from &#8220;rust&#8221; is thus obtained.</p>
+
+<p>It will be clear that in the treatment of the rubber preparatory
+to smoking the whole process should be continuous, and delay
+should be avoided if the best results are to be obtained.</p>
+
+<div class="figcenter"><a name="Fig41" id="Fig41"></a><img src="images/illo126.jpg" alt="The Newer Method of Hanging in the Open Air" />
+<p class="caption"><span class="smcap">The Newer Method of Hanging in the Open Air.</span></p></div>
+
+<p><a name="Sec9_23" id="Sec9_23"></a><span class="smcap">Smoking of Rubber.</span>&mdash;The assumption may have been noted
+above that the sheet is to be smoked. As far as our knowledge
+extends, none but small native estates now prepare sheet rubber
+of any other type, with the exception of certain patent processes.
+Air-dried sheets are generally made on small-holdings, and are
+bought in the market chiefly for the purpose of macerating
+and making into blanket crepe. We have no intention, therefore,
+of discussing the possibilities or qualities of air-dried
+sheets, as the output of sheet-rubber from our estates is always
+in smoked form. The drying (or, properly, smoking) stage
+will be discussed in <a href="#Ch11">Chapter XI</a>.</p>
+
+
+<p class='pagenum'><a name="Page_110" id="Page_110">[110]</a></p>
+<hr class="c25" />
+<h2><a name="Ch10" id="Ch10"></a>CHAPTER X</h2>
+
+<h3><i>PREPARATION OF CREPE RUBBER</i></h3>
+
+
+<p><a name="Sec10_1" id="Sec10_1"></a><span class="smcap">No. 1, or Fine Pale Crepe.</span>&mdash;Considering first the preparation
+of the highest grade, fine pale crepe, it must be stated
+that the difficulties attached to the process are generally not
+sufficiently appreciated. In this pale rubber minor blemishes
+are so plainly apparent that their importance is highly exaggerated,
+and what would worthily escape notice in smoked
+rubber assumes disproportionate prominence in pale crepes.
+The very fact that such a delicate material as colourless coagulum
+has to be manipulated in coarse iron rollers, with the
+attendant oil and grease worries, should be sufficient to deter
+one from criticising too harshly the occasional lapses of an
+estate struggling to give of its best to the market. At the
+same time there can be no doubt that if precautions are taken
+to attend to all likely sources of contamination, defects in pale
+crepe may be avoided to a wonderful extent; and on some
+estates the observance of elementary rules enables the preparation
+of the finest pale crepe to be made almost mechanically.</p>
+
+<p><a name="Sec10_2" id="Sec10_2"></a><span class="smcap">Standardisation of Latex.</span>&mdash;The question of the standardisation
+of latex has been dealt with in a general way in <a href="#Ch7">Chapter
+VII.</a>, and the reader is now familiar with the trend of the
+argument in its favour. It will be recognised that the necessity
+for standardisation exists to the same degree in the correct
+preparation of pale crepe as in the case of smoked sheet.
+Unless the dry rubber content is invariable, and the quantities of
+chemicals fixed, the colour of the crepe may vary appreciably.</p>
+
+<p>It may be pointed out that it is not <i>essential</i> to adopt the
+same standard of dilution as for sheet preparation. Given
+that latices from all fields or divisions are fairly uniform, and
+of high rubber content, the standard may be taken at a figure
+equivalent, for example, to 2 lbs., or 2<span class="enum">1</span>&#8260;<span
+class="denom">2</span> lbs., or even 3 lbs.<span class='pagenum'><a name="Page_111" id="Page_111">[111]</a></span>
+per gallon. It is wise, nevertheless, to take a lower standard
+for several reasons. For instance:</p>
+
+<div class="blockquot"><p>(<i>a</i>) The average dry rubber content varies with climatic
+conditions, position of the cut on the tree, general health of
+the tree, etc. On a rainy day the dry rubber content may be
+lowered too greatly by adventitious circumstances.</p>
+
+<p>(<i>b</i>) Recording instruments often fail to give even approximately
+correct readings in rich latex. Errors may thus be
+made easily.</p>
+
+<p>(<i>c</i>) A fairly soft coagulum means easier working on the
+machines, less labour, and proportionately cheaper costs.</p></div>
+
+<div class="figcenter"><a name="Fig42" id="Fig42"></a><img src="images/illo128.jpg" alt="Three Grades of Crepe Rubber" />
+<p class="caption"><span class="smcap">Three Grades of Crepe Rubber.</span></p>
+<p class="center">Left to right: fine pale crepe; second quality pale crepe; compound
+crepe.</p></div>
+
+<p>It is advised, therefore, that for general purposes the same
+standard as that found suitable for sheet rubber should be
+taken&mdash;viz., 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber per gallon. At all events the
+standard should not exceed 2 lbs. per gallon.</p>
+
+<p><a name="Sec10_3" id="Sec10_3"></a><span class="smcap">Coagulation and Coagulant.</span>&mdash;Coagulation may be
+undertaken without any special arrangement of tanks, and is
+usually effected in the ordinary &#8220;Shanghai&#8221; glazed
+earthenware<span class='pagenum'><a name="Page_112" id="Page_112">[112]</a></span>
+jars containing about 45 gallons. Given reasonable care,
+and a fairly fool-proof system of calculation for the quantities
+of chemicals required, no difficulty need be experienced.</p>
+
+<div class="figcenter"><a name="Fig43" id="Fig43"></a><img src="images/illo129.jpg" alt="A Washing Shed" />
+<p class="caption"><span class="smcap">A Washing Shed.</span></p>
+<p class="capt350">Sheets are soaked in hot water in tanks in the background, and
+then scrubbed under a spray of cold water.</p></div>
+
+<p>On a larger scale it is advised that proper reception tanks,
+in which standardisation can be effected, should be installed.
+Where both sheet rubber and fine crepe are being prepared,
+the whole system of sheet-coagulating tanks may be employed
+with considerable advantage, even to the insertion of the
+partitions.</p>
+
+<p>If ordinary jars are used, and the coagulum is left until the<span class='pagenum'><a name="Page_113" id="Page_113">[113]</a></span>
+following morning, the mass of rubber has to be cut up into
+pieces of a size suitable for the machines. The knives or
+saws are sometimes rusty, and the colour of the coagulum is
+affected. The coolies often feed into the machines lumps
+which are too large, with the result that portions are thrust
+under the cheek-blocks and become stained.</p>
+
+<p>When a sheet-coagulating tank is used all labour of cutting
+the coagulum is obviated. The long strips are handled and
+fed into the rolls easily. It may be seen, likewise, that actual
+work is thus saved in machining.</p>
+
+<p><a name="Sec10_4" id="Sec10_4"></a><span class="smcap">Quantity of Coagulant.</span>&mdash;For a general discussion on
+the coagulant and quantities employed, the reader is referred
+to <a href="#Ch8">Chapter VIII</a>. It is there recommended that for latex
+standardised to a level of 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. per gallon, the proportion of
+pure acetic acid should be in the ratio of 1:1,200. Directions
+are there given for the making of the solution, and the calculation
+of the quantity required for any given volume of latex.</p>
+
+<p>It is pointed out that for average <i>undiluted</i> latex the basis of
+calculation, for quantities of acetic acid required, should be
+taken on the ratio 1:1,000. Where latex exceeds a dry rubber
+content of 3 lbs. per gallon, it may be necessary to increase
+the quantity of acid to 1:800.</p>
+
+<p>If a standard of 2 lbs. per gallon is adopted, the formula given
+for the 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. standard will not give full satisfaction, and the
+quantity of acid solution must be increased slightly in order
+to obtain complete coagulation. Assuming that the original
+solution is prepared in 1 per cent. strength, the following
+difference would be noted:</p>
+
+<div class="blockquot">
+
+<table summary="Table p113">
+
+<tr>
+<td class="left">(<i>a</i>)</td>
+<td colspan="2" class="left">One part pure acetic acid to 100 parts water (theoretically 99 parts).</td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">(<i>b</i>)</td>
+<td class="center br"><i>1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. per gallon.</i></td>
+<td class="center"><i>2 lbs. per gallon.</i></td>
+</tr>
+
+<tr>
+<td class="left">&nbsp;</td>
+<td class="left br">Of the above solution use 1 gallon to every 12 gallons of standardised latex.</td>
+<td class="left">Of the above solution use 1 gallon to every 10 or 11 gallons of standardised latex.</td>
+</tr>
+
+</table>
+</div>
+
+<p>It is not possible to lay down an exact figure governing all
+cases, as so much depends upon the treatment undergone by
+the latex before it reaches the store.<span class='pagenum'><a name="Page_114" id="Page_114">[114]</a></span></p>
+
+<p>Some estates continue to use solutions of greater strength,
+generally 5 per cent., in crepe preparation. While such
+solutions may be effectively stirred in when the latex is dilute,
+it is advised that for intimate mixture the solution need not be
+stronger than 1 per cent.</p>
+
+<p>In estimating the quantities of acetic acid required much
+depends upon the interval which is to elapse between the
+addition of acid and the time of working of the coagulum.
+If the rubber is to remain until next morning, the average
+formul&aelig; will be found suitable; but if it is required to work
+the coagulum with an interval of less than three hours, an excess
+of acid must be employed. The excess need be comparatively
+small, unless the interval is much reduced. For instance, it is
+the practice on some few estates to begin the machining of the
+coagulum about half an hour after coagulation commences;
+in which case it is usual to add from a quarter to a half of the
+normal quantity in excess. It need scarcely be pointed out
+that unless this procedure is strictly unavoidable it should be
+discouraged on account of the waste of coagulant involved.
+Incidentally, the use of strong solutions of acid under such
+circumstances may lead to increased deterioration of the rolls.</p>
+
+<p><a name="Sec10_5" id="Sec10_5"></a><span class="smcap">Colour of Fine Crepe.</span>&mdash;We are sometimes assured that
+manufacturers do not pay the attention to the question of
+colour which sale conditions would lead one to believe. As
+far as we are concerned, and as long as there is no direct traffic
+between producer and consumer, it must be recognised that
+in the vast majority of cases we are forced to concern ourselves
+only with the standards set up in the markets. This, in spite
+of the knowledge that, all other things being equal, the arbitrary
+distinctions in colour afford no indication of the intrinsic
+value of the rubber. Under present circumstances it is plain
+that if paleness is demanded it has to be supplied.</p>
+
+<p>Probably without exception all estates employ sodium
+bisulphite as the agent for the prevention of that darkening
+(oxidation) which is natural in drying rubber.</p>
+
+<p><a name="Sec10_6" id="Sec10_6"></a><span class="smcap">Sodium Bisulphite.</span>&mdash;A formula for use of this chemical
+is given in <a href="#Ch8">Chapter VIII.</a>, and is applicable to latex standardised
+to 1<span class="enum">1</span>&#8260;<span class="denom">2</span>
+lbs. dry rubber per gallon. If a higher standard is<span class='pagenum'><a name="Page_115" id="Page_115">[115]</a></span>
+chosen the quantity calculated as in (<i>b</i>) of that formula may
+be increased slightly, and the exact requirements found by
+experience. The caution must again be given that the employment
+of an excess of sodium bisulphite will lead to the production
+of an over-pale rubber, and a prolongation of the
+drying period. If thick crepes are made, an excess of the
+chemical is sometimes made visible by a greyish powder
+deposited on the edges of the strips of dry rubber.</p>
+
+<p>It must be emphasised that the formula in <a href="#Ch8">Chapter VIII.</a>
+indicates the <i>maximum</i> quantities required for use with standard
+latex. Many estates will find it expedient to use less of the
+chemical; and if it is found that the desired result is not
+obtained from normal proportions, attention should be directed
+to the points discussed in the following paragraph.</p>
+
+<p><a name="Sec10_7" id="Sec10_7"></a><span class="smcap">Evaluation and Deterioration of Sodium Bisulphite
+and Sodium Sulphite.</span>&mdash;Sodium bisulphite and sodium
+sulphite are both bought for our purpose in the form of a fine
+crystalline powder, and on analysis good specimens should
+contain over 90 per cent. pure substance, when packed in well-sealed
+vessels.</p>
+
+<p>It has often happened that shippers or local sellers, by
+inadvertence, have supplied the one chemical in place of the
+other&mdash;to the detriment of the rubber and the discomfiture
+of managers of estates. The error, as a rule, has not been
+detected for some time, and then perhaps only as a result of
+complaints or enquiries reaching the laboratories. To the
+layman, and certainly to the native who usually has charge of
+these substances, it is not a simple matter to distinguish between
+them without special knowledge. There are certain
+elementary tests, however, which can be applied on all estates
+serving to make the distinction, but affording no information
+regarding the actual quality of the chemicals. They are given
+in a comparative form on <a href="#Page_116">page 116</a>. Samples of doubtful
+specimens may be sent to the laboratories for analysis, but
+the bulk of the chemical should not be used.</p>
+
+<p>During the War some very poor shipments were received,
+and much trouble was caused. Under normal conditions there
+can be no question that it is to the interests of chemical manufacturers<span
+class='pagenum'><a name="Page_116" id="Page_116">[116]</a></span>
+to supply the best article; and it is anticipated that
+in future there should be no difficulty in procuring shipments
+of a high degree of purity.</p>
+
+<table id="Sec10_8" style="width: 80%;" summary="Table p116">
+
+<tr>
+<td class="left">&nbsp;</td>
+<td class="center br" style="width: 48%;"><i>Sodium Bisulphite.</i></td>
+<td class="left">&nbsp;</td>
+<td class="center" style="width: 48%;"><i>Sodium Sulphite.</i></td>
+</tr>
+
+<tr>
+<td class="right">1.</td>
+<td class="left br">If in good condition it has a powerful odour of sulphur dioxide.<a name="FNanchor_9_9"
+id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></td>
+<td class="right">1.</td>
+<td class="left">It  has  no perceptible odour.</td>
+</tr>
+
+<tr>
+<td class="right">2.</td>
+<td class="left br">In solution it should turn a blue litmus-paper red.</td>
+<td class="right">2.</td>
+<td class="left">In solution it should turn a red litmus-paper blue.</td>
+</tr>
+
+<tr>
+<td class="right">3.</td>
+<td class="left br">It exhibits a marked tendency to &#8220;cake&#8221; if the drum is allowed to remain open.</td>
+<td class="right">3.</td>
+<td class="left">The tendency to &#8220;cake&#8221; is less marked than in the case of the bisulphite.</td>
+</tr>
+
+</table>
+
+<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> High-grade sodium bisulphite has very little odour, but by the
+time it reaches the estate, and as a result of short exposure to the
+moist atmosphere of the tropics, a little decomposition sets in and
+a strong odour of sulphur dioxide gas is noticeable.</p></div>
+
+<p>It will be evident that, as sodium bisulphite under normal
+conditions gives off a gas when exposed to the atmosphere,
+it deteriorates in quality continuously. It is the potential
+presence of this gas which makes the powder effective as an
+anti-oxidant and disinfectant. It is within the experience of
+all accustomed to the handling of this chemical, that in addition
+to the loss of gas, the powder cakes into a hard mass on exposure.
+If only the top layer is caked, the remainder may be in
+fair condition; but no caked portions should be used, as they
+cannot be of good quality. They may, however, be used for
+the treatment of scrap rubber, to be discussed later.</p>
+
+<p><a name="Sec10_9" id="Sec10_9"></a><span class="smcap">Care of Sodium Bisulphite.</span>&mdash;The ready tendency of
+sodium bisulphite to deteriorate on exposure should give
+sufficient indication regarding its treatment in storage. It
+should be bought only in drums (or other air-tight containers),
+and should be stored in a dry place. No drum should be
+opened until required, and the common practice of keeping
+an open drum on the floor of the factory should be avoided.</p>
+
+<p>Drums are of two sizes, generally containing <span class="enum">1</span>&#8260;<span
+class="denom">4</span> or <span class="enum">1</span>&#8260;<span class="denom">2</span> cwt.
+respectively. It will be obvious that, although the prime cost
+may be cheaper with the larger quantity, it would always be<span class='pagenum'><a name="Page_117" id="Page_117">[117]</a></span>
+preferable to secure the smaller drums, as the loss on exposure
+will be less.</p>
+
+<p>Most commonly the 56 lb. drum is purchased. It should
+not be difficult to calculate the period during which the contents
+will be consumed, on the basis of a maximum of 1 lb. per
+100 gallons of latex. A 56 lb. drum, assuming no loss or
+waste, should be sufficient to treat <i>at least</i> 5,600 gallons of latex
+(say, 8,500 lbs. of rubber)&mdash;if the bisulphite is of first-class
+quality, and the use is applied only to the preparation of fine
+pale crepe.</p>
+
+<p>Where the quantity used per diem is small, it is advised that
+precautions should be taken to preserve the quality of the
+chemical when a drum is opened. It might be of advantage
+to place the contents of the drum in smaller sealed tins, or to
+have made a special container (with a closely fitting lid) into
+which the powder can be placed as soon as the drum has
+been opened.</p>
+
+<p><a name="Sec10_10" id="Sec10_10"></a><span class="smcap">Mixing Solution with Latex.</span>&mdash;Emphasis has been laid, in
+<a href="#Ch8">Chapter VIII.</a>, upon the necessity for care in the preparation
+of the solution. Equal regard must be given to the mixture
+of the solution with the latex.</p>
+
+<p>On a few estates it used to be the practice to add the powder
+to the solution of acid, with stirring. Obviously this led at least
+to a great loss of efficiency, owing to the rapid escape of the
+gas which was evolved.</p>
+
+<p>The solution of sodium bisulphite should be poured into the
+latex in as uniform a distribution as possible. The mixture
+of solution and latex should be thoroughly stirred, and if only
+natives are in charge a minimum period of five minutes should
+be prescribed before the addition of the coagulant. A thorough
+stirring should again follow the advent of the acid.</p>
+
+<p>If these elementary rules are not observed faithfully, the
+deficiency will most probably be manifested in the dry rubber
+in the shape of streaks of varying shades of colour.</p>
+
+<p>Finally it may be insisted upon that deteriorated sodium
+bisulphite should not be used. In order to obtain an effect
+double the quantity may be required, and the residual
+salts left in the rubber on evaporation of the moisture will<span class='pagenum'><a name="Page_118" id="Page_118">[118]</a></span>
+be responsible for prolonged drying, surface deposits, and
+possibly &#8220;spot disease.&#8221;</p>
+
+<p><a name="Sec10_11" id="Sec10_11"></a><span class="smcap">Former Methods of Making Pale Rubber.</span>&mdash;Merely as a
+matter of historic interest it may be mentioned that previous to
+the introduction of sodium bisulphite pale crepes were made
+in comparatively small quantity by various devices, among
+which the following might be quoted:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Use of excessive quantities of strong acetic acid.</p>
+
+<p>(<i>b</i>) Extreme dilution of latex in conjunction with excessive
+quantities of acid.</p>
+
+<p>(<i>c</i>) Extreme dilution in conjunction with steaming and
+excess of acid.</p>
+
+<p>(<i>d</i>) Extreme dilution of latex in conjunction with excess
+of acid and subsequent heating of the coagulum in hot water.</p>
+
+<p>(<i>e</i>) The use of excess of a mineral acid such as sulphuric acid.</p>
+
+<p>(<i>f</i>) The skimmings and very dilute latex, coagulated with
+excess of acid.</p></div>
+
+<p><a name="Sec10_12" id="Sec10_12"></a><span class="smcap">Working the Coagulum.</span>&mdash;Description of the details of
+necessary machinery for crepe-making is relegated to <a href="#Part3">Section
+III.</a> of this book. Here we shall treat only of the matter
+in general.</p>
+
+<p>In the preparation of crepe rubber heavy machinery is
+necessary, and ample engine-power must be available. The
+machines should comprise three types:</p>
+
+<div class="blockquot"><p>(<i>a</i>) With rolls cut in such fashion, and run at such different
+speeds, as to have a macerating effect upon the coagulum.
+Such machines or rolls will be referred to as &#8220;macerators.&#8221;</p>
+
+<p>(<i>b</i>) Intermediate rolls, grooved in varying designs and geared
+differentially. These reduce the thick rough crepe obtained
+from the macerators into a form suitable for passing to the
+rolls described in (<i>c</i>). They are sometimes called &#8220;crepers,&#8221;
+but as this term may be applied equally to the macerating
+rolls, they will be termed the &#8220;intermediate&#8221; rolls.</p>
+
+<p>(<i>c</i>) Smooth rolls usually run at approximately even speeds
+and, as their name denotes, devoid of any grooving. They
+are called &#8220;smooth&#8221; rolls or &#8220;finishers.&#8221;</p></div>
+
+<p>Without such equipment it is not possible to prepare the
+grade which is known as &#8220;fine pale crepe.&#8221; In the common
+acceptation of this term crepe of No. 1 quality generally
+connotes fineness and paleness with a thin crepe which has a
+good, smooth, and fairly well-knit texture.</p>
+
+<p><span class='pagenum'><a name="Page_119" id="Page_119">[119]</a></span>It is, of course, possible to make a thick pale crepe, using
+only the macerators and intermediates, but the &#8220;finish&#8221; will
+be that typical of the particular grooving of the intermediate
+rolls. For the preparation of crepe ordinarily, the possession
+of smooth rolls is a <i>sine qua non</i>.</p>
+
+<p>For reasons which will be explained more fully in the <a href="#Ch17">chapter</a>
+dealing with the defects of crepe rubber, the practice of
+preparing thick crepes direct from the coagulum is now very
+uncommon. Thick crepes are generally made by reworking
+dry rubber, either in the form of thin crepes or from air-dried
+sheets. The market for the latter in Malaya is confined almost
+entirely to Singapore, where factories buy native rubber and
+re-work it into thick crepe.</p>
+
+<p>The bulk of the output of No. 1 crepe from estates is in the
+form of thin &#8220;fine pale crepe.&#8221; The artificial standard set up
+by buyers and brokers necessitates this thin crepe being of
+even texture and fairly free from small holes (&#8220;looseness&#8221;).
+What difference the small holes are to make in the vulcanising
+properties of the rubber is beyond our knowledge; but such
+being the standard, it must be attained if the full price is to
+be obtained.</p>
+
+<p>In order to secure the desired effect the coagulum must be
+passed consecutively through the three types of rolls, and
+undergoes a varying degree of working in each.</p>
+
+<p>Given the necessary equipment of machines, it is possible
+to make a good specimen of thin pale crepe if the coagulum
+passes through all the rolls a total of twelve times (or even less in
+exceptional cases). There is no intention of suggesting that
+this is possible on all estates. Clearly the number of times
+the rubber passes through the rolls will depend upon the total
+efficiency of the machines. This in turn involves such factors
+as (<i>a</i>) the size of the rolls, (<i>b</i>) the number of machines of each
+type, (<i>c</i>) the gearing of the pinions, (<i>d</i>) the speed of the drive,
+etc. Again, much depends upon the nature of the coagulum
+worked. A fairly soft coagulum will offer less resistance, and
+conversely a dense coagulum will require more machining.</p>
+
+<p>It has been shown by the writers in previous publications
+that over-working of the coagulum has an effect on the vulcan<span class='pagenum'><a name="Page_120"
+id="Page_120">[120]</a></span>isation
+of the rubber; and this has been confirmed by others.<a name="FNanchor_10_10"
+id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a>
+Apart from this point, it should be recognised that over-working,
+beyond that necessary to produce a thin crepe of even texture,
+is to be deprecated, on the ground of economy, in working.</p>
+
+<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a
+href="#FNanchor_10_10"><span class="label">[10]</span></a> Bulletin No. 27, Department of Agriculture F.M.S., April, 1918,
+&#8220;Preparation and Vulcanisation of Plantation Para Rubber,&#8221;
+Eaton, Grantham and Day.</p></div>
+
+<p>Owing to the existing differences in equipment and speed of
+drive, etc., the regular practice of any one estate may be unsuitable
+for another. It remains, therefore, a matter of study
+for each estate to discover the minimum number of times which
+rubber should pass through the machines, consistent with the
+factors indicated above. In any case it may be assumed that if
+any factory cannot prepare a good crepe by passing the rubber,
+say, twelve times through the rolls, there is some deficiency
+in the machines, or of speed; the coagulum may be too hard, or
+the rolls may be badly worn.</p>
+
+<p><a name="Sec10_13" id="Sec10_13"></a><span class="smcap">Lower Grades of Crepe Rubber.</span>&mdash;Even a few years ago it
+was plain that the lower grades of crepe (<i>i.e.</i>, all grades lower
+than first latex rubber) were not sufficiently appreciated in
+the market. There was often a marked difference in price
+between a first-grade crepe and crepe made from naturally
+coagulated lump. This arose chiefly from lack of knowledge.
+It has since been recognised in some measure that no reason
+exists for such a wide difference in price, and more recently
+the margin between even the first-grade rubber and the lowest
+grade of scrap rubber has been a gradually diminishing one.
+Providing sufficient care is exercised in the preparation of the
+lower grades, one would expect to see but very small difference
+in prices between any two grades. It is true that adequate
+attention has been given to the preparation of the scrap grades
+only in comparatively recent years, and it is acknowledged that
+when high prices were ruling for first-grade rubbers sufficient
+attention was not generally given to the subject of the preparation
+of the lower grades.</p>
+
+<p><a name="Sec10_14" id="Sec10_14"></a><span class="smcap">Naturally Coagulated Lump Rubber.</span>&mdash;The grade of
+rubber made from the naturally coagulated lump which forms in
+buckets and carts is usually of a mixed colour, due to the fact<span class='pagenum'><a name="Page_121" id="Page_121">[121]</a></span>
+that the lumps oxidise very quickly. When they are allowed
+to remain overnight before being machined, it can be imagined
+that the colour of the dry crepe would be very dark, or would
+contain very dark streaks. Such is ordinarily the case, unless
+special precautions are taken.</p>
+
+<p>Providing that the coagulated lump is free from bark, leaves,
+and leaf-stems, and certain other precautions taken, the difference
+in price between coagulated-lump crepes and first-grade
+crepes should be very slight. Too often, however, not sufficient
+supervision is given to the coagulated-lump rubber, and it is
+common to see it come into the factory containing leaves and
+bark. These should be picked out before the latex is strained,
+but obviously it would be better to ensure that they did not
+enter the buckets in the first place.</p>
+
+<p>It would seem reasonable to suppose that if some means could
+be employed for preventing or checking the surface oxidation
+of naturally-coagulated lump rubber, there would be a corresponding
+improvement in the colour of the dry crepe. That
+such a method is practicable has been demonstrated on many
+estates. The lump when lifted out of the latex is allowed to
+drain for a few minutes, and is then (without squeezing) placed
+in a dilute solution of sodium bisulphite. A 1 per cent.
+solution is sufficiently powerful. It is not to be thought for a
+moment that by the use of sodium bisulphite any previous
+oxidation will be counteracted; all that is claimed for the
+treatment is that any further surface oxidation will be checked,
+and the rubber may be allowed to remain until the next day,
+for working, if it is so desired. It will probably be found that
+quite a quantity of latex has been expressed from the lumps
+by contraction, and acid may be added to obtain the rubber
+from this. On other estates the lump rubber is worked on the
+machines as it is received, and the resulting crepe is submerged
+in a weak solution of sodium bisulphite over-night.
+It is then rinsed in water and hung to drip before weighing and
+placing in the drying house. Under certain conditions some
+of the lump rubber darkens rapidly during transport to the store,
+and any such oxidised portions must be rejected if a uniform
+colour is to be expected in the crepe.</p>
+
+<p><span class='pagenum'><a name="Page_122" id="Page_122">[122]</a></span>Following the procedure indicated above, some estates find it
+possible to prepare from naturally coagulated lump rubber a
+crepe which can be classed as No. 1 grade.</p>
+
+<p><a name="Sec10_15" id="Sec10_15"></a><span class="smcap">Skimmings and Washings.</span>&mdash;The skimmings of tanks, as
+already shown, may be prepared sometimes as a second quality
+of smoked sheet; but generally they are amalgamated with
+the rinsings of cups and buckets, treated with sodium bisulphite
+and acid, and made into crepe form.</p>
+
+<p>The cup-washings, as they arrive at the store, represent a
+very dilute latex, the rubber from which is generally of a
+greyish colour.</p>
+
+<p>Bucket-washings should yield a good type of pale rubber if
+they are obtained properly. To obtain the maximum quantity of
+good rubber the buckets should first be rinsed. A gang should
+be taken, a small quantity (say a quart) of water poured into the
+first bucket, and this dilute latex used progressively in all the
+buckets of that gang of tappers. The result is a fair latex
+which can be added to the bulk of No. 1 latex, provided it is free
+from dirt. Where sheet rubber is being prepared, carefully
+strained cup-washings or bucket-washings may be utilised
+in the dilution of the latex to the required standard, thus
+increasing slightly the percentage of first-grade rubber.</p>
+
+<p><a name="Sec10_16" id="Sec10_16"></a><span class="smcap">Tree-Scrap.</span>&mdash;As tree-scrap is a naturally coagulated rubber,
+it should be expected to show up well in quality. This is
+usually the case; but from what has been said of the effect of
+sun-heat it will be understood that if trees are not regularly
+&#8220;scrapped,&#8221; there is a danger that the crepes may be found
+to contain tacky streaks due to the inclusion of old scrap which
+has been sun-baked. In hot dry weather, on widely planted
+areas tapped on alternate days, it has been noticed that scrap
+remaining for two days often exhibits a resinous appearance,
+and feels sticky to the touch.</p>
+
+<p>If tree-scrap is to be made as a separate grade, as used to be
+the general custom, care should be taken to see that it is free
+from bark and dirt. On some estates where scrap-rubber is
+paid for per pound collected, it is usually the rule to insist
+that scrap shall be washed free from dirt and picked free of
+bark. This course is to be commended, but might probably<span class='pagenum'><a name="Page_123" id="Page_123">[123]</a></span>
+prove impracticable to the majority of estates. Theoretically,
+of course, the operation of machining should rid the scrap of
+all traces of bark; but in practice it does not do so.</p>
+
+<p>Some proportion of the tree-scrap is usually found to be
+heavily oxidised, and naturally if a crepe of uniform colour is
+to be obtained these dark scraps must be rejected, otherwise
+dark streaks will be formed. Coolies should be instructed
+to sort out the dark pieces before arriving at the store.</p>
+
+<p><a name="Sec10_17" id="Sec10_17"></a><span class="smcap">Bark-Shavings.</span>&mdash;It
+has been intimated in a <a href="#Sec5_16">previous section</a>
+that the method of obtaining and collecting bark-shavings
+varies with the type of labour employed.</p>
+
+<p>Where the scrap is removed from the edge of the bark on
+each occasion before tapping, the amount of rubber to be
+extracted from the dry shavings is very small&mdash;so small, in
+fact, that when the price of rubber is low, it is doubtful whether
+it pays to collect and work the material.</p>
+
+<p>On the other hand, where trees are not &#8220;scrapped&#8221; before
+tapping, the bark-shavings and tree-scrap are collected together,
+and the amount of rubber derived from the mixture may be
+30 to 40 per cent. upon the gross weight&mdash;depending chiefly
+upon the quality of the tapping (<i>i.e.</i>, in this case, the
+thickness of the paring). Another factor influencing this
+figure would be the effect of using an anti-coagulant on
+the cuts.</p>
+
+<p>Bark-shavings entail such wear upon the ordinary machines
+during working, especially if fairly free from rubber, that
+unless the factory is equipped with a special &#8220;scrap-washer&#8221;
+it is advised that this material should be sent for working to a
+factory having the necessary equipment. Whenever possible,
+bark-shavings should receive treatment on the day of collection.</p>
+
+<p>It used to be quite common to see heaps of bark-shavings
+accumulating on the floor of a factory, and generating excessive
+heat. Yet these heaps were allowed to stand about for a day
+or days. Is it any wonder then that tackiness was found to
+develop when the rubber was dry? It is here definitely laid
+down that no heaps of bark-shavings should be accumulated
+even for half a day. Tanks should be provided in which the
+shavings should be submerged in water.</p>
+
+<p><a name="Sec10_18" id="Sec10_18"></a><span class='pagenum'><a name="Page_124" id="Page_124">[124]</a></span><span
+class="smcap">Earth-Scrap.</span>&mdash;Of all grades of crepe this is the one most
+liable to become tacky in transit. This tackiness to a large
+extent cannot be avoided, as old pieces of earth-scrap may be
+brought in amongst the bulk. Probably these old pieces have
+been exposed to the sun for days, and have become quite
+resinous. It would be practically impossible to go through all
+earth-scrap in order to find these odd pieces, but unless this
+were done one could not guarantee that the earth-rubber
+would always be free from tackiness. The difficulty does not
+appear, however, on estates where earth-rubber is collected
+systematically at very frequent intervals.</p>
+
+<p><a name="Sec10_19" id="Sec10_19"></a><span class="smcap">Fibrous Matter in Low-Grade Rubbers.</span>&mdash;It is sometimes
+found in this and other lower grade rubbers that pieces
+of cloth or cotton-waste are concealed. Coolies may have
+used them for cleaning cups, or the store coolies may have been
+at fault. Earth-scraps especially should be examined, before
+working, for such extraneous matter.</p>
+
+<p><a name="Sec10_20" id="Sec10_20"></a><span class="smcap">Scrap-Washers.</span>&mdash;These are heavy machines specially
+devised for the treatment of lower grade rubbers. In these
+the raw rubber is well masticated and freed from impurities, if
+the machine functions efficiently.</p>
+
+<p>There are several types of these machines, all of which are
+efficient. That best known is the &#8220;Universal&#8221; washer, made
+by Joseph Baker, Sons, and Perkins, Ltd. (formerly Perkins
+Engineering Company). Coming into local favour during the
+War, the &#8220;U.E.&#8221; scrap-washer, made by the United Engineering
+Company (Singapore), gives very good service. The &#8220;C.C.C.&#8221;
+washer, made by the Colombo Commercial Company, is suitable
+for the purposes of an average estate. There are others, less
+well known. Most of these machines are made in varying
+sizes to meet the requirements of small, medium, or large
+estates; and if funds are available, a scrap-washer should be
+regarded as an essential item in the machinery of any estate
+employing engine power.</p>
+
+<p>The rate of output of scrap-washers will depend mainly upon
+the speed at which they are driven, and when ordering the
+equipment it would be advisable to state the ordinary speed of
+the back-shaft, length of drive, etc. It does not follow that the<span class='pagenum'><a name="Page_125" id="Page_125">[125]</a></span>
+larger the rate of output, the greater is the efficiency of the
+washer. The point is not as to what quantity of rubber can be
+taken out per hour, but what quantity is actually freed from
+impurities.</p>
+
+<p>It is advisable for the superintendent to obtain a thorough
+knowledge of the general construction and principles of the
+particular scrap-washer employed. In the past it was not
+uncommon to find superintendents innocent of the fact that
+a certain type of washer possessed movable parts upon which
+the efficiency of the cleansing largely depended. It was often
+found that these parts, which were intended to be removed
+and cleaned at intervals, had become firmly fixed and could not
+be removed for inspection.</p>
+
+<p>It must be recognised also that the machines are liable to
+considerable damage if extraneous substances are allowed to
+enter&mdash;for example, tapping-knives, stones, pieces of iron,
+spouts, etc., which are sometimes present in the loose scraps
+of rubber or shavings, owing to the carelessness of coolies.
+Under the best regulated-system, such accidents occasionally
+occur, but a great deal of trouble could be avoided by having
+it understood that each charge must be sorted over before
+entering the washer.</p>
+
+<p>Again a deal of extra work, and much wear and tear, is caused
+by the <i>abuse</i> of the scrap-washer&mdash;<i>e.g.</i>, in the cleansing of
+earth-scrap. As this reaches the factory it often contains a
+quantity of internal or adhering earth. Before entering the
+washer a good proportion of the external soil could be removed
+if the scraps were thrown into a tank and given a thorough
+soaking and stirring. In a similar manner dry bark-shavings,
+which have been allowed to accumulate, could be
+softened.</p>
+
+<p>In the actual working of scrap-washers instructions are
+generally given by the makers. These sometimes advise the
+introduction of warm water (or of steam into the cold water
+supply) for an interval during the working of each charge.
+Where possible, such instructions should be followed, as
+by this means the individual pieces of rubber are massed
+together, in the final stage, into a &#8220;sausage&#8221; form which
+is<span class='pagenum'><a name="Page_126" id="Page_126">[126]</a></span>
+easy to transport and to manipulate in the ordinary crepeing
+battery.</p>
+
+<p><a name="Sec10_21" id="Sec10_21"></a><span class="smcap">Compound Crepes.</span>&mdash;The attitude of both buyers and sellers
+with regard to the types of lower grade rubbers appears to be
+changing. In the past, from any one estate there might be
+obtained as many as six grades of crepe below No. I. These
+comprised:</p>
+
+<div class="blockquot"><p>(1) A pale rubber (often streaked) obtained from coagulation
+of cup washings and bucket rinsings.</p>
+
+<p>(2) A pale rubber (often streaked) obtained by coagulation of
+the skimmings from the surface of the No. 1 latex.</p>
+
+<p>(3) A streaked and dull rubber prepared from naturally-coagulated
+clots found in cups, buckets, and latex carts.</p>
+
+<p>(4) A streaked rubber prepared from scrap which had coagulated
+upon the face of the cut bark.</p>
+
+<p>(5) A brownish and streaked rubber made by maceration of
+bark-shavings to which pieces of tree-scrap adhered.</p>
+
+<p>(6) A dark rubber, often tacky, prepared from scrap found in
+or on the ground near the base of the trees. As it is often a
+matter of weeks between any two regular collections, it is
+easy to understand why the dry rubber was more liable to be
+&#8220;tacky&#8221; than any other grade of crepe.</p></div>
+
+<p>It will have been evident to all who have acquaintance with
+these grades, as shipped from many different estates, that
+the diversity in the various shipments must have been rather
+bewildering. There appeared to be a regrettable lack of
+uniformity, even in the appearance of, say, a bark scrap rubber
+from any two estates. When, in addition to these variations,
+the further complication of condition of cleanliness is introduced,
+one may realise the difficulty attaching to the evaluation
+of these rubbers as they appeared upon the market.</p>
+
+<p>Although the foregoing paragraph is written in the past
+tense, it should be pointed out that within certain limits the
+trouble continues to exist with respect to the output of a
+great number of estates.</p>
+
+<p>In the case of many, it has been realised that the manufacturer
+does not want to buy a large number of &#8220;parcels,&#8221; all
+differing in some respect. It is probably correct to state that
+what a manufacturer requires is a big &#8220;parcel&#8221; uniform
+in<span class='pagenum'><a name="Page_127" id="Page_127">[127]</a></span>
+appearance and treatment, even though the colour may not
+be so light as that of many smaller lots. This statement is
+modified with the proviso that the rubber, no matter what its
+colour or appearance may be, must be free from dirt, grit,
+and bark.</p>
+
+<p>The difficulty of making a uniform product from several
+types of lower grade rubbers has been successfully solved on
+several estates by the preparation of a &#8220;compound&#8221; crepe
+composed of a mixture of the best lower grades in approximately
+definite proportions daily. Naturally the shade of colour of
+this compound crepe will depend largely upon the types of
+rubber employed, but as a rule it is somewhat darker than the
+highest of the types employed in the mixture. To the writers
+this seems immaterial as long as the manufacturer is offered
+a larger and more uniform lot which can be given uniform
+treatment in vulcanisation processes. Neither would it
+appear that the seller suffers any monetary loss. In point of
+fact it will be found probably that the reverse is the case.
+For instance, supposing it were decided to mix for a compound
+crepe&mdash;</p>
+
+<div class="blockquot"><p>(<i>a</i>) Naturally coagulated lump rubber.</p>
+
+<p>(<i>b</i>) Tree-scrap.</p>
+
+<p>(<i>c</i>) Bark-shavings scrap.</p></div>
+
+<p>The product would be darker in colour than (<i>a</i>) and slightly
+better than (<i>b</i>). Let it be granted that there might be a
+monetary loss on (<i>a</i>), it is probable that there would be a slight
+gain in comparison with the usual prices obtained for (<i>b</i>)
+and (<i>c</i>). Now, as a general rule, the actual percentage of crop
+made into (<i>b</i>) is appreciably less than that made into (<i>c</i>) and
+still less than (<i>b</i>) and (<i>c</i>) together. Apparently, therefore,
+there would be a margin of profit on the whole by making a
+compound crepe. It may be pointed out, on the other hand,
+that there might be expended on the manufacture of this crepe
+more time and labour, but as against this the labour of sorting
+and grading would be simplified.</p>
+
+<p>Unfortunately this process is not open to estates which do
+not possess a scrap-washer. <i>It is essential that the rubber should
+be free from grit, sand, and bark particles.</i> In the absence of a<span class='pagenum'><a name="Page_128" id="Page_128">[128]</a></span>
+scrap-washer for the cleansing of the bark-shavings, it would be
+futile to attempt to make a compound crepe containing that
+type of rubber, as one would run the risk of spoiling the whole.
+It seems certain that in course of time a scrap-washer will be
+considered as necessary a piece of machinery as an ordinary
+crepeing machine in the factories of estates having sufficient
+means. Until that time the preparation of compound crepes
+must be the privilege only of well-equipped estates, unless
+other estates can send their lower grade rubbers for treatment
+in a scrap-washer to their more fortunate neighbours.</p>
+
+<p>In previous publications a diminution in the number of
+grades of crepe rubber has been advocated, and it is gratifying
+to find that in many cases the amending grades suggested have
+been improved upon. Many estates now make only three
+grades of crepe&mdash;viz.:</p>
+
+<div class="blockquot"><p>(<i>a</i>) No. 1. From latex coagulated in the store.</p>
+
+<p>(<i>b</i>) No. 2. Compound.</p>
+
+<p>(<i>c</i>) No. 3. Earth-rubber.</p></div>
+
+<p>It will be seen that the compound crepe includes all types
+between fine pale crepe and earth-rubber. Naturally one
+could not safely recommend the inclusion of earth-rubber in
+any compound crepe, as the risk of possible &#8220;tackiness&#8221; in the
+whole would be serious. In the case of the bark-shavings
+rubber to be incorporated, it is first cleaned alone in the scrap-washer.
+Then all types are mixed together again in the scrap-washer
+in proportions ruled by the experience of the usual
+average percentages of each grade of the crop.</p>
+
+<p>Besides the estates having only three grades, there are others
+which make four&mdash;viz.:</p>
+
+<div class="blockquot"><p>(<i>a</i>) No. 1. From latex coagulated in the store.</p>
+
+<p>(<i>b</i>) No. 2. Compound, from cup washings, etc., skimmings,
+and naturally coagulated lump.</p>
+
+<p>(<i>c</i>) No. 3. Compound, from tree-scrap and bark-shavings
+rubber.</p>
+
+<p>(<i>d</i>) No. 4. Earth-scrap.</p>
+
+<p>Other variations are possible, but their number is limited,
+and they all conduce to simplification of working, and a supply
+to the market of rubber having greater uniformity.</p></div>
+
+<p><a name="Sec10_22" id="Sec10_22"></a><span class='pagenum'><a name="Page_129" id="Page_129">[129]</a></span><span
+class="smcap">Need for Increased Care with Lower Grade Rubber.</span>&mdash;In
+the ordinary procedure of estate-working there appears to be
+an undesirable variety in the style of lower grade crepes. On
+some estates an examination of these rubbers would appear to
+suggest that there need be no expenditure of care in the preparation
+or the form in which it is made. This is a great mistake.
+With the exception of the lowest grade (earth-rubber), it
+would not be unfair to state that the quality of the rubbers on
+testing should be very little inferior to the No. 1 product.
+Often, as in the case of naturally coagulated rubbers, they are
+superior in some respects to ordinary fine pale crepe. Doubtless
+manufacturers are aware of these facts, but what course is
+open to them if they find the rubber spoiled for their purpose
+by the presence of particles of sand, grit, or bark? The possible
+injury caused by these ingredients cannot be insisted upon too
+strongly, and it must be evident that great care should be
+exercised in the preparation of the lower grades of crepe.</p>
+
+<p>As to the particular form of the lower grade crepe rubber,
+one may apply the remarks made under the <a href="#Sec10_1">section</a> dealing
+with the best grades. It is common to find thin crepes, medium
+crepes, and &#8220;blanket&#8221; crepes. More often than otherwise,
+the medium and thicker crepes are prepared direct in those
+forms. It follows that they are liable to attacks of &#8220;spot&#8221;
+disease, which, however, is not easily visible in the lowest grades,
+owing to the dark colour of the rubber. Furthermore, it is
+not possible to cleanse the rubber so thoroughly if thick crepes
+are made.</p>
+
+<p><a name="Sec10_23" id="Sec10_23"></a><span class="smcap">Block Rubber.</span>&mdash;Few estates now prepare block rubber,
+which is essentially crepe rubber pressed into blocks. In the
+ordinary process the fresh coagulum is lightly rolled into thin
+crepe, which is then vacuum-dried. There are slight variations
+in the subsequent procedure. Sometimes the rubber as it
+comes from the vacuum drier is merely allowed to remain on
+racks overnight before blocking. In other instances, the
+sticky rubber from the vacuum drier is passed once or twice
+through wet, smooth rolls and hung to dry for some days. The
+dry crepe is then folded into the pressing box or cut to suit the
+size of the box. Pressure is applied for some time, and finally<span class='pagenum'><a name="Page_130" id="Page_130">[130]</a></span>
+the rubber is taken out in one homogeneous mass. Naturally
+the appearance of the block depends upon the quality of the
+parent crepe. Some block rubber is made up thick; other is
+made in slabs about 3 inches or 4 inches in thickness. With
+the latter, it should be possible, when held up to the light, to
+see the shape of a hand held between it and the source of light.</p>
+
+<p>It is possible that an erroneous idea of the strength of block
+rubber has been formed. It should only be necessary to
+point out that essentially block rubber is merely pressed crepe
+rubber. It is inconceivable that the mere action of pressing
+layers of crepe together would increase the physical quality
+of the rubber.</p>
+
+<p>The advantages which block rubber possesses are the compactness
+of the output, its ease of packing, and a saving in
+freight; but there is the disadvantage, from the consumer&#8217;s
+point of view, that extra labour is involved in the preparatory
+work of cutting up the blocks.</p>
+
+<p><a name="Sec10_24" id="Sec10_24"></a><span class="smcap">Smoked Crepe and Sheet Clippings.</span>&mdash;There appears to be
+no certain demand for any grade of smoked crepe, and probably
+all which is put into the market is really comprised of (1) clippings
+obtained from the ends of sheets, (2) sheets which have
+been malformed in machining, or (3) sheets showing the
+presence of many &#8220;bubbles.&#8221;</p>
+
+<p>As to the first class it might be explained that through
+defective rolling, thick ends or edges may be caused. These
+show signs of contained moisture when the bulk of the sheet is
+perfectly dry, and as undue delay would otherwise result these
+moist strips are trimmed and either returned to the smoke-house,
+or machined to form crepe.</p>
+
+<p>Similarly a torn or otherwise badly formed sheet, when
+brought from the smoke-house, may be made into crepe, rather
+than it should prejudice the selling price of the bulk under
+ruling conditions.</p>
+
+<p>In the same manner, although &#8220;bubbles&#8221; have no influence
+upon the quality of the rubber on vulcanisation, sheets thus
+affected are generally made into crepe.</p>
+
+<p>It cannot possibly be argued that rubber of this description
+would be in any way inferior to the best smoked sheet for<span class='pagenum'><a name="Page_131" id="Page_131">[131]</a></span>
+manufacturing purposes, but owing to the prevailing system
+of evaluation for market purposes, it is necessary to resort to
+the expedients indicated above.</p>
+
+<p>On some estates the rubber specified in the three classes
+mentioned is not made into crepe, but cut up into small pieces
+and shipped as &#8220;sheet clippings&#8221; or &#8220;sheet trimmings&#8221;&mdash;a
+procedure which would appear to be justified by a steady
+demand. In point of fact, the buyers are really obtaining a
+first-class article (except in superficial appearance) at a reduced
+price.</p>
+
+
+<p class='pagenum'><a name="Page_132" id="Page_132">[132]</a></p>
+<hr class="c25" />
+<h2><a name="Ch11" id="Ch11"></a>CHAPTER XI</h2>
+
+<h3><i>DRYING OF RUBBER</i></h3>
+
+<p><a name="Sec11_1" id="Sec11_1"></a><span class="smcap">Air-Drying of Crepe.</span>&mdash;It is still the prevailing custom to
+air-dry crepe rubbers. A few estates, it is true, have artificial
+driers installed, and in some necessary cases others will be
+erected. But in the majority of cases where money has been
+expended in building air-drying sheds, as long as it is only
+possible to ship rubber regularly air-drying is likely to remain
+in favour.</p>
+
+<p>The great drawback to air-drying is that one is so dependent
+upon the weather conditions. In favourable weather the
+rubber dries well, but in a long period of wet weather rubber
+may accumulate at an alarming rate, and the accommodation
+is sometimes severely taxed. Of course, the rate of drying
+under the best conditions is mainly dependent on the thickness
+of the crepe, and every endeavour should be made to maintain
+a thin style of preparation. If this precaution is not taken,
+the rubber is liable to recurrent attacks of &#8220;spot&#8221; disease,
+and one&#8217;s troubles are very much augmented. This is a
+disability to which rubber treated in artificial driers is not
+liable. Still, air-dried rubber can be made equal, if not
+superior, in appearance to pale rubbers prepared by other
+processes.</p>
+
+<p>For the lowest grades of crepe air-drying is always likely to
+remain the only method, as it would be extremely unsafe to
+submit them to heat.</p>
+
+<p>It is noted in ordinary practice that the rate of drying on
+different estates, for the same type of rubber, may vary widely.
+Naturally the construction of the house has a great effect, and
+this subject will receive attention in a <a href="#Ch15">subsequent chapter</a>.</p>
+
+<p>Similarly the position of the drying-shed exerts an important
+influence, and the erection of the building in low-lying sur<span class='pagenum'><a
+name="Page_133" id="Page_133">[133]</a></span>roundings
+is always calculated to prolong the drying period
+appreciably. Incidentally this means that the building must
+be larger than a normal rate of drying would otherwise demand.</p>
+
+<p>The combination of a poor type of drying-house, a low-lying
+situation, and a prolonged wet season, might render it advisable
+to abandon the air-drying of high grade crepes in favour of
+artificial drying.</p>
+
+<p><a name="Sec11_2" id="Sec11_2"></a><span class="smcap">Artificial Driers for Crepe.</span>&mdash;It is more common to find
+artificial driers in use in Ceylon than in Malaya, possibly
+because these driers have been in use in Ceylon for other
+products. Some time ago the question of installing artificial
+driers received the serious attention of a number of estates in
+this country, chiefly on account of the incidence of fungoid and
+bacterial diseases in crepe rubber. The simple treatment
+for the prevention of these diseases is to get the rubber dry in
+the shortest possible space of time. In most cases it is found
+sufficient to roll crepe thin for air-drying in order to prevent
+the appearance of coloured spots. It is found, however, that
+some drying-houses are so badly planned and constructed,
+that quick drying under even the best of conditions is a practical
+impossibility. Cases have been known in which the disease
+may disappear almost entirely during a period of freedom from
+rain, only to recur as soon as wet weather sets in again. There
+can be no doubt that, on the whole, the number of cases of
+&#8220;spot&#8221; disease is on the decline; but equally it is certain that
+a very few estates will always be liable to outbreaks as long as
+drying is attempted in existing houses. For these reasons it
+is a poor policy to temporise, and the only sound policy in
+extreme cases would be to give up ordinary air-drying in
+favour of some method of artificial drying. As regards the
+majority of estates preparing pale crepe for various reasons, it
+is not expected that any will instal artificial driers. Money
+has been expended in elaborate buildings which certainly
+do the work for which they were designed. As long, therefore,
+as the accommodation is sufficient, and regular shipments
+are the rule, it is expected that ordinary air-drying will still
+remain the general practice.</p>
+
+<p>Of the better-known artificial driers, there are only three<span class='pagenum'><a name="Page_134" id="Page_134">[134]</a></span>
+which merit serious consideration in these pages. They are
+the vacuum driers, the Colombo Commercial Company&#8217;s
+hot-air drier, and the Michie-Golledge process.</p>
+
+<p><a name="Sec11_3" id="Sec11_3"></a><span class="smcap">Vacuum Driers.</span>&mdash;The vacuum drier is so well known that
+only a brief description need be given. It consists of a
+chamber heated by steam pipes and capable of having the
+contained air and moisture withdrawn by a pump. This
+description sounds very simple, and in practice the operation
+of vacuum drying is really a simple one, and can well be
+entrusted to an intelligent coolie under efficient supervision.
+Indicators are fitted which show the vacuum pressure and the
+pressure of steam in the heating pipes which travel underneath
+horizontal slabs upon which trays may be placed. Still,
+in spite of the apparent simplicity of the process, there would
+appear to be a number of little details which, if overlooked,
+prove to be factors influencing the result to a considerable
+degree. Thus it is not uncommon to find complaints that
+the rubber is not dry when packed. The writers have seen
+rubber taken from a vacuum drier still containing a visible
+quantity of moisture. One would have imagined that continuous
+working of the drier would give the experience necessary
+to obtain dry rubber, but, apparently, such is not the case in a
+number of instances. Elaborate instructions are given by the
+makers, but often they are more honoured in the breach than
+in the observance. Really, there are only two points to bear
+in mind:</p>
+
+<div class="blockquot"><p>(1) That the rubber must be fairly thin.</p>
+
+<p>(2) That the temperature be not allowed to rise too high.
+Some makers advise 140&deg; F. as a maximum, but no harm
+results from a temperature of 150&deg; to 160&deg; as long as the
+interval is not prolonged.<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a></p></div>
+
+<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a
+href="#FNanchor_11_11"><span class="label">[11]</span></a> These figures refer to temperatures recorded by thermometers
+placed in the folds of the rubber.</p></div>
+
+<p>These two points presume that the vacuum drier is true to
+its name, and that one can obtain a maximum steady pressure.
+The machines are so well made now that no drier should be
+taken over from those responsible for its erection unless it can
+show a vacuum pressure of 28 inches within fifteen minutes of<span class='pagenum'><a name="Page_135" id="Page_135">[135]</a></span>
+starting the pump; and with the pump stopped, there should
+not be a greater fall in pressure than 1 inch within ten minutes
+after stopping the pump.</p>
+
+<p>One of the most frequent sources of error is the control of
+steam pressure which is responsible for the temperature of the
+drier. It is quite unnecessary and unwise to maintain any
+steam pressure once the drying is well under way. All that is
+necessary is to heat the chamber well, with a steam pressure of
+5 lbs., before inserting the rubber. As soon as the maximum
+vacuum pressure has been obtained, steam should be shut off
+from the heating pipes, and it will be found that the temperature
+is well maintained throughout the operation with a rise of ten
+to twenty degrees at the end. If the drier is working at a
+vacuum pressure of 28 inches, and if the crepe has been
+prepared thin enough, the rubber should be quite dry within
+two hours. Should the operation have to be extended to two and
+a half hours at 28 inches vacuum pressure, it is a sign that the
+crepe is too thick. On such occasions it is often noticed that
+these thicker crepes are not thoroughly dry, having moist
+spots enclosed in them. On re-rolling, these moist patches
+become easily visible, and are a source of great annoyance,
+inasmuch as they take quite a long time to dry out.</p>
+
+<p>As mentioned before, the crepe for vacuum drying should be
+thin. There is no necessity to give it a superfine finish, and the
+presence of small holes is quite permissible, as they disappear
+on subsequent re-rolling. The thin crepe may be folded loosely
+to the length (or breadth) of the tray several times, but in no
+other way can the drier be expected to perform its work satisfactorily.
+A case was noted in which thin crepe was excellently
+prepared, and four or five layers were rolled together
+for vacuum drying. Naturally this mode of procedure does not
+give the drier a fair chance, and it would be ridiculous to judge
+vacuum drying on the results. After two and a half hours at a
+temperature of 145&deg; F. the rubber appeared to be only about
+three parts dry, and the subsequent air-drying extended well
+into a fortnight.</p>
+
+<p>It is the common practice to screw up the door of the chamber
+as tightly as possible. As a rule it is found in course of time<span class='pagenum'><a name="Page_136" id="Page_136">[136]</a></span>
+that the obtainable maximum vacuum pressure decreases.
+This may be attributed solely to the forcible screwing up of the
+door. Around the inside edges of the door are strips of rubber
+compound, the function of which is to form a tight joint. Should
+the door be screwed up too tightly, these strips become deformed
+in course of time, and slight leaks occur. It should be pointed
+out that it is only necessary to screw up the door at the beginning
+of the operation. When the vacuum has been obtained, the screw
+pressure may be released, as the atmospheric pressure outside
+the chamber is more than ample to keep the door in a close
+fitting position. This will be obvious from the fact that the
+difference in pressure between the inside and the outside of
+the door amounts to, say, 28 inches atmospheric pressure&mdash;<i>i.e.</i>,
+nearly 14 lbs. per square foot. By slackening the screw handles,
+therefore, as soon as the indicator shows the maximum working
+vacuum pressure, the life of the door joints may be prolonged,
+and the drier will remain efficient for a longer time.</p>
+
+<p>A careful consideration of the question of temperature leads
+one to the conclusion that the practice of placing a thermometer
+through the roof of the chamber does not enable one to determine
+the temperature correctly. In the same way a thermometer
+suspended behind the observation window cannot indicate
+the temperature of the rubber, as in both of these positions
+the thermometer must be influenced by radiation from the walls
+of the chamber. The only position in which the correct temperature
+could be indicated is between the folds of crepe.
+This can be arranged easily so as to enable one to read the
+temperature from the observation window.</p>
+
+<p><a name="Sec11_4" id="Sec11_4"></a><span class="smcap">Colombo Commercial Company&#8217;s Drier.</span>&mdash;The drier of the
+Colombo Commercial Company consists in principle of a
+number of small chambers or units in which crepe rubber is
+placed, and through which hot air is passed. As in the case of
+vacuum drying, a great deal depends upon the preliminary
+treatment of the rubber. If the crepe is not rolled thin enough
+drying will be unduly prolonged, with a possibility that the
+rubber will become tacky. The temperature usually obtained
+is about 150&deg; F., and if the rubber is thin the production of
+an installation of two chambers should be at the rate of 1 lb.<span class='pagenum'><a name="Page_137" id="Page_137">[137]</a></span>
+of dry rubber per minute. The usual period of drying is
+under two hours. One advantage which this drier has over the
+vacuum drier is that the chamber can be opened at any time
+for a short period to withdraw or insert trays. The thin crepe
+is folded several times, as in the case of vacuum-drying.</p>
+
+<p>Figures obtained from the actual working of a drier in
+Ceylon are given below:</p>
+
+<table summary="Table p137">
+
+<tr>
+<td colspan="7" class="center bt br bb"><span class="smcap">Chamber 1.&mdash;Temperature 160&deg;-180&deg;F.</span></td>
+<td rowspan="2" class="center bt bb"><span class="smcap">Chamber 2.&mdash;<br />Temperature<br />150&deg;-165&deg;F.</span></td>
+</tr>
+
+<tr>
+<td class="center bb br"><i>No. of<br />Tray.</i></td>
+<td colspan="2" class="center br bb"><i>Drying<br />Period.</i></td>
+<td colspan="2" class="center br bb"><i>Weight of<br />Wet Rubber.</i></td>
+<td colspan="2" class="center br bb"><i>Weight of<br />Dry Rubber.</i></td>
+</tr>
+
+<tr>
+<td class="left br">&nbsp;</td>
+<td class="center fsize80">Hrs.</td>
+<td class="center fsize80 br">Mins.</td>
+<td colspan="2" class="center fsize80 br">Lbs.</td>
+<td colspan="2" class="center fsize80 br">Lbs.</td>
+<td class="left">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">1</td>
+<td class="right" style="padding-right: .5em;">1</td>
+<td class="right br" style="padding-right: .5em;">22</td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">7</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">Worked similarly</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">2</td>
+<td class="right" style="padding-right: .5em;">1</td>
+<td class="right br" style="padding-right: .5em;">42</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">to No. 1. Yielded</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">3</td>
+<td class="right" style="padding-right: .5em;">1</td>
+<td class="right br" style="padding-right: .5em;">57</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">in 2 hrs. 23 mins.</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">4</td>
+<td class="right" style="padding-right: .5em;">1</td>
+<td class="right br" style="padding-right: .5em;">57</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">70<span class="enum">3</span>&#8260;<span class="denom">4</span> lbs. dry rubber,</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">5</td>
+<td class="right" style="padding-right: .5em;">1</td>
+<td class="right br" style="padding-right: .5em;">57</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;">&nbsp;</td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">5</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;"><span class="enum">3</span>&#8260;<span class="denom">4</span></td>
+<td class="left">from 87<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. wet</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">6</td>
+<td class="right" style="padding-right: .5em;">1</td>
+<td class="right br" style="padding-right: .5em;">57</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">rubber.</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">7</td>
+<td class="right" style="padding-right: .5em;">2</td>
+<td class="right br" style="padding-right: .5em;">0</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">8</td>
+<td class="right" style="padding-right: .5em;">2</td>
+<td class="right br" style="padding-right: .5em;">0</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">9</td>
+<td class="right" style="padding-right: .5em;">2</td>
+<td class="right br" style="padding-right: .5em;">11</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">6</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">5</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">10</td>
+<td class="right" style="padding-right: .5em;">2</td>
+<td class="right br" style="padding-right: .5em;">11</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right br" style="padding-right: 1.25em;">11</td>
+<td class="right" style="padding-right: .5em;">2</td>
+<td class="right br" style="padding-right: .5em;">11</td>
+<td class="right" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right br bb" style="padding-right: 1.25em;">12</td>
+<td class="right bb" style="padding-right: .5em;">2</td>
+<td class="right br bb" style="padding-right: .5em;">18</td>
+<td class="right bb" style="padding-right: 0; padding-left: 1em;">7</td>
+<td class="left br bb" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right bb" style="padding-right: 0; padding-left: .75em;">6</td>
+<td class="left br bb" style="padding-left: 0; padding-right: .5em;">&nbsp;</td>
+<td class="left bb">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="bb br">&nbsp;</td>
+<td colspan="2" class="bb br">&nbsp;</td>
+<td class="right bb" style="padding-right: 0; padding-left: 1em;">88</td>
+<td class="left br bb" style="padding-left: 0;"><span class="enum">1</span>&#8260;<span class="denom">2</span></td>
+<td class="right bb" style="padding-right: 0; padding-left: .75em;">80</td>
+<td class="left br bb" style="padding-left: 0; padding-right: .5em;"><span class="enum">3</span>&#8260;<span class="denom">4</span></td>
+<td class="left bb">&nbsp;</td>
+</tr>
+
+</table>
+
+<p>It will be seen, therefore, that the drier had an output in
+2 hrs. 23 mins. of 141<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs., which is at the rate of 1 lb. per
+minute approximately.</p>
+
+<p>As the rubber leaves the driers it resembles vacuum-dried
+rubber in being surface-sticky. This stickiness is only
+temporary, and is got rid of by passing the crepe through wet
+rolls. Opinions differ as to when this rolling should be given.
+On some estates the rubber is only allowed to cool a little
+before passing through the rolls; on others it is given a day
+or so before rolling. The methods of rolling also differ.
+In some factories the rubber has been cut to lengths before
+drying, and these lengths are merely rolled together by simple
+pressure. Other estates prefer to re-macerate the crepe while
+still fairly warm and soft. It is probable that little harm, if any,<span class='pagenum'><a name="Page_138" id="Page_138">[138]</a></span>
+results from this re-maceration while the rubber is soft,
+as it is more easily worked in this condition. The thick
+rubber is then generally hung for a few days to air-dry before
+packing. As most of the moisture taken up by the dry rubber
+is surface moisture, three or four days is usually found ample
+for air-drying.</p>
+
+<p><a name="Sec11_5" id="Sec11_5"></a><span class="smcap">Michie-Golledge System.</span>&mdash;The Michie-Golledge system
+comprises a process of preparation and drying. The latex is
+diluted with two, three, or four volumes of water and coagulated
+with acid in a vessel which is rotated with a churning motion.
+In this cylinder there are curved and fixed blades. The revolving
+cylinder and its ribs force the latex against the curved
+blades so as to cause an eddy in the middle of the machine.
+Here the rubber coagulates and accumulates, the remaining
+liquor whirling round outside the blades. It can be imagined
+that with such dilute latex, the coagulum is very soft and
+spongy. This soft mass is passed through a machine which
+cuts it into &#8220;worms&#8221; about <span class="enum">3</span>&#8260;<span class="denom">16</span> inch in section. These are
+placed upon wire trays and dried by means of hot air. The
+&#8220;worms&#8221; when dry are re-macerated and built up into medium
+and thick crepes. The colour of the rubber prepared by this
+process is usually very good. When treated in a Colombo
+drier the &#8220;worms&#8221; usually require about two hours to dry,
+so that crepe rubber may be packed at latest on the fourth
+or fifth day, as in the case of vacuum-dried rubber.</p>
+
+<p><a name="Sec11_6" id="Sec11_6"></a><span class="smcap">Rate of Air-Drying of Crepe Rubber.</span>&mdash;In spite of the
+facts that some estates have been making thin pale crepes for
+years, and that so much has been written concerning the
+preparation of this grade of rubber, one occasionally meets
+with a case in which an estate seems to be unable to prepare thin
+pale crepe, or if it does the period of drying is much longer
+than obtains on most estates.</p>
+
+<p>Again, when cases of infection by spot disease in fairly thin
+crepes are submitted, it is usually found that the particular
+crepes are of that type which, though fairly thin, show whitish
+spots of moisture when the bulk of the rubber is nearly dry.
+This type of crepe is to be noted for the excessive period of
+drying in comparison with other crepes of equal thinness.<span class='pagenum'><a name="Page_139" id="Page_139">[139]</a></span>
+It has been advanced elsewhere<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a
+href="#Footnote_12_12" class="fnanchor">[12]</a> that a factor of the most
+considerable importance in the rate of drying of crepe rubber
+is the type of drying-house and its situation. This accounts
+very largely for observed differences in the rate of drying of
+thin crepes on different estates. Yet even where two drying-houses
+may be of the same type, and the situations may be
+comparable, one still observes that one thin crepe dries more
+quickly than another. It has been remarked also that a thin crepe
+in one old drying-house dries in a shorter period than a similar
+crepe in another more modern house, although the methods
+of coagulation and preparation exhibit no apparent diversity.
+In all these conflicting cases allowance is made for the weather
+conditions, and the observed differences seem to be inexplicable.
+It has always been the opinion of the writers that the
+actual rolling of the rubber plays an important part in determining
+the rate of drying of crepe, apart from the question of
+thinness; and it seemed possible that this factor would account
+for the discrepancies noted above, either partially or wholly.</p>
+
+<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a
+href="#FNanchor_12_12"><span class="label">[12]</span></a> &#8220;Preparation of Plantation Rubber,&#8221; Morgan, 1913, chapters
+xii. and xiii.</p></div>
+
+<p>With a view to determining to what degree the drying of
+crepe rubber was hastened by the extent to which the rubber
+was rolled, experiments were made. It was hoped, also, that
+some idea would be gained of the particular stage in crepe
+rolling which had the greatest effect upon the rate of drying.
+In preparing crepe in the estate in the ordinary way the coagulum
+is passed through three sets of rollers, and the stages
+may be described as:</p>
+
+<div class="blockquot"><p>(1) Rough rolling.</p>
+
+<p>(2) Medium rolling.</p>
+
+<p>(3) Smooth rolling.</p></div>
+
+<p>In the first the coagulum is broken down by passing through
+the machines until a thick rough crepe is formed. This passes
+to the intermediate rollers, where it is worked down to a medium
+crepe. The rubber finally goes to the smooth running at
+approximately even speeds. Passing through these a number
+of times it emerges as a thin uniform crepe, free from &#8220;<span
+class='pagenum'><a name="Page_140" id="Page_140">[140]</a></span>lumpiness&#8221;
+and free from holes, which should dry in from ten to
+twelve days.</p>
+
+<p>In the experiment the rubber was passed through the
+machines with varying frequency, the number of times in each
+machine being progressively increased, while the working on
+the other machines remained constant.</p>
+
+<p>It was determined that the rate of drying was affected only
+by the extent to which the crepe was worked in the smooth
+rolls. The less often the rubber passed through these rolls,
+the slower the rate of drying. Beyond a limit in the other
+direction, increased rolling did not reduce the period of drying.
+It follows, therefore, that crepes which have a good thin finish
+should dry in a minimum period.</p>
+
+<div class="figcenter"><a name="Fig44" id="Fig44"></a><img src="images/illo157.png" alt="Drying Graph. Pale Crepe (Thin)" />
+<p class="caption"><span class="smcap">Drying Graph. Pale Crepe (Thin).</span></p></div>
+
+<p><a name="Sec11_7" id="Sec11_7"></a><span class="smcap">When does
+Air-Drying take place?</span>&mdash;Experiments<a name="FNanchor_13_13"
+id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a>
+were conducted with a view to discovering, if possible, the rate
+at which crepe rubber dries, and the extent of drying during
+the night under weather conditions such as prevail ordinarily
+in Malaya. It is to be remembered that, during the day, most
+drying-houses are fairly open and that the temperature ranges
+from about 88&deg; F. in the lower rooms to over 100&deg; in the upper
+rooms (near the roof) when the sun shines. At night, however,
+there is usually a decided drop in the temperature, and unless<span class='pagenum'><a name="Page_141" id="Page_141">[141]</a></span>
+it is a very clear night the air is generally saturated with moisture.
+In addition the drying-house is closed as thoroughly
+as possible, and we should expect the atmosphere of the house
+to be laden with moisture from the wet and drying rubber.
+It would be a just inference, therefore, that the rate of drying
+during the night would be much less than the rate of drying
+during the day, and the results of experiments confirm this
+very fully. One was hardly prepared, however, to find that,
+under certain circumstances and at a certain stage, the amount
+of drying is nil; not only so, but it was found under certain
+conditions that the amount of drying which took place was
+negative&mdash;<i>i.e.</i>, the rubber weighed slightly more when taken
+out in the morning than it had weighed the previous afternoon.</p>
+
+<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a
+href="#FNanchor_13_13"><span class="label">[13]</span></a> Rubber Growers&#8217; Association, Malaya Local Report, No. 2, 1914.</p></div>
+
+<p><a name="Sec11_8" id="Sec11_8"></a><span class="smcap">Crepe may Increase in Weight.</span>&mdash;As an instance of the
+kind of result obtained a graph is here given of the rate of drying
+of a batch of pale crepe. This was hung to dry in the top
+room of a drying-house in which rubber ordinarily dries quickly.
+The rubber was hung in a good position, with the bulk of
+output, near a window which was open for some time during
+the day. In order to restrict the day interval of drying to the
+actual period in which the sun was likely to be in evidence,
+the day was taken to begin at 8 a.m. and end at 4 p.m., the night
+interval covering the remaining sixteen hours. Thus the night
+interval was twice as long as the period of day drying. The
+lengths of crepe were weighed carefully at 8 a.m. and 4 a.m.,
+and the average of the several weights was plotted in a graph.</p>
+
+<p>The weights are placed vertically and the duration of drying
+horizontally. It will be seen that the rubber was quite dry
+and fit for packing on the sixth day, as far as could be judged
+in the usual way by casual inspection. Peculiarly enough at
+this time it weighed slightly more than had been registered on
+the fourth and fifth days, but the difference did not amount
+to more than about 0&middot;4 per cent. In examining the graph it
+should be borne in mind that the steeper the slope of the curve
+downwards the quicker the rate of drying, and that when the
+curve takes an upward direction there is an addition of moisture
+instead of abstraction. It will be noted that when drying
+takes place the slopes more nearly approximating the vertical<span class='pagenum'><a name="Page_142" id="Page_142">[142]</a></span>
+represent the extent of day drying, and that often the night
+drying is represented either by a very flat curve or even by
+an upward curve which shows the addition of moisture. A
+striking feature of the experiment is shown by the rapidity
+with which drying takes place during the first few days and the
+comparative slowness with which the remaining moisture is
+got rid of. Thus, from the graph, it may be calculated that
+about 80 per cent. of the total moisture content was lost in the
+first two days, and over 93 per cent. in two and a half days.
+Yet three days had to elapse before the remaining 7 per cent.
+of total moisture was lost&mdash;<i>i.e.</i>, before the rubber was judged
+to be ready for packing. It will be seen that after this stage
+had been reached the rubber alternately lost and gained in
+weight, with a tendency to increase. This increase was attributed
+to the presence of surface moisture after hanging overnight,
+when the rains had become frequent. Some light is
+thus shed upon a subject which has puzzled both shippers and
+receivers of crepe rubber.</p>
+
+<p><a name="Sec11_9" id="Sec11_9"></a><span class="smcap">Differences in Weight.</span>&mdash;It will be obvious that if rubber
+is allowed to hang after becoming dry, and is taken down,
+packed, and weighed in the early morning, it will weigh more
+than when it reaches a drier climate. The loss in weight
+under such circumstances might amount to even 1 per cent.
+It may seem to some an unnecessary refinement to introduce,
+but it would appear from the graph that rubber should be
+packed for preference in the afternoon if the weights are to be
+more nearly correct.</p>
+
+<p>It is extremely singular to note how quickly the curve
+changes its slope after the major portion of the moisture has
+evaporated, and it will be very plain that in the last stages any
+decrease in weight during the day would appear to be counterbalanced,
+or more than counterbalanced, by the addition of
+moisture during the night. It may be pointed out, however,
+that this increase in weight during the later stages of drying
+of pale crepe is mainly, if not altogether, due to surface moisture.
+The chief point of interest is the fact that in the case of thin
+pale crepe, quite 80 per cent. of the total moisture content is
+lost during the first two or three days, and that, owing to the<span class='pagenum'><a name="Page_143" id="Page_143">[143]</a></span>
+negative influence of the night atmosphere, the final drying is
+delayed. It will be understood that the foregoing results
+applied to thin pale crepe. Thin lower-grade crepes appeared
+to dry at more uniform rates, but the differences between the
+rates of drying at night and during the day were similarly
+notable.</p>
+
+<p><a name="Sec11_10" id="Sec11_10"></a><span class="smcap">Aids to Normal Air-Drying.</span>&mdash;These experiments were
+undertaken in a drying-house, favourably situated for rapid
+drying, in which the average period of drying for thin crepes
+is nine days. It is easy to imagine that the condition of affairs
+as revealed would be much exaggerated in a drying-house
+situated on low-lying ground and surrounded by trees. In
+extreme cases of this nature the use of large fans and heating
+pipes has been advocated. It is believed that in some cases
+these installations have given satisfaction, but that in others
+the degree of improvement obtained has not been in economic
+proportion to the outlay incurred.</p>
+
+<p><a name="Sec11_11" id="Sec11_11"></a><span class="smcap">Smoke-Curing of Sheet Rubber.</span>&mdash;It will have been evident
+that one of the disadvantages of air-drying sheet is the incidence
+of moulds. Now it is found that moulds should not develop
+in smoke-curing; and if they do, then the smoke-curing has been
+insufficient or inefficient. The difference in the drying period
+also is a strong argument in favour of smoke-curing, so that all-round
+it is seen that there are many valuable advantages to
+be gained by smoke-curing sheet in comparison with air-drying,
+and no disadvantages.</p>
+
+<p>The manipulation of the rubber, after it leaves the marking
+rolls and preparatory to smoke-curing, has been discussed in
+<a href="#Ch9">Chapter IX</a>. It is sufficient only to allow adequate time for
+furnace water to drip from the sheets before transferring them
+to the smoke-house. As it is the general rule to roll sheet
+rubber in the morning, this arrangement fits in very well. The
+furnaces of the smoke-house are usually extinguished as soon
+as the sun is well risen, and the rest of the day is occupied
+in sorting dry sheets, etc. Towards noon the day&#8217;s wet sheets
+should have been admitted, and smoking may be commenced
+as soon as the sun is well in the west&mdash;say, at half-past four
+o&#8217;clock or earlier.</p>
+
+<p><span class='pagenum'><a name="Page_144" id="Page_144">[144]</a></span>It used to be the custom on a few estates to smoke during
+the daytime and to discontinue smoking at night. As the night-air
+in Malaya is usually heavily laden with moisture, it will be
+plain that such a policy was a topsy-turvy one. It is vastly
+more reasonable to smoke-cure at night; usually the heat of the
+sun during the day is quite sufficient in itself to promote the
+drying of rubber; but there is no reason why smoking should
+not be carried on in the daytime in wet weather, should it be
+found expedient to do so.</p>
+
+<p><a name="Sec11_12" id="Sec11_12"></a><span class="smcap">Recording Instruments.</span>&mdash;During the night the care of the
+smoke-houses is usually in the hands of natives, except for
+occasional surprise visits from a European superintendent.
+To all acquainted with the ways of the native it must be plain
+that means must be provided for the checking of the temperatures
+attained in the smoke-house. Ordinary thermometers
+are quite unsuitable, and even thermometers registering
+maximum and minimum temperatures are of little avail,
+inasmuch as they record only the degree of heat attained at a
+particular moment, and do not indicate any period during which
+a particular temperature was maintained.</p>
+
+<p>It is evident that something more informative is required.
+There are many types of suitable recording instruments or
+&#8220;pyrometers,&#8221; some of which can be electrically connected,
+so as to cause the ringing of a bell, placed in the superintendent&#8217;s
+office or house, on the attainment of a certain temperature.
+The type best known in estate practice is that named the
+&#8220;Thermograph,&#8221; in which a pen traces a curve or graph on
+a plotted piece of paper carried by a rotating cylinder which is
+actuated by clockwork. Such instruments can be purchased
+through most of the local firms dealing in estate supplies.
+From experience it can be asserted that, given intelligent attention,
+these instruments yield very satisfactory results. The
+apparatus should not be placed always in one position in the
+smoke-house, but should be moved frequently so as to obtain
+information regarding the distribution of heat.</p>
+
+<p><a name="Sec11_13" id="Sec11_13"></a><span class="smcap">Temperature of Smoke-Curing.</span>&mdash;In the question of temperature
+of drying, it is well to be as strict as possible; not
+that any great harm will result from a rise of 10&deg; above that<span class='pagenum'><a name="Page_145" id="Page_145">[145]</a></span>
+recommended, but because the higher the temperature recorded
+the larger the fires must have been, and consequently the more
+real danger there was of the store becoming ignited. It has
+been shown<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14"
+class="fnanchor">[14]</a> that the temperature giving the maximum benefit
+of drying and quality was found experimentally to be
+rather above the temperature usually prescribed for smoke-houses,
+but in the experimental work there was no danger
+from fire.</p>
+
+<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span
+class="label">[14]</span></a> &#8220;Preparation of Plantation Rubber,&#8221; Morgan, 1913, chapter x.</p></div>
+
+<p>The figure given in previous publications as a maximum
+working temperature for smoke-houses was 110&deg; F., but certainly
+the temperature may be as high as 130&deg; if it is considered
+safe to allow fires to be so arranged. One or two estates are
+known to work at temperatures of 130&deg; F. and over, in spite of
+the recommendations of the writers. If those estates care to
+risk it they may do so, with increased rapidity of drying;
+but no responsibility can be taken for whatever may happen
+in smoke-houses where the temperature is allowed to remain,
+as in one case, at 160&deg; F. Naturally the range of temperature
+is strictly limited by the properties of the substance to be
+treated, and with a substance such as rubber it would be far
+better to err on the side of caution than to risk damage to such
+a commodity, apart from the consideration of the possible
+destruction of the building.</p>
+
+<p><a name="Sec11_14" id="Sec11_14"></a><span class="smcap">Period of Drying.</span>&mdash;Considerable differences are noted in
+the periods of drying on various estates; but, as there is more
+than one factor influencing the results, it is not easy at first
+to find why these differences should exist. Really there are
+three factors:</p>
+
+<div class="blockquot"><p>(1) Relative thickness of rubber.</p>
+
+<p>(2) Extent and quality of rolling.</p>
+
+<p>(3) Temperature of drying.</p></div>
+
+<p>It is presumed that the smoke-houses are identical in type
+and efficiency, and that smoking is in force for the same length
+of time each day. There need be no discussion of these
+points; the effect of each is so obvious. The thinner the sheet,
+the quicker the rate of drying; the better the sheet has been<span class='pagenum'><a name="Page_146" id="Page_146">[146]</a></span>
+rolled, the shorter the period of drying; the higher the temperature,
+the more rapid the drying.</p>
+
+<p>It has been shown in <a href="#Ch9">Chapter IX.</a> that the condition of the
+sheet after rolling depends primarily upon the standard of
+dilution of the latex and the original thickness of the coagulum.
+If these factors are correctly controlled, the rolling should give
+a sheet which is fairly soft and porous&mdash;<i>i.e.</i>, it should not have
+been subjected to such pressure as to make it both thin and
+hard. An average sheet of rubber which has been well rolled
+should be smoke-dried at a temperature of 120&deg; F. in about
+ten days. If sheets take appreciably longer to dry, then the
+three foregoing factors must be examined.</p>
+
+<p>On the other hand, it is often found that thin sheets made
+from very dilute latex dry so quickly that they are considered to
+be fully smoke-cured in from five to seven days. It frequently
+happens in such cases, however, that the smoking is insufficient,
+and by the time the rubber reaches home it has begun to show
+signs of surface moulds. It is evident, therefore, from this
+discussion that:</p>
+
+<div class="blockquot"><p>(1) If smoked sheet develops surface moulds within a short
+period after smoking, the duration of curing has been insufficient,
+or the quality of the smoking is at fault.</p>
+
+<p>(2) The actual time taken to smoke-dry rubber may be
+insufficient to smoke-cure it.</p>
+
+<p>(3) The rate of drying of smoked sheet depends upon&mdash;</p>
+
+<div class="blockquot"><p>(<i>a</i>) The relative thickness of the rubber.</p>
+
+<p>(<i>b</i>) The preliminary treatment of rolling.</p>
+
+<p>(<i>c</i>) The temperature of the smoke-house, and</p>
+
+<p>(<i>d</i>) The type of smoke-house used. This point will
+be treated in a <a href="#Sec15_8">subsequent chapter</a>.</p></div></div>
+
+<p><a name="Sec11_15" id="Sec11_15"></a><span class="smcap">Fuels for Smoking.</span>&mdash;The general idea formerly held was
+that the beneficial effects of smoking were to be attributed to
+the constituents of the smoke, and chiefly the creosotic substances.
+This is not now the opinion of the writers, who
+attribute the effect largely to the temperature of drying and
+constituents of the smoke other than creosotic substances.
+There can be no doubt that the presence of creosotic bodies is
+responsible largely for the absence of moulds and the <span class='pagenum'><a name="Page_147" id="Page_147">[147]</a></span>existence
+of the typical odour, but it is becoming increasingly
+known that the employment of substances rich in creosote is
+not required or desirable.</p>
+
+<p>Estates used to be put to considerable expense in the purchase
+of &#8220;bakau&#8221; (a mangrove timber rich in creosote and creating
+much heat), under the idea that it was the best material and
+almost indispensable. Most estates now restrict themselves
+to the consumption of timber obtained from their own areas.
+Thinning-out programmes are largely responsible for the
+supply, but the local authorities are much concerned regarding
+future supplies; and consideration has been given in some
+quarters to the question of the development of quick-growing
+trees on estates with a view to safeguarding the future. This
+seems to be desirable, as it is difficult to imagine that the place
+of timber can be taken by any other material in the smoke-curing
+of rubber. Unless some such precautions are taken
+it is not difficult to predict that, in course of time, some estates
+will be able to continue the preparation of smoked sheets only
+at considerable expense in obtaining suitable fuel from a
+distance.</p>
+
+<p>It is not true that <i>any kind of timber</i> is suitable as a fuel to be
+used in a smoke-house. All timbers are suitable, either alone
+or in mixture with others, provided that the wood is not too
+green.</p>
+
+<p>Naturally an absolutely dead and crumbling wood will
+smoulder, but does not develop sufficient smoke. A green
+timber will give an acrid and moist smoke, but demands the
+consumption of a certain amount of dry timber in addition if
+it is to be used.</p>
+
+<p>Rubber-tree prunings and sawn rubber trees obtained by
+thinning-out may be used in mixture with dead wood, provided
+the logs are stacked to dry in the sun for some weeks before use.
+If the timber is too green, steam is formed as well as smoke, and
+the sheets of rubber may have a moist surface glaze.</p>
+
+<p><a name="Sec11_16" id="Sec11_16"></a><span class="smcap">Sun-Drying Sheet Rubber.</span>&mdash;Among the first curious sights
+which impress the visitor or newcomer to this country is
+the spectacle of sheet rubber hanging in the sun on native
+holdings. From what one has learned of the extraordinary<span class='pagenum'><a name="Page_148" id="Page_148">[148]</a></span>
+care which must be exercised in all the processes of rubber
+preparation, one fails to understand how such rubber reaches
+the market without becoming tacky. That some of it does
+become slightly tacky is certain, but on the whole native
+rubber, though crudely prepared, is usually sound. The
+native idea of giving sheet rubber a preliminary drying in the
+sun is to hasten the total period of drying. That the period
+is curtailed would seem to be the case, but it is open to doubt,
+as the effect of sun-drying, if unduly prolonged, is to create
+a thin surface film of dry rubber which retards the drying
+of the rubber below the surface. Working with wet crepe
+rubber, the writer found that, to all external appearances, there
+was no effect upon the rubber when it was allowed to sun-dry
+for four or five hours. With periods of from six to ten hours
+the crepe becomes slightly sticky, chiefly on that portion
+across the support. When removed to the air-drying house
+this tackiness developed further, and the rubber, on the line
+of support, became so weak that it stretched and broke.</p>
+
+<p>Reasoning by analogy, it would appear that no apparent
+harm would result to sheet rubber from sun-drying for periods
+up to four or five hours. From experience (see <a href="#Ch9">Chapter IX.</a>),
+not the slightest ill-effect is found to result from the short
+interval of preliminary drying or dripping practised on many
+estates preparatory to smoke-curing.</p>
+
+<p><a name="Sec11_17" id="Sec11_17"></a><span class="smcap">Artificial Driers for Sheet Rubber.</span>&mdash;It is understood
+that when vacuum driers were first applied to the drying of
+rubber it was thought possible to dry sheet rubber in this
+way. The practice was found to be impossible, as the length
+of time required and the temperature were responsible for
+the destruction of the form of the rubber; it became tacky
+and semi-liquid.</p>
+
+<p><span class="smcap">The &#8220;Chula&#8221; Drier.</span>&mdash;Although several suggestions of
+devices for artificially drying sheet have been made, only one
+is known to be in use at the present time. In the original form
+this was used for drying other tropical products. It consists
+of a large iron chamber, in which are several compartments
+divided by means of baffle-plates. At one end there is a small
+furnace and, by means of a fan, smoke and hot air are drawn<span class='pagenum'><a name="Page_149" id="Page_149">[149]</a></span>
+through the compartments. Owing to the temperature
+attained (140&deg; to 160&deg; F.) sheet rubber cannot be completely
+dried in the chambers, and is, as a rule, only treated in
+this manner for one or two days. Drying is then completed
+in an ordinary air-drying house. It is claimed that drying is
+expedited, and that the rubber can be packed in ten days.</p>
+
+<p>In the more recent modification, the smoke and hot air
+which leave the Chula drier pass through a large room in which
+may be hung either sheet or crepe rubber. It would seem
+that all sources of danger have not been eliminated from the
+process, as on one estate a wooden room containing rubber
+was ignited by a spark which passed through the drier.</p>
+
+<p>Yet another form exists in which the furnace is outside the
+main building, and in the ordinary course of working only
+heats a series of open pipes through which air is drawn by a
+powerful fan. By means of a valve it is possible to allow
+smoke from the furnace to pass into the room with the hot air
+for the preparation of smoked rubber. The hot air or smoke
+is distributed in the lower room by means of main and branch
+pipes, and passes through an open floor to the room above.
+With such an arrangement it is possible, therefore, to prepare
+either air-dried or smoke-cured rubber. If the method could
+be successfully applied to the drying of crepe it would be of
+great assistance on some estates. There would seem to be a
+difficulty in working it for the drying of sheer rubber and crepe
+together, as the temperature suitable for the one is excessive
+for the other. Given an efficient control over the temperature
+of the hot air, the house should be successful in the drying of
+crepe, provided the rubber is not hung in folds of too great
+length. For smoke-curing sheet rubber the period is said to be
+reduced by several days in comparison with the time occupied
+in an ordinary smoke-house, but it is not clear that such a
+system would have any advantage over a modern smoke-house,
+in types of which rubber can be fully cured in periods ranging
+from five to ten days.</p>
+
+
+<p class='pagenum'><a name="Page_150" id="Page_150">[150]</a></p>
+<hr class="c25" />
+<h2><a name="Ch12" id="Ch12"></a>CHAPTER XII</h2>
+
+<h3><i>SORTING, GRADING, AND PACKING</i></h3>
+
+
+<p>The question of standardising the output of our plantations is
+one which has occupied attention for some years, with a not
+inconsiderable degree of success.</p>
+
+<p><a name="Sec12_1" id="Sec12_1"></a>Meanwhile opinion is growing in favour of proceeding along
+the line of reducing the number of plantation grades to a
+minimum. At present some confusion exists. Some estates
+make up tree-scrap and bark-shavings together; one estate
+puts tree-scrap, earth-scrap, and bark-shavings into one
+uniform crepe; other estates have three or more separate scrap
+grades&mdash;<i>e.g.</i>, lump-rubber and &#8220;washings,&#8221; tree-scrap, earth-scrap,
+and bark-shavings scrap. There is a movement on
+foot at present to try to restrict plantation rubber to three
+grades:</p>
+
+<p><span class="smcap">Crepes</span>&mdash;1. <i>First Quality Latex.</i>&mdash;<i>I.e.</i>, crepe made from the
+true coagulum obtained from the regulated coagulation of
+strained latex. This is a pale rubber, and may be prepared
+satisfactorily if the directions given in preceding chapters are
+followed. Naturally there must be, in all factories, some
+defective rubber of this grade. For various reasons the crepe
+may be of inferior colour, or is slightly contaminated with
+dirt or traces of oil and grease, etc. This defective rubber
+should be placed aside most rigorously and plainly marked as
+&#8220;off-quality.&#8221;</p>
+
+<p>If a proper scheme of standardisation of latex and chemicals
+is followed, there should not be any such variety in shades of
+colour, such as was common in No. 1 crepe in the past.</p>
+
+<p>Comparatively few estates in Malaya now prepare thick
+(or blanket) crepes in the No. 1 grade, but in such cases the
+same rules must be applied as govern the sorting of thin fine
+pale crepes.</p>
+
+<p><span class='pagenum'><a name="Page_151" id="Page_151">[151]</a></span>2.
+<i>Compound Crepe, No. 1.</i>&mdash;In this it is proposed to include
+cup-coagulated lumps, coagulated lumps from transport
+vessels, skimmings, bucket rinsings, cup-washings, and tree-scrap.
+It has been shown in <a href="#Ch10">Chapter X.</a> that strict care is
+necessary to eliminate all oxidised (dark) scraps. These are
+relegated to a lower grade. The possession of a &#8220;scrap-washer&#8221;
+is necessary if the best results are to be obtained.</p>
+
+<p>On some estates the ingredients of this compound crepe,
+while fresh, are placed in a common jar or tank to which a
+quantity of sodium bisulphite (1 per cent. solution) and acid
+are added. The resulting conglomerate mass is cut up for
+working.</p>
+
+<p>3. <i>Compound Crepe, No. 2.</i>&mdash;This grade would include the
+remaining lower grades&mdash;viz., bark-shavings, scrap, and earth-rubber
+scrap.</p>
+
+<p><a name="Sec12_2" id="Sec12_2"></a><span class="smcap">Reduction Carried too Far.</span>&mdash;However desirable it may
+be to diminish the number of grades, it must be pointed out that
+diminution and simplification are not necessarily synonymous
+terms in this matter. It is well known that on estates where
+the earth-rubber is only brought in at lengthy intervals, say of
+a week, the resulting crepe is sometimes very tacky. This is
+only natural, and is due to the prolonged exposure to the
+sun&#8217;s rays. With the improved machinery now at our disposal,
+and with the increasing attention which will be given to the
+lower grades in the future, it is possible to prepare from average
+bark-shavings crepe free from bark, and of quite a good colour.
+Where trees are not &#8220;scrapped&#8221; before tapping, there would
+seem to be no objection to amalgamating the rubber obtained
+from the bark-shavings with the No. 1 Compound crepe;
+and it would be a distinct danger and possible loss if this good
+rubber were to be mixed with earth rubber. The liability
+of the latter to become tacky is well recognised; and if possible
+it should be maintained as a separate grade, in which it would
+be permissible to mix only rubber obtained from actually
+dry shavings from &#8220;scrapped&#8221; trees, or heavily-oxidised
+scraps which have been rejected from other grades.</p>
+
+<p><span class="smcap">Sheets.</span>&mdash;Broadly there are no fine distinctions to be made at
+present in the grading of smoked-sheet rubber; it is either<span class='pagenum'><a name="Page_152" id="Page_152">[152]</a></span>
+No. 1, or if any so-called defect is visible the sheets must be
+rejected and plainly marked as &#8220;off-quality.&#8221;</p>
+
+<p>Clippings (trimmings) may either be made into crepe or
+shipped under their own description.</p>
+
+<p><a name="Sec12_3" id="Sec12_3"></a><span class="smcap">Rubber Growers&#8217; Association&#8217;s Recommendations.</span>&mdash;Taking
+the foregoing arguments into full consideration, it
+would seem that, strictly speaking, the number of grades
+cannot be reduced to less than four at present without producing
+some amount of confusion.</p>
+
+<p>In its handbook,<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15"
+class="fnanchor">[15]</a> the Rubber Growers&#8217; Association remarks:</p>
+
+<div class="blockquot"><p>&#8220;The fewer grades the better, and regularity of each grade
+is most important.</p>
+
+<p>&#8220;The grading should be as follows:</p>
+
+<div class="blockquot"><p>&#8220;(No. 1) Fine crepe (or No. 1 sheet), made from the free
+or liquid latex.</p>
+
+<p>&#8220;(No. 2) Clean light brown crepe, made from lumps and
+skimmings.</p>
+
+<p>&#8220;(No. 3) Scrap crepe, made from tree-scrap.</p>
+
+<p>&#8220;(No. 4) Dark crepe, made from bark-shavings, earth
+rubber, and the lower quality of scrap.</p>
+
+<p>&#8220;Tacky rubber should be packed separately.</p></div>
+
+<p>&#8220;<i>Compound Scrap Crepe.</i>&mdash;Estates using scrap-washers
+should make a compound crepe of grades Nos. 2 and 3, which
+will make one compound free from bark and specks. All rubber
+intended for No. 4 should be most thoroughly washed.&#8221;</p></div>
+
+<div class="footnote"><p><a name="Footnote_15_15" id="Footnote_15_15"></a><a
+href="#FNanchor_15_15"><span class="label">[15]</span></a> &#8220;Preparation of Plantation Rubber,&#8221; 1917.</p></div>
+
+<p>Concerning these recommendations the remarks in preceding
+paragraphs should be studied.</p>
+
+<p><a name="Sec12_4" id="Sec12_4"></a><span class="smcap">Care in Sorting.</span>&mdash;Whether dealing with smoked-sheet,
+pale crepe, or lower grades, the strictest care is necessary in
+sorting and grading. This work must of necessity be relegated
+to coolies, and they should be trained men. Instructions
+must be definite, and doubtful specimens of rubber should
+always be placed aside for the decision of the European superintendent.
+Any pieces showing unmistakable signs of what
+are regarded as defects should be stringently rejected. In the
+case of pale crepe, when the defect is confined only to a small
+area it is permissible to cut out the affected portion. Similarly
+there can be no objection, in the case of smoked sheets, to<span class='pagenum'><a name="Page_153" id="Page_153">[153]</a></span>
+an occasional sheet being treated in this manner. On the
+majority of estates these rules are observed carefully, but some
+estates yet have to learn that defective pieces of rubber may not
+be concealed in a bulk of otherwise good quality. Samplers
+have often an uncanny knack of hitting upon the defective
+specimens, and it is entirely the fault of the estate&#8217;s sorters if
+these pieces are submitted as being representative of the mass.</p>
+
+<p><a name="Sec12_5" id="Sec12_5"></a><span class="smcap">Choice of Cases.</span>&mdash;Consumers complain justly of the presence
+of chips, splinters, and wood-dust. It will be evident,
+therefore, that whatever the type of case employed the interior
+surfaces should be smooth, there should be no cracks or gaps
+in the timber, and the cases should be cleaned out before using.
+There remains great room for improvement in the means
+and method of packing, and in spite of suggested alternatives
+we are at present restricted to the use of wooden cases.</p>
+
+<p>From comparisons of actual quality and fulfilment of the
+requirements indicated above, there can be no question that
+cases made of three-ply wood, such as the &#8220;Venesta,&#8221; are in
+every respect superior to the ordinary wooden cases of &#8220;Momi&#8221;
+type. The consideration of cost and available supplies, of
+course, enters largely into the question, and three-ply cases
+are not at present so largely employed as they deserve to be.</p>
+
+<p>A new type of case was recently exhibited in Singapore.
+It emanates from the U.S.A. and is made of a fibrous material,
+resembling in appearance a very stout cardboard. The complete
+case when assembled consists really of two boxes, one of
+which is inverted and slides down over the other. Packing is
+completed by means of stout wire, which is strained by a simple
+ratchet arrangement. It is claimed that from 225 to 250 lbs.
+of rubber can be contained. Other claims made amount to
+the statement that the case is practically indestructible under
+normal conditions of handling and shipping. A demonstration
+given certainly appeared to substantiate the statement
+fully. Rubber packed in cases of various and average type
+was allowed to fall from a height of about twenty feet. In all
+instances the wooden cases of every type were either smashed
+or badly burst, whereas the fibre cases were merely dented.
+These cases are obtained in flat sections, which, in assembling,<span class='pagenum'><a name="Page_154" id="Page_154">[154]</a></span>
+are folded and clamped by means of copper rivets in a special
+but simple machine. It was pointed out that objection might
+be lodged against the use of copper for this purpose.</p>
+
+<p>More recently there is announced a new packing case which
+is stated to be made from low-grade rubbers, but information
+is rather vague.</p>
+
+<p><a name="Sec12_7" id="Sec12_7"></a><span class="smcap">Bags.</span>&mdash;There are in local use stout canvas bags which have
+the advantage of being used many times, as long as they are
+waterproof and kept in good dry condition. Their employment
+for the conveyance of smoked-sheets would appear to
+be permitted, but crepe rubbers sent in them are often reported
+upon as being &#8220;massed&#8221; at the edges, and hence difficult to
+&#8220;sample.&#8221;</p>
+
+<p><a name="Sec12_8" id="Sec12_8"></a><span class="smcap">Bales.</span>&mdash;Attempts to bale rubber for the market have been
+frequent, but no success seems to have attended the efforts.
+In some quarters the failure has been ascribed to prejudice
+on the part of buyers, but it is the opinion of the writers
+that the objections to baling are, or could be, well-founded.
+Massed rubber often cannot be inspected properly, and hence
+is always open to suspicion that internally there may be unsuitable
+portions.</p>
+
+<p>There have been several schemes put forward for winding
+crepe rubber on spindles so as to form a cylindrical package
+complete in itself. We have seen the process, and certainly
+the method had much which appeared commendable. Apart
+from other objections which might be raised, there is always the
+one prominent objection mentioned in the preceding paragraph.</p>
+
+<p>While baling of rubber is thus not likely to suit the general
+market, there is no reason why, as in one or two instances, it
+should not be practised by agreement between producer and
+consumer. It is believed that &#8220;slab&#8221; rubber is shipped in
+bales from Sumatra to the U.S.A.</p>
+
+<p>Quite recently a proposal has been put forward to revert
+to a simple form of baling for ordinary plantation rubber.
+Under this scheme wooden cases are discarded, the packing
+material being composed of scrap-grade crepe rubber which,
+it is claimed, could be put to use by the manufacturer. An
+obvious drawback would be evident if these bales happened to<span class='pagenum'><a name="Page_155" id="Page_155">[155]</a></span>
+be exposed to direct sunlight or a continuous high temperature.
+The tackiness which might supervene would make the handling
+of such bales unpleasant, even if it did not affect the internal
+rubber.</p>
+
+<p><a name="Sec12_9" id="Sec12_9"></a><span class="smcap">Folding for Packing.</span>&mdash;In the packing of smoked sheets
+it would appear to be advisable to avoid, if possible, the folding
+of any pieces, as the objection is made that such rubber is
+difficult to &#8220;sample&#8221; on arrival, especially in cold weather.
+Sheets should be prepared or cut to such length that they occupy
+the full superficial area of the box, either singly or side by side.</p>
+
+<div class="figcenter"><a name="Fig45" id="Fig45"></a><img src="images/illo172.jpg" alt="A
+Shipment of Rubber, Packed and Ready for Transport" />
+<p class="caption"><span class="smcap">A Shipment of Rubber, Packed and Ready for Transport.</span></p></div>
+
+<p>The same remark applies to the packing of crepe rubbers,
+except that here we deal with units of folded rubber. Crepes
+are generally folded by hand, and coolies usually work to a
+certain dimension by means of a standard stick. The work is
+slow, but often gives employment, at a cheap rate of pay, to
+women and weak coolies.</p>
+
+<p><a name="Sec12_10" id="Sec12_10"></a>Several machines have been invented to replace this labour.
+The best of these yet seen has a simple device by means of
+which the length of the fold is adjustable to suit the size of<span class='pagenum'><a name="Page_156" id="Page_156">[156]</a></span>
+any packing case. It is called the &#8220;Senang&#8221; folder, and is
+made by the General Engineering Company (Radcliffe) Ltd.,
+Radcliffe, near Manchester.</p>
+
+<p><a name="Sec12_6" id="Sec12_6"></a><span class="smcap">Care in Assembling.</span>&mdash;Whatever the type of case employed,
+great care must be given to the assembling of parts and the
+final fastening. It is not uncommon to find in the operation
+of putting on the &#8220;strapping&#8221; that nails have been driven
+into the rubber. Extra bands of strapping are sometimes
+advised, and where these bands pass over the sides (not
+edges) of the case only specially short nails should be used.</p>
+
+<p>All wood should be planed, and in cases other than three-ply
+should be of stout wood, not less than <span class="enum">5</span>&#8260;<span class="denom">8</span> inch in thickness.
+All timber used should be of uniform type and thickness.</p>
+
+<p><a name="Sec12_11" id="Sec12_11"></a><span class="smcap">Methods of Packing.</span>&mdash;The usual method of packing crepe
+is to fold the lengths to some measure of the dimensions of the
+case. This is done in a haphazard fashion on some estates,
+with the result that either space is lost or the packing is badly
+arranged.</p>
+
+<p>Some ingenuity can be displayed in the packing of sheet
+rubber in order to avoid folding the sheets, which, besides
+increasing the difficulty of sampling, leads to loss of space.
+Endeavours are being continually made on estates to prepare
+sheet of such a size as to obtain the maximum benefit of space
+both in smoke-house accommodation and in packing. A few
+estates employ tanks of such calculated dimensions as will
+yield uniform sheets which pack flat and fill the superficial
+area of the case.</p>
+
+<p>In view of the contamination which sometimes characterises
+the employment of wooden cases it is sometimes advised that
+the interior should be lined with sheets, or pieces of crepe,
+the ends of which are later folded over the top of the mass.
+In this manner it is stated that contamination is confined only
+to the exterior of the contents of the case.</p>
+
+<p><a name="Sec12_12" id="Sec12_12"></a><span class="smcap">Weight of Contents.</span>&mdash;The dimensions of average cases
+are 19 inches by 19 inches by 24 inches, giving a capacity of
+5 cubic feet.</p>
+
+<p>In these it is possible to pack 150 lbs. of crepe rubber and
+200 lbs. of sheet rubber (about 5 per cent. more in cases of<span class='pagenum'><a name="Page_157" id="Page_157">[157]</a></span>
+three-ply wood). It may be noted that boxes arrive in better
+condition when fully packed. The foregoing figures are not
+adhered to strictly. For example, some estates find it expedient
+to ship rubber in actual ton lots, and for this purpose pack
+only 140 lbs. of crepe per case, giving sixteen cases to the ton.
+Other estates, using presses, pack more per case than the
+quantities noted above. At present there does not appear
+to be any definite regularity in practice.</p>
+
+<div class="figcenter"><a name="Fig46" id="Fig46"></a><img src="images/illo174.jpg"
+alt="On its Road to the Railway: Bullock-Cart Transport" />
+<p class="caption"><span class="smcap">On its Road to the Railway: Bullock-Cart Transport.</span></p></div>
+
+<p>In all instances it should be the invariable rule that the
+rubber should be weighed before packing, and that all cases
+should contain uniform nett quantities of any particular
+type of rubber. Invoicing, etc., will thus be greatly facilitated.
+If these practices are followed, and the rubber always weighed
+on the same scales (assuming it to be perfectly dry when packed)
+complaints of &#8220;short-weight&#8221; should be infrequent.</p>
+
+<p><a name="Sec12_13" id="Sec12_13"></a><span class="smcap">&#8220;Short&#8221; Weights.</span>&mdash;In some cases the occurrence of
+&#8220;short&#8221; weights on arrival at ports would appear to be
+inexplicable. It often happens that the constituent parts of
+wooden cases have been in stock for a considerable period.<span class='pagenum'><a name="Page_158" id="Page_158">[158]</a></span>
+If for no other reason than that indicated below, all cases, either
+before or after assembling, should be thoroughly dried in the
+sun. &#8220;Short&#8221; weight could be accounted for to some degree
+by a lack of observance of this elementary rule, as it is most
+probable that there would be a perceptible difference in weight
+of the wooden case in a drier atmosphere.</p>
+
+<div class="blockquot"><p>(<i>a</i>) If rubber is weighed in the box, and the average tare of
+the case deducted from the gross weight (in order to obtain
+the nett weight), any loss in the weight of the timber would
+appear as a deficiency of rubber at the distant port.</p>
+
+<p>(<i>b</i>) Whether the same effect would be produced eventually
+in the case of rubber which is weighed before packing will
+depend upon the method of weighing at the warehouse. If
+the rubber is weighed in the box, any observed deficiency
+would be attributed to a loss of weight in the rubber.</p></div>
+
+
+<p class='pagenum'><a name="Page_159" id="Page_159">[159]</a></p>
+<hr class="c25" />
+<h2><a name="Part3" id="Part3"></a>PART III</h2>
+
+<h3>MACHINERY AND BUILDINGS</h3>
+
+
+<h2><a name="Ch13" id="Ch13"></a>CHAPTER XIII</h2>
+
+<h3><i>MACHINES</i></h3>
+
+
+<p><a name="Sec13_1" id="Sec13_1"></a>The number of manufacturers of machines for preparing
+rubber would seem to be on the increase, and there can be
+little doubt that this competition will result in a continued
+improvement in the design of machines. It cannot be denied
+that there has been room for such improvement, and it is
+believed that manufacturers will display judgment in putting
+only their best quality into the work. While design and finish
+are very excellent in their way, it is to be regretted that in a
+number of cases in the past the material of rolls has been found
+to be of inferior quality. Generally, the complaint seemed
+to be that the rolls were too soft, and that the &#8220;grinding&#8221; effect
+was far too great. The damage to pale rubber in such cases
+is considerable, as it is impossible to keep the rolls free from
+fine dark powder. The effect is generally noticed more in the
+smooth rolls with which a finish is put upon the crepe.</p>
+
+<p>Cases have occurred frequently in which rolls have been
+returned, because of the injury caused to pale rubber, and there
+can be little doubt that the life of quite a large number of rolls
+is even now far too short in comparison with the expense
+involved.</p>
+
+<p>It is a moot point, however, in many instances how far the
+quality of the rolls is actually responsible for the damage done
+to the rubber. In the experience of the writers it is certain that
+complaints regarding the rolls were unjustifiable, and that the
+injury had been caused by carelessness in the &#8220;feeding&#8221; of the
+machine. Especially in the case of smooth finishing rolls, it is<span class='pagenum'><a name="Page_160" id="Page_160">[160]</a></span>
+clear that if the rolls are allowed to run idle for more than the
+briefest possible interval grinding must take place.</p>
+
+<p><a name="Sec13_2" id="Sec13_2"></a><a name="Sec13_3" id="Sec13_3"></a>The complaints apply not only to the rolls themselves, but also
+to the brass linings for shaft-bearings. Cases are known in
+which a brass &#8220;liner&#8221; was so worn within a few weeks as to be
+quite useless. If the matter ended there it would not be so bad;
+but there is always the possibility of particles of brass finding
+their way into trays, and so into the rubber. The damage which
+ensues to the rubber is quite irreparable. This particular defect
+arising from the presence of brass will be dealt with in a <a href="#Ch17">later
+chapter</a>. But here again it is necessary to point out that such
+wear on brass liners may be caused by the standards (ends) of
+the rolls being eccentric; and the case may be analogous to the
+placing of &#8220;new wine in old bottles.&#8221;</p>
+
+<p><a name="Sec13_4" id="Sec13_4"></a><i>En passant</i> it may be remarked that in any case brass liners
+are not strictly necessary. White-metal alloys are in use on
+rubber machines, and cast-iron bearings have been employed
+satisfactorily for years.</p>
+
+<p>It would be well for managers to remember, therefore, that
+when machines have to be ordered, nothing but the best is
+good enough, and that the difference between good machinery
+and passable machinery is probably immensely greater in effect
+than any saving in expenditure would warrant.</p>
+
+<p><a name="Sec13_5" id="Sec13_5"></a><span class="smcap">Adequacy of Machines.</span>&mdash;In general, the factories which
+prepare sheet rubber are usually equipped with adequate
+machinery. This arises from the fact that machines are necessary
+for preparing all grades below the first, even if they are not
+necessary for the making of sheet. Thus all the necessary
+macerators and finishing machines are installed, but the
+major part of the output is in sheet form. For the preparation
+of sheet, no heavy machinery is required; all that is necessary
+are light machines for rolling the sheets and expressing as much
+moisture as possible. To obtain a pattern on the sheet, another
+light machine may be used. It may be imagined, then, that
+the work of rolling sheet rubber by power machines is small,
+and that a large quantity of rubber can be worked off in a
+comparatively short time. It follows, therefore, that the
+preparation of the lower crepe grades can be proceeded<span class='pagenum'><a name="Page_161" id="Page_161">[161]</a></span>
+with at once, and that the whole work of the factory is
+expedited.</p>
+
+<p>The case of factories which have to prepare all first-grade
+rubber in crepe form is quite different, especially when thin
+rubber has to be made. The care which has to be exercised
+in preparing pale crepe rubber is very great in comparison
+with what is demanded by sheet rubber. The rubber has
+to go first through the uneven-speed macerators, from there
+to the intermediate rollers, thence to the finishing rollers.
+Considerable ingenuity has to be displayed in the arrangement
+of the machines, so that one section will not work faster or slower
+than another. More often than not, the attempt to arrive at
+such a desirable arrangement fails, owing to an insufficiency
+of machines. Such a statement will probably read strangely
+to the uninitiated; but an example will make it plain. A factory
+may have a battery of six machines, one only of which is a finishing
+machine (smooth rolls). With five macerators and intermediate
+machines working continuously, it will be more than
+the work of one finishing pair of rolls to keep pace, especially
+as so much more care has to be exercised in finishing than in
+rough crepe-making. The obvious course to adopt is to substitute
+a pair of smooth rolls, with suitable gear ratio, for a
+pair of macerators or &#8220;intermediates.&#8221;</p>
+
+<p>If, however, the macerators and intermediates are already
+fully occupied the whole of the time, any such change would be
+of small benefit. What is really needed in this case is more
+machinery.</p>
+
+<p>It might be pertinently asked what constitutes an adequate
+equipment of machines for crepe-making. The writers cannot
+give a number, but have no hesitation in stating that if a factory
+cannot complete its whole day&#8217;s work before dark, it is inadequately
+equipped. No work should be done after dark, if
+possible, as it cannot receive the supervision which crepe-making
+demands. To make comparison between the number
+of machines in any two factories and their respective outputs
+is not sound argument, as the out-turn of two similar machines
+will depend upon the speed at which the rolls travel&mdash;<i>i.e.</i>, the
+gearing between the machines and the engines. Thus, while<span class='pagenum'><a name="Page_162" id="Page_162">[162]</a></span>
+one machine will out-turn 40 lbs. of crepe per hour, another
+may only have an output of 30 lbs., although the machines may
+be identical in pattern. To make calculations based on a rate
+per hour for any known make of machine, and to apply those
+calculations to the existing machinery in any factory, in an
+attempt to judge whether there is a sufficient number of
+machines, would be a mistake, unless one were also supplied
+with the relative speeds at which the rolls work.</p>
+
+<p>Finally, on the question of adequacy of machines, it must be
+pointed out that an insufficient number of machines must result
+in a poor product, since all rolls have to be used for all grades.
+Even with the greatest possible care it happens that pale crepe
+is sometimes spoiled because it is contaminated with foreign
+matter, resulting from the working of lower grades on the same
+machines. This is one of the great arguments in another
+direction for the installation of a scrap-washer.</p>
+
+<p>In conclusion, the writers can only give their opinion that
+one must not decide the question of adequacy by the number
+of existing machines, but by the time taken each day in working
+off the rubber, providing one can be satisfied that the best
+arrangement of the existing machines has been made.</p>
+
+<p><a name="Sec13_6" id="Sec13_6"></a><span class="smcap">Ideal Arrangement.</span>&mdash;As to what this best arrangement
+may be, guidance can be obtained from the results of experience
+here given. It must be premised that the output of any factory
+preparing fine pale crepe is limited by the output of the smooth
+finishing rolls. Broadly, it will be recognised that if there
+is any excess of capacity in a battery it should be found in the
+smooth-roll machines. This sufficiency, or excess of capacity,
+may sometimes be attained by an alteration in the gearing of
+the drive of the rolls from the back-shaft, or by an addition to
+the number of machines. In the former case, there are practicable
+limits of speed, beyond which the second alternative
+measure must be adopted.</p>
+
+<p><a name="Sec13_7" id="Sec13_7"></a><span class="smcap">Speed.</span>&mdash;The usual speed at which the back-shaft travels
+ranges from 60 to 70 revolutions per minute. Taking first
+the macerating machines, the intermediate gearing between
+the shaft and the rolls should give a driving speed of about
+20 revolutions per minute on the faster-travelling roll. This<span class='pagenum'><a name="Page_163" id="Page_163">[163]</a></span>
+is equivalent, with a 15-inch diameter roll, to a peripheral
+speed of about 60 to 65 feet per minute.</p>
+
+<p>The intermediate and smooth rolls can be arranged to travel
+more quickly, but the maximum comfortable speed for proper
+feeding and control appears to be about 25 revolutions per
+minute on even-speed rolls. In view of the fact that the rubber
+at each successive machine becomes longer and thinner, it will
+be seen that a smooth-roll machine could not cope with the
+output of a macerator in the same period of time. If, therefore,
+the macerator is fully occupied for the greater part of the
+time, an additional smooth-roll machine must be installed,
+even though the existing one has been &#8220;speeded up&#8221; to practicable
+limits.</p>
+
+<p>For the information of the uninitiated it might be explained
+that in the macerating and intermediate machines the cog-wheels
+driving the two rolls are of different sizes (<i>i.e.</i>, differentially
+geared), as opposed to the smooth rolls on which the
+cog-wheels are usually of the same size (<i>i.e.</i>, even speed). The
+idea in the one case is to exert a &#8220;working&#8221; influence upon
+the rubber while it is being washed by the stream of water
+coming from above; in the smooth rolls a squeezing action
+only is effected.</p>
+
+<p>To give an idea of the ratio of the speeds of the rolls in each
+machine in a typical working battery, the following particulars
+may be noted:</p>
+
+<p><a name="Sec13_8" id="Sec13_8"></a><span class="smcap">Gear Ratios.</span>&mdash;</p>
+
+<table summary="Table p163">
+
+<tr>
+<td>&nbsp;</td>
+<td colspan="5" class="center">Machine.</td>
+<td class="center">Differential Ratio.</td>
+</tr>
+
+<tr>
+<td class="right">1.</td>
+<td colspan="5" class="left">Macerator</td>
+<td class="center">32-17</td>
+</tr>
+
+<tr>
+<td class="right">2.</td>
+<td colspan="2" class="left">Intermediate</td>
+<td colspan="3">(coarse grooved)</td>
+<td class="center">32-17</td>
+</tr>
+
+<tr>
+<td class="right">3.</td>
+<td colspan="2" class="center">&#8222;</td>
+<td colspan="3">(fine grooved)</td>
+<td class="center">30-19</td>
+</tr>
+
+<tr>
+<td class="right">4.</td>
+<td class="left">Smooth</td>
+<td colspan="4">(uneven speed)</td>
+<td class="center">30-19</td>
+</tr>
+
+<tr>
+<td class="right">5.</td>
+<td class="center">&#8222;</td>
+<td colspan="3">(finishing)</td>
+<td>&nbsp;</td>
+<td class="center">25-24</td>
+</tr>
+
+<tr>
+<td class="right">6.</td>
+<td class="center">&#8222;</td>
+<td colspan="3" class="center">(&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&#8222;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;)</td>
+<td>&nbsp;</td>
+<td class="center">25-24</td>
+</tr>
+
+</table>
+
+<p>It will be seen that the so-called &#8220;even-speed&#8221; smooth rolls
+run at approximately the same rate.</p>
+
+<p>It is advised that in all cases the gear wheels should be cut
+helically. Those who have experience of the noise of some
+batteries after they are slightly worn will appreciate such a
+remark.</p>
+
+<p><a name="Sec13_9" id="Sec13_9"></a><span class='pagenum'><a name="Page_164" id="Page_164">[164]</a></span><span
+class="smcap">Grooving of Rolls.</span>&mdash;Concerning the choice of grooving,
+there is divergence of opinion, some managers preferring one
+type, which others reject in favour of another type. Provided
+any particular type can be shown to be as effective as required,
+no necessity for laying down hard-and-fast rules seems to exist.</p>
+
+<p>The following particulars serve to describe a battery well
+known to the writers, and accustomed to produce the finest
+quality of thin pale crepe and lower grades:</p>
+
+<table summary="Table p164">
+
+<tr>
+<td colspan="3" class="center bt br bb"><i>Machine.</i></td>
+<td class="center bt br bb"><i>Grooving.</i></td>
+<td colspan="2" class="center bt bb"><i>No. of Times<br />Rubber passes<br />through.</i></td>
+</tr>
+
+<tr>
+<td class="right top">1.</td>
+<td colspan="2" class="left top br">Macerator</td>
+<td class="left br">Deep horizontal grooves;<br />square-cut, <span class="enum">5</span>&#8260;<span
+class="denom">16</span> inch &times; <span class="enum">5</span>&#8260;<span class="denom">16</span> inch<br />
+&times; <span class="enum">5</span>&#8260;<span class="denom">8</span> inch spaces</td>
+<td class="right bottom" style="padding-left: 3em; vertical-align: bottom;">3</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right top">2.</td>
+<td colspan="2" class="left top br">Intermediate</td>
+<td class="left br">Horizontal grooves; <span class="enum">3</span>&#8260;<span class="denom">16</span> inch<br />
+ &times; <span class="enum">3</span>&#8260;<span class="denom">16</span> inch &times; <span class="enum">3</span>&#8260;<span
+class="denom">8</span> inch spaces</td>
+<td class="right" style="padding-left: 3em; vertical-align: bottom;">2</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right top">3.</td>
+<td colspan="2" class="center top br">&#8222;</td>
+<td class="left br">Fine spiral grooves; <span class="enum">1</span>&#8260;<span class="denom">8</span> inch<br />
+&times; <span class="enum">1</span>&#8260;<span class="denom">8</span> inch &times;
+<span class="enum">1</span>&#8260;<span class="denom">4</span> inch spaces</td>
+<td class="right bottom" style="padding-left: 3em; vertical-align: bottom;">2</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right">4.</td>
+<td colspan="2" class="left br" style="padding-right: .5em;">Geared smooth</td>
+<td class="left br">Nil</td>
+<td class="right" style="padding-left: 3em; vertical-align: bottom;">1</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right">5.</td>
+<td colspan="2" class="left br">&#8220;Even&#8221; smooth</td>
+<td class="left br">&nbsp;&#8222;</td>
+<td class="right" style="padding-left: 3em; vertical-align: bottom;">1</td>
+<td>&nbsp;</td>
+</tr>
+
+<tr>
+<td class="right bb">6.</td>
+<td class="center bb">&#8222;</td>
+<td class="center bb br">&#8222;</td>
+<td class="left br bb">&nbsp;&#8222;</td>
+<td class="right bb" style="padding-left: 3em; vertical-align: bottom;">1</td>
+<td class="bb">&nbsp;</td>
+</tr>
+
+<tr>
+<td colspan="3" class="bb br">&nbsp;</td>
+<td class="center bb br">Total</td>
+<td class="center bb" style="padding-left: 3em; vertical-align: bottom;">10</td>
+<td class="left bb">times</td>
+</tr>
+
+</table>
+
+<p>The actual rate of output of this installation is the capacity
+of the last smooth machine. This is about 180 lbs. per hour,
+while the output of the macerator is approximately double
+this amount. Thus the macerator only works for about half
+the time. This applies also to the two intermediate machines.
+After a study of the preliminary remarks, it would not be
+difficult to suggest methods for improving the condition of
+affairs. It would appear that, in order to obtain a uniform
+rate of working in such a battery, the relative peripheral speeds
+of the several machines should be&mdash;(1), (2), and (3) 100; (4) 150;
+(5) and (6) 200. The remarks on the practical limits of speed
+should be borne in mind. In this case the smooth rolls
+travelled at 23 revolutions per minute.</p>
+
+<p>As already stated, it is not intended to lay down definitely
+that, <i>e.g.</i>, horizontal grooving alone should be cut on macerating
+rolls. Some estates employ with satisfaction a deep square-<span class='pagenum'><a name="Page_165" id="Page_165">[165]</a></span>cut
+spiral <span class="enum">1</span>&#8260;<span class="denom">4</span> inch by <span class="enum">1</span>&#8260;<span class="denom">4</span> inch by <span class="enum">1</span>&#8260;<span class="denom">4</span> inch or <span class="enum">1</span>&#8260;<span class="denom">2</span> inch spacing; others
+use a large diamond pattern. Similarly various types of grooving
+are cut in the intermediate rolls.</p>
+
+<div class="figcenter"><a name="Fig47" id="Fig47"></a><img src="images/illo182.jpg" alt="A Battery of Machines" />
+<p class="caption"><span class="smcap">A Battery of Machines.</span></p>
+<p class="capt500">On the left, light marking rolls for sheet rubber; on the right,
+heavy machines for crepe preparation. In the middle background,
+&#8220;scrap-washing&#8221; machines outside the main building.</p></div>
+
+<p>It has been remarked in the <a href="#Ch10">chapter</a> dealing with crepe preparation
+that much depends upon the condition of the coagulum.
+There is no necessity, or desirability, for having a standard
+higher than 2 lbs. dry rubber per gallon, and it has been
+argued that it would be better to select a standard of 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs.
+The tougher the coagulum, the more the power required,
+and the slower the rate of output of the leading machines.</p>
+
+<p>In ordering machines for crepe-making, only large rolls
+should be considered&mdash;<i>e.g.</i>, rolls having a diameter of 12 inches
+to 18 inches and from 15 inches to 18 inches face.</p>
+
+<p><a name="Sec13_10" id="Sec13_10"></a><span class="smcap">Rolls Running Hot or &#8220;Free.&#8221;</span>&mdash;If the rolls are found
+to become hot, work on that machine should be stopped, and an<span class='pagenum'><a name="Page_166" id="Page_166">[166]</a></span>
+examination made, otherwise there is the possibility of the
+crepe becoming sticky and &#8220;tacky&#8221; when dry.</p>
+
+<p>Although comparatively cold water may be flowing upon the
+rubber and the rolls, little alleviation may be noticed, inasmuch
+as the source of heat lies generally at the bearing ends of the rolls.
+This may be tested by placing the hand on the top of the
+&#8220;standard&#8221; of the machine. The development of the heat
+may be due to lack of lubrication, worn bearings, or sometimes
+faulty setting-up of the machines.</p>
+
+<p>Allusion has been made to the necessity for avoiding the
+running &#8220;free&#8221; of rolls&mdash;<i>i.e.</i>, in the absence of rubber. The
+grinding of the rolls, when working close together, produces
+a fine powder, which causes a more or less pronounced deposit
+on pale crepe. When the rolls have been in action for some
+time and become slightly worn, this deposit may be confined
+only to the edges of the rubber.</p>
+
+<p><a name="Sec13_11" id="Sec13_11"></a><span class="smcap">Sheeting Machines.</span>&mdash;The foregoing paragraphs have dealt
+entirely with machines for crepe preparation. Concerning
+machines for use in sheet-making, the ground has been mainly
+covered in <a href="#Ch9">Chapter IX</a>.</p>
+
+<p>Where both crepe and sheet are made, it is permissible and
+advantageous to use the heavy smooth rolls for the rolling
+of the sheets, and it is only necessary to instal one or two light
+machines for placing a pattern on the rubber.</p>
+
+<p>Where a heavy battery does not exist, light machines with
+smooth rolls may be employed satisfactorily. Even engine-power
+is not necessary for the preparation of excellent sheets,
+but the output is limited where hand-power only is employed.
+Estates are known on which upwards of 1,000 lbs of sheet
+rubber are made daily with hand-power machinery in one
+station. Beyond this figure, it is deemed advisable to instal
+a small engine, say of 7-9 horse-power. This is ample to drive
+a battery of three smooth-roll machines and two markers,
+and yet have sufficient reserve to actuate a small pump for the
+water supply.</p>
+
+<p><a name="Sec13_12" id="Sec13_12"></a><span class="smcap">Lubrication of Machines.</span>&mdash;It must always appear to those
+inexperienced in engineering matters that existing methods
+for lubricating rubber machinery are distinctly crude, when<span class='pagenum'><a name="Page_167" id="Page_167">[167]</a></span>
+one considers the delicacy of the material to be prepared.
+Many existing machines are still lubricated with oil, which has
+to be administered in generous quantities. Generally, such
+machines have been so designed that the excess of oil may
+find an easy passage into the tray which receives the rubber.
+If not, it drops just outside the tray to the floor, and is washed
+away in great gouts. Even where grease-cap lubricators are
+fitted it is common to find that the excess can often be transferred
+from the bearings to the trays and so to the rubber.
+One would have expected from the attention which is being
+given to machinery for rubber estates that some improvement
+in lubrication methods would have been devised.</p>
+
+<p>It is probable, however, that a great deal of the disabilities
+attaching to present methods of lubrication might be obviated
+if closer attention were given to the actual operation of the
+lubricators. Coolies should not be allowed to handle them,
+and the responsibility should be placed upon a foreman or
+the engine-driver.</p>
+
+<p><a name="Sec13_13" id="Sec13_13"></a><span class="smcap">Trays.</span>&mdash;The most unsuitable and damage-causing part of
+the vast majority of machines, without doubt, is the tray. On
+nearly all machines the tray is wider than the effective portion
+of the rolls, so that any excess of lubricant may drop into it.
+On others, not only is the tray wider than the rolls, but its
+edge either is in contact with the shaft of a roll or just a small
+distance away. The edge of the tray is thus favourably situated
+for acting as a &#8220;wipe,&#8221; and the lubricant is transferred to the
+inside of the tray. Considering that the effective portion of
+rolls is about two-thirds of their length, it must be unnecessary
+to have trays wider than the length of the rolls. For the preparation
+of fine crepe trays are quite superfluous, and their
+place can be taken by a narrow piece of board if required. If
+the bed of the machines has been covered with glazed tiles,
+even a piece of board is not necessary. Where trays have been
+removed from the fine-crepe rolls on a number of estates, a
+marked decrease in the number of spoiled pieces of rubber has
+resulted.</p>
+
+<p>It must be recorded that the foregoing paragraph appeared
+in our 1913 publication. After a lapse of over seven years,<span class='pagenum'><a name="Page_168" id="Page_168">[168]</a></span>
+the remarks remain as true as when originally written. One
+of us is continually meeting with cases in which the defects
+are plainly attributable to the cause indicated above, and
+the fault often lies with the management of estates. On most
+machines the trays are not fixtures, and could be removed
+if desired.</p>
+
+<p><a name="Sec13_14" id="Sec13_14"></a><span class="smcap">Arrangement of Machines.</span>&mdash;In considering the future
+arrangement of machines, the first care should be to see that
+machines and windows are to be found together.<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a
+href="#Footnote_16_16" class="fnanchor">[16]</a> Of all the
+factory operations, rolling of rubber should be given the maximum
+light. At the same time it would not be advisable always
+to choose a southern aspect, unless outside shades were supplied.
+The best position for setting up machines, therefore, is along
+a wall having a number of windows. This is extremely convenient
+also from the view of power transmission, and gives
+the maximum free floor space to the factory. In setting up
+machines, foresight must be displayed, otherwise one may find,
+when future extensions are made, that the extra machines
+may obstruct an entry or exit.</p>
+
+<div class="footnote"><p><a name="Footnote_16_16" id="Footnote_16_16"></a><a
+href="#FNanchor_16_16"><span class="label">[16]</span></a> Windows imply the existence of walls. Such is the conventional
+design of factories. It may be pointed out that walls are not
+necessary. The roof may be supported on pillars between which
+expanded metal of large size may be placed. This fulfils all requirements
+and gives the maximum of light and air. Many new factories
+have been erected to such a design.</p></div>
+
+<p>For the actual erection of machines, no labour should be
+accepted without European supervision. At present there
+are machines which are practically useless owing to faulty workmanship,
+and on many machines bearings run hot for no apparent
+or explicable reason. Whether the fault lies with the
+turning of the rolls or the setting of the machine cannot be
+decided; but at any rate too much care cannot be expended on
+the supervision of setting up machines.</p>
+
+<p>There is no reason why everything in a factory should not
+be made as easy to clean as possible. For this desirable condition
+all machines should have the beds faced with tiles. A
+word of caution should be given against using marble slabs
+under the machines, as they would be eroded in time by the<span class='pagenum'><a name="Page_169" id="Page_169">[169]</a></span>
+slight amount of acid washed out of the rubber. There
+would be no such objection against the use of white glazed
+tiles, if they are well set.</p>
+
+<p><a name="Sec13_15" id="Sec13_15"></a><a name="Sec13_16" id="Sec13_16"></a><span
+class="smcap">Access to Back of Machine.</span>&mdash;In a few factories it has
+been noticed that the drainage of water from the machines
+runs to the front of them. This means that the coolies
+are put to unnecessary inconvenience and discomfort, and
+they often suffer from sore feet. All water should drain
+to the back of the machines. The necessity for seeing
+that these drains are kept clear might then induce those in
+charge to examine the back of the machines. It is often the
+case that, while the front of the rolls and tray are kept clean,
+little attempt is made to cleanse those parts which are not visible
+or accessible from the front. There should be no need to
+point out that any labour expended in such &#8220;front-window&#8221;
+work is rendered useless by the contamination from accumulations
+of old rubber and grease at the back of the machines.
+In the course of visiting factories one of us has many times
+seen great surprise exhibited by the manager or assistants on
+being shown the state of affairs at the back of the machines.
+There should have been no occasion for such surprise, for the
+back of the machines is quite as accessible to them as to the
+visitor.</p>
+
+<p>In conclusion it might be said that the manager needing
+advice as to the best machines cannot go far wrong in purchasing
+any of the better-known makes, such as Shaw&#8217;s, Bridge&#8217;s,
+Robinson&#8217;s, Bertram&#8217;s, Walker&#8217;s, Carter&#8217;s, Iddon&#8217;s, etc. This
+list does not include local manufacturers such as the &#8220;United
+Engineers.&#8221; It must not be imagined that their machines are
+not recommended. As a matter of fact, their machines compare
+well with those made at Home. It would be well to judge
+in the final decision upon&mdash;</p>
+
+<div class="blockquot"><p>1. Cost.</p>
+
+<p>2. The experience of those already using the machines.</p>
+
+<p>3. Simplicity of parts.</p>
+
+<p>4. Lubrication system.</p>
+
+<p>5. Mode of adjusting rolls.</p>
+
+<p>6. Fitting of trays.</p></div>
+
+<p><a name="Sec13_17" id="Sec13_17"></a><span class='pagenum'><a name="Page_170" id="Page_170">[170]</a></span><span
+class="smcap">Engines.</span>&mdash;It is not intended here to discuss particular
+makes of engines, or even to attempt to lay down definite
+statements with regard to the type of engine. Without a
+full knowledge of local circumstances, it is not possible to
+recommend whether the engine shall be oil-driven, gas-driven,
+or steam-driven.</p>
+
+<p>Assuming a copious supply of very cheap timber, there could
+be no objection to the employment of a steam-engine; but
+for most estates such a choice is out of the question.</p>
+
+<p>Again, in deciding between oil and gas, local economic
+factors must be considered. Suction-gas plants are now made,
+in which a wonderful variety of refuse can be consumed in
+the production of gas, whereas ordinarily estates are restricted
+to the use of either charcoal or anthracite coal. Both oil and
+gas driven engines are eminently suitable for the purpose of a
+rubber factory, and the results obtained on different estates
+with either are often discussed in favour of one or the other.
+The selection ultimately narrows itself down to one of cost of
+running, in which availability of supplies becomes an essential
+feature.</p>
+
+<p><a name="Sec13_18" id="Sec13_18"></a><span class="smcap">Power.</span>&mdash;No matter what type is selected, there should be
+made an ample allowance for margin of power. The general
+experience of estates has been that when the first portion of
+the estate comes into bearing, there is a desire to avoid great
+outlay, which should really have been secured in the original
+capital. The result has been that as later the estate expands,
+the original power unit is found to be inadequate, and a larger
+engine has to be purchased. In a short while the original
+engine is found to be unsuitable even as a &#8220;stand-by,&#8221; inasmuch
+as it is incapable of doing more than a portion of the
+work required. This means eventually that another large
+engine is required. Had sufficient margin of power been
+allowed originally, only two engines would have been bought,
+as against the three indicated above. Without going into finer
+details, it is usual to allow a rate of 10 horse-power per heavy
+machine used for crepe preparation. In actual practice, when a
+battery is working under full load, the power demanded is
+about 6 horse-power per machine. Thus a 50 horse-power<span class='pagenum'><a name="Page_171" id="Page_171">[171]</a></span>
+engine running six machines and a scrap-washer is really
+running with only a small margin of power, and if large pieces
+of hard coagulum are placed in the washer or the macerator
+there may be a sudden stoppage. Assuming an average
+estate commences with only three machines for crepe-making,
+on an expanding programme, allowance of power should be
+made for six machines and a scrap-washer, if the purchase
+of larger power units is to be avoided later.</p>
+
+
+<p class='pagenum'><a name="Page_172" id="Page_172">[172]</a></p>
+<hr class="c25" />
+<h2><a name="Ch14" id="Ch14"></a>CHAPTER XIV</h2>
+
+<h3><i>FACTORIES</i></h3>
+
+
+<p><a name="Sec14_1" id="Sec14_1"></a><span class="smcap">General Construction.</span>&mdash;On the question of general construction
+there is little to be said, except that buildings are
+now being properly designed in more permanent form than
+were some of the earlier buildings. On the whole there is
+little fault to be found with factories in general, except in so
+far as the output has outgrown the accommodation.</p>
+
+<p>Most factories are now erected in iron, but there are a few
+which are built of bricks. It should be premised that a factory
+in which rubber is to be prepared should be as light and airy
+as possible. In this respect quite a number of the older
+factories are lacking, and they seem to have been designed to
+exclude as much air and light as possible. Under these
+circumstances, the building is always dark, there is always an
+air of dampness, dirt may accumulate, and there is usually a
+bad smell. Rubber prepared under these conditions is always
+liable to be below the high standard which should be attained,
+and the general tone of the factory is depressing.</p>
+
+<p><a name="Sec14_2" id="Sec14_2"></a><span class="smcap">Plenty of Light.</span>&mdash;The old idea that light must be excluded
+is now known to be erroneous; so that in designing a factory,
+provision should be made for ample light and air. It should not
+be forgotten that in tropical climates, iron buildings may become
+uncomfortably hot, as most of our older factories are. Usually
+it will be found that the ventilation is imperfect. There is a
+lack of window space, and the roof is imperfectly ventilated.
+The ridge of the roof should be opened up by means of a
+&#8220;jack-roof,&#8221; so that the warm air rising naturally may escape
+at the highest point of the building. These are defects which
+should be remedied in old buildings.</p>
+
+<p>As a rule no rubber remains in the factory at night-time,
+except in the form of coagulum, the loss of any of which would<span class='pagenum'><a name="Page_173" id="Page_173">[173]</a></span>
+be noted with ease. The conventional idea of enclosing the
+factory with walls of galvanised sheeting, wood, or brick, is
+not strictly necessary. In modern buildings these walls are
+replaced by large-mesh expanded metal, thus making the
+machine-room perfectly light and plentifully ventilated.
+Under such conditions, dirt cannot accumulate unseen, and
+the general tone of the work is raised.</p>
+
+<p><a name="Sec14_3" id="Sec14_3"></a><a name="Sec14_4" id="Sec14_4"></a><span
+class="smcap">The Floor.</span>&mdash;The floor should be of thick concrete, and
+have a good surface layer of cement. Preparations are now
+advertised for which claims are made that their employment
+renders the surface of such floors waterproof and dustproof.
+If these claims can be substantiated when the use is applied to
+the floors of rubber factories, the employment of a preparation
+of this nature should result in a considerable saving of expense
+and trouble. Preferably the floor should not be flat, but should
+slope slightly from the longitudinal middle of the building to
+the sides on either hand. If the floor is level it usually results
+in accumulation of water, the cement breaks in patches, and
+the factory always appears to be dirty.</p>
+
+<p><span class="smcap">Position of Machines.</span>&mdash;All machines should be arranged
+adjacent to and parallel with one of the long sides of the building,
+and should be raised about 6 inches above the floor, so that
+water may escape easily. Tanks for the reception of latex,
+scrap rubber, etc., should be placed along the opposite wall
+to the machines, and the intermediate length of the building
+should be entirely free from fixtures. It was not uncommon in
+older factories to find the engine situated in the middle of the
+floor, so that what with the space occupied by the engine, and
+the space rendered unavailable by the belt-drive, the real
+accommodation of the factory was sadly diminished. In no
+modern factory should the engines be brought into the main
+room. They should always be accommodated in a special compartment,
+situated outside the wall, along the inside of which
+machines are placed. In this way considerable floor space is
+left available, and the machines may be worked by direct drive.
+Not only so; but if a suction-gas plant is worked, there can
+then be no excuse for particles of coal or charcoal dust being
+found in the factory.</p>
+
+<p><span class='pagenum'><a name="Page_174" id="Page_174">[174]</a></span><span
+class="smcap">Position of Engines.</span>&mdash;It scarcely need be pointed out that
+if the engines are placed outside the wall which is opposite
+the machines, a long belt-drive would be necessitated, and
+that the presence of the belt would prevent the use of end doors.
+It is presumed in these arguments that two engines are to be
+installed. One can hardly imagine a modern factory in full
+working being equipped with only one engine, which might
+possibly have an excess of power necessary to drive all the
+machines. In the case of breakdown, which sometimes happens
+in the best supervised factories, it would be small consolation
+to know that this excess of power was present theoretically.</p>
+
+<p><a name="Sec14_5" id="Sec14_5"></a><span class="smcap">How many Storeys.</span>&mdash;There can be no doubt that, taking
+all things into consideration, the best type of factory is that
+consisting only of one floor. The factory should be quite
+separate from all other buildings, and if attempts are made
+to conserve ground space by putting a drying-room over the
+factory, much trouble will ensue, especially if pale crepes
+are to be made. In the first place, the factory is made very
+much darker, and hence more difficult to keep clean;
+secondly, the ventilation of the factory is seriously interfered
+with; and thirdly, it is manifestly prejudicing the drying
+of rubber to place it directly over a room which is always
+more or less awash with water. At night such a building
+would reek with a moisture-laden atmosphere, and little
+drying could be expected to take place in that interval. From
+actual experience it has been shown that rubber hung to
+dry in such a room, situated over a damp factory, is very
+liable to attacks of &#8220;spot&#8221; diseases, since the presence of
+perpetual moisture is favourable to the development of these
+diseases. If a double-storey building has to be worked, it will
+be readily seen that no first-grade rubber should be allowed
+to dry in it. The accommodation over the factory may be
+restricted to the purpose of receiving lower grade rubber which
+is not so liable to &#8220;spot&#8221; diseases, and possibly does not take
+so long to dry as first-grade rubbers of equal thickness. It is
+evident, therefore, that the erection of double-storey factories
+is false economy, as separate drying-houses have to be built
+eventually. This conclusion does not apply with the same<span class='pagenum'><a name="Page_175" id="Page_175">[175]</a></span>
+force to factories worked in conjunction with smoke-houses for
+preparing sheet rubber, but, nevertheless, such a factory should
+not have another floor above the work-room.</p>
+
+<p><a name="Sec14_6" id="Sec14_6"></a><span class="smcap">Verandahs.</span>&mdash;One of the worst features in many factories
+is the necessity for coolies to bring latex into the factory.
+As already mentioned, the floors of factories are usually running
+with water (or should be), and it can be imagined that the
+passage to and fro of scores of coolies must bring in a great
+quantity of dirt. Not only so; the very presence of the coolies
+is a hindrance to the efficient working of the factory, and considerable
+floor-space and time are wasted.</p>
+
+<p>This feature in factory working is all the more annoying
+because the necessity for it could so easily be obviated. All
+that is necessary is the erection of a wide, open verandah outside
+the wall of the factory. Here all latex could be received
+and strained, scrap-rubbers could be received and passed
+through an opening into tanks placed in convenient position.
+Water could be laid on in this verandah so that coolies might
+wash their buckets, and the whole verandah might be enclosed
+only with expanded metal so as to avoid interference with the
+lighting of the factory. In this way it would be quite unnecessary
+for any field coolie to enter the factory proper, and
+this would facilitate cleanliness. Such an arrangement has
+been discussed by the writers many times during the last
+few years, but the number of estates which have made such
+provision is still in the minority, and the same slipshod and
+dirt-making procession of coolies continues to walk through
+the factories, and the same piles of bark-shavings and scrap-rubber
+continue to accumulate and ferment in a few instances.</p>
+
+<p>An indication of types of verandahs is given in <a href="#Ch7">Chapters VII.</a>
+and <a href="#Ch9">IX</a>. These are not intended to be representative of a
+universal design, but may be suggestive in the planning of
+others according to local conditions.</p>
+
+<p><a name="Sec14_7" id="Sec14_7"></a><span class="smcap">Situation of Tanks.</span>&mdash;It will be noted that these verandahs
+are raised from the ground-level to a height of about 3 feet
+in order that latex may be gravitated, with a slight fall, into the
+coagulating tanks which are within the factory. There exists
+a real necessity for this practice, inasmuch as otherwise to<span class='pagenum'><a name="Page_176" id="Page_176">[176]</a></span>
+obtain gravitation of latex (which is quicker and cheaper than
+handling) the coagulating tanks would have to be either
+placed on the floor or sunk beneath the level. The risk of
+contamination of latex or coagulum under such circumstances
+would be appreciable. Apart from this, it is advisable to
+have the coagulating tanks raised to a height of between 2 and
+3 feet, to secure the advantage of ease of working in the
+processes of coagulation and the handling of coagulum&mdash;a not
+inconsiderable factor.</p>
+
+<p>In some modern designs it is proposed to place the coagulating
+tanks in a separate building. This would seem to be an
+unnecessary refinement in a new building, if observance is
+given to the suggestions made in previous paragraphs.</p>
+
+<p><a name="Sec14_8" id="Sec14_8"></a><span class="smcap">Designs and &#8220;Lay-Out.&#8220;</span>&mdash;In a
+previous publication<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17" class="fnanchor">[17]</a>
+comment was made upon grievous errors in designs prepared
+by those inexperienced in the requirements of the tropics.
+There is little ground now for complaint, and local engineering
+firms are fully capable of advising upon, and constructing,
+suitable buildings.</p>
+
+<div class="footnote"><p><a name="Footnote_17_17" id="Footnote_17_17"></a><a
+href="#FNanchor_17_17"><span class="label">[17]</span></a> &#8220;Preparation of Plantation Rubber,&#8221; Morgan, 1913.</p></div>
+
+<p>In considering the first installation of a factory and equipment
+one always has to weigh the question of prime cost against
+the probability of future expansion of crop. If it should be
+decided at first merely to cater for contemporary requirements,
+the fullest consideration should be given in discussing design
+of building and lay-out of machinery to the practicability of
+later extension. The site should be large enough for the
+eventual group of buildings, the building should be easily
+capable of extension with the least cost, and the same forethought
+should govern the lay-out of the machinery.</p>
+
+<p><a name="Sec14_9" id="Sec14_9"></a><span class="smcap">Drains.</span>&mdash;Lastly, there is the question of drains. Generally
+speaking, all factories are well provided with drains, and the
+only difficulty is that of getting an adequate fall for efficient
+drainage. But there is a certain amount of laxity exhibited
+in the matter of providing sieves in drains. To anyone acquainted
+with factory working, it must be apparent that quite
+a lot of small pieces of rubber are washed into the drains.
+This rubber should be collected at intervals during the day;<span class='pagenum'><a name="Page_177" id="Page_177">[177]</a></span>
+but in many instances that collected is only a fraction of what
+escapes. Wherever possible the drainings of a factory should
+be carried as far as is practicable from the buildings by means
+of cement drains. Too often these are short, and lead into
+earthen drains. Even if no pieces of rubber are present,
+the serum from the coagulum is subject to decomposition, the
+effluvium from which is objectionable.</p>
+
+<p><a name="Sec14_10" id="Sec14_10"></a><span class="smcap">Water Supply.</span>&mdash;It is essential that a good supply of water
+should be available. This should be distributed by pipes all
+round the building, so that a hose may be used in every part
+for the thorough cleansing of the factory at intervals during
+the hours of working.</p>
+
+<p>Summing up, it might be said that a good factory, therefore,
+should have the following features:</p>
+
+<div class="blockquot"><p>1. Plenty of windows, or walls of expanded metal.</p>
+
+<p>2. A jack-roof in the ridge, and hence a good system of ventilation.</p>
+
+<p>3. Engines in compartments outside the walls of the factory.</p>
+
+<p>4. Machines close to and parallel with the wall outside of
+which the engines are placed.</p>
+
+<p>5. Latex tanks and other fixtures along the wall opposite the
+machines.</p>
+
+<p>6. A long middle free space, at either end of which a large
+double door should be placed in the end walls.</p>
+
+<p>7. A good concrete and cement floor sloping slightly from
+the middle towards each long wall.</p>
+
+<p>8. An abundant water supply, and several lengths of hose.</p>
+
+<p>9. The building should be of only one floor, and have ample
+head room.</p>
+
+<p>10. There should be an outside, open verandah upon which
+latex may be received, etc.; preferably outside the wall which
+is opposite to the machines.</p>
+
+<p>11. The system of drainage should be thorough, and the
+drains should be adequately screened, so that all particles of
+rubber may be collected.</p></div>
+
+
+<p class='pagenum'><a name="Page_178" id="Page_178">[178]</a></p>
+<hr class="c25" />
+<h2><a name="Ch15" id="Ch15"></a>CHAPTER XV</h2>
+
+<h3><i>OTHER BUILDINGS</i></h3>
+
+
+<p><a name="Sec15_1" id="Sec15_1"></a><span class="smcap">Drying-Houses for Crepe.</span>&mdash;It has already been shown in the
+previous <a href="#Ch15">chapter</a> that one type of drying-houses&mdash;viz., that over
+a factory&mdash;stands condemned, except for the drying of low-grade
+rubbers. Generally speaking, a great advance has been made
+in the design of crepe drying-houses during recent years, and
+it has been possible even to improve older ones so as to bring
+them into line with the more modern buildings. Houses
+for drying crepe rubber may be of one floor, two floors, or
+even three floors. Doubtless those built with three floors
+were designed with a view to economising the available site
+for factory buildings, and as long as the ventilation is good there
+can be no very great objection to them. It might be pointed
+out, however, that even with the best of ventilation the air
+passing successively through three layers of rubber must
+be fairly saturated with moisture by the time it leaves the
+building. The effect of this upon the rate of drying in the
+uppermost chamber will not be so marked as it will be in the
+middle floor, as the temperature of the top floor must be
+many degrees higher than that of the other two rooms. It
+would be expected, therefore, that the rate of drying in the
+middle storey would be slower than that in either of the
+other two.</p>
+
+<p>In houses of two floors this objection would not have to be
+met, and drying-houses of this type are successful and common.</p>
+
+<p><a name="Sec15_2" id="Sec15_2"></a><span class="smcap">How Many Storeys?</span>&mdash;Again nothing could be urged
+against a building of two or three storeys in which the ground
+floor was occupied as a packing-room, except that, by negligence
+in not allowing wet crepe a preliminary dripping period,
+water might fall upon the packed rubber below.</p>
+
+<p><span class='pagenum'><a name="Page_179" id="Page_179">[179]</a></span>As a matter of experience, such a house is, taking all into
+consideration, the cheapest and most suitable type for any estate
+with an increase in output. Even at the outset there should
+be a separate room in which sorting and packing is undertaken.
+This is conveniently the lower room of a drying-house. The
+only stipulation to be made for a house with two storeys is
+that the floor of the upper room should be of an open pattern,
+so that the air may circulate right through the building. This
+is usually and very successfully attained by laying down wide
+slats of wood, with spaces of an inch or more between them.
+It is not advisable to have spaces wider than 1<span class="enum">1</span>&#8260;<span class="denom">2</span> inches,
+otherwise there is a certain amount of danger to the limbs of
+individuals who have to work or supervise in the building.
+In any case, it is very convenient to have pathways of planks
+running the whole length of the floor, so that the supervision
+is made more convenient. If this is done, there can be no objection
+to the custom of suspending the rubber of a lower chamber
+from the slats of the floor of the upper room. At present, in
+some drying-houses, this means of suspension is used, but no
+planks are laid down, and it becomes necessary to walk over
+the drying rubber. This is a detail, but it is one which does
+not make for the improvement of rubber, and the expenditure
+of a small sum would be sufficient to rectify the matter.</p>
+
+<p>From every point of view, it would be desirable to have the
+floor of the packing-shed (or the packing-room in a combined
+house) raised from the ground, to a height of, say, 3 feet;
+or the height of a bullock-cart or motor-lorry. Not only is
+ventilation improved, but there would be a great saving in
+labour. Packed cases could be wheeled directly on a level
+with the cart or lorry.</p>
+
+<p>A great many estates favour drying-houses of one storey.
+These are eminently suitable, provided that the site is suitable,
+and that the relative dimensions of the house are favourable
+to efficient ventilation. It is a common mistake to find buildings
+of which the breadth is out of proportion to the height.
+Obviously, if the height is not considerably in excess of the
+breadth, ventilation will be defective. For a single-storey
+drying-house, the maximum height should bear the ratio to the<span class='pagenum'><a name="Page_180" id="Page_180">[180]</a></span>
+breadth of 3:2, and in a house of this type specially long pieces
+of crepe can be utilised. Naturally, in a house of two storeys,
+this factor is not likely to be neglected, and if the lower room
+is used for packing purposes the rate of drying should be rapid.
+Again, when a single-storey building is contemplated, it is well
+to make strict examination of local conditions. If the site is
+low-lying and surrounded by trees it will be clear that tall
+buildings are required, and that a house of more than one floor
+is to be preferred. Considerations of this nature would have
+prevented the erection of some dry-sheds which do not give
+a satisfactory rate of drying.</p>
+
+<p><a name="Sec15_3" id="Sec15_3"></a><span class="smcap">Ventilation.</span>&mdash;No matter how many floors there may be in
+a drying-house, the greatest attention should be given to the
+question of ventilation. It is an elementary point in the study
+of ventilation problems that the best system of natural ventilation
+is obtained by admitting cool air near or through the floor
+and providing an exit for the warmer air at the highest point
+in the building. It is not often that such a rule is infringed
+in the ventilation of rubber drying-houses, but several of the
+older buildings erred in this respect. In a good modern house
+there is a space (about 2 feet in height) all round the base of
+the walls merely closed with expanded metal; this admits cool
+air. An exit for warm air is provided in the ridge of the roof
+by either ventilation chimneys or by a jack-roof. The latter
+is preferable, as it provides for a more free and uniform escape.</p>
+
+<p>In some drying-houses, besides the ridge openings, the space
+along the eaves is left open. This would seem to be undesirable,
+as it provides for the entrance of outer air, which
+might combat the ascending warm air and so interfere with
+the natural upward currents. Provided that a jack-roof or
+other suitable openings have been installed, there is, therefore,
+no necessity for the existence of open spaces at the eaves, and
+they probably do more harm than good.</p>
+
+<p>In the tropics, on days of sunshine, there must always
+be an upward current of air in well-designed houses. Temperatures
+of 105&deg; F. are easily recorded in the ridge space of a
+building, while the temperature in the lower part of the house
+may be at least 15&deg; F. lower. On the floor of an upper room a<span class='pagenum'><a name="Page_181" id="Page_181">[181]</a></span>
+temperature of 90&deg; F. is commonly noted, and in buildings
+with three storeys the usual day temperature of the top room
+is about or over 100&deg; F. Even, therefore, when there is no
+trace of a breeze, there must be a displacement of air in an
+upward direction, though it may not be detected without
+tests being applied.</p>
+
+<p>It is often asked whether a temperature of 100&deg; F., such as
+is obtained in the upper room, is calculated to injure the quality
+of the rubber. There need be no fear on this ground; the
+experience of many estates goes to show not only that no harm
+results, but also that the drying of the rubber is expedited.
+There would seem to be no reason why crepe rubber should not
+be dried at a temperature of 100&deg; F. It must be understood,
+however, that higher temperatures for crepe rubber are not
+recommended, as it has been proved that the rubber is affected.
+The fact becomes obvious with continued treatment at temperatures
+much above 100&deg; F., for the rubber stretches and breaks
+across the support.</p>
+
+<p><a name="Sec15_4" id="Sec15_4"></a><a name="Sec15_5" id="Sec15_5"></a><a name="Sec15_6" id="Sec15_6"></a><span
+class="smcap">Windows.</span>&mdash;Concerning the subject of window space in a
+drying-house, there has been much discussion at various times.
+Years ago it was common to find windows widely open with
+the sunshine streaming in. Naturally, tackiness developed
+in some of the rubber, and care was then taken to keep the
+windows closed. Thus the rooms were darkened and air
+excluded. There followed a period in which windows were
+fitted with ruby-coloured glass to keep out the actinic rays
+of the sun, which were responsible for tackiness, and excess of
+light, which was supposed to be responsible for the rapid
+oxidation of rubber. Unless special precautions were observed
+in the processes of coagulation and preparation, it was not
+proved that the exclusion of light prevented or lessened the
+natural oxidation of crepe rubber. Since the introduction of
+sodium bisulphite for the prevention of oxidation, there has
+been no cause to worry as to the possible effect of light, as no
+perceptible darkening of the rubber takes place. It follows,
+therefore, that no trouble need be taken to exclude light,
+although the necessity for excluding direct sunshine still exists.
+Windows may be left open as long as the sun does not reach<span class='pagenum'><a name="Page_182" id="Page_182">[182]</a></span>
+them. This can usually be arranged in a drying-house by
+manipulating the windows at intervals during the day, so that
+those in the shady side of a building are always open, while
+those on the sunny side are always closed. If it is thought
+that this manipulation cannot be entrusted with success to
+the store coolies, the case may be met by having all windows
+constructed on the louvre pattern, so that, although the windows
+are closed all day, air and light are not excluded. Should it
+be desired to retain the existing type of windows, which open
+outwards, and to keep them open all day, a simple arrangement
+of ruby-coloured cloth on an outstanding wooden frame may
+be placed within the walls of the building, or the shutters
+of the windows may be hinged at the top to open outwards.
+Unless there is a pronounced breeze, or it is required to
+examine the rubber closely, there is no necessity to have windows
+open, except in the case of a house in which the bottom floor
+is used as a packing-room. The windows of this chamber
+may remain open during the day, to advantage in sorting and
+packing, and also to the proper ventilation of the building.
+Thus the direct rays of the sun are rendered harmless, while
+air and light are allowed to enter.</p>
+
+<p><a name="Sec15_7" id="Sec15_7"></a><span class="smcap">Hot-Air Drying-Houses.</span>&mdash;Mention has already been made
+of the existence of a system of drying in which hot air is forced
+into a drying-house by means of a powerful fan. Provided
+that the temperature of the hot air could be so regulated as
+not to exceed 100&deg; F., there would be merit in the system.
+Such matter of regulation could be solved by having a duct in
+the main air passage, through which cool air could be admitted
+in such proportion as to modify the temperature of the hot air.
+As the process is worked at present, the temperature attained
+is often well above 100&deg; F., and there is a danger of thin crepe
+placed in this house over-night being found upon the floor
+in the morning. Unless the crepe is prepared thick and cut
+into fairly short lengths, it will not bear its own weight at
+higher temperatures; and if it is made thick, drying is impracticably
+prolonged. It is probable that, with a temperature
+of 100&deg; F., and a steady current of air, average thin crepe would
+dry in such a drying-house within six or seven days. This<span class='pagenum'><a name="Page_183" id="Page_183">[183]</a></span>
+would be an improvement upon the usual rate of drying in most
+factories, although several ordinary drying-houses are known
+in which thin crepe will dry naturally in that period.</p>
+
+<p><a name="Sec15_8" id="Sec15_8"></a><span class="smcap">Smoke-Houses.</span>&mdash;No discussion of theoretical considerations
+regarding the process of smoke-curing will be attempted here.
+We are concerned only with the necessity for supplying a
+demand for smoke-cured sheet rubber. Broadly, the process
+is akin to the smoke-curing of herrings, and the objects are
+much the same&mdash;viz., (1) drying, (2) preservation&mdash;except
+that while herrings are only dried partially, rubber should be
+dried perfectly.</p>
+
+<p>On a small scale a primitive smoke-house could be built
+easily and cheaply, and such a building might be fully as
+efficacious as the most elaborate and expensive installation.
+In the early days of estates it was not uncommon to see temporary
+smoke-houses constructed of wood, and roofed with
+&#8220;attaps&#8221; (palm leaves). Some of the best rubber in the
+market has come from wooden buildings, but naturally the risk
+of destruction by fire is considerable.</p>
+
+<p>For imperative reasons it may be sometimes found necessary
+to smoke rubber when the only available building is a single-storey
+one. As a temporary measure, the building may be
+converted into a smoke-house by placing the fires in pits sunk
+deeply into the ground, and effectively screened above by iron
+baffle plates. But it is not advisable that smoking be continued
+in such a single-storey building, as the best effects are not
+obtained, and the risk of fire is far too great.</p>
+
+<p><a name="Sec15_9" id="Sec15_9"></a><span class="smcap">Usual Types.</span>&mdash;At first sight it would appear that the best
+type of smoke-house would be one consisting of a tall building,
+covering a comparatively small superficial area, and having
+a number of superimposed chambers in which the rubber could
+be hung to dry. In practice there are several solid objections
+which limit the height and the number of floors. Chief
+among these is the question of temperature. If smoke-curing
+is to be effective, a certain temperature must be attained and
+maintained. To obtain such results in a house of excessive
+height would be difficult, if not impossible, under normal
+conditions. It would be found that the chamber immediately<span class='pagenum'><a name="Page_184" id="Page_184">[184]</a></span>
+above the furnace-room would be overheated if the temperature
+in the upper rooms was within the desired range, etc.</p>
+
+<p>Until recent years smoke-houses could be classed as belonging
+to one of two types:</p>
+
+<div class="blockquot"><p>(1) Those having external furnaces.</p>
+
+<p>(2) Those having internal furnaces.</p></div>
+
+<p>The number of the former existing at the present time must
+be very small, as it has been shown that the arrangement of
+the furnace outside the house is unsatisfactory in comparison
+with the other type of house. In discussing the question of
+smoke-houses, therefore, it will be understood that the standard
+type accepted is that having an internal furnace. In its
+original form it was known as a &#8220;Kent&#8221; drier, and consisted
+of a tall two-storey wooden building. The walls of the lower
+chamber had the form of an inverted and truncated pyramid.
+By this arrangement it was possible to obtain from a comparatively
+small fire sufficient smoke and heat to cure the
+product placed in the room above. This is the principle
+upon which many smoke-houses in Malaya are designed.
+On a very large scale it is not claimed that the sloping sides
+of the lower chamber lead to economy in the number of fires,
+but merely divert the smoke in an upward direction. It is
+acknowledged that vertical lower walls are quite effective,
+and it is an easier matter to fit in doors.</p>
+
+<p><a name="Sec15_10" id="Sec15_10"></a>It may be noted that the usual type of smoke-house now in
+general use consists of a building of two storeys, in the lower of
+which are situated the furnaces, while rubber is hung on
+racks in the upper room. Sometimes there may be a third
+storey, also used as a drying (curing) chamber. As a rule the
+drying-room is one long unit, as also is the furnace chamber;
+but in some cases they are subdivided by vertical partitions
+into smaller chambers, for ease of working and better control.
+This applies with some force in the case of very long houses
+standing in an open space. It is sometimes found in such
+cases that at certain seasons the prevailing winds have the
+effect of making drying and curing uneven in parts of the
+building.</p>
+
+<p><span class='pagenum'><a name="Page_185" id="Page_185">[185]</a></span>With these exceptions, the ordinary type of smoke-house
+functions very efficiently, and is capable of drying average
+sheet (from standardised latex) in a period ranging from
+seven to eleven days. Should the building not be capable of
+such performance, in spite of the strict observance of all rules
+laid down for the processes of preparation, then there is some
+defect in ventilation or in the distribution of heat.</p>
+
+<p><a name="Sec15_11" id="Sec15_11"></a><span class="smcap">General Ventilation.</span>&mdash;The ordinary rules of ventilation
+in drying-houses apply equally to a smoke-house. There
+should be a slow current of air and smoke from the lowest
+point to the highest point in the building.</p>
+
+<p>In spite of all that has been written on this subject, it is
+by no means uncommon to encounter the idea that a smoke-house
+should be perfectly closed in order to get good results.
+As to what must become of the (say) 25 per cent. of moisture
+which the rubber contains there is no knowledge. In dozens
+of cases, when complaints regarding slowness of drying have
+been investigated, it has been necessary to point out the need
+for providing a rational system of ventilation.</p>
+
+<p>Naturally only a slow current of air and smoke is required.
+The creation of an appreciable draught would have the effect
+of increasing the fuel consumption of the furnaces, raising
+dust from the ash, and of causing a temperature higher than
+that which is known to be desirable. It will be clear, therefore,
+that if there are to be any openings at the base of the walls
+they should be small in area, and should have some device by
+means of which the current of air can be efficiently regulated.
+In the usual case the construction of the building is not
+calculated to render it air-tight, and the necessity for providing
+special air inlets does not arise.</p>
+
+<p><a name="Sec15_12" id="Sec15_12"></a><span class="smcap">Windows.</span>&mdash;Windows are not strictly necessary, and are only
+intended to be of service during the time in which coolies are
+at work within the building. The operations of examining
+rubber, turning sheets, removing dry rubber, cleaning racks
+and floors, and putting wet rubber into position, usually occupy
+some hours daily. During this interval the windows should
+be widely opened if the weather is favourable, and should remain
+so until the fires have been lighted. It should not be forgotten<span class='pagenum'><a name="Page_186" id="Page_186">[186]</a></span>
+that during the heat of the day quite an appreciable degree of
+drying is possible. Advantage can be taken of this; but there
+is no necessity to extend the interval unduly, and it is of
+greater advantage to proceed with smoke-curing when the
+work in the drying-chambers has ceased.</p>
+
+<p><a name="Sec15_13" id="Sec15_13"></a><span class="smcap">Racks of Supports.</span>&mdash;Still referring to the usual type of
+smoke-house, it may be remarked that in the upper room
+bays of racks run at right angles to a central passage down the
+length of the building. Narrower passages run between the
+bays of the racks to facilitate ease in handling and inspection.
+The wooden supports may be placed about 3 inches apart
+horizontally, and 15 or 18 inches apart vertically. A full
+bay of racks should contain nine or more lines of support
+in each of the planes which are 15 or 18 inches apart vertically.
+The number of these planes is governed only by the height of
+the room, measured from the floor to eaves. The supports
+should be of smooth timber, and need not exceed 1<span class="enum">1</span>&#8260;<span class="denom">2</span> inches
+square in section.</p>
+
+<p>It is usual and advisable to smooth off the rectangular edges
+of the supports or bars, to avoid the incidence of splinters
+of wood adhering to the rubber. The bars should not be
+fixtures, but may either be accommodated in slots, or may
+rest <i>between</i> two nails, so that it is possible to give them a
+rotary motion by turning the projecting ends. This practice
+is followed in smoke-houses, the idea being to move the drying
+sheets slightly each day, with a view to the prevention of a
+pronounced mark across the sheets.</p>
+
+<p>Care should be taken to see that the vacant racks are thoroughly
+cleaned before fresh rubber is placed upon them,
+otherwise a distinct dirty mark is caused across the middle of
+the sheet. This mark usually cannot be removed, even by
+scrubbing with water. Where this mark occurs regularly in
+all sheets, attention should be turned to the openings beneath
+the bays of racks, if open fire furnaces are employed. It will
+generally be found that gauze of too wide mesh has been fitted.
+This should be removed or covered with a finer gauze.</p>
+
+<p>A more effective way of dealing with the trouble, provided
+other precautions have been taken, is to have plenty of spare<span class='pagenum'><a name="Page_187" id="Page_187">[187]</a></span>
+wooden bars. It should be a rule stringently enforced that,
+as soon as racks are emptied, the bars should be removed to
+the factory to be cleansed thoroughly. A spare set should enter
+the smoke-house with each batch of fresh rubber. The actual
+number of spare sets required could be limited to a two days&#8217;
+supply, and the extra cost would be recouped easily.</p>
+
+<p><a name="Sec15_14" id="Sec15_14"></a><span class="smcap">Floor of Drying-Chamber.</span>&mdash;The floor of the chamber is
+usually of planks, except that the space under each bay of
+racks should be filled with expanded metal. With the use of
+wood fires there is always a large amount of light ash formed,
+which may find its way into the upper chamber. To counteract
+this, screens of fine mesh gauze are laid over the expanded
+metal. This gauze may be fitted into a movable wooden
+frame, so that when it becomes necessary to clean it the whole
+may be removed.</p>
+
+<p>The difficulty is that with furnaces of the &#8220;open-fire&#8221; type
+the rise of dust is so great that the gauze screens soon become
+clogged, especially as the slight tarry matter in the smoke
+condenses on the gauze, causing the dust to adhere. With
+the better types of furnaces, the employment of gauze screens
+is not necessary, as there should be very little rise of dust.
+It is sufficient to use only expanded metal, to prevent any
+displaced pieces of rubber falling into the furnace chamber.</p>
+
+<p><a name="Sec15_15" id="Sec15_15"></a><span class="smcap">Furnaces Generally.</span>&mdash;The crudest and dirtiest method of
+fuel consumption in the preparation of smoked-sheet rubber
+is that of making a fire on the ground. This is still a common
+practice, and should be condemned as being both wasteful and
+harmful. Under prevailing conditions coolies will, in spite of
+instructions, heap up a pile of logs in order to save themselves
+the trouble of stoking the fire in small quantity and at regular
+intervals. A small supply of water is kept at hand with which
+to quench the fire somewhat if it threatens to cause trouble.
+Naturally a large quantity of fine ash is thus thrown up, and
+the rubber above receives the deposit. If the coolie does not
+happen to be sufficiently awake, of course a house burns
+occasionally.</p>
+
+<p>From this primitive type of furnace, others have been evolved.
+These usually take the form of more or less shallow trucks,<span class='pagenum'><a name="Page_188" id="Page_188">[188]</a></span>
+the majority of which are similar in principle to the fire on the
+ground, except that the container can be withdrawn from the
+house for the purpose of removing the ash. Sometimes they
+are even more objectionable than the ground fire, inasmuch as,
+being raised above the ground level, an under-draught through
+fire-bars is caused, and consumption of fuel is so much the
+more rapid.</p>
+
+<p><a name="Sec15_16" id="Sec15_16"></a><span class="smcap">Pits.</span>&mdash;It is clear that large fires are not desirable, and
+that combustion should be slow, provided that the necessary
+temperature can be maintained. The lines along which the
+development of furnaces needed to extend are therefore plain.
+The simplest device adopted was the digging of pits in the
+ground. Sometimes these pits received the addition of an
+iron truncated cone which was movable. Naturally the
+combustion was slow, but sufficient heat was obtained if the
+pits were large enough or in sufficient number. An objection
+was that the ash had to be cleared <i>in situ</i>, and in the process
+the earthen pits gradually increased in size. In all cases it was
+necessary to suspend an iron baffle-plate above the furnaces
+to distribute smoke and arrest any sparks.</p>
+
+<p><a name="Sec15_17" id="Sec15_17"></a><span class="smcap">&#8220;Pot&#8221;
+Furnaces.</span>&mdash;The next development was the employment
+of &#8220;pot-furnaces.&#8221; These consist of iron drums,
+sometimes merely resting on the ground, and sometimes
+mounted on trucks for easy withdrawal. These drums radiate
+sufficient heat if present in sufficient numbers, and the fuel
+consumption is low. They are usually manipulated by
+starting a fire in the bottom and packing in logs cut to the
+necessary length. Some have no lids, while others are fitted
+with perforated caps.</p>
+
+<p>It was considered necessary in some instances to punch a few
+small holes near the base of the drum in order to ensure a very
+slight upward draught. In a few cases this perforation has
+been exaggerated to the form of a hinged door. Unless this
+can be closed with ease, and is closed according to instructions,
+part of the object of this type of furnace is defeated; fuel consumption
+is rapid, and the temperature is too high. In the
+original form &#8220;pot-furnaces&#8221; have been found to be effective on
+many estates, and are still employed with satisfaction.</p>
+
+<p><a name="Sec15_18" id="Sec15_18"></a><span class='pagenum'><a name="Page_189" id="Page_189">[189]</a></span><span
+class="smcap">Iron Stoves.</span>&mdash;Working on exactly the same principle,
+on some estates one finds small iron stoves in use. Sometimes
+broad pipes are attached for the better distribution of the
+smoke; if this is the case it should be noted that the pipes should
+have a slight downward slope, and that the &#8220;bend&#8221; at the end
+should be turned downwards. In this way condensed moisture
+and creosotic matter falls to the ground, and does not lodge in
+the pipe. The life of the conduit is thus prolonged. Usually
+such stoves are in use where the &#8220;head-room&#8221; of a smoking
+chamber is insufficient for other types, or where the nature of
+the site does not permit of sunken furnaces being installed.
+They are of value likewise on occasions where the fuel supply
+is limited to a rich timber such as mangrove-logs (&#8220;bakau&#8221;),
+when it is necessary to ensure a low combustion with low cost
+of fuel.</p>
+
+<p><a name="Sec15_19" id="Sec15_19"></a><span class="smcap">Horizontal Drum-Furnaces.</span>&mdash;To overcome difficulties
+inherent to drums or &#8220;pot-furnaces,&#8221; the next development
+was that in which the drum was made to assume a horizontal
+position, and adapted ingeniously to a simple system of working
+from the outside of the building. Reference to the drawings
+given will explain how this is effected. In the first illustration
+(No. 2) it will be noted that the drum is supported upon brick
+pillars, with one end projecting through the wall of the building.
+At the other end a short chimney is mounted, having within it
+a &#8220;damper&#8221; which is adjustable from the outside. Over this
+chimney is suspended a simple baffle-plate, made from a Chinese
+iron cooking-pan. The outer end of the drum is furnished
+with a hinged and latched door, in which a small air-regulator
+is accommodated.</p>
+
+<p>In the second set of drawings (No. 1) the drum is increased
+in size and fitted in a special manner for incorporation with a
+distinct type of building. Such a scheme was first put into
+effect by Mr. R. C. Sherar, the manager of Third Mile Estate,
+Seremban, F.M.S., and for ease of reference the house and
+furnace will hereafter be mentioned when necessary as the
+&#8220;Third Mile&#8221; type.</p>
+
+<p class='pagenum'><a name="Page_190" id="Page_190">[190]</a></p>
+
+<div class="figcenter"><a name="Fig48" id="Fig48"></a><img src="images/illo207a.png" alt="'Third Mile' Type; Horizontal Drum" />
+<p class="caption"><span class="smcap">&#8220;Third Mile&#8221; Type; Horizontal Drum.</span></p>
+<p class="capt500">This type of furnace is suitable for adapting to existing buildings
+with perpendicular lower walls.</p></div>
+
+<div class="figcenter"><a name="Fig49" id="Fig49"></a><img src="images/illo207b.png" alt="Third Mile' Type of Furnace, used in Conjunction
+with 'Third Mile' Smoke-House" />
+<p class="caption"><span class="smcap">&#8220;Third Mile&#8221; Type of Furnace, used in Conjunction<br />
+with &#8220;Third Mile&#8221; Smoke-House.</span></p></div>
+
+<p>It will be seen that the furnace has at the farther end a door
+for the removal of ash. As this, if badly fitting, may result<span class='pagenum'><a name="Page_191" id="Page_191">[191]</a></span>
+in too great a draught, it is well to insist upon good workmanship.
+Other adjustable air-inlets are provided, and the drum
+is enclosed in a brick chamber.</p>
+
+<p><a name="Sec15_20" id="Sec15_20"></a><span class="smcap">Rate of Combustion.</span>&mdash;However successful this furnace
+may have proved in the hands of trained coolies, one must feel
+that with such a number of air-inlets (whether accidental or
+designed) there would always be present the possibility of
+obtaining too rapid a combustion. In the original forms of
+drums or pot-furnaces of various kinds, a very slow rate of
+combustion was attained. Naturally a relatively larger proportion
+of carbon remained unconsumed, and there was a small
+proportion of ash. In these respects the furnaces resembled
+charcoal-burners. In point of fact, some estates used this
+principle for the dual purpose of smoke-curing the rubber, and
+at the same time obtaining a supply of charcoal to provide
+fuel for their suction-gas engines. This is a consideration
+in times when managers are desirous of discovering any devices
+which tend towards reduction of costs.</p>
+
+<p>It will be clear that, under ordinary circumstances, the condition
+of what remains after the combustion of the fuel gives
+an indication of the rate at which the wood has burned, and this
+test should apply to all furnaces. That in which there is the
+most ash and the least charcoal is the one least to be desired.
+In direct connection with this consideration, one must recognise
+that a fire which is sunk below the level of the ground exposes
+the least surface from which heat may radiate; and hence, in
+order to obtain the maximum benefit of heat from a slow-combustion
+furnace, it should be above ground-level, or
+should have a superstructure from which the heat may be
+dissipated.</p>
+
+<p>Simple drum furnaces, with slow combustion, have the
+further advantages that a &#8220;charge&#8221; of fuel will need no attention
+for possibly eight to ten hours, and practically no ash
+is found to be ejected. These advantages have great practical
+importance. The first minimises any disabilities arising from
+neglect on the part of coolies, and the second makes for increased
+cleanliness in the drying-chamber. While these advantages
+would appeal to most estates, there would appear to be a further<span class='pagenum'><a name="Page_192" id="Page_192">[192]</a></span>
+advantage to small estates which have only temporary timber
+smoke-houses. With a slow rate of combustion in a furnace
+of this type, danger from fire is diminished considerably.</p>
+
+<p>Bearing in mind the slow rate of combustion, and hence the
+comparatively low temperature obtained, it will be plain that
+drum furnaces should be employed in larger number than
+ordinary open-hearth fires; and the drums can be so placed as
+to ensure the best possible uniform distribution of heat and
+smoke.</p>
+
+<p>Large furnaces are sometimes seen, with flues of brickwork.
+In view of the foregoing remarks, it will be obvious that these
+tend to large fires and a rapid combustion, and hence must be
+classed as undesirable.</p>
+
+<p><a name="Sec15_21" id="Sec15_21"></a><span class="smcap">Brick Stoves.</span>&mdash;Developing from &#8220;drum&#8221; furnaces, another
+type comes into existence. In principle it consists of an enclosed
+brick furnace, with feeding door, and a low conical
+dome surmounted by an adjustable cap or spark-arrester. The
+rate of combustion can be influenced by a suitable movement
+of the cap, which is operated by a screw. This type of furnace
+has been installed on several estates by the engineering department
+of Messrs. Harrisons and Crosfield, and is understood
+to give satisfaction.</p>
+
+<p><a name="Sec15_22" id="Sec15_22"></a><span class="smcap">Pataling Type.</span>&mdash;With the exception of the &#8220;Third Mile&#8221;
+type already mentioned, all the furnaces described are open to
+a strong objection, in that the coolies have to enter a room,
+usually filled with hot smoke, in order to attend to the fires.
+The mere opening of the door of the building is sufficient to
+fan most fires into a blaze and to raise sparks. Apart from
+these points, it is natural for coolies to avoid entering too often,
+with the result that they generally stoke with the maximum
+load of timber. Even should they not sleep the danger is
+clearly great.</p>
+
+<p class='pagenum'><a name="Page_193" id="Page_193">[193]</a></p>
+
+<div class="figcenter"><a name="Fig50" id="Fig50"></a><img src="images/illo210a.png" alt="Side Sectional
+Elevation (Pataling Type of Furnace)" />
+<p class="caption"><span class="smcap">Side Sectional Elevation (Pataling Type of Furnace).</span></p></div>
+
+<div class="figcenter"><a name="Fig51" id="Fig51"></a><img src="images/illo210b.png" alt="Pataling Type of Furnace" />
+<p class="caption"><span class="smcap">Pataling Type of Furnace.</span></p></div>
+
+<p>To obviate these drawbacks, furnaces which are fed from the
+outside of the building were designed. There have been
+various forms, but as they were first installed on Pataling Estate,
+in the present form, they may be known under the description
+of the Pataling type of furnace. They are eminently satisfactory,
+and have a low rate of fuel consumption. They are<span class='pagenum'><a name="Page_194" id="Page_194">[194]</a></span>
+very safe, and in fact, if worked with average intelligence in
+supervision, can be regarded as being fool-proof. There is
+practically no ejection of fine ash, and no fine-mesh screens
+need be employed. They can be adapted to any building
+having either vertical or sloping walls of galvanised iron.</p>
+
+<p>In essential the furnace consists of a shallow pit below
+ground-level, lined with brick, and having a square brick
+superstructure rising 4 feet above the floor of the building.
+On top of the brick walls rests a sheet of boiler-plate perforated
+with small holes. The hearth being below ground-level, and
+with the extra 4 feet of height above the floor, it follows that
+if ash is disturbed it is confined.</p>
+
+<div class="figcenter"><a name="Fig52" id="Fig52"></a><img src="images/illo211.jpg" alt="Large Smoke-House of
+Ordinary Construction, with Shielded Ventilators Permanently Open" />
+<p class="caption"><span class="smcap">Large Smoke-House of Ordinary Construction, with Shielded<br />
+Ventilators Permanently Open.</span></p>
+<p class="capt500">In foreground, movable folding racks on which sheets &#8220;drip&#8221; in
+the open air. This smoke-house is equipped with brick furnaces
+fed from the outside (Pataling Estate).</p></div>
+
+<p>From the <a href="#Fig50">drawings</a> it may be seen that the pit is prolonged
+to the side wall of the building, with steps leading up to the
+ground-level. The top and sides of the opening are made
+with galvanised sheeting, forming a kind of short tunnel in<span class='pagenum'><a name="Page_195" id="Page_195">[195]</a></span>
+which the coolie may stand upright. The outer face of the
+brick furnace forms the inner end of the tunnel, and accommodates
+the door of the furnace. The bottom of the pit is filled
+up with clay and stones almost to the level of the bottom of
+the door. This ensures a very shallow hearth, and guards against
+an unduly large fire. Obviously it is not desirable or necessary
+to make the hearth of fire-bars, as was done in one instance,
+with the provision of a door below for removing the ash. This
+would lead only to a strong draught being created, with a high
+rate of fuel consumption.</p>
+
+<div class="figcenter"><a name="Fig53" id="Fig53"></a><img src="images/illo212.jpg" alt="Brick and Cement
+Superstructure of Furnace Inside the Building, but fed from Outside" />
+<p class="caption"><span class="smcap">Brick and Cement Superstructure of Furnace Inside the<br />
+Building, but fed from Outside.</span></p>
+<p class="capt500">On the top of the superstructure rests a sheet of perforated boiler-plate.
+The actual fire-pit is below ground-level, and to the left
+may be seen parts of the sides and top of the downward approach,
+from the outside, to the door of the fire-pit.</p></div>
+
+<p>The openings can be screened by a narrow sloping lean-to,
+which serves to keep out rain, and provides shelter for the stock
+of fuel and the coolie. The iron furnace-door should be well
+made, with an easily worked latch; but it is not necessary that
+it should be perfectly fitting. Any slight aperture will serve<span class='pagenum'><a name="Page_196" id="Page_196">[196]</a></span>
+to provide the necessary air-inlet, but in any case it should
+not be more than slight.</p>
+
+<p><a name="Sec15_23" id="Sec15_23"></a><span class="smcap">Consumption of Fuel.</span>&mdash;Regarding this furnace, it may be
+said in conclusion that it is more satisfactory in general working
+than any other furnaces yet encountered. Obtaining information
+from over sixty estates, on the question of fuel consumption
+compared with output of rubber, it was found that,
+as far as ordinary smoke-houses were concerned, the Pataling
+type of furnace showed the lowest unit consumption of fuel.</p>
+
+<div class="figcenter"><a name="Fig54" id="Fig54"></a><img src="images/illo213.jpg" alt="General View of Shelters covering Approaches to
+Furnaces" />
+<p class="caption"><span class="smcap">General View of Shelters covering Approaches to
+Furnaces.</span></p></div>
+
+<p>This was at the rate of slightly less than 1 lb of fuel per 1 lb of
+thoroughly cured sheet rubber. The figure on some estates
+mounted as high as 4<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. of fuel per lb. of rubber. Naturally
+this factor may have been affected by failure to utilise the drying
+space to its fullest capacity, but in the main the high rate of
+consumption could be attributed solely to the deficiencies of
+the furnaces.</p>
+
+<p><a name="Sec15_24" id="Sec15_24"></a><span class="smcap">Floor of Furnace-Room.</span>&mdash;As a rule no attempt is made to
+improve the natural earthen floor. Whether open-hearth fires,<span class='pagenum'><a name="Page_197" id="Page_197">[197]</a></span>
+truck furnaces, or drums are employed, it is usual to find a
+floor with an inch or two of dust upon it. Where all endeavours
+are directed in other directions towards cleanliness, it appears
+strange that this should be overlooked. In contrast, houses
+employing the Pataling type of furnace (or others) have concrete
+and cement floors, which can be kept quite clean. Cleanliness
+should be as zealously attempted in the smoke-house as
+in other departments.</p>
+
+<div class="figcenter"><a name="Fig55" id="Fig55"></a><img src="images/illo214.jpg" alt="Near View of Shelter" />
+<p class="caption"><span class="smcap">Near View of Shelter.</span></p>
+<p class="center">Steps lead downwards where the wall of the smoke-house has
+been removed.</p></div>
+
+<p><a name="Sec15_25" id="Sec15_25"></a><span class="smcap">Roof.</span>&mdash;In any type of smoke-house, the roof should fit
+tightly at the eaves, and the only vent should be in or near the
+roof-ridge.</p>
+
+<p>In an ordinary smoke-house, the opening should take the form
+either of a low jack-roof or of squat chimneys protected against
+rain. If a jack-roof is chosen, it may be so low as to need no
+scheme of adjustment, or otherwise adjustable swing shutters
+must be provided. The chimneys may be made with such low
+fitting between the cap and the body that no interior swinging
+flaps are required.</p>
+
+<p><span class='pagenum'><a name="Page_198" id="Page_198">[198]</a></span>During the operation of smoke-curing the smoke vents must
+remain open to a degree which is arrived at by experience.
+Failure to provide a comparatively free egress for smoke and
+moisture will bring trouble in its train. After a house has been
+in use for some time, it will be noted that the timber becomes
+covered with a shiny tarry coating deposited by the smoke.
+If the rubber remained in the house for an equal period, it
+would take on the same appearance. During the interval
+between the entry and the exit of the rubber some amount
+of deposit does take place, and it is this mixture of creosotic
+substances which plays a part in fitting the rubber to withstand
+growths of mildew which would otherwise form.</p>
+
+<p>If proper smoke-vents are not provided, the moisture evaporating
+from the sheets is unable to escape quickly enough, with
+the result that a great deal condenses at night-time upon the
+inner surface of the comparatively cool roof, and falls back
+upon the rubber in unsightly black &#8220;drips,&#8221; which leave a
+distinct mark on the sheet. Even if vents are open, this may
+happen during seasons of rain. The temperature of the moist
+smoke in the roof-ridge may be as high as 130&deg; to 140&deg; F.,
+while the outer atmosphere may have been cooled by rain to
+70&deg; F. Such a difference on the two surfaces of the roof must
+lead to condensation within the house, with consequent
+&#8220;dripping.&#8221; It used to be the custom to drape sacking
+material above the bays of racks in order to prevent the drops
+of liquid falling upon the rubber; but often for want of renewal
+the last state was worse than the first. Modern houses have
+often an inner lining, a few inches below the roof. This is
+made of soft wood which receives any product of condensation
+and absorbs it.</p>
+
+<p><span class="smcap">Other Types of Smoke-House.</span>&mdash;So far we have confined
+the arguments to smoke-houses of the usual type. There
+are others which vary in either design and method of working,
+or in the material of the structure. Mention may be made
+of the most prominent of these.</p>
+
+<p><a name="Sec15_25a" id="Sec15_25a"></a><span class="smcap">Brick Houses.</span>&mdash;Some houses are constructed of brick, and
+may have one or two storeys above the furnace chamber. The
+floors are sometimes made of ferro-concrete, and the furnaces<span class='pagenum'><a name="Page_199" id="Page_199">[199]</a></span>
+may also be of this material. These brick houses give satisfaction,
+but there would seem to be some difficulty in obtaining
+and maintaining the desired temperature, although it is not
+quite plain why this should be so. The principle of these
+buildings is the same as that of the ordinary iron house, and
+the suggestions made in previous paragraphs apply with
+equal force.</p>
+
+<p><a name="Sec15_26" id="Sec15_26"></a><span class="smcap">&#8220;Third Mile&#8221; Type.</span>&mdash;Reference has been made to the
+&#8220;Third Mile&#8221; type of furnace. This is an integral part of a
+smoke-house, which for clearness of distinction may be known
+as the &#8220;Third Mile&#8221; type of smoke-house, the original of
+which was erected on the Third Mile Estate, Seremban, F.M.S.</p>
+
+<div class="figcenter"><a name="Fig56" id="Fig56"></a><img src="images/illo216.png" alt="'Third Mile' Type of Smoke-House" />
+<p class="caption"><span class="smcap">&#8220;Third Mile&#8221; Type of Smoke-House.</span></p></div>
+
+<p>In essence the design consists of a building, having two
+storeys for rubber-drying, and a shallow inverted pyramidal
+base, ending on the ground in &#8220;Third Mile&#8221; furnace, already
+described and illustrated.</p>
+
+<p>It will be seen that the principles of ventilation employed are
+those indicated for an ordinary house&mdash;viz., air-inlet near the<span class='pagenum'><a name="Page_200" id="Page_200">[200]</a></span>
+ground (with little draught), and smoke-vent at the roof-ridge.
+The windows shown in the drawing are only for purposes of
+inspection of the rubber during the day, and form no part of
+the scheme of ventilation during the hours of smoking.</p>
+
+<p>It is claimed that the efficiency of the house is high. Certainly
+the work of attending to the furnaces is simplified, and there
+should be small ground for excuse if negligence is displayed.</p>
+
+<p><a name="Sec15_27" id="Sec15_27"></a><span class="smcap">Jackson House.</span>&mdash;This was brought into notice under the
+description of the &#8220;Jackson Cabinet,&#8221; and it was claimed
+that average sheets could be dried in a few days. It consisted
+of a small house of one storey, having several tiers of racks.
+Smoke and heat were generated in a small stove placed outside
+the wall. A smoke vent was provided in the roof. These
+cabinets had a certain vogue as part of a small unit installation,
+with a fair degree of success. It is not clear, however, that
+such speed in drying is required. (This point will receive
+further attention in a <a href="#Sec17_20">subsequent chapter</a>.)</p>
+
+<p><a name="Sec15_28" id="Sec15_28"></a><span class="smcap">&#8220;Devon&#8221;
+Type.</span>&mdash;In its full original design this type owes
+its origin to Mr. H. E. Nixon, General Manager of the Devon
+Estates, Malacca, where it forms part of unit divisional installations
+worked under a scheme of decentralisation.</p>
+
+<p>The original units consisted of a building erected with an
+iron framework covered with sheets of asbestos-slate, and a
+roof of galvanised iron.</p>
+
+<p>The novelty in design lies in the utilisation of external
+platforms upon which the racks of bars supporting the sheets
+of rubber may be drawn out of the smoking chambers, and
+on which the racks are loaded and unloaded. By this device
+it is possible to remove the contents of any compartment
+bodily without interfering with the continuity of curing in the
+other compartments. That is to say, smoking in such a house
+can proceed day and night if necessary, and yet the rubber in
+any part of the house can be examined, can be removed, or can
+be replaced without cessation of smoking.</p>
+
+<p>It will be seen from the illustrations that the house is more
+or less of the same general design as the &#8220;Third Mile&#8221; type,
+with the addition of external platforms. It has two storeys
+for the reception of rubber; and a basal furnace-room with<span class='pagenum'><a name="Page_201" id="Page_201">[201]</a></span>
+sloping sides converging downwards into a pit containing a large
+drum-furnace. This is mounted on a low truck, and travels
+on a short length of railway.</p>
+
+<div class="figcenter"><a name="Fig57" id="Fig57"></a><img src="images/illo218.jpg" alt="General
+View of Double 'Devon' Type of Smoke-House." />
+<p class="caption"><span class="smcap">General View of Double &#8220;Devon&#8221; Type of
+Smoke-House.</span></p>
+<p class="capt350">The platforms are common to both units. Building of brick with
+iron roof (Batu Caves Estate).</p></div>
+
+<p>Each of the curing-rooms is divided into four compartments
+(making eight compartments in all). These are closed by
+swing doors, each of which is the full width of a compartment,
+and has a slight overlapping edge. Through these doors light
+railways run into the house and out upon the platforms. On<span class='pagenum'><a name="Page_202" id="Page_202">[202]</a></span>
+the rails &#8220;bays&#8221; of racks run, and when fully loaded they
+are easily moved. The racks were designed with a frame of
+stout hard wood, but light angle-iron could be utilised.</p>
+
+<div class="figcenter"><a name="Fig58" id="Fig58"></a><img src="images/illo219.jpg" alt="General View of Double
+'Devon' Smoke-House and Factory Buildings" />
+<p class="caption"><span class="smcap">General View of Double &#8220;Devon&#8221; Smoke-House and Factory Buildings.</span></p>
+<p class="capt500">Timber in foreground cut to length for stoking. Note water-tower and engine cooling-tanks
+adjacent to factory.</p></div>
+
+<p>The chimney style of smoke-vent has an internal butterfly
+flap, which is controlled by means of a wire from the outside.
+In the ordinary course of smoke-curing, it is advised that this
+flap should be permanently open so as to reduce the possibility<span class='pagenum'><a name="Page_203" id="Page_203">[203]</a></span>
+of internal condensation of moisture and creosotic matter.
+The exact degree to which it should be open must be found
+by experience.</p>
+
+<div class="figcenter"><a name="Fig59" id="Fig59"></a><img src="images/illo220.jpg" alt="View of
+Platform of 'Devon' Smoke-House; Doors of Compartments Open, and
+One Rack Partially Withdrawn" />
+<p class="caption"><span class="smcap">View of Platform of &#8220;Devon&#8221; Smoke-House; Doors of Compartments Open, and<br />
+One Rack Partially Withdrawn.</span></p>
+<p class="center">Note below each rack opening through which smoke rises, covered with wire netting.</p></div>
+
+<p>Although reference has been made several times to
+compartments, it should be understood that the chambers
+are not subdivided internally by means of partitions.
+There exists only the external effect of compartments in<span class='pagenum'><a name="Page_204" id="Page_204">[204]</a></span>
+the form of the eight swinging doors which allow for the
+withdrawal of, or insertion of, any one unit of racks
+at any time without interference with the bulk of the
+rubber.</p>
+
+<p class='pagenum'><a name="Page_205" id="Page_205">[205]</a></p>
+
+<div class="figcenter"><a name="Fig60" id="Fig60"></a><img src="images/illo221.jpg" alt="Double 'Devon' Smoke-House of Brick, with Roof of
+Chinese Tiles, showing Loading Platforms with Racks Withdrawn from Smoking Chambers" />
+<p class="caption"><span class="smcap">Double &#8220;Devon&#8221; Smoke-House of Brick, with Roof of<br />
+Chinese Tiles, showing Loading Platforms with Racks<br />
+Withdrawn from Smoking Chambers.</span></p>
+<p class="center">Federated Engineering Co., Ltd., Kuala Lumpur.</p></div>
+
+<p><a name="Sec15_29" id="Sec15_29"></a><span class="smcap">Detailed Description.</span>&mdash;As enquiries are often received it
+is permissible to reproduce the following detailed description
+of the original house. This appeared in the Fourth Local
+Report (Malaya) 1916, issued to subscribers by the Rubber
+Growers&#8217; Association.<span class='pagenum'><a name="Page_206" id="Page_206">[206]</a></span></p>
+
+<div class="blockquot"><p>&#8220;The house has a steel frame-work, 22 feet long, 16 feet
+wide, and 22 feet high. Of the length, 14 feet is occupied
+by the platforms, and 8 feet by the chambers. These measurements
+can be varied. The whole of the width (16 feet) is
+occupied by compartments of which one series is placed above
+the other.</p></div>
+
+<div class="figcenter"><a name="Fig61" id="Fig61"></a><img src="images/illo222.jpg" alt="Side View of Preceding
+Photograph, showing External Arrangement for Stoking Furnaces" />
+<p class="caption"><span class="smcap">Side View of Preceding Photograph, showing External<br />
+Arrangement for Stoking Furnaces.</span></p>
+<p class="center">Federated Engineering Co., Ltd., Kuala Lumpur.</p></div>
+
+<div class="blockquot"><p>&#8220;<i>Platforms.</i>&mdash;The loading verandahs or platforms are of
+ordinary &#8217;seriah&#8217; timber.</p></div>
+
+<div class="blockquot"><p>&#8220;<i>Compartments and Furnace Chamber.</i>&mdash;These are enclosed
+with Bell&#8217;s &#8217;Poilite&#8217; sheets, each of which measures 8 feet by
+4 feet by <span class="enum">3</span>&#8260;<span class="denom">16</span> inch. The sheets are affixed to the steel stanchions,
+doors, etc., by galvanised bolts (1 inch by <span class="enum">1</span>&#8260;<span class="denom">4</span> inch) which pass
+through iron flats measuring 8 feet by 2 inches by <span class="enum">3</span>&#8260;<span class="denom">8</span> inch
+(about). These iron flats hold the sheets at the edges. The
+dimensions of the compartments are 8 feet by 8 feet by 4 feet.</p>
+
+<div class="figcenter"><a name="Fig62" id="Fig62"></a><img src="images/illo223.jpg" alt="Front
+View of Double 'Devon' Type of Smoke-House" />
+<p class="caption"><span class="smcap">Front View of Double &#8220;Devon&#8221; Type of Smoke-House.</span></p>
+<p class="center">Glenmarie Estate: Batu Tiga Co.</p></div>
+
+<p>&#8220;<i>Racks.</i>&mdash;These are eight in number, and measure just
+under 8 feet by 8 feet by 4 feet. The capacity of each is
+roughly about 450 lbs., of dry sheet rubber. The racks are
+mounted on 6-inch iron wheels, running on rails of stock size,
+&#8217;T&#8217; iron (1<span class="enum">3</span>&#8260;<span class="denom">4</span>
+inches by 1<span class="enum">3</span>&#8260;<span class="denom">4</span> inches by
+<span class="enum">1</span>&#8260;<span class="denom">4</span> inch).</p>
+
+<p><span class='pagenum'><a name="Page_207" id="Page_207">[207]</a></span>&#8220;The sheets are hung on split bamboos. To prevent these
+projecting over the edge of the rack and catching in the doors
+when the rack is moved in or out, a thin strip of wood, about
+<span class="enum">1</span>&#8260;<span class="denom">2</span> inch high, is nailed along the sides of the rack.</p>
+
+<div class="figcenter"><a name="Fig63" id="Fig63"></a><img src="images/illo224.jpg" alt="Side
+View of Double 'Devon' Type of Smoke-House" />
+<p class="caption"><span class="smcap">Side View of Double &#8220;Devon&#8221; Type of Smoke-House.</span></p>
+<p class="capt350">Building constructed of galvanised iron. Shows door to furnace
+chamber, and ventilator.</p></div>
+
+<p>&#8220;<i>Furnace.</i>&mdash;This is of the type that aims at slow combustion.
+It consists of a cast-iron cylinder, 3 feet in diameter and 4 feet
+high, carried on a truck made of a sheet of boiler-plate, and
+mounted on small wheels, so that the whole can be moved
+easily out of, and into, the furnace chamber for easy cleaning
+and stoking.</p>
+
+<p>&#8220;The furnace chamber is a pit lined with concrete, just<span class='pagenum'><a name="Page_208" id="Page_208">[208]</a></span>
+wide enough to take the trolley, and about 12 feet long. The
+top of the furnace, which is almost flush with the ground-level,
+consists of a sheet of zinc or galvanised iron with numerous
+holes about 3 inches in diameter. Over these holes are strips
+of mosquito gauze, as flame and dust arresters (see <a href="#Footnote_18_18">note</a> below).
+There are no holes in the sides or bottom of the cylinder.</p>
+
+<p>&#8220;Over the furnace is hung a baffle-plate, measuring 4 feet
+by 4 feet. Above this, on the first floor-level, the bottom of
+the compartments is covered with wire netting, to prevent any
+rubber dropping accidentally into the furnace chamber. The
+furnace chamber is fitted with an iron-frame door, swinging
+on perpendicular hinges.</p>
+
+<p>&#8220;<i>Method of Stoking.</i>&mdash;The timber used is a mixture of
+jungle wood and rubber-tree wood, cut to lengths of about 1<span class="enum">1</span>&#8260;<span class="denom">2</span>
+feet. In the ordinary way the furnace is charged at 6 p.m.,
+and at six-hour intervals a little more fuel is added, but a new
+charge is not necessary. During the daytime, when the heat
+of the sun is sufficient to raise the temperature appreciably,
+a smaller fire is maintained.</p>
+
+<p>&#8220;<i>Temperature.</i>&mdash;There is no difficulty in maintaining a
+temperature of 120&deg; F. By continuous smoking, average sheets
+prepared from standardised latex can be fully cured in five days.
+This represents 110 hours of smoke-curing, which is at least
+equal to ten days&#8217; intermittent smoking in an ordinary house.</p>
+
+<p>&#8220;<i>Capacity.</i>&mdash;There are eight racks, each accommodating
+450 lbs. of standardised sheet rubber. The loading capacity
+of the house, therefore, is 3,600 lbs. As each charge is cured in
+five days, the monthly output may be 21,000 lbs.</p>
+
+<p>&#8220;The cubic capacity is 2,048 cubic feet. As there are no gangways,
+etc., this is fully utilised. This gives a rate of monthly
+output capacity to over 10<span class="enum">1</span>&#8260;<span class="denom">4</span> lbs. dry rubber per cubic foot of
+drying space; an excellent figure much in advance of values
+obtained in the great majority of ordinary smoke-houses.&#8221;<a name="FNanchor_18_18"
+id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a></p></div>
+
+<div class="footnote"><p><a name="Footnote_18_18" id="Footnote_18_18"></a><a
+href="#FNanchor_18_18"><span class="label">[18]</span></a> Since the above was written, it has been found possible to
+eliminate the gauze. A mild steel top has been made, perforated
+with 2-inch holes. Practically no dust is ejected from the furnace,
+and there are no flames.</p></div>
+
+<p>Owing to shortage of supplies during the War, similar
+buildings have been erected with frames of well-seasoned
+hard wood, which was protected by strips of asbestos-slate or
+galvanised iron. The latter material was also substituted in
+the covering walls. Later, houses were erected of brick,
+with other minor modifications. As a natural development, the<span class='pagenum'><a name="Page_209" id="Page_209">[209]</a></span>
+latest buildings consist of two of the original houses face to
+face, under a common roof, and served by common platforms.</p>
+
+<p>As originally designed, the house was intended to meet the
+needs of a small estate, or a division of an estate, having a
+maximum output of about 20,000 lbs. of sheet rubber per
+month. The possibility of an extension of this idea has been
+shown to be great.</p>
+
+<p>The furnace has been described as situated in a pit. Situated
+on a bank or on sloping ground, it was easy to arrange for
+withdrawal of the furnace. In some cases this has not been
+possible, and various modifications have been effected. The
+most satisfactory yet encountered is that in which a shallow
+brick pit is surmounted by an iron cone, about 4 feet in height.
+This is fitted with a cap having small perforations. The fire
+burns in the pit, and the heat is radiated by the cone. It
+would have been more effective to have allowed greater height
+in the furnace chamber, and to have employed the travelling
+drum-furnace as in the original design.</p>
+
+<p>In order to avoid interference in draught by a space between
+the bottom of the doors of the compartments and the platform
+(due to the presence of rails), the floor of the platform is laid
+level with the top of the rails; or to the bottom of the doors is
+attached a swinging flap, notched for accommodating the rails
+when in position.</p>
+
+<hr class="c05" />
+
+<p>There are in use houses of other designs, which all more or
+less vary only in some modifications from the types described.
+Hence they do not call for special comment. Recently a
+rather distinct departure has been noted in a structure designated
+the &#8220;Barker&#8221; smoke-house.</p>
+
+<p><a name="Sec15_30" id="Sec15_30"></a><span class="smcap">Barker Patent.</span>&mdash;In essential this consists of a long narrow
+structure erected with an appreciable slope from one end to the
+other. At the lower end is a small furnace enclosed in a brick
+compartment. The smoke from this furnace travels up the
+slope to the other end, at which the rubber enters. The
+sheets are hung on bars which are attached to a unit framework.
+This frame slides, by its own weight, upon timber
+side supports. A sufficient number of these units occupies<span class='pagenum'><a name="Page_210" id="Page_210">[210]</a></span>
+the full effective length of the structure. The removal of
+&#8220;stops&#8221; at the lower end enables the foremost frame to be
+removed, and the succeeding frames slide into a new position.
+Thus the freshly prepared sheets, entering at the higher end,
+gradually and automatically move towards the furnace as the
+frames of dry rubber are removed from the lower end.</p>
+
+<div class="figcenter"><a name="Fig64" id="Fig64"></a><img src="images/illo227.jpg" alt="The New 'Barker'
+Type of Smoke-House: a Small Unit" />
+<p class="caption"><span class="smcap">The New &#8220;Barker&#8221; Type of Smoke-House: a Small Unit.</span></p>
+<p class="capt500">The racks slide automatically from top to bottom on withdrawal
+of the lower frames through door at front. The furnace is contained
+in the brick compartment at the lower (front) end.</p></div>
+
+<p>Thus far only small units have been seen. It is claimed
+that, properly prepared, sheet rubber can be smoke-cured in
+about five or six days, and it is stated that installations have
+been in successful working for sufficiently long periods to
+prove their efficacy. The device is better known in Java and
+Sumatra than in Malaya. The capacity of a unit building is
+stated to be 7,000 lbs. per month, calculating on a six days&#8217;
+cycle of working. In a more recent design provision is made
+at the lower end for a water tank, into which all rubber can be
+discharged in case of fire.</p>
+
+
+<p class='pagenum'><a name="Page_211" id="Page_211">[211]</a></p>
+<hr class="c25" />
+<h2><a name="Ch16" id="Ch16"></a>CHAPTER XVI</h2>
+
+<h3><i>OTHER BUILDINGS (continued) AND SITUATION OF
+BUILDINGS</i></h3>
+
+
+<p><a name="Sec16_1" id="Sec16_1"></a><a name="Sec16_2" id="Sec16_2"></a><span
+class="smcap">Sorting-Room and Packing-Room.</span>&mdash;It is in these departments
+that most factory installations are lacking. More often
+than one cares to acknowledge, sorting and packing are done
+under conditions which place a premium upon poor work.
+As a consequence, consignments of rubber are often marred
+by the inclusion of defective specimens. The result is that
+shipments may be rejected when tendered against contracts,
+or that allowances in price have to be made. In many instances
+it would not be fair to lay the blame upon the manager or an
+assistant, as it is obviously impossible for an individual to inspect
+every piece of rubber. Neither would it be strictly fair in some
+cases to ascribe the fault to pure carelessness on the part of
+the coolies.</p>
+
+<p>Often the only provision made for this important work is the
+lower room of a drying-shed, which may also contain hanging
+rubber. Under these circumstances, space is cramped, and
+the light often poor. Small defects may pass unnoticed, and
+the general surroundings do not conduce to keen work.</p>
+
+<p>Where, for economic reasons, the sorting and packing operations
+are conducted in the drying-shed, there should be ample
+space free from hanging rubber, and it should not be possible
+for wet rubber placed in the upper room to drip upon the dry
+rubber below or upon packed cases. There should be plenty
+of light, and for this reason windows should be ample. Usually
+the window-frames are fitted with wooden shutters, which
+are preferably hung on horizontal hinges from the top of the
+frame. By this device it is not necessary to close all windows
+during a shower of rain, and rubber may be stacked near a
+window with reasonable chance that direct sunlight will not
+be allowed to fall upon it.</p>
+
+<p><span class='pagenum'><a name="Page_212" id="Page_212">[212]</a></span>In dealing with smoked sheet, it is advised that the rubber
+to be examined should be placed upon tables facing the windows,
+so that each piece may be scrutinised in a strong light.</p>
+
+<p>Crepe rubber also is best examined in a strong light, but
+preferably with one&#8217;s back towards the source of light or at an
+angle to it. For this work coolies usually are most efficient
+when sitting on the floor.</p>
+
+<p>It will be clear from the foregoing remarks that the best
+conditions would be secured in a separate building especially
+constructed. A single room would be all that is required;
+at one end sorting could be undertaken, while packing could
+be done at the other end. No hanging rubber should be
+allowed in the room.</p>
+
+<p>The floor should be of hard timber, and raised from the
+ground, to the height approximately of a bullock-cart or motor-lorry,
+as the case may be. The boxes of rubber could thus be
+transported by small hand-trucks on a level with the transport
+vehicle, reducing labour to the minimum.</p>
+
+<p>The ventilation of the building should be good, especially
+if cases of rubber are to be stored therein; and the entire
+structure should be weather-proof.</p>
+
+<p><a name="Sec16_3" id="Sec16_3"></a><a name="Sec16_4" id="Sec16_4"></a><span class="smcap">Store-Rooms
+for Rubber and Storage.</span>&mdash;The question
+of storage of rubber in factory buildings has always possessed
+importance, but has demanded increased consideration recently.</p>
+
+<p><a name="Sec16_5" id="Sec16_5"></a>From experience in this country, it is clear that cement floors
+for store-rooms or packing-sheds are the least suitable. They
+are often visibly damp, especially in the early morning. To
+allow rubber, packed or unpacked, to remain upon a cement
+floor in the tropics, is to court trouble from moulds, external
+or internal. If the employment of a cement floor is unavoidable,
+the rubber and boxes should be raised on wooden supports,
+giving a clearance of at least 3 or 4 inches, and there should be
+clear ventilation space between tiers of boxes.</p>
+
+<p><a name="Sec16_6" id="Sec16_6"></a>Experience indicates that the best type of floor is that already
+advised for sorting and packing rooms&mdash;<i>i.e.</i>, a good hard timber
+floor raised at least 3 feet above ground-level. Apart from the
+advantage in labour specified in the previous paragraphs, this
+provision of ample ventilation space below the floor is a great<span class='pagenum'><a name="Page_213" id="Page_213">[213]</a></span>
+consideration in the preservation of the timber. Raised store-rooms
+become essential in low-lying districts which are at all
+subject to flooding, yet the writer has seen many boxes of rubber
+damaged by flood-water entering a packing-room situated on
+the level.</p>
+
+<p>The question has often been raised recently as to the length
+of the period during which rubber may be safely stored in this
+country. The answer can be only supplied by experience, of
+which up to the present we have none possible of being classed
+as reliable. Whatever storage may have been done in the past
+has been influenced greatly by the unsuitability of the storage
+accommodation, and the fact that often the rubber was not
+prepared with a view to prolonged storage.</p>
+
+<p>While the market demand was strong, rubber was being
+shipped and passed into circulation, at a rate which did not
+demand investigation of the subject of local storage. In the
+year 1918 conditions were such as to bring the matter into prominence,
+and we were able to tender advice on the lines given
+in this chapter. The necessity passed, but has again arisen.</p>
+
+<p><a name="Sec16_7" id="Sec16_7"></a>Our experience goes to prove that if rubber is properly
+prepared and thoroughly dried before packing, it will remain
+in good condition for a period of a year or more in this country.
+How much beyond a year it may be kept remains to be determined.
+The assumption of &#8220;proper preparation&#8221; leaves great
+room for reservations.</p>
+
+<p>In the case of crepe rubbers, there is no great difficulty, provided
+that the recognised methods and formul&aelig; are employed,
+and that the rubber is packed only when perfectly dry. Under
+those conditions, the higher grades of crepe remain apparently
+unaffected on storing. Any appreciable deterioration may be
+attributed to defective preparation or external causes, such as
+accidental damage by water.</p>
+
+<p>The prolonged storage of lower grade rubbers is attended by
+more risk, especially in the case of the lowest grade (earth-scrap)
+from estates which neglect the practice of regular and
+frequent collection of the raw product. The same reservation
+applies to crepes made from tree-scrap which is not collected
+daily. In these types of crepe rubber &#8220;tackiness&#8221; may be<span class='pagenum'><a name="Page_214" id="Page_214">[214]</a></span>
+initially present only in small degree, but the final damage may
+be immensely greater by close contact of the folded rubber
+during prolonged storage.</p>
+
+<p><a name="Sec16_8" id="Sec16_8"></a>When we come to discuss the possibility of storage of smoked
+sheets, the difficulties become immensely greater. We have
+yet no reliable experience as to the keeping properties of this
+grade when properly prepared, fully cured, correctly packed,
+and stored under the best of local conditions. It is understood,
+of course, that in the qualification by the term &#8220;local&#8221; conditions,
+we assume it to be more difficult to store rubber
+generally in Malaya than in a temperate climate. The average
+temperature and humidity of the atmosphere are here much
+more favourable to the development of mould growths than
+would be the case, say, in Great Britain.</p>
+
+<p>In discussing this question, as far as it refers to the preservation
+by storing of smoked sheet rubber, it is not fair to draw
+conclusions as to the likely behaviour of packed rubber from
+data based upon observation of loose specimens. We have
+samples of smoked sheets prepared in 1910, and these, superficially,
+appear to have remained unchanged. No mould is
+present and, as far as intermittent observation enables us to
+judge, moulds have never been incident. Whether such rubber
+would have been preserved in this condition had it formed part
+of a packed case, is a point upon which we have no experience;
+neither can we give any opinion. It seems true, however,
+that loose specimens &#8220;keep&#8221; better than bulk samples of the
+same preparation.</p>
+
+<p>It cannot be argued that the present good condition of these
+old specimens may be due to correct preparation. In those
+days methods and formul&aelig; were rather haphazard, especially
+in view of the fact that the daily variability of dry rubber
+content of latices was not then recognised.</p>
+
+<p>One would rather submit the factor of adequate smoke-curing
+as the chief influence in the superficial preservation of
+smoked sheets. Ten or eleven years ago it was considered
+advisable to allow the rubber to remain in the smoke-house for
+a period extending well beyond that necessary for ordinary
+drying. As a result, very dark rubber was produced, which<span class='pagenum'><a name="Page_215" id="Page_215">[215]</a></span>
+was thoroughly impregnated with the products of wood combustion.
+There would seem to be little doubt that this
+procedure was responsible for the prolonged freedom from
+mould growths.</p>
+
+<p>Market standards have varied to some degree since, with a
+tendency to prefer a paler product than that in vogue, say,
+six or seven years ago. Moreover, standardised methods of
+preparation have been introduced, with the result that sheets
+of a desirably high standard can be produced in from ten to
+fourteen days, when smoke-curing is conducted only during
+night hours. Some estates are equipped with smoke-houses
+which, by continuity of working day and night, provide smoke-dried
+rubber in from five to six days; but the actual hours of
+smoke-curing are approximately equal to those of the ordinary
+type of house.</p>
+
+<p><a name="Sec16_9" id="Sec16_9"></a><a name="Sec16_10" id="Sec16_10"></a>This tendency towards the production of sheets paler in
+colour than the old standard is probably largely responsible in
+the present for the commonly observed incidence of surface
+moulds on stored smoked sheets, and also for some complaints of
+&#8220;under-curing,&#8221; where the term specifically refers to a failure
+to dry and cure the rubber thoroughly. Boxes of smoked sheets,
+which had been stored for varying periods up to five months,
+were recently inspected, and, in the majority of instances,
+surface moulds were found to be plentiful. In all cases it
+was observed that the trouble was intensified where boxes of
+rubber were stored in contact with cement floors.</p>
+
+<p>This &#8220;under-curing&#8221; is not a question solely of the duration
+of smoke-drying, although probably the modern practice of
+curtailing the period has exerted a great influence. To make
+this clear, it may be stated that, given two batches of uniformly
+prepared wet sheets, it would be possible to smoke-cure them
+for equal periods in different houses, so as to produce one batch
+very much paler in colour than the other, although the total
+hours of actual smoke-curing would be identical. In order to
+produce such effects, all that is necessary is to employ different
+timbers for fuel or different types of furnaces. In the one case
+there would be produced heat and very little smoke, while in
+the other the necessary heat would be obtained plus plenty<span class='pagenum'><a name="Page_216" id="Page_216">[216]</a></span>
+of smoke. The best results naturally are obtained by the
+employment of the happy medium, and if smoked sheets have
+to be stored, the ordinary period of smoke-curing should be
+prolonged to an interval consistent with the capacity of the
+smoke-house.</p>
+
+<p>All precautions taken in preparation and curing can be
+nullified, as already indicated, by unsuitable storage conditions.</p>
+
+<p><a name="Sec16_11" id="Sec16_11"></a><span class="smcap">Tool-Sheds and Store-Rooms.</span>&mdash;In some factories it is
+the rule to see lime, cement, spare rolls, sieves, and a general
+heterogeneous assortment occupying part of the rubber-drying
+rooms. The inconvenience is often great; and it certainly
+seems that these stores and tools are of sufficient value to be
+accommodated in suitable buildings.</p>
+
+<p><a name="Sec16_12" id="Sec16_12"></a><span class="smcap">Situation of Factory Buildings.</span>&mdash;There can be no doubt
+that a great deal of the &#8220;spot&#8221; disease trouble, and the general
+slowness of drying, can be attributed in many factories to the
+unsuitability of the site chosen. Probably the idea which
+actuated those responsible for the choice of site generally was
+proximity to a water supply. This would account for the fact
+that a number of factories are situated in valleys or near
+swamps. More often than not, also, the actual clear space is
+very limited, and rubber trees grow close up to the walls of
+the buildings. Under such circumstances, it is difficult to
+see how these buildings can be anything but dark and damp,
+and it is not difficult to understand the slow rate of drying.
+In a few cases the sites chosen proved to be so unsuitable that
+the estates were confronted with a very serious problem, the
+solution to which was, either the erection of another complete
+set of buildings in a more suitable spot or the installation of
+artificial driers.</p>
+
+<p>It must be laid down as an axiom that the first essential in a
+suitable site is that water may be brought to it easily, but, as
+already indicated, this does not mean that the buildings need
+be placed in actual proximity to the water-supply. The mistakes
+made by pioneers in this work are not likely to be repeated,
+and it is common now to note well-designed and comprehensive
+schemes in which the water is pumped to a reservoir placed at a
+suitable elevation, whence the supply is gravitated to bungalows,<span class='pagenum'><a name="Page_217" id="Page_217">[217]</a></span>
+coolie lines, and the factory. The importance of securing a
+plentiful supply of good water for factory purposes cannot
+be exaggerated, and it is a point which is only thoroughly
+appreciated on estates where smoke-sheet rubber has to be
+prepared.</p>
+
+<p>The second essential, but of equal importance, is that there
+shall be an ample open space on which the sun may shine all
+day. There must be no trees too near the buildings, and there
+should be no adjacent swamps. Preferably, the site should be
+on a raised position, so that it will be impossible for surrounding
+trees to cut off sunshine, even when they are fully grown.
+From such an arrangement it will follow that the factory will
+be light and airy, and the drying-houses will receive the
+maximum of benefit to drying from direct sunshine on the roof
+and walls. There can be little doubt that these considerations
+play a most important part in determining the rate of drying
+of the rubber, and where comparisons are made between the
+rates of drying in various drying-houses all these factors enter
+into the question and contribute to the total result. Presuming
+that the thin crepes made in two factories are equal in thickness,
+it is not uncommon to find that in a drying-house, situated
+in a wide open space, the period of drying may be as low as
+six or seven days; while in another drying-house, situated near
+a swamp and surrounded by trees, the period may be as high
+as eighteen days to twenty-one days. The figures quoted are
+not fictitious, but are facts actually noted in the course of the
+writers&#8217; experience.</p>
+
+<p><a name="Sec16_13" id="Sec16_13"></a>A great deal also depends upon the exact position of buildings.
+Thus, to obtain the maximum of light in a factory, it will be
+obviously beneficial to erect it with the long sides running east
+and west, so that the windows face the north and south, and
+the large end doors face the east and west respectively. At
+first sight it would appear that the best position for the machines
+would be on the north side of the building where no sun can
+enter; but a moment&#8217;s consideration shows that the south
+side would give the best results. By the time the sun has come
+round to the south, it is usually high in the heavens, and the
+direct sunshine does not fall very far into the room. Even<span class='pagenum'><a name="Page_218" id="Page_218">[218]</a></span>
+should it play upon the machines for an hour or two during the
+day, no harm could result to the rubber which was being worked,
+as no piece would remain there a sufficiently long time to be
+injured in the slightest degree. Placed in this position, the
+maximum benefit of light would be obtained, whereas if the
+length of the building ran east and west, the machines would
+have only either the morning or afternoon light.</p>
+
+<p>While it is advisable to erect a factory running east and west,
+the drying-houses should run north and south. In this position
+the maximum wall area will be exposed to the sun during the
+day, and it will be possible to manipulate the windows of the
+drying-rooms so that those along one side are open, and it will
+never be necessary to close all the windows at any time of the
+day. Thus the windows facing east will be closed, and those
+facing west will be open until after midday; then <i>vice versa</i>.
+With such an arrangement a more uniform temperature may
+be obtained than by any other arrangement of the buildings.
+If the building ran east and west, the windows on the north
+side could remain open all day, while those facing south would
+have to remain closed practically all day. The south side
+of the house would be heated by the sun, while the north side
+would remain cool, and the rates of drying would be correspondingly
+unequal. The total wall area heated by the sun at<span class='pagenum'><a name="Page_219" id="Page_219">[219]</a></span>
+any time of the day would be less in this position than if the
+house ran north and south.</p>
+
+<p>Similarly, to obtain the best drying effect during the daytime
+in a smoke-house the building should run north and south. By
+this means the temperature will be maintained to the maximum
+possible by sun heat, and the rate of drying will correspond.</p>
+
+
+<div class="figcenter"><a name="Fig65" id="Fig65"></a><img src="images/illo235.png" alt="Suggested Arrangement of Building" />
+<p class="caption"><span class="smcap">Suggested Arrangement of Building.</span></p></div>
+
+<p><i>References to <a href="#Fig65">Sketch Plan</a>.</i></p>
+
+<p>Drying-house No. 2 should be of two storeys, and unless a
+separate sorting and packing room is to be built, No. 1 should
+also have two floors (see <a href="#Sec16_2">previous notes</a> on packing-rooms).</p>
+
+<p>In the factory&mdash;</p>
+
+<div class="blockquot"><p><i>V</i> shows the position of the verandah, which may be quite
+open and only divided from the inner room by</p>
+
+<p><i>S</i>, a wall composed of very strong expanded metal, which
+allows light and air to enter the factory.</p>
+
+<p><i>T,T</i> are the glazed tile tanks for the reception of latex,
+scrap rubbers, and bark-shavings.</p>
+
+<p><i>M</i> shows the position of the machines on the south side
+of the factory, with the direction of extensions, and</p>
+
+<p><i>E,E</i> the compartments in which the engines are bedded.
+In these positions it is possible to obtain direct drive to the
+machines.</p>
+
+<p><i>D,D</i> are large double swing or sliding doors (the latter for
+preference always). These, while suiting transport of rubber,
+provide also for a free draught of air.</p></div>
+
+<p>If possible the scrap-washing machine should be placed
+outside the wall of the factory, and tanks for the reception
+of scrap rubbers may then be situated in convenient
+proximity.</p>
+
+<p>Economy of labour is obtained by grouping all factory
+buildings as closely as possible, but it should be borne in mind
+that smoke-houses should be regarded as a possible source of
+danger from fire. This point has a practical bearing upon
+rates of insurance, and it is essential that the smoke-house
+should be situated at a minimum of 50 feet from any other
+building or group of buildings. In this connection, also, it<span class='pagenum'><a name="Page_220" id="Page_220">[220]</a></span>
+may be noted, as being of further practical interest, that, in
+the insurance of smoke-houses, preferential rates are given to
+those having a good type of slow-combustion furnace.</p>
+
+<p><a name="Sec16_14" id="Sec16_14"></a><span class="smcap">Choosing a Factory Site.</span>&mdash;Sufficient has been written to
+make it clear that the choice of a site for factory buildings is
+a matter demanding weighty consideration. Much, of course,
+depends upon the planted area, and the rate at which it comes
+into bearing. Under certain circumstances which will be
+obvious, it is permissible to instal first a group of buildings of
+a temporary nature only, the future site and permanent buildings
+to be chosen later when the main portion of the estate
+comes into bearing. Often, however, one finds that, from lack
+of forethought, the estate has been committed to considerable
+expense in the establishment of equipment, which later is proved
+to be unfavourably situated with regard to the majority of the
+area in ultimate bearing. In such case, transport of latex is
+fraught with difficulties and may be expensive.</p>
+
+<p>In the instance of an estate which will gradually come into
+bearing, it is not easy to decide whether a temporary installation
+shall first be provided, or whether, in anticipation of future
+demands, a complete equipment shall be erected. So much
+depends upon the financial aspect of the question, and upon
+the rate at which areas will come into bearing. As far as is
+possible, the best policy would be that of a compromise under
+which the site would suit later requirements, and the factory
+would be so planned as to be capable of future easy extensions
+both of buildings and machinery.</p>
+
+<p>It is not possible to lay down any definite data as regards
+requirements based on acreage, or to make comparisons
+between any two estates of similar acreage. The important
+factors determining such requirements are:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Area.</p>
+
+<p>(<i>b</i>) Shape of the estate.</p>
+
+<p>(<i>c</i>) Topography of the estate.</p>
+
+<p>(<i>d</i>) Available supplies of water.</p></div>
+
+<p>Naturally the ideal site for factory buildings would lie in a
+central position, given other favourable conditions.</p>
+
+<p><a name="Sec16_15" id="Sec16_15"></a><span class='pagenum'><a name="Page_221" id="Page_221">[221]</a></span><span
+class="smcap">Centralisation or Decentralisation.</span>&mdash;It is the experience
+of a number of estates that, all other conditions being favourable,
+there is a limit beyond which the centralisation of factory work
+leads to an unwieldy position. We are not here concerned
+with the few extremely large estates running into tens of thousands
+of acres. In those cases the total area would be divided
+into economic sections. The argument there would resolve
+itself into a discussion on the size of an economic section.
+This, in turn, would be dependent upon the type of main product,
+involving the question of transport of latex or coagulum,
+and the possible provision of batteries of heavy machinery.</p>
+
+<p>The differentiation between the transport of latex and coagulum,
+respectively, is a most important one, and has a powerful
+influence in determination of the maximum of centralisation
+possible. Whereas properly prepared coagulum may be safely
+transported by bullock-cart, light-railway, or motor vehicle
+for many miles, latex, on the other hand, demands very careful
+treatment. Anti-coagulants may be employed to preserve
+fluidity, but only within certain limits. Even under these
+conditions, other factors (chiefly climatic) exert an influence
+which renders the transport of latex for any distance a matter
+of anxiety.</p>
+
+<p>It will be plain, therefore, that the limits of centralisation
+of factory work are much narrower for the preparation of sheet
+rubber than is the case when crepe rubber is to be made. In
+actual experience the preparation of a high standard and a
+high percentage of smoked sheet is attended with considerable
+difficulty in those cases where the factory processes have been
+ultra-centralised. Apart from the difficulties inherent to the
+transport of latex in a state of good preservation, there is the
+added difficulty of dealing quickly with large volumes of latex
+brought from various quarters. None of these should be
+allowed to remain standing if the best results are to be secured;
+but obviously there must at times be some congestion. Even
+on a small scale it is often found that the latest batches of latex
+are unfit for the preparation of good sheet rubber, and the
+trouble may be easily exaggerated when working on a large
+scale.</p>
+
+<p><span class='pagenum'><a name="Page_222" id="Page_222">[222]</a></span>The centralisation of work on crepe preparation, therefore,
+is limited only to a comparatively slight degree by distance
+of transport, and in the main only by the size of the necessary
+equipment of machinery and drying accommodation.</p>
+
+<p><a name="Sec16_16" id="Sec16_16"></a>The successful preparation of sheet rubber is, on the contrary,
+governed chiefly by the factor of transport. With this consideration
+in view, several large estates, preparing sheet rubber
+as the chief grade, have found it necessary to decentralise the
+factory work, with very satisfactory results. Outlying sections
+are given uniform and complete equipments of necessary
+buildings on a small scale, and hand-driven light machines.
+Uniform coagulating tanks are installed, and the methods and
+quantities of chemicals employed are carefully standardised.
+Experience has shown that often the best sheet rubber coming
+to the market has been prepared on small estates; and the same
+applies to the product of these decentralised stations on large
+estates. There is no <i>a priori</i> reason why the product from one
+station should differ in the smallest particular from that of
+another, apart from minor fluctuations which are due to variable
+weather conditions affecting the latex. If the contrary is
+found to be the case, it indicates failure on the part of the
+person responsible to follow the regular rules and methods.</p>
+
+<p>In the natural scheme of development of a large estate, it
+would be necessary, of course, to have a comparatively small
+centrally situated factory, equipped with power and heavy
+machinery for working scrap rubbers in the preparation of
+crepe grades below No. 1 in quality. As the yield per acre
+increases, or the area in bearing expands, it would be advisable
+later to increase the size of the central factory and buildings
+so as to permit of the preparation of a proportion of the crop
+in the form of No. 1 crepe rubber, in order to be able to comply
+with prevailing market demands under which preferential
+rates fluctuate between pale crepe and smoked sheet.</p>
+
+
+<p class='pagenum'><a name="Page_223" id="Page_223">[223]</a></p>
+<hr class="c25" />
+<h2><a name="Part4" id="Part4"></a>PART IV</h2>
+
+<h3>THE FINISHED RUBBER</h3>
+
+
+<h2><a name="Ch17" id="Ch17"></a>CHAPTER XVII</h2>
+
+<h3><i>DEFECTS IN CREPE RUBBERS</i></h3>
+
+
+<p><a name="Sec17_1" id="Sec17_1"></a><span class="smcap">General Style of Finish.</span>&mdash;Broadly, there is no single and
+definite style of finish, but on the whole it may be stated that
+the greater proportion of crepe rubbers are prepared in a thin
+form and with a close-knit texture or finish.</p>
+
+<p>Very little thick or blanket crepe is now made on estates in
+Malaya, so that beyond the mention of that type little need be
+written. A fair amount of blanket crepe is sold in the Singapore
+market, but it should generally be regarded as re-made
+rubber&mdash;<i>i.e.</i>, it may have been prepared from thin crepes, or
+from native pale sheets, in local rubber-washing factories.
+In appearance these crepes have a rough finish, and vary in
+colour according to the crude material employed.</p>
+
+<p>The general preference of the market at present is for a thin,
+smooth-finished crepe, with a close-knitted surface&mdash;<i>i.e.</i>, free
+from what is described as &#8220;laciness.&#8221; What effect this
+looseness of finish can possibly have upon the quality of the
+rubber is not understood, but the standard type set up by the
+market must be comparatively free from small holes.</p>
+
+<p>Under existing conditions governing the sale and purchase
+of rubber, various &#8220;standards&#8221; are set up. These really have
+no bearing upon the intrinsic qualities of the rubber, and are
+concerned almost entirely with superficial attributes. They are
+necessary in the absence of any proper scheme of evaluation
+for the establishment of certain standards of comparison, which
+imply that the rubber is apparently clean, free from certain
+recognised defects, and has been carefully prepared&mdash;as far<span class='pagenum'><a name="Page_224" id="Page_224">[224]</a></span>
+as can be determined by a superficial examination. Thus the
+question of &#8220;finish&#8221; has attained disproportionate importance,
+but must be respected when preparing rubber for sale.</p>
+
+<p>Under ordinary conditions, thin crepe rubber, as it leaves the
+finishing machines, has what may be termed &#8220;deckled&#8221; edges.
+On many estates, in order to comply with market conditions,
+the edges of the wet crepe are trimmed, and the trimmings
+re-made into lengths of crepe. This is done under the impression
+that the market price is influenced by the evenness of the
+edges of crepe rubbers.</p>
+
+<p>Again, it sometimes happens that, owing to &#8220;wear&#8221; of the
+rolls, the finished dry crepe may show a faint but distinct
+pattern of mark&mdash;a diamond or a horizontal bar. Since these
+are not accepted under the &#8220;standard&#8221; comparisons, rubber
+exhibiting these characteristics does not obtain the top market
+price. In other words, these innocent and innocuous marks
+are regarded as defects and penalised accordingly.</p>
+
+<p>Enough has been written to show how very important
+becomes the question of finish. It will be acknowledged
+that the superficial qualities demanded in the &#8220;standard&#8221;
+market type can be reproduced by any estate having adequate
+machinery and ample facilities for drying and handling the
+rubber.</p>
+
+<p>Methods of preparation and formul&aelig; for the employment of
+chemicals are so well laid down that, up to the stage of machining,
+no difficulty need be encountered. But the standard type
+of finish in the dry crepes cannot be obtained unless the estate
+factory is fully equipped with the three types of rolls necessary&mdash;<i>i.e.</i>,
+macerators, intermediate crepers, and smooth finishing-rolls.
+This subject has received full discussion in <a href="#Ch13">Chapter XIII.</a>,
+and is here only mentioned with the view of emphasising the
+point that no estate can be blamed for a lack of &#8220;finish&#8221; in
+crepe rubbers if the equipment of machinery is inadequate
+or in poor condition.</p>
+
+<p>If, on the other hand, the factory has ample machinery for
+requirements, and a good finish cannot be obtained on the
+thin crepe, then it is time the rolls were attended to and changed,
+or that the ratios of the driving pinions were altered.</p>
+
+<p><a name="Sec17_2" id="Sec17_2"></a><span class='pagenum'><a name="Page_225" id="Page_225">[225]</a></span><span
+class="smcap">Dirty Edges.</span>&mdash;It seems to be almost impossible to keep old
+machines clean, and it is equally difficult to keep the edges of
+crepe free from oil and dirt. Usually these dark edges are to be
+found on crepe which is rather wide, and it will be noticed that
+where wide crepe is made, unless special precautions are taken,
+the edges of the rubber often pass under the edges of the hopper
+and so pick up dirt and oil. On most machines it is a great
+mistake to attempt the preparation of wide crepe; nothing but
+narrow crepe must be made. To obtain this it is necessary
+to decrease the width of the hopper placed above the rolls.
+This can easily be effected by blocks of heavy hard wood, cut to
+shape and fastened in position.</p>
+
+<p>Sometimes the dark edges of crepe are due to another cause.
+Rolls may be gradually worn in the middle, so that to obtain
+a good finish it becomes increasingly necessary to tighten up
+the screws which regulate the distance between the rolls.
+It thus happens that just at, and beyond, the edges of the
+rubber the rolls grind upon each other, and fine particles of
+iron and graphite are transferred to the rubber. In such a case
+it is evident that either the rolls must be &#8220;turned&#8221; or that
+a new pair of rolls must be substituted.</p>
+
+<p><a name="Sec17_3" id="Sec17_3"></a><span class="smcap">Iron-Stains.</span>&mdash;One of the causes of iron-stain on rubber has
+been mentioned in the preceding paragraph. This particular
+kind of iron-stain must not be confounded with rust-stain,
+and gives a dark dirty colour. It results from the grinding
+together of the rolls, and is usually noticed in the finishing of
+fine pale crepe. For this operation it is necessary to screw
+up the rolls tightly, and it will be plain that, whenever the rolls
+are vacant of rubber, there is a tendency for them to grind
+upon each other, thus setting free fine particles of iron and
+graphite. In order to avoid this, one must be careful to see
+that between the working of each length of fine crepe the rolls
+should be occupied with another piece of rubber, which may
+be kept for the purpose. In some factories this trouble
+apparently does not exist, while in others the amount of wear
+on the rolls is surprisingly great, and the damage done to
+the rubber is excessive. The only way in which this difference
+can be accounted for is that there must be a great difference in<span class='pagenum'><a name="Page_226" id="Page_226">[226]</a></span>
+the quality of the roll material. Some rolls seem to be excessively
+soft, and from these contamination by iron-stain is
+great. For this reason rolls are sometimes rejected, and there
+would appear to be an objection to any but chilled steel rolls
+for the final stage of finishing crepe rubbers.</p>
+
+<p><a name="Sec17_4" id="Sec17_4"></a><span class="smcap">Rust-Stains.</span>&mdash;Rust-stains, on the other hand, throw the
+responsibility entirely upon the labour and supervision of the
+factory. Rust is formed upon the rolls when they are at rest,
+and any one passing pale rubber between the rolls before they
+have been thoroughly cleaned is guilty of culpable negligence.
+Even when apparently clean, a piece of lower grade rubber
+should be passed through the rolls several times so as to
+remove any slight trace of rust remaining.</p>
+
+<p>Rust-stains have also been caused in a few cases by the
+large knives which are used to cut up lumps of coagulum,
+or by allowing freshly coagulated rubber to come into contact
+with iron vessels in the factory.</p>
+
+<p>A similar appearance has been traced in a few instances to
+contamination of the coagulum in transit by the dust of the
+reddish rock (laterite) employed in localities for road-making.</p>
+
+<p><a name="Sec17_5" id="Sec17_5"></a><span class="smcap">Oil-Marks.</span>&mdash;The origin of oil-marks in crepe has already
+been described in <a href="#Ch13">Chapter XIII</a>. The whole question resolves
+itself into one of cleanliness, moderation in lubrication, and
+supervision. The machines should be inspected every day,
+and once a week rolls may be swabbed down with a 10 per cent.
+solution of caustic soda applied by means of a piece of cloth
+fastened round the end of a stick. Immediately after this
+operation water should be turned on and the rolls set in motion,
+so that all traces of caustic soda are thoroughly removed. If
+possible, lubrication by oil should be substituted by grease
+lubrication through screw caps.</p>
+
+<p>Particular attention should be paid to the back of the
+machines. None but the individual in charge of engines
+should be allowed to lubricate the machines, and he should
+be held responsible for any excess of lubricant.</p>
+
+<p><a name="Sec17_6" id="Sec17_6"></a>As a rule oil-marks are restricted to the edges or the proximity
+of the edges of crepe, but sometimes the streak is to be found
+in the middle of the length. In such a case it is almost certain<span class='pagenum'><a name="Page_227" id="Page_227">[227]</a></span>
+that the oil or grease has been picked up by the rubber in the
+tray. It sometimes happens, if the &#8220;liners&#8221; of the bearings
+are eccentrically worn, that a few drops of dirty oil or a particle
+of grease are squirted out to some distance. These usually
+find a resting-place in the tray, and the contamination may
+then appear in any part of the rubber.</p>
+
+<p>It will be clear, therefore, that all trays beneath machines
+should be examined as the probable source of danger from
+contamination by oil and dirt. If the trays are as wide as or
+wider than the effective portion of the rolls, they should be
+discarded. In their place (except sometimes in the case of
+the macerating machine) all that is necessary is a movable piece
+of board, in width not less than from 4 to 6 inches shorter than
+the width of the rolls. Any oil or grease ejected from the bearings
+will thus be allowed to fall clear of the board; and defects
+due to oil streaks, etc., will be very much diminished, if not
+entirely obviated.</p>
+
+<p>This point in connection with the damage possible by the
+existence of wide trays is commended to the notice of manufacturers
+of machines for plantations, as it is common to find
+that trays are made which contravene the rule prescribed by
+experience. In fact, trays on some machines have been so
+designed as to act as &#8220;traps&#8221; for all dirty matter exuding from
+the bearings. Not only so; they are sometimes made of such
+a shape and height that oil or grease lodging upon the edges
+act as a &#8220;wipe&#8221; to the rolls, thus increasing the possibility
+of contamination. Until this defect was investigated, it was
+common to note continued contamination of pale crepes in spite
+of all precautions taken in cleaning the rolls at frequent intervals.
+The trouble due to this cause is intensified when the
+same machines are employed for the preparation of scrap-rubber
+crepes and No. 1 crepe. Small pieces of scrap find
+their way towards the bearings and lodge on the edges of the
+trays. Unless a thorough inspection is made before proceeding
+with the working of the No. 1 (pale) grade, contamination may
+be continuous.</p>
+
+<p><a name="Sec17_7" id="Sec17_7"></a><span class="smcap">Dirt.</span>&mdash;Streaks due to the presence of dirt (as apart from oil
+or grease contamination, or that due to pieces of oxidised scrap)<span class='pagenum'><a name="Page_228" id="Page_228">[228]</a></span>
+are unusual, and when they do appear their origin seems to be
+somewhat of a mystery. It could scarcely be advanced that
+the dirt was picked up on the machines, as it is difficult to imagine
+where such dirt could come from. In one or two instances
+there has been fairly clear evidence that the dirt was contained
+in the coagulum, and the only explanation fitting the case is
+that it fell into the latex after straining and during the course
+of coagulation. On cutting open lumps of coagulum brought
+in from the field division, it has sometimes been noticed that
+dirt is included, and the foregoing explanation is the only
+reasonable one. How it was possible for dirt to get into the
+latex must be left for explanation to those better acquainted
+with the conditions under which the latex was coagulated.</p>
+
+<p><a name="Sec17_8" id="Sec17_8"></a><span class="smcap">Holes.</span>&mdash;On some estates it would seem impossible, with the
+existing machines, to make really good crepe. The complaint
+is that, if thin crepe is attempted, it is invariably found to be
+&#8220;full of holes&#8220;; and as, apparently, the presence or absence
+of small holes in crepe rubber is a factor which influences
+buyers, this defect must be avoided at all costs. Why this
+matter of small holes in thin crepe should weigh so heavily
+with buyers is a matter which the writers are not in a position
+to explain. As a matter of fact, the presence of small holes is
+most generally an indication that the rubber has received the
+minimum amount of working on the rolls consistent with good
+washing. Further working would only be undertaken with
+the idea of so consolidating the rubber as to get rid of holes in
+order to meet the market scheme of valuation.</p>
+
+<p>This is usually achieved by making a very thin crepe and
+rolling together two lengths when wet. The resulting crepe
+may be slightly thicker than ordinary, and the method employed
+may be usually detected by the appearance of the edges unless
+these are trimmed.</p>
+
+<p><a name="Sec17_9" id="Sec17_9"></a><span class="smcap">Greenish and Tacky Streaks.</span>&mdash;Occasionally one meets
+cases in which pale crepe exhibits streaks varying in colour
+from a decided green to an almost black in which the greenish
+tinge is scarcely perceptible. Experience indicates that these
+streaks are much more dangerous than they appear superficially,
+inasmuch as they contain traces of brass from the<span class='pagenum'><a name="Page_229" id="Page_229">[229]</a></span>
+&#8220;liners&#8221; of the bearings. The presence of the copper in
+brass is responsible for a gradual disintegration of the rubber,
+commonly recognised as &#8220;tackiness.&#8221; In fact, copper may be
+said to be a &#8220;poison&#8221; to rubber, and every effort should be
+made to avoid possible sources of contamination. The effect
+may be proved easily and perceptibly by fastening together
+several pieces of crepe rubber by means of a brass &#8220;paper-fastener.&#8221;
+In course of time a salt of copper, green in colour,
+will be formed, and it will be found that the portions of rubber
+in contact with the fastener have &#8220;perished&#8221; and become
+tacky.</p>
+
+<p>This contamination of crepe rubber may take place in two
+ways:</p>
+
+<div class="blockquot"><p>(1) By the ejection of actual particles of brass from the
+bearings of machines, due to eccentric grinding of the
+&#8220;standards&#8221; of the rolls upon the brass &#8220;bushes.&#8221; These
+particles are carried by exuded oil or grease into trays, and
+thence to the rubber.</p>
+
+<p>(2) By the action of an acid lubricant upon the brass, with
+the formation of a metallic soap which has a decided green
+colour, unless obscured by the dark colour of the oil or grease.
+It is transferred to the crepe rubber in the manner indicated
+above.</p></div>
+
+<p>The inevitable effect, apart from the superficial defect, is
+incipient tackiness. The extent to which this may develop
+will depend upon the amount of the copper compound present,
+but it should be remembered that an exceedingly small trace
+is capable of causing a disproportionately large amount of
+damage. This effect is further magnified if the &#8220;tacky&#8221; piece
+of rubber is packed in close contact with previously unaffected
+rubber.</p>
+
+<p>When the defect is discovered, the affected portions should be
+cut out, and the cuttings should be burned. To mix them
+with the lowest scrap grades, as may be done thoughtlessly,
+is only inviting further trouble.</p>
+
+<p>Besides the source of danger already indicated, it may be
+found, but far less frequently, that contamination may arise
+from the presence in the rubber of small pieces of the brass
+mesh which is generally used for straining latex.</p>
+
+<p><a name="Sec17_10" id="Sec17_10"></a><a name="Sec17_11" id="Sec17_11"></a><span class='pagenum'><a name="Page_230"
+id="Page_230">[230]</a></span>The view appears to be held in some quarters that these
+tacky streaks and patches in crepe rubber may arise from
+contamination with oil or grease alone. This does not agree
+with our experience. An experiment was made to test the
+point using fresh oil and grease drawn from drums in stock,
+specimens of the same lubricants to which traces of a copper
+salt were added, and samples of lubricants taken from the
+bearings of several machines. The treated pieces of rubber were
+placed in contact with untreated pieces of crepe which served as
+&#8220;blanks.&#8221;</p>
+
+<p>Notes were made at intervals extending over a period of two
+years. The conclusions arrived at were:</p>
+
+<div class="blockquot"><p>(1) Although there was surface discoloration, no tackiness
+had been caused by fresh (unadulterated) lubricant; neither
+were the &#8220;blanks&#8221; affected.</p>
+
+<p>(2) In the majority of specimens upon which had been
+smeared a small streak of lubricant taken from the bearings
+of machines, tackiness had supervened, and had developed
+likewise in the contact &#8220;blanks.&#8221;</p>
+
+<p>(3) In all cases where a trace of copper salt had been used to
+adulterate the fresh lubricant, tackiness was to be noted in
+the course of a short period (a week upwards) after the rubber
+was dry. Development was slow, but progressive, over the
+full period of experiment, and the &#8220;blanks&#8221; in contact were
+affected. The degree of affection was determined by the
+proportion of copper salt employed. In the worst cases the
+affected strip of rubber had deteriorated and disintegrated to
+such a degree as to cause a distinct longitudinal gap, the edges
+of which appeared to consist of a moist gummy substance of a
+deep syrup colour. The adjacent blanks in some cases exhibited
+a similar appearance in lesser degree, or were merely
+affected by a characteristic brownish stain.</p></div>
+
+<p>These observations regarding the possibility of damage to
+crepe rubbers from the existence of brass &#8220;liners&#8221; or &#8220;bushes&#8221;
+in the bearings of the machines lead to the natural query as
+to whether the use of brass is necessary. Experience shows
+that it is not necessary. Machines in use for years have been
+running with plain bearings of iron or other metallic substances.
+Satisfaction is obtained without the use of brass.</p>
+
+<p><a name="Sec17_12" id="Sec17_12"></a><span class="smcap">Cotton and other Fibre.</span>&mdash;One of the most
+frequent<span class='pagenum'><a name="Page_231" id="Page_231">[231]</a></span>
+complaints made against low grade crepes is the presence of
+fibre&mdash;generally classed in a wholesale fashion as &#8220;cotton-waste.&#8221;</p>
+
+<p>It is true that some years ago most of the complaints were
+genuine in referring the cause to cotton-waste. The defect
+arose chiefly owing to the careless use of this material in the
+factory. Lumps of waste when discarded were often thrown
+to the ground, and became mixed with the heaps of scrap
+rubber and bark-shavings awaiting attention. The fault was
+one of sheer negligence, and nothing can be advanced in extenuation.
+Even when the soiled waste was thrown into the
+external drains, it often returned to the factory mixed up
+with the scraps of rubber recovered by means of the drain-screens.</p>
+
+<p>As far as the complaint concerns itself with cotton-waste
+only, the remedy is plain, and lies in the power of the management
+by reason of the ability to restrict the use of &#8220;waste&#8221;
+only to the engine-drivers and mechanics.</p>
+
+<p>In the vast majority of cases, however, the defect arises from
+circumstances beyond the direct control of the factory, and
+under conditions which make it difficult to check the evil.
+Although against instructions, and for the purpose of fulfilling
+other orders, some coolies persist in using pieces of cloth for
+cleaning cups. In course of time, unless the practice is detected,
+this cloth becomes coated with rubber. Careless coolies throw
+it away, when it may be collected by the individuals who
+gather earth-scrap; or it may be brought into the factory in the
+tappers&#8217; scrap-bag.</p>
+
+<p>Cases have been known in which the fibrous matter observed
+in the dry crepe rubber was of such a nature as to indicate that
+the source might be attributed to leaf-stalks which had passed
+through the scrap-washer. It is an easy matter to condemn
+the sorting as being careless, but it is another matter to instil
+into the mind of factory coolies such a respect for easy and sane
+precautions that the practice of them will be continued when
+the eye of the supervisor is not fixed upon the workers.</p>
+
+<p>It will be clear that contamination by fibrous matter should
+be limited practically to the lowest grades of rubber.</p>
+
+<p><span class='pagenum'><a name="Page_232" id="Page_232">[232]</a></span>The appearance of cotton-waste in high-grade crepes must
+be most unusual, and the writers have not yet seen a case in a
+drying-house. That it does occur, however, seems to be evident
+from brokers&#8217; reports. It is extremely difficult to imagine
+how the waste enters the rubber. One possible explanation
+is that a coolie may have been cleaning the rolls surreptitiously
+with waste, which may have passed later into the rolls together
+with rubber. Another explanation was offered in one factory
+by the observed fact that coolies engaged in cutting up coagulum,
+ready for passing into the machines, kept a wad of waste
+for the purpose of keeping the knife-blade clean. This may
+have found its way into the rolls. It must be recorded that in
+the course of many years of experience no case has been seen
+in any drying-house of contamination of the higher grades of
+crepe by fibrous matter.</p>
+
+<p><a name="Sec17_13" id="Sec17_13"></a><span class="smcap">Bark and Grit.</span>&mdash;With ordinary machines and the usual
+process of working, it would seem impossible to wash and
+macerate some of the scrap rubbers sufficiently to free them
+entirely from bark. This applies specially to the grade of
+rubber prepared from bark-shavings. Specimens have been
+handled in which it was practically impossible to detect bark,
+but in such instances the amount of working necessary would be
+such as to interfere seriously with the regular working of the
+factory. Even with the employment of special scrap-washing
+machines, complaints of the presence of bark in dry crepe have
+been received, but it is certain that this mode of operation
+reduces the quantity of bark to a minimum. While fully
+realising that the amount of working it is possible to give in
+proportion to the existing machinery and the output per day
+is limited, it must be recognised that the working of lower grades
+of rubber is usually insufficient, and that where possible it is
+the duty of estates to pay more attention to these lower grades.
+A considerable improvement in this direction has been noticed
+of recent years. It is not uncommon to encounter managers
+who fail to appreciate that complaints regarding the presence
+of bark in the lower grades are founded on legitimate grounds,
+and that they are not frivolous objections put forward for the
+purpose of depressing the price of the article. The sooner such<span class='pagenum'><a name="Page_233" id="Page_233">[233]</a></span>
+an idea is jettisoned the better. There would appear to be a
+good future demand for the lower grades, and it is only natural
+that consumers will be willing to pay the best price only for an
+article which is clean.</p>
+
+<p><a name="Sec17_14" id="Sec17_14"></a>The same arguments apply to the complaints regarding the
+presence of sand and grit. The quantity of the latter found
+in low-grade crepes from some estates is surprisingly high.
+Its presence can often be shown by the simple device of spreading
+a piece of crepe over the upturned and hollowed palm of
+one hand, while striking the rubber with the other hand.</p>
+
+<p>The incidence of bark in higher grades of crepe may be due
+to inadvertence or to gross negligence. In the former class
+one might put those occasions on which pieces of bark are embedded
+in lumps of naturally coagulated rubber. A piece of
+bark-shaving may fall unnoticed into latex and be partially
+responsible for the coagulation which takes place. This piece
+of coagulated lump may be massed with others, and hence,
+unless each small piece is cut up, the bark is not perceived.
+Or again, by some unknown means, a piece of shaving may drop
+into a jar of latex, and so become embedded in the coagulum.
+Sometimes this becomes evident on cutting up the rubber,
+but it is quite as likely to pass unseen. On the whole, the
+presence of bark in first-grade rubber is most unusual, and
+should be seen before the rubber is packed.</p>
+
+<p>In the class due to negligence may be included cases in which
+careless coolies place the cup upon the ground before tapping.
+Pieces of shavings fall into the cup, and coolies are too lazy to
+pick them out. More often than not coagulation in the cup is
+caused. As it is impossible for the European staff to supervise
+each individual tree tapped, some cases must continue to pass
+unheeded. Sometimes bark-shavings are brought in with the
+latex, and if a broken sieve is being used, these, with other impurities,
+pass into the jar, and are embedded in the coagulated
+rubber. This must be classified as negligence, for no manager
+would willingly allow the use of a broken sieve. Again,
+naturally coagulated lump rubber on arrival at the factory sometimes
+contains evident pieces of bark, leaves, and stems of leaves.
+For lack of supervision the average coolie would not think of<span class='pagenum'><a name="Page_234" id="Page_234">[234]</a></span>
+picking out these obvious impurities, and would pass the whole
+mass into the machines.</p>
+
+<p><a name="Sec17_15" id="Sec17_15"></a><span class="smcap">Oxidation Streaks.</span>&mdash;Since the introduction of sodium
+bisulphite defects due to streaks, caused by portions of the coagulum
+becoming oxidised, have practically ceased to exist. In the
+usual course, and without the use of an antiseptic agent, the
+freshly coagulated rubber has a surface darkened by oxidation.
+Unless this dark surface were carefully cut off, there would
+result a crepe containing dark streaks caused by the mixture
+of the oxidised surface portion with the bulk of the paler
+coagulum. The presence of oxidation streaks in No. 1 crepes,
+now being made, would imply either that no anti-oxidant substance
+was in use, or that the quantity necessary to prevent this
+surface oxidation is exceedingly small. Although the price
+obtained would appear to be influenced by the presence of
+oxidation streaks, no evidence can be obtained that the actual
+quality of the rubber suffers to the same degree as does the
+appearance&mdash;<i>i.e.</i>, there is no evidence to show that a pale rubber,
+in which surface oxidation has been inhibited, is intrinsically
+superior to one in which slight natural oxidation has been
+incident.</p>
+
+<p><a name="Sec17_16" id="Sec17_16"></a><span class="smcap">&#8220;Yellow
+Latex&#8221; Streaks.</span>&mdash;This appearance of &#8220;yellow-latex&#8221;
+streaks in not common, and may be accounted for by
+incomplete mixture of two different latices. It is a fact of
+common observation that, when a new portion of bark is
+being tapped for the first time, there is a distinct yellow tinge
+in the latex excluded. As tapping progresses, this colour
+vanishes; usually it may persist for a period varying from two
+weeks to more than a month. Should this latex be poured into
+ordinary latex without thorough mixing, it is sometimes found
+that, when the crepe rubber is dry, there are distinct yellow
+streaks. It should be remembered that, as the rubber content
+of the latex from first tappings is high, this latex is lighter
+than latex which is more dilute, so that the mixed latices must
+be well stirred with a broad paddle to obtain intimate mixture.
+It would be much better to keep yellow latex apart, and coagulate
+it separately, if at all possible. In such case the resultant
+crepe may be of a distinct canary yellow in tint.</p>
+
+<p><span class='pagenum'><a name="Page_235" id="Page_235">[235]</a></span>In scrap-crepes of the higher grade this distinct yellow colour
+is often visible in streaks which indicate the presence of
+tree-scrap, etc., obtained from recently opened tapping areas.</p>
+
+<p><a name="Sec17_17" id="Sec17_17"></a><span class="smcap">Bisulphite Streaks.</span>&mdash;These, again, arise from defective
+mixing. In the dry rubber it is seen that there are streaks of
+colourless rubber in a general mass, which may be of varying
+shades of yellow; or, a length of exceedingly pale rubber is
+apparently streaked in patches with a darker shade of colour.
+A solution of sodium bisulphite is heavier than latex, and there
+would be a tendency, therefore, for the chemical to sink in
+the large mixing jar. Unless stirring is thorough it is possible
+that portions of the latex would not be in contact with sodium
+bisulphite while others receive more than a fair share. Especially
+would this effect be seen where coagulation takes place
+quickly, and experience bears out the truth of the suggestion.
+Another factor which has some bearing on the point is the
+strength of solution in which sodium bisulphite is used. In
+the ordinary course of working, the acid coagulant is added
+immediately after sodium bisulphite has been stirred in.
+Should a strong solution of the bisulphite be used, and if coagulation
+takes place quickly, it is easy to see that the possibilities
+of obtaining a uniform and intimate mixture are small. Probably
+in no factory is the sodium bisulphite now added to latex
+in powder form, but it has been found that if care is not taken
+to see that all the bisulphite has dissolved before the solution
+is added to latex streaks may result in the dry rubber. The
+undissolved particles sink to the bottom of the coagulating jar
+or tank, and there slowly dissolve, forming local strong solutions.
+The effect upon the rubber in the vicinity of these
+strong solutions is much more marked than in the bulk of the
+coagulum, and hence lighter streaks or patches appear in the dry
+rubber. In spite of apparently complete mixture by good
+stirring, it will be seen that it is possible, therefore, to have
+failed in this direction if any undissolved powder remains in the
+solution of sodium bisulphite.</p>
+
+<p><a name="Sec17_18" id="Sec17_18"></a><span class="smcap">&#8220;Spot&#8221; Disease.</span>&mdash;Few managers of estates preparing pale
+crepe rubbers are unacquainted with this defect. It is manifested
+by the appearance of small coloured spots varying in<span class='pagenum'><a name="Page_236" id="Page_236">[236]</a></span>
+density (<i>i.e.</i>, number to a unit area) and differing in hue. The
+most common colours are black and orange, but &#8220;spots&#8221;
+of brick-red, yellow, violet and ruby and green tints have been
+noted, the last named very seldom. Sometimes in place of
+definite &#8220;spots,&#8221; or colonies, the colour is spread over practically
+the whole surface of the rubber as a &#8220;flush.&#8221;</p>
+
+<p><a name="Sec17_19" id="Sec17_19"></a>These coloured spots, or &#8220;flushes,&#8221; indicate infection by
+minute fungi, which are present in the latex prior to coagulation.
+The infection of the latex takes place in the field by means of
+spores, which are only visible with a microscope.</p>
+
+<p><a name="Sec17_25" id="Sec17_25"></a>It is not feasible to discuss any method of preventing this
+infection of latex by air-borne spores, as the eventual preventive
+measures are so simple. But it may be believed that under
+ordinary weather conditions most latices are infected before
+reaching the factory. It is likewise true that even fine pale
+crepes shipped in perfect condition may contain possibilities
+of trouble in the form of &#8220;dormant&#8221; spores, the development
+of which may commence and continue if favourable conditions
+arise.</p>
+
+<p>The subject of &#8220;&#8216;Spot&#8217; Diseases&#8221; has been treated fully in
+previous publications,<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19"
+class="fnanchor">[19]</a> and it is not proposed here to enter
+into any lengthy discussion.</p>
+
+<div class="footnote"><p><a name="Footnote_19_19" id="Footnote_19_19"></a><a href="#FNanchor_19_19"><span
+class="label">[19]</span></a> &#8220;Preparation of Plantation Rubber,&#8221; Sidney Morgan, 1913.
+&#8220;Spotting of Plantation Rubber,&#8221; Keith Bancroft, 1913; Bulletin
+No. 16, F.M.S. Department of Agriculture. &#8220;Spotting of Prepared
+Plantation Rubber,&#8221; A. Sharpies, 1914; Bulletin No. 19, F.M.S.
+Department of Agriculture.</p></div>
+
+<p><a name="Sec17_20" id="Sec17_20"></a>If any reader is desirous of producing the defect experimentally,
+all that is necessary is to prepare a piece of crepe rubber
+of rather more than ordinary thickness, roll it up while wet,
+and place aside for some days.</p>
+
+<p>This experiment reproduces the conditions favourable for
+the development of the spores, and spots of various colours
+may result. It will be clear that the chief factor influencing the
+result is the continued presence of plenty of moisture.</p>
+
+<p>This condition may be created inadvertently in the course
+of factory practice, if piles of crepe rubber are allowed to
+remain for any appreciable period before hanging to dry.
+For this reason batches of wet crepe should always be placed
+on edge, to allow free drainage of surface moisture, if the rubber
+cannot be taken at once to the drying-sheds.</p>
+
+<div class="figcenter"><a name="Fig66" id="Fig66"></a><img src="images/illo254.jpg" alt="Three
+Specimens of Fine Pale Crepe suffering from 'Spot' Disease" />
+<p class="caption"><span class="smcap">Three Specimens of Fine Pale Crepe suffering from<br />
+&#8220;Spot&#8221; Disease.</span></p></div>
+
+<p><span class='pagenum'><a name="Page_238" id="Page_238">[238]</a></span></p><p><span
+class='pagenum'><a name="Page_237" id="Page_237">[237]</a></span></p><p>The condition also is provided if the thickness of the crepe
+is excessive. In some factories, having no smooth-roll finishing
+machines, the crepes may have a distinct raised pattern upon
+them. It is usual to note that if &#8220;spot&#8221; disease appears in such
+crepes, it is incident to much greater degree in the thicker
+portions of the rubber&mdash;<i>i.e.</i>, upon the raised pattern.</p>
+
+<p><a name="Sec17_21" id="Sec17_21"></a>The direct connection between the rate of drying and the
+appearance of coloured spots or flushes is thus established, and
+it only remains to adopt precautionary measures which will
+lead to an avoidance of delay (1) between machining and
+hanging, (2) in drying.</p>
+
+<p><a name="Sec17_22" id="Sec17_22"></a><a name="Sec17_23" id="Sec17_23"></a>It
+is indicated, therefore, that, if spot disease is to be avoided,
+the prime consideration is the preparation of a thin crepe which
+will dry quickly under average conditions. It may sometimes
+happen that even very thin crepes will sometimes be found
+affected on some estates. In such instances, it will be found
+that the design or situation of the drying-house is at fault, and
+that specially favourable conditions for the development of
+the fungi have been created by excessively wet weather.
+Should the trouble persist in spite of the preparation of the
+thinnest crepe, it would be advisable either to abandon this
+form of No. 1 product or to consider the installation of artificial
+aids to drying.</p>
+
+<p>We have not yet encountered any case in which it was found
+necessary to treat the latex with an antiseptic or disinfectant
+substance for the prevention of &#8220;spot&#8221; disease. There appears
+to be an idea held in some quarters that sodium bisulphite
+may be so employed as a fungicide. This does not agree with
+our experience, which is confirmed by Sharpies (Bulletin No. 19,
+F.M.S. Department of Agriculture).</p>
+
+<p>In 1913 experiments with chinosol were undertaken at the
+Pataling Laboratory of the Rubber Growers&#8217; Association, and
+an account of the method of treatment was given in a printed
+report issued to subscribers. Dr. P. Arens,<a name="FNanchor_20_20" id="FNanchor_20_20"></a><a
+href="#Footnote_20_20" class="fnanchor">[20]</a> of the Malang<span class='pagenum'><a name="Page_239" id="Page_239">[239]</a></span>
+Experimental Station (Java), has also recommended the use
+of chinosol. The substance is expensive, but is effective
+in very small quantity. On the whole, given average conditions
+in factory practice, such aids should not be necessary,
+and where keen supervision is not available may lead to other
+difficulties.</p>
+
+<div class="footnote"><p><a name="Footnote_20_20" id="Footnote_20_20"></a><a
+href="#FNanchor_20_20"><span class="label">[20]</span></a> &#8220;Guide to the Preparation of Rubber,&#8221; Arens, 1918; Communications
+from the Experimental Station (Malang, Java).</p></div>
+
+<p>It has already been remarked that it is possible for &#8220;spot&#8221;
+disease to develop in dry rubber which previously gave no
+evidence of the presence of fungi. The condition necessary
+to such an occurrence is supplied by the presence of moisture.
+Thus, to state instances which are by no means uncommon,
+if a box of rubber is allowed to remain exposed to rain, or is
+damaged by flood-water, or by sea-water during transit, or
+(sometimes) if the rubber is packed in a damp case, the crepe
+on arrival at its destination may be found to be affected to a
+degree dependent upon the extent of wetting and the duration
+of the wetting period.</p>
+
+<p>No means are known by which these coloured spots, due to
+the growth of chromogenic organisms, can be removed from the
+rubber. Naturally, although they may be present in the darker
+lower grades of crepe, they are not so easily visible as in pale
+crepe. It follows, therefore, that every possible precautionary
+measure must be taken when pale crepe has to be prepared.</p>
+
+<p>We are often asked whether it is possible for an infected piece
+of rubber to affect sound rubber hanging in the same building;
+and whether, in case of &#8220;spot&#8221; disease appearing, it is necessary
+to disinfect the drying-house.</p>
+
+<p><a name="Sec17_24" id="Sec17_24"></a>In a general sense, the answer to both queries is in the negative.
+It has not been proved possible to transmit the disease
+from one piece of crepe to another, except by the closest possible
+contact and in the presence of an abundance of moisture.</p>
+
+<p>A dry crepe, even when in close contact with an infected
+dry specimen, has not been found to be affected.</p>
+
+<p>Unless, therefore, pieces of rubber are pressed together,
+under favourable conditions as to moisture, there has been
+observed no transfer of disease.</p>
+
+<p>Similarly it has not been found that the presence of spotted
+rubber in one part of the drying-house has been responsible for<span class='pagenum'><a name="Page_240" id="Page_240">[240]</a></span>
+an outbreak of disease in another part of the same building.
+Furthermore, after the removal of diseased rubber from the
+drying-shed, freshly prepared rubber may be hung on the same
+supports without becoming affected, and without any intermediate
+treatment of the wooden bars, providing the crepe is
+thin and weather conditions are good. In our experience,
+no case has been observed in which the disease has been communicated
+to freshly prepared rubber by reason of the previous
+presence of affected rubber. In our opinion, therefore, any
+scheme for disinfecting the interior of a drying-house, as a
+preventive measure against the spread of &#8220;spot&#8221; disease,
+is unnecessary.</p>
+
+<p>All other things being equal, it is plain that much will depend,
+as to the incidence of coloured spots, upon the design and
+situation of the drying-house. Sufficient has been written in
+previous chapters to indicate the importance of these points
+as affecting the rate of drying, upon which hinges the possibility
+of the appearance of &#8220;spot&#8221; disease.</p>
+
+<p><a name="Sec17_26" id="Sec17_26"></a>In conclusion, the chief points in any discussion of this subject
+may be summarised thus:</p>
+
+<div class="blockquot"><p>1. No coagulum should be left without working for longer
+than the ordinary period. Otherwise, the prevailing conditions
+are very favourable for the development of the disease.</p>
+
+<p>2. Thin crepe only should be made. The quicker the rate
+of drying the less possibility is there of the coloured spots
+appearing.</p>
+
+<p>3. Crepe should never be allowed to remain folded overnight,
+and batches of folded wet crepe should be placed on
+edge to drain off surface moisture. The rubber should be hung
+to dry as soon as possible.</p>
+
+<p>4. Several species of fungi causing coloured spots have been
+recognised, and it has been proved conclusively that it is possible
+to infect latex and also fresh coagulum.</p>
+
+<p>5. As far as our present knowledge goes, it appears that
+infection takes place chiefly, if not entirely, by means of the
+latex in the field-vessels. It may take place during transport
+also, or even during coagulation.</p>
+
+<p>6. While it is certain that infection can be caused by contact,
+it has not yet been shown that infection of the finished wet
+rubber takes place in the drying-houses by means of air-borne
+spores&mdash;at least, under ordinary drying conditions.</p>
+
+<p><span class='pagenum'><a name="Page_241" id="Page_241">[241]</a></span>7. There is reason to believe that no further infection takes
+place once the rubber is well into the drying stage, and that dry
+rubber is not infected even by contact. From this one might
+infer that, as long as rubber remains dry, infection cannot take
+place during the voyage to the port of consignment.</p>
+
+<p>8. Coloured spots do not appear until the rubber is about
+half dry, because that period is necessary for the development
+of the fungus to that stage in its life-history when it excretes
+colouring matter. The fungus in its earlier and colourless
+stage may have been present from the time the latex entered the
+cup.</p>
+
+<p>9. The natural habitat of the fungi would appear to be decaying
+vegetable matter in the field.</p>
+
+<p>10. Finally, if it is found impossible to be rid of fungoid-spot
+disease after having exercised all care and observed all
+known precautions, nothing remains but to supersede the
+ordinary drying process by some system of quick drying, such
+as the vacuum-drying process or a hot-air draught system,
+in which the rubber dries so quickly that any possibility of
+appearance of &#8220;spots&#8221; is entirely removed.</p></div>
+
+<p><a name="Sec17_27" id="Sec17_27"></a><span class="smcap">Surface Moulds or Mildews on Crepe Rubber.</span>&mdash;Defects
+of this nature are most uncommon in the higher grades of crepe
+rubber, but cases of affection in the lower grades are not rare.</p>
+
+<p>It will be evident from all previous discussions that the
+incidence of these moulds must be due to an extremely slow rate
+of drying. The necessary conditions would be supplied by
+one or more of the following causes:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Making the crepe too thick.</p>
+
+<p>(<i>b</i>) Hanging the crepe in a badly ventilated or badly situated
+building.</p>
+
+<p>(<i>c</i>) Occasionally by abnormally wet weather.</p>
+
+<p>(<i>d</i>) Allowing piles of crepe to remain too long before hanging.</p>
+
+<p>(<i>e</i>) Using excessive quantities of deteriorated sodium bisulphite.
+In short, any factor contributing towards a retarded
+rate of drying may be responsible for the appearance of
+surface mildews. The last mentioned cause is of not infrequent
+occurrence. Knowing the chemical to be of poor quality,
+relatively more is used to produce the desired anti-oxidant
+effect. Unless the rubber is particularly well washed on the
+rolls, there remains within it a residue of sodium <i>bisulphate</i>,
+an oxidation product of the bisulphite. This is hygroscopic
+to some degree&mdash;<i>i.e.</i>, it takes up moisture from the atmosphere.<span
+class='pagenum'><a name="Page_242" id="Page_242">[242]</a></span>
+Hence drying is delayed, and even should mildews not develop
+the chemical may sometimes be seen on the surface of the
+rubber as a whitish &#8220;bloom.&#8221;</p></div>
+
+<p>The enumeration of the possible causes of mildews on crepe
+rubber is sufficient to indicate the necessary precautions to be
+taken, and the discussion will not be extended further.</p>
+
+<p><a name="Sec17_28" id="Sec17_28"></a><a name="Sec17_29" id="Sec17_29"></a><span
+class="smcap">Tackiness in Rubber.</span>&mdash;&#8220;Tackiness&#8221; is a term used to
+denote a deterioration of rubber which renders it sticky, and,
+beyond this, implies that some physical and chemical change
+in the nature of the substance has taken place. In fact, it is
+no longer &#8220;rubber,&#8221; but an oxidation product containing much
+resinous matter. It does not behave as rubber, and hence
+its value is much depreciated.</p>
+
+<p>With modern ideas of erection of factories to guard against
+the introduction of direct sunlight, it was hoped that this defect
+had practically ceased to exist. In one grade of rubber it would
+be expected that tackiness would continue to appear. Earth-rubber,
+often exposed to direct sunlight for a week, would
+naturally become tacky, and this tackiness cannot be avoided
+unless the earth-scrap is to be collected more frequently. But
+in many cases even the higher grades of rubber show signs of
+tackiness. Experiments have been carried out at various times
+and in various places to determine the cause of tackiness. For
+some time the theory of bacterial origin was in favour, but none
+of the experimental results was convincing. Bacteria may be
+present in tacky rubber; but, on the other hand, many cases of
+bacteria in rubber have been observed in which there was no
+tackiness. Experiments were made by one of us some years
+ago with a view to testing the bacterial theory by inoculating
+latex with small pieces of tacky rubber. In opposition to the
+results which were stated to have been obtained, there was no
+spread of tackiness. Other investigators have obtained similar
+results. One writer proposed to explain tackiness as caused
+by excess of moisture. This perfectly simple explanation unfortunately
+displays only a profound ignorance of the subject,
+and does not take into account the fact that tackiness is incident
+in rubber after dryness has been reached. It need not be
+pointed out to planters in Malaya that wet sheets of rubber<span class='pagenum'><a name="Page_243" id="Page_243">[243]</a></span>
+are often exposed to direct sunlight by workers of native
+holdings, with no resulting harm as long as plenty of moisture
+is present in the rubber.</p>
+
+<p><span class="smcap">Tackiness the Result of a Slow Process of Change.</span>&mdash;As
+stated above, tackiness does not appear until the rubber is
+dry, and even then it is to be noted that it is possible for tackiness
+to appear in rubber arriving in London, which showed
+no indications of tackiness when packed for shipment.</p>
+
+<p><span class="smcap">Tackiness caused by Traces of Copper Salts.</span>&mdash;Spence,
+as the result of investigations, has pointed out that none of the
+various theories put forward to account for tackiness&mdash;viz.,
+the action of bacteria, premature putrefaction, oxidation,
+excess of moisture, the action of enzymes, etc.&mdash;have any
+basis in scientific proof, and believes that the cause of tackiness
+cannot be directly attributed to bacteria. It has been stated
+that the only known way of causing rubber to become tacky
+is to expose it to sunlight or heat. While agreeing that in the
+ordinary way this statement is correct as far as one rules out the
+employment of chemical substances, it must be pointed out
+that tackiness of the worst degree may be caused by the presence
+of traces of copper or copper salts. This point has already
+been touched upon in a preceding paragraph dealing with the
+defect of &#8220;green streaks&#8221; in pale crepe rubber.</p>
+
+<p><a name="Sec17_30" id="Sec17_30"></a>In the course of laboratory experiments tackiness has often
+been induced by the use of traces of copper salts. The rate
+at which tackiness is induced appears to be dependent upon
+the amount of copper salt used, but once it begins, the rubber
+molecule is very rapidly broken down, and resins are formed.
+As the formation of resins is accompanied by the inclusion of
+oxygen in the chemical constitution, it would be expected
+that dry rubber becoming tacky should increase in weight.
+This is found to be the case, and to give an idea of how this
+weight increases with the progress of tackiness, the results
+below may be studied.</p>
+
+<p>It will be seen that the maximum quantity of copper sulphate
+used amounted to 0&middot;025 per cent, (approx.) upon the weight
+of latex taken. Now it is highly probable that only a fraction
+of this quantity was retained in the rubber on coagulation,<span class='pagenum'><a name="Page_244" id="Page_244">[244]</a></span>
+the remainder being in solution in the serum. Furthermore,
+as the rubber was well washed and worked down to thin crepe,
+<i>the total quantity of copper salt remaining in the dry crepe must
+have been exceedingly small</i>. Yet the effect is most marked and
+should impress upon all managers the necessity for guarding
+against any possible contamination caused by brass or copper.</p>
+
+<table summary="Table p244">
+
+<tr>
+<td rowspan="2" class="center bt br bb"><i>Sample.</i></td>
+<td rowspan="2" colspan="2" class="center bt br bb"><i>Amount of Copper Salt.</i></td>
+<td colspan="6" class="center bt bb"><i>Weight of Rubber.</i></td>
+</tr>
+
+<tr>
+<td class="center br bb">When Dry.</td>
+<td class="center br bb">After<br />Interval<br />of Four<br />Weeks.</td>
+<td class="center br bb">Further<br />Interval<br />of Seven<br />Weeks.</td>
+<td class="center br bb">Further<br />Interval<br />of Three<br />Weeks.</td>
+<td colspan="2" class="center bb">Percentage<br />in Increase<br />in Weight.</td>
+</tr>
+
+<tr>
+<td class="br">&nbsp;</td>
+<td colspan="2" class="br">&nbsp;</td>
+<td class="center fsize80 br">Grms.</td>
+<td class="center fsize80 br">Grms.</td>
+<td class="center fsize80 br">Grms.</td>
+<td class="center fsize80 br">Grms.</td>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="center br top">1</td>
+<td colspan="2" class="left br">0&middot;02 grms. copper sulphate,<br />per 100 c.c. latex</td>
+<td class="rightbot br" style="padding-right: 1.5em;">430</td>
+<td class="rightbot br" style="padding-right: 1em;">441</td>
+<td class="rightbot br" style="padding-right: 1em;">482</td>
+<td class="rightbot br" style="padding-right: 1em;">488</td>
+<td class="rightbot" style="padding-right: 0;">13&middot;</td>
+<td class="leftbot" style="padding-left: 0;">5</td>
+</tr>
+
+<tr>
+<td class="center br top">2</td>
+<td colspan="2" class="left br">Ditto</td>
+<td class="rightbot br" style="padding-right: 1.5em;">428</td>
+<td class="rightbot br" style="padding-right: 1em;">439</td>
+<td class="rightbot br" style="padding-right: 1em;">481</td>
+<td class="rightbot br" style="padding-right: 1em;">486</td>
+<td class="rightbot" style="padding-right: 0;">13&middot;</td>
+<td class="leftbot" style="padding-left: 0;">55</td>
+</tr>
+
+<tr>
+<td class="center br top">3</td>
+<td class="left">0&middot;01 grms. copper sulphate,<br />per 100 c.c. latex</td>
+<td rowspan="2" class="right br" style="font-size: 2.5em; vertical-align: middle;">}</td>
+<td rowspan="2" class="right br" style="padding-right: 1.5em; vertical-align: middle;">962</td>
+<td rowspan="2" class="right br" style="padding-right: 1em; vertical-align: middle;">987</td>
+<td rowspan="2" class="right br" style="padding-right: 1em; vertical-align: middle;">1035</td>
+<td rowspan="2" class="right br" style="padding-right: 1em; vertical-align: middle;">1036</td>
+<td rowspan="2" class="right" style="padding-right: 0; vertical-align: middle;">7&middot;</td>
+<td rowspan="2" class="left" style="padding-left: 0; vertical-align: middle;">7</td>
+</tr>
+
+<tr>
+<td class="center br top">&nbsp;</td>
+<td class="left">0&middot;01 grms. copper acetate,<br />per 100 c.c. latex</td>
+</tr>
+
+<tr>
+<td class="center br bb top">4</td>
+<td colspan="2" class="left br bb">0&middot;025 grms. copper sulphate,<br />per 100 c.c. latex</td>
+<td class="rightbot br bb" style="padding-right: 1.5em;">502</td>
+<td class="rightbot br bb" style="padding-right: 1em;">513</td>
+<td class="rightbot br bb" style="padding-right: 1em;">558</td>
+<td class="rightbot br bb" style="padding-right: 1em;">560</td>
+<td class="rightbot bb" style="padding-right: 0;">11&middot;</td>
+<td class="leftbot bb" style="padding-left: 0;">5</td>
+</tr>
+
+</table>
+
+<p>In view of the effect thus produced by the addition of traces
+to latex of a copper salt, and the observed effect on rubber of
+contact with copper salts, one may imagine the result produced
+some years ago when on an estate smoked sheets were washed
+with a solution of copper sulphate as a remedy for surface
+moulds!</p>
+
+<p>With the exception of this chemical action we know of no
+other means by which tackiness is produced, beyond those of
+direct sunshine and heat. Cases governed by these two causes
+are common on estates. They are confined chiefly to the lowest
+grades of scrap rubber, when the component raw materials
+have been exposed to the sun for a period before being brought
+to the factory.</p>
+
+<p>It is now comparatively rare to find cases of tackiness in the
+higher grades of crepe, and when they occur, one may look
+for evidence of gross carelessness in the admission of direct
+sunshine. Usually this means the failure of some individual
+to regulate window shutters according to the position of the<span class='pagenum'><a name="Page_245" id="Page_245">[245]</a></span>
+sun in the sky. More rarely does it happen that tackiness may
+have been induced by placing thin crepe rubber too near the
+iron roof of the drying-shed.</p>
+
+<p>Regarding the question as to whether tackiness may be communicated
+by direct contact, opinion appears to be divided.
+It has been stated that sound rubber left in contact with tacky
+specimens was found to be unaffected after two years. On the
+other hand, it is claimed that tackiness has been induced in a
+sound rubber by infecting it with small pieces which were
+tacky. In a preliminary article on the effect of copper and
+copper salts upon pieces of dried and sound crepe<a name="FNanchor_21_21"
+id="FNanchor_21_21"></a><a href="#Footnote_21_21" class="fnanchor">[21]</a> it was
+noted, after one year, that tackiness had been communicated
+from the treated portion to the &#8220;blank&#8221; in contact. There
+is sufficient evidence to warrant the injunction that tacky
+rubber should be excluded from contact with sound rubber.
+If shipped it should be packed separately.</p>
+
+<div class="footnote"><p><a name="Footnote_21_21" id="Footnote_21_21"></a><a
+href="#FNanchor_21_21"><span class="label">[21]</span></a> Report I., 1916 (Sidney Morgan), Rubber Growers&#8217; Association
+(Malaya).</p></div>
+
+<p>Compounds have been put upon the market which assumedly
+claim to be cures for tackiness. These are merely palliatives,
+consisting of starch, talc, or chalk powders, which counteract
+stickiness.</p>
+
+<p><span class="smcap">No Cure for Tackiness.</span>&mdash;At the present stage of our
+knowledge, there appears to be no cure for tackiness. Neither
+do we see the necessity for a cure when the phenomenon may
+be avoided by taking simple precautions, which may be briefly
+summarised thus:</p>
+
+<div class="blockquot"><p>(1) Any permanent openings through which it is possible
+for direct sunlight to enter, whether large or small, should
+either be totally closed or provided with some substance which
+cuts off the direct effect of the sunlight&mdash;<i>e.g.</i>, ruby glass or
+ruby glazed cloth.</p>
+
+<p>(2) Rubber should under no circumstances be placed near
+any source of heat.</p>
+
+<p>(3) No rubber should be hung in a drying-room in such a
+position adjacent to a window or door that it is possible for
+sunshine to reach it, even should coolies neglect to obey rules.</p>
+
+<p>(4) Instruments or vessels of copper or brass should not
+be used where acids are employed.</p></div>
+
+<p><a name="Sec17_31" id="Sec17_31"></a><span class='pagenum'><a name="Page_246" id="Page_246">[246]</a></span></p><p><span
+class="smcap">Lack of Uniformity in Colour.</span>&mdash;The complaint is far
+less real than it was a few years ago. The introduction by
+the Rubber Growers&#8217; Association of the &#8220;Metrolac&#8221; led to
+uniform dilution of latices varying in rubber content. Previously
+the only known method of obtaining uniformity in colour
+and appearance was that by which latices from all fields were
+mixed together in bulk. Even so the uniformity applied only
+to the one bulking operation, and any other day&#8217;s results might
+show considerable variation from the first standard.</p>
+
+<p>This does not take into account any observed differences in
+shade of colour attributable to natural oxidation which might
+vary in intensity from day to day. The introduction of sodium
+bisulphite as an anti-oxidant exerted a great influence upon the
+colour of pale crepes generally; but considerable variation would
+still have been notable but for the adoption of the scheme for
+uniform dilution, in addition to the use of small quantities
+of anti-oxidant.</p>
+
+<p>On most estates it is now possible, with slight exceptions due
+to abnormal conditions, so to treat the latex that the pale
+crepes prepared on any one day differ in no perceptible degree
+from the product of any other day. Where this is not the
+case it must be suspected that there has been some carelessness
+in manipulating the latex or the chemicals. Attention has been
+drawn to the fact that there may be exceptional cases, when the
+determining factors lie beyond the control of factory processes&mdash;<i>e.g.</i>,
+heavy rains causing over-dilution of latex, the yielding of
+&#8220;yellow&#8221; latex from newly opened areas, etc. But on the
+whole there is now no reason why the general average product
+from any estate should not be uniform in colour and appearance.
+Furthermore, it should be possible for large groups of estates,
+by the adoption of uniform methods, to produce similar rubber
+from all the plantations. Moreover, apart from some differences
+caused by factors which still need determination,
+the total product in a general sense should not only be
+uniform in appearance but uniform in physical and chemical
+properties.</p>
+
+<p><a name="Sec17_32" id="Sec17_32"></a><span class="smcap">Block Rubber.</span>&mdash;This mode of preparation is employed only
+in comparatively few instances. The block is prepared from<span class='pagenum'><a name="Page_247" id="Page_247">[247]</a></span>
+crepe rubber, which has been dried either in a hot-air drier
+or in a vacuum chamber.</p>
+
+<p>There is another type of block which is made by placing layers
+of dry crepe under considerable pressure. This is not the
+true type of block, and the layers are quite distinct&mdash;<i>i.e.</i>, they
+do not amalgamate. Usually this pressed rubber consists of
+lower grades of crepe, and it should not be popular, inasmuch
+as it leaves too wide an opportunity for the inclusion of dirt,
+bark particles, and other impurities, which cannot be seen
+generally on account of the protective colour of the rubber.</p>
+
+<p>In the true type of block, the layers are in a plastic condition,
+due to heat, when they leave the drying-chamber; and being
+immediately submitted to great pressure the result is a homogeneous
+mass in which the layers disappear by amalgamation.
+Only the best grade of crepe is employed, and given the absence
+of defects in the layers there should be no complaint regarding
+the final block.</p>
+
+<p>Prepared in slabs which are three or four inches in thickness,
+the product is easily handled, and should be sufficiently translucent
+to make it possible to distinguish the shape of the hand
+when held between the block and the light. This is not possible
+when blocks are made of greater thickness.</p>
+
+<p>The only complaints which it should be possible to lodge
+against block rubbers are:</p>
+
+<div class="blockquot"><p>(<i>a</i>) The inclusion of dirt and other matter.</p>
+
+<p>(<i>b</i>) The use of layers of crepe which have some defect.</p>
+
+<p>(<i>c</i>) The inclusion of air-bubbles.</p></div>
+
+<p>The remedy for (<i>a</i>) and (<i>b</i>) lies in the hands of the factory
+superintendent. The last ground of complaint is dependent
+upon the style of preparation of the original layers of crepe.</p>
+
+<p>When layers of crepe are placed one upon the other, and submitted
+to great pressure, it is natural to suppose that air would
+be contained in spaces, and would be unable to escape. To
+guard against this, it would seem necessary to prepare the crepe
+thin and with a fairly good surface finish.</p>
+
+<p>It must be obvious to all acquainted with the processes
+involved in the preparation of block rubber, that no possibility<span class='pagenum'><a name="Page_248" id="Page_248">[248]</a></span>
+exists for the presence of air-bells actually enclosed <i>in</i> thin
+crepe. When the vacuum-dried crepe is folded preparatory
+to the blocking process it is apparent that between the layers
+there must always be a considerable volume of air, a small
+proportion of which is bound to be retained owing to the nature
+of the surface of crepe rubber.</p>
+
+<p>That this has always been true of the preparation of block
+rubber cannot be denied. It is possible, of course, for one type
+of block to show the presence of air-bells more than another
+type, the proportion of air enclosed in blocking depending
+upon the nature of the crepe of which the block is composed.
+A block built up of layers of smooth, fine crepe would be expected
+to contain less air-bells than a block composed of layers
+of a rough crepe.</p>
+
+<p>Block rubber has been seen which was free from air-bells,
+but this was the thin variety of block prepared for show
+purposes with far greater care, probably, than would be
+expended in commercial preparations.</p>
+
+
+<p class='pagenum'><a name="Page_249" id="Page_249">[249]</a></p>
+<hr class="c25" />
+<h2><a name="Ch18" id="Ch18"></a>CHAPTER XVIII</h2>
+
+<h3><i>DEFECTS IN SHEET RUBBER</i></h3>
+
+
+<p>Before proceeding to deal with defects in the rubber as it is
+put upon the market a brief account will be given of faults
+which may be noted in the preparatory stages.</p>
+
+<p><a name="Sec18_1" id="Sec18_1"></a><span class="smcap">Milky Residue or Serum.</span>&mdash;If the serum is not clear after
+the ordinary period allowed for coagulation, it indicates one of
+the following possible causes:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Failure to obtain complete mixture by thorough stirring.</p>
+
+<p>(<i>b</i>) Insufficiency of acid solution. This may be real or
+indirectly due to the presence of an excess of anti-coagulant
+such as formalin or sodium sulphite.</p>
+
+<p>(<i>c</i>) In cases where other coagulants than acetic or formic
+acids have been employed the failure may be due to an excess
+of, or an unsuitable, coagulant&mdash;<i>e.g.</i>, hydrochloric acid.</p></div>
+
+<p><a name="Sec18_2" id="Sec18_2"></a><span class="smcap">Coloured Surface Blotches and Unpleasant Odour.</span>&mdash;Sometimes
+the surface of the coagulum exhibits yellowish or
+bluish streaks and patches. It will be found generally that
+the yellowish colour is possessed by a slimy substance, of
+offensive odour, which may be scraped from the surface.
+Either insufficient acid has been used, or the mixing of latex
+and coagulant has been at fault.</p>
+
+<p><a name="Sec18_3" id="Sec18_3"></a><span class="smcap">Dark Discoloration of the Rubber.</span>&mdash;This may be stated
+to be a natural process when fresh rubber is exposed to the
+atmosphere. It is usually described as &#8220;oxidation,&#8221; and it
+will be noted to be absent, or to occur to less degree, on those
+portions of the rubber which are protected from the atmosphere
+by being below the surface of the remaining liquid. This
+surface change may be prevented (see <a href="#Ch8">Chapters VIII.</a> and <a href="#Ch9">IX.</a>)
+by the use of small quantities of sodium sulphite (for preference)
+or bisulphite.</p>
+
+<p><a name="Sec18_4" id="Sec18_4"></a><a name="Sec18_5" id="Sec18_5"></a><a name="Sec18_6" id="Sec18_6"></a><span
+class="smcap">Soft Coagulum, Spongy under-surface, Tearing of
+Coagulum.</span>&mdash;If the whole mass of coagulum is too soft, while<span
+class='pagenum'><a name="Page_250" id="Page_250">[250]</a></span>
+coagulation appears to be complete, over-dilution of the latex
+has occurred. This may apply also to the case in which the
+under-surface only is spongy and soft. If coagulating-tanks
+are employed, the upper edge may be comparatively hard,
+while the lower is soft and weak. Often the spongy portion
+may adhere to the partitions. This prevents the natural
+rise of the coagulum, due to retraction, as the mass &#8220;sets.&#8221;
+The pull between the free upper portion and the adhering
+lower edge causes splitting and tearing of the coagulum, with
+marked porosity (spongy appearance). The two factors to
+receive attention are the standard of dilution and the condition
+of the surfaces of the partitions. If these have minute cracks
+into which latex can penetrate, and in which coagulation takes
+place, the boards should be discarded. Given the conditions
+indicated above, the tearing and splitting of rubber in coagulating
+tanks is sometimes augmented by the practice of flooding
+the tanks when coagulation is judged to be complete. The
+surface water finds its way downwards between strips of coagulum
+and the partitions, thus increasing the upward tension
+between the free and adhering portions. The main idea
+governing the practice of flooding the tanks is to prevent
+&#8220;oxidation&#8221; (darkening) of the upper edges. If a small
+quantity of sodium sulphite is employed as an anti-oxidant
+and to retard coagulation, it is not necessary to flood tanks.</p>
+
+<p><a name="Sec18_7" id="Sec18_7" ></a><span class="smcap">&#8220;Pitting&#8221;
+of Surfaces.</span>&mdash;In pan coagulation this &#8220;pitted&#8221;
+appearance is usually limited to the under-surface, while coagulum
+prepared in tanks may exhibit the defect on both faces.
+The existence of these numerous &#8220;pits,&#8221; or small depressions,
+points to the presence of bubbles of gas which have been unable
+to escape freely. As the formation and retention of gas-bubbles
+is not a normal occurrence in coagulation, we are led
+to infer that some special conditions must have arisen. These
+may be supplied by one or more of the following contributory
+causes:</p>
+
+<div class="blockquot"><p>(<i>a</i>) The latex had begun to &#8220;sour&#8221; before arrival at the
+factory or while waiting to be treated. This premature coagulation
+is usually checked or diminished by the employment of
+anti-coagulants (see <a href="#Ch8">Chapters VIII.</a> and <a href="#Ch9">IX.</a>). It
+is generally<span class='pagenum'><a name="Page_251" id="Page_251">[251]</a></span>
+accompanied by the appearance of enclosed gas-bubbles in
+the dry rubber.</p>
+
+<p>(<i>b</i>) There may have been a slight insufficiency of coagulant,
+or the admixture was not thorough, thus allowing a slow putrefactive
+change to take place in the incompletely coagulated areas.</p>
+
+<p>(<i>c</i>) The wooden partitions may not have been effectively
+cleansed. The existence of a thin slime, of bacterial origin,
+is sometimes noted. This is accountable for putrefactive
+effects in the surfaces of the coagulum, or in the serum, giving
+rise to the formation of gases. If these cannot escape freely,
+by reason of adhesion between the coagulum and the partitions,
+&#8220;pitting&#8221; occurs.</p></div>
+
+<p><a name="Sec18_8" id="Sec18_8"></a><span class="smcap">Thickened Ends or Edges, after Rolling.</span>&mdash;As a rule
+these defects may be ascribed to the employment of too rich
+a latex, or faulty manipulation. Even if the standard of
+dilution should be correct it sometimes happens that, in the
+preliminary rolling of a long strip of rubber, coolies begin
+in the middle, rolling with a forward pressure and tension
+towards the ends of the strip. This is generally not so much
+the fault of the coolie as being due to the lack of proper facilities
+for preliminary rolling. The table should be about 3 feet in
+height, so that ease of working is obtained merely by natural
+pressure due to the position in which the worker stands. The
+use of a heavy wooden roller would contribute towards this
+result, inasmuch as it obviates the use of force, and the pressure
+is almost entirely in a vertical direction.</p>
+
+<p><a name="Sec18_9" id="Sec18_9"></a><span class="smcap">Mis-shapen Sheets.</span>&mdash;It is sometimes noted that sheets may
+be wider and thicker at the ends than in the middle. Manipulation
+alone, as indicated above, is not solely responsible.
+The primary cause is to be traced to over-dilution of latex,
+giving a very soft coagulum which responds too readily to
+tension and pressure. Faulty treatment in rolling exaggerates
+the tendency for the strip of sheet to become narrow and thin
+in the middle, wider and thicker at the ends.</p>
+
+<p><a name="Sec18_10" id="Sec18_10"></a><span class="smcap"><a name="Sec18_11" id="Sec18_11"></a><a name="Sec18_12"
+id="Sec18_12"></a><a name="Sec18_13" id="Sec18_13"></a>Thickened Patches, Torn Sheets, &#8220;Dog-Ears,&#8221; Creases.</span>&mdash;These
+elementary defects are all due to careless working.
+While occasional errors cannot be avoided, there is no real
+excuse for the continuance of trouble to any degree, under
+average supervision.</p>
+
+<p>Thickened patches are often caused in conjunction with torn<span class='pagenum'><a name="Page_252" id="Page_252">[252]</a></span>
+sheets, and the trouble may be ascribed to faulty practice in
+allowing too heavy a pile of wet strips to accumulate before
+machining. Or a comparatively small pile may have been
+transported some distance. It is difficult to separate the strip,
+and occasionally the separation is only effected at the expense
+of two sheets, one of which is torn and the other has a portion
+of the first strip adhering to it.</p>
+
+<p>&#8220;Dog-ears&#8221; due to the folding over of corners of the sheets,
+and creases due to the rumpling of the coagulum, are generally
+the result of haste and lack of average care. Machine coolies,
+more often than not, will not be at any pains to straighten out
+folds before passing the coagulum through the rolls.</p>
+
+<p><a name="Sec18_14" id="Sec18_14"></a><span class="smcap">Greasiness before Smoking.</span>&mdash;Under ordinary methods of
+working this should never be encountered. It may be taken
+to show that the machined rubber has been allowed to remain,
+either hanging or in piles, far too long before entering the
+smoke-house. The appearance is most marked if the rubber
+has remained in a cool and moist atmosphere&mdash;<i>e.g.</i>, if it has
+been hanging over-night in a closed and badly-ventilated factory.
+In a marked degree this is to be observed in the preparation of
+air-dried sheets, unless they are exposed, when freshly prepared,
+to the action of the sun for a period. This period, in the case
+of rubber prepared on native small-holdings, generally extends
+over several days&mdash;until the sheets are more than half dry.</p>
+
+<p>In the preparation of smoked sheet, the greasy appearance
+and the cause outlined contribute to a defect which is eventually
+described as &#8220;stretching rusty.&#8221;</p>
+
+<p><a name="Sec18_15" id="Sec18_15"></a><span class="smcap">Surface Blemishes.</span>&mdash;The coagulum, during coagulation
+and subsequently, can be contaminated in various ways. In
+most cases a little intelligence or increased care would prevent
+the occurrence of these defects.</p>
+
+<p>When the coagulum remains over-night, in the absence of a
+cover, it is not uncommon to note the presence of dirt (from the
+roof above, or blown in from the outside), the droppings of mice
+and rats, flies and small insects. In theory these should be
+seen and removed by the factory hands. In practice, except
+while under immediate supervision, the extraneous matter is
+often rolled into the soft coagulum.</p>
+
+<p><span class='pagenum'><a name="Page_253" id="Page_253">[253]</a></span>A fairly common cause of this surface contamination is the
+exhaust from the power-unit; generally the worst offender is a
+steam-engine. Grit and smuts continually find their way into
+the factory, alighting on the tables, in the latex, in the water,
+and on the freshly prepared rubber. They are rolled into the
+soft rubber and lead to marked depreciation in the selling value.
+The radical remedy seems obvious, but is often beset with
+many difficulties not unconnected with financial considerations.</p>
+
+<p>Other superficial blemishes, such as those due to the presence
+of rust marks, oil or grease patches, etc., are self-explanatory,
+if a little thought is brought to bear upon them; and it is not
+proposed here to discuss such defects more fully.</p>
+
+<hr class="c05" />
+
+<p>Having now dealt with certain defects which are visible
+in wet rubber, we come to the discussion of others which are
+only perceptible either during or after the drying period. As
+far as is known no plantations of any size now prepare sheets
+other than in the form of smoke-dried rubber, with the exception
+of a few which make a special form of thick and partially air-dried
+product known as &#8220;slab&#8221; rubber.</p>
+
+<p>It is not proposed, therefore, to treat in any detail with air-dried
+sheet rubber. Certain obvious defects are common to
+both air-dried and smoke-cured sheets, and these will be first
+discussed.</p>
+
+<p><a name="Sec18_16" id="Sec18_16"></a><span class="smcap">Unevenness of Appearance.</span>&mdash;This lack of uniformity may
+refer either to size or colour, or to both. Apart from any
+other contributory causes, this variation is due, in pan sheet,
+to a neglect to standardise the dilution of all latices, or to lack
+of uniformity in the quantity of standardised latex placed in
+each receptacle.</p>
+
+<p>Where tanks are employed all sheets from the same tank
+should be of the same size before rolling, and any subsequent
+disparity in thickness and length must be attributed to some
+alteration in the width of the gap between the rolls of the
+machines.</p>
+
+<p>Unless all latices are standardised by means of an instrument,
+it is of course probable that the content of one tank may be
+found to differ from that of another.<span class='pagenum'><a name="Page_254" id="Page_254">[254]</a></span></p>
+
+<p>In a general sense, whether air-dried or smoke-cured sheets
+are considered, a thin strip will dry more quickly than a thick
+one, and should be paler in colour when viewed by transmitted
+light&mdash;<i>i.e.</i>, when the rubber is held between the eye and the
+source of light.</p>
+
+<p>It is necessary, therefore, to guard against the possibility of
+variations in thickness caused by faulty manipulation. The
+distance between the squeezing rolls (smooth) and between
+the marking rolls (patterned) should be adjusted and should
+remain set until the conclusion of work. In a factory having
+nothing beyond average requirements in equipment of machines
+it should not be necessary to have to interrupt the work of the
+smooth rolls or &#8220;markers&#8221; by having to make adjustments.
+This is, however, inevitable if there is only one smooth-roll
+machine, as it is always desirable to reduce the thickness of
+the coagulum by at least two stages through even-speed smooth
+rolls. In some factories there are three light power-driven
+smooth-roll machines, the gaps between pairs of rolls being
+set so as to obtain a gradual thinning effect upon the fresh
+coagulum, which is then passed once between patterned rolls.
+With such equipment it is found possible, in some cases, to
+omit the preliminary hand-rolling, and the strips of coagulum
+from the tank are passed direct through rolls set with a wide gap.
+This work demands much care, as it is necessary to avoid any
+distortion of the coagulum which may be caused by its own
+weight and length.</p>
+
+<p><a name="Sec18_17" id="Sec18_17"></a><span class="smcap">Variation due to Oxidation.</span>&mdash;The subject of oxidation
+has been mentioned in the <a href="#Ch18">opening paragraphs</a> of this chapter.
+It will have been learned that oxidation is a natural process,
+and that it may be prevented by the employment of anti-oxidants
+such as the sulphite or bisulphite of soda. In earlier
+days it was sometimes prevented by steeping the thin rubber
+in very hot water.</p>
+
+<p>In the absence of an anti-oxidant the degree of oxidation may
+vary daily and in different batches of latex on any one day, so
+that there is always the possibility of a lack of uniformity due
+to oxidation effects. This would be more evident in air-dried
+sheets than in smoke-cured rubber, as in the latter case the<span class='pagenum'><a name="Page_255" id="Page_255">[255]</a></span>
+darkening of the surface would be masked by the colour induced
+by the smoke-drying process.</p>
+
+<p>To obviate this variation anti-oxidants are used on most
+estates, but the accidental or misinformed abuse of these
+chemicals may lead to further lack of uniformity. Hence it
+is necessary to follow carefully the formul&aelig; prescribed by
+experience.</p>
+
+<p><a name="Sec18_18" id="Sec18_18"></a><span class="smcap">Colour of Smoked Sheets.</span>&mdash;It may be of interest to note
+that the effect known as oxidation is attributed to the presence
+of micro-organisms called enzymes (ferments) in the latex. It
+can also be produced artificially in various ways&mdash;<i>e.g.</i>, by the
+use of the crude product of wood-distillation (pyroligneous
+acid) as a coagulant, or by the addition to the latex of small
+quantities of a phenol such as carbolic acid. It is thus possible
+to prepare in sheet form a rubber which has the appearance of
+having been smoke-cured, although it may never have been in
+a smoke-house.</p>
+
+<p>It will be clear, therefore, that apart from other causes, the
+colour of the cured sheets may be influenced by oxidation of
+the fresh coagulation, and by the constituents of the smoke.
+It follows that the smoke from timbers which are richer than
+others in certain chemical bodies set free by combustion
+will produce a rubber darker in colour.</p>
+
+<p>There is thus no real connection between colour and period
+of cure, although in a general sense the longer the interval
+the darker the colour.</p>
+
+<p>Similarly it is now plain that when anti-oxidants are employed
+in excess the paleness of the rubber is in no degree truly indicative
+of the period during which the rubber has been smoke-cured.</p>
+
+<p>The influence of the effect of the hypsical condition of the
+wet rubber upon the final colour must be thoroughly grasped.
+One may take two sheets of apparently the same thickness,
+and smoke-cure them in juxtaposition within the same house,
+only to find that one dries much more rapidly than the other.
+As a consequence, the first, when fully cured, will be of a medium
+golden brown colour; while the other, owing to protracted
+smoking, will be dark. Evidently there must be some distinct<span class='pagenum'><a name="Page_256" id="Page_256">[256]</a></span>
+difference between the two in physical condition prior to the
+smoking. Here the factor involved is the rubber-content of
+the latex. Given two pieces of coagulum of identical thickness,
+but prepared from latices of different dry rubber content,
+it will be obvious that to reduce them to similar thickness, more
+pressure will be necessary in one case&mdash;<i>i.e.</i>, that piece of coagulum
+will be much more dense (more consolidated)&mdash;while the
+other will be comparatively soft and porous. Into the latter
+warm smoke can penetrate much more easily, and the internal
+moisture can escape more rapidly. The full cure may be made,
+say, within twelve days, while the tougher sheet may demand
+up to twenty days.</p>
+
+<p>To attain uniformity in colour, therefore, the following
+points must be studied and controlled as far as is possible:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Uniform dilution of all latices.</p>
+
+<p>(<i>b</i>) Uniform dimensions of coagulating receptacles.</p>
+
+<p>(<i>c</i>) Uniform volumes of standardised latex.</p>
+
+<p>(<i>d</i>) Uniform quality and quantities of chemicals.</p>
+
+<p>(<i>e</i>) Uniform methods of manipulating the coagulum.</p>
+
+<p>(<i>f</i>) Uniform conditions of fuel and accommodation during
+smoke-curing.</p></div>
+
+<p><a name="Sec18_19" id="Sec18_19"></a><span class="smcap">Surface Gloss.</span>&mdash;In the choice of fuel there is room for control
+if one has good timber available. This point opens up a
+discussion on the vexed question of &#8220;over-smoking,&#8221; as the
+term is sometimes applied to a pronounced dry glossy appearance
+of the surface of sheets.</p>
+
+<p>Three main factors are involved:</p>
+
+<div class="blockquot"><p>(1) The nature of the fuel.</p>
+
+<p>(2) The ratio between furnace capacity and the capacity of
+the smoke-house.</p>
+
+<p>(3) The rate of combustion.</p>
+
+<p>Obviously any fuel which yields an excessive quantity of tarry
+matter or creosotic substance would conduce to the formation
+of a heavy glaze on the rubber. Such fuel, therefore, should at
+most only be employed as the smaller portion in a mixture with
+&#8220;dead&#8221; timber.</p></div>
+
+<p>It is impossible to lay down any general rules for the guidance
+of estates, as the timber available varies so widely in
+nature. Experience must be the only guide, and it should not<span class='pagenum'><a name="Page_257" id="Page_257">[257]</a></span>
+be difficult to obviate the defect. Even so, there must be minor
+differences between the results obtained on estates, so that it
+is not possible to make strict estimations of the smoke-curing
+period by an examination of the surface appearance of rubber,
+even under the best of conditions. Some estates find that
+the rubber has a distinct gloss in ten days, while others may
+smoke-cure for twice that period without difficulty. Evidently,
+therefore, the question of available fuel is of prime importance.
+It may be remarked that very satisfactory results are always
+obtained from the use of fairly dry timber obtained from thinned
+rubber trees, mixed with the &#8220;dead&#8221; timber of old logs and
+stumps found on the estates.</p>
+
+<p>Obviously if a smoke-house has a superabundance of furnaces,
+producing more heat and smoke than is required, glazing will
+result. The point is tested by the average temperature maintained
+and the average rate of drying. The result of a high
+temperature would be the possibility of volatile tarry matter
+being driven in excess to the upper chamber. That this
+effect is eventually produced even at optimal temperatures
+is evident from an examination of the wood-work within the
+upper room.</p>
+
+<p>It is clear, also, that the rate of combustion exerts an influence.
+In a general sense a rapid consumption of fuel would augment
+the quantity of tarry matter passing into the upper chamber
+over any given period, and the possibility of glazing would
+be increased.</p>
+
+<p>On the other hand, it is possible that a surface glaze might
+be formed if the temperature were uniformly too low, especially
+if the rubber were rather thick. The rate of drying would be
+so slow, that if a timber rich in tarry matter were employed,
+the rubber might be exceedingly glossy.</p>
+
+<p>In order to guard against the appearance of a heavy glaze,
+then, the following points must be observed:</p>
+
+<div class="blockquot"><p>1. The fuel must be carefully selected by experience.</p>
+
+<p>2. The sheets must not be thick. No sheets should be
+thicker than <span class="enum">1</span>&#8260;<span class="denom">8</span> inch measured in average section across the ribs.</p>
+
+<p>3. The temperature must not be too high. An average
+working temperature of 120&deg; to 125&deg; F. should be ample.</p>
+
+<p><span class='pagenum'><a name="Page_258" id="Page_258">[258]</a></span>4. If the sheets are fairly thick, a low average temperature
+should be avoided. No lower average than 110&deg; F. should be
+allowed.</p></div>
+
+<p><a name="Sec18_20" id="Sec18_20"></a><span class="smcap">Dull, Black Surface.</span>&mdash;This is the opposite of the previous
+case, and generally is accompanied by a fairly heavy darkening
+of the surface due to &#8220;oxidation&#8221; effects. The fuel used is too
+&#8220;dead,&#8221; and needs the addition of some substance containing
+a fair amount of creosotic matter. The appearance of the
+rubber does not justify the assumption that it has been over-smoked.
+As a matter of fact, this type of rubber often becomes
+affected by mildew fairly rapidly, thus showing that the
+smoking has been inefficient.</p>
+
+<p>It may happen that an estate is in the habit of using a fuel
+which gives even to a thin sheet a heavy glaze in a comparatively
+brief period. The general custom is to soak such sheets
+in cold water, and then to scrub the surfaces, sometimes using
+soap, in order to cleanse the rubber and free it from the glaze.
+This operation may be done too well, in which case the rubber
+will have a dull appearance, and may be rather more liable to
+develop surface mildew after a time.</p>
+
+<p><a name="Sec18_21" id="Sec18_21"></a><span class="smcap">Moist Glaze, Greasiness of Surface.</span>&mdash;This describes the
+condition of sheet rubber when taken from the smoke-house.
+Sometimes the greasiness does not develop until the rubber
+has been out of the smoke-house for a day or two.</p>
+
+<p>As far as experience shows at present it may be due to two
+causes:</p>
+
+<div class="blockquot"><p>(<i>a</i>) The use of an excess of sodium bisulphite or sodium
+sulphite. The use of sodium bisulphite is not recommended
+generally for sheet-making. It may cause the rubber to be too
+pale in colour, and the abuse of it may delay the drying unduly.
+In the latter case, a trace of the salt may remain within the
+rubber or upon the surface. If so, as the substance remaining
+is fairly hygroscopic, it will take up moisture from the atmosphere
+and may cause the surface of the sheets to have a moist
+and shiny appearance. The moist surface deposit comes away
+upon the hand when the sheets are touched, and is difficult
+to remove entirely. On some estates a very small quantity of
+the bisulphite is employed, as it is found to be of service in the
+prevention of bubbles, but in unskilled hands the method is open
+to abuse, and is, therefore, not recommended for general use.</p>
+
+<p><span class='pagenum'><a name="Page_259" id="Page_259">[259]</a></span>A large number of estates now use sodium sulphite in very
+small quantities as an anti-coagulant and a preservative for latex
+in the field. The abuse of this very useful substance carries
+its own penalty. The substance is hygroscopic; and if an excess
+is present the drying period will be protracted, and the
+sheets will have a very moist surface film.</p>
+
+<p>It may be found sometimes that only some of the sheets are
+affected. This indicates that, whereas uniform quantities of a
+solution of sodium sulphite have been served out in all fields,
+the proportion may have been excessive in the case of fields
+giving a latex of comparatively low rubber content. What suits
+the latex from old trees may be excessive probably for the latex
+of younger trees. This is not an infallible rule, as in the case
+of older fields in which immature bark is being tapped, it is
+to be noted that the dry rubber content of latex may be less
+than that of latex obtained from younger trees.</p>
+
+<p>This type of moist glaze is not easy to remove. Ordinary
+surface washing had but a temporary effect, and the trouble
+recurs. The only way of dealing with the difficulty is to soak
+the sheets for days in running water (or in successive changes
+of water) and to re-smoke until dry.</p>
+
+<p>(<i>b</i>) The second type of moist glaze is not so difficult to deal
+with, and may be removed as a rule by washing the sheets when
+the rubber is otherwise apparently dry.</p>
+
+<p>It appears to be mainly a matter of unsuitable fuel for smoking
+and of failure to provide adequate ventilation. A large number
+of estates have been &#8220;thinning-out&#8221; or are doing so systematically.
+The logs thus obtained are often used as fuel in the
+very green stage. The smoke thus generated must be moist,
+and if the building is entirely closed, this moisture must be
+deposited eventually upon the rubber and racks. Some estates
+have surmounted the difficulty by opening up the roof-ridge
+slightly so as to allow the moisture to escape with some of the
+smoke; but if the logs from rubber-trees are to be used, they
+should be stacked in the sun for some time. Even then,
+preferably, they should not be used alone. A judicious
+admixture of dead and rotting jungle-timber appears to give
+very satisfactory results.</p></div>
+
+<p><a name="Sec18_22" id="Sec18_22"></a><span class="smcap">Virgin Spots and Patches.</span>&mdash;If the description really
+indicates the defect it simply means that portions of the sheets
+are not dry. When cut they exhibit the typical whitish, opaque
+appearance described as &#8220;virgin.&#8221; It is doubtful whether
+any rubber put upon the market as No. 1 product nowadays<span class='pagenum'><a name="Page_260" id="Page_260">[260]</a></span>
+can have this complaint levelled at it. In the extreme case
+it points to gross negligence on the part of the packer.</p>
+
+<p>Sometimes what are taken to be small spots of &#8220;virgin&#8221;
+are really patches of tiny air or gas bubbles. The point can
+be easily determined by cutting through the patch and examining
+the cut edges.</p>
+
+<p><a name="Sec18_23" id="Sec18_23"></a><span class="smcap">Surface Moulds or Mildew.</span>&mdash;During the last two years,
+complaints regarding the incidence of &#8220;mouldy rubber&#8221; (<i>i.e.</i>,
+relating chiefly to the presence of mildews on the surface)
+have become increasingly common.</p>
+
+<p>To judge by the comments of producers, who as a rule never
+again see their rubber after it leaves the estate, one would infer
+that the defect is imaginary, and that the complaints are made
+solely with a view to repudiation of contracts or the general
+cheapening of an article of commerce. They can often point
+out, with a certain amount of truth, that there has been no
+change in the methods of preparation or curing, and that
+previously there were no complaints.</p>
+
+<p>It is forgotten, however, that in former years the smaller
+output of rubber was taken into consumption more rapidly than
+of recent years. That is to say, the interval between smoke-curing
+and the employment of the rubber in the manufacture
+of goods did not demand such a long period of storage. Hence
+the effects of smoke-curing are now more likely to vanish.</p>
+
+<p>Going still further back in the history of plantation rubber,
+we can point to the time when smoked sheets were allowed,
+or had, to remain in the curing-sheds for very extended periods.
+Loose specimens of rubber prepared during that decade still
+exhibit no signs of mildew growth.</p>
+
+<p>In later years a demand arose for sheets paler in colour than
+the old type, and in order to meet that demand, a change had
+to be made in methods. This led to a system of working
+whereby it was possible to smoke-dry sheets thoroughly in
+from twelve to fourteen days. This interval was further
+reduced on many estates, until some were producing rubber
+which appeared to satisfy all requirements after only five or
+six days&#8217; curing. This does not refer to the case of estates
+having smoke-houses of &#8220;continuous-working&#8221; type, but to<span class='pagenum'><a name="Page_261" id="Page_261">[261]</a></span>
+those on which smoking was confined practically to the hours
+of night. Under former conditions of rate of production
+and consumption, this short period of smoke-curing would
+possibly have been ample; but even this is very doubtful, as
+often the rubber would not stand the relatively short journey
+from the estate to Singapore without mildew-growth being
+incipient. We have often received specimens of rubber sent
+from estates for criticism, and have noted that within a comparatively
+brief period mildew was to be seen.</p>
+
+<p>The whole matter resolves itself into a question of thorough
+efficiency of smoking. This is not dependent on duration of
+smoking alone, but involves other factors, such as the kind of fuel
+employed, the rate of combustion of fuel, the average temperature
+sustained, the ventilation of the smoke-house, and the
+situation of the building. Other occasional contributory
+factors are contemporary adverse climatic conditions and the
+possible abuse of an anti-coagulant such as sodium sulphite.</p>
+
+<p>It has been shown that after a time, given suitable conditions
+involving the presence of moisture, moulds may appear on sheets
+which were apparently fully smoke-cured, and that under the
+same conditions other and older samples were unaffected. It
+is argued that the latter sheets had evidently been smoked
+more efficiently than the others. Hence it is fair to assume
+that, except under very special conditions, which do not apply
+to the ordinary procedure in the shipping, storage, and sale of
+rubber, moulds will not develop upon sheets which have been
+properly smoked. The term &#8220;properly smoked&#8221; signifies
+efficient smoking for all practical purposes under ordinary
+procedure, and implies or includes all the advantageous factors
+which have been discussed or alluded to in preceding paragraphs.</p>
+
+<p>Without discussing in wearisome detail conditions which
+may give rise to the incidence of mildew on properly smoked
+rubber, it may be pointed out that the following are favourable
+to the growth of moulds:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Storing sheets in a damp place before packing.</p>
+
+<p>(<i>b</i>) Packing sheets in wooden cases which are not thoroughly
+dry.</p>
+
+<p><span class='pagenum'><a name="Page_262" id="Page_262">[262]</a></span>(<i>c</i>)
+Piling up cases of rubber in a badly ventilated store-room.</p>
+
+<p>(<i>d</i>) Placing the cases on a cement floor.</p>
+
+<p>(<i>e</i>) Wetting of cases by sea-water or by rain during transport,
+etc.</p></div>
+
+<p><a name="Sec18_24" id="Sec18_24"></a><span class="smcap">Black Streaks, Spots or Patches.</span>&mdash;The origin of these is
+not difficult to trace. They are caused by drippings from the
+roof, and contain condensation products from smoke plus
+moisture. The ventilation of the roof-ridge should receive
+attention, and if the trouble persists it will be necessary to
+place some absorbent screen below the sloping roof. Sackcloth
+is sometimes used, but leads to a worse state of affairs
+unless changed frequently. In most modern smoke-houses
+having an iron roof there is an inner lining of soft timber.</p>
+
+<p>There scarcely seems a necessity to discuss the case in which
+an iron roof has become perforated by the action of smoke.
+The remedy is too obvious to describe.</p>
+
+<p><a name="Sec18_25" id="Sec18_25"></a><span class="smcap">Whitish or Grey Streaks.</span>&mdash;This is a very uncommon
+defect, and is generally to be traced to a building in which fairly
+new galvanised sheets have been employed. The zinc surface
+becomes oxidised, and the whitish powder which is formed
+&#8220;flakes,&#8221; or is carried away by drops of moisture condensing
+on the surface of the iron sheets.</p>
+
+<p><a name="Sec18_26" id="Sec18_26"></a><span class="smcap">Rust.</span>&mdash;Sometimes if a sheet is stretched forcibly and
+allowed to retract quickly, the hitherto clear surface will be
+seen to be marred by a &#8220;rusty&#8221; deposit. The rubber is then
+described as &#8220;stretching rusty,&#8221; and its value is depreciated.</p>
+
+<p><a name="Sec18_27" id="Sec18_27"></a>This defect has caused more trouble during recent years than
+any other. It is not proposed here to argue the question as
+to whether the presence of this film, which appears when some
+rubbers are stretched, is detrimental to the physical qualities
+of the product on vulcanisation. With the mere statement of
+opinion that it could do no apparent harm, we may pass to the
+aspect of the case as it affects the buyer and consumer. If
+one were to judge by the attention drawn to the appearance of
+smoke sheet-rubber after it has been stretched and allowed to
+retract, one would imagine the defect to be of comparatively
+sudden and recent incidence. This is not so. The peculiarity
+must have existed for years, and perhaps became more marked<span class='pagenum'><a name="Page_263" id="Page_263">[263]</a></span>
+as so many estates abandoned the former common practice
+of allowing varying quantities of water to be placed in the
+collecting cups. As the substances which cause the defect to
+be visible are partially soluble in water, it would follow that
+when working with the very dilute latices which were characteristic
+of the earlier years of the plantation industry, the remaining
+liquid in the pan after coagulation would contain an appreciable
+quantity of soluble substances which would otherwise
+have been retained in the coagulum.</p>
+
+<p>Conversely, the richer the latex, the greater the percentage
+of protein matter retained in the coagulum. In the case of
+very rich latex, it must be within the knowledge of every
+manager that the quantity of remaining liquid in the pans
+would be almost nil. We may assume that the greater part
+of these soluble proteins would be enclosed in the structure of
+the rubber, but as the fresh coagulum must retain a quantity
+of liquid amounting to from 60 to 70 per cent. by weight
+(we are now referring to rich latices), it follows that some of
+the soluble protein matter must be removed when the coagulum
+is placed under pressure. Even after the pressure is released
+more of the contained liquid will exude from the surface of the
+rubber; and from experience it is easy to imagine that this
+exudation, becoming progressively feebler, will continue until
+the rubber begins to dry. Then, with the evaporation of the
+surface moisture, the protein matter, either in original form
+or as a degradation product, remains on the surface of the
+rubber as a thin, solid film or crust. As drying continues,
+the interior moisture escaping through the pores of the rubber
+evaporates, leaving behind the substances hitherto held in
+solution. Should, however, the sheet be thick and/or the
+temperature of drying low, the rubber may dry first on the
+outside, forming a thin skin of dry rubber, which delays
+further drying indefinitely.</p>
+
+<p>It will be seen, therefore, that sheets which have been
+prepared from rich latex or from too deep a layer of comparatively
+dilute latex will have a surface film of dry protein matter.
+Moreover, these sheets will be slow in drying, and in all
+probability will have a surface gloss and a dark colour. Hence<span class='pagenum'><a name="Page_264" id="Page_264">[264]</a></span>
+it is not difficult to understand that some brokers regarded
+the presence of the so-called &#8220;rust&#8221; as an indication of over-smoking.</p>
+
+<p>To show that this is not so, and further that the presence
+of rust has nothing whatever to do with smoke-curing, it may
+be stated that <i>the presence of this protein film may be seen on
+unsmoked sheets</i> which have been prepared from rich latex, from
+too deep a layer of more dilute latex, or from some thick
+sheets which have been rolled only very lightly. In fact, the
+presence of the protein film was noted on unsmoked sheet in
+1910, when it was seen to resemble a thin yellowish glaze
+which could be scraped off with a pen-knife. Later, sufficient
+of this substance was removed from some very thick air-dried
+sheets, or thin slabs, to fill a small test-tube.</p>
+
+<p>When the sheets were bent or twisted, the apparent surface
+of the rubber (<i>i.e.</i>, the protein glaze) cracked in all directions.
+In the case of sheets prepared from less rich latex, the surface
+film naturally is extremely thin, and no cracking is observed.</p>
+
+<p>If the fresh sheets are placed in a smoke-house, the drying
+film will take up colour from the constituents of the smoke, and
+it will be invisible. Somewhat analogous to the instance of a
+transparent glass giving a visible and opaque powder when
+crushed, so the transparent film on stretching breaks up into
+a visible powder which is lighter in colour than the rubber on
+which it is superimposed.</p>
+
+<p>It will be noted that since the introduction of standard
+methods of preparation, involving uniform dilution of latex,
+say, to a content of 1<span class="enum">1</span>&#8260;<span class="denom">4</span>
+or 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber per gallon, complaints
+as to &#8220;rust&#8221; have decreased considerably.</p>
+
+<p>It is to be further noted as a peculiar fact that while two
+estates may be apparently working on identical lines, both as
+regards manipulation of latex and subsequent treatment of the
+coagulum, the rubber of the one may always be free from rust,
+while that of the other is often, if not always, condemned for
+the alleged defect. Obviously, in such a case, there must be
+an initial difference between the two latices as regards the
+percentage of proteins present; or there must be some small
+unrecognised difference at some stage of working.</p>
+
+<p><a name="Sec18_28" id="Sec18_28"></a><span class='pagenum'><a name="Page_265" id="Page_265">[265]</a></span>It
+will now be clear that &#8220;rust&#8221; is caused by a film of matter
+which is formed on the surface of the pressed coagulum,
+being there deposited by the exudations from within the
+rubber and through the pores. It is, therefore, necessary to
+avoid any conditions which will favour the formation of this
+deposit&mdash;<i>e.g.</i>, allowing sheets to remain too long in a moist
+atmosphere before placing in the smoke-house.</p>
+
+<p><a name="Sec18_29" id="Sec18_29"></a>At present there would seem to be only two methods which
+are successful in the prevention of a &#8220;rusty&#8221; appearance in the
+dry rubber. Singularly enough, the two methods appear to be
+directly opposed in principle. They are:</p>
+
+<div class="blockquot"><p>A. <span class="smcap">The Hot-Water Treatment.</span>&mdash;This method has been
+in constant use on estates which have old trees giving rich
+latices. These latices are always diluted to a uniform standard
+daily. Some estates which formerly suffered from the defect
+now experience no difficulty, and in other instances, where
+no complaint has yet been received, the treatment has been
+followed consistently.</p>
+
+<p>(1) After the sheets have been through the marking rolls,
+it is the general custom to allow them to drip for about three
+hours. This interval is really excessive for the mere draining
+away of the surface water, but as a rule it is just sufficient to
+allow a portion of the liquid retained in the rubber to exude.
+It has been shown that this liquid may contain some protein
+matter in solution. Sometimes in the case of thick sheets
+which have been subjected to pressure so much of this matter is
+exuded as to form a thin surface slime which is distinctly
+evident to the touch. If the sheets are allowed to hang overnight,
+the presence of the exuded matter may be detected
+also by its odour.</p>
+
+<p>(2) Obviously, any method which will remove this surface
+film should be of great benefit. It is found that the best
+results are obtained by allowing sheets to drip for about two
+hours, and then placing them in hot water for five or ten minutes.
+The water should be hot as the hand can conveniently bear,
+and it need hardly be pointed out that the same water should
+not be used for the whole day&#8217;s output. For preference there
+should be three or four vessels, each capable of holding a fair
+proportion of the total number of sheets, and frequent changes
+of hot water.</p>
+
+<p>(3) After remaining in the hot water for the period mentioned,
+the sheets are removed singly, each one being surface
+washed or swilled as it is taken out.</p>
+
+<p><span class='pagenum'><a name="Page_266" id="Page_266">[266]</a></span>(4)
+<i>It is important to see that the sheets are now well washed or
+scrubbed under running cold water, or in frequent changes of
+water.</i> The reason for this procedure is plain. If the sheets
+are merely hung again to drip after removing from the hot
+water, some moisture is bound to remain on the surface of the
+sheet. As this surface moisture contains some protein matter
+in solution, it is evident that, as the water evaporates, the solid
+protein is again deposited on the surface of the rubber. This
+would explain why some estates were unsuccessful with the
+hot-water treatment. It is not essential that the running
+water should be cold; it may be conveniently lukewarm if
+drawn from the cooling tanks of the engines. But it is essential
+for the best results that there should be running water, so that
+the substance in solution is carried away. If the sheets are
+merely washed in a large vessel, which has been filled with
+clean water, it must be obvious that, by the time some scores
+of sheets have been washed, the protein matter in solution on
+the surface of the sheets has been transferred to the washing
+water, so that the later sheets of the batch are liable to show
+the defect again on drying.</p>
+
+<p>B. The second method is much more simple, and entails
+no extra labour such as is demanded by the first method. A
+successful issue, however, is rather more uncertain, and the
+method appears to give the best results with sheet-rubber
+prepared on young estates or from more dilute latex.</p>
+
+<p>In this method, the sheets after rolling are allowed to drip
+for a very short interval, so that the surface water is mainly
+removed. The sheets are then placed in the smoke-house,
+and smoking is commenced at once. In some cases where the
+defect had appeared continuously for a long period, it was
+found to vanish entirely as soon as the method was adopted;
+but when tried on some of the older estates, the results were
+very doubtful, and a return was made to the hot-water treatment.</p>
+
+<p>The explanation of the action which takes place is rather
+obscure, but two theories may be advanced.</p>
+
+<p>(<i>a</i>) It may be assumed that the interval given for dripping
+is too brief to allow for the exudation of the internal moisture
+containing dissolved protein matter.</p>
+
+<p>In such case, the rubber is still in a highly porous condition,
+and it might be advanced that the heat of the smoke may help
+to maintain that condition. Thus the contained liquid might
+evaporate so quickly as to leave behind the dissolved substances
+in the minute cellular structure of the rubber. In other words,
+instead of the internal moisture exuding slowly to the surface<span class='pagenum'><a name="Page_267" id="Page_267">[267]</a></span>
+in liquid form, it may leave the rubber, even in the first stages,
+in an evaporated condition, just as it does in the subsequent
+stages of drying. Thus no dissolved protein matter would be
+brought to the surface of the sheet and be deposited there.</p>
+
+<p>(<i>b</i>) The other theory also demands the first assumption propounded
+in the preceding theory, but subsequently perhaps is
+less feasible as it assumes a chemical action of which we have
+no definite knowledge.</p>
+
+<p>The idea is that as the rubber is in a porous condition, and
+is placed quickly in an atmosphere of smoke, the heat may
+maintain that condition to such a degree, that some constituents
+of the smoke may enter the rubber and cause the precipitation
+<i>in situ</i> of the protein matter held in solution by the contained
+water or other liquid. The contained liquid would be water
+which has in solution possibly a very slight trace of the coagulant
+employed, of sugars, of protein matter, and of inorganic
+salts. Of these the substances which would evaporate would
+be probably the water and the coagulant in most cases. If a
+salt had been used as a coagulant, the dissolved trace would be
+deposited within the rubber in this case, whereas if a rich latex
+had been employed or a thicker sheet made from more dilute
+latex, some of the salt would be brought to the surface and there
+deposited together with the protein matter. This has actually
+been experienced in practice, and it has been possible to remove
+minute crystals from the edges of the rubber so prepared.</p></div>
+
+<p>It will be evident that in order for either theory to contain
+an element of probability, the rubber must be soft (porous)
+when placed in the smoke-house, and must also be fairly thin.
+It is observed in all cases where the method has been successfully
+employed that both these conditions are generally fulfilled&mdash;at
+all events the rubber is fairly thin. When thicker sheets
+are made, either from rich latex or from a deeper layer of
+comparatively dilute latex, the method is not uniformly successful.</p>
+
+<p><a name="Sec18_30" id="Sec18_30"></a><span class="smcap">Other Views on &#8220;Rust&#8221; Causation.</span>&mdash;Later experimental
+work on &#8220;rust&#8221; formation by Hellendoorn<a name="FNanchor_22_22" id="FNanchor_22_22"></a><a
+href="#Footnote_22_22" class="fnanchor">[22]</a> leads to the
+observation that &#8220;rustiness&#8221; is caused, not actually by the
+deposition of original serum-substances, but by the decomposition
+thereof, under the action of aerobic micro-organisms.</p>
+
+<div class="footnote"><p><a name="Footnote_22_22" id="Footnote_22_22"></a><a href="#FNanchor_22_22"><span
+class="label">[22]</span></a> &#8220;The Cause of Rustiness in Sheet-Rubber,&#8221; H. J. Hellendoorn,
+Archief voor de Rubbercultuur, October, 1919 (Communication from
+the Central Rubber Station, Buitenzorg, Java).</p></div>
+
+<p><span class='pagenum'><a name="Page_268" id="Page_268">[268]</a></span>Without
+going into a full discussion of the subject, the following
+points noted in the experimental work may be quoted:</p>
+
+<div class="blockquot"><p>1. Rustiness could apparently be produced at any time
+merely by keeping freshly rolled sheets for periods varying
+from twenty-four to forty-eight hours in a moist atmosphere.</p>
+
+<p>2. Sheets placed immediately in a temperature of, say, 110&deg;
+to 130&deg; F. never showed &#8220;rust&#8220;; but if air-dried at ordinary
+room temperature, &#8220;rust&#8221; might appear.</p>
+
+<p>3. &#8220;Rust&#8221; can be prevented by soaking freshly prepared
+sheets in dilute solutions of disinfectants&mdash;<i>e.g.</i>, formalin, sodium
+bisulphite, or chinosol.</p>
+
+<p>If subsequently the sheets are hung for any length of time
+in a moist atmosphere, the protective effect of the disinfectant
+gradually vanishes and &#8220;rustiness&#8221; may be produced.</p>
+
+<p>The same disinfecting effect may be obtained by the use of
+steam or hot water. It was found that there was less liability
+to the formation of &#8220;rust&#8221; when sheets were immersed in
+water at a temperature of 95&deg; to 120&deg; F., whilst steeping at
+140&deg; F. gave complete freedom.</p>
+
+<p>4. It was shown that the micro-organisms which cause
+decomposition of the serum-products flourish only in the
+presence of air&mdash;<i>i.e.</i>, they are aerobic in character. It is not
+uncommon to find, therefore, that &#8220;rust&#8221; may be incident
+only on those parts of a sheet which have been exposed for
+some time to air and moisture before being placed in a warm
+smoke-room.</p>
+
+<p>5. The optimal temperature for development of the particular
+organisms appeared to be about 100&deg; F., in a moist
+atmosphere.</p>
+
+<p>6. Soaking the sheets in water (except the short immersion
+in hot water, which we recommend), even for a period extending
+over a week, does not hinder the formation of &#8220;rust.&#8221;</p>
+
+<p>7. Rustiness may be prevented by placing the sheets in a
+sufficiently warmed smoke-house as long as there is adequate
+ventilation and a moist atmosphere does not persist.</p>
+
+<p>The simplest means of prevention is to soak the sheets
+first for a short period in water, and then to hang them to
+drip for a few hours in a well-ventilated place, outside the
+factory and under cover.<a name="FNanchor_23_23" id="FNanchor_23_23"></a><a href="#Footnote_23_23" class="fnanchor">[23]</a></p></div>
+
+<div class="footnote"><p><a name="Footnote_23_23" id="Footnote_23_23"></a><a
+href="#FNanchor_23_23"><span class="label">[23]</span></a> We advise and practise hanging sheets in the open, without
+shade or cover.</p></div>
+
+<p>It will be gathered that, although there may be a slight difference
+between our previous views and those advanced by<span class='pagenum'><a name="Page_269" id="Page_269">[269]</a></span>
+Hellendoorn as to the exact cause of formation of the &#8220;rusty&#8221;
+film, the general conclusions are identical with those given by
+us in preceding paragraphs and previously advised in the
+Malayan reports of the Rubber Growers&#8217; Association.</p>
+
+<p><a name="Sec18_31" id="Sec18_31"></a><span class="smcap">Bubbles.</span>&mdash;The presence of bubbles in sheet-rubber has
+for years been the bane of some managers&#8217; existence, and the
+bone of contention between sellers and buyers. Taking the
+argument down to bed-rock, producers urge that the presence
+of bubbles has no influence upon the ultimate quality of the
+rubber on vulcanisation. They assert that the alleged defect
+is merely a peg upon which to hang an unreal grievance,
+serving the purpose of the buyer under the existing conditions
+of sale. All this may be true, but as long as the present system
+continues, it must be recognised that &#8220;kicking against the
+pricks&#8221; is a futile recreation.</p>
+
+<p>The sympathy of the writers is certainly on the side of the
+producers, inasmuch as they realise how extremely difficult,
+and even impossible at times, it is for the most careful individual
+to prepare sheet-rubber free from this blemish.</p>
+
+<p><a name="Sec18_32" id="Sec18_32"></a>Much has been written, and many have been the discussions,
+on this vexed subject; and it is recognised that sometimes, in
+spite of all precautions, there may suddenly be an incidence
+of bubbles in rubber which is ordinarily free from them.
+It must be allowed that climatic conditions and physiological
+variations affecting the metabolic functions of the trees exert
+an influence which is difficult at times to combat, and often
+beyond human control.</p>
+
+<p>The contributory causes are many and varied. It should
+be premised that, although the defect is described as &#8220;air-bubbles,&#8221;
+it is seldom that the appellation is strictly correct.
+Rarely do the bubbles contain air. In the vast majority of
+cases they contain gases in minute quantity. These gases
+may be considered to arise, broadly, from some decomposition
+of substances (other than rubber), contained either in the
+coagulum or in the serum. In a general way, if this decomposition
+is evidenced by an unpleasant odour, it is described
+under the term of &#8220;putrefaction.&#8221; We are not concerned here
+with the question as to how far such decomposition may be<span class='pagenum'><a name="Page_270" id="Page_270">[270]</a></span>
+ascribed to a purely chemical action, or to the indirect result
+of the presence of certain bacteria or other micro-organisms.
+Suffice it to state that, at least as far as field operations influence
+the result, the decomposition is generally to be attributed to
+the work of micro-organisms. Conditions favourable to the
+incidence and development of these are to be found when
+absolute cleanliness in all details is not aimed at.</p>
+
+<p>With this preamble we may proceed to classify possible
+causes of the formation of bubbles into two groups:</p>
+
+<div class="blockquot"><p>(<i>a</i>) Those originating in field operations.</p>
+
+<p>(<i>b</i>) Others which may arise after the arrival of the latex
+at the factory.</p></div>
+
+<p><a name="Sec18_33" id="Sec18_33"></a><span class="smcap">In the Field.</span>&mdash;Decomposition may be caused by:</p>
+
+<div class="blockquot"><p>(1) Spouts, buckets, and cups being dirty. Regular
+cleaning is necessary. If the buckets are allowed to be taken
+to the lines by tappers, trouble may ensue. Within the
+writers&#8217; experience it has been shown that an otherwise baffling
+case of premature flocculation of latex was traced to the
+presence of acid substances in the buckets, which had been
+used by coolies for preparing their food.</p>
+
+<p>(2) Delay in commencing work. This means similar delay
+in collecting the latex which is exposed to greater heat than
+under ordinary circumstances.</p>
+
+<p>(3) Exposure to the sun&#8217;s rays. The heating of the latex
+may provide improved conditions favourable to the development
+and action of micro-organisms.</p>
+
+<p>(4) Allowing latex to stand too long before collection.
+This usually is the result of giving tappers too great a task.</p>
+
+<p>(5) The addition of water to the latex, either purposely or
+accidentally, in the form of rain. The water may be slightly
+acid in character, or it may carry micro-organisms from the
+bark into the latex.</p>
+
+<p>(6) Tapping trees at too great a height. The latex generally
+has an abnormal distance to travel before reaching the cup.</p>
+
+<p>(7) Sometimes the latex from old trees, or from trees after
+wintering (just prior to full renewal of leaf), contains more than
+the usual proportion of substances (<i>e.g.</i>, sugars), which are
+capable of effecting flocculation or coagulation.</p>
+
+<p>(8) Too great a distance for transport. The trouble arising
+from this cause is likely to be much increased if the journey
+has to be made over bad roads. In such case the physical<span class='pagenum'><a name="Page_271" id="Page_271">[271]</a></span>
+action augments the effect likely to be produced by long
+standing.</p></div>
+
+<p>The foregoing do not include all possible causes, but serve to
+indicate the directions from which trouble may be mainly
+anticipated. It will be plain that any latex which exhibits
+symptoms of premature coagulation (or minute flocculation)
+should be regarded as a potential source of bubbles in sheet-rubber.</p>
+
+<p>It will be equally obvious that the employment in the field
+of any harmless substance of an anti-coagulant nature is to be
+encouraged. This point is discussed in detail in <a href="#Ch5">Chapter V</a>.</p>
+
+<p><a name="Sec18_34" id="Sec18_34"></a><span class="smcap">In the Factory.</span>&mdash;As a general rule it may be understood
+that the mischief has been done before the latex is handled at
+the factory. Sometimes it is perceptible from the peculiar
+appearance of the latex, and in such case the batch should
+not be used for the preparation of sheet-rubber. Often it is
+found that only the last to arrive at the store is visibly affected.
+This should not be mixed with other apparently normal latex,
+as it is capable of acting as a &#8220;leaven&#8221; to the bulk.</p>
+
+<p>Contributory factors in the store are:</p>
+
+<div class="blockquot"><p>(1) Lack of cleanliness of utensils, particularly of coagulating
+dishes or tanks.</p>
+
+<p>The trouble becomes acute sometimes where wooden
+tanks are employed. Unless the tank and the partitions are
+thoroughly and regularly cleansed, the wood may become
+coated with a bacterial slime, which is capable of causing
+what may be termed &#8220;fermentation&#8221; of the latex layers in
+contact.</p>
+
+<p>The tank should be thoroughly cleaned occasionally with
+a weak (5 per cent.) solution of sodium bisulphite. The
+partitions should be scrubbed and placed in the sun twice or
+three times a week.</p>
+
+<p>(2) Allowing latex to stand too long before treatment. This
+point needs no further expansion.</p>
+
+<p>(3) The use of a latex of too high a rubber content. Such
+latices are difficult to handle in order to secure uniform mixture
+with the coagulant.</p>
+
+<p>(4) The use of too concentrated a solution of coagulant.
+In conjunction with (3) there may be a rapid and irregular
+coagulation, giving rise not only to decomposition in parts<span class='pagenum'><a name="Page_272" id="Page_272">[272]</a></span>
+(and subsequent formation of gas), but also to the formation
+of true &#8220;air-bubbles&#8221; by inclusion of air during stirring.</p>
+
+<p>(5) The use of insufficient coagulant. Coagulation is slow
+and incomplete.</p>
+
+<p>(6) Defective straining and skimming. Small flocculated
+particles of rubber may pass, or be rubbed through, the
+strainer. If allowed to remain, they act as local points of
+danger.</p>
+
+<p>(7) The proximity of the coagulating latex to some source of
+heat, or exposure to sunlight.</p>
+
+<p>(8) Any delay of drying in the preliminary stages, either
+before or after the rubber enters the smoke-house.</p></div>
+
+<p><a name="Sec18_35" id="Sec18_35"></a><span class="smcap">Blisters.</span>&mdash;This description aptly fits the case in which
+sheet-rubber in the smoke-house exhibits large bubbles of
+gas which distend the surface of the rubber. When subjected
+to pressure, small &#8220;balloons&#8221; are formed, which burst with
+a perceptible report. It was formerly the belief that this
+defect was occasioned solely by an abnormally high temperature.
+That such is not the case can be shown by the experience of
+estates which have had only the rubber of a particular day or
+short period affected under normal factory conditions.</p>
+
+<p>At the same time it is not disputed that the heat of the smoke-house
+exerts an influence (causing expansion and distension),
+but it is advanced that the gases had begun to form before the
+rubber entered the house.</p>
+
+<p>The view held is that decomposition had supervened or was
+taking place&mdash;probably from one or more of the causes enumerated
+in the preceding paragraphs. The heat of the smoke-house
+only serves to exaggerate the effect. It is acknowledged
+that the degree of decomposition must be initially greater than
+in the ordinary incidence of &#8220;bubbles.&#8221;</p>
+
+<p>Beyond this point we are not in a position to put forward
+any definite supposition as to the apparently haphazard occurrence
+of the phenomenon.</p>
+
+<p>It is to be noted, fortunately, that the defect is comparatively
+rare, and seldom appears on estates which employ an anti-coagulant
+in the field. While we have examined persistent
+cases, one of which led to a temporary discontinuance of the
+preparation of smoked sheet rubber, we have not yet been able<span class='pagenum'><a name="Page_273" id="Page_273">[273]</a></span>
+to arrive at any satisfactory idea of the exact conditions governing
+the incidence of &#8220;blisters.&#8221; Our investigations only lead
+us to two observations:</p>
+
+<div class="blockquot"><p>(<i>a</i>) That blisters have appeared on the rubber of some
+estates after wintering, and during the period of new leaf-development.</p>
+
+<p>(<i>b</i>) That the defect has been noted on other estates during
+a period when there were frequent but not heavy rains, and
+when there was a comparatively low average temperature.</p></div>
+
+<p>In either case, as the factors are beyond human control,
+it would be expected that without any change being made in
+estate procedure, the trouble would vanish as mysteriously
+as it appeared. This is our experience; but as showing the
+possible intensive effect of a high temperature in the smoke-house,
+it may be remarked that very infrequently, in a batch of
+sheets exhibiting ordinary bubbles, a few hanging directly
+above the furnaces show signs of a slight blistering effect.</p>
+
+<p><a name="Sec18_36" id="Sec18_36"></a><span class="smcap">&#8220;Spot&#8221;
+Disease in Sheet Rubber.</span>&mdash;That &#8220;spot&#8221; disease
+may appear in air-dried sheets was evident at the beginning of
+the outbreak in the spring of 1911. The first cases noticed
+took the form of pink and bluish &#8220;blushes&#8221; spreading over
+the whole of the sheets. Later, fungoid spots began to appear.
+These mainly took the form of red or black blotches, and were
+very unsightly. As &#8220;spot&#8221; disease cannot develop in smoked
+rubber, the obvious and simple course to adopt was to smoke-cure
+the sheets. When it is stated that &#8220;spots&#8221; do not develop
+in smoke-cured rubber, it is understood that the smoke-curing
+must be efficient and must commence as soon as the rubber
+has been rolled, and the surface water has drained away. If
+the sheets are allowed to air-dry for a few days, the disease may
+develop, and then smoke-curing will not get rid of the coloured
+patches. The operation of smoke-curing will not get rid of the
+coloured patches. The operation of smoke-curing may tone
+down the colour, but the spots would still remain evident.</p>
+
+<p><a name="Sec18_37" id="Sec18_37"></a><span class="smcap">Support Marks.</span>&mdash;It frequently occurs that one sees across
+the middle of smoked sheets a wide mark. This is where the
+wooden support in the smoking-chamber has been. As a rule,
+even in the most careful cases a faint mark may always be seen,<span class='pagenum'><a name="Page_274" id="Page_274">[274]</a></span>
+but in many instances this mark is exaggerated to such an
+extent as to point to lack of care on the part of the store supervision.
+If bays of racks remain empty over-night, they may
+possibly become covered with a light sprinkling of fine wood-ash
+and tarry deposit. Wet rubber placed upon these racks
+will pick up and retain the impurities, and more often than not
+they cannot be washed out. It is incumbent upon the manager
+to see that empty racks are thoroughly cleansed before placing
+wet rubber upon them. The better plan is to arrange that the
+bars can be removed easily from sockets. There should be
+in stock sufficient &#8220;spares&#8221; for, say, two days&#8217; rubber. When
+the dry rubber is removed, the bars should likewise be taken
+away, to be cleansed and kept in the factory until again required.
+This will ensure that fresh rubber always rests upon
+a clean support.</p>
+
+<p>On some estates, in order to guard against a pronounced
+&#8220;bar-mark,&#8221; sheets are moved and turned daily.</p>
+
+<p>In other smoke-houses the upper surface of the bar is
+chiselled in concave form, so as to admit of the passage of
+smoke below the surface resting on the bar.</p>
+
+<p><a name="Sec18_38" id="Sec18_38"></a><span class="smcap">Stickiness.</span>&mdash;This
+is not to be confounded with &#8220;tackiness,&#8221;
+from which the rubber does not recover. Stickiness is
+only temporary, and may be remedied. As a general rule, it
+is due to packing sheets, which have not a good raised &#8220;ribbing,&#8221;
+and which may have been coated with light tarry deposits
+(see <a href="#Sec18_21">Glaze</a>). This surface film may be removed by washing
+the sheets, or scrubbing them, with cold water. Usually a
+further two days&#8217; air-drying will make the rubber fit for packing;
+and if the smoke-curing has been efficient, there should be no
+need to anticipate trouble from mildew. Some estates adopt
+this practice daily with success, as a form of insurance against
+complaints of surface deposits.</p>
+
+<p><a name="Sec18_39" id="Sec18_39"></a><span class="smcap">Ribbing, Surface Pattern.</span>&mdash;While we know that the passing
+of sheets of rubber between rolls, causing a particular raised
+pattern to appear, has no effect upon the actual quality of the
+rubber, there is a great deal of practical advantage gained.</p>
+
+<p>The practice ensures an increase of superficial area which is
+an aid in drying, improves the appearance of the rubber for<span class='pagenum'><a name="Page_275" id="Page_275">[275]</a></span>
+selling purposes, and is of distinct advantage in enabling the
+rubber when packed to travel in better condition. Sheets do
+not become so closely packed; sampling and general handling
+are easier on delivery.</p>
+
+<p>As long as the plane surfaces are sufficiently and regularly
+distorted, there would seem to be no limits to the type of
+pattern or &#8220;mark&#8221; which may be placed upon the rubber.
+But in actual practice the variety is small. The most popular
+type of &#8220;ribbing&#8221; is that best described as a small diamond
+effect, produced by a pair of rolls cut with closely placed
+narrow grooves running spirally. The spirals travel in the same
+direction on both rolls, producing close-cut ribbing running
+in opposite directions on the surfaces of the sheet. On sheets
+of standard thickness, the result approaches a diamond effect.</p>
+
+<p>A few other patterns are employed, notably that producing
+longitudinal stripes of varying thickness. On the whole, the
+type of pattern would seem to be immaterial, if the points already
+indicated are achieved.</p>
+
+<p>It is seldom one encounters a case nowadays in which the
+&#8220;marking&#8221; is unsuitable, but a few estates may be using an
+old type of patterned roll on which the full diamond grooving
+is cut. As this appears on both sides of the sheet of rubber,
+and as the ribbing does not coincide, a blurred effect is seen
+when the sheet is viewed against the light.</p>
+
+<p><a name="Sec18_40" id="Sec18_40"></a><span class="smcap">Thick Ends, &#8220;Sheet Clippings.&#8220;</span>&mdash;It rarely happens,
+even with good equipment and average supervision, that the
+preparation of smoked sheet is unaccompanied by slight defects.
+For instance, in spite of rules and regulations regarding manipulation
+of the coagulum, it is not uncommon to find that some
+sheets, after rolling, have slightly thickened ends. In the
+ordinary course of events these might delay drying considerably.
+It is the practice on some estates to cut off these thickened ends
+while the rubber is still wet. The pieces are then machined
+into crepe form, but as no sodium bisulphite may have been
+used, the resulting rubber cannot be classed as No. 1 Standard
+Crepe.</p>
+
+<p>The other alternative is to trim the ends when the bulk of
+the rubber is thoroughly smoke-dried. The moisture containing<span class='pagenum'><a name="Page_276" id="Page_276">[276]</a></span>
+portions are then returned to the smoke-house until
+dry, and are subsequently packed without further treatment as
+&#8220;smoked-sheet clippings.&#8221; It will be plain that, except in
+the particularity of form, these clippings differ in no degree
+from the original sheets; and, owing to extra smoke-curing,
+may arrive in even better condition. One must be prepared,
+however, to find that a slightly lower price is offered. Whether
+the price obtained would be comparable with that commanded
+by the crepe made from wet sheet slipping would depend
+upon general ruling market conditions, and the degree of care
+exercised in guarding against the inclusion of any inferior
+pieces of rubber. In ordinary factory practice, there could be
+no room for abuse under the latter clause.</p>
+
+<p><a name="Sec18_41" id="Sec18_41"></a><span class="smcap">Other Infrequent Defects.</span>&mdash;This chapter will be closed
+with a reference to other small defects which, although infrequent,
+cannot be classed as minor complaints. In point of
+fact, when they occur, they assume an importance, in the eyes
+of the consumer, which is not, perhaps, sufficiently appreciated
+by producers.</p>
+
+<p><a name="Sec18_42" id="Sec18_42"></a><span class="smcap">Dirt.</span>&mdash;Trouble from this source should be absent, but carelessness
+on the part of packing coolies may be responsible for
+occasional complaints. How the dirt is incident may remain
+a mystery, but it has been noted that sheets have at times been
+thrown upon a cement floor. A certain amount of loose dust
+may thus adhere to the rubber.</p>
+
+<p><a name="Sec18_43" id="Sec18_43"></a><span class="smcap">Ash.</span>&mdash;The source of this surface deposit scarcely needs
+indication. Where open-hearth furnaces are employed, and
+the wire-mesh floor screens are not perfectly sound, fine ash
+may find its way into the upper chamber. If this trouble is
+persistent in spite of precautions, the sheets should be surface-washed
+and air-dried before packing.</p>
+
+<p><a name="Sec18_44" id="Sec18_44"></a><span class="smcap">Bark.</span>&mdash;Complaints of the presence of particles of bark in
+sheet rubber used to be fairly frequent, but are now less
+common. The trouble may be traced to the use of defective
+straining sieves when the latex is being handled.</p>
+
+<p><a name="Sec18_45" id="Sec18_45"></a><span class="smcap">Splinters.</span>&mdash;The use of packing-cases of unplaned soft
+timber is responsible for complaints of this nature on delivery.
+Without here discussing the larger question of the ideal packing<span class='pagenum'><a name="Page_277" id="Page_277">[277]</a></span>
+case, it is sufficient to emphasise that the interior surfaces of
+wooden chests should be planed. The cases are often so
+damaged in transit, that splinters of wood may be found
+throughout the contents. The device adopted on some estates
+may go far to prevent this. The cases are first lined with loose
+sheets, and finally other sheets are arranged to overlap at the
+top of the case. The bulk is thus enclosed in a wrapping of
+sheets, and any splinters or other deleterious substances are
+confined to the surface of the mass.</p>
+
+
+<p class='pagenum'><a name="Page_278" id="Page_278">[278]</a></p>
+<hr class="c25" />
+<h2><a name="Part5" id="Part5"></a>PART V</h2>
+
+<h3>GENERAL</h3>
+
+<h2><a name="Ch19" id="Ch19"></a>CHAPTER XIX</h2>
+
+<h3><i>CHOICE OF COAGULANT</i></h3>
+
+
+<p><a name="Sec19_1" id="Sec19_1"></a>Almost without exception, the agent employed in the coagulation
+of plantation (<i>Hevea</i>) rubber is acetic acid, or in
+some cases formic acid. Under ordinary trade conditions
+supplies are always obtainable at reasonable prices, but during
+the recent War the question of possible substitutes was brought
+greatly to the fore. Fortunately the subject of coagulation
+and coagulants had been previously studied to such effect in
+laboratory practice, that there would have been small difficulty
+in prescribing agents other than acetic acid in cases of expediency.
+As far as our knowledge extends, all the possible
+substances which have the power of coagulating latex have
+been tested. They include mineral acids, organic acids,
+compounds known chemically under the general term of
+&#8220;salts,&#8221; alcohols, sugars, etc.</p>
+
+<p><a name="Sec19_2" id="Sec19_2"></a>The heading of this chapter must be seen to &#8220;beg the
+question,&#8221; inasmuch as it leads to the assumption that a
+coagulant (in the popular sense) is necessary to secure coagulation.
+In point of fact, methods are sometimes employed which
+depend upon no artificial coagulant to produce the desired
+effect. To these methods reference will be made <a href="#Ch20">later</a>.</p>
+
+<p>In this section it is proposed to describe briefly the more
+important agents which are used, or might be used, in effecting
+coagulation. In the class of those which are not in common
+use some could be used as expedients, while others are only of
+scientific interest.</p>
+
+<p><a name="Sec19_3" id="Sec19_3"></a><span class='pagenum'><a name="Page_279" id="Page_279">[279]</a></span><span
+class="smcap">Acetic Acid.</span>&mdash;There is no need to enter into a discussion of
+the merits of this agent. In practice it remains the cheapest
+and safest coagulant known at present.</p>
+
+<p><a name="Sec19_4" id="Sec19_4"></a><span class="smcap">Formic Acid.</span>&mdash;This agent is equally as safe to use as acetic
+acid, and as easy to handle. Bulk for bulk its coagulative power
+is higher than that of acetic acid. Its pre-war shipping price,
+when taken in conjunction with its coagulative power, was
+slightly below that of acetic acid, but local prices put the
+balance in favour of the latter. If prevailing costs put it on
+terms of parity with acetic acid, there would appear to be no
+reason why formic acid should not have a widely-extended
+use on plantations.</p>
+
+<p><a name="Sec19_5" id="Sec19_5"></a><a name="Sec19_6" id="Sec19_6"></a><span class="smcap">Citric
+Acid, Tartaric Acid.</span>&mdash;The acids of the extracted
+juices of most tropical fruits consist, to a large degree, of citric
+or tartaric acids. These can be used in place of acetic acid
+as satisfactory coagulants in case of emergency; but the questions
+of availability of supplies and of costs preclude their more
+general adoption.</p>
+
+<p><a name="Sec19_7" id="Sec19_7"></a><span class="smcap">Oxalic Acid.</span>&mdash;This is a satisfactory coagulant as far as
+observed effect is concerned. It produces a rubber paler than
+ordinary coagulants (without the use of sodium bisulphite),
+as it has the nature of an anti-oxidant.</p>
+
+<p>It would not be a safe agent in the hands of coolies, as it is
+classed as a poison.</p>
+
+<p><a name="Sec19_8" id="Sec19_8"></a><span class="smcap">Sulphuric Acid.</span>&mdash;During the War, in a period of shortage
+of acetic acid and of high prices, this agent was used with
+success on some estates.</p>
+
+<p>It scarcely need be remarked that it is a dangerous substance
+to handle, and that its employment must be accompanied by
+close European supervision.</p>
+
+<p>At prevailing prices during the War it was very much cheaper
+than acetic acid, and even at the present reduced cost of the
+latter the advantage still lies with sulphuric acid.</p>
+
+<p>It must be emphasised, however, that the abuse of this agent
+to any but the slightest degree is harmful to the resultant
+rubber. Hence its use would be sanctioned <i>only in the absence
+of the commoner, and much safer, coagulants</i>.</p>
+
+<p>In view of the possible incidence of such an emergency,<span class='pagenum'><a name="Page_280" id="Page_280">[280]</a></span>
+the following notes are given. It is impressed that strict adherence
+to the rules must be given.</p>
+
+<p><span class="smcap">Handling Sulphuric Acid.</span>&mdash;(<i>a</i>) Always use glass or glazed
+earthenware vessels.</p>
+
+<p>(<i>b</i>) Pour slowly and avoid splashing. Drops finding their way
+to clothing or other fibrous material will destroy it locally; and
+if thrown upon any part of the body may cause painful burns.</p>
+
+<p>(<i>c</i>) When diluting this agent always remember to pour the
+acid into the water (<i>i.e.</i>, the lesser into the greater), and never
+<i>vice versa</i>. Pour the acid carefully and slowly down the side
+of the vessel, and stir well.</p>
+
+<p><a name="Sec19_8d" id="Sec19_8d"></a>(<i>d</i>) Should strong acid be spilled, do not throw water upon
+it. A supply of sand or dry earth should be kept close at hand.
+Throw this upon the acid.</p>
+
+<p><span class="smcap">Storing Sulphuric Acid.</span>&mdash;(<i>a</i>) Jars or cases should be
+handled as seldom, and as carefully, as possible. If the acid
+is contained in a case, the top should be plainly indicated.</p>
+
+<p>(<i>b</i>) Stocks should be stored in a detached building which
+should not be damp. Jars or cases should not stand on a
+wooden floor if possible.</p>
+
+<p>(<i>c</i>) See (<i><a href="#Sec19_8d">d</a></i>) above.</p>
+
+<p><span class="smcap">Buying Sulphuric Acid.</span>&mdash;(<i>a</i>) Commercial acid of specific
+gravity 1&middot;84 is the best of its kind. It contains impurities
+which are non-injurious to rubber preparation.</p>
+
+<p>(<i>b</i>) It is always advisable, if possible, to buy the acid in
+small jars containing not more than 100 lbs. each. Smaller
+jars, with a content not exceeding 50 lbs., would be preferable.</p>
+
+<p>(<i>c</i>) If the acid is bought in jars, it should be stipulated that
+the stoppers be covered with a plaster head, and that the
+containing crate or case should have prominent labels or
+marks indicating the top of the case.</p>
+
+<p><span class="smcap">Formula for Use of Sulphuric Acid.</span>&mdash;It will be understood
+that as this formula has been calculated for working with latex,
+having a consistency of 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber per gallon, it applies
+in a strict degree only to such latex. In other cases, where the
+dilution of the latex is not known, the formula will serve as a basis
+for experiment until the correct quantity has been discovered.</p>
+
+<p>(Sulphuric acid of specific gravity 1&middot;84.)</p>
+
+<div class="blockquot"><p><span class='pagenum'><a name="Page_281" id="Page_281"><span class="fsize110">[281]</span></a></span><span
+class="smcap">Note.</span>&mdash;The directions must be followed carefully, and
+glass measuring vessels should be used if procurable.</p>
+
+<p>(<i>a</i>) Measure out 1 pint of strong acid, and pour it carefully
+and slowly <i>down the inner surface</i> of a jar containing 20 gallons
+of water. Do not pour it directly into the water.</p>
+
+<p>The heavy acid will sink to the bottom of the jar, and a good
+mixture must be obtained by stirring well.</p>
+
+<p>(<i>b</i>) Of this solution (which is approximately 1 per cent. by
+weight), use 1 gallon to 20 gallons of latex.</p></div>
+
+<p>Readers are doubtless now well aware of the corrosive
+action of strong sulphuric acid, and we scarcely need point out
+that even the dilute acid should not be kept in contact with
+the usual iron vessels found in factories. The mixing of
+solutions should be done in one of the glazed earthenware
+jars commonly in use.</p>
+
+<p>The formula given above works out at approximately 1 part
+strong acid to 2,000 parts of latex (of dry rubber content 1<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs.
+per gallon). The formula for using acetic acid with the same
+latex works out at about 1: 1,200. It will be apparent, therefore,
+that relatively sulphuric acid is a more powerful coagulant
+than acetic acid. In terms of dry rubber obtained from latex
+of the consistency indicated above&mdash;</p>
+
+<div class="blockquot"><p>1 lb. sulphuric acid will produce 300 lbs. dry rubber.
+1 lb. acetic acid will produce 180 lbs. dry rubber.</p></div>
+
+<p>With both acids selling at the same rate, sulphuric acid
+would be more economical in use; when its cost is less than
+that of acetic acid, which is the normal condition, the economic
+advantage in favour of sulphuric acid is augmented still
+further.</p>
+
+<p>It may be found that the standard formula for sulphuric
+acid will not always give a perfectly clear remaining serum,
+even though an attempt is made daily to work to a uniform
+consistency for all latices. It is inevitable that the manipulation
+of the latices should be slightly in error on occasions, or that
+a small mistake might occur in preparing the solution of acid.
+Hence a clear remaining serum after coagulation may be
+secured less often than a slightly turbid serum. This is as it
+should be. The minimum quantity of acid may be adjusted<span class='pagenum'><a name="Page_282" id="Page_282">[282]</a></span>
+so closely as to give such results. If a clear serum is obtained
+always, that should be an indication of continual excess of
+coagulant. Naturally, if a milky serum is always obtained,
+the reverse is the case.</p>
+
+<p>As a last word on the subject, it may again be emphasised
+that the use of sulphuric acid is not advised, except in an
+emergency; and that the greatest possible care must be exercised
+in the observance of the strict formula for use.</p>
+
+<p><a name="Sec19_9" id="Sec19_9"></a><span class="smcap">Hydrochloric Acid, Nitric Acid.</span>&mdash;These mineral acids
+would prove more expensive than sulphuric acid. In addition
+they are much more uncertain in action. For example, the
+use of a certain excess of hydrochloric acid would not hasten
+coagulation, but would prevent it. Above all their effect, in
+excess, is deleterious to the rubber.</p>
+
+<p><a name="Sec19_10" id="Sec19_10"></a><span class="smcap">Hydrofluoric Acid.</span>&mdash;This has a strong corrosive action
+on porcelain or glass. Hence it has to be contained in bottles
+of gutta-percha or lead. It is mentioned here merely because
+some years ago it found a use as a coagulant, chiefly in Ceylon.
+It was sold in the form of a 10 per cent. solution under the
+name of &#8220;Purub,&#8221; and was the subject of a patent.</p>
+
+<p>It is effective as a coagulant, and has also an anti-oxidant
+action, which was its chief recommendation when cheap and
+harmless anti-oxidants were not commonly known. It is
+comparatively expensive, and, as indicated above, difficult to
+handle and store. In short, it has nothing to commend it,
+in comparison with acetic or formic acids.</p>
+
+<p><a name="Sec19_11" id="Sec19_11"></a><span class="smcap">Alum.</span>&mdash;This substance has been used for years by native
+rubber producers as a coagulant. It fulfils the desired purpose,
+and its popularity was maintained because of the ease with
+which it could be stored and handled. Unfortunately, this
+facility often led to the use of an excess, and native sheets
+were often criticised as being brittle. Investigations have
+shown that alum, even in minimum proportions, has an appreciably
+harmful effect upon the quality of the rubber prepared
+by its use as a coagulating agent. Its employment by native
+rubber producers has now been largely superseded by acetic
+acid in some form.</p>
+
+<p><a name="Sec19_12" id="Sec19_12"></a><span class="smcap">Pyroligneous Acid.</span>&mdash;This is otherwise
+known under the<span class='pagenum'><a name="Page_283" id="Page_283">[283]</a></span>
+names of &#8220;crude acetic acid&#8221; and &#8220;crude wood vinegar.&#8221;
+Owing to the shortage of acetic acid during the War, attention
+was directed towards the possibility of making an effective
+coagulant locally by what is termed the &#8220;dry distillation of
+wood&#8220;&mdash;<i>i.e.</i>, the wood is not burned but heated in a retort.
+The enquiries could be placed in two classes:</p>
+
+<div class="blockquot"><p>1. Those which aimed at making the pure, strong acid of
+commerce.</p>
+
+<p>2. Those which sought information concerning a crude
+coagulant (pyroligneous acid) on estates.</p></div>
+
+<p>Regarding the first class, we can do no better than reproduce
+our remarks published in the April local report of the Rubber
+Growers&#8217; Association for 1916&mdash;with the reservation that,
+on account of a threatened shortage of timber, a local scheme
+might not now be feasible:</p>
+
+<div class="blockquot"><p>&#8220;Probably the most common enquiry encountered since
+the rise in the price of acetic acid is concerned with the possibility
+of making acetic acid in this country. It may be stated
+that the proposition is a feasible one, even on a fairly large
+scale. We have the essentials necessary for such a scheme in:</p>
+
+<div class="blockquot"><p>&#8220;1. A good supply of suitable timbers, the most valuable of
+which, possibly, is mangrove timber, locally known as &#8217;bakau.&#8217;
+Other suitable timbers are known, but as far as preliminary
+experiments show mangrove timber gives the best yield.
+At present this timber is in great demand as a fuel for steam
+plants, but with the extension of the local coal industry the
+timber may become cheaper.</p>
+
+<p>&#8220;2. There would appear to be less valuable timber which
+would be suitable for heating the retorts. Or, local coal might
+be used.</p>
+
+<p>&#8220;3. Supplies of lime at reasonable rates are available, as the
+limestone formation in the peninsula is quite considerable in
+extent.</p>
+
+<p>&#8220;4. Supplies of sulphuric acid are available from Japan,
+Australia, Burma, etc., even at the present time, although
+naturally rates are higher than normal. Under ordinary conditions,
+supplies from England and parts of Europe would
+be much cheaper than at current rates.</p>
+
+<p>&#8220;For the benefit of many readers perhaps a brief and nontechnical
+description of the preparation of acetic acid would<span class='pagenum fsize100'><a name="Page_284" id="Page_284">[284]</a></span>
+not be amiss, and would explain the necessity for the essentials
+indicated above. In brief, the process is as follows:</p>
+
+<p>&#8220;(<i>a</i>) A suitable timber is heated in a closed retort. This
+is termed &#8217;dry distillation,&#8217; and results eventually in the
+carbonisation of the wood&mdash;<i>i.e.</i>, charcoal is obtained in the
+retort.</p>
+
+<p>&#8220;(<i>b</i>) Tar, vapours and gases are distilled over during the
+carbonisation of the wood. These liquors and gases pass
+through condensers. The gases pass away, while the condensed
+liquors separate out into (1) wood tar, (2) a watery liquor called
+pyroligneous acid or crude wood vinegar.</p>
+
+<p>&#8220;(<i>c</i>) The pyroligneous acid is separated from the tar, and
+again distilled to obtain the acetic acid present.</p>
+
+<p>&#8220;(<i>d</i>) This crude acid is steam-heated with milk of lime, which
+fixes the acid, forming calcium acetate (or acetate of lime).</p>
+
+<p>&#8220;(<i>e</i>) Eventually the calcium acetate is taken out in the form of
+a thick paste, which is spread to dry. When dry this &#8217;grey
+acetate&#8217; is the main source of all glacial acetic acid now made.</p>
+
+<p>&#8220;(<i>f</i>) The acetic acid is released from the &#8217;acetate of lime&#8217;
+by the action of sulphuric acid. It is then distilled several
+times, and under various conditions, in order to increase its
+strength. In the past copper tubes were used for this purpose,
+but owing to the fact that traces of copper were found to be
+injurious to rubber, some works instal tubes of glazed earthenware
+for the distillation.</p></div>
+
+<p>&#8220;Such is the process in outline, and it will be seen that no proposal
+to manufacture <i>glacial acetic acid</i> on an estate could be
+considered feasible, although it would not present any great
+difficulty on a large scale and under skilled direction. Furthermore,
+the cost of the plant would be far too great for any estate.&#8221;</p></div>
+
+<p>Although it is clear that pure acetic acid is beyond the scope
+of an estate, crude pyroligneous acid has been produced on a
+varying scale in this country and in Ceylon. In the latter
+country some success was obtained by the distillation of
+coconut shells with comparatively inexpensive plant. In this
+country, wood-distillation was practised on a few estates,
+but improved facilities for obtaining pure acetic led to a
+termination of the experiments, although sufficient crude acid
+could then be made at a reasonable cost.</p>
+
+<p>The pyroligneous acid obtained, is generally clear, after
+nitration, and of a dark brown colour. It has a peculiar odour<span class='pagenum'><a name="Page_285" id="Page_285">[285]</a></span>
+reminiscent of smoked sheet-rubber, or of creosotic substances
+in general.</p>
+
+<p>Its acid content depends chiefly upon:</p>
+
+<div class="blockquot"><p>(<i>a</i>) The kind of timber heated in the retort.</p>
+
+<p>(<i>b</i>) The efficiency of the apparatus.</p>
+
+<p>(<i>c</i>) Condition of the timber as to moisture.</p>
+
+<p>(<i>d</i>) The temperature employed, and rate of working.</p>
+
+<p>(<i>e</i>) The point at which distillation ceases (<i>i.e.</i>, the duration of
+interval between commencement of heating and cessation of
+collection).</p></div>
+
+<p>Samples received from estates for testing purposes were found
+to contain equivalents varying from 2 per cent. to 10 per cent.
+of acetic acid.</p>
+
+<p>They were all suitable coagulants when used in quantity
+calculated from the discovered acidity, but produced rubber
+darker than ordinary when air-dried. This effect was not of
+much importance in the preparation of smoked sheets, but to
+produce a pale crepe it was necessary to employ sodium
+bisulphite as an anti-oxidant.</p>
+
+<p>This darkening in colour is to be ascribed to the presence of
+traces of phenols,<a name="FNanchor_24_24" id="FNanchor_24_24"></a><a href="#Footnote_24_24" class="fnanchor">[24]</a>
+which are stated to exert an effect upon the
+rubber during and after vulcanisation.<a name="FNanchor_25_25" id="FNanchor_25_25"></a><a
+href="#Footnote_25_25" class="fnanchor">[25]</a> This subject will be
+discussed in <a href="#Ch17">another section</a>.</p>
+
+<div class="footnote"><p><a name="Footnote_24_24" id="Footnote_24_24"></a><a
+href="#FNanchor_24_24"><span class="label">[24]</span></a> Whitby, <i>Journal Soc. Chem. Industry</i>, vol. xxxv., No. 9, 1916.</p></div>
+
+<div class="footnote"><p><a name="Footnote_25_25" id="Footnote_25_25"></a><a
+href="#FNanchor_25_25"><span class="label">[25]</span></a> See also &#8220;Preparation and Vulcanisation of Plantation Rubber&#8221;
+(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of
+Agriculture, April, 1918.</p></div>
+
+<p>With this provision the crude pyroligneous acid which
+can be produced on estates, could be employed as a coagulant
+until such time as the price of glacial acetic acid was so low
+as to make the production of the crude acid non-profitable.
+This point would be determined from a knowledge of the cost
+of production per gallon, and the percentage of acetic acid per
+unit. For example, if the cost of production (including cost
+of timber for distillation, cost of fuel for heating the retort,
+cost of labour, etc.) was 60 cents per gallon of crude acid
+containing 9 per cent. of acetic acid, that would be equivalent
+approximately to buying glacial acetic acid at $30 per demijohn
+of 44 lbs.</p>
+
+<p><a name="Sec19_13" id="Sec19_13"></a><span class='pagenum'><a name="Page_286" id="Page_286">[286]</a></span></p><p><span
+class="smcap">Smoked Water.</span>&mdash;A weak solution of pyroligneous acid
+may also be obtained by passing smoke through water. With
+this object in view, a machine was designed by the Federated
+Engineering Company of Kuala Lumpur. In this the principle
+of retorting was not employed. Smoke was produced by
+ordinary combustion in a compartment of the apparatus, and
+was drawn through water by the action of a high-speed fan
+worked by hand. A solution, equivalent in effect to a 2 per cent.
+solution of acetic acid, could be obtained at a comparatively
+cheaper cost than crude pyroligneous acid produced by dry
+distillation as it was then being practised. This was chiefly
+because of the wasteful methods of fuel combustion, in the
+latter process, in the heating of the retort.</p>
+
+<p><a name="Sec19_14" id="Sec19_14"></a><span class="smcap">Chinese Vinegar.</span>&mdash;This agent was found to be a satisfactory
+coagulant, and, <i>a priori</i>, there is no reason why it should not be
+suitable, as it is essentially a dilute solution of acetic acid.</p>
+
+<p>The qualities sold were generally colourless, and were
+probably the result of acetic fermentation of rice.</p>
+
+<p>Samples tested showed a varying content of acetic acid,
+ranging roughly from 3 per cent. to 8 per cent.; but on this basis
+of valuation it was found generally that the price bore no
+relation to the degree of efficiency.</p>
+
+<p>It was advanced not only that the vinegar was an efficient
+substitute for glacial acetic acid, but that it was also cheaper.
+This latter claim was proved to have no foundation in fact, even
+at the high price of acetic acid prevailing during the period of
+stress. It is not likely, therefore, that vinegar can displace acetic
+acid, except as an expedient.</p>
+
+<p><a name="Sec19_15" id="Sec19_15"></a><span class="smcap">Sulphurous Acid.</span>&mdash;The anti-oxidant effect of sodium
+bisulphite and sodium sulphite is due to the liberation of the
+gas, sulphur dioxide. This gas dissolves easily in water, forming
+an acid solution called sulphurous acid.</p>
+
+<p>This acid solution is an effective coagulant in fairly small
+quantity. Not only so, but it produces, in addition, the anti-oxidant
+effect noted in the employment of sodium bisulphite.
+It is thus possible to produce rubber varying in shade of
+paleness by means of a single solution.</p>
+
+<p>In the event of sulphurous acid being used, it would be<span class='pagenum'><a name="Page_287" id="Page_287">[287]</a></span>
+necessary to import cylinders of sulphur dioxide from which
+the solution could be prepared in factories each day. There
+would be no insurmountable difficulty in this, as it is only
+necessary to pass the gas through a series of closed vessels
+containing water. Enough solution could be prepared at one
+time for three or four days, but preferably the solutions should
+be as fresh as possible. Altogether there would seem to be
+possibilities in the use of sulphurous acid for preparing pale
+crepe rubbers, providing the cost is within comparable limits
+with the commoner coagulants at present in use, and that no
+adverse effect on the rubber can be shown to result. If the
+cost did not exceed the combined cost of acetic acid and sodium
+bisulphite, the employment of sulphurous acid solution might be
+worthy of consideration. There is one drawback to the use of
+sulphurous acid solution, and that lies in the proximity of the
+limits of the quantities necessary for coagulation and that which
+is in excess, and prevents coagulation. Thus, with ordinary
+field latex having about 20 per cent. dry rubber content, the
+minimum necessary for coagulation per 100 c.c. of latex is
+about 8 c.c. of a 1 per cent. solution. The maximum quantity
+possible for use is about 15 c.c. of a 1 per cent, solution, so that
+great care would have to be exercised in avoiding an excess of
+coagulant, otherwise coagulation would be effectually prevented.</p>
+
+<p>It is believed that the preparation of rubber by this method
+is the subject of a patent secured by Messrs. Boake, Roberts, and
+Co., London.</p>
+
+<p><a name="Sec19_16" id="Sec19_16"></a><span class="smcap">Sugars.</span>&mdash;Coagulation may be effected by the addition of
+small quantities of sugars.<a name="FNanchor_26_26" id="FNanchor_26_26"></a><a
+href="#Footnote_26_26" class="fnanchor">[26]</a> These are assumed to be effective
+by fermentative conversion into lactic and acetic acids. The
+presence of lactic acid is supposed to have a twofold effect:</p>
+
+<div class="blockquot"><p>(<i>a</i>) As a direct coagulant.</p>
+
+<p>(<i>b</i>) In its action upon certain organisms which, in the
+ordinary course of events, would delay or prevent coagulation.
+Although work on an experimental scale has been done, as<span class='pagenum fsize100'><a name="Page_288" id="Page_288">[288]</a></span>
+far as we know no practical application has been made of the
+employment of sugars as coagulating agents.</p></div>
+
+<div class="footnote"><p><a name="Footnote_26_26" id="Footnote_26_26"></a><a
+href="#FNanchor_26_26"><span class="label">[26]</span></a> &#8220;Preparation and Vulcanisation of Plantation Para Rubber&#8221;
+(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of
+Agriculture; Gorter and Swart, Bulletin No. 6, West Java Expt.
+Station.</p></div>
+
+<p><a name="Sec19_17" id="Sec19_17"></a><span class="smcap">Various Salts.</span>&mdash;Of experimental interest only it may be
+recorded that coagulation has been effected by means of various
+chemical &#8220;salts&#8220;&mdash;<i>e.g.</i>, calcium chloride, barium chloride,
+magnesium chloride, sodium chloride, aluminium sulphate,
+magnesium sulphate, sodium sulphate, etc. None of these
+has been found to have any practical application, except,
+perhaps, calcium chloride, which is used in small quantity as
+an accelerating agent in a special process of anaerobic coagulation,
+which will receive mention in the <a href="#Ch20">following chapter</a>.</p>
+
+<p>At one period during the War and the dearth of acetic acid,
+it was found that there were available in England large supplies
+of the acid sulphate of sodium (sodium hydrogen sulphate),
+which proved to be an effective coagulant. Experimental
+work gave satisfactory results, but no practical application
+resulted when supplies of acetic acid were again obtainable.</p>
+
+<p><a name="Sec19_18" id="Sec19_18"></a><span class="smcap">Various Proprietary Compounds.</span>&mdash;We have seen many
+proprietary coagulants advertised and pass into the limbo of
+forgotten things. They can generally be divided into two
+classes. The first embraces those founded upon a woefully
+incomplete knowledge of requirements. The second covers
+those which meet requirements, but for which exaggerated
+claims are made and excessive prices charged.</p>
+
+<p>As as instance of a substance which fell under both classifications
+might be mentioned the case of &#8220;Coagulatex.&#8221; Pretentious
+claims were made, and it was emphasised that the
+liquid contained no <i>vegetable acids</i>. Acetic and formic acids
+might be quoted as examples of vegetable acids, and as these
+have been shown to be the most satisfactory coagulants now
+employed one fails to imagine where lay the value of the
+guarantee given by the advertisers of &#8220;Coagulatex.&#8221;</p>
+
+<p>On analysis the liquid was found to consist mainly of sulphuric
+acid, against the indiscriminate use of which warnings
+have been given. Thus it was a dangerous substance for
+common use.</p>
+
+<p>Furthermore, comparing the value with its sulphuric acid
+content, it was found that the price required for &#8220;Coagulatex<span
+class='pagenum'><a name="Page_289" id="Page_289">[289]</a></span>&#8221;
+was roughly four times the contemporary cost of commercial
+sulphuric acid in the Federated Malay States.</p>
+
+<p>Those in charge of estates should realise, therefore, that no
+proprietary coagulants should be adopted until a proper
+report of tests, and a comparative valuation, has been obtained
+from one of the research laboratories.</p>
+
+<p><a name="Sec19_19" id="Sec19_19"></a><span class="smcap">Carbonic Acid Gas, Carbon Dioxide.</span>&mdash;Now of only scientific
+interest, it may be noted that some years ago great claims
+were made for the use of carbon dioxide gas as a coagulant.
+In actual practice we were unable to effect coagulation by passing
+the dry gas into latex. It was suggested that the original
+investigators were misled by failure to secure a dry and clean
+gas. It would appear that probably the gas was prepared by
+the action of hydrochloric acid upon marble or limestone.
+Unless intervening &#8220;washers&#8221; and &#8220;driers&#8221; were used, the
+liberated gas, when passed into latex, would carry with it traces
+of hydrochloric acid, which would effect coagulation.</p>
+
+<p><a name="Sec19_20" id="Sec19_20"></a><span class="smcap">Alcohol.</span>&mdash;In the cheap form of methylated spirit, alcohol
+has been employed by us as a speedy coagulant for many years.
+Latex run slowly into alcohol coagulates instantaneously. The
+method has been in common laboratory use.</p>
+
+<p>The employment of alcohol has also been made the part-subject
+of a patent process of coagulation, to which reference
+will be made in the <a href="#Ch20">succeeding chapter</a>.</p>
+
+<p><a name="Sec19_21" id="Sec19_21"></a><span class="smcap">Vegetable Extracts.</span>&mdash;At various times experimental work
+has been directed towards the use of liquids of purely vegetable
+origin, such as the juices of tropical fruits, and of a waste product
+of tropical industry&mdash;the so-called &#8220;milk&#8221; (or water)
+of ripe coconuts.</p>
+
+<p>In the former class there is usually a natural acidity, but in
+coconut water the acidity is chiefly the result of fermentation
+of the carbohydrate (sugar) constituents.</p>
+
+<p>These substances were all found to effect a more or less
+satisfactory coagulation, but it is unlikely that they would be
+suitable for practical application on a large scale.</p>
+
+<p>As being more directly related to the subject of coagulation
+in general than to coagulants in particular, a discussion of
+several special processes will be relegated to the <a href="#Ch20">ensuing chapter</a>.</p>
+
+
+<p class='pagenum'><a name="Page_290" id="Page_290">[290]</a></p>
+<hr class="c25" />
+<h2><a name="Ch20" id="Ch20"></a>CHAPTER XX</h2>
+
+<h3><i>SPECIAL METHODS OF PREPARATION</i></h3>
+
+
+<p>Every year appears to bring forth some new ideas in the mode
+of rubber preparation. Some of them are based in principle
+upon the oldest known method&mdash;<i>i.e.</i>, the native Brazilian process
+of making &#8220;Hard Para.&#8221; Others strike a new note, and in a
+few cases the claims put forward are substantially confirmed
+by results. In other instances the claims are too pretentious,
+and discredit may be brought upon schemes which, although
+lacking in comparative success, are yet commendable for the
+ingenuity manifested.</p>
+
+<p>To the present not one of these new methods has been able
+to compete to any marked degree in general practice with the
+established methods of ordinary preparation. A few continue
+to find local application, but most have either been abandoned
+or are gradually falling into desuetude.</p>
+
+<p>We do not propose to discuss in fine detail all the various
+claims made on behalf of these special processes, or to enter
+into controversies. The aim is to present to the reader an
+outline embodying the main principles and advantages claimed.</p>
+
+<p><a name="Sec20_1" id="Sec20_1"></a><span class="smcap">Da Costa Process.</span>&mdash;Briefly, this was a method by which
+coagulation was effected with smoke. The smoke was
+generated by the combustion of wood in a special compartment,
+and was forced into latex by means of a jet of steam. It was
+really only applied to the preparation of coagulum intended
+for crepe form. The exact degree of coagulation effected
+was uncertain, and the final colour of the rubber precluded it
+from being classed as a modern No. 1 product.</p>
+
+<p><a name="Sec20_2" id="Sec20_2"></a><span class="smcap">&#8220;Byrne Curing&#8221; Process.</span>&mdash;This is a process for treating
+coagulum obtained by ordinary methods.</p>
+
+<p><span class='pagenum'><a name="Page_291" id="Page_291">[291]</a></span>It was the subject of a patent obtained by Messrs. E. J. and
+F. A. Byrne, and at one time had a considerable vogue on
+estates. The chief claim advanced was that the rubber produced
+was in all respects equal to Fine Hard Para, and could
+be shipped while still moist without detriment to the physical
+qualities.</p>
+
+<p>The principle of the process was the treatment of coagulum,
+in either sheet or thick crepe form, with vapours produced by
+the volatilisation of two special fluids. This treatment was
+undertaken in comparatively small wooden sheds, in which
+the coagulum was placed. The &#8220;smoke&#8221; was conducted into
+the curing sheds from furnaces outside the building. The
+sheds were covered externally with &#8220;felt&#8221; material to prevent
+leakage of the vapours, and a very dense smoke was
+obtained.</p>
+
+<p>The furnaces were specially designed, and consisted essentially
+of a &#8220;hot-plate&#8221; heated by a powerful kerosene blast-flame.
+On top of the machine were two reservoirs controlled
+by taps. In these were placed the special fluids which were
+released in definite proportion. The composition of the
+fluids was not divulged, but it is assumed that the principal
+ingredients were (<i>a</i>) wood tar products, (<i>b</i>) crude pyroligneous
+or acetic acid. The mixture of these, dropping on the hot plate
+at the correct temperature, spontaneously volatilised, to form
+dense whitish fumes, having an intense and not disagreeable
+odour of wood combustion. A duct led from the back of the
+machine into the curing-shed, where the vapours were distributed
+through perforations in the pipe.</p>
+
+<p>The coagulum usually remained under treatment in the shed
+for three to four hours, and then was removed for ordinary
+air-drying. When taken from the curing-shed it had a pinkish
+colour, which later developed into a dark brown by a natural
+process of oxidation. The exterior of the rubber, on shipment,
+resembled the appearance of smoked sheets; while the interior,
+on cutting, was seen to be still white. As packed for shipping,
+the rubber contained from 10 to 15 per cent. of original
+moisture, for the usual sheet form, and even more when &#8220;slab&#8221;
+rubber was prepared.</p>
+
+<p><span class='pagenum'><a name="Page_292" id="Page_292">[292]</a></span>Originally either crepe or sheet rubber was made, but later
+the preparation of the crepe form was displaced largely by
+&#8220;slab&#8221; rubber. These &#8220;slabs&#8221; were really very thick
+sheets, which had been subject to only slight pressure.</p>
+
+<p>Still later the preparation of the &#8220;slab&#8221; form was displaced
+by &#8220;loaf&#8221; rubber. This form was built up by winding
+together ordinary thin sheets which had been subject to the
+&#8220;cure.&#8221; Only slight tension was needed, during the operation
+of winding, to cause close adhesion of the component wet
+layers, and the final result was a &#8220;loaf&#8221; or roll dark in colour,
+and apparently dry when examined superficially. On being
+cut, even after an interval of months, the middle portion was
+still so moist as to be quite white.</p>
+
+<p>In course of time it was discovered that all the claims made
+for the process could not be substantiated, and for various
+reasons (which need not be detailed) most of the estates which
+had adopted the scheme reverted to ordinary methods of
+preparation. At the time of writing few, if any, continue to
+work the process. It appears to be agreed, as the result of
+investigations, that in no degree does the process yield advantage
+over ordinary methods.</p>
+
+<p><a name="Sec20_3" id="Sec20_3"></a><span class="smcap">Freezing Process.</span>&mdash;A patent was secured a few years ago
+to cover a process whereby coagulation was effected by
+refrigeration.</p>
+
+<p>Latex remained for several hours in the refrigerating chambers
+of an ordinary ice-making plant. The resulting solid mass,
+on being thawed, yielded a coagulum appearing in no way to
+differ from that obtained by ordinary methods of coagulation.</p>
+
+<p>Provided the process exerted no influence for good or evil
+upon the quality of the resulting dry rubber, the value of it
+would appear to depend upon the relative cost of working, plus
+considerations of capital expenditure and depreciation on the
+plant. At the present time it would be difficult to imagine
+that the cost of preparation alone would compare favourably
+with that sustained by ordinary coagulative methods.</p>
+
+<p>Furthermore, beyond the expensive refrigerating plant, the
+usual machinery of a factory would still be required if the
+ordinary market demands are to be met.</p>
+
+<p><span class='pagenum'><a name="Page_293" id="Page_293">[293]</a></span>Finally,
+it has not been found<a name="FNanchor_27_27" id="FNanchor_27_27"></a><a
+href="#Footnote_27_27" class="fnanchor">[27]</a> that any advantage in the final
+physical qualities of the rubber is obtained by the employment
+of this process.</p>
+
+<div class="footnote"><p><a name="Footnote_27_27" id="Footnote_27_27"></a><a
+href="#FNanchor_27_27"><span class="label">[27]</span></a> &#8220;Preparation and Vulcanisation of Plantation Rubber&#8221; (Eaton,
+Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture.</p></div>
+
+<p><a name="Sec20_4" id="Sec20_4"></a><span class="smcap">Wickham Process.</span>&mdash;This process, invented by Sir Henry
+Wickham, aimed at the production of a rubber resembling
+Fine Hard Para. The principle employed was that underlying
+the preparation of the best rubber in Brazil&mdash;viz., coagulation of
+superimposed thin layers of latex by the action of smoke and
+heat.</p>
+
+<p>In essential the machine employed consisted of a rotating
+drum into which latex and smoke entered. The result was
+the formation of thin &#8220;skins&#8221; of rubber which, coagulating
+<i>in situ</i>, formed a mass corresponding to &#8220;Fine Hard.&#8221;</p>
+
+<p>That the rubber was fully satisfactory as to quality is
+acknowledged, but economically and in practical utility the
+process was unsuccessful, the rate of output being so low.</p>
+
+<p><a name="Sec20_5" id="Sec20_5"></a><span class="smcap">Derry Process.</span>&mdash;The invention of Mr. R. Derry, late of
+the Singapore Botanic Gardens, this in principle resembled the
+Wickham and other processes. It aimed at a mechanical
+imitation of the native method of producing Fine Hard Para.</p>
+
+<p>In place of the rotating drum, an endless belt was used. This
+travelled over pulleys, more or less horizontally placed. The
+upper of these could be raised to varying height above the
+level of the other, and likewise could be so adjusted as to
+tighten the belt.</p>
+
+<p>The under layer of the belt impinged, in its travel, upon the
+surface of a layer of latex contained in a shallow tray. The
+belt was operated by hand-power, and the height of the latex
+trays was adjustable.</p>
+
+<p>The trays of latex were situated at the lower end of the
+machine which lay outside the smoking-chamber. It will be
+understood that the vastly major part of the total length of belt
+was always within the chamber.</p>
+
+<p>Smoke was generated by combustion of wood in an external
+structure, was brought into the chamber by a wide duct, and<span class='pagenum'><a name="Page_294" id="Page_294">[294]</a></span>
+was then distributed below the belt by means of perforated
+pipes.</p>
+
+<p>The thin film of latex picked up by the belt was coagulated
+partly by the action of smoke constituents by evaporation due
+to heat. Assuming (1) that the belt was of adequate length,
+(2) that the rate of travel was not excessive, (3) that the latex
+was not too dilute, (4) that the temperature of the smoke
+was sufficiently high, (5) that the smoke was sufficiently dense
+and not too damp&mdash;then the process should be a continuous one.</p>
+
+<p>It will be clear that success could only be obtained by a
+careful adjustment of all these factors. The latex must, necessarily,
+be of a fairly rich consistency (at least 2<span class="enum">1</span>&#8260;<span class="denom">2</span> lbs. dry rubber
+per gallon), but unfortunately there is considerable difficulty
+in maintaining such latex in a state of fluidity for the period
+demanded by this process, without loss of latex. Naturally, the
+addition of an anti-coagulant would retard the rate of output
+of the machine to a marked degree.</p>
+
+<p>The layer of rubber thus formed on the belt was stripped off,
+and hung for further air-drying, as it still contained a fair
+percentage of moisture.</p>
+
+<p>As a really practicable method for treating plantation latex,
+the process failed by reason of its low rate of output over a
+given interval. This alone was sufficient to condemn it, apart
+from the facts (1) that it was not shown to be a cheaper method
+than coagulation by acetic acid, (2) that the resulting rubber was
+not proved to be of superior intrinsic value to rubber prepared
+by ordinary methods.</p>
+
+<p><a name="Sec20_6" id="Sec20_6"></a><span class="smcap">Spontaneous Coagulation.</span>&mdash;All readers will be aware
+of the phenomenon of the curdling or souring of milk. The
+behaviour of <i>Hevea</i> latex, under certain conditions, may be taken
+to be analogous. Difficulty is experienced in maintaining
+fluidity&mdash;a difficulty which appears to vary in great degree
+according to locality, nature of soil, age of trees, the relative
+demand made upon the trees by the system of tapping employed,
+etc.</p>
+
+<p><a name="Sec20_7" id="Sec20_7"></a>It is sometimes found, before the latex reaches the store, that
+it may exhibit one of various stages of premature (spontaneous)
+coagulation:</p>
+
+<div class="blockquot"><p><span class='pagenum fsize100'><a name="Page_295" id="Page_295">[295]</a></span>(<i>a</i>)
+To all appearances it may be quite fluid, but a close
+examination shows it to consist mainly of a serum containing
+very minute particles of rubber in suspension (microscopic
+coagulation).</p>
+
+<p>(<i>b</i>) In a later stage these particles coalesce to form larger
+&#8220;flocks&#8221; (macroscopic coagulation).</p>
+
+<p>(<i>c</i>) The whole, or practically the whole, of the latex may have
+coagulated, forming one mass of rubber with a milky residual
+serum.</p></div>
+
+<p>Passing from this aspect of the question, it may be noted as
+peculiar facts that:</p>
+
+<div class="blockquot"><p>(1) A shallow layer of latex is less likely to coagulate spontaneously
+(<i>i.e.</i>, without the addition of a coagulant) than a
+deeper volume.</p>
+
+<p>(2) The shallow layer, and also the surface of the deeper
+volume (where exposed to air), on standing will be found to
+develop a superficial film of finely coagulated particles, yellowish
+in colour, and having an offensive odour due to decomposition
+of protein matter.</p>
+
+<p>(3) While this partial coagulation is confined only to the
+surface of a shallow layer of latex, it will be found that below
+the surface film of the deeper volume a much more definite
+coagulation has taken place. The coagulation will be practically
+complete, and the coagulum, apart from a spongy appearance,
+is normal in character. This coagulum is free from the
+offensive odour noted above.</p>
+
+<p>(4) On testing the surface film of both the shallow layer and
+the deeper volume, it will be found to be <i>alkaline</i> in character;
+whilst the lower liquid surrounding the main portion of the
+coagulum in the deeper volume of latex is of an <i>acid</i> nature.</p></div>
+
+<p><a name="Sec20_8" id="Sec20_8"></a>These observed facts are sufficient to indicate that there are
+apparently <i>two distinct types of spontaneous coagulation</i>, and that
+the latter takes place particularly where the latex is more or
+less out of contact with the atmosphere. We may, therefore,
+differentiate thus:</p>
+
+<div class="blockquot"><p><a name="Sec20_9" id="Sec20_9"></a>(<i>a</i>) <i>In contact with air (aerobic)</i>: incomplete spontaneous
+coagulation, accompanied by yellowish slime, offensive in
+odour and alkaline in character.</p>
+
+<p><a name="Sec20_10" id="Sec20_10"></a>(<i>b</i>) <i>Out of contact with air (Anaerobic)</i>: Practically or wholly
+complete. There is no offensive odour under normal conditions
+and the serum is acid in character.</p></div>
+
+<p><a name="Sec20_11" id="Sec20_11"></a><span class='pagenum'><a name="Page_296" id="Page_296">[296]</a></span>It
+is concluded<a name="FNanchor_28_28" id="FNanchor_28_28"></a><a href="#Footnote_28_28"
+class="fnanchor">[28]</a> that there are present in latex, on collection
+in the field, two types of organisms. Those which work in
+contact with air (aerobic) show a tendency to <i>prevent</i> coagulation
+and to form an alkaline yellow slime on the surface of the
+latex. The others, which work in the absence of air (anaerobic),
+may, under favourable conditions, cause complete coagulation
+unaccompanied by any decomposition or offensive odour
+within a normal period. If air is rigidly excluded, the coagulum
+obtained is quite satisfactory for all purposes.</p>
+
+<div class="footnote"><p><a name="Footnote_28_28" id="Footnote_28_28"></a><a
+href="#FNanchor_28_28"><span class="label">[28]</span></a> &#8220;Preparation and Vulcanisation of Plantation Rubber&#8221; (Eaton,
+Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture,
+1918; &#8220;De la Coagulation naturelle du Latex d&#8217;Hevea
+Brasiliensis&#8221; (Denier and Vernet), <i>Comptes Rendus l&#8217;Acad&eacute;mie des
+Sciences</i>, No. 3, July, 1917.</p></div>
+
+<p><a name="Sec20_12" id="Sec20_12"></a>This type of coagulation, without the employment of a
+chemical coagulant, and under anaerobic conditions, was the
+subject of a patent granted in 1914 to Messrs. Maude, Crosse
+and others. The process has been in use on Cicely Estate
+(Perak) for some years. With subsequent slight modifications
+the apparatus consisted in essential of a tank with a loose cover.
+The flanges of the cover were sufficiently long to dip into a
+water-seal surrounding the tank. Thus the cover may rise
+and fall without an inrush of air.</p>
+
+<p><a name="Sec20_13" id="Sec20_13"></a>Coagulation, in fact, can be effected thus in any kind of air-tight
+receptacle; and experimentally the reader can obtain a
+satisfactory result by filling completely with latex the bottle
+which has a loose stopper.</p>
+
+<p>Under the patent held the coagulum may be prepared either
+for crepe-making, or for sheets by a modification of the tank.</p>
+
+<p>The crepe when dry does not have the bright appearance
+of the ordinary &#8220;Fine Pale&#8221; standard prepared with the aid
+of the anti-oxidant sodium bisulphite.</p>
+
+<p>Unfortunately the addition of this substance to the latex in
+normal proportions is not possible under anaerobic conditions,
+as it is found to prevent coagulation, probably owing to its
+sterilising effect upon the anaerobic organisms.</p>
+
+<p>To prevent the oxidation of the rubber in actual practice,
+the freshly prepared crepe is soaked in a solution of sodium<span class='pagenum'><a name="Page_297" id="Page_297">[297]</a></span>
+bisulphite before hanging to dry. The resulting colour of
+the rubber is quite good.</p>
+
+<p>It was shown by Eaton and Grantham that anaerobic coagulation
+is slightly uncertain in action. Owing probably to
+variations in the composition of the latices, or to the extent
+of infection by organisms, coagulation may one day be complete
+and on other days less satisfactory.</p>
+
+<p><a name="Sec20_14" id="Sec20_14"></a>They found further that, by the addition of small quantities
+of sugars, coagulation under both aerobic and anaerobic conditions
+was improved. The conclusion formed was that the
+addition of sugars created a medium favourable to the development
+of anaerobic organisms and unfavourable to those which
+cause decomposition of the natural nitrogenous constituents
+of latex.</p>
+
+<p>This work was confirmed by Gorter and Swart,<a name="FNanchor_29_29"
+id="FNanchor_29_29"></a><a href="#Footnote_29_29" class="fnanchor">[29]</a> who attributed
+the action to the conversion of sugar to lactic, acetic,
+and succinic acids by fermentation.</p>
+
+<div class="footnote"><p><a name="Footnote_29_29" id="Footnote_29_29"></a><a
+href="#FNanchor_29_29"><span class="label">[29]</span></a> Gorter and Swart, Bulletin No. 6, West Java Station.</p></div>
+
+<p>Denier and Vernet, whose work has already been mentioned,
+studied the presence of the organisms in latex, and succeeded
+in isolating one which, under anaerobic conditions, effects
+coagulation within twenty-four hours. Sometimes to produce
+complete coagulation it was found necessary to employ small
+quantities of sugars&mdash;<i>e.g.</i>, 1 gramme per litre of latex (1:1,000).</p>
+
+<p><a name="Sec20_15" id="Sec20_15"></a>It is to be noted also that the addition of small quantities
+of soluble calcium (lime) salts to latex has much the same
+effect as the employment of sugars. Recent investigations<a name="FNanchor_30_30"
+id="FNanchor_30_30"></a><a href="#Footnote_30_30" class="fnanchor">[30]</a>
+showed that the addition of 0&middot;5 to 1 gramme of calcium chloride
+per litre of latex caused complete coagulation in closed vessels
+within twenty-four hours, a result agreeing with the findings
+of Barrowcliff.</p>
+
+<div class="footnote"><p><a name="Footnote_30_30" id="Footnote_30_30"></a><a
+href="#FNanchor_30_30"><span class="label">[30]</span></a> &#8220;Archief voor de Rubbercultuur,&#8221; Nederlands Indies, 1920,
+4, 273.</p></div>
+
+<p>On page 308 of the same publication, experiments on the
+effect of sugars are described, in connection with <i>aerobic</i>
+coagulation. Observations from a further set of experiments
+tended to indicate a direct connection between the effects of
+tapping and spontaneous coagulation. It is suggested that<span class='pagenum'><a name="Page_298" id="Page_298">[298]</a></span>
+heavy tapping causes a diminution in the latex of those substances
+which act in some way as accelerating agents in
+coagulation&mdash;<i>e.g.</i>, sugars. The smaller the proportion of these
+substances, the slower and less complete is natural (spontaneous)
+coagulation.</p>
+
+<p><a name="Sec20_16" id="Sec20_16"></a><span class="smcap">Ilcken-Down Process.</span>&mdash;This process is the subject of
+patents granted in 1915 to Messrs. Ilcken and Down. It has
+been in fair prominence, and has been tried experimentally
+on several estates and in public demonstration.</p>
+
+<p>It is a coagulating process, and, in the original specification,
+employed as agents a mixture of alcohol (in the form of methylated
+spirit) and benzene (petrol), or alcohol with petrol and
+coal-tar naphtha. The mixture was injected in the form of a
+fine spray into the latex, contained in a tank specially fitted
+with paddles.</p>
+
+<p>Later modifications covered the addition of a small quantity of
+glycerine; or, failing supplies of that substance, coconut oil.</p>
+
+<p>Many advantages are claimed for the process, but most of
+them cannot be substantiated. The two chief claims are:</p>
+
+<div class="blockquot"><p>1. The production of a uniform standard of rubber.</p>
+
+<p>2. The obtainment from a unit volume of latex of a greater
+weight of rubber than can be obtained from an equal volume
+of the same latex by ordinary coagulation with acetic acid. It
+is to be inferred that the agents employed have the power of
+adding to the coagulum some of the substances which usually
+remain in solution in the clear serum.</p></div>
+
+<p>Regarding the first of these claims, it has been shown<a name="FNanchor_31_31"
+id="FNanchor_31_31"></a><a href="#Footnote_31_31" class="fnanchor">[31]</a> that
+the rubber is not uniform in its behaviour on vulcanisation,
+and that its variability is similar to that of rubber prepared by
+other processes.</p>
+
+<div class="footnote"><p><a name="Footnote_31_31" id="Footnote_31_31"></a><a
+href="#FNanchor_31_31"><span class="label">[31]</span></a> &#8220;Preparation and Vulcanisation of Plantation Rubber&#8221;
+(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department
+of Agriculture, 1918.</p></div>
+
+<p>The second claim has been the subject of much controversy.
+Experiments made on estates under the supervision of, or
+in the absence of, the patentees have given conflicting results.
+When varying factors have been eliminated, the general
+conclusion was that no increase in weight of rubber was
+obtained.</p>
+
+<p><span class='pagenum'><a name="Page_299" id="Page_299">[299]</a></span>Private
+laboratory investigations led to a similar verdict, and
+Eaton<a name="FNanchor_32_32" id="FNanchor_32_32"></a><a href="#Footnote_32_32"
+class="fnanchor">[32]</a> records a confirmatory finding. More recently the
+claims made for the process were investigated in Java<a name="FNanchor_33_33"
+id="FNanchor_33_33"></a><a href="#Footnote_33_33" class="fnanchor">[33]</a> under
+varying conditions. Three series of experiments were made:</p>
+
+<div class="footnote"><p><a name="Footnote_32_32" id="Footnote_32_32"></a><a
+href="#FNanchor_32_32"><span class="label">[32]</span></a> <i>Ibid.</i></p></div>
+
+<div class="footnote"><p><a name="Footnote_33_33" id="Footnote_33_33"></a><a
+href="#FNanchor_33_33"><span class="label">[33]</span></a> &#8220;Archief voor de Rubbercultuur&#8221; (De Vries and Spoon), Central
+Rubber Station, Java, May, 1921.</p></div>
+
+<div class="blockquot"><p>(1) During the rainy monsoon and at a height of 1,800 feet.</p>
+
+<p>(2) During the dry monsoon on a low-country estate.</p>
+
+<p>(3) In the experimental gardens at Buitenzorg during bright
+sunny weather and the most favourable conditions.</p></div>
+
+<p>The agents used were (<i>a</i>) a mixture of alcohol and fusel oil,
+(<i>b</i>) alcohol and petrol (benzene).</p>
+
+<p>In these experiments no advantage in weight of rubber was
+obtained by the Ilcken-Down process, and it would thus appear
+that the principal claim fails to be substantiated.</p>
+
+<p>The general composition of the rubber was approximately
+the same as ordinary crepe obtained from undiluted latex.
+The rubber on vulcanisation was found to be normal in
+behaviour, and was similar to the controls.</p>
+
+<p>The coagulum ordinarily is affected by oxidation, and does
+not produce a fine pale crepe. To remedy this defect the
+freshly prepared crepe is soaked in a solution of sodium
+bisulphite and sulphuric acid.</p>
+
+<p>It may be noted that in the recent experiments coagulation
+was effected in vacuum in a specially designed wooden tank.
+From a study of the <a href="#Sec20_6">previous section</a> on &#8220;Spontaneous
+Coagulation,&#8221; the reader will perceive that results equal to
+those obtained by the Ilcken-Down process can be obtained
+<i>without</i> the necessity of using such agents as alcohol, petrol, or
+fusel oil.</p>
+
+<p><a name="Sec20_17" id="Sec20_17"></a><span class="smcap">Slab Rubber.</span>&mdash;This type of preparation has been the
+subject of much discussion of recent years. There is nothing
+really special in the mode of preparation, and in its original
+form &#8220;slab&#8221; rubber is only a thick sheet which may be
+obtained by coagulation with acetic acid or other agents.</p>
+
+<p>The coagulum, when removed from the serum, is subjected
+to comparatively slight pressure, and the &#8220;slab&#8221; thus made is<span
+class='pagenum'><a name="Page_300" id="Page_300">[300]</a></span>
+either placed to air-dry at once, or may be subject to treatment
+in other liquids before drying.</p>
+
+<p>The rubber is not allowed to remain until wholly dry, but is
+shipped while still containing an appreciable percentage of
+enclosed moisture.</p>
+
+<p>It is claimed<a name="FNanchor_34_34" id="FNanchor_34_34"></a><a href="#Footnote_34_34"
+class="fnanchor">[34]</a> that the production of &#8220;slab&#8221; rubber by
+standardised methods eliminates to a great degree the variability
+which at present characterises plantation rubber, and
+that a fast-curing medium is obtained. These claims will be
+discussed in <a href="#Part6">later chapters</a> dealing with the vulcanisation of
+rubber, and demand no notice in this section.</p>
+
+<div class="footnote"><p><a name="Footnote_34_34" id="Footnote_34_34"></a><a
+href="#FNanchor_34_34"><span class="label">[34]</span></a> &#8220;Preparation and Vulcanisation of Plantation Rubber&#8221;
+(Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department
+of Agriculture, 1918.</p></div>
+
+<p>From the producers&#8217; point of view, it may be noted that the
+preparation of slab rubber is a simple process, but not altogether
+as pleasant probably as might be desired, when undertaken
+in crude form.</p>
+
+<p>The appearance of the partially dry slabs is unattractive,
+but that does not signify if the quality of the vulcanised
+product satisfies requirements.</p>
+
+<p>For the average producer, the difficulty lies in having to meet
+the demands of the general market. Even, therefore, if one
+assumes that the intrinsic qualities of slab rubber are all that
+the claims advance, it would be necessary for the producer to
+be assured of definite and regular sales.</p>
+
+<p>At present it would probably be fair to state that practically
+all the &#8220;slab&#8221; rubber being prepared is produced by those
+who are also consumers. They are thus in the enviable
+position of being able to satisfy their requirements as to the
+mode of preparation. Until such time, therefore, as there
+exists a regular demand for &#8220;slab&#8221; rubber in the general
+market, the vast majority of estates must proceed on ordinary
+lines of preparation.</p>
+
+<p class='pagenum'><a name="Page_301" id="Page_301">[301]</a></p>
+
+<hr class="c25" />
+<h2><a name="Part6" id="Part6"></a>PART VI</h2>
+
+<h3>VULCANISATION</h3>
+
+<h4>(<span class="smcap">By Dr. H. P. Stevens</span>)</h4>
+
+<h2><a name="Ch21" id="Ch21"></a>CHAPTER XXI</h2>
+
+<h3><i>INTRODUCTORY DEALING WITH TREATMENT
+AND VULCANISATION</i></h3>
+
+
+<p>In the foregoing chapters the methods of treating latex,
+coagulating, rolling and curing, or drying, have been described
+in great detail. These details will give the reader some
+idea of the precautions taken, and procedure necessary to
+produce rubber which will be acceptable to the market.
+The expressions &#8220;inferior rubber,&#8221; &#8220;defective crepe,&#8221;
+&#8220;poor quality sheets,&#8221; etc., are frequently met with, but these
+expressions must not be taken to indicate any defect in the
+rubber for manufacturing purposes, but merely that the rubber
+is defective for selling purposes&mdash;that is to say, being unsightly,
+it will not fetch the full market price.</p>
+
+<p><a name="Sec21_1" id="Sec21_1"></a>Raw rubber, as produced on the plantations, is almost invariably
+subjected to the process of vulcanisation in the production
+of manufactured rubber articles as we know them.
+Previous to the advent of plantation rubber, the raw material
+was purchased by the manufacturer in a moist and impure
+condition; frequently the rubber was adulterated with sand,
+dirt, and even small stones. Consequently it was the invariable
+practice of the rubber manufacturer to wash the raw rubber
+and convert it into crepe, which was then hung and air-dried
+before use. The effect on the rubber, if of high grade, was more
+severe than the washing and crepeing process on the plantation,
+because the rubber was not a soft coagulum but generally<span class='pagenum'><a name="Page_302" id="Page_302">[302]</a></span>
+dried on the surface and semi-hard. The power required
+was considerable, and the resulting crepe was consequently
+softer and more susceptible to heat than plantation first latex
+crepe. Much of the &#8220;wild&#8221; rubber was soft and tacky and
+inferior to &#8220;earth-scrap.&#8221;</p>
+
+<p>Vulcanising in its simplest aspect consists in mixing the
+rubber with sulphur and heating the product under regulated
+conditions. The effect of heat on the inferior grades of &#8220;wild&#8221;
+rubber is very marked. A soft, sticky, and resinous material
+is transformed into a relatively tough and elastic product.
+The effect of vulcanising on the better grades is less marked,
+but immediately apparent. On the other hand, the effect of
+vulcanising is least apparent on first latex plantation grades,
+because in these we have a raw rubber prepared in a manner
+best suited to retain its natural characteristics.</p>
+
+<p>The need of vulcanising in the process of manufacturing
+rubber goods became an axiom in pre-plantation days, and
+it is only quite recently that attempts have been made to
+utilise raw rubber directly, without vulcanisation, particularly
+for shoe soles. For this purpose a thick dense crepe has been
+found satisfactory. Smoked sheet rubber is not generally
+suitable, apparently owing to its microphysical structure. It is
+possible that the process of rolling in the making of dense crepe
+compacts the rubber particles, yielding a harder and more
+resilient product. The rolling must not be carried too far, or the
+&#8220;working&#8221; of the rubber will approximate to a preliminary
+mastication, and the product will be weakened.</p>
+
+<p>The utilisation of crepe rubber directly has not yet been
+sufficiently tested to enable a definite conclusion to be reached
+as to its future scope, but it is obvious that for use in a raw state
+some modification in preparation may be advantageous. The
+present method&mdash;<i>e.g.</i>, coagulation with acetic acid&mdash;does not
+yield the hardest and toughest rubber.</p>
+
+<p><a name="Sec21_2" id="Sec21_2"></a>Hardness and toughness are actual drawbacks in the utilisation
+of rubber which is required for vulcanising. When the
+output of plantation rubber began to increase and to displace
+the inferior wild sorts, manufacturers complained of the increased
+power consumption of their machines. The power<span class='pagenum'><a name="Page_303" id="Page_303">[303]</a></span>
+was required mainly to &#8220;break down&#8221; or &#8220;mill&#8221; the rubber
+preliminary to the mixing with sulphur and other ingredients.
+It is obvious that a material such as raw rubber cannot be
+mixed with powders such as sulphur with a pestle and mortar,
+or in any simple form of mixing machine. This difficulty was
+overcome by the earlier experimenters by immersing the rubber
+in a bath of molten sulphur. The latter was gradually absorbed
+and &#8220;dissolved&#8221; in the rubber, and the heat of the bath
+caused the dissolved sulphur to combine with the rubber to
+produce vulcanised rubber. The limitations of such a process
+are apparent. Thus the vulcanised rubber retains the form in
+which it was originally shaped. Moreover, other ingredients,
+such as mineral matters, cannot be dissolved or absorbed by
+the rubber in this manner. The method eventually adopted
+consisted in &#8220;breaking down,&#8221; &#8220;milling,&#8221; or &#8220;masticating&#8221;
+the rubber by passing it continuously between differentially
+geared steam-heated rollers. By this means a high-grade rubber
+is converted into a soft, plastic mass, which will &#8220;take up&#8221;
+sulphur, mineral matter, and other ingredients as desired.
+The mixing operation may be carried through on the same
+roller machine as was used for breaking down the rubber, or
+separate machines of other designs may be adopted. Details
+of the process will be found in books dealing with rubber
+manufacturing.<a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href="#Footnote_35_35"
+class="fnanchor">[35]</a> It will suffice here to explain that when
+rubber is kneaded between two hot rollers moving at different
+speeds the rubber forms a continuous band around the slower
+moving roller, and if the distance between the rollers be adjusted
+the excess of rubber held back by the nip of the rollers will
+form a &#8220;bank&#8221; or moving wedge-shaped mass on the top of the
+nip. This closes the space between the rollers, so that sulphur
+and powder placed on the rubber pass round towards the nip,
+and are there driven into the rubber. In this manner it is easy
+to mix, say, 10 per cent. of sulphur into the rubber without
+a single particle falling through. In technical mixes where
+large quantities of powders require to be mixed there is always
+some caking, and part of the powder falls between the rollers<span class='pagenum'><a name="Page_304" id="Page_304">[304]</a></span>
+into a tray underneath. This is swept up with a broom and
+put back on to the rollers, the process being repeated until the
+whole of the ingredients have been incorporated.</p>
+
+<div class="footnote"><p><a name="Footnote_35_35" id="Footnote_35_35"></a><a
+href="#FNanchor_35_35"><span class="label">[35]</span></a> For instance, &#8220;India-Rubber and its Manufacture,&#8221; by H. L.
+Terry.</p></div>
+
+<p><a name="Sec21_3" id="Sec21_3"></a>From this description it follows that, preliminary to mixing,
+it is necessary to thoroughly masticate or &#8220;plasticise&#8221; the raw
+rubber. Much of the &#8220;wild&#8221; rubber was of so inferior a
+quality that it very readily broke down, and but little mastication
+was necessary. It was soft and resinous, and readily took
+up the powders which were to be mixed with it. The better
+grades of wild rubber, such as Fine Para, were more difficult
+to break down, but not so difficult as most plantation rubber,
+because they had already received a preliminary &#8220;working&#8221;
+in the process of washing and crepeing, and we have already
+explained that such treatment takes more power than the crepeing
+of the soft moist coagulum on the plantations. The amount
+of &#8220;working&#8221; or &#8220;plasticising&#8221; produced in the rubber is
+connected with the power expended; the greater the expenditure
+of power, <i>caeteris paribus</i>, the greater the working effect
+on the rubber. Although the manufacturers possessed a relatively
+soft rubber in the form of washed Fine Para, it was customary
+in most cases to employ this rubber in conjunction with
+washed lower grades to produce a soft plastic material for
+further treatment. Now, however, the manufacturer has
+little else but plantation to deal with, and most of it more difficult
+to break down than washed Para crepe. This is the reason
+why a hard, tough rubber is no longer a desideratum with
+manufacturers, although originally taken as an indication of
+good quality. For the majority of purposes they want something
+which will break down easily. Hence if a rubber could
+be produced answering to these requirements, without loss of
+vulcanising quality, it would be preferred.</p>
+
+<p><a name="Sec21_4" id="Sec21_4"></a>Having incorporated sulphur and other ingredients, the
+plastic mass is sheeted and run between layers of calico to prevent
+the superimposed sheets from adhering. From this
+&#8220;calendered sheet&#8221; the article, whatever it may be, is built
+up. The calender rollers are heated so as to keep the rubber
+compound plastic. There is a limit to the thickness of the
+sheet which can be produced. It is a difficult operation to<span class='pagenum'><a name="Page_305" id="Page_305">[305]</a></span>
+perform satisfactorily so as to yield a smooth surface and a
+sheet free from enclosed air. When cool the rubber hardens
+and is readily handled. The object to be manufactured is
+then built up from the calendered sheet. Thus in the manufacture
+of a motor tyre the tread is built up on the casing
+or carcase by laying the sheets on the canvas and rolling these
+with a hand or power operated roller, so that they adhere firmly,
+the first layer to the canvas of the casing and subsequent
+layers to one another. This rough description will suffice
+to illustrate how important it is that the rubber when mixed
+should be plastic enough to give a smooth sheet, and to allow
+the sheet to be manipulated in building up the article in process
+of manufacture. The testing of rubber in regard to its plasticity
+and power to absorb finely divided mineral matter will
+be discussed in a <a href="#Ch22">later chapter</a>. We may, however, point
+out here, that the mineral matter is not generally added as an
+adulterant, but because of certain specific properties it confers
+on the product.</p>
+
+<p>To proceed with our outline of vulcanisation, we have now
+arrived at the stage at which the goods are built up and ready
+for vulcanising. For this purpose they are generally enclosed
+in some manner, either in metal moulds bolted together, or
+tightly wrapped in cloth, as, <i>e.g.</i>, in the manufacture of inner
+tubes, hose, etc. In the latter case, you can detect the cloth
+mark on the finished product. Sometimes the rubber is
+spewed&mdash;that is, driven out of a barrel by means of an endless
+screw revolving in it. In this way rubber tubing, perambulator
+tyres, and such articles, may be made. More recently even
+tyre treads and the shaped rubber for band tyres (heavy solid
+tyres) have been extruded in this manner, for the process is
+much cheaper than building up a tyre from calendered sheet,
+and then cutting the mass to shape by hand. But for spewing
+the rubber mass must be very soft and plastic; this condition
+is not obtainable unless the raw rubber originally used can be
+made thoroughly plastic without damage. Nor can it be
+effected with a rubber mass containing much finely divided
+mineral matter, as this hardens the mixture.</p>
+
+<p>For other purposes the rubber is swollen in a solvent, such as<span class='pagenum'><a name="Page_306" id="Page_306">[306]</a></span>
+coal-tar naphtha, and subsequently masticated; the soft dough
+is then shaped or spread on cloth, and vulcanised after allowing
+the solvent to evaporate. Here, again, the properties of the raw
+rubber are of immense importance. Thus, the more plastic
+the dough, the less solvent required, and the less there is to
+drive off before vulcanising. The plasticity of the dough will
+depend on the plasticity of the raw rubber, and so forth. It is
+evident that the physical properties of the raw rubber are of
+great importance. They directly affect the manufacturing
+operations up to the vulcanising stage, and indirectly affect
+the results obtained on vulcanising.</p>
+
+<p>The actual vulcanising consists of heating the mass of mixed
+rubber for a definite time and at a definite temperature, each
+&#8220;heat&#8221; being chosen to suit the particular mixture. These
+data are arrived at empirically&mdash;that is, by trying a number of
+&#8220;heats&#8221; and choosing that which appears the most suitable.
+The suitability will depend on the nature of the article, the
+service to which it is to be put, and the time it is intended to
+last. All vulcanised rubber goods, whatever the process, have
+a limited life or period during which they can be relied on to
+give useful service. After a time, vulcanised rubber tends to
+harden, cracks appear on the surface when the article is bent
+or stretched, and eventually the rubber becomes rotten and
+&#8220;perished.&#8221; This tendency varies with the quality of the
+original raw rubber and the conditions of vulcanising. Before
+plantation rubber was available, the manufacturers were
+dependent on inferior wild grades for a great part of their
+output, and, consequently, the goods made from these inferior
+rubbers never showed very good mechanical properties and
+soon deteriorated. The severest critics of plantation rubber
+have admitted the advantages to the manufacturers of the
+replacement of the lower wild grades by plantation rubber.<a name="FNanchor_36_36"
+id="FNanchor_36_36"></a><a href="#Footnote_36_36" class="fnanchor">[36]</a>
+But even the best grades give a vulcanised product which<span class='pagenum'><a name="Page_307" id="Page_307">[307]</a></span>
+rapidly deteriorates if the vulcanisation is carried too far.
+This results from too long heating, or too high a temperature,
+and the product is termed &#8220;overvulcanised&#8221; or &#8220;overcured.&#8221;<a
+name="FNanchor_37_37" id="FNanchor_37_37"></a><a href="#Footnote_37_37" class="fnanchor">[37]</a>
+The appearance of the product is deceptive, as the physical
+properties are remarkably good if the overvulcanising is not
+more than 50 to 100 per cent. in excess of the normal cure.
+Only in the case of very much overvulcanised rubber do we
+obtain a product which is brittle from the beginning.</p>
+
+<div class="footnote"><p><a name="Footnote_36_36" id="Footnote_36_36"></a><a
+href="#FNanchor_36_36"><span class="label">[36]</span></a> See Williams, &#8220;The Rubber Industry,&#8221; 1914, p. 284. It must
+also be remembered that the inferior wild grades were derived from
+latices often containing a large proportion of &#8220;resinous&#8221; matter,
+and which could not yield a really high grade of vulcanised rubber
+whatever the care and skill employed in preparation.</p></div>
+
+<div class="footnote"><p><a name="Footnote_37_37" id="Footnote_37_37"></a><a
+href="#FNanchor_37_37"><span class="label">[37]</span></a> The terms &#8220;curing&#8221;
+and &#8220;vulcanising&#8221; are generally employed
+as if synonymous. Twiss has suggested that the former
+be applied in regard to a change in physical properties, and the latter
+to the chemical change whereby sulphur is combined with the rubber.
+The term &#8220;curing&#8221; is also applied to the process of preparation of
+raw rubber. This must be kept in mind so as to avoid confusion.</p></div>
+
+<p>The degree of vulcanising will vary with the type of article
+to be produced, and where a long life is desired, the tendency
+will be to &#8220;undervulcanise&#8221;; but if the best mechanical
+properties are desired, the tendency will be towards &#8220;overvulcanising,&#8221;
+or, more correctly, &#8220;fully&#8221; vulcanising. These
+considerations are aptly illustrated by reference to pneumatic
+tyres. The inner tube need not possess high tensile strength,
+provided that it is easily distensible, for the reason that, during
+use, it is protected by the casing of the tyre proper, which
+confines and supports it against the air-pressure applied.
+Inner tubes are therefore cured to give a long life without
+developing the maximal physical properties. On the other
+hand, the casing and tread of the tyre are required to withstand
+severe mechanical conditions&mdash;particularly the constant
+flexing of the cover, and the abrasion of the road surface. Tyres
+are not stored for any long period, and, when put into service,
+have a limited period of useful life. Consequently it is needful
+to develop maximal mechanical properties, and vulcanisation
+is therefore carried further than in the manufacture of inner
+tubes.</p>
+
+<p>The rate of cure is controlled by a number of factors in
+addition to the period and temperature of vulcanisation, in
+particular by the proportion and nature of the other ingredients,
+especially sulphur and accelerators, and also by the rubber
+itself. The main complaint as regards plantation rubber is<span class='pagenum'><a name="Page_308" id="Page_308">[308]</a></span>
+that it varies excessively in this respect. This matter will not
+be discussed here, but is only introduced in order to explain
+the importance of a constant rate of vulcanising to the manufacturer.
+Plantation rubber should, therefore, be prepared
+so as to be as uniform as possible in this respect, and the earlier
+part of this book gives full details of the precautions advised,
+and in many cases adopted on the plantations. Unfortunately,
+it is impossible to secure uniformity of methods among all
+producers, even when they are Europeans, to say nothing of the
+native producers, who account for perhaps one-third of the
+output. Hence the importance of branding the rubber whenever
+possible, so that the manufacturer may identify the rubber
+he purchases. If found satisfactory, he can then secure further
+supplies from the same estate.</p>
+
+<p class='pagenum'><a name="Page_309" id="Page_309">[309]</a></p>
+
+<hr class="c25" />
+<h2><a name="Ch22" id="Ch22"></a>CHAPTER XXII</h2>
+
+<h3><i>TESTING OF PLANTATION RUBBER</i></h3>
+
+
+<p>This subject may be subdivided into (<i>a</i>) Tests on the raw
+rubber; (<i>b</i>) tests on the vulcanised rubber.</p>
+
+<p><a name="Sec22_1" id="Sec22_1"></a><a name="Sec22_2" id="Sec22_2"></a>The tests on the raw rubber may be carried out (1) on the
+sample of sheet and crepe as received. For this purpose the
+rubber is cut into a strip, which is clamped between grips and
+gradually stretched to breaking-point. The ring testing
+machine can be adapted for this purpose by replacing the
+rollers with clamps. As the thickness of the samples to be
+tested will vary, it is advisable to cut the strips of such a width
+that the cross-sectional area of all test pieces is the same&mdash;say,
+40 sq. mm. The method is applicable to both sheet
+and crepe rubber. <a name="Sec22_3" id="Sec22_3"></a>(2) Tests may be made as to the behaviour
+of the rubber during milling or mastication. Small batches
+are milled under uniform conditions, preferably in an enclosed
+masticator such as Baker and Perkins supply. The power
+taken (as measured by the current taken to drive the motor
+actuating the machine) and the time are recorded. A further
+test may be applied to the milled or masticated rubber, to
+ascertain the amount and the time taken to incorporate a
+finely divided mineral matter, such as carbon black, zinc
+oxide, or one of the refined clays.<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a
+href="#Footnote_38_38" class="fnanchor">[38]</a> The results are not very
+exact, and the difference in plasticity and dryness noted are
+usually less than found when working with full-sized machines
+in the factory. (3) The rubber, either raw or masticated, may
+be &#8220;dissolved&#8221; in a &#8220;solvent,&#8221; such as benzene, and the
+viscosity of the &#8220;solution&#8221; measured. Generally speaking,
+the less viscous the solution, the more plastic the rubber.</p>
+
+<div class="footnote"><p><a name="Footnote_38_38" id="Footnote_38_38"></a><a
+href="#FNanchor_38_38"><span class="label">[38]</span></a> Bulletin Rubber Growers&#8217; Association, January, 1921, p. 43;
+August, 1921, p. 340.</p></div>
+
+<p>The testing of vulcanised rubber has been treated in such<span class='pagenum'><a name="Page_310" id="Page_310">[310]</a></span>
+detail in the recent works of Whitby<a name="FNanchor_39_39"
+id="FNanchor_39_39"></a><a href="#Footnote_39_39" class="fnanchor">[39]</a>
+and De Vries<a name="FNanchor_40_40" id="FNanchor_40_40"></a><a href="#Footnote_40_40" class="fnanchor">[40]</a> that a
+few special points only will be dealt with here. The preparation
+of samples for testing involves first the sheeting of the
+mixture of rubber, sulphur, and other ingredients, if any. The
+sheets may be 1 to 2 mm. thick. They are soft and adherent,
+and must be kept between layers of calico to prevent adhesion.
+A sheet of rubber is then built up by laying three or four sheets
+evenly upon one another, and pressing together to form a
+sheet 5 mm. thick. The thick sheet is then roughly cut to
+shape and vulcanised in a mould by heating in steam under
+pressure. From the vulcanised sheet so obtained the rings
+for testing are cut (45 mm. internal diameter. 5 mm. face,
+and 4 mm. thick). Rings obtained in this manner will not
+vary in diameter or thickness (reckoned as sections of a tube),
+as these are controlled by the size of the punch, but will vary a
+little in the face, as this is controlled by the thickness of the
+sheet, which depends on the completeness with which the mould
+is closed. More recently smaller moulds have been adopted,
+one mould for each ring, and an annular space for moisture to
+develop a pressure during vulcanising and prevent porosity.
+The moulds are vulcanised in an oil bath, or oven of some
+description, in which a constant temperature is maintained.
+I have adopted for some years a third method. The principle
+is that used in the factory for making annular-shaped rubber
+articles, such as washers, rings, elastic bands, etc. An aluminium
+mandrel, 45 mm. external diameter, is taken, and the
+thin rubber sheet is wrapped round this, so as to build up a
+tube about 4 mm. thick, the surplus rubber is cut off, and the
+edge bevelled with a wet knife. The manipulation will vary
+somewhat with the type of compound to be treated; thus, in
+some cases, it is sufficient to well roll the tube with a hand
+roller to secure adhesion. In other cases it is better to wipe
+the sheet of compound with a rubber solvent previous to
+rolling. In the latter case time must be given for the solvent
+to evaporate before vulcanising. The tube is next tightly
+wrapped in wet cloth, and is then ready for the vulcaniser.<span class='pagenum'><a name="Page_311" id="Page_311">[311]</a></span>
+Or the tube may be enclosed in moulds which form an outer
+circular shell and take the place of the cloth, but for most
+purposes, and in particular for the rubber-sulphur mixing
+usually employed, it is sufficient to use cloth to obtain even
+and regular tubes. The tube, after vulcanising, is slipped on
+to a wooden mandrel and cut into rings on a lathe. Of these
+rings the internal diameter is constant, for this is formed on
+the mandrel, also the face, which can be cut accurately in the
+lathe, but the external diameter, and consequently the thickness,
+may vary a little.</p>
+
+<div class="footnote"><p><a name="Footnote_39_39" id="Footnote_39_39"></a><a
+href="#FNanchor_39_39"><span class="label">[39]</span></a> &#8220;Plantation Rubber and the Testing of Rubber.&#8221;</p></div>
+
+<div class="footnote"><p><a name="Footnote_40_40" id="Footnote_40_40"></a><a
+href="#FNanchor_40_40"><span class="label">[40]</span></a> &#8220;Estate Rubber.&#8221;</p></div>
+
+<p>It appears, therefore, that all methods result in rings of
+approximately the correct size, and it is usual to check, and, if
+necessary, make an allowance for variation in dimensions.
+It is not possible to do this, even approximately, with soft
+rubbers, as the rubber gives under the pressure of the micrometer.
+No doubt a photographic method would give more
+accurate results, but would take too long. I have found that
+a very close approximation is obtainable by weighing the rings
+as the specific gravity of the standard rubber mix is known.
+It is not necessary to weigh each ring, but the whole five or
+ten taken for testing may be weighed together.</p>
+
+<p><a name="Sec22_5" id="Sec22_5"></a><a name="Sec22_6" id="Sec22_6"></a>The next point that arises is the choice of a formula for the
+test mix. Practically all the work to date has been carried out
+on mixtures of rubber with 7 to 10 per cent. of sulphur. For
+some purposes&mdash;<i>e.g.</i>, detecting variation in rate of cure&mdash;this
+mixing is satisfactory, but for other purposes it is not. Nor
+is the behaviour of a rubber-sulphur mixing a sure guide to the
+behaviour of one containing other ingredients, such as litharge.
+Thus, two samples vulcanised satisfactorily when mixed with
+sulphur only, but one of them gave unsatisfactory results in
+the presence of litharge. It has long been recognised that
+mineral ingredients may modify the product when vulcanised,
+but the modification is not necessarily uniform. Consequently,
+tests should also be made, when practicable, with vulcanised
+rubber containing other ingredients in addition to sulphur.</p>
+
+<p><a name="Sec22_4" id="Sec22_4"></a><a name="Sec22_7" id="Sec22_7"></a>As regards physical tests on the vulcanised products, these
+usually involve determination of breaking load and elongation
+at rupture (usually recorded as final length&mdash;that is, including<span
+class='pagenum'><a name="Page_312" id="Page_312">[312]</a></span>
+the original length reckoned either as unity or as 100 units).
+Simultaneously a load-stretch curve is recorded on an autographic
+attachment. The type of curve varies with (1) state
+of cure, or degree to which the rubber is vulcanised; (2) proportion
+of sulphur and/or other ingredients; (3) specific nature of
+the rubber used. The last factor is almost negligible compared
+with the two former&mdash;at any rate for average quality rubber.
+As (2) is kept constant for any batch of tests, or even for every
+test, it follows that the load-stretch curve is mainly dependent
+on the state of cure, and the degree of vulcanising may be
+measured by comparing either the elongation produced at a
+given load or the load produced at a given elongation. Either
+set of figures is readily determined by measuring up the load-stretch
+diagram.</p>
+
+<p>The peculiar type of the curves has long been a subject of
+comment and speculation. Special properties have been attributed
+to the &#8220;slope&#8221; or inclination of the upper and approximately
+straight portion of the curve. According to the writer&#8217;s
+investigations, the &#8220;slope&#8221; is largely dependent on the degree
+of vulcanisation, so that it is difficult to &#8220;place&#8221; as an index
+of the specific nature of a rubber.<a name="FNanchor_41_41" id="FNanchor_41_41"></a><a
+href="#Footnote_41_41" class="fnanchor">[41]</a> Moreover, it has recently
+been shown that the peculiar type of curve given by vulcanised
+rubber is the result of plotting the load against the sectional
+area of the unstretched test piece, whereas this area decreases
+progressively as the test piece stretches. If this decrease be
+allowed for, the curve obtained is an equilateral hyperbola.<a name="FNanchor_42_42"
+id="FNanchor_42_42"></a><a href="#Footnote_42_42" class="fnanchor">[42]</a>
+Preliminary experiments with rubber compounded with large
+proportions of finely divided mineral matter, such as carbon
+black, show that the load-stretch curves obtained autographically
+are likewise reducible to equilateral hyperbol&aelig;.</p>
+
+<div class="footnote"><p><a name="Footnote_41_41" id="Footnote_41_41"></a><a
+href="#FNanchor_41_41"><span class="label">[41]</span></a> Bulletin R.G.A., October, 1921, p. 397.</p></div>
+
+<div class="footnote"><p><a name="Footnote_42_42" id="Footnote_42_42"></a><a
+href="#FNanchor_42_42"><span class="label">[42]</span></a> <i>Hatschek Journal Soc. Chem. Ind.</i> 1921; <i>Trans.</i>, p. 251.</p></div>
+
+
+<p class='pagenum'><a name="Page_313" id="Page_313">[313]</a></p>
+<hr class="c25" />
+<h2><a name="Ch23" id="Ch23"></a>CHAPTER XXIII</h2>
+
+<h3><i>THE PROPERTIES OF RUBBER</i></h3>
+
+
+<p>This section, like the last, is divisible into two subsections.
+The first deals with <a href="#Sec23_1">raw rubber</a>, the second with <a href="#Sec23_3">vulcanised
+rubber</a>.</p>
+
+<p><a name="Sec23_1" id="Sec23_1"></a><a name="Sec23_2" id="Sec23_2"></a>We have already explained that, until recently, rubber was not
+used in the unvulcanised condition, but that the excellent
+physical properties of plantation rubber have made this
+possible. It is interesting to compare the physical properties
+of raw rubber with that vulcanised with sulphur. A compact
+sample of crepe as received from the East will give breaking
+strain of over 30 kilos per sq. cm. and over 300 per cent. elongation.
+When mixed with sulphur and vulcanised, a breaking
+strain of 150 kilos and elongation of 1,000 per cent. are not
+unusual. It is possible that crepe rubber would give higher
+figures if it could be prepared in the form of a compact ring,
+as used for tests on vulcanised rubber. In any case, the
+figures for vulcanised rubber are much in excess of those
+for raw crepe rubber. It must also be remembered that a
+breaking strain of 150 kilos is not permanent with vulcanised
+rubber, for reasons which will be explained later.<a name="FNanchor_43_43"
+id="FNanchor_43_43"></a><a href="#Footnote_43_43" class="fnanchor">[43]</a> To obtain
+a reasonably permanent vulcanised product, the vulcanisation
+would not be carried further than to give a figure of 100 kilos.
+On the other hand, raw rubber is remarkable on account of its
+great permanency, although subject to some physical changes
+at ordinary atmospheric temperatures. Tensile tests, although
+valuable, do not tell us all about the physical properties of a
+sample of rubber. Abrasion tests, or tests designed to measure
+resistance to wear and tear, would be more valuable, but, unfortunately,
+these properties do not lend themselves to simple<span class='pagenum'><a name="Page_314" id="Page_314">[314]</a></span>
+tests. There are grounds for believing that raw rubber is
+superior in some respects to fully vulcanised rubber, if prepared
+without the addition of finely divided mineral substances which
+exert a toughening effect.</p>
+
+<div class="footnote"><p><a name="Footnote_43_43" id="Footnote_43_43"></a><a
+href="#FNanchor_43_43"><span class="label">[43]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1916, p. 872.</p></div>
+
+<p>Sheet rubber gives results in some ways inferior to compact
+crepe rubber when subjected to physical tests. Tensile
+strength seldom exceeds 15 kilos, but the elongation is usually
+higher&mdash;up to 600 or 700 per cent. That is to say, it stretches
+more, but breaks more easily. If, however, we take into consideration
+the diminution in sectional area of the test piece
+during stretching, it will be seen that crepe and sheet rubber
+have compensating properties.</p>
+
+<p>As this matter of sectional area reduction during stretching
+is important, both for raw and vulcanised rubber, it may be
+briefly referred to here. When rubber is stretched, the volume
+does not appreciably alter&mdash;at any rate, as regards uncompounded
+rubber. Hence the reduction of sectional area on
+stretching bears a simple relationship to the amount of stretching.
+If we double the length of the test piece, we halve the
+sectional area; if we treble the length, we reduce it to one-third,
+and so forth. Hence, if we multiply the breaking strain by the
+final length (<i>i.e.</i>, length at break, taking the original length = 1),
+we obtain a figure, the &#8220;tensile product,&#8221; which embodies both
+breaking strain and stretching capacity. In effect it gives us
+the breaking strain calculated on the sectional area at the
+<i>moment of rupture</i> of the test piece. Adopting this formula,
+we obtain for crepe&mdash;</p>
+
+<table style="width: 50%;" summary="Formula p314-1">
+
+<tr>
+<td class="center" style="width: 25%;"><i>Tensile<br />Strength.</i></td>
+<td class="padr">&nbsp;</td>
+<td class="center" style="width: 25%;"><i>Final Length&mdash;i.e.,<br />Elongation + 1.</i></td>
+<td class="padr">&nbsp;</td>
+<td class="center" style="width: 25%;"><i>Tensile<br />Product.</i></td>
+</tr>
+
+<tr>
+<td class="center">30</td>
+<td class="center">&times;</td>
+<td class="center">4</td>
+<td class="center">=</td>
+<td class="center">120</td>
+</tr>
+
+</table>
+
+<p>and for smoked sheet</p>
+
+<table style="width: 50%;" summary="Formula p314-2">
+
+<tr>
+<td class="center" style="width: 25%;">15</td>
+<td class="center">&times;</td>
+<td class="center" style="width: 25%;">8</td>
+<td class="center">=</td>
+<td class="center" style="width: 25%;">120</td>
+</tr>
+
+</table>
+
+<p>The difference in properties between crepe and sheet may
+probably be attributed to the heavier rolling of the crepe;
+which compacts the rubber. But if the crepe is rolled too much,
+the tensile strength falls, and there is no increased elongation
+to compensate. For the same reason, crepe which has been<span class='pagenum'><a name="Page_315" id="Page_315">[315]</a></span>
+rerolled in this country is inferior to crepe as received direct
+from the plantation. At the most it is permissible to unite
+two or three layers of thin crepe to a thicker one by a single
+passage through even speed rollers, if the physical properties
+of the original rubber are to be conserved.<a name="FNanchor_44_44"
+id="FNanchor_44_44"></a><a href="#Footnote_44_44" class="fnanchor">[44]</a></p>
+
+<div class="footnote"><p><a name="Footnote_44_44" id="Footnote_44_44"></a><a
+href="#FNanchor_44_44"><span class="label">[44]</span></a> Bulletin R.G.A., February, 1922, p. 64.</p></div>
+
+<p>Attempts to prepare crepe for use in a raw state, by rerolling
+uneven or irregular surfaced crepe in this country, only result
+in a rubber with inferior physical properties. Nor can sheet be
+rerolled to give crepe of good physical properties. The power
+required to break down the sheet and the heat developed,
+even on cold rollers, are an indication of physical properties
+destroyed. For subsequent vulcanisation this is not a matter
+of importance, because the vulcanising process restores to the
+rubber the properties which are lost in the process of rolling
+and milling or mastication.</p>
+
+<p>Raw rubber has been used to some extent for proofing
+purposes, as for the manufacture of material for hoods of
+motor-cars. In this case no attempt is made to preserve the
+physical properties. The rubber is masticated, mixed, taken
+up with solvent and spread on the cloth exactly as if it were to
+be vulcanised.</p>
+
+<p><a name="Sec23_3" id="Sec23_3"></a><a name="Sec23_4" id="Sec23_4"></a><span
+class="smcap">Vulcanised Rubber.</span>&mdash;We have already explained that the
+properties of vulcanised rubber are dependent, to some extent,
+on the specific nature of the raw rubber, or what De Vries
+terms the &#8220;inner qualities.&#8221; That is to say, differences appear
+on vulcanising which are not apparent from the tests made on
+the raw rubber. Indeed, no investigation or analysis of the
+raw rubber can enable one to foresee exactly how the rubber
+will behave on vulcanisation. This illustrates the deficiency
+in our knowledge of vulcanisation. When dealing with soft,
+resinous, or decomposed rubbers, it is safe to anticipate a weak
+vulcanised product; but when we come to deal with a number
+of samples of &#8220;standard&#8221; crepe or sheet&mdash;<i>i.e.</i>, sheet or crepe
+passing a certain standard of appearance&mdash;it is found that
+differences in vulcanising properties cannot be foreseen. This
+matter is, however, not so great a drawback as might be imagined,
+for reasonably well prepared consignments of standard crepe or<span class='pagenum'><a name="Page_316" id="Page_316">[316]</a></span>
+sheet differ but little from one another, and the difference is
+mainly in the ease with which they break down, or the rate or
+speed with which they vulcanise, and not with the properties
+of the vulcanised product. Many of the plantation scrap grades
+are equal to or nearly equal to &#8220;standard&#8220;; but some of these,
+as also the rubber produced by native holders, show appreciable
+variation, and are the source of most of the complaints which
+emanate from manufacturers. We shall consider in turn the
+different grades and the effect of the usual surface defects,
+such as mould, spots, etc.</p>
+
+<p><a name="Sec23_5" id="Sec23_5"></a><span class="smcap">Crepe Rubber.</span>&mdash;Oil marks and tackiness are the most
+serious defects from the manufacturing standpoint. In the first
+part of this book we have shown that damage caused by the
+so-called oil marks is not due to the oil, but to traces of copper
+from the bearings of the machines. There are several metallic
+compounds which cause deterioration of rubber both raw and
+vulcanised, but copper is the most deadly, and rubber showing
+signs of deterioration is rightly rejected by the manufacturers.</p>
+
+<p>The only other defect of crepe rubber which has any bearing
+on its use in manufacture is mould. Crepe rubber very seldom
+shows the ordinary surface moulds not uncommon in sheet-rubber.
+There are, however, microscopic growths which
+cause the development of coloured spots referred to in detail
+in the earlier part of this book. The rubber hydrocarbon itself
+does not appear to be affected by the moulds, but some of the
+serum constituents are altered, with the result that the rubber
+vulcanises more slowly than it otherwise would do. For this
+reason, crepe rubber with coloured spots may give rise to
+trouble in the factory.</p>
+
+<p><span class="smcap">Sheet Rubber.</span>&mdash;The commonest defect is mould.<a
+name="FNanchor_45_45" id="FNanchor_45_45"></a><a href="#Footnote_45_45" class="fnanchor">[45]</a> This is
+usually of a light surface type, easily brushed off, and numbers of
+vulcanising tests failed to trace any reduction in rate of vulcanising
+or other defect due to this. In spite, however, of the
+harmlessness of light surface moulds, they are looked upon
+with suspicion by the manufacturer. Occasionally samples
+of smoked sheet are offered contaminated with a &#8220;heavy&#8221; type<span
+class='pagenum'><a name="Page_317" id="Page_317">[317]</a></span>
+of mould. The sheet feels damp and &#8220;heavy&#8221; or flabby,
+and contains an excess of moisture; sometimes a moist exudation
+is noticeable on the surface, and &#8220;virgin&#8221; patches are
+present. Such sheet vulcanises more slowly than F.A.Q.
+samples, but does not necessarily show other defects after
+washing and drying.</p>
+
+<div class="footnote"><p><a name="Footnote_45_45" id="Footnote_45_45"></a><a
+href="#FNanchor_45_45"><span class="label">[45]</span></a> Bulletin R.G.A., February, 1921, p. 97; April, 1921, p. 190; June,
+1921, p. 243; November, 1921, p. 472.</p></div>
+
+<p>&#8220;Stretching rusty,&#8221; as already explained, is due to a dry
+film on the surface of the sheet, and according to a recent
+investigation, this film consists, not of serum substances, but
+of a microscopic mould growth, which presumably grows on
+the serum substances. A sample of sheet which stretches
+rusty gives the rubber a &#8220;dry&#8221; appearance, and for a long
+time manufacturers mistook the surface film for resin. On
+the assumption that such rubber was &#8220;resinous&#8221; they rejected
+it, and to this day it is regarded as a defect, although it has no
+influence on the vulcanising properties of the rubber.</p>
+
+<p>It is hardly necessary to point out that defective appearance,
+such as is due to thickened edges, faint markings, bubbles, and
+so forth, have no effect on the vulcanising properties of the
+rubber. They only point to some irregularity or carelessness
+in preparation. The only justification for distinguishing
+between rubber of good and bad appearance is that the former
+bears the impress of careful preparation, and is therefore more
+likely to be uniform in rate of vulcanising.</p>
+
+<p>Similar considerations apply to the colour of smoked sheet,
+which may vary from a pale yellow-brown, through various
+shades of red-brown to dark brown. There are various factors
+affecting the colour, but the buyer can see but one&mdash;viz., the
+&#8220;degree&#8221; of smoking&mdash;and the rubber, from his point of view,
+may be undersmoked or oversmoked. No doubt the degree
+of smoking affects the vulcanising properties, but to a less
+extent than was at one time imagined. In a recent paper<a name="FNanchor_46_46"
+id="FNanchor_46_46"></a><a href="#Footnote_46_46" class="fnanchor">[46]</a>
+it has been shown that the average breaking strain and rate of
+cure of a number of samples of smoked sheets were practically
+the same for light as for dark sheets.</p>
+
+<div class="footnote"><p><a name="Footnote_46_46" id="Footnote_46_46"></a><a
+href="#FNanchor_46_46"><span class="label">[46]</span></a> Bulletin R.G.A., December, 1921, p. 521.</p></div>
+
+<p><a name="Sec23_6" id="Sec23_6"></a><span class="smcap">Variation in Physical Properties.</span>&mdash;A very large number
+of tests on vulcanised specimens of plantation rubber have been<span class='pagenum'><a name="Page_318" id="Page_318">[318]</a></span>
+carried out. The rubber was almost invariably mixed with
+7 to 10 per cent. of sulphur, and no other ingredient, and
+vulcanised to give the maximal breaking load. Unfortunately,
+this determination is subject to a very appreciable experimental
+error, so that a large number of determinations are necessary to
+give a reliable figure. It is quite impracticable to make a
+large number of determinations in routine testing, on account
+of the labour involved. It is usual to make five, or possibly
+ten, determinations, although some investigators have been
+content with two. It is generally conceded that any exceptionally
+low figures should be ignored, as probably caused by
+some flaw or irregularity in the test piece. On the other hand,
+a study of actual determinations shows an occasional excessively
+high figure, and it is questioned whether this also should
+be left out of account. Others ignore all except the highest
+figure, and take this to represent the true breaking strain.
+As a consequence, the figures published by different workers
+show considerable variation. De Vries has analysed a large
+number of the figures obtained in systematic examination of
+estate samples, and has constructed curves to illustrate the
+results.<a name="FNanchor_47_47" id="FNanchor_47_47"></a><a
+href="#Footnote_47_47" class="fnanchor">[47]</a> It is open to question how far the variations shown
+are attributable to experimental error. The figures show,
+however, that the variation in breaking strain is relatively
+small, and not very different for crepe and sheet rubber. In
+our opinion, undue importance should not be attached to very
+high or exceptionally high figures for breaking strain, which
+are occasionally met with. Provided the figure does not fall
+much below the average, the sample may be regarded as
+satisfactory. It is very seldom that any sample of first latex
+estate rubber does not show satisfactory figures.</p>
+
+<div class="footnote"><p><a name="Footnote_47_47" id="Footnote_47_47"></a><a
+href="#FNanchor_47_47"><span class="label">[47]</span></a> &#8220;Estate Rubber,&#8221; p. 466.</p></div>
+
+<p><a name="Sec23_7" id="Sec23_7"></a><span class="smcap">The Rate of Cure or Rate of Vulcanisation</span> is subject
+to more exact measurement, whether this be based on the
+physical or the chemical properties of the rubber. If the
+testing machine be provided, as is usual, with an autographic
+attachment, the position of the curves traced on the recording
+paper gives a measurement of the rate of cure. These load-stretch
+curves, to which reference has already been made,<span class='pagenum'><a name="Page_319" id="Page_319">[319]</a></span>
+take up a definite position in accordance with the physical
+properties; it is only the length of the curve, or the point where
+it terminates (which gives the breaking strain and elongation
+at break), which is largely fortuitous.</p>
+
+<p>As a measure of rate of cure we may take the actual measurements
+made on the record.<a name="FNanchor_48_48" id="FNanchor_48_48"></a><a
+href="#Footnote_48_48" class="fnanchor">[48]</a> It is convenient to measure the
+elongation produced by a load of 130 kilos per sq. cm., as all
+fully vulcanised rings of soft rubber should give higher breaking
+load figures. For less cured or weaker samples a lower figure
+may be taken, such as 60 kilos. We have found that when
+fully vulcanised to give the maximal breaking strain, the elongation
+at a load of 130 kilos is in the neighbourhood of 850 per
+cent. (final length 950 per cent.). This applies to ordinary
+samples of estate rubber under the conditions of testing
+indicated above. If, however, the proportion of sulphur be
+considerably reduced, or mineral ingredients in a fine state
+of division be added to the mixing, or accelerators, whether
+organic or inorganic, be employed, the above relationship no
+longer holds. Nor does it hold with regard to plantation
+rubber prepared in an exceptional manner, as, for instance,
+matured coagulum or &#8220;slab.&#8221;</p>
+
+<div class="footnote"><p><a name="Footnote_48_48" id="Footnote_48_48"></a><a
+href="#FNanchor_48_48"><span class="label">[48]</span></a> Bulletin R.G.A., June, 1921, p. 246.</p></div>
+
+<p>There is a second method of determining the rate of cure&mdash;namely,
+by analysing a vulcanisate produced under standard
+conditions, and determining the amount of sulphur which has
+entered into chemical combination with the rubber. For this
+purpose the weighed sample is cut thin or creped thin, and
+exhaustively extracted with acetone to remove any &#8220;free&#8221;
+sulphur&mdash;that is, sulphur not in combination with the rubber.
+The sulphur remaining is then determined and calculated as
+a percentage of the raw rubber contained in the sample taken.
+This gives the so-called coefficient of vulcanisation.</p>
+
+<p>If we compare the coefficient with the time of cure at a
+constant temperature for an ordinary sample of plantation
+rubber, they are found to be approximately proportional, so
+long as the sulphur is in sufficient excess. The amount of
+combined sulphur is, therefore, an index of the time vulcanisation
+has been in progress (under standard conditions of<span class='pagenum'><a name="Page_320" id="Page_320">[320]</a></span>
+temperature, etc.), and, therefore, the coefficient is a measure
+of the rate of cure.</p>
+
+<p>The change in position of the load-stretch curve is not
+directly proportional to the time of heating, and it therefore
+follows that it is also not directly proportional to the coefficient.
+For ordinary samples of crepe and sheet the relationship is,
+however, not very far removed from proportionality. This
+applies particularly to sheet rubber. The relationship is readily
+seen on plotting one against the other and tracing the curves.
+For sheet we get an almost straight line; for crepe there is
+some curvature.<a name="FNanchor_49_49" id="FNanchor_49_49"></a><a href="#Footnote_49_49"
+class="fnanchor">[49]</a> For ordinary estate samples of sheet and
+crepe rubber the maximal breaking strain is obtained when the
+coefficient reaches approximately five units, so that this corresponds
+to the elongation of 850 per cent. at a load of 130 kilos.</p>
+
+<div class="footnote"><p><a name="Footnote_49_49" id="Footnote_49_49"></a><a
+href="#FNanchor_49_49"><span class="label">[49]</span></a> Bulletin R.G.A., June, 1921, p. 246, October, 1921, p. 398.</p></div>
+
+<p>Either physical or chemical methods may, therefore, be used
+for determining the rate of cure of ordinary sheet or crepe
+rubber, but great care must be taken when interpreting the
+results obtained with rubber prepared in an unusual manner.
+The rate of cure may be expressed in terms of the time taken
+to vulcanise the rubber at a constant temperature (in our case
+138&deg; C.), so as to give an elongation of 850 per cent. at a load
+of 130 kilos, or to give a coefficient of five units. The higher
+the figure so obtained, the slower curing the rubber. To
+express the results more directly as rate of cure, we have adopted
+the plan of taking an average crepe rubber, calling the rate of
+cure 100 units, and expressing the rate of cure of other samples
+in these terms. Thus, a sample which gave a coefficient of
+four only, in the time taken by the standard to give a coefficient
+of five, would have a rate of cure four-fifths of the standard,
+that is, 80; or if a sample takes only two hours to give an elongation
+of 850 per cent., whereas the standard takes three hours,
+the rate of cure of the sample will be <span class="enum">3</span>&#8260;<span
+class="denom">2</span> of standard or 150.<a name="FNanchor_50_50"
+id="FNanchor_50_50"></a><a href="#Footnote_50_50" class="fnanchor">[50]</a></p>
+
+<div class="footnote"><p><a name="Footnote_50_50" id="Footnote_50_50"></a><a
+href="#FNanchor_50_50"><span class="label">[50]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1918, p. 280.</p></div>
+
+<p>As stated, the coefficient is approximately directly proportional
+to the time of cure; it is also independent of the proportion
+of sulphur, if in fair excess, and in the presence of inert
+ingredients. It is also independent of the amount of mastication<span class='pagenum'><a name="Page_321" id="Page_321">[321]</a></span>
+given to the original raw rubber, however great. On
+the other hand, the position of the load-stretch curve is variously
+modified by these factors&mdash;in some respects, therefore, the
+coefficient is a more reliable index. However, the coefficient
+is influenced by accelerators, so that here also great care must
+be exercised when interpreting results. For the purpose of
+detecting variations in rate of cure, it is best to choose a mixing
+which is particularly sensitive. In the first place, there must
+be an ample excess of sulphur; and in the second place, no
+ingredient should be added which will complicate the load-stretch
+curves, and no accelerators should be present which
+may possibly tend to obscure the vulcanising properties of
+the rubber itself. It has been found, therefore, that the best
+mixing to use consists of rubber with an excess of sulphur&mdash;say,
+in the proportion 9:1 without other ingredients. The rate of
+cure of a specimen of plantation rubber is attributed to the
+presence of certain natural vulcanising catalysts, because it is
+found that carefully purified raw rubber (that is, with the
+resinous and nitrogenous constituents removed) vulcanises
+very slowly or hardly at all, but that on replacing the extracted
+matter the rate of vulcanising is restored. The natural catalysts
+contained in the extracted matter are influenced to a varying
+degree by some of the common ingredients of manufactured
+rubber articles. This applies particularly to litharge (oxide
+of lead), to which reference has already been made. Thus,
+acetone extraction of raw rubber to remove resinous matter has
+but little effect on the vulcanising properties of a mixture of
+rubber and sulphur. But if litharge be a constituent, it is
+found that acetone-extracted rubber will hardly vulcanise at all.
+From this, it follows that a rubber giving a low acetone extract
+may be found to vulcanise exceptionally slowly in a mixing containing
+litharge, whereas it shows no such defect when compounded
+with sulphur only.<a name="FNanchor_51_51" id="FNanchor_51_51"></a><a
+href="#Footnote_51_51" class="fnanchor">[51]</a> Litharge is used to a very large
+extent, as it has a balancing effect in a rubber compound&mdash;that
+is to say, it allows of appreciable variation in vulcanising conditions,
+without corresponding alteration in the state of cure.<a name="FNanchor_52_52"
+id="FNanchor_52_52"></a><a href="#Footnote_52_52" class="fnanchor">[52]</a></p>
+
+<div class="footnote"><p><a name="Footnote_51_51" id="Footnote_51_51"></a><a
+href="#FNanchor_51_51"><span class="label">[51]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1916, p. 874.</p></div>
+
+<div class="footnote"><p><a name="Footnote_52_52" id="Footnote_52_52"></a><a
+href="#FNanchor_52_52"><span class="label">[52]</span></a> <i>Ibid.</i>, 1915, p. 524.</p></div>
+
+<p><a name="Sec23_8" id="Sec23_8"></a><span class='pagenum'><a name="Page_322" id="Page_322">[322]</a></span><span
+class="smcap">Influence of Various Factors in Raw Rubber Preparation
+on the &#8220;Rate of Cure,&#8221; or &#8220;Rate of Vulcanisation.&#8221;</span>&mdash;As
+the capacity of a rubber for vulcanisation depends on the
+presence of small quantities of accessory substances in the
+serum which act as catalysts, the rate of vulcanisation (or
+curing) will depend on the nature and quantity of such substances
+present in the rubber. A very small quantity of these
+substances has a considerable influence on rate of vulcanising,
+and as the substances are difficult to isolate and identify, our
+knowledge of their formation and chemical nature is not as
+definite as is desirable. Substances have been isolated having
+the characteristics of &#8220;simpler bases.&#8221; Bodies of this class
+are formed by putrefaction of organic matter, and can be
+separated in much larger quantity from coagulated latex, which
+has been allowed to putrefy before working up than from
+such which has been worked up without giving time for an
+appreciable amount of putrefaction to take place. Further,
+rubber from putrefied coagulum vulcanised much faster than
+that ordinarily prepared, so that we are justified in connecting
+the putrefaction bases with the rate of vulcanisation. Moreover,
+it has been shown that any treatment of the latex or
+coagulum which inhibits the development of putrefactive
+organisms also prevents the rubber vulcanising as fast as would
+otherwise have been the case.<a name="FNanchor_53_53" id="FNanchor_53_53"></a><a
+href="#Footnote_53_53" class="fnanchor">[53]</a> Also, the crude bases isolated
+from fast vulcanising rubber have the power of increasing
+the rate of vulcanisation when added to ordinary slow vulcanising
+rubber.<a name="FNanchor_54_54" id="FNanchor_54_54"></a><a href="#Footnote_54_54" class="fnanchor">[54]</a></p>
+
+<div class="footnote"><p><a name="Footnote_53_53" id="Footnote_53_53"></a><a
+href="#FNanchor_53_53"><span class="label">[53]</span></a> Eaton and Co-workers: See Bulletin No. 27, F.M.S. Department
+of Agriculture.</p></div>
+
+<div class="footnote"><p><a name="Footnote_54_54" id="Footnote_54_54"></a><a
+href="#FNanchor_54_54"><span class="label">[54]</span></a> <i>Journal Soc. Chem. Ind.</i>, 1917, p. 365.</p></div>
+
+<p>On the other hand, there are one or two facts which are
+difficult although not impossible to fit in with theory. Thus,
+although the putrefaction bases are very easily soluble in water
+and acetone, they cannot be removed by washing on the creping
+rollers, or by acetone extraction. This may be due to the power
+of colloidal substances to retain other crystalloidal substances,
+such as the bases, which, in consequence, cannot be washed out.
+A parallel case is the retention of small quantities of water<span class='pagenum'><a name="Page_323" id="Page_323">[323]</a></span>
+soluble substances in the soil. Also, the theory does not explain
+why rubber obtained by evaporation of latex at relatively high
+temperatures is fast vulcanising, although the possibility of
+putrefaction is excluded.</p>
+
+<p>As regards practical results, it follows that the rate of vulcanisation
+(or cure) of a sample of rubber will depend on the
+time allowed to elapse between the collection of the latex and
+treatment till the rubber is dry, as also on atmospheric conditions.
+Thus, slow drying will result in an increased rate of
+cure, for it gives an opportunity for putrefactive organisms to
+play a part. The results will, however, be influenced by the
+extent to which the rubber was washed previous to hanging,
+and so forth. Smoking is an antiseptic process and will,
+therefore, tend to inhibit the action of micro-organisms and
+produce a slower vulcanising rubber. On the other hand,
+sheet contains more serum than crepe, so that there is more
+food material for growth of micro-organisms. The net result
+is to give a rubber (sheet) which usually vulcanises a little
+faster than crepe.</p>
+
+<p>Among other factors controlling the rate of cure, special
+mention should be made of the nature and amount of coagulants.
+Weak &#8220;organic&#8221; acids, such as acetic, lactic, tartaric,
+etc., used in the minimal proportions (1 to 1,200 of standardised
+latex in the case of acetic acid), give the fastest vulcanising
+rubber; &#8220;strong&#8221; mineral acids, such as sulphuric acid, even
+when used in the minimal proportions (1 to 2,000), yield slower
+vulcanising rubber. Acid salts, such as alum, are intermediate
+in effect. Increased proportions of coagulant cause a reduction
+in rate of vulcanising with all coagulants, and the effect is
+least noticeable in crepe rubber, intermediate in sheet rubber,
+and most pronounced in &#8220;slab&#8221; rubber (discussed below).<a
+name="FNanchor_55_55" id="FNanchor_55_55"></a><a href="#Footnote_55_55" class="fnanchor">[55]</a></p>
+
+<div class="footnote"><p><a name="Footnote_55_55" id="Footnote_55_55"></a><a
+href="#FNanchor_55_55"><span class="label">[55]</span></a> Bulletin R.G.A., July, 1919, p. 39; September, 1920, p. 343;
+November, 1920, p. 433; October, 1921, p. 393; March, 1922, p. 134.</p></div>
+
+<p><a name="Sec23_9" id="Sec23_9"></a><span class="smcap">Other Types of Plantation Rubber.</span>&mdash;We have up to now
+confined our attention to ordinary thin air-dried crepe and
+smoked sheet, as almost all plantation rubber is now marketed
+in one or other of these two forms. There are, however, other
+types, to which reference has been made. Of these, the most<span class='pagenum'><a name="Page_324" id="Page_324">[324]</a></span>
+important is the thick blanket crepe, made chiefly in Ceylon
+by rolling together thin crepe, which has been artificially dried
+(Colombo drier or vacuum drier). The heat of the driers causes
+a surface stickiness, which is got rid of by rolling several thin
+layers together to give one thick one. This rubber vulcanises
+at about the same rate as ordinary thin crepe, for the relatively
+high temperature of drying does not appear to influence the
+rate of cure. The rubber is generally softer than air-dried
+crepe, and is easily &#8220;let down&#8221; in naphtha; it is, therefore,
+suitable for some solution work. Generally speaking, the
+properties of blanket crepe do not differ materially from ordinary
+thin crepe. Another type of rubber seldom met with is
+matured slab or crepe, prepared from it. This type of rubber
+is being made in small quantities on one or two estates, who
+supply direct to the manufacturer. The method of preparation
+has already been described. It is unsuitable for sale in
+the open market, as it contains a variable amount of moisture,
+has the various surface defects such as slime, mould, and &#8220;rust,&#8221;
+and there is the additional disadvantage that it is not easy to
+judge of its cleanliness or freedom from coarse impurities by
+inspection. If the slab rubber be creped and air-dried on the
+spot, the product is of satisfactory appearance, except that it
+is of low colour and may be streaked. As the crepe so produced
+vulcanises almost as fast as the original slab, the crepe
+embodies all the advantages of a fast curing rubber with few
+of the disadvantages of the slab itself. We have made experiments
+from time to time, and found that by a judicious use of
+sodium bisulphite it is possible to produce a fast vulcanising
+crepe rubber sufficiently even and light in colour to satisfy
+the Standards Committee.</p>
+
+<p>A fast curing raw rubber is not necessarily a desirable type
+for all manufacturing purposes. In the vulcanising of large
+masses of rubber, a slower rather than a faster vulcanising rubber
+may be desirable, so as to give ample time for the heat to penetrate
+and spread evenly throughout the mass. But for many
+purposes a fast curing rubber enables a larger output to be
+obtained, so that artificial organic accelerators are coming
+more and more into use. The addition of such accelerators<span class='pagenum'><a name="Page_325" id="Page_325">[325]</a></span>
+might be obviated, if a suitable fast curing rubber were available,
+but it is essential that such rubber should be uniform. It is
+just in this respect that slab rubber or crepe made therefrom
+is found to be deficient.<a name="FNanchor_56_56" id="FNanchor_56_56"></a><a
+href="#Footnote_56_56" class="fnanchor">[56]</a> The rate of cure depends on the functions
+of wild bacteria, which are naturally sensitive to changes
+of conditions, such as temperature, etc. The coagulated
+rubber depends on chance circumstances for infection, and, as
+a natural result, the activity of the bacteria and the nature and
+amounts of active vulcanising agent produced will vary and
+be difficult to control. Consequently, the rate of cure of slab
+rubber shows considerably greater variation than ordinary
+crepe or sheet.<a name="FNanchor_57_57" id="FNanchor_57_57"></a><a
+href="#Footnote_57_57" class="fnanchor">[57]</a> This, in our opinion, is the main difficulty
+of utilising &#8220;slab,&#8221; or crepe prepared from it. Experience
+in other industries, using micro-organisms, has shown that
+the only method of control has been to replace the wild growths
+by cultures of some particular strain, as, for instance, in yeasts
+for brewing. To control the rate of cure of slab, it might be
+possible to use a special culture for the purpose.</p>
+
+<div class="footnote"><p><a name="Footnote_56_56" id="Footnote_56_56"></a><a
+href="#FNanchor_56_56"><span class="label">[56]</span></a> Bulletin R.G.A., January, 1920, p. 6; January, 1921, p. 47.</p></div>
+
+<div class="footnote"><p><a name="Footnote_57_57" id="Footnote_57_57"></a><a
+href="#FNanchor_57_57"><span class="label">[57]</span></a> <i>Ibid.</i>, January, 1920, p. 68.</p></div>
+
+<p>Other less usual methods of preparation, referred to in the
+earlier part of this book, do not call for particular mention, as
+the properties of the rubber do not differ much from ordinary
+sheet or crepe. It is mainly a matter of variation in rate of cure.</p>
+
+<p><a name="Sec23_10" id="Sec23_10"></a>This short account of the vulcanising properties of plantation
+rubber would not be complete without a reference to Fine Hard
+Para, the premier rubber of the Amazon. This rubber has
+come to be regarded as the standard high-grade product with
+which plantation rubber may be compared, and many manufacturers
+are still of the opinion that it is unsurpassed by any
+plantation product. Yet, when subjected to the ordinary
+vulcanising tests, we find that samples of Fine Hard Para give
+figures very similar to average plantation rubber; indeed, it is
+not difficult to find specimens of plantation rubber which give
+appreciably higher figures on testing. It is claimed, however,
+that Fine Para is more uniform than plantation rubber,
+and can be relied on always to give the same results. Yet
+tests on a series of Fine Hard Para specimens gave variations in<span class='pagenum'><a name="Page_326" id="Page_326">[326]</a></span>
+rate of cure similar to those found for plantation. Some figures
+were published, which tended to show that the variation was
+smaller for Fine Para, but it turned out that each of the samples
+taken for examination consisted actually of a number of slices
+cut from different balls, so that greater uniformity was not unexpected.<a
+name="FNanchor_58_58" id="FNanchor_58_58"></a><a href="#Footnote_58_58" class="fnanchor">[58]</a>
+The superiority of Fine Para is, therefore, somewhat
+of a mystery. It is probable that some manufacturers prefer
+to use it because they feel safer with it, and know actually
+how it will behave from long experience. In one respect
+Fine Para is possibly superior to most plantation rubber&mdash;that
+is, for the preparation of raw rubber solution for sticking the
+seams of waterproof garments, and for similar purposes. The
+method of preparation may well influence the strength of the
+raw rubber when used for this purpose. Plantation rubber
+has been prepared in the same manner as Brazilian Para, in
+particular on an estate in Java. The product resembles Brazilian
+Para in appearance. Vulcanising tests gave satisfactory
+figures, but, as already stated, this would not serve to show that
+the rubber was equal to Brazilian Para from the manufacturer&#8217;s
+standpoint.</p>
+
+<div class="footnote"><p><a name="Footnote_58_58" id="Footnote_58_58"></a><a
+href="#FNanchor_58_58"><span class="label">[58]</span></a> Bulletin R.G.A., September, 1920, p. 347.</p></div>
+
+
+<p class='pagenum'><a name="Page_327" id="Page_327">[327]</a></p>
+<hr class="c25" />
+<h2><a name="INDEX" id="INDEX"></a>INDEX</h2>
+
+<table summary="Index">
+
+<tr>
+<td class="left">Acetic acid,</td>
+<td class="right"><a href="#Page_74">74</a>, <a href="#Page_279">279</a></td>
+</tr>
+
+<tr>
+<td class="left">Acid, acetic,</td>
+<td class="right"><a href="#Page_74">74</a>, <a href="#Page_279">279</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, carbonic, gas,</td>
+<td class="right"><a href="#Page_289">289</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, formic,</td>
+<td class="right"><a href="#Page_279">279</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, hydrochloric,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, hydrofluoric,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, mixing, with latex,</td>
+<td class="right"><a href="#Page_79">79</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, nitric,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, oxalic,</td>
+<td class="right"><a href="#Page_279">279</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, pyroligneous,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, quantity of,</td>
+<td class="right"><a href="#Page_76">76</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, sulphuric,</td>
+<td class="right"><a href="#Page_279">279</a>, <a href="#Page_286">286</a></td>
+</tr>
+
+<tr>
+<td class="left">Acids for coagulation, effect of, on rate of cure,</td>
+<td class="right"><a href="#Page_323">323</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, quantities necessary for modern requirements,</td>
+<td class="right"><a href="#Page_78">78</a></td>
+</tr>
+
+<tr>
+<td class="left">Air-drying, aids to normal,</td>
+<td class="right"><a href="#Page_143">143</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, of crepe, rate of,</td>
+<td class="right"><a href="#Page_138">138</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, progress of,</td>
+<td class="right"><a href="#Page_140">140</a></td>
+</tr>
+
+<tr>
+<td class="left">Alcohol, coagulation with,</td>
+<td class="right"><a href="#Page_289">289</a></td>
+</tr>
+
+<tr>
+<td class="left">Alum, coagulation with,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td class="left">Anti-coagulant for transport,</td>
+<td class="right"><a href="#Page_61">61</a></td>
+</tr>
+
+<tr>
+<td class="left">Anti-coagulants,</td>
+<td class="right"><a href="#Page_46">46</a></td>
+</tr>
+
+<tr>
+<td class="left">Artificial driers,</td>
+<td class="right"><a href="#Page_133">133</a>, <a href="#Page_148">148</a></td>
+</tr>
+
+<tr>
+<td class="left">Ash on sheet,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">Assembling cases for shipment,</td>
+<td class="right"><a href="#Page_156">156</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Bags for packing,</td>
+<td class="right"><a href="#Page_154">154</a></td>
+</tr>
+
+<tr>
+<td class="left">Bakau,</td>
+<td class="right"><a href="#Page_147">147</a></td>
+</tr>
+
+<tr>
+<td class="left">Bales for packing,</td>
+<td class="right"><a href="#Page_154">154</a></td>
+</tr>
+
+<tr>
+<td class="left">Bark in crepe,</td>
+<td class="right"><a href="#Page_232">232</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; shavings,</td>
+<td class="right"><a href="#Page_56">56</a>, <a href="#Page_123">123</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; sheet,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">Bases in vulcanised rubber,</td>
+<td class="right"><a href="#Page_322">322</a></td>
+</tr>
+
+<tr>
+<td class="left">Basket plants,</td>
+<td class="right"><a href="#Page_10">10</a></td>
+</tr>
+
+<tr>
+<td class="left">Blanket crepe, properties of,</td>
+<td class="right"><a href="#Page_324">324</a></td>
+</tr>
+
+<tr>
+<td class="left">Blemishes of surface,</td>
+<td class="right"><a href="#Page_252">252</a></td>
+</tr>
+
+<tr>
+<td class="left">Blister in sheet,</td>
+<td class="right"><a href="#Page_272">272</a></td>
+</tr>
+
+<tr>
+<td class="left">Block rubber,</td>
+<td class="right"><a href="#Page_129">129</a>, <a href="#Page_246">246</a></td>
+</tr>
+
+<tr>
+<td class="left">Breaking down of rubber,</td>
+<td class="right"><a href="#Page_304">304</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; load of test piece,</td>
+<td class="right"><a href="#Page_311">311</a></td>
+</tr>
+
+<tr>
+<td class="left">Bubbles in sheet,</td>
+<td class="right"><a href="#Page_269">269</a></td>
+</tr>
+
+<tr>
+<td class="left">Buildings,</td>
+<td class="right"><a href="#Page_159">159</a></td>
+</tr>
+
+<tr>
+<td class="left">Bulking latex,</td>
+<td class="right"><a href="#Page_69">69</a></td>
+</tr>
+
+<tr>
+<td class="left">Byrne curing process,</td>
+<td class="right"><a href="#Page_270">270</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Calendered sheet,</td>
+<td class="right"><a href="#Page_304">304</a></td>
+</tr>
+
+<tr>
+<td class="left">Carbon dioxide,</td>
+<td class="right"><a href="#Page_289">289</a></td>
+</tr>
+
+<tr>
+<td class="left">Carbonic acid gas,</td>
+<td class="right"><a href="#Page_289">289</a></td>
+</tr>
+
+<tr>
+<td class="left">Cases, choice of, for packing,</td>
+<td class="right"><a href="#Page_153">153</a></td>
+</tr>
+
+<tr>
+<td class="left">Catalysts, natural, in rubber,</td>
+<td class="right"><a href="#Page_312">312</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, vulcanising,</td>
+<td class="right"><a href="#Page_312">312</a></td>
+</tr>
+
+<tr>
+<td class="left">Centralisation of factories,</td>
+<td class="right"><a href="#Page_221">221</a></td>
+</tr>
+
+<tr>
+<td class="left">Chinese vinegar,</td>
+<td class="right"><a href="#Page_286">286</a></td>
+</tr>
+
+<tr>
+<td class="left">Chinosol,</td>
+<td class="right"><a href="#Page_238">238</a></td>
+</tr>
+
+<tr>
+<td class="left">&#8220;Chula&#8221; drier,</td>
+<td class="right"><a href="#Page_148">148</a></td>
+</tr>
+
+<tr>
+<td class="left">Clippings, sheet,</td>
+<td class="right"><a href="#Page_275">275</a></td>
+</tr>
+
+<tr>
+<td class="left">Coagulant,</td>
+<td class="right"><a href="#Page_111">111</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, choice of,</td>
+<td class="right"><a href="#Page_74">74</a>, <a href="#Page_278">278</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, quantity of,</td>
+<td class="right"><a href="#Page_113">113</a></td>
+</tr>
+
+<tr>
+<td class="left">Coagulation,</td>
+<td class="right"><a href="#Page_74">74</a>, <a href="#Page_111">111</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; centres,</td>
+<td class="right"><a href="#Page_62">62</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, premature,</td>
+<td class="right"><a href="#Page_46">46</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, spontaneous,</td>
+<td class="right"><a href="#Page_294">294</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; with alcohol,</td>
+<td class="right"><a href="#Page_289">289</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; sugars,</td>
+<td class="right"><a href="#Page_287">287</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; various salts,</td>
+<td class="right"><a href="#Page_288">288</a></td>
+</tr>
+
+<tr>
+<td class="left">Coagulum, soft,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, spongy undersurface of,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, tearing of,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, transport of,</td>
+<td class="right"><a href="#Page_59">59</a>, <a href="#Page_63">63</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, working of,</td>
+<td class="right"><a href="#Page_103">103</a></td>
+</tr>
+
+<tr>
+<td class="left">Coefficient of vulcanisation,</td>
+<td class="right"><a href="#Page_319">319</a></td>
+</tr>
+
+<tr>
+<td class="left">Collecting latex,</td>
+<td class="right"><a href="#Page_38">38</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; pails,</td>
+<td class="right"><a href="#Page_48">48</a></td>
+</tr>
+
+<tr>
+<td class="left">Collection, advantages of early,</td>
+<td class="right"><a href="#Page_60">60</a></td>
+</tr>
+
+<tr>
+<td class="left">Combustion, rate of, in smoke house,</td>
+<td class="right"><a href="#Page_191">191</a></td>
+</tr>
+
+<tr>
+<td class="left">Compound crepes,</td>
+<td class="right"><a href="#Page_126">126</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; No. 1,</td>
+<td class="right"><a href="#Page_151">151</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; No. 2,</td>
+<td class="right"><a href="#Page_151">151</a></td>
+</tr>
+
+<tr>
+<td class="left">Contents of cases, weight of,</td>
+<td class="right"><a href="#Page_156">156</a></td>
+</tr>
+
+<tr>
+<td class="left">Copper salts, cause of tackiness,</td>
+<td class="right"><a href="#Page_243">243</a></td>
+</tr>
+
+<tr>
+<td class="left">Cotton fibre in crepe,</td>
+<td class="right"><a href="#Page_230">230</a></td>
+</tr>
+
+<tr>
+<td class="left">Creosotic substances,</td>
+<td class="right"><a href="#Page_146">146</a></td>
+</tr>
+
+<tr>
+<td class="left">Crepe, air-drying of,</td>
+<td class="right"><a href="#Page_132">132</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bark in,</td>
+<td class="right"><a href="#Page_232">232</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bearing of defects in, on manufacture,</td>
+<td class="right"><a href="#Page_316">316</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bisulphite streaks in,</td>
+<td class="right"><a href="#Page_235">235</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, colour of fine,</td>
+<td class="right"><a href="#Page_114">114</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, dirt in,</td>
+<td class="right"><a href="#Page_227">227</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, dirty edges of,</td>
+<td class="right"><a href="#Page_225">225</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, drying houses for,</td>
+<td class="right"><a href="#Page_178">178</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, fibre in,</td>
+<td class="right"><a href="#Page_230">230</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, general style of finish,</td>
+<td class="right"><a href="#Page_223">223</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, grades of,</td>
+<td class="right"><a href="#Page_150">150</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, greenish, tacky streaks in,</td>
+<td class="right"><a href="#Page_228">228</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, iron stains on,</td>
+<td class="right"><a href="#Page_225">225</a></td>
+</tr>
+
+<tr>
+<td class="left"><span class='pagenum'><a name="Page_328" id="Page_328">[328]</a></span>Crepe, No. 1 fine pale,</td>
+<td class="right"><a href="#Page_110">110</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, oil marks on,</td>
+<td class="right"><a href="#Page_226">226</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, oxidation streaks in,</td>
+<td class="right"><a href="#Page_234">234</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, rate of air-drying of,</td>
+<td class="right"><a href="#Page_138">138</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, rust stains on,</td>
+<td class="right"><a href="#Page_226">226</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, smoked,</td>
+<td class="right"><a href="#Page_130">130</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, surface moulds on,</td>
+<td class="right"><a href="#Page_241">241</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, weight increased in drying house,</td>
+<td class="right"><a href="#Page_141">141</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, yellow latex streaks in,</td>
+<td class="right"><a href="#Page_234">234</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; rubber, defects in,</td>
+<td class="right"><a href="#Page_223">223</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, lower grades of,</td>
+<td class="right"><a href="#Page_120">120</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, preparation of,</td>
+<td class="right"><a href="#Page_110">110</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, tensile strength of,</td>
+<td class="right"><a href="#Page_313">313</a></td>
+</tr>
+
+<tr>
+<td class="left">Cups, cleaning,</td>
+<td class="right"><a href="#Page_40">40</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, water in,</td>
+<td class="right"><a href="#Page_44">44</a></td>
+</tr>
+
+<tr>
+<td class="left">Cure, rate of,</td>
+<td class="right"><a href="#Page_318">318</a></td>
+</tr>
+
+<tr>
+<td class="left">Curing,</td>
+<td class="right"><a href="#Page_307">307</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Da Costa process,</td>
+<td class="right"><a href="#Page_290">290</a></td>
+</tr>
+
+<tr>
+<td class="left">Decentralisation of factories,</td>
+<td class="right"><a href="#Page_221">221</a></td>
+</tr>
+
+<tr>
+<td class="left">Defects of sheet, infrequent,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">Derry process,</td>
+<td class="right"><a href="#Page_293">293</a></td>
+</tr>
+
+<tr>
+<td class="left">Designs and &#8220;layout&#8221; of tanks,</td>
+<td class="right"><a href="#Page_176">176</a></td>
+</tr>
+
+<tr>
+<td class="left">Dirt in sheet,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">Discoloration of rubber, dark,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">Drains for tanks,</td>
+<td class="right"><a href="#Page_176">176</a></td>
+</tr>
+
+<tr>
+<td class="left">Drier, Colombo Commercial Company&#8217;s,</td>
+<td class="right"><a href="#Page_136">136</a></td>
+</tr>
+
+<tr>
+<td class="left">Driers, artificial&mdash;for crepe rubber,</td>
+<td class="right"><a href="#Page_133">133</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, for sheet rubber,</td>
+<td class="right"><a href="#Page_148">148</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, &#8220;Chula,&#8221;</td>
+<td class="right"><a href="#Page_148">148</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, vacuum,</td>
+<td class="right"><a href="#Page_134">134</a></td>
+</tr>
+
+<tr>
+<td class="left">Drum furnaces, horizontal,</td>
+<td class="right"><a href="#Page_189">189</a></td>
+</tr>
+
+<tr>
+<td class="left">Drying chamber, floor of,</td>
+<td class="right"><a href="#Page_187">187</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, arrangements of,</td>
+<td class="right"><a href="#Page_186">186</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; houses for crepe,</td>
+<td class="right"><a href="#Page_178">178</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, hot air,</td>
+<td class="right"><a href="#Page_182">182</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, ventilation of,</td>
+<td class="right"><a href="#Page_185">185</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, windows of,</td>
+<td class="right"><a href="#Page_185">185</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; of rubber,</td>
+<td class="right"><a href="#Page_132">132</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, period of,</td>
+<td class="right"><a href="#Page_145">145</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, rate of, effect on rate of cure,</td>
+<td class="right"><a href="#Page_323">323</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Earth scrap,</td>
+<td class="right"><a href="#Page_124">124</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, collection of,</td>
+<td class="right"><a href="#Page_58">58</a></td>
+</tr>
+
+<tr>
+<td class="left">Edges, thickened, after rolling,</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">Elongation of test piece,</td>
+<td class="right"><a href="#Page_311">311</a></td>
+</tr>
+
+<tr>
+<td class="left">Ends, thickened, after rolling,</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">Engines,</td>
+<td class="right"><a href="#Page_170">170</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, position of,</td>
+<td class="right"><a href="#Page_174">174</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Factories,</td>
+<td class="right"><a href="#Page_172">172</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, centralisation of,</td>
+<td class="right"><a href="#Page_221">221</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, decentralisation of,</td>
+<td class="right"><a href="#Page_221">221</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, number of floors,</td>
+<td class="right"><a href="#Page_174">174</a>, <a href="#Page_178">178</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, ventilation of,</td>
+<td class="right"><a href="#Page_180">180</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, windows of,</td>
+<td class="right"><a href="#Page_181">181</a></td>
+</tr>
+
+<tr>
+<td class="left">Factory buildings, situation of,</td>
+<td class="right"><a href="#Page_216">216</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, choosing site for,</td>
+<td class="right"><a href="#Page_220">220</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, ideal arrangement of,</td>
+<td class="right"><a href="#Page_162">162</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; operation,</td>
+<td class="right"><a href="#Page_65">65</a></td>
+</tr>
+
+<tr>
+<td class="left">Fibre cotton, in crepe,</td>
+<td class="right"><a href="#Page_230">230</a></td>
+</tr>
+
+<tr>
+<td class="left">Field maintenance,</td>
+<td class="right"><a href="#Page_13">13</a></td>
+</tr>
+
+<tr>
+<td class="left">Fine hard Para properties of,</td>
+<td class="right"><a href="#Page_325">325</a></td>
+</tr>
+
+<tr>
+<td class="left">First latex and other grades, percentage of,</td>
+<td class="right"><a href="#Page_59">59</a></td>
+</tr>
+
+<tr>
+<td class="left">Floor of drying chamber,</td>
+<td class="right"><a href="#Page_187">187</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; factories,</td>
+<td class="right"><a href="#Page_173">173</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; furnace room,</td>
+<td class="right"><a href="#Page_196">196</a></td>
+</tr>
+
+<tr>
+<td class="left">Formalin,</td>
+<td class="right"><a href="#Page_87">87</a></td>
+</tr>
+
+<tr>
+<td class="left">Formic acid,</td>
+<td class="right"><a href="#Page_74">74</a>, <a href="#Page_279">279</a></td>
+</tr>
+
+<tr>
+<td class="left">Formula for test mix,</td>
+<td class="right"><a href="#Page_311">311</a></td>
+</tr>
+
+<tr>
+<td class="left">Freezing (coagulation) process,</td>
+<td class="right"><a href="#Page_293">293</a></td>
+</tr>
+
+<tr>
+<td class="left">Fuel, consumption of,</td>
+<td class="right"><a href="#Page_196">196</a></td>
+</tr>
+
+<tr>
+<td class="left">Fuels for smoking,</td>
+<td class="right"><a href="#Page_146">146</a></td>
+</tr>
+
+<tr>
+<td class="left">Furnace room, floor of,</td>
+<td class="right"><a href="#Page_196">196</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, Petaling type of,</td>
+<td class="right"><a href="#Page_192">192</a></td>
+</tr>
+
+<tr>
+<td class="left">Furnaces, horizontal drum,</td>
+<td class="right"><a href="#Page_189">189</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, &#8220;pot,&#8221;</td>
+<td class="right"><a href="#Page_188">188</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Germination,</td>
+<td class="right"><a href="#Page_6">6</a></td>
+</tr>
+
+<tr>
+<td class="left">Grades, number of,</td>
+<td class="right"><a href="#Page_151">151</a></td>
+</tr>
+
+<tr>
+<td class="left">Grading,</td>
+<td class="right"><a href="#Page_150">150</a></td>
+</tr>
+
+<tr>
+<td class="left">Grafting,</td>
+<td class="right"><a href="#Page_8">8</a></td>
+</tr>
+
+<tr>
+<td class="left">Grass squares,</td>
+<td class="right"><a href="#Page_14">14</a></td>
+</tr>
+
+<tr>
+<td class="left">Greasiness before smoking,</td>
+<td class="right"><a href="#Page_252">252</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; of surface,</td>
+<td class="right"><a href="#Page_258">258</a></td>
+</tr>
+
+<tr>
+<td class="left">Grit in crepe,</td>
+<td class="right"><a href="#Page_232">232</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Hand rolling sheets,</td>
+<td class="right"><a href="#Page_104">104</a></td>
+</tr>
+
+<tr>
+<td class="left">Hevea Brasiliensis,</td>
+<td class="right"><a href="#Page_1">1</a></td>
+</tr>
+
+<tr>
+<td class="left">Hot air drying houses,</td>
+<td class="right"><a href="#Page_182">182</a></td>
+</tr>
+
+<tr>
+<td class="left">Hydrochloric acid,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td class="left">Hydrofluoric acid,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Ilcken-Down process,</td>
+<td class="right"><a href="#Page_298">298</a></td>
+</tr>
+
+<tr>
+<td class="left">Instruments, method of using,</td>
+<td class="right"><a href="#Page_100">100</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, recording,</td>
+<td class="right"><a href="#Page_144">144</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, standardising,</td>
+<td class="right"><a href="#Page_98">98</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Lallang, eradication of,</td>
+<td class="right"><a href="#Page_15">15</a></td>
+</tr>
+
+<tr>
+<td class="left">Latex, bulking,</td>
+<td class="right"><a href="#Page_69">69</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; cups, choice of,</td>
+<td class="right"><a href="#Page_40">40</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, decomposition of, in the field,</td>
+<td class="right"><a href="#Page_270">270</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, first and other grades, percentage of,</td>
+<td class="right"><a href="#Page_59">59</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, first quality,</td>
+<td class="right"><a href="#Page_150">150</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, mixing acid with,</td>
+<td class="right"><a href="#Page_79">79</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, mixing sodium bisulphite solution with,</td>
+<td class="right"><a href="#Page_117">117</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, preliminary treatment of,</td>
+<td class="right"><a href="#Page_65">65</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, reception of, at the store,</td>
+<td class="right"><a href="#Page_65">65</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, standard,</td>
+<td class="right"><a href="#Page_96">96</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, standardisation of,</td>
+<td class="right"><a href="#Page_69">69</a>, <a href="#Page_110">110</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, straining,</td>
+<td class="right"><a href="#Page_67">67</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, transport of,</td>
+<td class="right"><a href="#Page_59">59</a></td>
+</tr>
+
+<tr>
+<td class="left"><span class='pagenum'><a name="Page_329" id="Page_329">[329]</a></span>Light, importance of, in factories,</td>
+<td class="right"><a href="#Page_172">172</a></td>
+</tr>
+
+<tr>
+<td class="left">Litharge,</td>
+<td class="right"><a href="#Page_312">312</a></td>
+</tr>
+
+<tr>
+<td class="left">Load stretch curve,</td>
+<td class="right"><a href="#Page_312">312</a>, <a href="#Page_319">319</a>, <a href="#Page_320">320</a>, <a href="#Page_321">321</a></td>
+</tr>
+
+<tr>
+<td class="left">Low grade rubbers, fibrous matter in,</td>
+<td class="right"><a href="#Page_124">124</a></td>
+</tr>
+
+<tr>
+<td class="left">Lower grade rubber, care in manufacture,</td>
+<td class="right"><a href="#Page_129">129</a></td>
+</tr>
+
+<tr>
+<td class="left">Lubrication of machines,</td>
+<td class="right"><a href="#Page_166">166</a></td>
+</tr>
+
+<tr>
+<td class="left">Lump rubber, naturally coagulated,</td>
+<td class="right"><a href="#Page_120">120</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Machinery,</td>
+<td class="right"><a href="#Page_159">159</a></td>
+</tr>
+
+<tr>
+<td class="left">Machines, access to,</td>
+<td class="right"><a href="#Page_169">169</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, adequacy of,</td>
+<td class="right"><a href="#Page_160">160</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, arrangement of,</td>
+<td class="right"><a href="#Page_168">168</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, lubrication of,</td>
+<td class="right"><a href="#Page_166">166</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, position of,</td>
+<td class="right"><a href="#Page_173">173</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, sheeting,</td>
+<td class="right"><a href="#Page_166">166</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, speed of,</td>
+<td class="right"><a href="#Page_162">162</a></td>
+</tr>
+
+<tr>
+<td class="left">Mangrove,</td>
+<td class="right"><a href="#Page_147">147</a></td>
+</tr>
+
+<tr>
+<td class="left">Marking sheets,</td>
+<td class="right"><a href="#Page_105">105</a></td>
+</tr>
+
+<tr>
+<td class="left">Metrolac,</td>
+<td class="right"><a href="#Page_98">98</a>, <a href="#Page_100">100</a></td>
+</tr>
+
+<tr>
+<td class="left">Michie-Golledge system,</td>
+<td class="right"><a href="#Page_138">138</a></td>
+</tr>
+
+<tr>
+<td class="left">Mildew on surface,</td>
+<td class="right"><a href="#Page_260">260</a></td>
+</tr>
+
+<tr>
+<td class="left">Milky residue on serum,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">Mixing acid with latex,</td>
+<td class="right"><a href="#Page_79">79</a></td>
+</tr>
+
+<tr>
+<td class="left">Moist glaze of surface,</td>
+<td class="right"><a href="#Page_258">258</a></td>
+</tr>
+
+<tr>
+<td class="left">Mould on surface,</td>
+<td class="right"><a href="#Page_260">260</a></td>
+</tr>
+
+<tr>
+<td class="left">Moulds, surface, on crepe,</td>
+<td class="right"><a href="#Page_241">241</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Natural catalysts,</td>
+<td class="right"><a href="#Page_312">312</a></td>
+</tr>
+
+<tr>
+<td class="left">Nitric acid,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td class="left">Nurseries,</td>
+<td class="right"><a href="#Page_9">9</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Overcured,</td>
+<td class="right"><a href="#Page_307">307</a></td>
+</tr>
+
+<tr>
+<td class="left">Overvulcanised,</td>
+<td class="right"><a href="#Page_306">306</a></td>
+</tr>
+
+<tr>
+<td class="left">Oxalic acid,</td>
+<td class="right"><a href="#Page_279">279</a></td>
+</tr>
+
+<tr>
+<td class="left">Oxidation, prevention of,</td>
+<td class="right"><a href="#Page_56">56</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, variation due to,</td>
+<td class="right"><a href="#Page_254">254</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Packing,</td>
+<td class="right"><a href="#Page_150">150</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bags for,</td>
+<td class="right"><a href="#Page_154">154</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bales for,</td>
+<td class="right"><a href="#Page_154">154</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, cases, choice of,</td>
+<td class="right"><a href="#Page_153">153</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, folding for,</td>
+<td class="right"><a href="#Page_155">155</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, methods of,</td>
+<td class="right"><a href="#Page_156">156</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, rooms,</td>
+<td class="right"><a href="#Page_211">211</a></td>
+</tr>
+
+<tr>
+<td class="left">Pale crepe, No. 1 fine,</td>
+<td class="right"><a href="#Page_110">110</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, rubber, former methods of making,</td>
+<td class="right"><a href="#Page_118">118</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, sheet,</td>
+<td class="right"><a href="#Page_89">89</a></td>
+</tr>
+
+<tr>
+<td class="left">Patches,</td>
+<td class="right"><a href="#Page_259">259</a>, <a href="#Page_260">260</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, virgin,</td>
+<td class="right"><a href="#Page_259">259</a></td>
+</tr>
+
+<tr>
+<td class="left">Payment by result,</td>
+<td class="right"><a href="#Page_53">53</a></td>
+</tr>
+
+<tr>
+<td class="left">Perished rubber,</td>
+<td class="right"><a href="#Page_306">306</a></td>
+</tr>
+
+<tr>
+<td class="left">Physical properties of rubber, variation of,</td>
+<td class="right"><a href="#Page_317">317</a></td>
+</tr>
+
+<tr>
+<td class="left">Pits for smoke houses,</td>
+<td class="right"><a href="#Page_188">188</a></td>
+</tr>
+
+<tr>
+<td class="left">Pitting of surface,</td>
+<td class="right"><a href="#Page_250">250</a></td>
+</tr>
+
+<tr>
+<td class="left">Plantation rubber, testing of,</td>
+<td class="right"><a href="#Page_309">309</a></td>
+</tr>
+
+<tr>
+<td class="left">Planting,</td>
+<td class="right"><a href="#Page_1">1</a></td>
+</tr>
+
+<tr>
+<td class="left">Plasticising of rubber,</td>
+<td class="right"><a href="#Page_304">304</a></td>
+</tr>
+
+<tr>
+<td class="left">Plasticity of plantation rubber,</td>
+<td class="right"><a href="#Page_309">309</a></td>
+</tr>
+
+<tr>
+<td class="left">&#8220;Pot&#8221; furnaces,</td>
+<td class="right"><a href="#Page_188">188</a></td>
+</tr>
+
+<tr>
+<td class="left">Power units,</td>
+<td class="right"><a href="#Page_170">170</a></td>
+</tr>
+
+<tr>
+<td class="left">Premature coagulation,</td>
+<td class="right"><a href="#Page_46">46</a></td>
+</tr>
+
+<tr>
+<td class="left">Preparation, special methods of,</td>
+<td class="right"><a href="#Page_290">290</a></td>
+</tr>
+
+<tr>
+<td class="left">Pyroligneous acid,</td>
+<td class="right"><a href="#Page_282">282</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Racks,</td>
+<td class="right"><a href="#Page_186">186</a></td>
+</tr>
+
+<tr>
+<td class="left">Rate of cure,</td>
+<td class="right"><a href="#Page_307">307</a></td>
+</tr>
+
+<tr>
+<td class="left">Raw rubber, physical properties of,</td>
+<td class="right"><a href="#Page_313">313</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, tests on,</td>
+<td class="right"><a href="#Page_309">309</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, uses of,</td>
+<td class="right"><a href="#Page_315">315</a></td>
+</tr>
+
+<tr>
+<td class="left">Recommendations, Rubber Growers&#8217; Association,</td>
+<td class="right"><a href="#Page_152">152</a></td>
+</tr>
+
+<tr>
+<td class="left">Recording instruments,</td>
+<td class="right"><a href="#Page_144">144</a></td>
+</tr>
+
+<tr>
+<td class="left">Ribbing of sheet,</td>
+<td class="right"><a href="#Page_274">274</a></td>
+</tr>
+
+<tr>
+<td class="left">Rolling,</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">Rolls, grooving of,</td>
+<td class="right"><a href="#Page_164">164</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; running hot,</td>
+<td class="right"><a href="#Page_165">165</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; &#8220;free,&#8221;</td>
+<td class="right"><a href="#Page_165">165</a></td>
+</tr>
+
+<tr>
+<td class="left">Roof of smoke house,</td>
+<td class="right"><a href="#Page_197">197</a></td>
+</tr>
+
+<tr>
+<td class="left">Rubber, drying of,</td>
+<td class="right"><a href="#Page_132">132</a></td>
+</tr>
+
+<tr>
+<td class="left">Rubber Growers&#8217; Association, Recommendations,</td>
+<td class="right"><a href="#Page_152">152</a></td>
+</tr>
+
+<tr>
+<td class="left">Rubber, properties of,</td>
+<td class="right"><a href="#Page_313">313</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, smoking,</td>
+<td class="right"><a href="#Page_109">109</a></td>
+</tr>
+
+<tr>
+<td class="left">Rust, cause of,</td>
+<td class="right"><a href="#Page_267">267</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; on sheet,</td>
+<td class="right"><a href="#Page_262">262</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, treatment to prevent,</td>
+<td class="right"><a href="#Page_265">265</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Scrap washers,</td>
+<td class="right"><a href="#Page_57">57</a>, <a href="#Page_124">124</a></td>
+</tr>
+
+<tr>
+<td class="left">Screw plug, unsatisfactory,</td>
+<td class="right"><a href="#Page_73">73</a></td>
+</tr>
+
+<tr>
+<td class="left">Seed at stake,</td>
+<td class="right"><a href="#Page_10">10</a></td>
+</tr>
+
+<tr>
+<td class="left">Seeds,</td>
+<td class="right"><a href="#Page_2">2</a></td>
+</tr>
+
+<tr>
+<td class="left">Selection,</td>
+<td class="right"><a href="#Page_5">5</a></td>
+</tr>
+
+<tr>
+<td class="left">Senang folder,</td>
+<td class="right"><a href="#Page_156">156</a></td>
+</tr>
+
+<tr>
+<td class="left">Serum, milky residue on,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">Sheet, ash on,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bark in,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bearing of defects on, in manufacture,</td>
+<td class="right"><a href="#Page_316">316</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, blisters in,</td>
+<td class="right"><a href="#Page_272">272</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, bubbles in,</td>
+<td class="right"><a href="#Page_269">269</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, clippings,</td>
+<td class="right"><a href="#Page_130">130</a>, <a href="#Page_275">275</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, creases in,</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, dirt in,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, &#8220;dog ears,&#8221;</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, grades of,</td>
+<td class="right"><a href="#Page_151">151</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, infrequent defects of,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, pale,</td>
+<td class="right"><a href="#Page_89">89</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, ribbing of,</td>
+<td class="right"><a href="#Page_274">274</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; rubber, artificial driers for,</td>
+<td class="right"><a href="#Page_148">148</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, defects in,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, preparation of,</td>
+<td class="right"><a href="#Page_89">89</a></td>
+</tr>
+
+<tr>
+<td class="left"><span class='pagenum'><a name="Page_330" id="Page_330">[330]</a></span>Sheet rubber, rolling and marking of,</td>
+<td class="right"><a href="#Page_102">102</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, tensile strength of,</td>
+<td class="right"><a href="#Page_313">313</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, rust on,</td>
+<td class="right"><a href="#Page_262">262</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, splinters in,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, stickiness in,</td>
+<td class="right"><a href="#Page_274">274</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, style of,</td>
+<td class="right"><a href="#Page_101">101</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, support marks on,</td>
+<td class="right"><a href="#Page_273">273</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, surface pattern of,</td>
+<td class="right"><a href="#Page_274">274</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, thick ends of,</td>
+<td class="right"><a href="#Page_275">275</a></td>
+</tr>
+
+<tr>
+<td class="left">Sheeting machines,</td>
+<td class="right"><a href="#Page_166">166</a></td>
+</tr>
+
+<tr>
+<td class="left">Sheets, mis-shapen,</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, thickened patches in,</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, torn,</td>
+<td class="right"><a href="#Page_251">251</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, unevenness of appearance,</td>
+<td class="right"><a href="#Page_253">253</a></td>
+</tr>
+
+<tr>
+<td class="left">Short weights,</td>
+<td class="right"><a href="#Page_157">157</a></td>
+</tr>
+
+<tr>
+<td class="left">Skimming,</td>
+<td class="right"><a href="#Page_100">100</a></td>
+</tr>
+
+<tr>
+<td class="left">Skimmings,</td>
+<td class="right"><a href="#Page_122">122</a></td>
+</tr>
+
+<tr>
+<td class="left">Slab rubber,</td>
+<td class="right"><a href="#Page_299">299</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, properties of,</td>
+<td class="right"><a href="#Page_324">324</a></td>
+</tr>
+
+<tr>
+<td class="left">Slope,</td>
+<td class="right"><a href="#Page_312">312</a></td>
+</tr>
+
+<tr>
+<td class="left">Smoke curing of sheet rubber,</td>
+<td class="right"><a href="#Page_143">143</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, temperature of,</td>
+<td class="right"><a href="#Page_144">144</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, houses,</td>
+<td class="right"><a href="#Page_183">183</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, Barker patent,</td>
+<td class="right"><a href="#Page_209">209</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, Devon type,</td>
+<td class="right"><a href="#Page_200">200</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, iron stoves for,</td>
+<td class="right"><a href="#Page_189">189</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, Jackson type,</td>
+<td class="right"><a href="#Page_200">200</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; of brick,</td>
+<td class="right"><a href="#Page_198">198</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; rate of combustion in,</td>
+<td class="right"><a href="#Page_192">192</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, roof of,</td>
+<td class="right"><a href="#Page_197">197</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, &#8220;Third Mile&#8221; type,</td>
+<td class="right"><a href="#Page_199">199</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, types of,</td>
+<td class="right"><a href="#Page_198">198</a></td>
+</tr>
+
+<tr>
+<td class="left">Smoked crepe,</td>
+<td class="right"><a href="#Page_130">130</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; sheets, colour of,</td>
+<td class="right"><a href="#Page_255">255</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; water for coagulation,</td>
+<td class="right"><a href="#Page_286">286</a></td>
+</tr>
+
+<tr>
+<td class="left">Smoking, effect on rate of cure,</td>
+<td class="right"><a href="#Page_323">323</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, greasiness before,</td>
+<td class="right"><a href="#Page_252">252</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; rubber,</td>
+<td class="right"><a href="#Page_109">109</a></td>
+</tr>
+
+<tr>
+<td class="left">Smooth rolling of sheets,</td>
+<td class="right"><a href="#Page_104">104</a></td>
+</tr>
+
+<tr>
+<td class="left">Sodium bisulphite,</td>
+<td class="right"><a href="#Page_80">80</a>, <a href="#Page_114">114</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, abuse of,</td>
+<td class="right"><a href="#Page_85">85</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, care of,</td>
+<td class="right"><a href="#Page_116">116</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, deterioration of,</td>
+<td class="right"><a href="#Page_115">115</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, evaluation of,</td>
+<td class="right"><a href="#Page_115">115</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, making a solution of,</td>
+<td class="right"><a href="#Page_85">85</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, quantity of,</td>
+<td class="right"><a href="#Page_84">84</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, residual traces of,</td>
+<td class="right"><a href="#Page_86">86</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; solution, mixing, with latex,</td>
+<td class="right"><a href="#Page_117">117</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; sulphite,</td>
+<td class="right"><a href="#Page_86">86</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, deterioration of,</td>
+<td class="right"><a href="#Page_115">115</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, evaluation of,</td>
+<td class="right"><a href="#Page_115">115</a></td>
+</tr>
+
+<tr>
+<td class="left">Sorting,</td>
+<td class="right"><a href="#Page_150">150</a>, <a href="#Page_152">152</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; rooms,</td>
+<td class="right"><a href="#Page_211">211</a></td>
+</tr>
+
+<tr>
+<td class="left">Spewing,</td>
+<td class="right"><a href="#Page_305">305</a></td>
+</tr>
+
+<tr>
+<td class="left">Splinters in sheet,</td>
+<td class="right"><a href="#Page_276">276</a></td>
+</tr>
+
+<tr>
+<td class="left">Spontaneous coagulation,</td>
+<td class="right"><a href="#Page_294">294</a></td>
+</tr>
+
+<tr>
+<td class="left">Spot disease,</td>
+<td class="right"><a href="#Page_235">235</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash; in sheet rubber,</td>
+<td class="right"><a href="#Page_273">273</a></td>
+</tr>
+
+<tr>
+<td class="left">Spots,</td>
+<td class="right"><a href="#Page_259">259</a>, <a href="#Page_262">262</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, virgin,</td>
+<td class="right"><a href="#Page_259">259</a></td>
+</tr>
+
+<tr>
+<td class="left">Standard latex,</td>
+<td class="right"><a href="#Page_96">96</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; sheet,</td>
+<td class="right"><a href="#Page_102">102</a></td>
+</tr>
+
+<tr>
+<td class="left">Standardising instruments,</td>
+<td class="right"><a href="#Page_98">98</a></td>
+</tr>
+
+<tr>
+<td class="left">Stickiness in sheet,</td>
+<td class="right"><a href="#Page_274">274</a></td>
+</tr>
+
+<tr>
+<td class="left">Stock solution, method of making,</td>
+<td class="right"><a href="#Page_75">75</a></td>
+</tr>
+
+<tr>
+<td class="left">Storage of rubber,</td>
+<td class="right"><a href="#Page_212">212</a>, <a href="#Page_216">216</a></td>
+</tr>
+
+<tr>
+<td class="left">Stoves, iron, for smoke houses,</td>
+<td class="right"><a href="#Page_189">189</a></td>
+</tr>
+
+<tr>
+<td class="left">Straining latex,</td>
+<td class="right"><a href="#Page_67">67</a></td>
+</tr>
+
+<tr>
+<td class="left">Streaks,</td>
+<td class="right"><a href="#Page_262">262</a></td>
+</tr>
+
+<tr>
+<td class="left">Stumps,</td>
+<td class="right"><a href="#Page_9">9</a></td>
+</tr>
+
+<tr>
+<td class="left">Sugars, coagulation with,</td>
+<td class="right"><a href="#Page_287">287</a></td>
+</tr>
+
+<tr>
+<td class="left">Sulphuric acid,</td>
+<td class="right"><a href="#Page_280">280</a>, <a href="#Page_286">286</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, buying,</td>
+<td class="right"><a href="#Page_280">280</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, formula for use of,</td>
+<td class="right"><a href="#Page_280">280</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, storing,</td>
+<td class="right"><a href="#Page_280">280</a></td>
+</tr>
+
+<tr>
+<td class="left">Sun-drying sheet rubber,</td>
+<td class="right"><a href="#Page_147">147</a></td>
+</tr>
+
+<tr>
+<td class="left">Support marks on sheet,</td>
+<td class="right"><a href="#Page_273">273</a></td>
+</tr>
+
+<tr>
+<td class="left">Surface blotches, coloured,</td>
+<td class="right"><a href="#Page_249">249</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, dull or black,</td>
+<td class="right"><a href="#Page_258">258</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; pattern of sheet,</td>
+<td class="right"><a href="#Page_274">274</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Tackiness, cause of,</td>
+<td class="right"><a href="#Page_243">243</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, copper salts cause of,</td>
+<td class="right"><a href="#Page_243">243</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; in rubber,</td>
+<td class="right"><a href="#Page_242">242</a></td>
+</tr>
+
+<tr>
+<td class="left">Tanks,</td>
+<td class="right"><a href="#Page_90">90</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, care of,</td>
+<td class="right"><a href="#Page_94">94</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, designs and &#8220;layout,&#8221;</td>
+<td class="right"><a href="#Page_176">176</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, drains for,</td>
+<td class="right"><a href="#Page_176">176</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, installation of,</td>
+<td class="right"><a href="#Page_93">93</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, situation of,</td>
+<td class="right"><a href="#Page_175">175</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, water-supply for,</td>
+<td class="right"><a href="#Page_177">177</a></td>
+</tr>
+
+<tr>
+<td class="left">Tapping,</td>
+<td class="right"><a href="#Page_38">38</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, former systems of,</td>
+<td class="right"><a href="#Page_29">29</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; knives,</td>
+<td class="right"><a href="#Page_38">38</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; systems,</td>
+<td class="right"><a href="#Page_38">38</a></td>
+</tr>
+
+<tr>
+<td class="left">Tartaric acid,</td>
+<td class="right"><a href="#Page_279">279</a></td>
+</tr>
+
+<tr>
+<td class="left">Tensile product,</td>
+<td class="right"><a href="#Page_314">314</a></td>
+</tr>
+
+<tr>
+<td class="left">Test mix, formula for,</td>
+<td class="right"><a href="#Page_311">311</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; pieces, making of,</td>
+<td class="right"><a href="#Page_310">310</a></td>
+</tr>
+
+<tr>
+<td class="left">Testing of plantation rubber,</td>
+<td class="right"><a href="#Page_307">307</a></td>
+</tr>
+
+<tr>
+<td class="left">Thick ends of sheet,</td>
+<td class="right"><a href="#Page_275">275</a></td>
+</tr>
+
+<tr>
+<td class="left">Thinning,</td>
+<td class="right"><a href="#Page_19">19</a></td>
+</tr>
+
+<tr>
+<td class="left">Timber for smoking,</td>
+<td class="right"><a href="#Page_147">147</a></td>
+</tr>
+
+<tr>
+<td class="left">Tool sheds,</td>
+<td class="right"><a href="#Page_216">216</a></td>
+</tr>
+
+<tr>
+<td class="left">Transport,</td>
+<td class="right"><a href="#Page_60">60</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; by coolie,</td>
+<td class="right"><a href="#Page_62">62</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; of coagulum,</td>
+<td class="right"><a href="#Page_59">59</a>, <a href="#Page_63">63</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; of latex,</td>
+<td class="right"><a href="#Page_59">59</a></td>
+</tr>
+
+<tr>
+<td class="left">Trays,</td>
+<td class="right"><a href="#Page_167">167</a></td>
+</tr>
+
+<tr>
+<td class="left">Treatment of rubber in the factory,</td>
+<td class="right"><a href="#Page_301">301</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; to prevent rust,</td>
+<td class="right"><a href="#Page_265">265</a></td>
+</tr>
+
+<tr>
+<td class="left">Tree scrap,</td>
+<td class="right"><a href="#Page_55">55</a>, <a href="#Page_122">122</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, care of,</td>
+<td class="right"><a href="#Page_56">56</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, oxidation of,</td>
+<td class="right"><a href="#Page_56">56</a></td>
+</tr>
+
+<tr>
+<td class="left">Trees per acre,</td>
+<td class="right"><a href="#Page_26">26</a></td>
+</tr>
+
+<tr>
+<td class="left">Trenches, silt catchment,</td>
+<td class="right"><a href="#Page_11">11</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left"><span class='pagenum'><a name="Page_331" id="Page_331">[331]</a></span>Uniformity,</td>
+<td class="right"><a href="#Page_90">90</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; in colour, lack of,</td>
+<td class="right"><a href="#Page_246">246</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Vacuum driers,</td>
+<td class="right"><a href="#Page_134">134</a></td>
+</tr>
+
+<tr>
+<td class="left">Variation due to oxidation,</td>
+<td class="right"><a href="#Page_254">254</a></td>
+</tr>
+
+<tr>
+<td class="left">Vegetable extracts,</td>
+<td class="right"><a href="#Page_289">289</a></td>
+</tr>
+
+<tr>
+<td class="left">Ventilation of drying houses,</td>
+<td class="right"><a href="#Page_185">185</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; factories,</td>
+<td class="right"><a href="#Page_180">180</a></td>
+</tr>
+
+<tr>
+<td class="left">Verandas,</td>
+<td class="right"><a href="#Page_175">175</a></td>
+</tr>
+
+<tr>
+<td class="left">Virgin spots,</td>
+<td class="right"><a href="#Page_258">258</a></td>
+</tr>
+
+<tr>
+<td class="left">Viscosity of rubber solution,</td>
+<td class="right"><a href="#Page_309">309</a></td>
+</tr>
+
+<tr>
+<td class="left">Vulcanisation,</td>
+<td class="right"><a href="#Page_301">301</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, rate of,</td>
+<td class="right"><a href="#Page_318">318</a></td>
+</tr>
+
+<tr>
+<td class="left">Vulcanised rubber,</td>
+<td class="right"><a href="#Page_318">318</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; &mdash;, tests on,</td>
+<td class="right"><a href="#Page_309">309</a></td>
+</tr>
+
+<tr>
+<td class="left">Vulcanising,</td>
+<td class="right"><a href="#Page_307">307</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; catalysts,</td>
+<td class="right"><a href="#Page_312">312</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash;, &#8220;heat,&#8221;</td>
+<td class="right"><a href="#Page_306">306</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Washers, scrap,</td>
+<td class="right"><a href="#Page_57">57</a>, <a href="#Page_124">124</a></td>
+</tr>
+
+<tr>
+<td class="left">Washings,</td>
+<td class="right"><a href="#Page_122">122</a></td>
+</tr>
+
+<tr>
+<td class="left">Water-supply for tanks,</td>
+<td class="right"><a href="#Page_177">177</a></td>
+</tr>
+
+<tr>
+<td class="left">Weeding, clean,</td>
+<td class="right"><a href="#Page_13">13</a></td>
+</tr>
+
+<tr>
+<td class="left">Weights, &#8220;short,&#8221;</td>
+<td class="right"><a href="#Page_157">157</a></td>
+</tr>
+
+<tr>
+<td class="left">Wickham process,</td>
+<td class="right"><a href="#Page_293">293</a></td>
+</tr>
+
+<tr>
+<td class="left">Windows of drying houses,</td>
+<td class="right"><a href="#Page_185">185</a></td>
+</tr>
+
+<tr>
+<td class="left">&mdash; factories,</td>
+<td class="right"><a href="#Page_181">181</a></td>
+</tr>
+
+<tr>
+<td class="left">Working of rubber,</td>
+<td class="right"><a href="#Page_304">304</a></td>
+</tr>
+
+<tr>
+<td colspan="2">&nbsp;</td>
+</tr>
+
+<tr>
+<td class="left">Yields,</td>
+<td class="right"><a href="#Page_23">23</a>, <a href="#Page_25">25</a></td>
+</tr>
+
+</table>
+
+<div class="bbox">
+<p class="center">Transcriber's notes:</p>
+<ul>
+  <li>Some minor typographical and lay-out errors have been corrected.</li>
+  <li>Inconsistencies in spelling have not been corrected.</li>
+  <li>Changes made to original text:
+    <ul>
+    <li>Table of Contents:
+      <ul>
+        <li><i>Early collection of latex transport</i> changed to <i>Early collection of latex</i>&mdash;<i>Transport</i>.</li>
+        <li><i>Roof brick built houses</i> changed to <i>Roof</i>&mdash;<i>Brick built houses</i>.</li>
+        <li>Named sections in Table of Contents do not always match one-to-one with named sections in text. Links point to the
+            sections most closely resembling the description in the Table of Contents. Occasionally multiple links point to
+            the same section in the text; some named sections in the text are not mentioned in the Table of Contents.</li>
+        <li>The order of the sections under Chapters XII and XXII has been changed slightly to reflect the order of the sections
+            in the text.</li>
+      </ul>
+    </li>
+    <li><i>Tephrosia candiad</i> changed to <i>Tephrosia candida</i>.</li>
+    <li><i>Archiev</i> changed to <i>Archief</i>.</li>
+    <li><i>about <span class="enum">1</span>&#8260;<span class="denom">2</span> square</i> changed to <i>about <span
+        class="enum">1</span>&#8260;<span class="denom">2</span> inch square</i>.</li>
+    <li><i>asbesto-slate</i> changed to <i>asbestos-slate</i> as elsewhere.</li>
+    <li><i>Formaline</i> changed to <i>Formalin</i> as elsewhere.</li>
+    <li>Footnotes moved to under the paragraph they belong to.</li>
+  </ul></li>
+  <li>Page 141: <i>The lengths of crepe were weighed carefully at 8 a.m. and 4 <b>a</b>.m.</i> should probably read <i>The lengths of
+      crepe were weighed carefully at 8 a.m. and 4 <b>p</b>.m.</i></li>
+</ul>
+</div>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of The Preparation of Plantation Rubber, by 
+Sidney Morgan
+
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+</body>
+</html>
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+Project Gutenberg's The Preparation of Plantation Rubber, by Sidney Morgan
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Preparation of Plantation Rubber
+
+Author: Sidney Morgan
+
+Contributor: Henry P. Stevens
+
+Release Date: March 7, 2011 [EBook #35510]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK RUBBER ***
+
+
+
+
+Produced by Chris Curnow, Harry LamA(C), Robin Curnow and
+the Online Distributed Proofreading Team at
+http://www.pgdp.net
+
+
+
+
+
+
+
+
+
+  +----------------------------------------------------------------------+
+  |                       TRANSCRIBER'S NOTES:                           |
+  |                                                                      |
+  | * Minor typographical and lay-out errors have been corrected.        |
+  | * Inconsistencies in spelling (e.g. hyphenated vs. non-hyphenated    |
+  |   words) have not been corrected.                                    |
+  | * Italics are represented by underscores as in _text_.               |
+  | * The original book uses a V symbol to describe V-shaped cuts. These |
+  |   V symbols are represented as [V].                                  |
+  | * Changes made to original text:                                     |
+  |   * Table of Contents:                                               |
+  |     * "Early collection of latex transport" changed to "Early        |
+  |       collection of latex--Transport".                               |
+  |     * "Roof brick built houses" changed to "Roof--Brick built        |
+  |       houses".                                                       |
+  |     * The order of the sections under Chapters XII and XXII has been |
+  |       changed slightly to reflect the order of the sections in the   |
+  |       text.                                                          |
+  |   * "Tephrosia candiad" changed to "Tephrosia candida".              |
+  |   * "Archiev" changed to "Archief".                                  |
+  |   * "about 1/2 square" changed to "about 1/2 inch square".           |
+  |   * "asbesto-slate" changed to "asbestos-slate" as elsewhere.        |
+  |   * "Formaline" changed to "Formalin" as elsewhere.                  |
+  | * Footnotes moved to under the paragraph they belong to.             |
+  | * Page 141: "The lengths of crepe were weighed carefully at 8 a.m.   |
+  |   and 4 a.m." should probably read "The lengths of crepe were weighed|
+  |   carefully at 8 a.m. and 4 p.m."                                    |
+  +----------------------------------------------------------------------+
+
+
+
+
+                       THE PREPARATION OF PLANTATION
+                                   RUBBER
+
+
+
+
+                              THE PREPARATION
+                                    OF
+                             PLANTATION RUBBER
+
+                                    BY
+
+                          SIDNEY MORGAN, A.R.C.S.
+
+ VISITING AGENT FOR ESTATES IN THE EAST; FORMERLY SENIOR SCIENTIFIC OFFICER
+        AND NOW HONORARY ADVISER TO THE RUBBER GROWERS' ASSOCIATION
+                                 IN MALAYA
+
+               WITH A PREFACE AND A CHAPTER ON VULCANIZATION
+
+                                    BY
+
+      HENRY P. STEVENS, M.A. (OXON.,) PH.D., F.I.C.
+
+      CONSULTING CHEMIST TO THE RUBBER GROWERS' ASSOCIATION IN LONDON
+
+
+                           CONSTABLE & CO. LTD.
+                         LONDON : BOMBAY : SYDNEY
+                                   1922
+
+
+                        PRINTED IN GREAT BRITAIN BY
+                BILLING AND SONS, LTD., GUILDFORD AND ESHER
+
+
+
+
+PREFACE
+
+
+Mr. Sidney Morgan's work on Plantation Rubber in the East is so well known
+that he hardly needs introduction.
+
+An earlier book, published in 1914, by the Rubber Growers' Association,
+entitled "The Preparation of Plantation Rubber," was well received and
+widely read. This book dealt in a very practical manner with problems with
+which the industry had to contend. A second edition was subsequently
+published. Both editions are now out of print. The present opportunity was
+therefore taken to revise the original work, with the result that it has
+been enlarged and practically rewritten. The information given is brought
+up-to-date, and covers the whole process of production, commencing with the
+planting of the tree, passing on to the collection, coagulation, and curing
+of the rubber, and concluding with the packing for export. In the course of
+his work for the Association, Mr. Morgan carried out a great deal of
+industrial research in rubber production, including lengthy experiments on
+tapping, the use of different coagulants and different conditions of
+coagulation, and also on varying modes of rolling, drying, and smoking
+rubber. He also went very fully into the types of construction and details
+of the machinery and buildings employed on estates.
+
+Much of this valuable work has escaped notice, owing to its having been
+published in reports with limited circulation. Also a great deal of
+information was supplied to planters in a quiet and unobtrusive fashion, in
+interviews, visits to estates, and on other similar occasions. The
+knowledge and experience thus accumulated has been embodied in the present
+volume. The subject-matter should interest not only those actually engaged
+in rubber planting, but those otherwise directly or indirectly connected
+with the industry, such as importers, brokers, and particularly the rubber
+manufacturers in this country and in America. My experience has been that
+manufacturers as a whole have but a vague idea as to the methods employed
+in the preparation of plantation rubber, and this work provides them with
+the opportunity of obtaining an insight into the actual operations on the
+estates. It is most desirable that a closer bond should unite the
+plantation and manufacturing rubber industries. Such a result is best
+promoted by a better understanding of the problems with which each is
+confronted. Perhaps I may go so far as to suggest that some leading
+scientific officer in the employment of one of the large manufacturing
+concerns may take in hand a book which will give the planters the
+equivalent of information in regard to the manufacturing industry which the
+planters are now offering to the manufacturers.
+
+The photographs in the earlier part of the book will give the layman some
+conception of the enormous amount of labour that must be expended in the
+opening up, planting, trenching, and weeding the plantations which have
+replaced the virgin jungle. The authors are indebted for most of these
+photographs to Mr. H. Sutcliffe, one of the mycologists of the Rubber
+Growers' Association. The pictures of spotless coagulating tanks and tiled
+verandahs regularly hosed down will indicate the cleanliness necessary for
+the preparation of the beautifully clean sheet and crepe rubber which
+became available with the advent of plantation rubber. These results are
+largely due to the work of Sidney Morgan and his colleagues, on whom the
+planters have relied for technical guidance and advice.
+
+As regards my own contribution this is confined to a general outline of the
+subject. I have, therefore, omitted reference to a number of matters which
+would have been dealt with in detail had space permitted. The information
+given is based on researches on vulcanisation carried out for the Rubber
+Growers' Association by the writer over a period of nine or ten years. It
+was not found practicable to give detailed references in all cases. The
+reports on which the conclusions are based will, however, be found among
+the regular quarterly reports made by the writer for the Association up to
+June, 1919. Subsequent reports have been published in the Monthly Bulletin
+of the Rubber Growers' Association. We are indebted to the Association for
+permission to publish details from these reports, and also for the use made
+of numerous earlier reports published both in London and in the East.
+
+
+
+
+CONTENTS
+
+
+  PART I
+  _FIELD OPERATIONS_
+
+                                                                      PAGE
+  CHAPTER I
+  PLANTING
+
+  Seeds--Seed selection--Strain improvement by bad propagation--
+  Nurseries--Stumps--Seed at stake--Basket plants--Preparation
+  of land--Danger of disease--Clean clearing--Loss of top-soil--
+  Silt-trenches on slopes                                                1
+
+  CHAPTER II
+  FIELD MAINTENANCE
+
+  Clean weeding--Selective weeding--Loss of top-soil--Grass
+  ridges--Lallang eradication--_Mimosa gigantea_ (_M.
+  invisa_)--Green cover-plants--Connection between weeding,
+  soil conservation, and soil improvement                               13
+
+  CHAPTER III
+  THINNING OF AREAS
+
+  Original planting per acre--Ultimate stand per acre--Close-
+  planting _versus_ wide-planting--When to commence
+  thinning operations--How to select in preliminary rounds--
+  Later selections based on yields of individuals--Yields per
+  tree, present and future--Trees per acre                              19
+
+  CHAPTER IV
+  TAPPING SYSTEMS
+
+  Former methods--Former systems--Tendency to reduce number of
+  tapping cuts and frequency of tapping--Period allowed for
+  bark-renewal--Modern systems--Superimposed cuts--Single cuts,
+  etc.--Tapping experiments--R.G.A. experiment--Alternate-daily
+  _versus_ daily tapping                                                28
+
+  CHAPTER V
+  TAPPING AND COLLECTING
+
+  Tapping knives--Personal equation in use of knives--Choice of
+  latex cups--Cleaning of cups--Water in cups--Premature
+  (spontaneous) coagulation--Prevention of spontaneous
+  coagulation--The use of anti-coagulants in the field--
+  Collecting pails--Payment by result--Methods for calculation
+  of yields per coolie--Tree-scrap, oxidation of--Prevention of
+  oxidation--Bark-shavings--Collection and storage of shavings--
+  Treatment of shavings--Collection of earth-scrap                      38
+
+  CHAPTER VI
+  TRANSPORT OF LATEX AND COAGULUM
+
+  Percentages of "first" latex and other grades--Early
+  collection of latex--Transport, nature of--Light railways--
+  Motor-lorries--Bullock-carts--Care of transport vessels--Use
+  of an anti-coagulant during transport--Transport by coolie--
+  Coagulation centres (stations)--Transport of coagulum                 59
+
+
+  PART II
+  _FACTORY OPERATIONS_
+
+  CHAPTER VII
+  PRELIMINARY TREATMENT OF LATEX
+
+  Reception at store--Receptacles--Jars--Tanks--Necessity for
+  close supervision--Need for utmost cleanliness--Straining of
+  latex--Strainers--Facilitation of straining--Bulking of latex
+  --Standardised dilution of latex--Facilities for receiving and
+  handling latex--Reception verandahs--Receiving vessels--Types
+  of installations                                                      65
+
+  CHAPTER VIII
+  COAGULATION
+
+  Choice of coagulant--Strength of acid solution--Making stock
+  solution--Quantity for use--Quantities under modern
+  requirements--Care in mixing--Method of mixing with latex--Use
+  of sodium bisulphite as an anti-oxidant--Quantities for use--
+  Formulae--Abuse of the chemical--Residual traces in the dry
+  rubber--Use of sodium sulphite as an anti-coagulant,
+  quantities for use--Formulae--Use of Formalin as anti-coagulant
+  --Formulae for use                                                     74
+
+  CHAPTER IX
+  PREPARATION OF SHEET RUBBER
+
+  Pale (air-dried) sheets--Uniformity of product--Pans _versus_
+  tanks--The ideal tank--Modern installations--Care of tanks--
+  Standardised dilution of latex--Variation in dimensions and
+  density of coagulum--Standardising instruments--Method of
+  using--Skimming latex--Style of sheets--Standard sheets--
+  Rolling and marking--When to work the coagulum--Hand-rolling--
+  Power smooth-rolling--Marking rolls--Preparation for smoke-
+  curing--Caution against accumulation of wet sheets--Hot-water
+  treatment--Dripping in the open air--When to place in smoke-
+  house                                                                 89
+
+  CHAPTER X
+  PREPARATION OF CREPE RUBBER
+
+  First consideration, fine pale crepe--Standardised dilution of
+  latex--Coagulation and coagulant--Quantities of coagulant--
+  Colour of rubber--Sodium bisulphite (use of)--Evaluation and
+  deterioration of the bisulphite and sulphite of sodium--To
+  distinguish between these two chemicals--Care of sodium
+  bisulphite--Mixing solution with latex--Former methods of
+  making pale rubber--Working the coagulum--Lower grades of
+  crepe--Naturally coagulated lump--Skimmings and washings--
+  Tree-scrap--Bark-shavings--Earth-scrap--Fibrous matter in low-
+  grade rubbers--Scrap-washers--Compound crepes--Increased care
+  with lower grades--Block rubber from crepe--Smoked crepe
+  _versus_ sheet clippings                                             110
+
+  CHAPTER XI
+  DRYING OF RUBBER
+
+  Air-drying of crepes--Artificial driers for crepes--Vacuum
+  drying--Hot-air driers--Michie-Golledge system--Rate of air-
+  drying--When drying takes place--Increase in weight of drying
+  crepe--Differences in weight--Aids to normal drying--Smoke-
+  curing of sheet rubber--Instruments for recording temperature
+  --Temperatures of smoke-house--Period of drying--Fuels for
+  smoking--Sun-drying of sheet rubber--Artificial driers for
+  sheet rubber                                                         132
+
+  CHAPTER XII
+  SORTING, GRADING, AND PACKING
+
+  Reducing number of grades--Reduction carried too far--R.G.A.
+  recommendations--Care in sorting--Choice of packing cases--
+  Bags--Bales--Folding of crepe--Mechanical folders--Care in
+  assembling--Methods of packing--Weight of contents--Short
+  weights                                                              150
+
+
+  PART III
+  _MACHINERY AND BUILDINGS_
+
+  CHAPTER XIII
+  MACHINES
+
+  Quality of metal in rolls--Nature of roll-bearings--Brass
+  liners--Liners of alloy or of cast-iron--Adequacy of machines
+  --Arrangement of battery--Speed of machines--Gear ratios--
+  Grooving of rolls--Heating of rolls--Sheeting machines--
+  Lubrication--Trays--Position of battery--Drainage of battery--
+  Access to back of machines--Engines--Power                           159
+
+  CHAPTER XIV
+  FACTORIES
+
+  General construction--Plenty of light--Floors--Drainage of--
+  How many storeys--Verandahs--Tanks, situation of--Designs and
+  lay-out--Drains--Water supply                                        172
+
+  CHAPTER XV
+  OTHER BUILDINGS
+
+  Drying-houses for crepe rubber--How many storeys--Ventilation
+  --Windows--Effect of light--Effect of direct sun-rays--Hot-air
+  houses--Smoke-houses--Various types--Ordinary smoke-houses--
+  General ventilation--Windows--Racks of supports--Floors--
+  Furnaces in general--Pit-fires--Pot-fires--Iron stoves--
+  Horizontal drum-furnaces--Rate of combustion--Brick stoves--
+  Pataling type of--Consumption of fuel--Floor of furnace room--
+  Roof--Brick built houses--"Third Mile" type--Jackson cabinet--
+  Devon type--Detailed description of--Barker patent design            178
+
+  CHAPTER XVI
+  OTHER BUILDINGS (_continued_), AND SITUATION OF BUILDINGS
+
+  Sorting-room--Packing room--Store rooms--Storage of rubber--
+  Need for special accommodation--Floor of store room--Local
+  conditions--Temperature and humidity--Incidence of moulds--
+  Effect upon smoked sheets--Tool-sheds and stores--Situation of
+  buildings--Position with respect to points of the compass--
+  Choosing a factory site--Centralisation--Decentralisation            211
+
+
+  PART IV
+  _THE FINISHED RUBBER_
+
+  CHAPTER XVII
+  DEFECTS IN CREPE RUBBERS
+
+  General style of finish--Dirty edges--Iron-stains--Rust-stains
+  --Oil-marks--Trays--Dirt--Holes--Greenish and tacky streaks--
+  Not due to oil _per se_--Tackiness and copper--Cotton and
+  other fibre--Bark and grit--Sand--Oxidation streaks--Yellow
+  streaks--Bisulphite streaks--Spot disease--Cause of--Influence
+  of rate of drying--Percentage of moisture--Humidity of
+  atmosphere--Prevention of disease--Infection by contact--
+  Outbreak of dormant spores--Rules to be observed--Surface
+  moulds or mildew--Tackiness in general--Full discussion of--
+  Experimental reproduction--Lack of uniformity in colour--
+  Defects in block rubber                                              223
+
+  CHAPTER XVIII
+  DEFECTS IN SHEET RUBBER
+
+  Defective coagulation--Coloured surface blotches--General
+  darkening of surface--Soft coagulum--Spongy underface--Tearing
+  --"Pitting" of surface--Thick ends or edges--Mis-shapen sheets
+  --Thick patches--Torn sheets--"Dog-ears"--Creases--Greasiness
+  of surface before smoking--Surface blemishes--Uneven
+  appearance--Variation due to oxidation--Colour when dry--
+  Surface gloss--Dull surface--Moist glaze and greasiness--
+  Virgin spots--Surface moulds or mildew--Black streaks or spots
+  --White or grey streaks--Rust--Theories on formation of--
+  Prevention of--Two methods--Other views on causation--Bubbles
+  --Causes of formation--In the field--In the factory--Blisters
+  --"Spot" disease in sheet rubber--Support marks--Stickiness--
+  Surface pattern--Sheet clippings--Other infrequent defects--
+  Dirt--Ash--Bark--Splinters                                           249
+
+  PART V
+  _GENERAL_
+
+  CHAPTER XIX
+  CHOICE OF COAGULANT
+
+  Acetic acid in general use--Is a coagulant necessary?--Acetic
+  acid--Formic acid--Citric acid--Tartaric acid--Oxalic acid--
+  Sulphuric acid--Hydrochloric and nitric acids--Hydrofluoric
+  acid--Alum--Pyroligneous acid--Smoked water--Chinese vinegar--
+  Sulphurous acid--Sugars--Various salts--Proprietary compounds
+  --Carbonic acid gas--Alcohol--Vegetable extracts                     278
+
+  CHAPTER XX
+  SPECIAL METHODS OF PREPARATION
+
+  Da Costa process--Byrne curing process--Freezing process--
+  Wickham process--Derry process--Spontaneous coagulation--
+  Definition of--Discussion of types--AErobic--Anaerobic--
+  Organisms--Maude-Crosse patent--Method of operation--
+  Accelerating action of sugars--Accelerating action of soluble
+  calcium salts--Ilcken-Down process--Slab rubber                      290
+
+
+  PART VI
+  _VULCANISATION_
+
+  CHAPTER XXI
+  INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION
+
+  Wild rubber contrasted with plantation rubber--Milling and
+  mixing--Preparation for vulcanising--Vulcanising                     301
+
+  CHAPTER XXII
+  TESTING OF PLANTATION RUBBER
+
+  Tests on raw rubber--Breaking strain--Behaviour of rubber
+  during milling, etc.--Preparation for testing--Tests on
+  vulcanised rubber--Choice of a formula--Physical tests               309
+
+  CHAPTER XXIII
+  THE PROPERTIES OF RUBBER
+
+  Raw rubber--Physical tests--Vulcanised rubber--"Inner
+  qualities" of raw rubber--Defects of crepe and sheet--
+  Variation in physical properties--Rate of cure--Influence of
+  various factors in raw rubber on rate of cure--Other types of
+  plantation rubber--Fine para                                         313
+
+  INDEX                                                                327
+
+
+
+
+LIST OF ILLUSTRATIONS
+
+
+                                                                    PAGE
+  SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING                       2
+  FELLING LIGHT (SECONDARY) JUNGLE                                       3
+  SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED                 4
+  NEW CLEARING                                                           5
+  TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON
+    VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING                   6
+  LIGHT JUNGLE                                                           7
+  DENSE JUNGLE                                                           8
+  CLEARING READY FOR PLANTING                                            9
+  NEW CLEARING: SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING
+    DRAINED                                                             11
+  TYPICAL YOUNG CLEARING, WITH TIMBER                                   15
+  TYPICAL YOUNG CLEARING, WITH TIMBER                                   17
+  TYPICAL YOUNG PLANTED AREA                                            20
+  ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA                            21
+  WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO
+    TAPPING                                                             24
+  FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED
+    TOO LONG                                                            25
+  TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE                   31
+  THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE AND
+    ON RENEWED BARK                                                     33
+  SINGLE CUT ON HALF CIRCUMFERENCE (HALF-SPIRAL)                        35
+  A [V]-CUT ON HALF THE CIRCUMFERENCE                                   37
+  SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE                             41
+  EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING                         44
+  ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING               45
+  1. SHOWING EFFECT OF "WINTERING"                                      48
+  2. NEW GROWTH OF YOUNG LEAF ON SAME TREE                              49
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      50
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      51
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      52
+  EFFECTS OF DISEASE--"MOULDY ROT"                                      53
+  RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED WITH
+    FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER
+    COOLIE" BY SAMPLING OF LATEX                                        66
+  END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD
+    FOR RECEIVING LATEX AND FILLING TANK                                70
+  RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX                   71
+  ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH                      72
+  TWO VIEWS OF DILUTION AND MIXING TANKS                                81
+  UNIT MODERN COAGULATING TANK (TWO VIEWS)                              91
+  ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON THE
+    RIGHT                                                               92
+  CLOSER VIEW OF FOREGOING                                              93
+  ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF
+    GRAVITATING LATEX                                                   95
+  A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION             96
+  A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION
+    TANKS, RAISED, ON THE LEFT                                          97
+  THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN THE
+    FACTORY                                                            108
+  THE NEWER METHOD OF HANGING IN THE OPEN AIR                          109
+  THREE GRADES OF CREPE RUBBER                                         111
+  A WASHING SHED                                                       112
+  DRYING GRAPH. PALE CREPE (THIN)                                      140
+  A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT                 155
+  ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT                   157
+  A BATTERY OF MACHINES                                                165
+  "THIRD MILE" TYPE; HORIZONTAL DRUM                                   190
+  "THIRD MILE" TYPE OF FURNACE, USED IN CONJUNCTION WITH "THIRD
+    MILE" SMOKE-HOUSE                                                  190
+  SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE)                  193
+  PATALING TYPE OF FURNACE                                             193
+  LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED
+    VENTILATORS PERMANENTLY OPEN                                       194
+  BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE
+    BUILDING, BUT FED FROM OUTSIDE                                     195
+  GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES             196
+  NEAR VIEW OF SHELTER                                                 197
+  "THIRD MILE" TYPE OF SMOKE-HOUSE                                     199
+  GENERAL VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE                   201
+  GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND FACTORY
+    BUILDINGS                                                          202
+  VIEW OF PLATFORM OF "DEVON" SMOKE-HOUSE; DOORS OF COMPARTMENTS
+    OPEN, AND ONE RACK PARTIALLY WITHDRAWN                             203
+  DOUBLE "DEVON" SMOKE-HOUSE OF BRICK, WITH ROOF OF CHINESE
+    TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM
+    SMOKING CHAMBERS                                                   204
+  SIDE-VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL
+    ARRANGEMENT FOR STOKING FURNACES                                   205
+  FRONT VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE                     206
+  SIDE-VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE                      207
+  THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT                   210
+  SUGGESTED ARRANGEMENT OF BUILDING                                    218
+  THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM "SPOT"
+    DISEASE                                                            237
+
+
+
+
+THE PREPARATION OF PLANTATION RUBBER
+
+
+
+
+PART I
+
+FIELD OPERATIONS
+
+
+
+
+CHAPTER I
+
+_PLANTING_
+
+
+To criticise the methods of the pioneer planters of _Hevea Brasiliensis_
+presents no difficulty in the light of present comparative knowledge, and
+to be "wise after the event" is a failing which is not confined to those
+interested in modern planting methods. Looking at the matter broadly,
+however, it must be acknowledged that the pioneers, wrong though they may
+have been on some points, did remarkably well, considering that there
+existed no real knowledge on the subject and that the methods employed were
+perforce of an empirical nature. Although we know a little more concerning
+the scientific aspects of rubber planting, the sum total of that knowledge
+does not justify any drastic criticism of the methods employed by our
+predecessors. In fact, although we may be of opinion that on general lines
+there is little now to be learned regarding the planting of _Hevea
+Brasiliensis_, our present knowledge does not preclude the possibility that
+future investigations may bring against us charges similar to those
+sometimes levelled at the earlier planters.
+
+The main theme of the present volume is that of the preparation of rubber
+for the market. Hence it is not proposed to deal in detail with the work
+attaching to the opening and development of rubber estates. For this the
+reader is referred to the literature dealing specifically with rubber
+planting. Certain points in connection with planting may advantageously be
+treated in a general way according to modern knowledge, and of these it is
+proposed to discuss a few in the following pages.
+
+[Illustration: SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING.]
+
+SEEDS.--The view is now generally held that many areas were planted from
+seed which was not collected in a discriminate manner; and that probably
+the comparatively low yields obtained on areas of some estates may be due
+to the employment of seed from a poor strain. To be able to decide whether
+such explanation fits the case demands a full knowledge of all the possible
+factors governing the question of yields. It may, or may not, be a fact
+that seed from a poor strain is wholly or partially accountable for low
+yields; but whatever the degree in which the seed influences the result, it
+is an axiom that to obtain the best results in all planting industries a
+most judicious selection of seed should be made. In short, seed obtained
+from good-yielding specimens by selective treatment will eventually produce
+progeny of good-yielding strain.
+
+[Illustration: FELLING LIGHT (SECONDARY) JUNGLE.]
+
+The recognition of these principles as applied to the planting of _H.
+Brasiliensis_ has focussed recent attention upon the desirability of
+planting nurseries with seeds obtained from those trees which are known to
+be good producers of latex of normal consistency. It does not follow that
+the tree of most rapid growth and development is necessarily the best
+yielder; such is often not the case. In the matter of selection, therefore,
+one has to take other standards than that of size; and the issue is
+narrowed chiefly to a consideration of the yields of latex given by
+individual trees. It has been found by various experimenters that there is
+no necessity to proceed to such a refinement as the determination of the
+actual weight of rubber yielded. The dry rubber content of latices from the
+same trees is found to be so comparatively regular, allowing for climatic
+changes, that it is sufficient for the purposes of selection to measure the
+volumes of latex yielded by individual trees.
+
+[Illustration: SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED.]
+
+Unfortunately the industry is so young that the question of seed selection
+yet awaits study. The task presents certain practical difficulties, and
+would be by no means so easy to control as in the case of seed selection
+from other plants. It will be obvious that several generations of trees
+raised from selected seed would have to be under observation before any
+sound deductions could be made from statistics obtained in the course of
+the work. Thus the problem of seed-selection as it concerns the
+establishment of a high-yielding strain would involve many years of
+observation on the part of a trained man. Unfortunately neither the man nor
+the facilities for such experimental work exist at the present moment in
+the Federated Malay States. On the scientific side the industry is
+incommensurably staffed, and most of the workers' time is occupied with
+routine work connected with estate practice.
+
+[Illustration: NEW CLEARING.
+
+In the middle distance, felled trees awaiting burning; in the foreground, a
+flat and wet area with main drainage outlined.
+
+(_By courtesy of the manager of Membakut Estate, British North Borneo._)]
+
+[Illustration: TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON
+VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING.]
+
+SELECTION.--It is possible, however, that the question of strain
+improvement will be solved in another manner than that of successive
+breeding from the seeds of high-yielding trees. Such investigatory work is
+now occupying the attention of scientific organisations in the East, and
+credit is due to the stations in Java which have begun experimental work in
+this direction. In brief, the scheme may be outlined as follows. Trees
+known to be uniformly good yielders are kept under observation, and the
+seeds gathered carefully. These seeds are germinated in a special nursery,
+and the best-grown seedlings are selected for further operations. At a
+certain stage a bud is taken from a high-yielding parent tree and grafted
+upon the stem of the seedling. When this has "struck" the original head of
+the seedling is removed. This ensures that one has in the seedling both the
+stem and future branch system of the same strain as the parent
+high-yielding trees. It is possible to go a step farther, and by certain
+processes induce a new root system to grow above the existing roots, which
+are then removed. One is then able to guarantee that the roots, stem, and
+branches will be of the original high-yielding strain. An objection
+sometimes made against the third operation of inducing a new root system is
+that the original tap-root is removed and that the subsequent system
+consists only of laterals. Against this argument may be quoted the observed
+fact that in actual development any one of the laterals may under such
+circumstances function eventually as a tap-root.
+
+[Illustration: LIGHT JUNGLE.]
+
+On the whole, this system of propagation receives the approval of
+investigators, and removes the objections which may be advanced against the
+development of a scheme entirely founded upon successive breedings from
+selected seed. The course of the investigations, also, are thereby
+shortened considerably. Care must be exercised in the work of obtaining and
+grafting the buds, but it has now been proved that by exercising reasonable
+precautions which are not beyond the intelligence and ability of
+subordinates, an extremely high percentage of success can be attained.
+
+[Illustration: DENSE JUNGLE.]
+
+Until such time as this process becomes practicable the inception of a
+planted area must follow the lines usually adopted.
+
+NURSERIES.--The usual practice is to obtain seeds from some estate which
+has a reputation for good yields and for exercising care in the gathering
+and shipping of seeds. The seed is planted in specially prepared beds, and
+the percentage of germination noted for future reference. The plants should
+be tended carefully, and close observation made for the detection of
+disease or pests. It is not uncommon to find that owing to lack of care in
+the preparation of the seed-bed, the young plants are attacked by disease.
+
+[Illustration: CLEARING READY FOR PLANTING.
+
+Surface timber removed, but stumps remaining.]
+
+STUMPS.--At a stage, varying according to the requirements of the estate,
+when the plants are from twelve to eighteen months old, they are lifted
+from the earth. The roots and head are cut off, and the "stump" is ready
+for immediate planting in the field. Naturally any appreciable delay in
+planting, or unfavourable weather conditions, will militate against the
+chances of successful "striking"; and it is not uncommon to find that a
+certain number of "supplies" will be necessary.
+
+SEED AT STAKE.--A method sometimes adopted is to put out seed in the field,
+in prepared holes which indicate the exact position of the future trees.
+Usually three seeds are placed in each hole, and if two or three germinate,
+the plant having the healthiest appearance is retained, and the others
+removed. The possible objections to this method of planting are obvious to
+those acquainted with field conditions, but in actual practice planting
+seed "at stake" has often proved highly successful. Naturally the results
+obtained must depend upon the selection of good seeds, the care exercised
+in the preparation of the "holes," weather conditions, and the
+discrimination exercised in the selection of the plants to be
+retained--apart from such disabilities as the depredations of rats and
+other pests.
+
+BASKET PLANTS.--Yet another and perhaps the most popular method at present
+is the germination and growth of seedlings in baskets specially constructed
+for the purpose. These plants are kept under observation until of the
+required age and growth. They are then conveyed to the field, and the
+baskets are planted in prepared holes. The baskets, being of vegetable
+material, are liable to be attacked by various diseases while in the
+nursery or after planting. It is considered advisable, therefore, to treat
+them by dipping into some disinfectant such as tar, or a mixture of tar and
+one of the common proprietary disinfectants. Otherwise a disease may be
+conveyed from the basket to the seedling.
+
+PREPARATION FOR PLANTING.--There can be no other opinion than that ideally
+all land required for planting should be perfectly clear of timber of every
+description. After felling and burning, under ordinary conditions a certain
+amount of clearing is effected, but in actual practice this amounts to
+comparatively little. Big logs and stumps are left because the cost of
+clean clearing is judged to be prohibitive and non-economic. Surface timber
+is gradually cleared in the course of development, and usually large stumps
+are the last to be tackled. The objection to this procedure is really not
+strong, but unfortunately an important point is generally overlooked.
+Granted that most of the dreaded diseases travel beneath the surface of the
+ground by means of buried timber, it is plain that as far as stumps are
+concerned, the chief source of danger lies in the existence of the roots.
+If these were carefully exposed and removed, the isolated stumps would then
+not be such potential infection points. It follows from this argument that
+the importance of removing buried timber cannot be too strongly insisted
+upon. It is not uncommon to find that some years after the opening of an
+estate, and after surface timber has been removed, a large number of trees
+are affected with _Fomes lignosus_ (formerly known as _Fomes semitostus_).
+Such cases are directly attributable to the existence of buried timber, and
+no local treatment will be successful unless the whole of the area is dug
+over carefully, and all pieces of timber removed.
+
+[Illustration: NEW CLEARING; SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING
+DRAINED.
+
+(_By courtesy of manager, Membakut Estate, British North Borneo._)]
+
+SILT CATCHMENT TRENCHES.--Granted the ultimate necessity of clean clearing,
+it becomes necessary to take some precautions to prevent loss of soil by
+"wash" in young areas planted on sloping land. An argument often used in
+extenuation of the practice of allowing large surface timber to remain
+until it becomes rotten is that it is an aid in preventing loss of soil by
+wash. Its removal necessitates the institution of some method of preventing
+"wash." The establishment of terraces on steep slopes tends to the
+achievement of the desired result, but this method is not extended to more
+moderate slopes where loss by wash is still considerable. It is the opinion
+of the writers and others that the general case calls for the institution
+of silt catchment trenches, which, as the name denotes, fulfil the duty of
+catching any surface soil and of retaining rainwater. These trenches are
+usually laid out on contour, and do not exceed a length of 20 feet. They
+are usually from 18 inches to 2 feet wide and deep, and are so arranged on
+the slope that they occupy overlapping positions. The actual number of
+trenches required will depend upon the angle of slope; the steeper the
+slope the greater the number required--_i.e._, the shorter will be the
+length of slope between any two trenches. Given a clean area, it is obvious
+that the momentum acquired by running water (and hence the amount of soil
+removed) on any one slope will depend upon the distance travelled. It is
+advisable, therefore, to place a larger proportion of the trenches on the
+upper part of the slope than on the lower, so as to guard against the
+breaking down of the trench system under an abnormal downpour of rain.
+
+On land thus prepared the writer has seen areas successfully planted,
+which, under ordinary conditions, were condemned as being too steep for
+planting. It is true that these trenches necessitate continual upkeep until
+the soil becomes well shaded by trees, but the actual amount of work
+demanded in cleaning and maintaining the trenches will depend largely upon
+the thoroughness with which the original work was planned and executed.
+Whatever may be the weaknesses exposed as a result of providing an
+insufficient number of trenches of inadequate dimensions, there can be no
+question that they are a necessity.
+
+
+
+
+CHAPTER II
+
+_FIELD MAINTENANCE_
+
+
+CLEAN WEEDING.--Intimately connected with the growth and development of the
+rubber tree one has to consider the conditions under which it is allowed to
+mature. The argument has been used that, since the habitat of _Hevea
+Brasiliensis_ is in the jungle, we should be proceeding against nature by
+introducing conditions unlike those under which the "wild" rubber tree
+grows. It is difficult to treat such an argument seriously, as by quoting
+parallel instances in arboriculture it could be shown that growth,
+development, and yields are improved by cultivation of "wild" plants.
+
+It needs small experience with rubber-tree plantations to be convinced of
+the necessity for dealing with other growths, which would otherwise soon
+surround and overshadow young rubber trees.
+
+Apart from checking and preventing woody undergrowths it is considered
+advisable to keep the ground more or less free from light vegetable
+growths, which are roughly grouped under the heading of "weeds."
+
+Naturally, if these weeds are allowed to flourish and seed, their eventual
+eradication may be a matter of extreme difficulty and expense. It is the
+aim, therefore, of properly conducted estates generally to institute such a
+system of work that the weeding-gangs cover the whole estate at regular
+intervals; and, as a general rule, it may be accepted that the shorter the
+interval between successive visits by the gang to any particular area, the
+easier it is to keep weeds in check, and the cheaper the work will
+eventually be done. This procedure defines roughly what is implied by the
+term "clean weeding," and it is the policy adopted by most estates.
+
+Strict adherence to this practice in rubber cultivation has been inculcated
+by the older school of planters who obtained their experience in the
+cultivation of other crops such as tea, coffee, tobacco, etc.
+
+In latter years the wisdom of scrupulous clean weeding under all conditions
+has been questioned; and there can be no doubt that under certain special
+conditions a continuation of the policy of clean weeding is calculated to
+produce, in course of time, more harm than benefit. As an instance, the
+case might be cited of steep slopes on poor land. Continual clean weeding
+on such areas will lead eventually to a great loss of the surface soil,
+unless some precautions are adopted for catching and retaining the fine
+silt particles. It is to be noted that such a type of soil and slope, when
+the shade is appreciable, often produces no weeds heavier in growth than a
+very light grass. It is urged that the necessity for strict clean weeding
+on such soils does not exist, and, in fact, that it would be an injurious
+policy. Such arguments appear to be well founded in experience, and the
+writers are in thorough agreement that such special cases deserve special
+consideration. Rigid adherence to a policy of clean weeding, without regard
+to special conditions, would be most inadvisable.
+
+Nevertheless, such exceptional cases do not detract from the wisdom of
+clean weeding in general. Every planter of experience realises how easily
+fields become infested with weeds if the regular work is suspended or
+delayed. It is probably quite true that the harm due to the presence of
+some weeds on an occasion is negligible; but apart from this debatable
+point, there is the solid fact that if once an area is allowed to become
+weedy it may soon demand a much greater expenditure to bring it back to
+normal condition than if it had been regularly weeded. This is common
+experience, and for that reason alone a general policy of clean weeding is
+thoroughly sound; especially if combined with some system of
+silt-retention.
+
+GRASS SQUARES.--On some estates the practice of clean weeding is undertaken
+in combination with a system of silt-retention, which depends upon the
+development and maintenance of ridges. These are built up from the debris
+of weeding in the form of hollow squares. Grass is allowed to sprout and
+grow in these ridges, and when it attains a certain height it is trimmed
+down so as to keep it within bounds. The soil within the hollow square is
+clean weeded; and it is maintained that loss of soil by wash is avoided.
+Under certain conditions there is a great deal to be said in favour of the
+method, but in the opinion of the writers it should be regarded only as a
+method of expediency. It is not to be preferred to the more thorough
+practice of soil-retention by means of silt-trenches, although the latter
+method may be slightly more expensive in the end.
+
+[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER.
+
+Planted "rubber-stump" in foreground.]
+
+"LALLANG" ERADICATION.--The greatest bugbear of the planter in connection
+with weeding is the incidence of lallang. Many proposals have been put
+forward at various times for the complete eradication of this pest; but at
+present, under ordinary circumstances, there would seem to be no better
+method than by heavy and deep digging, followed by regular attention. The
+method is acknowledged to be expensive, but any half-hearted measure
+otherwise taken will eventually prove to be even more costly.
+
+One has to differentiate, of course, between the incidence of lallang
+attributable to negligence on the estate itself, and the occasional
+outbreaks near boundaries, due to seeds having been wind-borne from patches
+of lallang outside the boundaries But, in general, it would be safe to
+remark that the appearance of lallang could be taken as evidence of a
+failure to cover the area at sufficiently short intervals.
+
+As already intimated, the usual method of eradication of areas of lallang
+is by thorough digging, and the exposure of the strong root system to the
+sun. As a matter of interest it may be noted that recently some success has
+been obtained by another method[1] on areas which one may have in view for
+planting at some future date.
+
+[1] "Eradication of Lallang," W. P. Handover, _The Planter_, Vol. I., No.
+1, August, 1920.
+
+It consists in the employment of _Mimosa gigantea_, which eventually
+smothers the growth of lallang.
+
+The seeds are sown broadcast, in drills, or in pockets, amongst the
+lallang. In the course of about three months it overtops the grass and
+proceeds to travel. At this stage the whole mass is pressed down, and the
+pressing is repeated at regular intervals. Under favourable conditions, in
+about twelve months, an impenetrable mat has been formed, which gradually
+forms a good mulch. When it is desired to remove the Mimosa, the mass
+(pressed down) is cut and rolled up like a carpet. Cleared in this manner,
+the area then needs regular weeding, in order to check the development of
+any stray lallang shoots. In actual practice it was found that the cost of
+this method was approximately two-thirds that of the usual digging method.
+
+GREEN COVER PLANTS.--Some years ago it was quite common to find green
+cover-plants employed on estates with the primary idea of minimising
+weeding costs. With most of these it was found later that their value was
+not real, and that they harboured diseases, and pests. Moreover, when they
+were removed, it was often found that an abundant crop of lallang and
+weeds resulted.
+
+There can be no question that certain plants can be employed with
+advantage, not only in the control of weeds, but also by reason of benefit
+to the soil in which they are established. These plants are leguminous, and
+their use is restricted almost entirely to young areas, inasmuch as they
+will not continue to grow when shade becomes marked. Of those best known in
+modern practice might be mentioned _Tephrosia candida_ (Boga bean),
+_Centrosema Plumerii_, and _Dolichos Hoseii_ (Sarawak bean).
+
+[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER.
+
+Young rubber plants in foreground. Two of these are easily distinguishable,
+both with small crowns of leaves.]
+
+It is wrong to imagine, however, that the establishment of such leguminous
+cover-plants obviates weeding. So far is this from being the case, that in
+practice it is found that the weeding "rounds" must be conducted at first
+with the same regularity as in ordinary working, but that naturally there
+is much less work to be done.
+
+As the plants develop, they can be pruned or dug into the soil, as the case
+may be. The addition of the green material to the soil, either by digging
+or by burying in open trenches, is calculated to cause improvement in the
+condition of the soil. There may thus be a close connection between
+weeding, soil conservation, and soil improvement.
+
+
+
+
+CHAPTER III
+
+_THINNING OF AREAS_
+
+
+On this subject there is unanimity regarding the necessity for the
+operation. Divergence of opinion exists only as to a matter of degree.
+
+On the one hand there is the school of planters who would advocate the
+advisability of planting up to, say, 200 trees per acre, with subsequent
+thinning out by selection. At the other extreme there is the opinion that
+we should plant only a few more trees per acre than it is intended
+eventually to maintain, the argument being that by this method the growth
+and development of individual trees will be so much greater than in close
+planting that the necessity for drastic thinning out will not arise.
+
+Unfortunately for the latter school, a very important point is
+overlooked--viz., that size and general development are not criteria of
+yielding capacity. It might thus follow that a stand of ninety well-grown
+trees per acre might give very disappointing yields per acre. In a few
+instances this has been noted with 30 by 30 feet planting, but it is
+doubtful whether the factor influencing such results has been appreciated.
+
+The apostles of close-planting have this in their favour: that if the trees
+to be removed are selected on proper lines, it is possible to have all
+remaining trees of comparatively high-yielding strain. This is a very sound
+argument, but its practicability is limited very largely by the question of
+early growth and development. It would seem the sane course in any event
+not to plant more trees per acre than may grow normally, and without branch
+or root interference up to the fifth year (the normal first year of
+tapping).
+
+Before this stage has been reached, stunted or deformed trees will have
+been noted and removed, so that in the first year of tapping thinning
+proper can be commenced. In the past this has been effected wholly by
+selection of trees according to their general appearance and situation; but
+it is now safe to predict that future operations will be based upon sounder
+and more scientific lines.
+
+Trees will be selected for removal according to their individual yields, a
+standard which we have been advocating for years without much practical
+success. In Java and Sumatra much good work has been done in this
+direction, and recently a commencement has been made in the F.M.S.
+
+[Illustration: TYPICAL YOUNG PLANTED AREA.
+
+Heavy original jungle timber.]
+
+It is within the daily observation of all planters that certain trees
+regularly give greater yields than others, and that such trees are not to
+be distinguished by size or general development. Moreover, with slight
+variations, it has been found that a good yielding tree is consistently a
+good yielder, and the converse holds true.
+
+If, therefore, measurements of individual yields are taken at intervals,
+and the results recorded during the first year of tapping of an area, an
+excellent guide is obtained for the first round of thinning. It is found
+in actual practice that five, or even three, readings during the year are
+sufficient to give the indication required. It is not essential that
+simultaneous readings should be taken over a large area; in fact, such a
+step is really impracticable at first. The simplest method is to employ
+either--
+
+(_a_) A small uniform vessel in which the latex is measured by means of a
+thin slip of bamboo upon which graduations are marked.
+
+(_b_) A glass measure graduated regularly.
+
+[Illustration: ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA.]
+
+In both cases it is immaterial what units are represented by the
+graduations--whether cubic centimetres, quarter ounces, half-ounces, or
+ounces, as long as the unit is not too large. It is preferable to employ a
+fairly small unit, so that in taking readings from young trees a wider
+range may be obtained between poor yields and good yields. In the case of
+older trees a larger unit may be taken.
+
+The first stage in the operations is to number all trees in the field to
+be tested, and to prepare a rough register, with three or five vacant
+columns opposite each tree number.
+
+It is not advisable to commence the record of yields until the panel of
+bark has been under tapping for a month or two. It is found that an
+intelligent coolie can be taught the method of measuring and rough
+recording. The latter is accomplished by means of marks made upon the
+virgin bark of the tree above the tapped area. The marks may be made with a
+tapping knife, by means of paint, or with a lead pencil. The simplest form
+of record consists in putting one mark for each graduation of reading.
+
+In practice it is found that, commencing about an hour after the first tree
+has been tapped (in the case of young trees) and following the course taken
+by the tapper, the measurer of yields is able to do about 2 full tasks (650
+to 750 trees) per diem. Each day progress is made through the field.
+
+Obviously on such a small scale and utilising only one measuring coolie the
+comparison is restricted very much; but in any case this is immaterial as,
+owing to the personal equation of the tapper, comparison strictly should be
+limited and internal--_i.e._, it should really be confined to one task only
+at a time. In this way the worst trees in any task are indicated.
+
+The keeping of the records may be entrusted to a field clerk, but is better
+placed in the hands of a European. The register is taken into the field and
+the rough records found on the trees are noted in the columns against the
+tree number.
+
+Most planters are aware in a general way of the disparity between the
+yields of individual trees, but they would probably be surprised if they
+undertook the institution of such records.
+
+The following figures must not be taken as typical. They represent the
+average results from several tasks in a young field from which all
+ill-grown and deformed trees had been removed. It is immaterial what the
+units represent, as they are purely arbitrary and were selected for the
+purpose of obtaining a fairly wide range.
+
+Any trees which failed to yield sufficient latex to reach the first mark
+were registered at zero. The following percentages were obtained:
+
+  Zero                  3 per cent.
+  Above mark 1          6    "
+    "     "  2         16    "
+    "     "  3         42    "
+    "     "  4         12    "
+    "     "  5         14    "
+    "     "  6          6    "
+    "     "  7          0    "
+    "     "  8          1    "
+    "     "  9          0    "
+                      ---
+                      100    "
+
+It may be remarked that, judging by ordinary standards, it was impossible
+to discriminate between good yielders and others, and if thinning were to
+be done on the usual lines it is quite possible that some of the best
+yielding trees would be removed.
+
+Taking the mark No. 5 as the datum line, it will be noted that 79 per cent.
+of the trees come below and 21 per cent. above. In the latter proportion
+the majority lie close to the datum line. It will be seen that there are
+outstanding yielders even amongst these young trees, and that it would be
+possible to mark about 10 per cent. of the stand per acre at once for
+removal in the first round of thinning.
+
+In the case of old trees it is possible that one would encounter greater
+extremes of yields than those shown in the foregoing table, especially if a
+certain amount of thinning had been done previously on empirical lines.
+Sufficient has been written to show that the only reasonable basis for
+selection of trees in thinning is that of yields; and it is obvious that if
+the method be adopted the future yield per acre of any area is bound to be
+in excess of the same area as thinned on rule-of-thumb lines.
+
+YIELDS PER TREE.--A great feature is made in estate reports of the figure
+showing the average yield per tree per annum. Assuming an area to be
+yielding at the average high rate of 540 lbs. per acre per annum, with an
+average stand of ninety trees per acre, the yield per tree per annum
+averaged over all trees is 6 lbs. Keeping in mind the test-figures on a
+previous page, it will be obvious that some of these trees may have given
+very much more than 6 lbs. during the year, and some less. In view of
+present information it would not be surprising to find that a few might
+have been yielding upwards of 15 lbs. per annum. Unfortunately this
+information is only to be obtained by individual tests, and under normal
+estate conditions the facts escape notice. Cases are known in which
+out-standing individual trees have been known to yield at the rate of 25
+lbs. and more per annum.
+
+[Illustration: WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO
+TAPPING.]
+
+[Illustration: FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED
+TOO LONG.
+
+Note height and comparative lack of girth.]
+
+FUTURE YIELDS PER TREE.--It has been shown that by selective methods based
+on yields, poor trees can be eliminated. Whether by a process of
+seed-selection or by means of propagation based on bud-grafting and
+marcotting, it needs no great stretch of imagination to forecast future
+conditions under which trees may be bred which will be capable eventually
+of giving an average yield of 25 lbs. per annum over any given area.
+Yields of 1,000 lbs. per acre per annum should be obtained easily.
+
+TREES PER ACRE.--This brings us to the question as to how many trees one
+should leave to the acre after thinning operations. Figures have been given
+by various authorities, but it appears to the writer at the present time to
+be impossible to lay down a general rule. So much depends upon conditions.
+In certain cases where the soil is admittedly poor, the average growth
+below normal, and thinning has been postponed too long, the writer has been
+forced to the conclusion that it would be most inadvisable, and
+commercially unsound, to reduce the stand of trees below 120 per acre. In
+such instances the average yield per tree equalled only 3 lbs. per annum,
+and although the trees were upwards of nine or ten years old the crowns
+were small and sparse. It is doubtful whether such trees will ever exhibit
+any further development, and to thin them further would probably lead only
+to a diminution in the crop per acre.
+
+Under normal conditions of growth an arbitrary figure of eighty trees per
+acre has been selected as a standard by many estates. In these cases it
+would probably be correct to state that thinning was undertaken on almost
+purely empirical lines--_i.e._, that trees were not selected by tests of
+individual yields. As far as such a method retained the apparently most
+vigorous trees it was successful; but in view of what has been written it
+might explain some of the disappointing results which have followed upon
+such a system of thinning.
+
+It will be clear that any decision regarding the number of trees to be
+retained must be derived from a study of the detailed results of individual
+tests. If the large majority of the trees appear to be fairly uniform in
+yields the first thinning must be confined to comparatively few trees.
+Where there is, on the other hand, a good percentage of high-yielding trees
+the final stand per acre may be appreciably less. Unless and until such
+information is available, one cannot give any definite opinion as to the
+requisite number of trees to be retained per acre.
+
+Similarly, intelligence must be displayed in deciding which of several
+uniformly-yielding trees should be removed. In the average sense of this
+consideration one must pay no attention to symmetry of spacing, but when
+dealing with trees of fairly uniform yields one needs to study the
+characteristic development of the trees individually, in order to retain
+those which would appear to be most favourably situated with regard to
+surrounding trees.
+
+
+
+
+CHAPTER IV
+
+_TAPPING SYSTEMS_
+
+
+Broadly there are only two methods employed in obtaining the latex from
+_Hevea Brasiliensis_. The first is that employed in South America, where
+incisions are made by means of a light axe. The other is the system of
+excision, or paring, of the bark practised on plantations in the East.
+
+In the early days of the plantation industry, the South American method
+seems to have been employed, and the writer has knowledge of trees on one
+of our best-known estates in Malaya which still exhibit the outward and
+visible signs of that method. At a comparatively early stage, however, the
+method of excision was introduced. Curiously enough there appears to be no
+record of its inception or of the individual who was responsible for the
+substitution of this method. We have been so accustomed to regard it as one
+of the ordinary facts of estate procedure, that this point seems to have
+escaped notice and enquiry.
+
+As a variant of these two main methods, a slight vogue was for a short
+while obtained by the operation known as "pricking." This was generally
+combined with excision of bark, and was then known as the "paring and
+pricking" method; but the simple operation of pricking alone had its
+adherents, and various forms of instruments were designed to achieve the
+object. As a means for obtaining a flow of latex, pricking may have been
+effective, but the general difficulties attaching to the collection of the
+latex was such as to put the method out of favour.
+
+In the employment of "paring and pricking," a thin shaving of bark was
+excised on one occasion. At the next tapping no bark was excised, but a
+pricking instrument was used along the previously cut surface. It was not
+proved that any advantage was gained by this method, which was more
+commonly employed in Ceylon than elsewhere, and it would be surprising to
+find it in use at the present day.
+
+In the ordinary way the method of excision is practised in such a manner
+that the "cut" gradually descends to the base of the tree.
+
+Planters with original views, and of an enquiring nature, often query the
+common practice; and it has been suggested that "as the latex descends by
+the force of gravity," one's paring should be done in an upward direction,
+thus obtaining a greater pressure of latex--and hence a greater flow. It
+will be obvious that it would be no simple matter to collect effectively
+the latex thus obtained from the under edge of a sloping cut, but apart
+from this the argument would appear to be founded upon what is now accepted
+to be a fallacy--viz., that the latex _per se_ is manufactured in the
+leaves and gravitates down the tree.
+
+FORMER SYSTEMS OF TAPPING.--To hark back ten years in the plantation rubber
+industry is equivalent to delving into history, since development has been
+so rapid. It was then thought necessary to place upon the trees a number of
+simultaneous cuts which the modern planter would judge to be inconceivably
+excessive. Were it not for evidence in the shape of photographs extant, it
+would be difficult to convince a young planter that such systems were
+employed.
+
+It was not uncommon for trees to have from six to ten cuts, sometimes all
+placed on one half of the tree in a herring-bone fashion, and sometimes
+divided into two portions, each of which tapped the opposite quarter panel
+of the tree's circumference. Such superimposed cuts were spaced from 1 foot
+to 18 inches apart.
+
+On other occasions, a spiral cut was employed, commencing at a height of,
+say, 5 feet, and gradually descending to the cup at the base of the tree.
+
+Later systems varied from several cuts on a half-circumference, or on a
+quarter of the tree, tapped either daily, or on alternate days, to cases in
+which one-third or one-fifth of the tree was employed. Also popular were
+the systems of the [V] and half-spiral cuts on half the circumference.
+
+It did not take long to be recognised that with all these systems demanding
+a number of simultaneous parings from the same panel of bark, the rate of
+excision was so heavy that the period available for the renewal of bark was
+insufficient for continuous tapping.
+
+As a result most of the systems specified have fallen into desuetude, and
+the tendency has since been to reduce the number of cuts, or the
+periodicity of tapping, so as to allow for increasing periods of bark
+renewal.
+
+In the earlier days, a period of four years was thought to be an extremely
+generous allowance, whereas six years is now becoming recognised as a
+minimum necessity. Eight years is not regarded as extravagant, while with
+older bark on some estates periods of ten and twelve years have to be
+allowed for full renewal. Even so no finality has been reached, and no
+general rule can be laid down. Local conditions of planting and growth
+exercise great influence, and the writers have in mind instances in which a
+period of eight years has proved to be insufficient even for a first
+renewal after the excision of virgin bark.
+
+In the main the most popular systems of tapping are:
+
+     (_a_) One cut on a quarter of the tree, tapped daily.
+
+     (_b_) One cut on a third of the tree, tapped daily.
+
+     (_c_) One cut on half the circumference, tapped on alternate days.
+
+     (_d_) A [V] cut on half the circumference, tapped on alternate days.
+
+Variants and extremes are:
+
+     (1) One cut on a quarter, tapped on alternate days.
+
+     (2) One cut on a half, tapped daily.
+
+Superficially viewed the latter is four times as strenuous as the former,
+and the relative position seems to be inexplicable. It may be explained
+that as a rule the former system is practised on old trees with poorly
+renewed bark, in order to allow for adequate bark renewal; and the latter
+is employed in opening young trees just brought into tapping, when the rate
+of bark renewal is at a maximum.
+
+[Illustration: TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE.]
+
+A few estates in this country still continue to tap trees by means of two
+superimposed cuts on a quarter of the tree. This was a very popular system
+some four or five years ago, but it has come to be recognised by practical
+experience that any system employing superimposed cuts leads to a high
+consumption of bark without proportionate increase in yield. For instance,
+if one compares the system of two cuts on a quarter tapped daily with a
+similar system employing only one cut, one finds that the major quantity of
+latex is yielded by the lower cut, and that the single-cut system which
+excises approximately half the amount of bark gives about 80 per cent. of
+the yield obtained by the tapping of two superimposed cuts.
+
+Of experiments to test the relative values of different systems of tapping
+there have been many. Most of them suffered from the initial handicap that
+they dealt with systems which were then popular. In order to obtain any
+valid result they had to be undertaken over a long period. Meantime there
+was a progressive movement in actual estate practice towards a greater
+conservatism in bark removal, and hence the experiments as originally
+planned lost value.
+
+Moreover, in Malaya it was difficult for experimenters to obtain practical
+support in the form of areas of trees suitable for experiment. As a result
+experiments were often confined to small blocks of trees, and a small
+number of blocks, from which any conclusions derived were subject to
+considerable errors of experiment. Often comparisons were made between only
+two blocks, and no allowance was made for varying factors, such as initial
+differences in yielding capacities of the trees, soil conditions, or the
+personal equation of the tappers. As a general rule, therefore, the results
+were vitiated to a very appreciable extent.
+
+All these factors were later taken into consideration in an experiment
+undertaken on behalf of the Rubber Growers' Association. In this instance
+unique facilities were provided by the London Asiatic Rubber Company on
+their property at Semenyih Estate, and it is only fitting that the company
+should receive the recognition which its enterprise deserves.
+
+It would have been a great advantage to have included in that experiment
+other features which have since come into prominence, but the original
+scope of the experiment had to be confined to the point of comparing yields
+obtained in making comparative tests based on one system of tapping with
+different frequencies. Such data were required as a check upon a Ceylon
+tapping experiment which had attracted much attention. In that experiment
+trees were tapped at intervals ranging from one day to seven days; and it
+was concluded that after a period of three and a half years trees tapped
+with greater intervals gave yields equalling or exceeding those obtained
+from trees tapped with shorter intervals.
+
+[Illustration: THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE
+AND ON RENEWED BARK.]
+
+In the Semenyih experiment the system chosen was that which had the
+greatest contemporary vogue--viz., two superimposed cuts on a quarter of
+the tree. The various blocks were tapped respectively every day, every
+second day, and every third day.
+
+It was found that the conclusions drawn from the Ceylon experiment were not
+confirmed. After a period of three and a half years' continuous tapping
+neither the alternate-day system nor the third-day system gave results in
+any way approximating to the yield of the daily system.
+
+The actual average yields from these systems over the whole period were in
+the order of--
+
+    _Daily._          _Two Days._      _Three Days._
+  100 per cent.      60 per cent.      45 per cent.;
+
+and throughout the course of the experiment neither of the other sections
+showed any appreciable improvement in position relative to the daily
+section.
+
+In actual yields "per tapping" over the whole period the alternate-day and
+the third-day divisions showed advantages of 20 and 35 per cent.
+respectively over the daily portion.
+
+At the beginning of the second year of experiment another section of blocks
+was opened with a single cut on a quarter, tapped daily. This enabled
+direct comparison between the values of one cut and two cuts on a quarter
+in daily tappings and between a daily single cut and two cuts tapped
+alternate daily.
+
+It appeared that the daily single cut yielded over the period of experiment
+80 per cent. of that obtained by tapping two cuts daily; and that in the
+comparison between two cuts tapped alternate-daily and a single cut tapped
+daily the latter had an advantage of about 40 per cent. in yield.
+
+This result has been used by advocates of daily tapping generally, but it
+does not constitute a fair argument, inasmuch as the single cut was tapped
+twice as often, and its position was always relatively low on the hole of
+the tree. It has been shown in the comparison between the daily single cut
+and the two cuts daily that the influence on yields of the superimposed cut
+is relatively small. A fairer comparison would have been obtained if the
+two cuts tapped alternate-daily had been either amalgamated to form one
+long cut on half the tree or to form a [V] on half the tree, thus placing
+the cuts in the opposing sections on the same level. With the knowledge
+that the yield obtained from cuts is _always greater per tapping_ by using
+the alternate-daily system, it would appear to be plain that the one long
+cut on half the tree would at least equal the yield of the single short cut
+tapped daily on a quarter tree.
+
+[Illustration: SINGLE CUT ON HALF CIRCUMFERENCE (HALF SPIRAL).
+
+_Note._--In this particular instance the cut is changed to the opposite
+half of the tree every half-year.]
+
+Unfortunately no opportunity has been afforded up to the present of
+definitely proving this point by prolonged experiment under strict
+conditions. It is true that the view is held strongly in some quarters as a
+result of the experience of managers, chiefly on their own estates, that
+alternate-daily tapping generally gives better yields than daily tapping.
+
+In a number of instances this view is probably correct, and the writers are
+in agreement; but it is necessary to clear away some misconceptions which
+confuse the issue. In the main there are two schools, one of which plumps
+for alternate-daily tapping, while the other adheres strongly to daily
+excision. Great confusion exists, inasmuch as in many instances the
+disciples of these schools are really discussing different matters. In the
+case of managers who argue for alternate-daily tapping their experience is
+gained, with very few exceptions, from systems in which the excision covers
+half the circumference of the tree; whereas in almost all cases daily
+tapping is confined to a single cut on a quarter of the girth. Bearing on
+such a comparison there are, as far as the writers are aware, no reliable
+published experimental results. To compare the results obtained from one
+system practised on one estate with the results of the other system
+established on another estate is not strictly permissible, as we know that
+conditions generally may vary to an enormous degree.
+
+The controversy has raged, however, to such an extent that many who are not
+directly engaged in estate practice have obtained confused impressions. For
+instance, it appears to be the belief in some quarters that alternate-daily
+tapping, when applied to a single cut on a quarter of the tree, will yield
+more than an exactly similar cut tapped daily. In support of such a
+statement there does not appear to be any confirmation under normal
+conditions; although such a result might be obtained in the case of old
+trees which have been heavily over-tapped in the past, and on which the
+rate of bark renewal has been appreciably retarded. It might also be the
+case eventually when trees with the opposing frequencies have been tapped
+for a period extending into many years; but it is the opinion of the
+writers that under normal conditions such a result would be extremely
+doubtful.
+
+When we come, however, to a comparison of daily tapping on a single cut on
+a quarter with double the length of that cut on half the circumference, at
+the same height, tapped alternate-daily--whether in the form of one long
+cut or in the form of a [V]--we arrive at a contrast which gives a clear
+issue. As already stated, facts and figures of reliable experiment are
+wanting; but it is the opinion and experience of the writers that the
+alternate-daily system at least suffers no disadvantage on the point of
+yields, and in other respects, such as conservation of labour and costs, is
+superior to the daily system.
+
+[Illustration: A [V]-CUT ON HALF THE CIRCUMFERENCE.]
+
+
+
+
+CHAPTER V
+
+_TAPPING AND COLLECTING_
+
+
+TAPPING KNIVES.--The choice of a tapping knife is a subject upon which
+there is much divergence of opinion. This must be so because no known knife
+has such apparent outstanding superior features or claims as would enable
+one to settle the point. Moreover, the personal factor is so large that, as
+far as the knives in common use are concerned, it appears to exert the
+greatest influence. The possibility of obtaining the ideal knife, which
+will go to sufficient depth into barks of varying thickness to yield the
+maximum quantity of latex without wounding, is quite as remote at the
+present time as it was some years ago. Meanwhile the search for that ideal
+knife continues, and occasionally one learns of the alleged merits of some
+new instrument which, it is said, fulfils all requirements. It is only to
+be regretted, both for the sake of the inventor and for the expectant
+buyers, that the claims always fail in some one or more particulars.
+
+In Malaya probably the number of different types of tapping knives may
+amount to a half-dozen, but those most commonly in use are:
+
+     (1) The gouge--straight or bent.
+
+     (2) The ordinary farrier's knife.
+
+     (3) Modifications of the farrier's knife, such as the "Jebong."
+
+Argument on the respective merits of knives is popular, and discussion
+seems endless. It is claimed for the bent gouge that it is superior to the
+straight instrument, because, the leverage being downwards on the handle,
+the tendency is to lift the cutting edge upwards and out of the bark,
+whereas with a straight gouge the tendency is to push the knife downwards
+into the bark. It is claimed, therefore, that the average shavings taken
+off by the bent gouge should be thinner than those obtained by the use of
+the straight instrument.
+
+For similar reasons it is asserted that the "Jebong" and other
+modifications are superior to the original form of the farrier's knife.
+These points are generally accepted without great argument, but when
+comparisons are made between the gouge and the farrier's knife (with its
+modifications) the opinions of planters are so varied and conflicting as to
+be almost irreconcilable. Two opinions based on experience with both types
+of knives are often wholly contradictory.
+
+There can be no doubt that the likes and dislikes of operative coolies have
+a considerable influence in determining the measure of success obtained
+with any one knife. Should coolies have been accustomed to the use of a
+particular form of instrument they become quite expert, and any proposed
+change creates in the minds of coolies a prejudice which is considerable in
+effect on the quality of the handicraft. Such prejudice may be overcome in
+course of time, but in the interval not a little damage may have been done
+in the shape of tapping wounds. So considerable is this question of
+personal favour that even on estates where a standard pattern of knife is
+issued coolies often modify that knife slightly on their own accord. Such
+alteration is ignored by the superintendents as long as the quality of the
+tapper's work is maintained at a high standard.
+
+Naturally there is a limit to such leniency, and this limit is soon reached
+in the case of knives having adjustable parts controlled by screws, or nuts
+and bolts, etc. Some knives of this description really merit a much wider
+use than is afforded them at present; but in view of the potential damage
+which might be done as a result of adjustments made by the coolies these
+knives do not become popular.
+
+It is not proposed here to enter into a description of even recent
+instruments for which strong claims are being made by their inventors or
+vendors. If they possess the merits attributed to them they will soon find
+favour, as managers are always keen on studying the points of any new knife
+which will lead to a conservation of bark and a reduction in the number of
+wounds. On the whole, it may be advanced that the best general results are
+obtained by the adoption of a simple non-adjustable knife and the retention
+of its use.
+
+THE CHOICE OF LATEX CUPS.--It has come to be recognised that the maximum
+possible cleanliness is essential in all details of estate work, and the
+younger generation of planters could scarcely be aware that a few years ago
+it was deemed sufficient to use coco-nut shells for the reception of latex
+on individual trees.
+
+Terne-plate cups ousted the coco-nut shell, and they had the merit of being
+cheap. The interior coating of tin did not last long if the cups were
+properly cleaned. The iron being exposed, with a minutely roughened
+surface, each microscopic projection served as a point around which latex
+coagulated. Scrapping the film of interior rubber became more and more
+difficult, and often the cups were burnt in order to get rid of the
+accumulation of rubber. The last state of such cups was worse than the
+preceding one. On some estates fairly successful attempts were made to keep
+these cups clean by making the coolies bring them into the store each day.
+Terne-plate cups are not now in common use.
+
+Aluminium cups have their advocates, but much the same argument applies to
+the difficulty of keeping them clean as was used in the foregoing
+paragraph. On many estates, however, they are used with success, the usual
+method of treatment being to make the coolies bring them into the store and
+clean them there. Owing to the comparative lightness of the material such a
+scheme is more feasible than was the case with terne-plate cups.
+
+The cups now most in general use are either of glass or white-ware, and
+probably those of glass are the most extensively employed. There are many
+details to be studied in the choice between these two types of
+cups--_e.g._, percentage of breakage in transport and in the field, price
+when breakage is taken into account, etc.; but these apart the glass cups
+have one advantage--namely, the ability of the superintendents to see
+whether the cups have been properly cleaned. In the case of white-ware cups
+this means an inspection and handling of individual cups, whereas in the
+case of glass the point is settled by visual examination at a comparative
+distance.
+
+[Illustration: SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE.
+
+The opening cut covers two-fifths. Subsequent cuts occupy one-fifth of
+circumference.]
+
+Glass cups are made in two patterns, one having a flat bottom and the other
+a conical base. The latter is convenient for use when wire supports are
+employed, the cup fitting into a loop placed beneath the spout. Used on the
+ground its shape is an obvious disadvantage, as, unless a hole is scooped
+for its reception, it has to be propped up with sticks or stones. Often a
+touch is sufficient to upset the balance, and latex is lost.
+
+The flat-bottomed cup, on the other hand, may be used with success equally
+on a wire support or on the ground. It is sometimes said that owing to its
+shape the ease of cleaning, as compared with the half-spherical cup, is
+diminished, and that if the cups when not in use are kept inverted upon
+sticks placed near the foot of the tree the breakage is apt to be high.
+This latter objection is being rapidly removed as the practice of using
+these sticks is losing vogue for various reasons, and wire cup-holders will
+be in general use as soon as the cost of material becomes normal.
+
+There are on the market, and in fairly wide use, cups of Chinese and
+Japanese manufacture. These generally consist of brown earthenware with an
+interior glass finish. These are cheap in comparison with glass and
+white-ware cups, but it is a pity that the glass does not extend over the
+whole of the cup. The outer surface has a tendency to collect rubber and
+dirt. On some few estates small china bowls or saucers are still used and
+are quite satisfactory, except for the favour with which they are regarded
+by natives on the outskirts of the estates.
+
+CLEANING CUPS.--The question of cup-cleaning would appear to be a very
+simple one; but in practice it is quite a source of worry to managers,
+especially where a mixed labour force is employed. Tamil coolies can be
+made to clean their cups in the day's task and at odd times. Chinese
+coolies, more often than not, either refuse to give the necessary attention
+or else demand extra pay for the work.
+
+The method of cup-cleaning employed more popularly within recent years was
+that of daily washing. The tapper carried two buckets, one for receiving
+the latex and the other containing water. Pouring the latex in the bucket
+the coolie then added a little water to the cup and added these rinsings to
+the latex collected. The cup was next washed hastily in the bucket of water
+and replaced. By the time the coolie has emptied and washed some 200 cups
+(about half the task generally) the water has the consistency of dilute
+latex, and the wet cup when replaced becomes coated with a thin film of
+rubber. If the latex is always collected in one direction it will be clear
+that, while the cups at one end of the task are comparatively clean, those
+at the other end have the chance of being correspondingly dirty.
+
+Controversy has raged respecting this question of cup-washing, and many
+estates have abandoned it as a daily practice. Coolies have not to carry an
+extra bucket of water. The contents of the cups are poured into the
+latex-bucket, and the bulk of the latex film remaining is also removed by
+the aid of a finger. The cup is then replaced, a thin skin of rubber
+forming on the interior surface. As a general rule this is easily removed
+on the next occasion, except perhaps in dry weather. It is the custom on
+most estates employing this practice to have all cups receive special
+attention at regular intervals.
+
+There are certain economic factors entering into the difference of opinion
+regarding the two broad methods employed. In some cases--_e.g._, on old
+areas--it would be practically impossible to follow the older method of
+daily cup-washing, as the tappers have to employ two buckets for the
+collection of the latex. The employment of special coolies for cup-washing
+would be necessitated, such as may be seen sometimes on estates working
+Chinese "squatter" labour--where the man taps, a child assists in
+collecting, and another child, or the mother, washes the cups. It may be
+pointed out that in such instances the helpers are not paid by the estate.
+Their services merely mean a saving in time which is spent in the
+squatter's garden, and perhaps the permission to the tapper to work a
+larger number of trees than would be allotted ordinarily to a task.
+
+Again, on some estates, the tappers, while not being required to carry a
+bucket of water for cup-washing, are given an increased number of trees to
+tap. Furthermore, on hilly areas under tapping, it is often manifestly
+unfair to expect the tapper to be able to carry two buckets during
+collection, when the slope is such, as to make the manipulation of even one
+bucket a matter of difficulty.
+
+It will be seen, therefore, that there is no clear issue for argument
+concerning the two methods, and that the point must be decided on the
+economic factors peculiar to each estate or district.
+
+[Illustration: EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING.
+
+Note uneven surface and callosities.]
+
+[Illustration: ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING.]
+
+WATER IN CUPS.--Much discussion used to take place regarding the necessity
+or otherwise for placing a small quantity of water in the cups when
+tapping. It was recognised that the permission to use water (with the idea
+of preventing coagulation) led to much abuse, apart from the question as to
+the utility of the method. Dirty water was often used, although clean water
+may have been placed in the buckets when coolies left the muster-ground.
+The small quantity of water often exceeded the actual yield of pure latex
+by hundreds per cent., with the result that on arrival at the factory the
+diluted latex was below the standard desirable for the preparation of a
+good sheet-rubber.
+
+PREMATURE COAGULATION.--Other opinion to the contrary it is now generally
+acknowledged that the possibility of premature coagulation in the cup or
+bucket is at least not diminished by the addition of even clean water. The
+use of water often obtained from estate drains clearly led to increased
+trouble. The extent to which such premature coagulation takes place varies
+greatly under the influence of many factors--_e.g._:
+
+     (_a_) Cleanliness of cups and spouts (the latter an important item
+     often overlooked, and involving the presence of certain organisms
+     which effect coagulation).
+
+     (_b_) Climatic conditions.
+
+     (_c_) Rate and volume of flow of latex.
+
+     (_d_) Size of tappers' tasks (involving the length of interval between
+     tapping, and the collection of latex).
+
+     (_e_) Distance to be traversed between the site of the task and the
+     store.
+
+     (_f_) Care in collecting, to exclude extraneous matter.
+
+     (_g_) Nature of transport; agitation of the latex to be reduced to a
+     minimum.
+
+     (_h_) Nature of the soil, and situation of the estate.
+
+The last mentioned factor is of great importance. As a general rule it is
+noted that premature coagulation is less marked on estates situated on
+comparatively hilly land. The greatest effect is remarked on estates
+situated on the flat lands of the coastal area where peaty soils are a
+feature. On many such estates, in spite of the observance of all ordinary
+precautions, it is not possible to receive the latex at the factory without
+a large percentage of prematurely coagulated rubber being found in the
+transport vessels.
+
+ANTI-COAGULANTS.--For this reason on these (and other) estates, the use of
+small quantities of anti-coagulants is common. The effect of these is to
+keep the latex liquid and thus render possible the preparation of a higher
+percentage of first-grade rubber than would be otherwise obtained.
+
+Among the better known agents which have such an effect upon latex,
+formalin and sodium sulphite (not bisulphite) are the chief. The latter is
+the more popular as it is slightly cheaper and much more stable. As now
+used, it is in the form of an easily soluble powder (anhydrous sodium
+sulphite). The ordinary crystalline form of sodium sulphite as used in
+photography is not recommended, on account of its comparative lack of power
+and its poor keeping qualities.
+
+It will be obvious that, given two equal quantities of different latices,
+different amounts of an anti-coagulant may be required to produce the same
+effect. Hence it should be remembered that a formula which suits the needs
+of one field or one estate will not necessarily prove suitable in the case
+of another field or estate. Unless this point is appreciated trouble may
+ensue. On some estates it has been the custom to give equal quantities of
+sodium sulphite solution to all coolies irrespective of the ages of the
+trees in the fields to be tapped. Thus it happened that the latex from one
+field was found to have insufficient anti-coagulant present, while that
+from another field could only be coagulated by the addition of an excess of
+acid. In this matter the experience of the preliminary trials should have
+caused some discrimination to be exercised as to the quantities of solution
+to be issued in each field or division. It has been found sometimes that a
+moist glossiness in the smoked sheet could be attributed to the use of an
+excess of sodium sulphite. Traces of the salt remained in the rubber, and
+as the substance is hygroscopic, moisture was being absorbed from the air,
+to cause a surface deposit which often returned even after the sheets were
+surface-washed and re-dried.
+
+If sodium sulphite is to be used in the field, the following formula, which
+is in wide use, may serve as a basis for trials.
+
+
+_Formula for Use of Sodium Sulphite in the Field._
+
+     (_a_) Dissolve anhydrous sodium sulphite in water at the rate of 1
+     pound to 3 gallons.
+
+     (_b_) Of this solution each coolie is given about 3/4 pint. This is
+     usually sufficient for a task of 350 trees. The solution is used by
+     shaking a few drops into the cup or, diluted with an equal volume of
+     water, it is run down the main channel when the latex flows.
+
+[Illustration: 1. SHOWING EFFECT OF "WINTERING."]
+
+On some estates it is found either unnecessary or impracticable to use the
+solution in this manner. Instead the anti-coagulant is placed in the bottom
+of the bucket prior to the commencement of collection. The solution is made
+as in (_a_) above, and roughly half an ordinary latex-cupful is placed in
+each bucket.
+
+[Illustration: 2. NEW GROWTH OF YOUNG LEAF ON SAME TREE.]
+
+COLLECTING PAILS.--All vessels intended for the transport of latex should
+have a smooth and curved interior, so that cleansing may be easy.
+Preferably the interior and exterior surfaces should be glazed, but it is
+often found that the enamel chips easily, and that the handles are too
+frail in construction. The shoulder-pieces, to which the handles are
+joined, are often too lightly attached to the bucket. Something stouter in
+the shape of enamelled ware is required, without an appreciable increase in
+weight. Until such a utensil is available, the heavily galvanised and
+brass-bound milk-pails used on some estates are as good as anything at
+present in vogue, providing they are kept scrupulously clean.
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_a_) Note on right hand the panel next in order for tapping; a hopeless
+position.]
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_b_) The present cut badly infected; above there is no renewal of bark.]
+
+The collecting pails should be kept under cover, when not in use, either at
+the muster grounds or at the factory. On some estates coolies are allowed
+to take them to their quarters, where they are used for various purposes.
+Curious effects of this practice have sometimes been noticed. As an
+example might be quoted an instance in which premature coagulation was
+found to take place to a surprising degree. It was discovered eventually
+that the coolies (Javanese in this case) were in the habit of utilising the
+buckets for the preparation of their food. A liquid extract of a popular
+fruit was often made. This extract was very markedly acid in character,
+and as the buckets were not afterwards thoroughly cleansed, the latex of
+the following day suffered.
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_c_) As in (_b_); another tree.]
+
+Preferably all buckets should have a lid of slightly funnel shape. This is
+inverted during collection, and thus prevents much dirt falling into the
+latex.
+
+[Illustration: EFFECTS OF DISEASE--"MOULDY ROT."
+
+(_d_) At close quarters. Note wounds due, apparently, to bad tapping, but
+really caused by the disease.]
+
+PAYMENT BY RESULT.--The arguments for and against the institution of this
+practice are many. In actual result there can be no question that a higher
+yield is obtained by the adoption of a scheme under which the coolie is
+either given a bonus based on result or is paid at a definite rate per
+pound. It is fully recognised, both by advocates and opponents of payment
+by result, that the personal equation of the tapper is a very important
+factor. A good skilled tapper will always obtain a higher yield than an
+ordinary individual from the same task of trees, and without any more
+injury to the trees. It is argued, therefore, that such an operative should
+be given the benefit of his skill. Apart from this, it is claimed that even
+the average tapper does not do his best work if he knows that he will get
+his daily wage, no matter what his yield may be, as long as he does not
+injure the trees by wounding. It is claimed that this sense of security
+leads to shallow tapping which, while it has an agreeable appearance, does
+not produce the available amount of rubber.
+
+On the other hand, it is advanced in opposition that under a scheme of
+payment by result the tappers' only consideration is the matter of
+obtaining rubber, and that considerable damage in the form of wounds is
+done by over-deep tapping. That there is a great deal of truth in these
+statements is not to be doubted. Much, of course, depends upon the amount
+and quality of the supervision possible, and upon the standard demanded. It
+is a notable fact, however, that on estates which first introduced the
+system some years ago the quality of the tapping compares favourably with
+that of average estates, and in a few instances within the experience of
+the writer the tapping is of a high standard. Possibly these are
+exceptional instances, and there can be no doubt that the opposition of
+many managers of considerable experience is founded upon the deterioration
+in the standard of tapping which often follows the institution of payment
+of tappers by result.
+
+It will be recognised by planters that apart from the personal factor in
+tapping, the worker might be so unfortunate as to be placed in an area from
+which the yield is naturally low, either by reason of its youth or from
+other natural causes. Obviously such individuals are entitled to special
+consideration in respect of the rate per pound paid for the rubber
+obtained. Again, on very hilly land it may be not humanly possible for a
+worker to tap the usual number of trees. Hence to place him on a parity
+with other tappers, as far as wage-earning capacity is concerned, a higher
+rate than ordinary must be given. It will be plain, therefore, that on any
+one estate it is generally impossible to set a standard rate per pound for
+payment by result; the rate may vary, for example, from, say, 3 cents per
+pound in old and high-yielding tasks to 12 cents or more per pound on young
+areas of the same estate.
+
+Naturally the actual rates paid will primarily depend upon the average
+yield per tree or yield per acre, and the lower the average yield the
+higher the rates to be paid per pound. Thus, on low-yielding properties
+where the natural conditions render a high yield impossible the rate per
+pound may reach a figure of 22 cents (approximately 6d.).
+
+The methods of arriving at the yield of rubber brought in by individual
+tappers vary, but broadly they fall into two classes:
+
+     (_a_) That in which the volume of latex is ascertained (either by
+     measuring or by weighing), a sample is drawn, and the final
+     calculation made from the weight of the more or less dry sample.
+
+     (_b_) That in which, after noting the volume, the calculation is based
+     upon a reading of the dry rubber content of the latex, obtained by
+     means of an instrument such as the "Metrolac," or any other instrument
+     working on the same principle.
+
+Quite a number of estates which have not adopted the full system of payment
+by result yet employed some such method of checking the yields of
+individual coolies, as the observed results act as a great deterrent
+against various malpractices, such as neglecting to tap trees, adulteration
+of the latex, etc.
+
+TREE-SCRAP.--The thin film of latex which coagulates naturally upon the
+surface of the tapping cut after the latex has ceased to flow is known as
+"tree-scrap." Normally it is collected on all estates, but the method of
+collection varies according to the class of labour employed. On most
+estates, where the labour is Tamil or Javanese, it is supposed to be
+removed as fully as possible before the tapping cut is reopened. The narrow
+strips are then placed in a bag or basket carried by the tapper. Chinese
+tappers usually decline to follow this practice of first peeling off the
+scrap, and remove it by the operation of tapping, with the result that the
+scrap when brought into the store has adhering to it various shavings of
+bark. Unless these can be thoroughly cleaned off the scrap cannot truly be
+classed as "tree-scrap."
+
+OXIDATION OF TREE-SCRAP.--It is often noted that some scrap is dark in
+colour, and in this condition it is generally spoken of as "oxidised"
+scrap. The oxidation is probably due to an enzyme, and also to the presence
+of chemical substances of a phenolic nature. In the course of laboratory
+experiments with normal latex, it was found possible to reproduce this
+darkening due to oxidation by the addition of very small quantities of
+various phenols used in general chemical processes, and the rapidity with
+which the darkening was effected depended upon the quantity of the phenol
+added. If this rapidly oxidising latex be mixed with normal latex, it would
+seem that the whole bulk of the latex is affected by this tendency to rapid
+oxidation. It is observed that this condition under which any tree may
+yield rapidly oxidising latex is not a permanent one.
+
+CARE OF TREE-SCRAP.--As these scraps eventually give a grade of rubber
+which compares well with other and better-looking grades care should be
+exercised in collection and treatment so that its quality is not impaired
+in any way.
+
+TO PREVENT OXIDATION.--As a rule the scraps are picked over, and heavily
+oxidised pieces are sorted out; otherwise the crepe rubber prepared
+exhibits black streaks. The scraps should not be allowed to remain in the
+sun (which induces "tackiness"), and if they have to be kept over night
+they may be placed in a weak solution (1 per cent.) of sodium bisulphite to
+arrest oxidation. It should be recognised that such a solution will not
+"bleach" already darkened scrap-rubber, and the nature of its action is
+only anti-oxidant.
+
+BARK SHAVINGS.--In the matter of collecting bark-shavings much depends upon
+the organisation and nature of the labour force. Probably, on the majority
+of estates bark-shavings are collected systematically, but on quite a
+number considerable laxity in this respect has been noted. This may arise
+from lack of adequate supervision or from the peculiar systems of working
+which seem to pertain to Chinese labour. Granted that the trees are well
+"scrapped," and that the percentage of rubber obtained from shavings under
+such circumstances would be extremely small (say 2 per cent. by weight on
+the total output), it does not need much calculation to see that annually
+the loss of rubber to the estate must be considerable. It would also seem
+to follow that, if the adult labour declines to pick up bark-shavings
+carefully, it might pay to employ children for the purpose. Or, as is done
+in some places, the adult labour might find it advantageous to collect
+bark-shavings at low rates per pound.
+
+It is a well-known fact that if bark-shavings be allowed to accumulate in a
+heap for any but a short period, a fermentative and heating action is set
+up. The heat developed in these piles of shavings is so considerable that
+it is impossible to keep the hand in a heap for more than a second or two.
+Should this be allowed to persist, as would happen in the case of a
+breakdown of engine or machines, it usually results in the final crepe
+rubber becoming tacky when approaching dryness.
+
+To avoid this heating effect it is necessary to have spare jars or proper
+tanks in which the shavings may be soaked in water. In this condition
+bark-shavings may be kept for many days.
+
+For the same reason (_i.e._, the heating effect and consequent tackiness)
+the custom followed on some estates of allowing coolies to keep
+bark-shavings in their "lines" until they have accumulated a fair quantity
+cannot be commended, quite apart from the possibility of actual loss by
+theft, which is thus rendered easy.
+
+It will be clear that where the trees are scrapped efficiently before
+tapping, the amount of rubber to be obtained from the treatment of pure dry
+shavings would be almost nil, and would scarcely repay the cost of
+collection and working. In actual practice, however, it is not possible to
+guarantee that the shavings are free from some scrap-rubber. Shavings
+brought in by Tamils and Javanese carry only a small amount of rubber,
+whereas where Chinese tappers are employed the yield of rubber may be as
+high as 35 to 40 per cent. upon the total weight of the material treated.
+
+Few estates now are not equipped with "scrap-washers"--machines specially
+designed for removing the bark from the rubber--and if they function
+efficiently the resulting crepe should be free from bark-particles.
+
+COLLECTION OF EARTH-SCRAP.--This, the lowest grade of rubber, is found at
+the base of the tree. Theoretically, if proper precautions are observed,
+the amount should be comparatively small, but in actual practice it may be
+very appreciable. The usual contributory causes are:
+
+     (_a_) Failure to replace cups beneath the spouts of trees which
+     continue to drip latex after collection.
+
+     (_b_) Collection of latex at too early a stage.
+
+     (_c_) Failure on the part of the tapper to ensure the flow of latex,
+     by means of the spout, into the cup.
+
+     (_d_) Flowing of latex over the edge of the cut before it reaches the
+     vertical channel.
+
+     (_e_) "Wash-cuts" on wet days, when the volume of rainwater down the
+     tree is sufficient to wash the latex out of the cup.
+
+The amount of earth-scrap collected on any estate will depend, all other
+things being equal, upon the labour expended in its collection. Certainly
+on well-organised estates, having ample labour, the amounts collected are
+huge in comparison with other estates. The ground at the base of the tree
+below the latex-spout is systematically turned over with pointed sticks and
+large clots of rubber are often picked up. Here, again, it is advised that
+the collected earth-scrap should not be allowed to remain in heaps upon the
+floor of the factory. It should be placed in suitable tanks containing
+water, and quite a considerable portion of the cleansing work is thus taken
+from the machines.
+
+
+
+
+CHAPTER VI
+
+_TRANSPORT OF LATEX AND COAGULUM_
+
+
+PERCENTAGE OF FIRST LATEX AND OTHER GRADES.--One of the problems
+confronting any manager is the question of the percentage of first-grade
+rubber calculated upon the whole output. Inquiries are constantly being
+received for advice as to what the various percentages of each grade of
+rubber should be. This is a question to which no definite list of figures
+can apply. There are so many little factors influencing the result. Some
+estates are not particularly careful in collecting tree-scrap. Hence quite
+a quantity of tree-scrap finds its way into the crepe made from
+bark-shavings. On the other hand, bark-shavings are not collected
+systematically on some estates, and the total output is thereby diminished.
+In consequence the first-grade rubber shows a higher percentage than it
+would otherwise. Again, if the earth-rubber is not regularly collected the
+percentages of the best grades are higher than they should be. In comparing
+the percentages of each grade of rubber from any two estates, therefore,
+one should have all the information possible as to the various working
+details of the estates. Without wishing to lay down any definite
+proportions which can be applied to all estates it might be said that,
+taking averages over a large number of estates, the percentages to be aimed
+at are:
+
+  First-grade latex   75 per cent. to 80 per cent.
+  Other grades        20    "      "  25    "
+
+For these figures one promises that all lower grades are collected and
+accounted for carefully and regularly. The distribution of the lower grades
+will depend upon the field practices of the particular estate, but the
+following list might be given for an estate keeping all lower grades
+distinctly separate:
+
+  First-grade latex         75 per cent.
+  Cup-washings            }
+  Coagulated lump, etc.   } 10    "
+  Tree-scrap                 9    "
+  Bark-shavings              4    "
+  Earth rubber               2    "
+                           ---
+                           100    "
+
+Emphasis is again laid on the statement that these figures must not be
+accepted as a standard. Nevertheless, they may prove of some service to
+managers in giving an idea of what the general line of percentages may be.
+There are special circumstances, such as distance of transport and the
+nature of the land, which at present would render the attainment of more
+than 75 per cent. first-grade rubber impossible on some estates. Still the
+fact remains that if the percentage is low through distance of transport,
+etc., some method will have to be discovered by means of which the
+difficulty maybe overcome. On a few estates the percentage of first-grade
+rubber obtained sometimes reaches 85, but these results are rather out of
+the ordinary. An estate which collects all lower grades properly is doing
+well if the percentage of first-grade rubber is 75 or over.
+
+EARLY COLLECTION.--As already noted in the preceding chapter, one of the
+factors influencing premature coagulation is that of the interval elapsing
+between the commencement of tapping and the collection of latex. It will be
+seen that this ordinarily would depend, in turn, upon such considerations
+as the size of the tappers' tasks, the spacing of the trees, and the
+natural conformation of the land over which the tappers have to perform
+their tasks. In general it need only be remarked that every possible
+consideration should be given to this question, and that any delay should
+be avoided.
+
+TRANSPORT.--Wherever possible it is endeavoured to convey latex from field
+to factory by man-power. Tamil coolies, as a rule, place the bucket on the
+head; Chinese and Javanese coolies like to use a balanced carrying-pole.
+Where distance renders these methods too costly in time and labour, it is
+usual to have field centres where the latex is collected and dispatched to
+the factory generally (_a_) by means of vessels conveyed on light railways;
+(_b_) in large cans placed on motor-lorries; (_c_) in cylindrical
+galvanised drums supported on two wheels and drawn by bullocks. There may
+be variants, but these are the chief means of transport in bulk over a
+distance.
+
+Where possible, the best system is that employing a trolley-line, as great
+agitation of the latex is avoided, and the time in transit is much reduced.
+
+The usual method of transport by bullock power is slow, and as estate roads
+(and even Government roads) are often below the standard expected in this
+country, the jolting undergone by the latex is, to say the least, not
+calculated to afford a high yield of first-grade rubber. The late Mr. F. W.
+F. Day advocated the use of a circular perforated wooden grid, to be
+floated on the latex, in order to moderate the wave effect produced by
+jolting.
+
+Whatever the means of bulk-transport employed, it should be the care of
+those in charge to see that vessels are not allowed to remain in the sun
+longer than is necessary. Even during the journey they should be shaded in
+the best possible manner.
+
+These large transport vessels usually receive what is really only
+perfunctory attention in the matter of cleaning. They should receive the
+same care as would be exercised in dealing with milk cans in other
+countries. Ordinary sluicing with water is not sufficient, and if they
+cannot be sterilised by means of boiling water, they should be treated,
+after ordinary washing, with a 5 per cent. solution of sodium bisulphite
+every day.
+
+ANTI-COAGULANT FOR TRANSPORT.--When anti-coagulants are not used in the
+cups or buckets, it is advisable to use them in the bulk-transport vessels.
+Either formalin or sodium sulphite is of service, but the great objection
+advanced against the former is its loss due to evaporation while the carts
+are going to the fields or waiting at the centres. For this reason sodium
+sulphite is now generally employed.
+
+
+_Formula for Use of Sodium Sulphite in Transport._
+
+     (_a_) Dissolve 1 pound of powder in 3 gallons of water.
+
+     (_b_) Of this solution, place half a gallon in the vessel for every 30
+     to 40 gallons of latex.
+
+TRANSPORT BY COOLIE.--As already pointed out, the extent to which man-power
+can be used in transport of latex is generally limited. On small estates it
+is an easy matter for coolies to carry the latex to the factory, but on
+larger estates many difficulties may arise, which may also militate against
+the successful use of other means of transport. It is not uncommon to find,
+therefore, that a policy of decentralisation has been adopted.
+
+COAGULATION CENTRES.--Divisions of the estate have their own small stations
+at which latex is received and coagulated. In this way it is possible to
+receive latex without much delay, and with benefit to the resultant rubber,
+especially if prepared in sheet form. Much controversy has arisen regarding
+these decentralised establishments, but the fact remains that on large
+estates, which are efficiently controlled, the scheme has been highly
+successful from all points of view. On the other hand, it is alleged that
+this method of working increases costs, and often gives an unsatisfactory
+quality of rubber. Concerning the latter point it seems to be reasonable to
+expect that the European in charge of any division should be conversant
+with the method of preparation required, and should be capable of seeing
+that no mistakes are made. Given uniform equipment in all stations, and
+uniform rules for treatment of the latex, there does not appear to be any
+valid reason why the product of one station should be inferior to that of
+the others. Neither is it so in the case of several estates which might be
+quoted.
+
+In the matter of costs of working the writer has had to investigate several
+cases regarding which there was dissatisfaction. In some instances it was
+found that the stations had not been placed advantageously with respect to
+a water-supply; and instead of one or two coolies pumping for an hour or
+two, a larger number had to be employed for hours in the carriage of water
+from the nearest available source. This meant that, as the coolies were on
+daily wage, the force appeared to be much bigger than that usually
+required. In other cases there were too many store coolies, when often the
+place of some could have been taken for the necessary period by tappers
+arriving early from the nearer fields. Sometimes costs were increased by
+reason of the use of an excess of chemicals, owing to the lack of uniform
+rules throughout the several stations. In spite of all that has been
+written, and the verbal instructions that have been given, it was not
+uncommon to find unstable chemicals such as sodium bisulphite exposed to
+the moist air. In this way not only was there waste of material, but also
+the probability of inferior rubber being made.
+
+TRANSPORT OF COAGULUM.--On the whole if it is a question between the
+transport of latex and the transport of coagulum, the writer would always
+favour the latter, for reasons which have possibly been made clear in the
+preceding paragraphs. In effect, it should be recognised that the less
+handling and transport the latex receives the better the general result.
+
+If proper precautions are taken, the transport of coagulum intended for the
+preparation of crepe should present no difficulty, and should have no
+injurious effect upon the quality of the resultant rubber. It is only too
+common, nevertheless, to note defects, in the finished crepes, which can
+only be attributed to a failure to observe reasonable care in the transport
+of the coagulum. For example, it has been observed that a mass of coagulum
+from a coagulation station has been conveyed on the floor of a
+bullock-cart, or motor-lorry, previously used in the carriage of other
+materials. Unless the boards have been most scrupulously cleansed, the
+coagulum is found to be contaminated, often to a marked degree. Again,
+although the cart may be clean, it may have to travel some distance on
+roads carrying a fair amount of motor traffic. Even should the cart have a
+canopy, road-dust is often whirled through the open sides of the cart; and
+in the districts where red laterite roads are common, the stain of such
+dust often persists in the finished crepe. It scarcely need be remarked
+that coagulum should be transported in closed wooden boxes or in galvanised
+iron drums fitted with lids; and that preferably sufficient water should
+be present in these receptacles to allow the coagulum to float. All such
+containers should receive the same scrupulous attention as the vessels
+employed in the transport of latex.
+
+The successful transport of coagulum for sheet-making is fraught with much
+greater disabilities, and it is usual to note on most estates that the
+resulting sheets from out-stations are always inferior, in final result, to
+those coagulated and prepared at the central factory. If the flat pieces of
+coagulum are placed in piles of any height it is common to find, on arrival
+at the factory, that much adhesion has been caused. There is great
+difficulty in separating the pieces, and often the successful operation is
+impossible. It is usual to hand-roll the coagulum before transport, but it
+is often found that by the time the rubber reaches the factory it has
+become too hard for subsequent good results.
+
+One of the strong arguments in favour of the establishment of divisional
+stations is to be found in the preceding paragraph. Sheet-making, as it
+necessitates the employment of only light machines suitable for hand-power,
+is a feasible proposition in a field station. There is no reason for sheets
+made thus to be in any way inferior to those made at a central factory; in
+fact, they are often better, as the latex has the chance of being treated
+when comparatively fresh.
+
+If it is found necessary to transport sheet-coagulum, every possible
+precaution should be taken against piling the pieces.
+
+After hand-rolling some estates bring the rubber from the field-stations to
+the central factory in drums of water, others in shallow boxes containing
+not more than half a dozen sheets in a pile. A method proposed long ago,
+but not in practice, was to have a number of shallow trays subdivided so
+that each compartment held one sheet only. If these trays were properly
+made and carefully fitted there appeared to be no reason why they should
+not form sliding parts of a large box, in which squeezing and adhesion of
+the pieces of coagulum would be avoided. Naturally any such device would
+increase appreciably the weight to be transported, and on this ground would
+not find popular favour except where motor-power is used for road
+transport.
+
+
+
+
+PART II
+
+FACTORY OPERATIONS
+
+
+
+
+CHAPTER VII
+
+_PRELIMINARY TREATMENT OF LATEX_
+
+
+RECEPTION OF LATEX AT THE STORE.--Bearing in mind the remarks in Chapter
+VI. on the conditions under which latex is transported, it follows that
+nothing but the very best and most suitable vessels should be used in the
+store. A point to which adequate attention is not given in many factories
+might be mentioned here. Considering the importance attached to colour in
+the dry rubber by brokers and consumers, and knowing how extremely trivial
+are the causes which may mar the colour, it is rather surprising that
+better provision is not made for the reception and handling of latex in
+factories. Too often the receiving vessels are placed on the floor of the
+store close to the entrance. Coolies bringing in latex cannot avoid
+bringing with them quite a considerable amount of dirt. Presuming that a
+hose-pipe has been installed, and that the floor is constantly being
+sluiced down with water, no great harm will result. But would it not be
+ever so much better if the dirt were kept out? In how many factories is
+provision made for this? Such an arrangement is not difficult to make, and
+is already in practice on a few estates. A verandah is built outside the
+wall of the factory and all latex is received there. In another place open
+chutes are provided which terminate in the straining sieves. The coolie
+thus stands on the verandah where he removes coagulated lump and impurities
+from the latex, which is then poured down the chute, passing through the
+sieve into large coagulating jars or tanks.
+
+Too often it would appear, from the writers' observation, there is a lack
+of adequate supervision on the arrival of latex at the store. Much can be
+learned from an inspection of the coolies' buckets, and the cause of small
+defects in the finished rubber can often be thus traced. Leaves, stems,
+bark-shavings, and dirt appear in the buckets, and it is a source of
+constant surprise to imagine how even unintelligent coolies can allow such
+things to happen. These objects are removed before or during straining, but
+still they ought not to be there in the first place, and the fact that such
+a state of things exists is evidence of neglect on the part of the coolies
+or lack of supervision. Efforts are made in a large number of cases to cope
+with these troubles, but on some estates things are allowed to proceed in
+the same slipshod way, and too much responsibility is thrown on the
+straining process.
+
+[Illustration: RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED
+WITH FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER COOLIE" BY
+SAMPLING OF LATEX.]
+
+It is suggested that it should be the business of a European to supervise
+the reception of latex every day. This is at present quite impossible on
+some estates, but it does not alter the fact that this supervision should
+be provided, and is extremely necessary.
+
+It is surprising how the point is overlooked in many factories--not that
+they are in a dirty state, but they fall short of being classed as clean
+factories for want of the little that makes the difference. Possibly those
+in charge do not believe that all this fuss need be made, but the writers
+can assure them, from a practical knowledge of a very large number of
+factories, that cleanliness does pay.
+
+It might not be credited to Tamil coolies, but yet it is probably true,
+that the moral effect of working under the cleanest and best conditions has
+an influence upon the store coolies, and that their work is better in
+consequence. Everything which will tend to simplify the cleansing of the
+factory should therefore be installed. Hose-pipes, glazed tiles, clean
+floors, plenty of light and air are not fads or fancies, but considerable
+factors in determining the final quality of the rubber. There is
+considerable truth in the suggestion that the coagulating room and machine
+room should be as "spick and span" as a modern home dairy.
+
+STRAINING OF LATEX.--This is a most necessary process, and one which
+usually entails much trouble and time which one could wish avoided. It will
+be admitted that the trouble could be reduced greatly if the regulation of
+field processes could be made more stringent. In spite of knowledge that
+impurities must not be allowed to enter the cups, coolies will ignore the
+rule that the cup must not be placed in position until the bark shaving has
+been cut. The result is that pieces of bark fall into the cups, and coolies
+are generally too careless or too hurried to remove them.
+
+Again, when cups are placed on the ground, it is easy to see that dirt may
+adhere to them. In the collection of latex some of this dirt may fall into
+the bucket. Since the introduction of cup-holders on many estates the
+trouble from this source has decreased considerably, but, nevertheless, it
+may be taken for granted that even under the best of conditions all latex
+requires straining.
+
+The best type of strainer has yet to be evolved. Usually it consists in
+principle of a piece of fine brass mesh contained in some form of holder.
+Theoretically such a strainer should work well, but in actual practice
+nearly all strainers are a source of continual worry. Undiluted latex, as
+received at the factory, is of a rich consistency, containing very fine
+particles of dirt and often minute particles of prematurely coagulated
+rubber. The latter soon clog a fine mesh strainer, while the former may
+pass through. When the flow through the strainer becomes slow, the coolie
+in charge generally rubs the top surface of the sieve with a piece of
+coagulum, thus forcing material through the mesh. He then rubs the
+under-surface, with the result that undesirable matter falls into the
+strained latex. In theory it seems a simple matter to have a number of
+sieves ready so that a clean one may be substituted for a clogged one,
+which should be cleansed at once with water. In practice the factory coolie
+will probably only carry out instructions when the eye of the
+superintendent is alert. As a result of the rubbing and consequent strain,
+the brass mesh usually breaks away from its support and the fracture may
+not be detected for some time, during which irreparable damage may have
+been done to the resultant rubber.
+
+In view of the presence of the fine particles of dirt, to which allusion
+has been made, fine sieving of the latex appears to be essential,
+especially when sheet-rubber is to be prepared. The fine sieves are
+generally of the type known as "60 mesh," and they do not usually give
+thoroughly satisfactory results even when the gauze is supported and
+strengthened by means of cross-wires placed underneath. The general fault
+with these strainers is that a sufficiently wide "selvage" is not allowed
+in the clamped edges of the gauze, or that the edges of the support are so
+sharp and abrupt that the strands of the gauze are soon severed by the
+strain imposed in vigorous cleaning.
+
+Many estates use two strainers; the first a more robust one containing "30
+mesh" gauze, and the second the fine "60 mesh." Even this device does not
+bring about the desired immunity from trouble. Relief could be obtained if
+the latex were always in a more freely fluid form. Estates employing
+anti-coagulants in the field benefit in this respect. Other estates,
+although finally using the finest of mesh, experience far less trouble than
+most estates by reason of a difference in method of working. This can be
+explained by an outline of the system adopted on a particular estate:
+
+     (_a_) On arrival of the rich latex at the store, all visible
+     coagulated lumps and other extraneous matter are removed by the
+     tapper.
+
+     (_b_) Each tapper's latex is diluted with a quantity of water.
+
+     (_c_) The diluted latex passes through two sieves, one above the
+     other. The top sieve is of stout perforated zinc sheet, with 10
+     circular holes to the inch. This removes all large particles. The
+     lower is of "30 mesh" brass gauze, and practically no rubbing is
+     required. The latex is now in glazed-tile tanks, in which it is
+     further diluted to the required standard by means of a recording
+     instrument.
+
+     (_d_) The latex flows by means of a chute into the coagulating tanks,
+     passing through a large "60 mesh" sieve.
+
+It is not guaranteed that this method will furnish a complete absence of
+very fine particles of dirt in sheet rubber, as the human element enters so
+largely into the question; but it can be stated that no complaints have
+been received on the point of "specks of dirt" since this system was
+inaugurated.
+
+On the same estate fine sieving in the preparation of pale crepe has been
+abandoned as an unnecessary refinement. The two coarse sieves mentioned
+above are employed only, and it is to be acknowledged that the results
+justify the procedure.
+
+BULKING OF LATEX.--Not long ago advanced estates used to combine all latex
+before coagulation, in order to obtain uniformity of product. Previously it
+had been the custom to deal only with comparatively small separate volumes
+of latex, with obviously great disadvantage.
+
+Since the introduction of instruments such as the "Metrolac," by means of
+which any volume and all volumes of latex may be reduced to a common
+standard of dry rubber content, the necessity for "bulking" has passed. It
+is not now necessary to keep latex standing, perhaps for two hours,
+awaiting the arrival of other latex from distant fields.
+
+STANDARDISATION OF LATEX.--In modern practice, as already pointed out, it
+is possible now to handle any volume of latex with a view to its reduction
+to any required standard of dilution for the purpose of obtaining a
+uniform product. For the reception and subsequent handling of the latex
+various schemes have been devised, and they are usually planned in
+connection with coagulating tanks used in the preparation chiefly of sheet
+rubber.
+
+[Illustration: END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD
+FOR RECEIVING LATEX AND FILLING TANK.
+
+T, Sheet coagulation tank; C, cylinder for reception and dilution of latex;
+GG, gutter; PP, raised platform on verandah; SS, steps leading to platform;
+W, dwarf wall; EE, expanded metal partition; OO, open.]
+
+In the successful working of a tank it is necessary, in order to obtain the
+best results, to standardise all latex. This cannot be effected properly in
+the tank itself, and hence it is the practice to dilute each lot of latex
+to standard before it is run into the tank. In the ordinary way this would
+entail a great deal of labour in handling the diluted latex. To obviate
+this, the scheme outlined in the accompanying sketch has been suggested on
+several occasions and in various quarters. Such a scheme or modification of
+it has been put into successful practice on several estates. Although the
+drawing was made some considerable time ago when estates were not then
+prepared to go so far in this direction, subsequent modifications show only
+minor differences which, while leaving the original principle intact,
+testify to a fertility of resource in adapting the idea to existing
+circumstances and buildings. The drawing is _in toto_ almost a replica of
+the original installation now in successful use on the Kinrara Estate of
+the Ledbury Rubber Company. On this company's Ledbury Estate likewise a
+similar system is employed, except that the reception verandah is part of a
+natural formation and needed no such direct raising. Several other estates
+have now adopted the scheme, which has been proved to be of practical
+value. The writers make no claim to originality in the idea, which might
+have occurred to many independently on the introduction of coagulating
+tanks.
+
+[Illustration: RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX.]
+
+VERANDAH.--In reproducing the drawing it is believed that the sketch will
+convey practically all the information required. It may be explained that
+the coolies are allowed to enter only the outer part of the verandah. The
+buckets are handed across the low wall into the care of factory coolies,
+who strain the latex through gauze sieves into the latex cylinders.
+
+LATEX RECEPTION VESSELS.--These cylinders may be similar to the tanks
+commonly used for transport of latex from distant fields to the factory. An
+80-gallon cylinder is easily mounted by its trunnions on a suitable iron
+framework which is superimposed on a skeleton truck.
+
+[Illustration: ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH.]
+
+The latex is diluted down to standard in the cylinders, the truck is moved
+opposite the compartment to be filled, and a light movable gutter is placed
+beneath the vent of the outlet pipe. This pipe is fixed in the bottom of
+the cylinder, and is provided with a large stop-cock which is operated by a
+spanner key. The stop-cock should be of the simplest type, capable of being
+taken apart and assembled in a minute or so. The orifices should be large
+enough for a coolie to insert at least two or three fingers so as to
+facilitate cleaning, and the pipe should have no right-angle bends.
+
+On the inside of the cylinder a scale of gallons may be painted, so that
+one may possess a knowledge of the quantities run into, or required for the
+completion of, any compartment.
+
+A SCREW PLUG UNSATISFACTORY.--It may be of benefit to managers who
+contemplate such an installation to know that the adoption of a stop-cock
+in the vent pipe of the cylinder is the outcome of experience. In one
+instance the vent pipe as designed was fitted with a screw plug at the end.
+Unfortunately with this arrangement the flow could not be regulated, and
+owing to the "head" of the latex it dashed violently down the gutter,
+struck the bottom of the coagulating tank, and thence was scattered over
+the factory.
+
+ANOTHER INSTALLATION.--In another type of installation, in place of the
+vessels travelling upon a raised verandah platform, the standardised latex
+is conveyed to the coagulating tanks by means of drums supported by hooks
+to a chain-block and pulley which travels on an overhead gantry. This
+method is practicable, but may be regarded as less satisfactory in general
+working than the verandah method of treatment.
+
+A MODERN INSTALLATION.--In the most recent scheme for dealing with the
+reception of latex, its standardisation, and conveyance to the coagulating
+tank, the main principle of the first system outlined is retained; but the
+receptacles are not mobile. Glazed-tile tanks are employed, the capacity of
+each being approximately equivalent to that of each unit coagulating tank.
+
+The accompanying illustrations show the general arrangement and some
+details of the system of reception tanks employed on the well-known
+Pataling Estate.
+
+
+
+
+CHAPTER VIII
+
+_COAGULATION_
+
+
+Whether it is necessary to employ any coagulant, or whether latex should be
+allowed to coagulate naturally, will not be discussed at this stage.
+Neither will mention be made of any patent processes of coagulation which
+employ other than acid mediums. These subjects will be treated in a
+subsequent section of the book.
+
+CHOICE OF COAGULANTS.--It is not proposed here to enter into a discussion
+as to the merits of the dozens of known coagulants. Suffice it to state
+that acetic acid, although the oldest general coagulant, still remains the
+best and safest at the present time. There is a deal to be said in favour
+of the use of another organic acid, formic acid. It is equally as safe as
+acetic acid, and quite efficacious; the only drawback is that, taking all
+things into consideration, it is very slightly more expensive. Acetic acid,
+therefore, will always be implied in this chapter when the word "acid" is
+used.
+
+STRENGTH OF ACID SOLUTION.--In the old days it was the rule rather than the
+exception to find pure, undiluted acid used in coagulation. In many cases
+no harm resulted, for the simple reason that, owing to the large proportion
+of water in the latex, the acid was thereby very much diluted. The estates
+had to thank the over-dilution of the latex for the non-injury of the
+resulting rubber.
+
+Some estates make up a stock solution of 1 part acid to 20 of water, and
+use this with success because of the fair amount of added water present in
+the latex.
+
+It must be understood that what is being referred to now is not the
+absolute quantity necessary for coagulation, but the proportions--_i.e._,
+the respective volumes of acid and water in the solution of acid made up
+every day. That the strength of the acid solution, as well as the quantity
+used, has an effect upon coagulation can be easily demonstrated in the
+following way:
+
+Take separate and equal lots of the same latex, and to each add the same
+quantity of pure acid, but in each case diluted with varying quantities of
+water. It will be found that coagulation is quickest where pure acid is
+employed, and slowest where the acid is most dilute. It will also be found
+that, providing the quantity of acid employed was sufficient for
+coagulation, the best and most uniform coagulation is obtained from the use
+of the most dilute acid, within limits. It will often be found that where
+pure acid has been employed coagulation is local--_i.e._, we have lumpy
+coagulation, and often a very milky remaining liquor. This is due to the
+fact that, as coagulation is immediate upon the spot which is first touched
+by the pure acid, a deal of the acid is enclosed within the rubber at that
+spot, and hence other portions of the latex are deprived of acid. It is in
+such cases that most air-bubbles are enclosed.
+
+As the dilution of the acid solution is increased the mixing is more
+thorough and uniform. Coagulation is slower, and air-bubbles can escape to
+the surface.
+
+METHOD OF MAKING STOCK SOLUTION.--Experiments have been repeatedly made in
+the laboratory with acid solutions of varying dilution, from pure acid down
+to 1 part of acid in 500 parts of water. While it has been found that a 1
+in 5 solution can be used where the latex is very dilute (say, 1 part of
+latex to 5 parts of water), and a 1 in 20 solution may be used in fairly
+dilute latex (for crepe-making), it is undoubtedly a fact that for latex as
+generally "standardised" on estates a much more dilute solution of acid
+should be used--_e.g._, 1 in 100, or even 1 in 200, of water. It must be
+borne in mind that the quantity of acid necessary for coagulation is not
+changed, but merely the dilution. Let us take a concrete case to illustrate
+the point:
+
+     On an estate at present the stock solution is made up by diluting 1
+     pint of acid with 20 pints of water, and 1 gallon of this is necessary
+     to coagulate 50 gallons of pure latex.
+
+     It is desired to use a stock solution of 1 pint of acid to 100 pints
+     of water. Evidently, therefore, 5 gallons of this stock solution
+     contain only the same quantity of pure acid as 1 gallon of the old
+     solution contained, and it will be necessary to add 5 gallons for
+     every 50 gallons of pure latex. Thus:
+
+          1 to 20; 1 gallon necessary for 50 gallons pure latex.
+          1 to 100; 5 gallons necessary for 50 gallons pure latex.
+
+It may be pointed out that the quantities worked out in the foregoing
+examples are not absolutely and mathematically correct, but they are quite
+close enough for all practical purposes.
+
+It may be advanced by someone that if a dilute solution of acid, such as 1
+in 100, is used the bulk of this stock solution (5 gallons to 50 gallons of
+latex) is very great, and might be injurious to the quality of the
+resulting rubber. A moment's consideration will show that, after all, the
+volume of acid solution is only one-tenth that of the volume of latex. This
+can have no effect upon the quality of the rubber. Even dilution of the
+pure latex with half its bulk of water in the factory will have no effect
+upon the quality of the resulting rubber. It is to be remembered that,
+except in cases where the proportion of added water to latex is absurdly
+large, the main argument against putting water into the latex-cups is
+against the possible poor quality of the water rather than against the
+actual small quantity theoretically added. It is acknowledged that, where
+the water to be put into the cups can be guaranteed to be of good quality,
+no great objection would be raised against placing the smallest possible
+quantity of such water in the cups. But how many estates have such good
+water easily available to the coolies, and how many estates can be sure
+that only that smallest possible quantity would be used? It is a notorious
+fact that, even on estates where the quantity of water used was supposed to
+be a minimum, the proportion of water to latex in some cups often exceeded
+even three or four to one. In any case it may be stated as an elementary
+truism that the absence of water is more to be desired than water of
+doubtful quality.
+
+QUANTITY OF ACID.--As a result of repeated experimental work it has been
+found that, for pure average latex, the quantity of acid necessary for
+complete coagulation, reckoned in parts of pure acid to parts of latex, is:
+
+     1 part pure acid; 1,000 parts average latex.
+
+Where the latex is rather richer than average (above 30 per cent. dry
+rubber) probably a little more acid would be required, and similarly if the
+dry rubber content is lower the quantity of acid must be less.
+
+It used to be a common belief that the more dilute the latex the greater
+the quantity of acid necessary, but this would only apply to cases of
+extreme dilution of latex.
+
+As a matter of fact, up to certain limits of added water, the reverse is
+actually the case--_i.e._, the more water in the latex the less acid must
+be added, assuming that for pure latex the proportion of pure acid to latex
+is taken as 1 part to 1,000 parts. This was found to be the case up to
+dilutions of three or four times the volume of latex. To take concrete
+examples which will perhaps make the truth more clear:
+
+     Assuming we commence by making up our stock solution of acid by adding
+     100 parts of water to 1 part of pure acid, this gives us a mixture of
+     1 to 100. For 1 gallon of pure latex it would be necessary to add
+     one-tenth of its volume of the above mixture--_i.e._, 16 ozs.
+
+     Suppose we take a gallon of pure latex and add a gallon of water, we
+     now have 2 gallons of so-called latex. But we still have only 1 gallon
+     of real latex present in the diluted latex, and it is only necessary
+     to add sufficient acid to coagulate this gallon--_i.e._, 16 ozs.
+
+     Further, if 1 gallon of latex be diluted with 2, 3, or even 4 gallons
+     of water it is still only necessary to add 16 ozs. of the acid
+     mixture.
+
+     At dilutions beyond this limit, however, it is necessary to add a
+     little more acid to obtain complete coagulation.
+
+In the process of preparing sheet rubber it is very necessary to see that
+the minimum quantity of acid is used, otherwise visible defects are caused.
+But in coagulating latex intended for preparing crepe, where the rubber
+undergoes protracted washing on the machines, the presence of a slight
+excess of acid in coagulation is not calculated to cause any deterioration
+in the quality of the rubber. Advantage must not be taken of this statement
+to argue that more than a slight excess may be used without injury to the
+rubber, as it can be shown that the use of a large excess of acid results
+in an inferior rubber.
+
+QUANTITIES NECESSARY FOR MODERN REQUIREMENTS.--It may be commended to the
+notice of the beginner that any further experimental work as to the
+quantity of acetic acid necessary for complete coagulation would only
+involve a waste of time and energy.
+
+The general figure given in a preceding paragraph (1 part pure acid to
+1,000 parts of latex) may be accepted as the rough basis for working. In
+modern practice, however, undiluted latex is usually diluted to a standard
+which may vary on different estates from 1-1/4 lbs. to 1-1/2 lbs. dry
+rubber per gallon.
+
+Latices of these strengths can be coagulated at a ratio of 1 part pure acid
+to 1,200 parts of standardised latex; and this quantity need not be
+exceeded, except in cases where an appreciable amount of some
+anti-coagulant is present in the latex. The proportion may then be raised
+to 1 in 1,000.
+
+If considered advisable the acid may be used in a 1/2 per cent. solution
+for sheet preparation; but in any case it is advised for the sake of
+uniformity that a 1 per cent. solution should be employed in the
+preparation of both sheet rubber and crepe rubber. In most modern
+factories, measuring vessels of various capacities are to be found, and it
+is always more satisfactory to have the solution made up in approximately
+correct strength at the rate of 1 oz. of pure acid to 5 pints of water.
+Often, however, on some estates European supervision of this work is not
+possible, and the preparation of the acid solution has to be left in the
+hands of a (more or less) skilled coolie. It is thus necessary to find some
+less fine, but still approximately correct, method of procedure. In the
+East the kerosene tin is in universal favour for the carriage of water, and
+there is no reason why it should not be utilised as a standard measure for
+preparing the dilute acid solution, _providing it is not allowed to become
+rusty_. The capacity of the tin is 4 gallons (640 fluid ozs.), so that a
+one-hundredth part would be approximately 6-1/2 ozs. It is suggested that
+this quantity should be measured out by means of a glass graduated vessel,
+and then that an aluminium cup should be cut down so as to hold the exact
+quantity.
+
+This would reduce the making of a solution, sufficiently approximate to 1
+per cent. strength for all practical purposes, into a simple operation of
+mixing pure acid and water in the ratio of one cupful of acid to 1 kerosene
+tin of water.
+
+The actual quantity of solution required for the coagulation of any volume
+of standardised latex can be calculated easily from the ratio 1:1,200. As
+the strength of solution is 1:100 it will be seen that the quantity to be
+taken is _always one-twelfth_ that of the volume of latex--_e.g._:
+
+     (_a_) If the latex tank holds 90 gallons of standardised latex, 7-1/2
+     gallons of dilute acid solution are required.
+
+     (_b_) A tank containing 120 gallons of latex would need 10 gallons of
+     the 1 per cent. acid solution.
+
+It is assumed that all estates, not only in the preparation of sheet
+rubber, but also in the making of crepe rubber, always employ the system of
+standardising latex in order to obtain uniformity. They are ill-advised if
+they do not follow this practice; but in case average undiluted latex is
+treated in coagulation, the quantity of acetic acid to be used should be
+calculated from the ratio 1:1,000.
+
+If the acid solution is to be employed in 1 per cent. strength, _one-tenth_
+of the volume of latex to be treated will indicate the required quantity of
+solution necessary for complete coagulation unless anti-coagulants have
+been used, when the quantity must be increased as experience directs. It
+will be recognised, of course, that undiluted latex may only be used in any
+case for the preparation of crepe rubber; or in some exceptional case, such
+as the special preparation of "slab" rubber.
+
+CARE IN MIXING.--It is essential that the mixture of dilute acid and latex
+should be thoroughly intimate. This can only be attained by careful
+manipulation, especially in the case of sheet preparation. Where crepe
+rubber is to be made it may be permissible to employ a solution stronger
+than 1 per cent., but it is not advised. The acid should be poured into
+the latex while stirring, and the agitation should continue for such a
+period as to ensure thorough mixing in all parts.
+
+It will be appreciated that in the preparation of sheet rubber this period
+may not be unduly prolonged, otherwise the latex will have begun to
+coagulate before skimming and the placing of the partitions in their
+respective slots can be effected. Furthermore, while in the preliminary
+treatment for crepe rubber, the formation of enclosed bubbles and surface
+froth is immaterial. For sheet preparation it is essential that the
+stirring shall be done so carefully as to try to avoid internal bubbles and
+to reduce surface froth to a minimum. For crepe-making a perforated board,
+with handle attached at right angles to the face of the board, may be used;
+but in shallow sheet-coagulating tanks, broad paddles (which may or may not
+be perforated) give good results as long as there is a sufficient number
+used to cover the area of the tank in reasonable time. Obviously also,
+where the area of any tank or compartment is of any appreciable size, the
+dilute acid solution should be poured in from various points so as to
+obtain a good even distribution. In some cases the acid is distributed from
+a sprinkling can, but this is a refinement which experience shows to be
+unnecessary. In actual practice, working on a tank measuring 12 ft. by 4
+ft., no difficulty is found if coolies pour in acid solution from four
+points. The degree of success depends entirely upon experience and
+efficient supervision. This remark applies equally to the use of various
+devices, such as rakes with broad teeth, used as stirring implements. There
+is room for display of ingenuity in this direction, and it is found often
+that, while they are used successfully on one estate, they may be condemned
+on another.
+
+[Illustration: TWO VIEWS OF DILUTION AND MIXING TANKS.
+
+Below, on the right, coagulating tanks. At the far end strainers. Each
+dilution tank is of equal capacity to the corresponding coagulating tank.]
+
+USE OF SODIUM BISULPHITE.--Some few years ago a demand for pale crepe
+rubbers sprang up, and this demand has been maintained. The total quantity
+of pale rubber put on the market previously could only have amounted to
+very little, and that little was obtained by luck and various tricks in
+manipulation. It must be premised that if coagulation is allowed to take
+place, either naturally or with the aid of acetic acid, the resulting
+rubber will almost inevitably oxidise on the surface, except in the cases
+of very dilute or young latices. Even supposing that this darkening of the
+surface does not take place in the wet stage, it is often found that a
+rubber expected to dry to a pale colour does not fulfil expectations, and a
+dull neutral shade results. This darkening of crepe rubber may be
+attributed to a slow process of oxidation, which continues until the rubber
+is dry. From these remarks it will be seen that the process of oxidation is
+a natural one, and that any pale rubber formerly shipped was the outcome of
+circumstances outside the control of the estate, except in such cases where
+boiling of the coagulum, etc., was resorted to. The fact that one rubber
+happened to be a shade darker than another was absolutely no criterion as
+to the value of the rubber, but apparently the market thought, and still
+thinks, otherwise, although the actual necessities of manufacturers for a
+pale crepe to be employed in special processes must be comparatively small.
+
+The prevention of this natural oxidation was a problem which exercised the
+minds of all responsible for the preparation of pale rubbers, and much time
+and thought were expended upon it. Various theories were propounded, and
+the chief conclusion arrived at was that the darkening of rubber was to be
+prevented by excluding all the light possible from the drying houses. To
+this end windows were to be kept shut, or else they were provided with
+ruby-coloured glass, which incidentally kept out the air. In spite of these
+precautions, little success attended the expenditure of so much energy and
+thought. It was absolutely necessary that some chemical agent should be
+discovered which would make the preparation of pale crepe possible for any
+estate. This chemical would have to fulfil several requirements before it
+could become popular:
+
+     1. It must be a simple substance capable of being easily handled.
+
+     2. It must be very soluble, so that solutions could easily be made up
+     by inexpert workers.
+
+     3. It must be cheap.
+
+     4. It must be quite innocent of any harmful effect upon the quality of
+     the rubber.
+
+After months of investigation into the properties of other chemicals the
+writers decided that the only one which satisfactorily answered all
+requirements was sodium bisulphite. The writers make no pretension to any
+claim of having discovered the properties of this substance, which was a
+common chemical, and widely known. Even its action on latex was suspected
+before they engaged upon the work. These matters are only mentioned because
+the credit, if any, should be given to the laboratories of the Rubber
+Growers' Association.
+
+As soon as it began to be known on the market that sodium bisulphite was
+being used in the preparation of pale crepe, a great outcry was made, and
+estates were warned that no more rubber prepared in this way would be
+accepted. It was said that the chemical would destroy the "nerve" of the
+rubber,[2] and it was definitely stated that rubber prepared with this
+chemical was brittle. It must be remembered that brokers had some
+legitimate excuse in raising objections to the introduction of new and
+strange chemicals for preparing rubber, as they were quite without means of
+judging whether the rubber had suffered harm or not. Still, on the other
+hand, private tests had been made in conjunction with Messrs. Beadle and
+Stevens for fully eight months before the name of the chemical was
+mentioned in reports, and they had decided from the results of
+vulcanisation tests that the chemical was quite innocuous. Then, and only
+then, did we consider it advisable to recommend the use of sodium
+bisulphite in general estate practice. Owing to the initial prejudice
+against rubber prepared with sodium bisulphite, the results of our
+preliminary work were published by permission of the Rubber Growers'
+Association.[3] The original instructions to estates regarding the proper
+employment of this chemical were given in the private reports issued by the
+Rubber Growers' Association in 1911. At the present time it is probably
+accurate to state that it is now used by all estates preparing fine crepes.
+Representatives of manufacturers have sometimes given us to understand
+that the question of paleness of colour in such rubber is of no such
+importance as is impressed upon us as producers. While we are prepared to
+believe, we can only plead that from our point of view the supply arises
+from the demand. Such are the conditions governing the sale of rubber that,
+irrespective of the requirements of the ultimate user, we have to market
+rubber which is valued almost completely upon its appearance at the time of
+sale.
+
+[2] Williams, International Rubber and Allied Congress, London, 1914.
+
+[3] "The Employment of Sodium Bisulphite in the Preparation of Plantation
+Rubber," Beadle, Stevens, and Morgan, _India-rubber Journal_, August 2,
+1913.
+
+As long as such conditions prevail estates must continue to adopt any
+device of proved harmlessness, in order to obtain the best possible price
+for their product, and not because we desire to continue a practice which
+some assure us to be unnecessary, and which, moreover, adds somewhat to the
+cost of production.
+
+QUANTITIES OF SODIUM BISULPHITE.--It must be premised that, although sodium
+bisulphite is employed on some few estates in the preparation of sheet
+rubber, we do not advise the practice. It is unnecessary, and may lead to
+some little trouble and delay in drying. In any case, sodium sulphite gives
+the results desired for sheet rubber (see following). It must be
+understood, therefore, that we are concerned here, in the case of sodium
+bisulphite, with its employment in the preparation of fine pale crepe only.
+
+As the dry rubber contents of latices vary with the age of the trees, the
+general health of the trees, the seasons and general climatic conditions,
+the relative strain imposed by depletion of reserves through tapping, etc.,
+it will be clear that the effect produced by a definite quantity of sodium
+bisulphite in any given volume of latex will also vary--_i.e._, the effect
+depends upon the potential amount of rubber present. A dilute latex needs
+less sodium bisulphite than a richer latex to produce the same effect in
+colour.[4]
+
+[4] Incidentally there are certain occasions, as in the opening of areas of
+bark rested for long periods, when the latex is of a rich yellow colour.
+Sodium bisulphite will not "bleach" this colour, and it is well to remark
+again at this stage that the action of the chemical is only to avoid or
+arrest oxidation (darkening).
+
+Hence it follows that if in any factory uniform quantities of the solution
+are used for any given volume of undiluted latices from different areas of
+the estate, the effect upon the dry rubbers will vary. This explains why
+some estates obtain different shades of rubber in their fine pale crepes.
+
+The remedy obviously is to reduce the variation in latices by diluting them
+all to a standard rubber content as is done in sheet preparation. One is
+thus assured that the prescribed quantities of sodium bisulphite will meet
+requirements in every case, and that waste will be avoided.
+
+Working with a standard of 1-1/2 lbs. dry rubber per gallon the following
+formula should serve as a _maximum_:
+
+
+_Formula for Use of Sodium Bisulphite._
+
+     (_a_) Dissolve sodium bisulphite in water at the rate of 1 lb. to 10
+     gallons.
+
+     (_b_) Of this solution use 1 gallon to every 10 gallons of latex.
+
+MAKING A SOLUTION.--The making of a solution of the chemical would seem to
+be a simple matter, but to judge by the ill-effects sometimes observed in
+the dry rubber the simplicity of the operation appears to have been
+overrated. Great care must be exercised in preparing the solution, and the
+work should not be left to the few minutes preceding its actual
+requirement; such has been found to be the case in several factories, so
+that it is not surprising if the rubber is defective.
+
+The powder should be added gradually to water with thorough stirring, which
+should be continued for five minutes at least. Even then there may often be
+seen at the bottom undissolved particles, sand, and other impurity. It is
+necessary, therefore, in such cases to decant the solution through a piece
+of cotton cloth before using. No solid particles should be allowed to enter
+the latex.
+
+ABUSE OF SODIUM BISULPHITE.--It is now generally recognised that the abuse
+of sodium bisulphite, in the form of an excess, leads mainly to delay in
+the period of drying and the production of an overpale rubber.[5] It is
+probable that few estates, if any, now experience trouble due to this
+non-observance of the rules and quantities laid down for use.
+
+[5] "The Preparation of Plantation Rubber," Morgan, 1913, p. 74.
+
+RESIDUAL TRACES OF SODIUM BISULPHITE.--The prolongation of the drying
+period was attributed to the fact that traces of substances caused by the
+decomposition of sodium bisulphite remained in the rubber if the rubber
+were not sufficiently worked and washed on the rolls. These traces must
+have been very minute, but they were sufficient to retard the progress of
+drying. That much depended on the care exercised in washing is evident from
+the fact that samples prepared with varying quantities of the chemical show
+varying results on extraction. These samples were tested for the presence
+of sulphates. Of the series tested that sample prepared with bisulphite in
+the proportion of 1 part to 600 parts latex showed only a trace of sulphate
+present; while the one prepared 1:2,400 gave an equal quantity.
+Intermediate samples contained no trace of sulphate. On the whole,
+therefore, the presence of sulphate in crepe rubber is adventitious, and
+properly washed crepe prepared with moderate quantities of bisulphite may
+be taken as free from any residual quantities. Meanwhile there cannot
+possibly be any doubt of the advantages gained by the use of sodium
+bisulphite, and it would not be very wide of the mark if the statement were
+made that, in the event of this chemical being discarded, most contracts
+for pale crepe could not be fulfilled.
+
+SODIUM SULPHITE.--It would not be amiss to insist upon the point that while
+the nature of sodium _bisulphite_, as employed in the preparation of
+rubber, is anti-oxidant, sodium sulphite is employed chiefly for its
+anti-coagulant property. It is not used, therefore, in the making of crepe
+rubber, but is of service in the preparation of sheet rubber, where the aim
+is to keep the latex in good fluid condition as long as is necessary, and
+to retard coagulation slightly so that enclosed bubbles of gas or air may
+escape. Formulae have been given for its use in the field when required. On
+some estates this practice is not found necessary, but a quantity of
+solution is always placed in the bottom of the reception vessels prior to
+the straining of latex into them. Only a small quantity is used, and as a
+working basis the following formula may be adopted:
+
+
+_Sodium Sulphite: For Use in the Factory._
+
+     (_a_) Dissolve 2 ozs. of anhydrous sodium sulphite in a gallon of
+     water.
+
+     (_b_) The gallon of solution, placed in the bottom of the reception
+     jar or tank, is sufficient for the treatment of 40 gallons of
+     standardised latex (1-1/2 lbs. dry rubber per gallon).
+
+The warning previously given regarding the necessity for thoroughness in
+the preparation of solutions is here reiterated. Stirring should be
+thorough, say for five minutes, and if there is any sediment or undissolved
+matter the solution should be strained through cloth before using.
+
+Where uniform jars or tanks are in use, the majority of which will contain
+uniform quantities of latex daily, the practice of using the chemical can
+be made almost fool-proof even in the hands of coolies. A calculation is
+made of the quantity of powder required for each vessel daily. The
+necessary number of lots is weighed out each morning and each placed in an
+envelope. The process is thus simplified by the fact that the contents of
+an envelope, neither more nor less, are required for each unit reception
+vessel. Even the weighing can be done by a coolie if he is given a
+counterpoise (of lead, for example) equivalent to the required weight.
+
+It will not be found necessary to do any vigorous stirring of the solution
+with the latex, as the latter is strained into the solution and the
+continued addition of successive quantities is sufficient to give a good
+mixture.
+
+USE OF FORMALIN.--Few estates now use formalin (formaldehyde) as an
+anti-coagulant. It must be acknowledged that when not abused there are
+points in favour of its employment in preference to sodium sulphite, but
+these are outbalanced by certain disadvantages. The argument may be stated
+thus:
+
+     _Points for_: (1) If made up freshly it is an effective
+     anti-coagulant.
+
+     (2) Formalin being the solution of a gas in water, there is no
+     residual substance left in the rubber to delay drying.
+
+     (3) Its use gives a bright clear rubber.
+
+     _Points against_: (1) Its cost at all times is greater than that of
+     sodium sulphite.
+
+     (2) If the jar is not sealed there is loss by evaporation, thus
+     increasing the cost.
+
+     (3) Its effect upon the rubber is uncertain. Even in normal quantity
+     it is said to cause "brittleness" or "shortness."
+
+Certain few estates, however, have continued its use, and no trouble is
+claimed to ensue. The following formula is stated to give satisfactory
+results in the preparation of sheet rubber, when applied as in the
+preceding paragraphs bearing on the employment of sodium sulphite:
+
+
+_Formula for Use of Formalin (Formaldehyde)._
+
+     (_a_) 1 pint of formalin is diluted with 5 gallons of water.
+
+     (_b_) Of this solution 1 gallon is required for 50 gallons of
+     standardised latex.
+
+In noting this formula the writer gives no recommendation regarding its
+use. Whatever may be the actual facts regarding the effect of formalin upon
+the vulcanisation of rubber, when used in minimum proportions, there can be
+no question concerning its injurious effect if used in excess. Beyond this
+the factors of cost and loss militate against its wider employment.
+
+
+
+
+CHAPTER IX
+
+_PREPARATION OF SHEET RUBBER_
+
+
+PALE SHEET.--The first form in which plantation rubber was prepared was as
+"biscuits" or sheets. This form remained in favour for some years. The
+first biscuits or sheets were rather dark in colour owing to the natural
+oxidation which followed. Then it was discovered that by diluting the latex
+the degree of oxidation was diminished, and later it was found that if the
+soft coagulum were placed in almost boiling water for a short time the
+resulting rubber was pale. Thus there arose gradually a demand for pale
+sheet. With our present knowledge we are in a position to state that the
+pale biscuits were not in any way superior to the darker ones, and they
+were in most cases actually inferior.
+
+It was found also as time progressed that sheet rubber, on air-drying,
+became covered with external surface moulds, and that, more often than not,
+the smell of the drying rubber was the reverse of pleasant. Even when dry
+the sheets had to be continually brushed free from moulds, and by the time
+the rubber reached the market it was again usually mouldy. Such are, even
+now, the handicaps under which those who prepare pale sheets have to
+labour. Few, however, are the estates making pale sheets, and they are
+confined almost entirely to native holdings.
+
+To those accustomed only to the preparation of crepe rubber, where
+coagulation can be effected in large batches, the preparation of sheet
+rubber always seems to demand much more labour. As a matter of fact,
+although the preliminary operations certainly do demand more care and
+labour than in crepe-making, there are compensating advantages in the
+machining stage. For the preparation of sheet of the highest quality on any
+but the largest scale, elaborate installations of machinery are quite
+superfluous, as equal results can be obtained with pairs of rolls worked by
+hand.
+
+UNIFORMITY OF PRODUCT.--There will be no need to enter again into a
+discussion of the preliminary operations of receiving and straining latex
+for sheet-making. They have been fully dealt with in Chapter VII. It used
+to be the general custom to mix the acid and latex in each individual dish,
+and in some small or non-progressive factories that is still the procedure.
+Quite apart from the question of labour entailed, the process is quite
+unnecessary. Even if comparatively small volumes of latex are handled,
+standardisation by dilution should be the rule, and the acid solution
+should be added to the bulk. It is possible to stir in the acid and to
+ladle out uniform quantities in each pan or dish from a bulk volume of up
+to 40 gallons if the organisation is efficient.
+
+On any but a small scale the labour entailed in the handling and cleaning
+of pans is excessive, and shallow tanks are now employed on most estates.
+The reception and standardisation of latex by dilution has already been
+discussed in Chapter VII. The combination of this practice with the
+employment of shallow coagulating tanks has simplified working and reduced
+the cost of labour. It is not intended to enter into any lengthy discussion
+relative to the merits of sheets made in pans as against those made in
+tanks. It is granted that it is possible to make a "pan" sheet superior in
+appearance to the general average of "tank" sheets; but from an economic
+standpoint the introduction of the use of tanks into all but the smallest
+factories is only a matter of time, if the demand for this class of rubber
+persists.
+
+THE IDEAL TANK.--Even the most modern installations of sheet-coagulating
+tanks must be regarded as merely temporary devices, as, given facilities,
+the room for improvement is so wide.
+
+The first tanks made erred in being too large, and as the result of
+experience the size of units has now been reduced to a maximum of 12 feet
+by 4 feet by 1 foot deep.
+
+[Illustration: UNIT MODERN COAGULATING TANK (TWO VIEWS).
+
+Construction of brick and cement with lining of glazed tiles. Note slots
+incorporated in side tiles. Partition boards in piles in the background.]
+
+Tanks are at present constructed either of hard timber or of brick and
+cement faced with glazed tiles; both types have inherent drawbacks. The
+wooden tanks are difficult to keep clean and in "sweet" condition. The
+glazed tiles, unless extremely well laid, allow the acid serum (from which
+the rubber is removed) to percolate between the interstices. Thus "pockets"
+of liquid collect beneath the tiles, and in process of the decomposition of
+certain constituents dissolved in the serum evil-smelling gases are set
+free.
+
+[Illustration: ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON
+THE RIGHT.
+
+Note drainage cocks, chute, and sieve in position.]
+
+It should not be a matter of difficulty for manufacturers to make sheets of
+thick glass sufficiently large to form the bed-plate and side-pieces
+necessary in the lining of a tank. If such adjuncts could be secured, the
+disabilities indicated above would be perhaps wholly removed. Unless there
+is a demand from estates, however, it is idle to expect a supply to be
+forthcoming.
+
+An even greater improvement would take the form of unit tanks cast in
+glazed white-ware with the necessary slots incorporated in the sides. At
+present no known firm makes such tanks of sufficient size. A unit could
+measure (internally) 6 feet by 4 feet by 1 foot deep, with slots 1-1/2
+inches apart, and 3/8 inch in width. The tanks might be reinforced with
+iron bars, so that they could either be used alone or embedded in the usual
+brick structure. The junctions of the bed-plate and side-pieces could be
+finely rounded so as to facilitate cleaning, and at one end a draining-hole
+could be made, say, 1 inch in diameter.
+
+[Illustration: CLOSER VIEW OF FOREGOING.
+
+Note partitions in position and coagulum being removed.]
+
+Meantime both the hard-wood tanks and those of glazed tiles find their
+particular applications. The former is generally employed in smaller
+factories, or where future large increases of crop preclude the present
+installation of a fixed system. The latter find use in large factories, or
+where no new areas remain to come into bearing.
+
+MODERN INSTALLATION.--As an example of a modern installation of coagulating
+tanks, we can do no better than offer reproductions of the system now in
+use on Pataling Estate.
+
+A warning must be given against employing all tanks of stone-ware or cement
+unless well glazed. Almost without exception, irrespective of the material
+used in the construction of coagulating tanks, wooden partitions are
+employed. In the few exceptional cases the partitions are either of glass
+or of aluminium. The former would appear to be the ideal substance, were it
+not for initial cost and loss by breakage. These disabilities may possibly
+be overcome in course of time.
+
+CARE OF TANKS.--The use of aluminium would have been wider had it not been
+for lack of supplies and the question of cost during the War. A novel
+method of employing aluminium partitions was introduced in the factory of
+Tremelbye Estate. There were no slots in the sides of the glazed-tile
+tanks, but the necessary slots were very ingeniously created by means of
+aluminium "distance-pieces," the two long edges of which were turned at
+right angles to the face of each piece to a depth of about 1/4 inch. The
+ends of the thin aluminium partition moved in the slot thus formed between
+two adjacent "distance-pieces." The friction between the surfaces was
+sufficient to allow all the partitions, when in position, to be raised well
+above the floor of the tank, so that a uniform level of latex was obtained.
+Slight hand-pressure only was then required to push the partitions down.
+
+Naturally the cleansing of glass or aluminium partitions presents no
+difficulty, but in the case of wood failure to ensure thorough cleanliness
+leads to possible defects in the finished dry rubber. Provided the wood
+could be made waterproof, no trouble would ensue, and hence various
+measures have been tried with that object in view. When new the boards have
+been surface-waxed or varnished, and the treatment has been repeated on
+occasions. But in course of time the surface film of waterproof material
+has disappeared, partially or wholly, and the trouble recurs. When
+partitions become sodden with serum, the surfaces are liable to be coated
+with a slime, consisting largely of organic growths which have an effect
+upon the latex, causing "pitting" on the surface of the coagulum and
+enclosed bubbles within.
+
+[Illustration: ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF
+GRAVITATING LATEX.]
+
+It is recommended, therefore, that wooden tanks, after ordinary cleansing
+daily, should be swabbed out with a 5 per cent. solution of sodium
+bisulphite. Wooden partitions should receive the same treatment, and once a
+week at least (or every day if possible) they should be placed in the sun
+for an hour or two, care being taken that both sides of a partition are
+exposed in turn. Before being placed in the latex, all wooden partitions
+should be made wet on the surfaces.
+
+Some years ago the writers had made a partition of vulcanite, which
+apparently would have proved of great service but for the initial cost. The
+advent of the War put the matter out of the question, but it is possible
+now that such a material would be worthy of extended trial. Except in the
+matter of cost, it would appear to have advantages over any substance yet
+tried; and if it were possible for estates to supply their own lower grade
+rubbers direct, the cost might be reduced considerably.
+
+[Illustration: A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION.
+
+Behind wall in background are the tanks in which latex is standardized.
+Note vent, to the left, through which latex flows and wooden "stopper" on
+edge of tank.]
+
+STANDARD LATEX.--Enough has been written (see Chapter VII.) to familiarise
+the reader with the use of this term for the description of latex diluted
+daily to a level of dry rubber content. Whatever may be the practice
+elsewhere, it is now fairly general on estates in Malaya to reduce all
+latices to a uniform "strength" for the preparation of sheet rubber. It is
+claimed that only in this manner can uniformity of product be achieved.
+
+The selection of a standard has been the outcome of general experience. It
+has been found that if too high a standard is taken difficulties arise,
+such as (1) unsatisfactory and uneven coagulation, (2) too thick a coagulum
+for easy working in general, (3) too extended a period of drying and
+smoke-curing, and hence too dark a colour in the finished rubber.
+
+[Illustration: A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION
+TANKS, RAISED, ON THE LEFT.]
+
+On the other hand, too low a standard also brings trouble in its train. The
+coagulum is too porous, will not stand handling, and the resultant sheet is
+too thin unless an abnormal thickness of coagulum is prepared. Furthermore,
+over-dilution means an increase in the number of tanks required for any
+original volume of latex. This involves an increase in floor area, and
+perhaps in the size of the building. The soft sheets, when rolled, may
+spread to such a width as to cause the edges to be squeezed under the
+cheek-blocks of the machines, etc.
+
+For all practical purposes, whether sheets are prepared in pans or in
+tanks, it has been found that the optimum results are obtained by the
+adoption of a standard approximating and not exceeding 1-1/2 lbs. dry
+rubber per gallon. Primarily this standard has a direct connection and
+interdependence with the distance between the partitions (or between the
+slots) in coagulating tanks. The distance found most practicable is 1-1/2
+inches. This thickness of coagulum, when prepared from latex not exceeding
+a standard of 1-1/2 lbs. dry rubber per gallon, is found to yield a very
+satisfactory sheet in all respects.
+
+It will be seen that we have two possible main factors of variation:
+
+     (_a_) Distance between partitions, causing visible differences in
+     thickness of coagulum.
+
+     (_b_) Dry rubber content of latex, causing differences in the density
+     (_e.g._, hardness or softness) of the coagulum.
+
+The effect of variation in (_a_) will be clear. Even when latex of a
+standard of 1-1/2 lbs. per gallon is employed the resulting sheet may be
+either too thin or too thick.
+
+Similarly, as already argued, the use of too low or too high a standard of
+dilution (when the factor of distance between partitions is not allowed to
+vary) is capable of causing much difficulty. While this is correct,
+broadly, it is found in the experience of some estates that their
+requirements are satisfied by a slightly lower standard than 1-1/2 lbs. per
+gallon. Thus it is not uncommon to note the adoption of a standard
+equivalent to 1 lb. 4 ozs. or 1 lb. 6 ozs. dry rubber per gallon.
+Experience dictates, however, that for the recognised standard measurements
+of modern tanks the practical limits of satisfactory density of latex lie
+between 1-1/4 lbs. and 1-1/2 lbs. per gallon.
+
+STANDARDISING INSTRUMENTS.--For standardising latex by dilution all that is
+required is an instrument which will preserve a perpendicular position
+while floating in latex, will be sufficiently sensitive to indicate fairly
+small differences in density of latex, and has one mark on its aerial
+portion accurately indicating a density corresponding to the required
+standard. On scientific grounds it can be demonstrated that such an
+instrument as employed in common practice would not be strictly
+accurate.[6] It is not proposed, in this section of the book, to discuss
+such considerations.
+
+[6] De Vries, "Archief voor de Rubbercultuur."
+
+Instruments of this nature are represented by the "Metrolac" (originating
+from the Rubber Growers' Association) and other similar recorders. They
+generally consist of a submersible bulb with a projecting stem which is
+graduated. The "Metrolac" differs from others in that the bulb is of
+torpedo form (thus reducing "skin friction"), and the graduations on the
+stem indicate actual weight of dry rubber per gallon instead of the
+ordinary specific gravity figures.
+
+Theoretical considerations to the contrary, it is found in actual practice
+in Malaya and Ceylon that, although such instruments are naturally delicate
+and require careful manipulation, they are of considerable practical value
+and satisfy a definite requirement. Until an instrument of greater accuracy
+and equal simplicity can be discovered all estates should regard the
+possession of a few "Metrolacs" as essential.
+
+The nature of their construction and the average conditions under which
+they are used (and abused) make it impossible to rely upon their accuracy
+indefinitely or for any long period. It is always recommended, therefore,
+that there should be at least two instruments available, one of which may
+be in daily use, while the other is kept in safe custody and only employed,
+say, once a week for purposes of checking the accuracy or degree of
+inaccuracy of the other. This can be done with reasonable approximity by
+placing both instruments in a tall vessel containing well-mixed and diluted
+latex. Instruments showing a marked degree of inaccuracy should not be
+preserved; but in cases of necessity "Metrolacs" from estates belonging to
+company members of the Rubber Growers' Association may be sent to the
+laboratories for repair and adjustment.[7]
+
+[7] This applies to the gilt brass instruments. As the result of experiment
+the Rubber Growers' Association are now introducing glass instruments.
+These are necessarily more fragile, but while unbroken can be relied on to
+give correct readings.
+
+Where field coagulating stations have been instituted on estates, it is
+strictly necessary that instruments should be provided in all cases; and it
+should be a rule that these are tested and corrected weekly by a standard
+instrument employed for that purpose only. This need was well recognised by
+many estates when, during the War and the consequent shortage of supply of
+"Metrolacs," a demand arose which was met in some degree by crude
+instruments of local manufacture, such as that commonly known as the
+"Castlefield bobber," contrived and made by the enterprising manager of the
+estate of that name. The demand for the more accurate instruments can now
+be met.
+
+METHODS OF USING THE INSTRUMENTS.--The "Metrolac" was devised and
+introduced by the writers on behalf of the Rubber Growers' Association, and
+directions for its use were given. Tables were prepared by means of which
+simple calculations for the dilution of any given latex could be made.
+These did not find an extended application, inasmuch as in the majority of
+cases native workers only were in charge of the processes of rubber
+preparation. In point of fact, such calculations are not strictly
+necessary, as the operation of standardising the latex can be done quite
+simply and skilfully by a trained native. Latex as it reaches the store in
+average weather from any particular division or field does not vary greatly
+in density. The trained coolie or foreman, basing his practice on
+experience, adds to the latex a quantity of water, and then makes a first
+test with the standardising instrument. Several additions of water (with
+thorough stirring) may have to be made before a test indicates that the
+correct density has been obtained, but it is surprising how quickly a
+skilled worker will arrive at the desired standard. Extreme or absolute
+accuracy is not insisted upon or desired, as avoidable delay is to be
+deprecated, and the result in any case is sufficiently exact for practical
+purposes.
+
+SKIMMING.--During the gravitation of the latex from the reception vessels
+(in which the standardising of the latex is effected) to the coagulating
+tanks, much surface froth is usually caused. This is best removed by means
+of a thin board of a width slightly less than the breadth of the tank. The
+skimmings are sometimes placed in pans and subsequently made into a second
+grade of sheet rubber, or they receive treatment with a small proportion of
+sodium bisulphite and eventually appear as fine pale crepe. The practice
+varies usually according to the form in which the general No. 1 grade is
+prepared.
+
+On some estates a great deal of the frothing is avoided by placing in
+position at the receiving end of the tank a perforated partition. This
+partition may be made of wood, or of stout zinc (or aluminium) carrying ten
+circular holes to the inch. Through this the latex percolates, while the
+froth is retained on a small area. The froth is removed prior to the
+addition of the acid. After stirring in the acid solution most estates
+again skim the surface of the latex; but if the stirring has been performed
+properly there should be little froth. This, when it collapses, in any case
+will appear only on the upper edge of the strip of coagulum, and after
+rolling should not be visible. It would appear, therefore, that the second
+skimming is not necessary.
+
+STYLE OF SHEET.--Within the last few years the custom of making plain
+sheet--_i.e._, sheet having a plain surface--has gradually given place to
+the preparation of ribbed sheet--_i.e._, sheet having a pattern marked on
+the surface. It would probably be correct to say that plain (smooth) sheet
+is now only prepared by natives or by some estates just come into bearing.
+Even in the latter case there is no reason why smooth sheet should be made,
+as hand machines are sold which will do all the work required. It will be
+evident to anyone acquainted with rubber preparation that in the matter of
+actual quality of rubber the question of smoothness or a pattern can have
+no bearing on the result. One advantage claimed for ribbed sheet which may
+entirely justify the preference exhibited by consumers, relates to the
+question of packing. When rubber arrives at home it is frequently found to
+be in an almost solid block, due to the pressure of the sheets superimposed
+in the case. The smoother the surfaces of the rubber in contact the greater
+the adhesion and the denser will be the mass, and consequently the greater
+the difficulty in separating individual pieces. Under such circumstances it
+is plain that the difficulty is diminished if the sheets have a raised
+pattern on them. It is noted also that the liability to mildew-growth is
+greater the smoother the surfaces of the rubber.
+
+On these grounds the "marking" of sheet rubber is to be commended. These
+reasons apart, it is really astonishing the difference made in the
+appearance of the sheets by impressing upon them a ribbed pattern, and it
+is highly probable that the market value of the rubber is slightly
+increased. It is not our duty to attempt to reason why this simple
+operation should increase the market value of sheet rubber; it is
+sufficient to recognise that it is so, and that money may be thrown away by
+neglecting to cater for the taste of the market. Of the patterns impressed
+upon sheet rubber there is a variety, but the general style is that known
+as the "spirally close-cut ribbing."
+
+STANDARD SHEET.--Leaving for the present the question of pattern of mark,
+one cannot do better by way of introduction than to reproduce the
+instructions[8] given generally to estates.
+
+[8] "Handbook on Preparation of Rubber," Rubber Growers' Association, May,
+1917, p. 28.
+
+ROLLING AND MARKING OF SHEET RUBBER.--Working with standard latex it is
+found that strips of coagulum 1-1/2 inches in thickness require little
+rolling to produce sheets of desirable thickness.
+
+     (1) The sheets or strips are first given a preliminary rolling with a
+     heavy hand-roller made of hard wood. The roller is passed once in one
+     direction, and once in the reverse direction.
+
+     (2) The coagulum is then passed through smooth machines twice, once
+     with the rolls fairly open, and once with a narrower space. It is not
+     found advisable to close the smooth rolls so tightly that the rubber
+     is made too hard.
+
+     (3) The sheets or strips are then passed once through a pair of
+     marking rollers. Various types of patterns are used, but the one which
+     appears to give the most satisfactory results is that known as the
+     "close-cut spiral." This produces the semblance of a small diamond
+     pattern on the rubber. The surface of the sheet is raised in
+     well-defined ridges, which appear to present the maximum drying
+     surface exposed to the atmosphere of the smoke-house. Thus, not only
+     is the appearance of the sheet rendered attractive, but also the
+     period of drying is reduced. Starting with standard latex and
+     following the procedure here described for rolling and marking, sheets
+     should be ready for packing in ten or eleven days. If the period is
+     longer, it is possible that the design or structure of the smoke-house
+     is at fault.
+
+WHEN TO WORK THE COAGULUM.--Before proceeding to discuss other points the
+question remains to be settled as to how long it may be necessary or
+advisable to allow the coagulum to remain in the serum before rolling it.
+For reasons of practical economy in factory working, it is usual to allow
+sheet rubber to remain over night, and the coagulum receives attention
+early next morning. During the interval (averaging about eighteen hours),
+the coagulum consolidates, leaving an almost clear serum if the correct
+quantity of acid has been added to the latex. Any but the very slightest
+trace of milkiness in the serum indicates an insufficiency of coagulant. If
+the serum is always definitely clear, there may be grounds for believing
+that an excess is being used. If the quantity of coagulant has been
+calculated to an average nicety, the serum should be just dubiously free
+from milkiness.
+
+The firmness gained by the coagulum on standing in the serum overnight
+should enable it to be handled next morning without any marked stretching,
+and in some estates the rubber is put direct through the first pair of
+smooth rolls without a preliminary consolidation by means of hand-rolling.
+
+Some estates prefer to handle the coagulum while rather softer, as it is
+claimed:
+
+     (_a_) That the coagulum is easier to work, and sheets of improved
+     appearance can be made.
+
+     (_b_) That there is greater freedom from "bubbles."
+
+     (_c_) That the incidence of "rust" is lessened.
+
+     These claims are substantiated in practice; but in the case of the
+     third, it only holds provided that the rubber can be finished and
+     placed in the smoke-house almost as soon as the last sheet has been
+     machined.
+
+In such cases all latex must reach the store comparatively early in the
+day--_e.g._, before noon. Three hours is allowed for coagulation, and the
+working of the rubber is then commenced. As a general rule this means that
+the operations of rolling and marking must be completed, a short interval
+given for dripping, weighing must be done, and the rubber placed in the
+smoke-house before night falls (as a rule about 6.30 p.m.).
+
+Unless factories dealing with a large crop are well equipped with
+artificial light, such a course is not open to them; in any case it remains
+true that night work should be avoided if possible. If, however, it can be
+arranged without increasing the cost of production, there would appear to
+be no objection to the early working of the coagulum as described above.
+
+HAND-ROLLING.--As already indicated, some few estates do not give the
+strips of coagulum any preliminary hand-rolling, as the rubber is
+considered to be sufficiently firm to be handled into the first machine.
+
+On most estates hand-rolling is found necessary, owing to the tendency of
+the long strips to stretch unduly, giving badly shaped sheets. This
+hand-rolling should be done carefully, and is best effected on a specially
+constructed table. This consists essentially of an inch-thick hard-wood
+plank about 2 inches wider, and 4 or 5 feet longer, than the strip of
+coagulum. Along the edges of the plank, and at right angles to its upper
+flat surface, may be fastened strips of wood about 1/2 inch square in
+section, thus forming a shallow tray open at either end. These strips serve
+two purposes:
+
+     (_a_) As the wooden roller is wider than the plank, they prevent the
+     coagulum being rolled too thin and too firm.
+
+     (_b_) They prevent the coagulum being squashed too wide, and tend to
+     keep the edges straight.
+
+To avoid "thick ends" it is sometimes considered advisable to insert, at
+either end of the rolling table, shallow wedges about 6 inches long, of the
+same width as the table (between the edge-strips), and with the sharp end
+of the wedge pointing in the direction of the length of the table. The ends
+of the coagulum are drawn up and finished on these inclined planes.
+
+These points may appear to be extreme refinements, but as long as rubber is
+valued on such grounds we must endeavour to meet the system imposed upon
+us.
+
+SMOOTH-ROLLING.--It is advised that, after hand-rolling, the coagulum
+should be passed through at least two machines having smooth-rolls. On some
+estates three such machines are employed. The purpose of this procedure is
+to reduce the thickness of the coagulum gradually. The same could be
+effected, of course, on one machine; but obviously the distance between the
+rolls would have to be readjusted at each operation and for each piece of
+coagulum. Apart from the time thus wasted, there is the certainty, in view
+of the rough adjustment of the machines, that the chances of obtaining
+uniformly thick sheets would be slight.
+
+The machines should be arranged as a battery, with the marking rolls at one
+end, so that the operations are consecutive. It is erroneous to imagine
+that heavy machines (such as those used in crepe preparation) are required.
+Light machinery only is necessary for sheet-making; but any available heavy
+smooth-roll machines in a crepeing battery may serve admirably for the
+purpose.
+
+MARKING.--Heavy machines are unnecessary for the purpose of putting a
+pattern on sheet rubber. If the rubber has been properly prepared a light
+pair of rolls is capable of exerting sufficient pressure to cause a good
+upstanding pattern.
+
+Rolls are cut in various designs: some with "diamond" grooves on both
+rolls; some with grooves of varying width and depth encircling the
+circumference of the rolls, thus creating a "stripe" effect on the rubber;
+and some with diagonally-cut spiral grooves placed closely together. The
+last has the greatest vogue at present, while the first has almost gone out
+of favour. An objection lodged against the second design is that the edges
+of the grooves sometimes cut through the rubber, so that the dried sheet
+divides in strips. It would appear in such instances that either the
+coagulum was too thin and soft, or that the grooves had been cut too deeply
+and sharply. In any case the choice of a design is an arbitrary matter, and
+should depend upon the effect produced on the rate of drying and the
+general appearance.
+
+The popular "close-cut spiral" roll is machined with varying measurements,
+but the usual design has grooves 1/8 inch wide by 1/8 inch deep and 3/16
+inch apart.
+
+Many estates have a particular "brand" cut in the middle of the rolls for
+purposes of identification. If this is done it is advised that the main
+grooving of the rolls be carried into the "branding" strip; otherwise grip
+will be lacking on this portion, and a certain amount of "cockling" of the
+sheets will result.
+
+Sheets are often seen in which the potential effect of the grooving is
+reduced to a comparatively flat pattern in place of the desired ridges. The
+fault is generally attributed to the shortcomings of the marking rolls.
+While it is true that the grooving often deteriorates by friction-wear when
+the rolls are running "free," experience generally decides that the
+deficiency in the appearance of the rubber should be attributed to faulty
+previous preparation rather than to the marking rolls. Sets of rolls have
+been changed often without justification or an improved result. It would
+always be well to be certain first that the trouble did not emanate from
+the fact that the coagulum had been previously rolled so thin and hard that
+the rubber could not be squeezed so as to fill the grooves. This has been
+found to be a common fault, and the general effect is to delay drying in
+spite of the thinness of the rubber.
+
+Again, the trouble may have been due to an incorrect standardisation of the
+latex, generally in the direction of too heavy a density (too rich a latex)
+being employed. The original thickness of the coagulum would be normal, but
+owing to the abnormal rubber-content the effect of passing through the
+smooth rolls would be the production of a strip thicker and firmer than
+ordinary. If this firmness is appreciable the resistance of the rubber to
+the squeezing action of the marking rolls will result in a flat
+pattern--_i.e._, the grooves cannot be filled, and the ridges are low.
+
+It is advised that all rolls used in the preparation of sheet rubber should
+be at least 18 inches wide, in order to avoid the appearance of thickened
+edges which delay drying.
+
+Working with the correct standard of dilution of latex, and following the
+procedure indicated in the foregoing paragraphs, the dry sheet should not
+exceed an average thickness (over ridges and depressions) of 1/8 inch.
+
+PREPARATION FOR SMOKE-CURING.--It used to be the custom to allow sheet
+rubber to air-dry first for periods varying from one to several days.
+Naturally moulds were soon formed, and when the sheets were quite
+smoke-cured a mass of the dead moulds could be seen, if not over the whole
+sheet, at least in the corners of each diamond mark. It has been
+demonstrated in practice that there is no advantage in allowing sheets to
+air-dry partially before smoking. In fact, to obtain the greatest benefit
+from smoke-curing, sheet rubber should be placed in the smoke-house as soon
+as possible. The same effect of mould-growth may be noted if the wet sheets
+are placed in a smoke-house insufficiently heated.
+
+Other defects may arise which can be traced to faulty treatment of the
+marked coagulum prior to hanging in the smoke-house and subsequent to
+rolling. These will be enlarged upon in a subsequent section of the book,
+and at present it will suffice to indicate the procedure which experience
+directs as likely to give the best results.
+
+When the lengths of coagulum leave the marking machine they are usually
+laid in piles containing two dozen or more strips. The piles are then cut
+into the required lengths, the exact length generally being determined by
+the available perpendicular distance between the supports in the
+smoke-house. It is necessary to remark that the piles of sheets should not
+be allowed to accumulate, but should be dealt with in subsequent treatment
+progressively. If for some reason this is not possible, then all piles of
+sheets should be turned on edge so as to assist the draining away of the
+serum or "mother-liquor," which continues to ooze from the rubber for some
+time after the squeezing in the machines.
+
+Where hot water is available the freshly cut sheets should be passed into
+it as soon as possible, and given a thoroughly good swilling. The caution
+must be given that the hot water should be changed very frequently and, if
+possible, after every batch, say, of a hundred sheets.
+
+The sheets should then be carried immediately to racks on which they are
+hung to drip. Generally these racks are situated under cover, but there is
+no reason why they should not be placed in the open air without cover or
+shade. From continued experience of this practice over a period of years it
+is found advantageous and to be preferred to the usual method of allowing
+sheets to drip under cover.
+
+While the sheets are fresh and loaded with internal moisture, the effect of
+sun-heat upon the surface, when exposed for, say, two hours, is nil; and
+the safety of the process can be guaranteed, provided the stated limit is
+not exceeded to an appreciable extent.
+
+[Illustration: THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN
+THE FACTORY.]
+
+After dripping for an hour or so, the sheets should be placed in the
+smoke-house. If it is a bright sunny day, no extra precautions need be
+taken; but on cool, dull days it would be advisable to light the fires
+earlier than usual, consistent with the work required to be done in the
+house--_e.g._, in the removal of dry rubber. There would appear to be no
+reason why the dry sheets should not be first removed, so that on dull or
+wet days smoking can be commenced as soon as the wet rubber has been hung.
+
+On a few estates where the smoke-houses are worked continuously, except for
+a few hours in the morning, a portion of the building is separated by a
+partition for the reception of the wet rubber. The sheets are taken
+directly from the marking rolls and placed in the chamber, beneath which a
+fire is started. The sheets thus drip in a warm and smoke-laden atmosphere
+until next morning, when they are weighed and removed to the smoke-house
+proper. It is claimed that freedom from "rust" is thus obtained.
+
+It will be clear that in the treatment of the rubber preparatory to smoking
+the whole process should be continuous, and delay should be avoided if the
+best results are to be obtained.
+
+[Illustration: THE NEWER METHOD OF HANGING IN THE OPEN AIR.]
+
+SMOKING OF RUBBER.--The assumption may have been noted above that the sheet
+is to be smoked. As far as our knowledge extends, none but small native
+estates now prepare sheet rubber of any other type, with the exception of
+certain patent processes. Air-dried sheets are generally made on
+small-holdings, and are bought in the market chiefly for the purpose of
+macerating and making into blanket crepe. We have no intention, therefore,
+of discussing the possibilities or qualities of air-dried sheets, as the
+output of sheet-rubber from our estates is always in smoked form. The
+drying (or, properly, smoking) stage will be discussed in Chapter XI.
+
+
+
+
+CHAPTER X
+
+_PREPARATION OF CREPE RUBBER_
+
+
+NO. 1, OR FINE PALE CREPE.--Considering first the preparation of the
+highest grade, fine pale crepe, it must be stated that the difficulties
+attached to the process are generally not sufficiently appreciated. In this
+pale rubber minor blemishes are so plainly apparent that their importance
+is highly exaggerated, and what would worthily escape notice in smoked
+rubber assumes disproportionate prominence in pale crepes. The very fact
+that such a delicate material as colourless coagulum has to be manipulated
+in coarse iron rollers, with the attendant oil and grease worries, should
+be sufficient to deter one from criticising too harshly the occasional
+lapses of an estate struggling to give of its best to the market. At the
+same time there can be no doubt that if precautions are taken to attend to
+all likely sources of contamination, defects in pale crepe may be avoided
+to a wonderful extent; and on some estates the observance of elementary
+rules enables the preparation of the finest pale crepe to be made almost
+mechanically.
+
+STANDARDISATION OF LATEX.--The question of the standardisation of latex has
+been dealt with in a general way in Chapter VII., and the reader is now
+familiar with the trend of the argument in its favour. It will be
+recognised that the necessity for standardisation exists to the same degree
+in the correct preparation of pale crepe as in the case of smoked sheet.
+Unless the dry rubber content is invariable, and the quantities of
+chemicals fixed, the colour of the crepe may vary appreciably.
+
+It may be pointed out that it is not _essential_ to adopt the same standard
+of dilution as for sheet preparation. Given that latices from all fields or
+divisions are fairly uniform, and of high rubber content, the standard may
+be taken at a figure equivalent, for example, to 2 lbs., or 2-1/2 lbs., or
+even 3 lbs. per gallon. It is wise, nevertheless, to take a lower standard
+for several reasons. For instance:
+
+     (_a_) The average dry rubber content varies with climatic conditions,
+     position of the cut on the tree, general health of the tree, etc. On a
+     rainy day the dry rubber content may be lowered too greatly by
+     adventitious circumstances.
+
+     (_b_) Recording instruments often fail to give even approximately
+     correct readings in rich latex. Errors may thus be made easily.
+
+     (_c_) A fairly soft coagulum means easier working on the machines,
+     less labour, and proportionately cheaper costs.
+
+[Illustration: THREE GRADES OF CREPE RUBBER.
+
+Left to right: fine pale crepe; second quality pale crepe; compound crepe.]
+
+It is advised, therefore, that for general purposes the same standard as
+that found suitable for sheet rubber should be taken--viz., 1-1/2 lbs. dry
+rubber per gallon. At all events the standard should not exceed 2 lbs. per
+gallon.
+
+COAGULATION AND COAGULANT.--Coagulation may be undertaken without any
+special arrangement of tanks, and is usually effected in the ordinary
+"Shanghai" glazed earthenware jars containing about 45 gallons. Given
+reasonable care, and a fairly fool-proof system of calculation for the
+quantities of chemicals required, no difficulty need be experienced.
+
+[Illustration: A WASHING SHED.
+
+Sheets are soaked in hot water in tanks in the background, and then
+scrubbed under a spray of cold water.]
+
+On a larger scale it is advised that proper reception tanks, in which
+standardisation can be effected, should be installed. Where both sheet
+rubber and fine crepe are being prepared, the whole system of
+sheet-coagulating tanks may be employed with considerable advantage, even
+to the insertion of the partitions.
+
+If ordinary jars are used, and the coagulum is left until the following
+morning, the mass of rubber has to be cut up into pieces of a size suitable
+for the machines. The knives or saws are sometimes rusty, and the colour of
+the coagulum is affected. The coolies often feed into the machines lumps
+which are too large, with the result that portions are thrust under the
+cheek-blocks and become stained.
+
+When a sheet-coagulating tank is used all labour of cutting the coagulum is
+obviated. The long strips are handled and fed into the rolls easily. It may
+be seen, likewise, that actual work is thus saved in machining.
+
+QUANTITY OF COAGULANT.--For a general discussion on the coagulant and
+quantities employed, the reader is referred to Chapter VIII. It is there
+recommended that for latex standardised to a level of 1-1/2 lbs. per
+gallon, the proportion of pure acetic acid should be in the ratio of
+1:1,200. Directions are there given for the making of the solution, and the
+calculation of the quantity required for any given volume of latex.
+
+It is pointed out that for average _undiluted_ latex the basis of
+calculation, for quantities of acetic acid required, should be taken on the
+ratio 1:1,000. Where latex exceeds a dry rubber content of 3 lbs. per
+gallon, it may be necessary to increase the quantity of acid to 1:800.
+
+If a standard of 2 lbs. per gallon is adopted, the formula given for the
+1-1/2 lbs. standard will not give full satisfaction, and the quantity of
+acid solution must be increased slightly in order to obtain complete
+coagulation. Assuming that the original solution is prepared in 1 per cent.
+strength, the following difference would be noted:
+
+     (_a_) One part pure acetic acid to 100 parts water (theoretically 99
+     parts).
+
+     (_b_)  _1-1/2 lbs. per gallon._    |      _2 lbs. per gallon._
+                                        |
+     Of the above solution use 1 gallon | Of the above solution use 1
+     to every 12 gallons of standardised| gallon to every 10 or 11
+     latex.                             | gallons of standardised latex.
+
+It is not possible to lay down an exact figure governing all cases, as so
+much depends upon the treatment undergone by the latex before it reaches
+the store.
+
+Some estates continue to use solutions of greater strength, generally 5 per
+cent., in crepe preparation. While such solutions may be effectively
+stirred in when the latex is dilute, it is advised that for intimate
+mixture the solution need not be stronger than 1 per cent.
+
+In estimating the quantities of acetic acid required much depends upon the
+interval which is to elapse between the addition of acid and the time of
+working of the coagulum. If the rubber is to remain until next morning, the
+average formulae will be found suitable; but if it is required to work the
+coagulum with an interval of less than three hours, an excess of acid must
+be employed. The excess need be comparatively small, unless the interval is
+much reduced. For instance, it is the practice on some few estates to begin
+the machining of the coagulum about half an hour after coagulation
+commences; in which case it is usual to add from a quarter to a half of the
+normal quantity in excess. It need scarcely be pointed out that unless this
+procedure is strictly unavoidable it should be discouraged on account of
+the waste of coagulant involved. Incidentally, the use of strong solutions
+of acid under such circumstances may lead to increased deterioration of the
+rolls.
+
+COLOUR OF FINE CREPE.--We are sometimes assured that manufacturers do not
+pay the attention to the question of colour which sale conditions would
+lead one to believe. As far as we are concerned, and as long as there is no
+direct traffic between producer and consumer, it must be recognised that in
+the vast majority of cases we are forced to concern ourselves only with the
+standards set up in the markets. This, in spite of the knowledge that, all
+other things being equal, the arbitrary distinctions in colour afford no
+indication of the intrinsic value of the rubber. Under present
+circumstances it is plain that if paleness is demanded it has to be
+supplied.
+
+Probably without exception all estates employ sodium bisulphite as the
+agent for the prevention of that darkening (oxidation) which is natural in
+drying rubber.
+
+SODIUM BISULPHITE.--A formula for use of this chemical is given in Chapter
+VIII., and is applicable to latex standardised to 1-1/2 lbs. dry rubber per
+gallon. If a higher standard is chosen the quantity calculated as in (_b_)
+of that formula may be increased slightly, and the exact requirements found
+by experience. The caution must again be given that the employment of an
+excess of sodium bisulphite will lead to the production of an over-pale
+rubber, and a prolongation of the drying period. If thick crepes are made,
+an excess of the chemical is sometimes made visible by a greyish powder
+deposited on the edges of the strips of dry rubber.
+
+It must be emphasised that the formula in Chapter VIII. indicates the
+_maximum_ quantities required for use with standard latex. Many estates
+will find it expedient to use less of the chemical; and if it is found that
+the desired result is not obtained from normal proportions, attention
+should be directed to the points discussed in the following paragraph.
+
+EVALUATION AND DETERIORATION OF SODIUM BISULPHITE AND SODIUM
+SULPHITE.--Sodium bisulphite and sodium sulphite are both bought for our
+purpose in the form of a fine crystalline powder, and on analysis good
+specimens should contain over 90 per cent. pure substance, when packed in
+well-sealed vessels.
+
+It has often happened that shippers or local sellers, by inadvertence, have
+supplied the one chemical in place of the other--to the detriment of the
+rubber and the discomfiture of managers of estates. The error, as a rule,
+has not been detected for some time, and then perhaps only as a result of
+complaints or enquiries reaching the laboratories. To the layman, and
+certainly to the native who usually has charge of these substances, it is
+not a simple matter to distinguish between them without special knowledge.
+There are certain elementary tests, however, which can be applied on all
+estates serving to make the distinction, but affording no information
+regarding the actual quality of the chemicals. They are given in a
+comparative form on page 116. Samples of doubtful specimens may be sent to
+the laboratories for analysis, but the bulk of the chemical should not be
+used.
+
+During the War some very poor shipments were received, and much trouble was
+caused. Under normal conditions there can be no question that it is to the
+interests of chemical manufacturers to supply the best article; and it is
+anticipated that in future there should be no difficulty in procuring
+shipments of a high degree of purity.
+
+      _Sodium Bisulphite._           |     _Sodium Sulphite._
+                                     |
+  1. If in good condition it         | 1. It has no perceptible
+  has a powerful odour of            |    odour.
+  sulphur dioxide.[9]                |
+                                     |
+  2. In solution it should turn      | 2. In solution it should turn
+  a blue litmus-paper red.           |    a red litmus-paper blue.
+                                     |
+  3. It exhibits a marked tendency   | 3. The tendency to "cake"
+  to "cake" if the                   |    is less marked than in
+  drum is allowed to                 |    the case of the bisulphite.
+  remain open.                       |
+
+[9] High-grade sodium bisulphite has very little odour, but by the time it
+reaches the estate, and as a result of short exposure to the moist
+atmosphere of the tropics, a little decomposition sets in and a strong
+odour of sulphur dioxide gas is noticeable.
+
+It will be evident that, as sodium bisulphite under normal conditions gives
+off a gas when exposed to the atmosphere, it deteriorates in quality
+continuously. It is the potential presence of this gas which makes the
+powder effective as an anti-oxidant and disinfectant. It is within the
+experience of all accustomed to the handling of this chemical, that in
+addition to the loss of gas, the powder cakes into a hard mass on exposure.
+If only the top layer is caked, the remainder may be in fair condition; but
+no caked portions should be used, as they cannot be of good quality. They
+may, however, be used for the treatment of scrap rubber, to be discussed
+later.
+
+CARE OF SODIUM BISULPHITE.--The ready tendency of sodium bisulphite to
+deteriorate on exposure should give sufficient indication regarding its
+treatment in storage. It should be bought only in drums (or other air-tight
+containers), and should be stored in a dry place. No drum should be opened
+until required, and the common practice of keeping an open drum on the
+floor of the factory should be avoided.
+
+Drums are of two sizes, generally containing 1/4 or 1/2 cwt. respectively.
+It will be obvious that, although the prime cost may be cheaper with the
+larger quantity, it would always be preferable to secure the smaller
+drums, as the loss on exposure will be less.
+
+Most commonly the 56 lb. drum is purchased. It should not be difficult to
+calculate the period during which the contents will be consumed, on the
+basis of a maximum of 1 lb. per 100 gallons of latex. A 56 lb. drum,
+assuming no loss or waste, should be sufficient to treat _at least_ 5,600
+gallons of latex (say, 8,500 lbs. of rubber)--if the bisulphite is of
+first-class quality, and the use is applied only to the preparation of fine
+pale crepe.
+
+Where the quantity used per diem is small, it is advised that precautions
+should be taken to preserve the quality of the chemical when a drum is
+opened. It might be of advantage to place the contents of the drum in
+smaller sealed tins, or to have made a special container (with a closely
+fitting lid) into which the powder can be placed as soon as the drum has
+been opened.
+
+MIXING SOLUTION WITH LATEX.--Emphasis has been laid, in Chapter VIII., upon
+the necessity for care in the preparation of the solution. Equal regard
+must be given to the mixture of the solution with the latex.
+
+On a few estates it used to be the practice to add the powder to the
+solution of acid, with stirring. Obviously this led at least to a great
+loss of efficiency, owing to the rapid escape of the gas which was evolved.
+
+The solution of sodium bisulphite should be poured into the latex in as
+uniform a distribution as possible. The mixture of solution and latex
+should be thoroughly stirred, and if only natives are in charge a minimum
+period of five minutes should be prescribed before the addition of the
+coagulant. A thorough stirring should again follow the advent of the acid.
+
+If these elementary rules are not observed faithfully, the deficiency will
+most probably be manifested in the dry rubber in the shape of streaks of
+varying shades of colour.
+
+Finally it may be insisted upon that deteriorated sodium bisulphite should
+not be used. In order to obtain an effect double the quantity may be
+required, and the residual salts left in the rubber on evaporation of the
+moisture will be responsible for prolonged drying, surface deposits, and
+possibly "spot disease."
+
+FORMER METHODS OF MAKING PALE RUBBER.--Merely as a matter of historic
+interest it may be mentioned that previous to the introduction of sodium
+bisulphite pale crepes were made in comparatively small quantity by various
+devices, among which the following might be quoted:
+
+     (_a_) Use of excessive quantities of strong acetic acid.
+
+     (_b_) Extreme dilution of latex in conjunction with excessive
+     quantities of acid.
+
+     (_c_) Extreme dilution in conjunction with steaming and excess of
+     acid.
+
+     (_d_) Extreme dilution of latex in conjunction with excess of acid and
+     subsequent heating of the coagulum in hot water.
+
+     (_e_) The use of excess of a mineral acid such as sulphuric acid.
+
+     (_f_) The skimmings and very dilute latex, coagulated with excess of
+     acid.
+
+WORKING THE COAGULUM.--Description of the details of necessary machinery
+for crepe-making is relegated to Section III. of this book. Here we shall
+treat only of the matter in general.
+
+In the preparation of crepe rubber heavy machinery is necessary, and ample
+engine-power must be available. The machines should comprise three types:
+
+     (_a_) With rolls cut in such fashion, and run at such different
+     speeds, as to have a macerating effect upon the coagulum. Such
+     machines or rolls will be referred to as "macerators."
+
+     (_b_) Intermediate rolls, grooved in varying designs and geared
+     differentially. These reduce the thick rough crepe obtained from the
+     macerators into a form suitable for passing to the rolls described in
+     (_c_). They are sometimes called "crepers," but as this term may be
+     applied equally to the macerating rolls, they will be termed the
+     "intermediate" rolls.
+
+     (_c_) Smooth rolls usually run at approximately even speeds and, as
+     their name denotes, devoid of any grooving. They are called "smooth"
+     rolls or "finishers."
+
+Without such equipment it is not possible to prepare the grade which is
+known as "fine pale crepe." In the common acceptation of this term crepe of
+No. 1 quality generally connotes fineness and paleness with a thin crepe
+which has a good, smooth, and fairly well-knit texture.
+
+It is, of course, possible to make a thick pale crepe, using only the
+macerators and intermediates, but the "finish" will be that typical of the
+particular grooving of the intermediate rolls. For the preparation of crepe
+ordinarily, the possession of smooth rolls is a _sine qua non_.
+
+For reasons which will be explained more fully in the chapter dealing with
+the defects of crepe rubber, the practice of preparing thick crepes direct
+from the coagulum is now very uncommon. Thick crepes are generally made by
+reworking dry rubber, either in the form of thin crepes or from air-dried
+sheets. The market for the latter in Malaya is confined almost entirely to
+Singapore, where factories buy native rubber and re-work it into thick
+crepe.
+
+The bulk of the output of No. 1 crepe from estates is in the form of thin
+"fine pale crepe." The artificial standard set up by buyers and brokers
+necessitates this thin crepe being of even texture and fairly free from
+small holes ("looseness"). What difference the small holes are to make in
+the vulcanising properties of the rubber is beyond our knowledge; but such
+being the standard, it must be attained if the full price is to be
+obtained.
+
+In order to secure the desired effect the coagulum must be passed
+consecutively through the three types of rolls, and undergoes a varying
+degree of working in each.
+
+Given the necessary equipment of machines, it is possible to make a good
+specimen of thin pale crepe if the coagulum passes through all the rolls a
+total of twelve times (or even less in exceptional cases). There is no
+intention of suggesting that this is possible on all estates. Clearly the
+number of times the rubber passes through the rolls will depend upon the
+total efficiency of the machines. This in turn involves such factors as
+(_a_) the size of the rolls, (_b_) the number of machines of each type,
+(_c_) the gearing of the pinions, (_d_) the speed of the drive, etc. Again,
+much depends upon the nature of the coagulum worked. A fairly soft coagulum
+will offer less resistance, and conversely a dense coagulum will require
+more machining.
+
+It has been shown by the writers in previous publications that over-working
+of the coagulum has an effect on the vulcanisation of the rubber; and this
+has been confirmed by others.[10] Apart from this point, it should be
+recognised that over-working, beyond that necessary to produce a thin crepe
+of even texture, is to be deprecated, on the ground of economy, in working.
+
+[10] Bulletin No. 27, Department of Agriculture F.M.S., April, 1918,
+"Preparation and Vulcanisation of Plantation Para Rubber," Eaton, Grantham
+and Day.
+
+Owing to the existing differences in equipment and speed of drive, etc.,
+the regular practice of any one estate may be unsuitable for another. It
+remains, therefore, a matter of study for each estate to discover the
+minimum number of times which rubber should pass through the machines,
+consistent with the factors indicated above. In any case it may be assumed
+that if any factory cannot prepare a good crepe by passing the rubber, say,
+twelve times through the rolls, there is some deficiency in the machines,
+or of speed; the coagulum may be too hard, or the rolls may be badly worn.
+
+LOWER GRADES OF CREPE RUBBER.--Even a few years ago it was plain that the
+lower grades of crepe (_i.e._, all grades lower than first latex rubber)
+were not sufficiently appreciated in the market. There was often a marked
+difference in price between a first-grade crepe and crepe made from
+naturally coagulated lump. This arose chiefly from lack of knowledge. It
+has since been recognised in some measure that no reason exists for such a
+wide difference in price, and more recently the margin between even the
+first-grade rubber and the lowest grade of scrap rubber has been a
+gradually diminishing one. Providing sufficient care is exercised in the
+preparation of the lower grades, one would expect to see but very small
+difference in prices between any two grades. It is true that adequate
+attention has been given to the preparation of the scrap grades only in
+comparatively recent years, and it is acknowledged that when high prices
+were ruling for first-grade rubbers sufficient attention was not generally
+given to the subject of the preparation of the lower grades.
+
+NATURALLY COAGULATED LUMP RUBBER.--The grade of rubber made from the
+naturally coagulated lump which forms in buckets and carts is usually of a
+mixed colour, due to the fact that the lumps oxidise very quickly. When
+they are allowed to remain overnight before being machined, it can be
+imagined that the colour of the dry crepe would be very dark, or would
+contain very dark streaks. Such is ordinarily the case, unless special
+precautions are taken.
+
+Providing that the coagulated lump is free from bark, leaves, and
+leaf-stems, and certain other precautions taken, the difference in price
+between coagulated-lump crepes and first-grade crepes should be very
+slight. Too often, however, not sufficient supervision is given to the
+coagulated-lump rubber, and it is common to see it come into the factory
+containing leaves and bark. These should be picked out before the latex is
+strained, but obviously it would be better to ensure that they did not
+enter the buckets in the first place.
+
+It would seem reasonable to suppose that if some means could be employed
+for preventing or checking the surface oxidation of naturally-coagulated
+lump rubber, there would be a corresponding improvement in the colour of
+the dry crepe. That such a method is practicable has been demonstrated on
+many estates. The lump when lifted out of the latex is allowed to drain for
+a few minutes, and is then (without squeezing) placed in a dilute solution
+of sodium bisulphite. A 1 per cent. solution is sufficiently powerful. It
+is not to be thought for a moment that by the use of sodium bisulphite any
+previous oxidation will be counteracted; all that is claimed for the
+treatment is that any further surface oxidation will be checked, and the
+rubber may be allowed to remain until the next day, for working, if it is
+so desired. It will probably be found that quite a quantity of latex has
+been expressed from the lumps by contraction, and acid may be added to
+obtain the rubber from this. On other estates the lump rubber is worked on
+the machines as it is received, and the resulting crepe is submerged in a
+weak solution of sodium bisulphite over-night. It is then rinsed in water
+and hung to drip before weighing and placing in the drying house. Under
+certain conditions some of the lump rubber darkens rapidly during transport
+to the store, and any such oxidised portions must be rejected if a uniform
+colour is to be expected in the crepe.
+
+Following the procedure indicated above, some estates find it possible to
+prepare from naturally coagulated lump rubber a crepe which can be classed
+as No. 1 grade.
+
+SKIMMINGS AND WASHINGS.--The skimmings of tanks, as already shown, may be
+prepared sometimes as a second quality of smoked sheet; but generally they
+are amalgamated with the rinsings of cups and buckets, treated with sodium
+bisulphite and acid, and made into crepe form.
+
+The cup-washings, as they arrive at the store, represent a very dilute
+latex, the rubber from which is generally of a greyish colour.
+
+Bucket-washings should yield a good type of pale rubber if they are
+obtained properly. To obtain the maximum quantity of good rubber the
+buckets should first be rinsed. A gang should be taken, a small quantity
+(say a quart) of water poured into the first bucket, and this dilute latex
+used progressively in all the buckets of that gang of tappers. The result
+is a fair latex which can be added to the bulk of No. 1 latex, provided it
+is free from dirt. Where sheet rubber is being prepared, carefully strained
+cup-washings or bucket-washings may be utilised in the dilution of the
+latex to the required standard, thus increasing slightly the percentage of
+first-grade rubber.
+
+TREE-SCRAP.--As tree-scrap is a naturally coagulated rubber, it should be
+expected to show up well in quality. This is usually the case; but from
+what has been said of the effect of sun-heat it will be understood that if
+trees are not regularly "scrapped," there is a danger that the crepes may
+be found to contain tacky streaks due to the inclusion of old scrap which
+has been sun-baked. In hot dry weather, on widely planted areas tapped on
+alternate days, it has been noticed that scrap remaining for two days often
+exhibits a resinous appearance, and feels sticky to the touch.
+
+If tree-scrap is to be made as a separate grade, as used to be the general
+custom, care should be taken to see that it is free from bark and dirt. On
+some estates where scrap-rubber is paid for per pound collected, it is
+usually the rule to insist that scrap shall be washed free from dirt and
+picked free of bark. This course is to be commended, but might probably
+prove impracticable to the majority of estates. Theoretically, of course,
+the operation of machining should rid the scrap of all traces of bark; but
+in practice it does not do so.
+
+Some proportion of the tree-scrap is usually found to be heavily oxidised,
+and naturally if a crepe of uniform colour is to be obtained these dark
+scraps must be rejected, otherwise dark streaks will be formed. Coolies
+should be instructed to sort out the dark pieces before arriving at the
+store.
+
+BARK-SHAVINGS.--It has been intimated in a previous section that the method
+of obtaining and collecting bark-shavings varies with the type of labour
+employed.
+
+Where the scrap is removed from the edge of the bark on each occasion
+before tapping, the amount of rubber to be extracted from the dry shavings
+is very small--so small, in fact, that when the price of rubber is low, it
+is doubtful whether it pays to collect and work the material.
+
+On the other hand, where trees are not "scrapped" before tapping, the
+bark-shavings and tree-scrap are collected together, and the amount of
+rubber derived from the mixture may be 30 to 40 per cent. upon the gross
+weight--depending chiefly upon the quality of the tapping (_i.e._, in this
+case, the thickness of the paring). Another factor influencing this figure
+would be the effect of using an anti-coagulant on the cuts.
+
+Bark-shavings entail such wear upon the ordinary machines during working,
+especially if fairly free from rubber, that unless the factory is equipped
+with a special "scrap-washer" it is advised that this material should be
+sent for working to a factory having the necessary equipment. Whenever
+possible, bark-shavings should receive treatment on the day of collection.
+
+It used to be quite common to see heaps of bark-shavings accumulating on
+the floor of a factory, and generating excessive heat. Yet these heaps were
+allowed to stand about for a day or days. Is it any wonder then that
+tackiness was found to develop when the rubber was dry? It is here
+definitely laid down that no heaps of bark-shavings should be accumulated
+even for half a day. Tanks should be provided in which the shavings should
+be submerged in water.
+
+EARTH-SCRAP.--Of all grades of crepe this is the one most liable to become
+tacky in transit. This tackiness to a large extent cannot be avoided, as
+old pieces of earth-scrap may be brought in amongst the bulk. Probably
+these old pieces have been exposed to the sun for days, and have become
+quite resinous. It would be practically impossible to go through all
+earth-scrap in order to find these odd pieces, but unless this were done
+one could not guarantee that the earth-rubber would always be free from
+tackiness. The difficulty does not appear, however, on estates where
+earth-rubber is collected systematically at very frequent intervals.
+
+FIBROUS MATTER IN LOW-GRADE RUBBERS.--It is sometimes found in this and
+other lower grade rubbers that pieces of cloth or cotton-waste are
+concealed. Coolies may have used them for cleaning cups, or the store
+coolies may have been at fault. Earth-scraps especially should be examined,
+before working, for such extraneous matter.
+
+SCRAP-WASHERS.--These are heavy machines specially devised for the
+treatment of lower grade rubbers. In these the raw rubber is well
+masticated and freed from impurities, if the machine functions efficiently.
+
+There are several types of these machines, all of which are efficient. That
+best known is the "Universal" washer, made by Joseph Baker, Sons, and
+Perkins, Ltd. (formerly Perkins Engineering Company). Coming into local
+favour during the War, the "U.E." scrap-washer, made by the United
+Engineering Company (Singapore), gives very good service. The "C.C.C."
+washer, made by the Colombo Commercial Company, is suitable for the
+purposes of an average estate. There are others, less well known. Most of
+these machines are made in varying sizes to meet the requirements of small,
+medium, or large estates; and if funds are available, a scrap-washer should
+be regarded as an essential item in the machinery of any estate employing
+engine power.
+
+The rate of output of scrap-washers will depend mainly upon the speed at
+which they are driven, and when ordering the equipment it would be
+advisable to state the ordinary speed of the back-shaft, length of drive,
+etc. It does not follow that the larger the rate of output, the greater is
+the efficiency of the washer. The point is not as to what quantity of
+rubber can be taken out per hour, but what quantity is actually freed from
+impurities.
+
+It is advisable for the superintendent to obtain a thorough knowledge of
+the general construction and principles of the particular scrap-washer
+employed. In the past it was not uncommon to find superintendents innocent
+of the fact that a certain type of washer possessed movable parts upon
+which the efficiency of the cleansing largely depended. It was often found
+that these parts, which were intended to be removed and cleaned at
+intervals, had become firmly fixed and could not be removed for inspection.
+
+It must be recognised also that the machines are liable to considerable
+damage if extraneous substances are allowed to enter--for example,
+tapping-knives, stones, pieces of iron, spouts, etc., which are sometimes
+present in the loose scraps of rubber or shavings, owing to the
+carelessness of coolies. Under the best regulated-system, such accidents
+occasionally occur, but a great deal of trouble could be avoided by having
+it understood that each charge must be sorted over before entering the
+washer.
+
+Again a deal of extra work, and much wear and tear, is caused by the
+_abuse_ of the scrap-washer--_e.g._, in the cleansing of earth-scrap. As
+this reaches the factory it often contains a quantity of internal or
+adhering earth. Before entering the washer a good proportion of the
+external soil could be removed if the scraps were thrown into a tank and
+given a thorough soaking and stirring. In a similar manner dry
+bark-shavings, which have been allowed to accumulate, could be softened.
+
+In the actual working of scrap-washers instructions are generally given by
+the makers. These sometimes advise the introduction of warm water (or of
+steam into the cold water supply) for an interval during the working of
+each charge. Where possible, such instructions should be followed, as by
+this means the individual pieces of rubber are massed together, in the
+final stage, into a "sausage" form which is easy to transport and to
+manipulate in the ordinary crepeing battery.
+
+COMPOUND CREPES.--The attitude of both buyers and sellers with regard to
+the types of lower grade rubbers appears to be changing. In the past, from
+any one estate there might be obtained as many as six grades of crepe below
+No. I. These comprised:
+
+     (1) A pale rubber (often streaked) obtained from coagulation of cup
+     washings and bucket rinsings.
+
+     (2) A pale rubber (often streaked) obtained by coagulation of the
+     skimmings from the surface of the No. 1 latex.
+
+     (3) A streaked and dull rubber prepared from naturally-coagulated
+     clots found in cups, buckets, and latex carts.
+
+     (4) A streaked rubber prepared from scrap which had coagulated upon
+     the face of the cut bark.
+
+     (5) A brownish and streaked rubber made by maceration of bark-shavings
+     to which pieces of tree-scrap adhered.
+
+     (6) A dark rubber, often tacky, prepared from scrap found in or on the
+     ground near the base of the trees. As it is often a matter of weeks
+     between any two regular collections, it is easy to understand why the
+     dry rubber was more liable to be "tacky" than any other grade of
+     crepe.
+
+It will have been evident to all who have acquaintance with these grades,
+as shipped from many different estates, that the diversity in the various
+shipments must have been rather bewildering. There appeared to be a
+regrettable lack of uniformity, even in the appearance of, say, a bark
+scrap rubber from any two estates. When, in addition to these variations,
+the further complication of condition of cleanliness is introduced, one may
+realise the difficulty attaching to the evaluation of these rubbers as they
+appeared upon the market.
+
+Although the foregoing paragraph is written in the past tense, it should be
+pointed out that within certain limits the trouble continues to exist with
+respect to the output of a great number of estates.
+
+In the case of many, it has been realised that the manufacturer does not
+want to buy a large number of "parcels," all differing in some respect. It
+is probably correct to state that what a manufacturer requires is a big
+"parcel" uniform in appearance and treatment, even though the colour may
+not be so light as that of many smaller lots. This statement is modified
+with the proviso that the rubber, no matter what its colour or appearance
+may be, must be free from dirt, grit, and bark.
+
+The difficulty of making a uniform product from several types of lower
+grade rubbers has been successfully solved on several estates by the
+preparation of a "compound" crepe composed of a mixture of the best lower
+grades in approximately definite proportions daily. Naturally the shade of
+colour of this compound crepe will depend largely upon the types of rubber
+employed, but as a rule it is somewhat darker than the highest of the types
+employed in the mixture. To the writers this seems immaterial as long as
+the manufacturer is offered a larger and more uniform lot which can be
+given uniform treatment in vulcanisation processes. Neither would it appear
+that the seller suffers any monetary loss. In point of fact it will be
+found probably that the reverse is the case. For instance, supposing it
+were decided to mix for a compound crepe--
+
+     (_a_) Naturally coagulated lump rubber.
+
+     (_b_) Tree-scrap.
+
+     (_c_) Bark-shavings scrap.
+
+The product would be darker in colour than (_a_) and slightly better than
+(_b_). Let it be granted that there might be a monetary loss on (_a_), it
+is probable that there would be a slight gain in comparison with the usual
+prices obtained for (_b_) and (_c_). Now, as a general rule, the actual
+percentage of crop made into (_b_) is appreciably less than that made into
+(_c_) and still less than (_b_) and (_c_) together. Apparently, therefore,
+there would be a margin of profit on the whole by making a compound crepe.
+It may be pointed out, on the other hand, that there might be expended on
+the manufacture of this crepe more time and labour, but as against this the
+labour of sorting and grading would be simplified.
+
+Unfortunately this process is not open to estates which do not possess a
+scrap-washer. _It is essential that the rubber should be free from grit,
+sand, and bark particles._ In the absence of a scrap-washer for the
+cleansing of the bark-shavings, it would be futile to attempt to make a
+compound crepe containing that type of rubber, as one would run the risk of
+spoiling the whole. It seems certain that in course of time a scrap-washer
+will be considered as necessary a piece of machinery as an ordinary
+crepeing machine in the factories of estates having sufficient means. Until
+that time the preparation of compound crepes must be the privilege only of
+well-equipped estates, unless other estates can send their lower grade
+rubbers for treatment in a scrap-washer to their more fortunate neighbours.
+
+In previous publications a diminution in the number of grades of crepe
+rubber has been advocated, and it is gratifying to find that in many cases
+the amending grades suggested have been improved upon. Many estates now
+make only three grades of crepe--viz.:
+
+     (_a_) No. 1. From latex coagulated in the store.
+
+     (_b_) No. 2. Compound.
+
+     (_c_) No. 3. Earth-rubber.
+
+It will be seen that the compound crepe includes all types between fine
+pale crepe and earth-rubber. Naturally one could not safely recommend the
+inclusion of earth-rubber in any compound crepe, as the risk of possible
+"tackiness" in the whole would be serious. In the case of the bark-shavings
+rubber to be incorporated, it is first cleaned alone in the scrap-washer.
+Then all types are mixed together again in the scrap-washer in proportions
+ruled by the experience of the usual average percentages of each grade of
+the crop.
+
+Besides the estates having only three grades, there are others which make
+four--viz.:
+
+     (_a_) No. 1. From latex coagulated in the store.
+
+     (_b_) No. 2. Compound, from cup washings, etc., skimmings, and
+     naturally coagulated lump.
+
+     (_c_) No. 3. Compound, from tree-scrap and bark-shavings rubber.
+
+     (_d_) No. 4. Earth-scrap.
+
+     Other variations are possible, but their number is limited, and they
+     all conduce to simplification of working, and a supply to the market
+     of rubber having greater uniformity.
+
+NEED FOR INCREASED CARE WITH LOWER GRADE RUBBER.--In the ordinary procedure
+of estate-working there appears to be an undesirable variety in the style
+of lower grade crepes. On some estates an examination of these rubbers
+would appear to suggest that there need be no expenditure of care in the
+preparation or the form in which it is made. This is a great mistake. With
+the exception of the lowest grade (earth-rubber), it would not be unfair to
+state that the quality of the rubbers on testing should be very little
+inferior to the No. 1 product. Often, as in the case of naturally
+coagulated rubbers, they are superior in some respects to ordinary fine
+pale crepe. Doubtless manufacturers are aware of these facts, but what
+course is open to them if they find the rubber spoiled for their purpose by
+the presence of particles of sand, grit, or bark? The possible injury
+caused by these ingredients cannot be insisted upon too strongly, and it
+must be evident that great care should be exercised in the preparation of
+the lower grades of crepe.
+
+As to the particular form of the lower grade crepe rubber, one may apply
+the remarks made under the section dealing with the best grades. It is
+common to find thin crepes, medium crepes, and "blanket" crepes. More often
+than otherwise, the medium and thicker crepes are prepared direct in those
+forms. It follows that they are liable to attacks of "spot" disease, which,
+however, is not easily visible in the lowest grades, owing to the dark
+colour of the rubber. Furthermore, it is not possible to cleanse the rubber
+so thoroughly if thick crepes are made.
+
+BLOCK RUBBER.--Few estates now prepare block rubber, which is essentially
+crepe rubber pressed into blocks. In the ordinary process the fresh
+coagulum is lightly rolled into thin crepe, which is then vacuum-dried.
+There are slight variations in the subsequent procedure. Sometimes the
+rubber as it comes from the vacuum drier is merely allowed to remain on
+racks overnight before blocking. In other instances, the sticky rubber from
+the vacuum drier is passed once or twice through wet, smooth rolls and hung
+to dry for some days. The dry crepe is then folded into the pressing box or
+cut to suit the size of the box. Pressure is applied for some time, and
+finally the rubber is taken out in one homogeneous mass. Naturally the
+appearance of the block depends upon the quality of the parent crepe. Some
+block rubber is made up thick; other is made in slabs about 3 inches or 4
+inches in thickness. With the latter, it should be possible, when held up
+to the light, to see the shape of a hand held between it and the source of
+light.
+
+It is possible that an erroneous idea of the strength of block rubber has
+been formed. It should only be necessary to point out that essentially
+block rubber is merely pressed crepe rubber. It is inconceivable that the
+mere action of pressing layers of crepe together would increase the
+physical quality of the rubber.
+
+The advantages which block rubber possesses are the compactness of the
+output, its ease of packing, and a saving in freight; but there is the
+disadvantage, from the consumer's point of view, that extra labour is
+involved in the preparatory work of cutting up the blocks.
+
+SMOKED CREPE AND SHEET CLIPPINGS.--There appears to be no certain demand
+for any grade of smoked crepe, and probably all which is put into the
+market is really comprised of (1) clippings obtained from the ends of
+sheets, (2) sheets which have been malformed in machining, or (3) sheets
+showing the presence of many "bubbles."
+
+As to the first class it might be explained that through defective rolling,
+thick ends or edges may be caused. These show signs of contained moisture
+when the bulk of the sheet is perfectly dry, and as undue delay would
+otherwise result these moist strips are trimmed and either returned to the
+smoke-house, or machined to form crepe.
+
+Similarly a torn or otherwise badly formed sheet, when brought from the
+smoke-house, may be made into crepe, rather than it should prejudice the
+selling price of the bulk under ruling conditions.
+
+In the same manner, although "bubbles" have no influence upon the quality
+of the rubber on vulcanisation, sheets thus affected are generally made
+into crepe.
+
+It cannot possibly be argued that rubber of this description would be in
+any way inferior to the best smoked sheet for manufacturing purposes, but
+owing to the prevailing system of evaluation for market purposes, it is
+necessary to resort to the expedients indicated above.
+
+On some estates the rubber specified in the three classes mentioned is not
+made into crepe, but cut up into small pieces and shipped as "sheet
+clippings" or "sheet trimmings"--a procedure which would appear to be
+justified by a steady demand. In point of fact, the buyers are really
+obtaining a first-class article (except in superficial appearance) at a
+reduced price.
+
+
+
+
+CHAPTER XI
+
+_DRYING OF RUBBER_
+
+
+AIR-DRYING OF CREPE.--It is still the prevailing custom to air-dry crepe
+rubbers. A few estates, it is true, have artificial driers installed, and
+in some necessary cases others will be erected. But in the majority of
+cases where money has been expended in building air-drying sheds, as long
+as it is only possible to ship rubber regularly air-drying is likely to
+remain in favour.
+
+The great drawback to air-drying is that one is so dependent upon the
+weather conditions. In favourable weather the rubber dries well, but in a
+long period of wet weather rubber may accumulate at an alarming rate, and
+the accommodation is sometimes severely taxed. Of course, the rate of
+drying under the best conditions is mainly dependent on the thickness of
+the crepe, and every endeavour should be made to maintain a thin style of
+preparation. If this precaution is not taken, the rubber is liable to
+recurrent attacks of "spot" disease, and one's troubles are very much
+augmented. This is a disability to which rubber treated in artificial
+driers is not liable. Still, air-dried rubber can be made equal, if not
+superior, in appearance to pale rubbers prepared by other processes.
+
+For the lowest grades of crepe air-drying is always likely to remain the
+only method, as it would be extremely unsafe to submit them to heat.
+
+It is noted in ordinary practice that the rate of drying on different
+estates, for the same type of rubber, may vary widely. Naturally the
+construction of the house has a great effect, and this subject will receive
+attention in a subsequent chapter.
+
+Similarly the position of the drying-shed exerts an important influence,
+and the erection of the building in low-lying surroundings is always
+calculated to prolong the drying period appreciably. Incidentally this
+means that the building must be larger than a normal rate of drying would
+otherwise demand.
+
+The combination of a poor type of drying-house, a low-lying situation, and
+a prolonged wet season, might render it advisable to abandon the air-drying
+of high grade crepes in favour of artificial drying.
+
+ARTIFICIAL DRIERS FOR CREPE.--It is more common to find artificial driers
+in use in Ceylon than in Malaya, possibly because these driers have been in
+use in Ceylon for other products. Some time ago the question of installing
+artificial driers received the serious attention of a number of estates in
+this country, chiefly on account of the incidence of fungoid and bacterial
+diseases in crepe rubber. The simple treatment for the prevention of these
+diseases is to get the rubber dry in the shortest possible space of time.
+In most cases it is found sufficient to roll crepe thin for air-drying in
+order to prevent the appearance of coloured spots. It is found, however,
+that some drying-houses are so badly planned and constructed, that quick
+drying under even the best of conditions is a practical impossibility.
+Cases have been known in which the disease may disappear almost entirely
+during a period of freedom from rain, only to recur as soon as wet weather
+sets in again. There can be no doubt that, on the whole, the number of
+cases of "spot" disease is on the decline; but equally it is certain that a
+very few estates will always be liable to outbreaks as long as drying is
+attempted in existing houses. For these reasons it is a poor policy to
+temporise, and the only sound policy in extreme cases would be to give up
+ordinary air-drying in favour of some method of artificial drying. As
+regards the majority of estates preparing pale crepe for various reasons,
+it is not expected that any will instal artificial driers. Money has been
+expended in elaborate buildings which certainly do the work for which they
+were designed. As long, therefore, as the accommodation is sufficient, and
+regular shipments are the rule, it is expected that ordinary air-drying
+will still remain the general practice.
+
+Of the better-known artificial driers, there are only three which merit
+serious consideration in these pages. They are the vacuum driers, the
+Colombo Commercial Company's hot-air drier, and the Michie-Golledge
+process.
+
+VACUUM DRIERS.--The vacuum drier is so well known that only a brief
+description need be given. It consists of a chamber heated by steam pipes
+and capable of having the contained air and moisture withdrawn by a pump.
+This description sounds very simple, and in practice the operation of
+vacuum drying is really a simple one, and can well be entrusted to an
+intelligent coolie under efficient supervision. Indicators are fitted which
+show the vacuum pressure and the pressure of steam in the heating pipes
+which travel underneath horizontal slabs upon which trays may be placed.
+Still, in spite of the apparent simplicity of the process, there would
+appear to be a number of little details which, if overlooked, prove to be
+factors influencing the result to a considerable degree. Thus it is not
+uncommon to find complaints that the rubber is not dry when packed. The
+writers have seen rubber taken from a vacuum drier still containing a
+visible quantity of moisture. One would have imagined that continuous
+working of the drier would give the experience necessary to obtain dry
+rubber, but, apparently, such is not the case in a number of instances.
+Elaborate instructions are given by the makers, but often they are more
+honoured in the breach than in the observance. Really, there are only two
+points to bear in mind:
+
+     (1) That the rubber must be fairly thin.
+
+     (2) That the temperature be not allowed to rise too high. Some makers
+     advise 140 deg. F. as a maximum, but no harm results from a temperature of
+     150 deg. to 160 deg. as long as the interval is not prolonged.[11]
+
+[11] These figures refer to temperatures recorded by thermometers placed in
+the folds of the rubber.
+
+These two points presume that the vacuum drier is true to its name, and
+that one can obtain a maximum steady pressure. The machines are so well
+made now that no drier should be taken over from those responsible for its
+erection unless it can show a vacuum pressure of 28 inches within fifteen
+minutes of starting the pump; and with the pump stopped, there should not
+be a greater fall in pressure than 1 inch within ten minutes after stopping
+the pump.
+
+One of the most frequent sources of error is the control of steam pressure
+which is responsible for the temperature of the drier. It is quite
+unnecessary and unwise to maintain any steam pressure once the drying is
+well under way. All that is necessary is to heat the chamber well, with a
+steam pressure of 5 lbs., before inserting the rubber. As soon as the
+maximum vacuum pressure has been obtained, steam should be shut off from
+the heating pipes, and it will be found that the temperature is well
+maintained throughout the operation with a rise of ten to twenty degrees at
+the end. If the drier is working at a vacuum pressure of 28 inches, and if
+the crepe has been prepared thin enough, the rubber should be quite dry
+within two hours. Should the operation have to be extended to two and a
+half hours at 28 inches vacuum pressure, it is a sign that the crepe is too
+thick. On such occasions it is often noticed that these thicker crepes are
+not thoroughly dry, having moist spots enclosed in them. On re-rolling,
+these moist patches become easily visible, and are a source of great
+annoyance, inasmuch as they take quite a long time to dry out.
+
+As mentioned before, the crepe for vacuum drying should be thin. There is
+no necessity to give it a superfine finish, and the presence of small holes
+is quite permissible, as they disappear on subsequent re-rolling. The thin
+crepe may be folded loosely to the length (or breadth) of the tray several
+times, but in no other way can the drier be expected to perform its work
+satisfactorily. A case was noted in which thin crepe was excellently
+prepared, and four or five layers were rolled together for vacuum drying.
+Naturally this mode of procedure does not give the drier a fair chance, and
+it would be ridiculous to judge vacuum drying on the results. After two and
+a half hours at a temperature of 145 deg. F. the rubber appeared to be only
+about three parts dry, and the subsequent air-drying extended well into a
+fortnight.
+
+It is the common practice to screw up the door of the chamber as tightly as
+possible. As a rule it is found in course of time that the obtainable
+maximum vacuum pressure decreases. This may be attributed solely to the
+forcible screwing up of the door. Around the inside edges of the door are
+strips of rubber compound, the function of which is to form a tight joint.
+Should the door be screwed up too tightly, these strips become deformed in
+course of time, and slight leaks occur. It should be pointed out that it is
+only necessary to screw up the door at the beginning of the operation. When
+the vacuum has been obtained, the screw pressure may be released, as the
+atmospheric pressure outside the chamber is more than ample to keep the
+door in a close fitting position. This will be obvious from the fact that
+the difference in pressure between the inside and the outside of the door
+amounts to, say, 28 inches atmospheric pressure--_i.e._, nearly 14 lbs. per
+square foot. By slackening the screw handles, therefore, as soon as the
+indicator shows the maximum working vacuum pressure, the life of the door
+joints may be prolonged, and the drier will remain efficient for a longer
+time.
+
+A careful consideration of the question of temperature leads one to the
+conclusion that the practice of placing a thermometer through the roof of
+the chamber does not enable one to determine the temperature correctly. In
+the same way a thermometer suspended behind the observation window cannot
+indicate the temperature of the rubber, as in both of these positions the
+thermometer must be influenced by radiation from the walls of the chamber.
+The only position in which the correct temperature could be indicated is
+between the folds of crepe. This can be arranged easily so as to enable one
+to read the temperature from the observation window.
+
+COLOMBO COMMERCIAL COMPANY'S DRIER.--The drier of the Colombo Commercial
+Company consists in principle of a number of small chambers or units in
+which crepe rubber is placed, and through which hot air is passed. As in
+the case of vacuum drying, a great deal depends upon the preliminary
+treatment of the rubber. If the crepe is not rolled thin enough drying will
+be unduly prolonged, with a possibility that the rubber will become tacky.
+The temperature usually obtained is about 150 deg. F., and if the rubber is
+thin the production of an installation of two chambers should be at the
+rate of 1 lb. of dry rubber per minute. The usual period of drying is
+under two hours. One advantage which this drier has over the vacuum drier
+is that the chamber can be opened at any time for a short period to
+withdraw or insert trays. The thin crepe is folded several times, as in the
+case of vacuum-drying.
+
+Figures obtained from the actual working of a drier in Ceylon are given
+below:
+
+  -------------------------------------------------+-----------------------
+         CHAMBER 1.--TEMPERATURE 160 deg.-180 deg.F.       |
+  -------------------------------------------------|CHAMBER 2.--TEMPERATURE
+  _NO. OF | _DRYING  |  _WEIGHT OF  |  _WEIGHT OF  |      150 deg.-165 deg.F.
+   Tray._ | Period._ | Wet Rubber._ | Dry Rubber._ |
+  --------+----------+--------------+--------------+-----------------------
+          |Hrs. Mins.|     Lbs.     |     Lbs.     |
+     1    | 1    22  |     7-1/2    |      6       |Worked similarly
+     2    | 1    42  |     7-1/2    |      6       |to No. 1. Yielded
+     3    | 1    57  |     7-1/2    |      6       |in 2 hrs. 23 mins.
+     4    | 1    57  |     7-1/2    |      6       |70-3/4 lbs. dry rubber,
+     5    | 1    57  |     7        |      5-3/4   |from 87-1/2 lbs. wet
+     6    | 1    57  |     7-1/2    |      6       |rubber.
+     7    | 2     0  |     7-1/2    |      6       |
+     8    | 2     0  |     7-1/2    |      6       |
+     9    | 2    11  |     6-1/2    |      5       |
+    10    | 2    11  |     7-1/2    |      6       |
+    11    | 2    11  |     7-1/2    |      6       |
+    12    | 2    18  |     7-1/2    |      6       |
+  --------+----------+--------------+--------------+-----------------------
+          |          |    88-1/2    |     70-3/4   |
+  --------+----------+--------------+--------------+-----------------------
+
+It will be seen, therefore, that the drier had an output in 2 hrs. 23 mins.
+of 141-1/2 lbs., which is at the rate of 1 lb. per minute approximately.
+
+As the rubber leaves the driers it resembles vacuum-dried rubber in being
+surface-sticky. This stickiness is only temporary, and is got rid of by
+passing the crepe through wet rolls. Opinions differ as to when this
+rolling should be given. On some estates the rubber is only allowed to cool
+a little before passing through the rolls; on others it is given a day or
+so before rolling. The methods of rolling also differ. In some factories
+the rubber has been cut to lengths before drying, and these lengths are
+merely rolled together by simple pressure. Other estates prefer to
+re-macerate the crepe while still fairly warm and soft. It is probable that
+little harm, if any, results from this re-maceration while the rubber is
+soft, as it is more easily worked in this condition. The thick rubber is
+then generally hung for a few days to air-dry before packing. As most of
+the moisture taken up by the dry rubber is surface moisture, three or four
+days is usually found ample for air-drying.
+
+MICHIE-GOLLEDGE SYSTEM.--The Michie-Golledge system comprises a process of
+preparation and drying. The latex is diluted with two, three, or four
+volumes of water and coagulated with acid in a vessel which is rotated with
+a churning motion. In this cylinder there are curved and fixed blades. The
+revolving cylinder and its ribs force the latex against the curved blades
+so as to cause an eddy in the middle of the machine. Here the rubber
+coagulates and accumulates, the remaining liquor whirling round outside the
+blades. It can be imagined that with such dilute latex, the coagulum is
+very soft and spongy. This soft mass is passed through a machine which cuts
+it into "worms" about 3/16 inch in section. These are placed upon wire
+trays and dried by means of hot air. The "worms" when dry are re-macerated
+and built up into medium and thick crepes. The colour of the rubber
+prepared by this process is usually very good. When treated in a Colombo
+drier the "worms" usually require about two hours to dry, so that crepe
+rubber may be packed at latest on the fourth or fifth day, as in the case
+of vacuum-dried rubber.
+
+RATE OF AIR-DRYING OF CREPE RUBBER.--In spite of the facts that some
+estates have been making thin pale crepes for years, and that so much has
+been written concerning the preparation of this grade of rubber, one
+occasionally meets with a case in which an estate seems to be unable to
+prepare thin pale crepe, or if it does the period of drying is much longer
+than obtains on most estates.
+
+Again, when cases of infection by spot disease in fairly thin crepes are
+submitted, it is usually found that the particular crepes are of that type
+which, though fairly thin, show whitish spots of moisture when the bulk of
+the rubber is nearly dry. This type of crepe is to be noted for the
+excessive period of drying in comparison with other crepes of equal
+thinness. It has been advanced elsewhere[12] that a factor of the most
+considerable importance in the rate of drying of crepe rubber is the type
+of drying-house and its situation. This accounts very largely for observed
+differences in the rate of drying of thin crepes on different estates. Yet
+even where two drying-houses may be of the same type, and the situations
+may be comparable, one still observes that one thin crepe dries more
+quickly than another. It has been remarked also that a thin crepe in one
+old drying-house dries in a shorter period than a similar crepe in another
+more modern house, although the methods of coagulation and preparation
+exhibit no apparent diversity. In all these conflicting cases allowance is
+made for the weather conditions, and the observed differences seem to be
+inexplicable. It has always been the opinion of the writers that the actual
+rolling of the rubber plays an important part in determining the rate of
+drying of crepe, apart from the question of thinness; and it seemed
+possible that this factor would account for the discrepancies noted above,
+either partially or wholly.
+
+[12] "Preparation of Plantation Rubber," Morgan, 1913, chapters xii. and
+xiii.
+
+With a view to determining to what degree the drying of crepe rubber was
+hastened by the extent to which the rubber was rolled, experiments were
+made. It was hoped, also, that some idea would be gained of the particular
+stage in crepe rolling which had the greatest effect upon the rate of
+drying. In preparing crepe in the estate in the ordinary way the coagulum
+is passed through three sets of rollers, and the stages may be described
+as:
+
+     (1) Rough rolling.
+
+     (2) Medium rolling.
+
+     (3) Smooth rolling.
+
+In the first the coagulum is broken down by passing through the machines
+until a thick rough crepe is formed. This passes to the intermediate
+rollers, where it is worked down to a medium crepe. The rubber finally goes
+to the smooth running at approximately even speeds. Passing through these a
+number of times it emerges as a thin uniform crepe, free from "lumpiness"
+and free from holes, which should dry in from ten to twelve days.
+
+In the experiment the rubber was passed through the machines with varying
+frequency, the number of times in each machine being progressively
+increased, while the working on the other machines remained constant.
+
+It was determined that the rate of drying was affected only by the extent
+to which the crepe was worked in the smooth rolls. The less often the
+rubber passed through these rolls, the slower the rate of drying. Beyond a
+limit in the other direction, increased rolling did not reduce the period
+of drying. It follows, therefore, that crepes which have a good thin finish
+should dry in a minimum period.
+
+[Illustration: DRYING GRAPH. PALE CREPE (THIN).]
+
+WHEN DOES AIR-DRYING TAKE PLACE?--Experiments[13] were conducted with a
+view to discovering, if possible, the rate at which crepe rubber dries, and
+the extent of drying during the night under weather conditions such as
+prevail ordinarily in Malaya. It is to be remembered that, during the day,
+most drying-houses are fairly open and that the temperature ranges from
+about 88 deg. F. in the lower rooms to over 100 deg. in the upper rooms (near the
+roof) when the sun shines. At night, however, there is usually a decided
+drop in the temperature, and unless it is a very clear night the air is
+generally saturated with moisture. In addition the drying-house is closed
+as thoroughly as possible, and we should expect the atmosphere of the house
+to be laden with moisture from the wet and drying rubber. It would be a
+just inference, therefore, that the rate of drying during the night would
+be much less than the rate of drying during the day, and the results of
+experiments confirm this very fully. One was hardly prepared, however, to
+find that, under certain circumstances and at a certain stage, the amount
+of drying is nil; not only so, but it was found under certain conditions
+that the amount of drying which took place was negative--_i.e._, the rubber
+weighed slightly more when taken out in the morning than it had weighed the
+previous afternoon.
+
+[13] Rubber Growers' Association, Malaya Local Report, No. 2, 1914.
+
+CREPE MAY INCREASE IN WEIGHT.--As an instance of the kind of result
+obtained a graph is here given of the rate of drying of a batch of pale
+crepe. This was hung to dry in the top room of a drying-house in which
+rubber ordinarily dries quickly. The rubber was hung in a good position,
+with the bulk of output, near a window which was open for some time during
+the day. In order to restrict the day interval of drying to the actual
+period in which the sun was likely to be in evidence, the day was taken to
+begin at 8 a.m. and end at 4 p.m., the night interval covering the
+remaining sixteen hours. Thus the night interval was twice as long as the
+period of day drying. The lengths of crepe were weighed carefully at 8 a.m.
+and 4 a.m., and the average of the several weights was plotted in a graph.
+
+The weights are placed vertically and the duration of drying horizontally.
+It will be seen that the rubber was quite dry and fit for packing on the
+sixth day, as far as could be judged in the usual way by casual inspection.
+Peculiarly enough at this time it weighed slightly more than had been
+registered on the fourth and fifth days, but the difference did not amount
+to more than about 0.4 per cent. In examining the graph it should be borne
+in mind that the steeper the slope of the curve downwards the quicker the
+rate of drying, and that when the curve takes an upward direction there is
+an addition of moisture instead of abstraction. It will be noted that when
+drying takes place the slopes more nearly approximating the vertical
+represent the extent of day drying, and that often the night drying is
+represented either by a very flat curve or even by an upward curve which
+shows the addition of moisture. A striking feature of the experiment is
+shown by the rapidity with which drying takes place during the first few
+days and the comparative slowness with which the remaining moisture is got
+rid of. Thus, from the graph, it may be calculated that about 80 per cent.
+of the total moisture content was lost in the first two days, and over 93
+per cent. in two and a half days. Yet three days had to elapse before the
+remaining 7 per cent. of total moisture was lost--_i.e._, before the rubber
+was judged to be ready for packing. It will be seen that after this stage
+had been reached the rubber alternately lost and gained in weight, with a
+tendency to increase. This increase was attributed to the presence of
+surface moisture after hanging overnight, when the rains had become
+frequent. Some light is thus shed upon a subject which has puzzled both
+shippers and receivers of crepe rubber.
+
+DIFFERENCES IN WEIGHT.--It will be obvious that if rubber is allowed to
+hang after becoming dry, and is taken down, packed, and weighed in the
+early morning, it will weigh more than when it reaches a drier climate. The
+loss in weight under such circumstances might amount to even 1 per cent. It
+may seem to some an unnecessary refinement to introduce, but it would
+appear from the graph that rubber should be packed for preference in the
+afternoon if the weights are to be more nearly correct.
+
+It is extremely singular to note how quickly the curve changes its slope
+after the major portion of the moisture has evaporated, and it will be very
+plain that in the last stages any decrease in weight during the day would
+appear to be counterbalanced, or more than counterbalanced, by the addition
+of moisture during the night. It may be pointed out, however, that this
+increase in weight during the later stages of drying of pale crepe is
+mainly, if not altogether, due to surface moisture. The chief point of
+interest is the fact that in the case of thin pale crepe, quite 80 per
+cent. of the total moisture content is lost during the first two or three
+days, and that, owing to the negative influence of the night atmosphere,
+the final drying is delayed. It will be understood that the foregoing
+results applied to thin pale crepe. Thin lower-grade crepes appeared to dry
+at more uniform rates, but the differences between the rates of drying at
+night and during the day were similarly notable.
+
+AIDS TO NORMAL AIR-DRYING.--These experiments were undertaken in a
+drying-house, favourably situated for rapid drying, in which the average
+period of drying for thin crepes is nine days. It is easy to imagine that
+the condition of affairs as revealed would be much exaggerated in a
+drying-house situated on low-lying ground and surrounded by trees. In
+extreme cases of this nature the use of large fans and heating pipes has
+been advocated. It is believed that in some cases these installations have
+given satisfaction, but that in others the degree of improvement obtained
+has not been in economic proportion to the outlay incurred.
+
+SMOKE-CURING OF SHEET RUBBER.--It will have been evident that one of the
+disadvantages of air-drying sheet is the incidence of moulds. Now it is
+found that moulds should not develop in smoke-curing; and if they do, then
+the smoke-curing has been insufficient or inefficient. The difference in
+the drying period also is a strong argument in favour of smoke-curing, so
+that all-round it is seen that there are many valuable advantages to be
+gained by smoke-curing sheet in comparison with air-drying, and no
+disadvantages.
+
+The manipulation of the rubber, after it leaves the marking rolls and
+preparatory to smoke-curing, has been discussed in Chapter IX. It is
+sufficient only to allow adequate time for furnace water to drip from the
+sheets before transferring them to the smoke-house. As it is the general
+rule to roll sheet rubber in the morning, this arrangement fits in very
+well. The furnaces of the smoke-house are usually extinguished as soon as
+the sun is well risen, and the rest of the day is occupied in sorting dry
+sheets, etc. Towards noon the day's wet sheets should have been admitted,
+and smoking may be commenced as soon as the sun is well in the west--say,
+at half-past four o'clock or earlier.
+
+It used to be the custom on a few estates to smoke during the daytime and
+to discontinue smoking at night. As the night-air in Malaya is usually
+heavily laden with moisture, it will be plain that such a policy was a
+topsy-turvy one. It is vastly more reasonable to smoke-cure at night;
+usually the heat of the sun during the day is quite sufficient in itself to
+promote the drying of rubber; but there is no reason why smoking should not
+be carried on in the daytime in wet weather, should it be found expedient
+to do so.
+
+RECORDING INSTRUMENTS.--During the night the care of the smoke-houses is
+usually in the hands of natives, except for occasional surprise visits from
+a European superintendent. To all acquainted with the ways of the native it
+must be plain that means must be provided for the checking of the
+temperatures attained in the smoke-house. Ordinary thermometers are quite
+unsuitable, and even thermometers registering maximum and minimum
+temperatures are of little avail, inasmuch as they record only the degree
+of heat attained at a particular moment, and do not indicate any period
+during which a particular temperature was maintained.
+
+It is evident that something more informative is required. There are many
+types of suitable recording instruments or "pyrometers," some of which can
+be electrically connected, so as to cause the ringing of a bell, placed in
+the superintendent's office or house, on the attainment of a certain
+temperature. The type best known in estate practice is that named the
+"Thermograph," in which a pen traces a curve or graph on a plotted piece of
+paper carried by a rotating cylinder which is actuated by clockwork. Such
+instruments can be purchased through most of the local firms dealing in
+estate supplies. From experience it can be asserted that, given intelligent
+attention, these instruments yield very satisfactory results. The apparatus
+should not be placed always in one position in the smoke-house, but should
+be moved frequently so as to obtain information regarding the distribution
+of heat.
+
+TEMPERATURE OF SMOKE-CURING.--In the question of temperature of drying, it
+is well to be as strict as possible; not that any great harm will result
+from a rise of 10 deg. above that recommended, but because the higher the
+temperature recorded the larger the fires must have been, and consequently
+the more real danger there was of the store becoming ignited. It has been
+shown[14] that the temperature giving the maximum benefit of drying and
+quality was found experimentally to be rather above the temperature usually
+prescribed for smoke-houses, but in the experimental work there was no
+danger from fire.
+
+[14] "Preparation of Plantation Rubber," Morgan, 1913, chapter x.
+
+The figure given in previous publications as a maximum working temperature
+for smoke-houses was 110 deg. F., but certainly the temperature may be as high
+as 130 deg. if it is considered safe to allow fires to be so arranged. One or
+two estates are known to work at temperatures of 130 deg. F. and over, in spite
+of the recommendations of the writers. If those estates care to risk it
+they may do so, with increased rapidity of drying; but no responsibility
+can be taken for whatever may happen in smoke-houses where the temperature
+is allowed to remain, as in one case, at 160 deg. F. Naturally the range of
+temperature is strictly limited by the properties of the substance to be
+treated, and with a substance such as rubber it would be far better to err
+on the side of caution than to risk damage to such a commodity, apart from
+the consideration of the possible destruction of the building.
+
+PERIOD OF DRYING.--Considerable differences are noted in the periods of
+drying on various estates; but, as there is more than one factor
+influencing the results, it is not easy at first to find why these
+differences should exist. Really there are three factors:
+
+     (1) Relative thickness of rubber.
+
+     (2) Extent and quality of rolling.
+
+     (3) Temperature of drying.
+
+It is presumed that the smoke-houses are identical in type and efficiency,
+and that smoking is in force for the same length of time each day. There
+need be no discussion of these points; the effect of each is so obvious.
+The thinner the sheet, the quicker the rate of drying; the better the sheet
+has been rolled, the shorter the period of drying; the higher the
+temperature, the more rapid the drying.
+
+It has been shown in Chapter IX. that the condition of the sheet after
+rolling depends primarily upon the standard of dilution of the latex and
+the original thickness of the coagulum. If these factors are correctly
+controlled, the rolling should give a sheet which is fairly soft and
+porous--_i.e._, it should not have been subjected to such pressure as to
+make it both thin and hard. An average sheet of rubber which has been well
+rolled should be smoke-dried at a temperature of 120 deg. F. in about ten days.
+If sheets take appreciably longer to dry, then the three foregoing factors
+must be examined.
+
+On the other hand, it is often found that thin sheets made from very dilute
+latex dry so quickly that they are considered to be fully smoke-cured in
+from five to seven days. It frequently happens in such cases, however, that
+the smoking is insufficient, and by the time the rubber reaches home it has
+begun to show signs of surface moulds. It is evident, therefore, from this
+discussion that:
+
+     (1) If smoked sheet develops surface moulds within a short period
+     after smoking, the duration of curing has been insufficient, or the
+     quality of the smoking is at fault.
+
+     (2) The actual time taken to smoke-dry rubber may be insufficient to
+     smoke-cure it.
+
+     (3) The rate of drying of smoked sheet depends upon--
+
+          (_a_) The relative thickness of the rubber.
+
+          (_b_) The preliminary treatment of rolling.
+
+          (_c_) The temperature of the smoke-house, and
+
+          (_d_) The type of smoke-house used. This point will be treated
+          in a subsequent chapter.
+
+FUELS FOR SMOKING.--The general idea formerly held was that the beneficial
+effects of smoking were to be attributed to the constituents of the smoke,
+and chiefly the creosotic substances. This is not now the opinion of the
+writers, who attribute the effect largely to the temperature of drying and
+constituents of the smoke other than creosotic substances. There can be no
+doubt that the presence of creosotic bodies is responsible largely for the
+absence of moulds and the existence of the typical odour, but it is
+becoming increasingly known that the employment of substances rich in
+creosote is not required or desirable.
+
+Estates used to be put to considerable expense in the purchase of "bakau"
+(a mangrove timber rich in creosote and creating much heat), under the idea
+that it was the best material and almost indispensable. Most estates now
+restrict themselves to the consumption of timber obtained from their own
+areas. Thinning-out programmes are largely responsible for the supply, but
+the local authorities are much concerned regarding future supplies; and
+consideration has been given in some quarters to the question of the
+development of quick-growing trees on estates with a view to safeguarding
+the future. This seems to be desirable, as it is difficult to imagine that
+the place of timber can be taken by any other material in the smoke-curing
+of rubber. Unless some such precautions are taken it is not difficult to
+predict that, in course of time, some estates will be able to continue the
+preparation of smoked sheets only at considerable expense in obtaining
+suitable fuel from a distance.
+
+It is not true that _any kind of timber_ is suitable as a fuel to be used
+in a smoke-house. All timbers are suitable, either alone or in mixture with
+others, provided that the wood is not too green.
+
+Naturally an absolutely dead and crumbling wood will smoulder, but does not
+develop sufficient smoke. A green timber will give an acrid and moist
+smoke, but demands the consumption of a certain amount of dry timber in
+addition if it is to be used.
+
+Rubber-tree prunings and sawn rubber trees obtained by thinning-out may be
+used in mixture with dead wood, provided the logs are stacked to dry in the
+sun for some weeks before use. If the timber is too green, steam is formed
+as well as smoke, and the sheets of rubber may have a moist surface glaze.
+
+SUN-DRYING SHEET RUBBER.--Among the first curious sights which impress the
+visitor or newcomer to this country is the spectacle of sheet rubber
+hanging in the sun on native holdings. From what one has learned of the
+extraordinary care which must be exercised in all the processes of rubber
+preparation, one fails to understand how such rubber reaches the market
+without becoming tacky. That some of it does become slightly tacky is
+certain, but on the whole native rubber, though crudely prepared, is
+usually sound. The native idea of giving sheet rubber a preliminary drying
+in the sun is to hasten the total period of drying. That the period is
+curtailed would seem to be the case, but it is open to doubt, as the effect
+of sun-drying, if unduly prolonged, is to create a thin surface film of dry
+rubber which retards the drying of the rubber below the surface. Working
+with wet crepe rubber, the writer found that, to all external appearances,
+there was no effect upon the rubber when it was allowed to sun-dry for four
+or five hours. With periods of from six to ten hours the crepe becomes
+slightly sticky, chiefly on that portion across the support. When removed
+to the air-drying house this tackiness developed further, and the rubber,
+on the line of support, became so weak that it stretched and broke.
+
+Reasoning by analogy, it would appear that no apparent harm would result to
+sheet rubber from sun-drying for periods up to four or five hours. From
+experience (see Chapter IX.), not the slightest ill-effect is found to
+result from the short interval of preliminary drying or dripping practised
+on many estates preparatory to smoke-curing.
+
+ARTIFICIAL DRIERS FOR SHEET RUBBER.--It is understood that when vacuum
+driers were first applied to the drying of rubber it was thought possible
+to dry sheet rubber in this way. The practice was found to be impossible,
+as the length of time required and the temperature were responsible for the
+destruction of the form of the rubber; it became tacky and semi-liquid.
+
+THE "CHULA" DRIER.--Although several suggestions of devices for
+artificially drying sheet have been made, only one is known to be in use at
+the present time. In the original form this was used for drying other
+tropical products. It consists of a large iron chamber, in which are
+several compartments divided by means of baffle-plates. At one end there is
+a small furnace and, by means of a fan, smoke and hot air are drawn
+through the compartments. Owing to the temperature attained (140 deg. to 160 deg.
+F.) sheet rubber cannot be completely dried in the chambers, and is, as a
+rule, only treated in this manner for one or two days. Drying is then
+completed in an ordinary air-drying house. It is claimed that drying is
+expedited, and that the rubber can be packed in ten days.
+
+In the more recent modification, the smoke and hot air which leave the
+Chula drier pass through a large room in which may be hung either sheet or
+crepe rubber. It would seem that all sources of danger have not been
+eliminated from the process, as on one estate a wooden room containing
+rubber was ignited by a spark which passed through the drier.
+
+Yet another form exists in which the furnace is outside the main building,
+and in the ordinary course of working only heats a series of open pipes
+through which air is drawn by a powerful fan. By means of a valve it is
+possible to allow smoke from the furnace to pass into the room with the hot
+air for the preparation of smoked rubber. The hot air or smoke is
+distributed in the lower room by means of main and branch pipes, and passes
+through an open floor to the room above. With such an arrangement it is
+possible, therefore, to prepare either air-dried or smoke-cured rubber. If
+the method could be successfully applied to the drying of crepe it would be
+of great assistance on some estates. There would seem to be a difficulty in
+working it for the drying of sheer rubber and crepe together, as the
+temperature suitable for the one is excessive for the other. Given an
+efficient control over the temperature of the hot air, the house should be
+successful in the drying of crepe, provided the rubber is not hung in folds
+of too great length. For smoke-curing sheet rubber the period is said to be
+reduced by several days in comparison with the time occupied in an ordinary
+smoke-house, but it is not clear that such a system would have any
+advantage over a modern smoke-house, in types of which rubber can be fully
+cured in periods ranging from five to ten days.
+
+
+
+
+CHAPTER XII
+
+_SORTING, GRADING, AND PACKING_
+
+
+The question of standardising the output of our plantations is one which
+has occupied attention for some years, with a not inconsiderable degree of
+success.
+
+Meanwhile opinion is growing in favour of proceeding along the line of
+reducing the number of plantation grades to a minimum. At present some
+confusion exists. Some estates make up tree-scrap and bark-shavings
+together; one estate puts tree-scrap, earth-scrap, and bark-shavings into
+one uniform crepe; other estates have three or more separate scrap
+grades--_e.g._, lump-rubber and "washings," tree-scrap, earth-scrap, and
+bark-shavings scrap. There is a movement on foot at present to try to
+restrict plantation rubber to three grades:
+
+CREPES--1. _First Quality Latex._--_I.e._, crepe made from the true
+coagulum obtained from the regulated coagulation of strained latex. This is
+a pale rubber, and may be prepared satisfactorily if the directions given
+in preceding chapters are followed. Naturally there must be, in all
+factories, some defective rubber of this grade. For various reasons the
+crepe may be of inferior colour, or is slightly contaminated with dirt or
+traces of oil and grease, etc. This defective rubber should be placed aside
+most rigorously and plainly marked as "off-quality."
+
+If a proper scheme of standardisation of latex and chemicals is followed,
+there should not be any such variety in shades of colour, such as was
+common in No. 1 crepe in the past.
+
+Comparatively few estates in Malaya now prepare thick (or blanket) crepes
+in the No. 1 grade, but in such cases the same rules must be applied as
+govern the sorting of thin fine pale crepes.
+
+2. _Compound Crepe, No. 1._--In this it is proposed to include
+cup-coagulated lumps, coagulated lumps from transport vessels, skimmings,
+bucket rinsings, cup-washings, and tree-scrap. It has been shown in Chapter
+X. that strict care is necessary to eliminate all oxidised (dark) scraps.
+These are relegated to a lower grade. The possession of a "scrap-washer" is
+necessary if the best results are to be obtained.
+
+On some estates the ingredients of this compound crepe, while fresh, are
+placed in a common jar or tank to which a quantity of sodium bisulphite (1
+per cent. solution) and acid are added. The resulting conglomerate mass is
+cut up for working.
+
+3. _Compound Crepe, No. 2._--This grade would include the remaining lower
+grades--viz., bark-shavings, scrap, and earth-rubber scrap.
+
+REDUCTION CARRIED TOO FAR.--However desirable it may be to diminish the
+number of grades, it must be pointed out that diminution and simplification
+are not necessarily synonymous terms in this matter. It is well known that
+on estates where the earth-rubber is only brought in at lengthy intervals,
+say of a week, the resulting crepe is sometimes very tacky. This is only
+natural, and is due to the prolonged exposure to the sun's rays. With the
+improved machinery now at our disposal, and with the increasing attention
+which will be given to the lower grades in the future, it is possible to
+prepare from average bark-shavings crepe free from bark, and of quite a
+good colour. Where trees are not "scrapped" before tapping, there would
+seem to be no objection to amalgamating the rubber obtained from the
+bark-shavings with the No. 1 Compound crepe; and it would be a distinct
+danger and possible loss if this good rubber were to be mixed with earth
+rubber. The liability of the latter to become tacky is well recognised; and
+if possible it should be maintained as a separate grade, in which it would
+be permissible to mix only rubber obtained from actually dry shavings from
+"scrapped" trees, or heavily-oxidised scraps which have been rejected from
+other grades.
+
+SHEETS.--Broadly there are no fine distinctions to be made at present in
+the grading of smoked-sheet rubber; it is either No. 1, or if any
+so-called defect is visible the sheets must be rejected and plainly marked
+as "off-quality."
+
+Clippings (trimmings) may either be made into crepe or shipped under their
+own description.
+
+RUBBER GROWERS' ASSOCIATION'S RECOMMENDATIONS.--Taking the foregoing
+arguments into full consideration, it would seem that, strictly speaking,
+the number of grades cannot be reduced to less than four at present without
+producing some amount of confusion.
+
+In its handbook,[15] the Rubber Growers' Association remarks:
+
+[15] "Preparation of Plantation Rubber," 1917.
+
+     "The fewer grades the better, and regularity of each grade is most
+     important.
+
+     "The grading should be as follows:
+
+          "(No. 1) Fine crepe (or No. 1 sheet), made from the free or
+          liquid latex.
+
+          "(No. 2) Clean light brown crepe, made from lumps and skimmings.
+
+          "(No. 3) Scrap crepe, made from tree-scrap.
+
+          "(No. 4) Dark crepe, made from bark-shavings, earth rubber, and
+          the lower quality of scrap.
+
+          "Tacky rubber should be packed separately.
+
+"_Compound Scrap Crepe._--Estates using scrap-washers should make a
+compound crepe of grades Nos. 2 and 3, which will make one compound free
+from bark and specks. All rubber intended for No. 4 should be most
+thoroughly washed."
+
+Concerning these recommendations the remarks in preceding paragraphs should
+be studied.
+
+CARE IN SORTING.--Whether dealing with smoked-sheet, pale crepe, or lower
+grades, the strictest care is necessary in sorting and grading. This work
+must of necessity be relegated to coolies, and they should be trained men.
+Instructions must be definite, and doubtful specimens of rubber should
+always be placed aside for the decision of the European superintendent. Any
+pieces showing unmistakable signs of what are regarded as defects should be
+stringently rejected. In the case of pale crepe, when the defect is
+confined only to a small area it is permissible to cut out the affected
+portion. Similarly there can be no objection, in the case of smoked sheets,
+to an occasional sheet being treated in this manner. On the majority of
+estates these rules are observed carefully, but some estates yet have to
+learn that defective pieces of rubber may not be concealed in a bulk of
+otherwise good quality. Samplers have often an uncanny knack of hitting
+upon the defective specimens, and it is entirely the fault of the estate's
+sorters if these pieces are submitted as being representative of the mass.
+
+CHOICE OF CASES.--Consumers complain justly of the presence of chips,
+splinters, and wood-dust. It will be evident, therefore, that whatever the
+type of case employed the interior surfaces should be smooth, there should
+be no cracks or gaps in the timber, and the cases should be cleaned out
+before using. There remains great room for improvement in the means and
+method of packing, and in spite of suggested alternatives we are at present
+restricted to the use of wooden cases.
+
+From comparisons of actual quality and fulfilment of the requirements
+indicated above, there can be no question that cases made of three-ply
+wood, such as the "Venesta," are in every respect superior to the ordinary
+wooden cases of "Momi" type. The consideration of cost and available
+supplies, of course, enters largely into the question, and three-ply cases
+are not at present so largely employed as they deserve to be.
+
+A new type of case was recently exhibited in Singapore. It emanates from
+the U.S.A. and is made of a fibrous material, resembling in appearance a
+very stout cardboard. The complete case when assembled consists really of
+two boxes, one of which is inverted and slides down over the other. Packing
+is completed by means of stout wire, which is strained by a simple ratchet
+arrangement. It is claimed that from 225 to 250 lbs. of rubber can be
+contained. Other claims made amount to the statement that the case is
+practically indestructible under normal conditions of handling and
+shipping. A demonstration given certainly appeared to substantiate the
+statement fully. Rubber packed in cases of various and average type was
+allowed to fall from a height of about twenty feet. In all instances the
+wooden cases of every type were either smashed or badly burst, whereas the
+fibre cases were merely dented. These cases are obtained in flat sections,
+which, in assembling, are folded and clamped by means of copper rivets in
+a special but simple machine. It was pointed out that objection might be
+lodged against the use of copper for this purpose.
+
+More recently there is announced a new packing case which is stated to be
+made from low-grade rubbers, but information is rather vague.
+
+BAGS.--There are in local use stout canvas bags which have the advantage of
+being used many times, as long as they are waterproof and kept in good dry
+condition. Their employment for the conveyance of smoked-sheets would
+appear to be permitted, but crepe rubbers sent in them are often reported
+upon as being "massed" at the edges, and hence difficult to "sample."
+
+BALES.--Attempts to bale rubber for the market have been frequent, but no
+success seems to have attended the efforts. In some quarters the failure
+has been ascribed to prejudice on the part of buyers, but it is the opinion
+of the writers that the objections to baling are, or could be,
+well-founded. Massed rubber often cannot be inspected properly, and hence
+is always open to suspicion that internally there may be unsuitable
+portions.
+
+There have been several schemes put forward for winding crepe rubber on
+spindles so as to form a cylindrical package complete in itself. We have
+seen the process, and certainly the method had much which appeared
+commendable. Apart from other objections which might be raised, there is
+always the one prominent objection mentioned in the preceding paragraph.
+
+While baling of rubber is thus not likely to suit the general market, there
+is no reason why, as in one or two instances, it should not be practised by
+agreement between producer and consumer. It is believed that "slab" rubber
+is shipped in bales from Sumatra to the U.S.A.
+
+Quite recently a proposal has been put forward to revert to a simple form
+of baling for ordinary plantation rubber. Under this scheme wooden cases
+are discarded, the packing material being composed of scrap-grade crepe
+rubber which, it is claimed, could be put to use by the manufacturer. An
+obvious drawback would be evident if these bales happened to be exposed to
+direct sunlight or a continuous high temperature. The tackiness which might
+supervene would make the handling of such bales unpleasant, even if it did
+not affect the internal rubber.
+
+FOLDING FOR PACKING.--In the packing of smoked sheets it would appear to be
+advisable to avoid, if possible, the folding of any pieces, as the
+objection is made that such rubber is difficult to "sample" on arrival,
+especially in cold weather. Sheets should be prepared or cut to such length
+that they occupy the full superficial area of the box, either singly or
+side by side.
+
+[Illustration: A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT.]
+
+The same remark applies to the packing of crepe rubbers, except that here
+we deal with units of folded rubber. Crepes are generally folded by hand,
+and coolies usually work to a certain dimension by means of a standard
+stick. The work is slow, but often gives employment, at a cheap rate of
+pay, to women and weak coolies.
+
+Several machines have been invented to replace this labour. The best of
+these yet seen has a simple device by means of which the length of the fold
+is adjustable to suit the size of any packing case. It is called the
+"Senang" folder, and is made by the General Engineering Company (Radcliffe)
+Ltd., Radcliffe, near Manchester.
+
+CARE IN ASSEMBLING.--Whatever the type of case employed, great care must be
+given to the assembling of parts and the final fastening. It is not
+uncommon to find in the operation of putting on the "strapping" that nails
+have been driven into the rubber. Extra bands of strapping are sometimes
+advised, and where these bands pass over the sides (not edges) of the case
+only specially short nails should be used.
+
+All wood should be planed, and in cases other than three-ply should be of
+stout wood, not less than 5/8 inch in thickness. All timber used should be
+of uniform type and thickness.
+
+METHODS OF PACKING.--The usual method of packing crepe is to fold the
+lengths to some measure of the dimensions of the case. This is done in a
+haphazard fashion on some estates, with the result that either space is
+lost or the packing is badly arranged.
+
+Some ingenuity can be displayed in the packing of sheet rubber in order to
+avoid folding the sheets, which, besides increasing the difficulty of
+sampling, leads to loss of space. Endeavours are being continually made on
+estates to prepare sheet of such a size as to obtain the maximum benefit of
+space both in smoke-house accommodation and in packing. A few estates
+employ tanks of such calculated dimensions as will yield uniform sheets
+which pack flat and fill the superficial area of the case.
+
+In view of the contamination which sometimes characterises the employment
+of wooden cases it is sometimes advised that the interior should be lined
+with sheets, or pieces of crepe, the ends of which are later folded over
+the top of the mass. In this manner it is stated that contamination is
+confined only to the exterior of the contents of the case.
+
+WEIGHT OF CONTENTS.--The dimensions of average cases are 19 inches by 19
+inches by 24 inches, giving a capacity of 5 cubic feet.
+
+In these it is possible to pack 150 lbs. of crepe rubber and 200 lbs. of
+sheet rubber (about 5 per cent. more in cases of three-ply wood). It may
+be noted that boxes arrive in better condition when fully packed. The
+foregoing figures are not adhered to strictly. For example, some estates
+find it expedient to ship rubber in actual ton lots, and for this purpose
+pack only 140 lbs. of crepe per case, giving sixteen cases to the ton.
+Other estates, using presses, pack more per case than the quantities noted
+above. At present there does not appear to be any definite regularity in
+practice.
+
+[Illustration: ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT.]
+
+In all instances it should be the invariable rule that the rubber should be
+weighed before packing, and that all cases should contain uniform nett
+quantities of any particular type of rubber. Invoicing, etc., will thus be
+greatly facilitated. If these practices are followed, and the rubber always
+weighed on the same scales (assuming it to be perfectly dry when packed)
+complaints of "short-weight" should be infrequent.
+
+"SHORT" WEIGHTS.--In some cases the occurrence of "short" weights on
+arrival at ports would appear to be inexplicable. It often happens that the
+constituent parts of wooden cases have been in stock for a considerable
+period. If for no other reason than that indicated below, all cases,
+either before or after assembling, should be thoroughly dried in the sun.
+"Short" weight could be accounted for to some degree by a lack of
+observance of this elementary rule, as it is most probable that there would
+be a perceptible difference in weight of the wooden case in a drier
+atmosphere.
+
+     (_a_) If rubber is weighed in the box, and the average tare of the
+     case deducted from the gross weight (in order to obtain the nett
+     weight), any loss in the weight of the timber would appear as a
+     deficiency of rubber at the distant port.
+
+     (_b_) Whether the same effect would be produced eventually in the case
+     of rubber which is weighed before packing will depend upon the method
+     of weighing at the warehouse. If the rubber is weighed in the box, any
+     observed deficiency would be attributed to a loss of weight in the
+     rubber.
+
+
+
+
+PART III
+
+MACHINERY AND BUILDINGS
+
+
+
+
+CHAPTER XIII
+
+_MACHINES_
+
+
+The number of manufacturers of machines for preparing rubber would seem to
+be on the increase, and there can be little doubt that this competition
+will result in a continued improvement in the design of machines. It cannot
+be denied that there has been room for such improvement, and it is believed
+that manufacturers will display judgment in putting only their best quality
+into the work. While design and finish are very excellent in their way, it
+is to be regretted that in a number of cases in the past the material of
+rolls has been found to be of inferior quality. Generally, the complaint
+seemed to be that the rolls were too soft, and that the "grinding" effect
+was far too great. The damage to pale rubber in such cases is considerable,
+as it is impossible to keep the rolls free from fine dark powder. The
+effect is generally noticed more in the smooth rolls with which a finish is
+put upon the crepe.
+
+Cases have occurred frequently in which rolls have been returned, because
+of the injury caused to pale rubber, and there can be little doubt that the
+life of quite a large number of rolls is even now far too short in
+comparison with the expense involved.
+
+It is a moot point, however, in many instances how far the quality of the
+rolls is actually responsible for the damage done to the rubber. In the
+experience of the writers it is certain that complaints regarding the rolls
+were unjustifiable, and that the injury had been caused by carelessness in
+the "feeding" of the machine. Especially in the case of smooth finishing
+rolls, it is clear that if the rolls are allowed to run idle for more than
+the briefest possible interval grinding must take place.
+
+The complaints apply not only to the rolls themselves, but also to the
+brass linings for shaft-bearings. Cases are known in which a brass "liner"
+was so worn within a few weeks as to be quite useless. If the matter ended
+there it would not be so bad; but there is always the possibility of
+particles of brass finding their way into trays, and so into the rubber.
+The damage which ensues to the rubber is quite irreparable. This particular
+defect arising from the presence of brass will be dealt with in a later
+chapter. But here again it is necessary to point out that such wear on
+brass liners may be caused by the standards (ends) of the rolls being
+eccentric; and the case may be analogous to the placing of "new wine in old
+bottles."
+
+_En passant_ it may be remarked that in any case brass liners are not
+strictly necessary. White-metal alloys are in use on rubber machines, and
+cast-iron bearings have been employed satisfactorily for years.
+
+It would be well for managers to remember, therefore, that when machines
+have to be ordered, nothing but the best is good enough, and that the
+difference between good machinery and passable machinery is probably
+immensely greater in effect than any saving in expenditure would warrant.
+
+ADEQUACY OF MACHINES.--In general, the factories which prepare sheet rubber
+are usually equipped with adequate machinery. This arises from the fact
+that machines are necessary for preparing all grades below the first, even
+if they are not necessary for the making of sheet. Thus all the necessary
+macerators and finishing machines are installed, but the major part of the
+output is in sheet form. For the preparation of sheet, no heavy machinery
+is required; all that is necessary are light machines for rolling the
+sheets and expressing as much moisture as possible. To obtain a pattern on
+the sheet, another light machine may be used. It may be imagined, then,
+that the work of rolling sheet rubber by power machines is small, and that
+a large quantity of rubber can be worked off in a comparatively short time.
+It follows, therefore, that the preparation of the lower crepe grades can
+be proceeded with at once, and that the whole work of the factory is
+expedited.
+
+The case of factories which have to prepare all first-grade rubber in crepe
+form is quite different, especially when thin rubber has to be made. The
+care which has to be exercised in preparing pale crepe rubber is very great
+in comparison with what is demanded by sheet rubber. The rubber has to go
+first through the uneven-speed macerators, from there to the intermediate
+rollers, thence to the finishing rollers. Considerable ingenuity has to be
+displayed in the arrangement of the machines, so that one section will not
+work faster or slower than another. More often than not, the attempt to
+arrive at such a desirable arrangement fails, owing to an insufficiency of
+machines. Such a statement will probably read strangely to the uninitiated;
+but an example will make it plain. A factory may have a battery of six
+machines, one only of which is a finishing machine (smooth rolls). With
+five macerators and intermediate machines working continuously, it will be
+more than the work of one finishing pair of rolls to keep pace, especially
+as so much more care has to be exercised in finishing than in rough
+crepe-making. The obvious course to adopt is to substitute a pair of smooth
+rolls, with suitable gear ratio, for a pair of macerators or
+"intermediates."
+
+If, however, the macerators and intermediates are already fully occupied
+the whole of the time, any such change would be of small benefit. What is
+really needed in this case is more machinery.
+
+It might be pertinently asked what constitutes an adequate equipment of
+machines for crepe-making. The writers cannot give a number, but have no
+hesitation in stating that if a factory cannot complete its whole day's
+work before dark, it is inadequately equipped. No work should be done after
+dark, if possible, as it cannot receive the supervision which crepe-making
+demands. To make comparison between the number of machines in any two
+factories and their respective outputs is not sound argument, as the
+out-turn of two similar machines will depend upon the speed at which the
+rolls travel--_i.e._, the gearing between the machines and the engines.
+Thus, while one machine will out-turn 40 lbs. of crepe per hour, another
+may only have an output of 30 lbs., although the machines may be identical
+in pattern. To make calculations based on a rate per hour for any known
+make of machine, and to apply those calculations to the existing machinery
+in any factory, in an attempt to judge whether there is a sufficient number
+of machines, would be a mistake, unless one were also supplied with the
+relative speeds at which the rolls work.
+
+Finally, on the question of adequacy of machines, it must be pointed out
+that an insufficient number of machines must result in a poor product,
+since all rolls have to be used for all grades. Even with the greatest
+possible care it happens that pale crepe is sometimes spoiled because it is
+contaminated with foreign matter, resulting from the working of lower
+grades on the same machines. This is one of the great arguments in another
+direction for the installation of a scrap-washer.
+
+In conclusion, the writers can only give their opinion that one must not
+decide the question of adequacy by the number of existing machines, but by
+the time taken each day in working off the rubber, providing one can be
+satisfied that the best arrangement of the existing machines has been made.
+
+IDEAL ARRANGEMENT.--As to what this best arrangement may be, guidance can
+be obtained from the results of experience here given. It must be premised
+that the output of any factory preparing fine pale crepe is limited by the
+output of the smooth finishing rolls. Broadly, it will be recognised that
+if there is any excess of capacity in a battery it should be found in the
+smooth-roll machines. This sufficiency, or excess of capacity, may
+sometimes be attained by an alteration in the gearing of the drive of the
+rolls from the back-shaft, or by an addition to the number of machines. In
+the former case, there are practicable limits of speed, beyond which the
+second alternative measure must be adopted.
+
+SPEED.--The usual speed at which the back-shaft travels ranges from 60 to
+70 revolutions per minute. Taking first the macerating machines, the
+intermediate gearing between the shaft and the rolls should give a driving
+speed of about 20 revolutions per minute on the faster-travelling roll.
+This is equivalent, with a 15-inch diameter roll, to a peripheral speed of
+about 60 to 65 feet per minute.
+
+The intermediate and smooth rolls can be arranged to travel more quickly,
+but the maximum comfortable speed for proper feeding and control appears to
+be about 25 revolutions per minute on even-speed rolls. In view of the fact
+that the rubber at each successive machine becomes longer and thinner, it
+will be seen that a smooth-roll machine could not cope with the output of a
+macerator in the same period of time. If, therefore, the macerator is fully
+occupied for the greater part of the time, an additional smooth-roll
+machine must be installed, even though the existing one has been "speeded
+up" to practicable limits.
+
+For the information of the uninitiated it might be explained that in the
+macerating and intermediate machines the cog-wheels driving the two rolls
+are of different sizes (_i.e._, differentially geared), as opposed to the
+smooth rolls on which the cog-wheels are usually of the same size (_i.e._,
+even speed). The idea in the one case is to exert a "working" influence
+upon the rubber while it is being washed by the stream of water coming from
+above; in the smooth rolls a squeezing action only is effected.
+
+To give an idea of the ratio of the speeds of the rolls in each machine in
+a typical working battery, the following particulars may be noted:
+
+GEAR RATIOS.--
+
+               _Machine._            _Differential Ratio._
+
+  1. Macerator                              32-17
+  2. Intermediate (coarse grooved)          32-17
+  3.      "       (fine grooved)            30-19
+  4. Smooth (uneven speed)                  30-19
+  5.  "     (finishing)                     25-24
+  6.  "     ( "  )                          25-24
+
+It will be seen that the so-called "even-speed" smooth rolls run at
+approximately the same rate.
+
+It is advised that in all cases the gear wheels should be cut helically.
+Those who have experience of the noise of some batteries after they are
+slightly worn will appreciate such a remark.
+
+GROOVING OF ROLLS.--Concerning the choice of grooving, there is divergence
+of opinion, some managers preferring one type, which others reject in
+favour of another type. Provided any particular type can be shown to be as
+effective as required, no necessity for laying down hard-and-fast rules
+seems to exist.
+
+The following particulars serve to describe a battery well known to the
+writers, and accustomed to produce the finest quality of thin pale crepe
+and lower grades:
+
+  -----------------+-----------------------------------+-------------
+                   |                                   |_No. of Times
+     _Machine._    |         _Grooving._               |Rubber passes
+                   |                                   |  through._
+  -----------------+-----------------------------------+-------------
+  1. Macerator     | Deep horizontal grooves;          |
+                   | square-cut, 5/16 inch x 5/16 inch |
+                   | x 5/8 inch spaces                 |      3
+  2. Intermediate  | Horizontal grooves; 3/16 inch     |
+                   | x 3/16 inch x 3/8 inch spaces     |      2
+  3.     "         | Fine spiral grooves; 1/8 inch     |
+                   | x 1/8 inch x 1/4 inch spaces      |      2
+  4. Geared smooth | Nil                               |      1
+  5. "Even" smooth |  "                                |      1
+  6.    "     "    |  "                                |      1
+  -----------------+-----------------------------------+-------------
+                   |        Total                      |   10 times
+  -----------------+-----------------------------------+-------------
+
+The actual rate of output of this installation is the capacity of the last
+smooth machine. This is about 180 lbs. per hour, while the output of the
+macerator is approximately double this amount. Thus the macerator only
+works for about half the time. This applies also to the two intermediate
+machines. After a study of the preliminary remarks, it would not be
+difficult to suggest methods for improving the condition of affairs. It
+would appear that, in order to obtain a uniform rate of working in such a
+battery, the relative peripheral speeds of the several machines should
+be--(1), (2), and (3) 100; (4) 150; (5) and (6) 200. The remarks on the
+practical limits of speed should be borne in mind. In this case the smooth
+rolls travelled at 23 revolutions per minute.
+
+As already stated, it is not intended to lay down definitely that, _e.g._,
+horizontal grooving alone should be cut on macerating rolls. Some estates
+employ with satisfaction a deep square-cut spiral 1/4 inch by 1/4 inch by
+1/4 inch or 1/2 inch spacing; others use a large diamond pattern. Similarly
+various types of grooving are cut in the intermediate rolls.
+
+[Illustration: A BATTERY OF MACHINES.
+
+On the left, light marking rolls for sheet rubber; on the right, heavy
+machines for crepe preparation. In the middle background, "scrap-washing"
+machines outside the main building.]
+
+It has been remarked in the chapter dealing with crepe preparation that
+much depends upon the condition of the coagulum. There is no necessity, or
+desirability, for having a standard higher than 2 lbs. dry rubber per
+gallon, and it has been argued that it would be better to select a standard
+of 1-1/2 lbs. The tougher the coagulum, the more the power required, and
+the slower the rate of output of the leading machines.
+
+In ordering machines for crepe-making, only large rolls should be
+considered--_e.g._, rolls having a diameter of 12 inches to 18 inches and
+from 15 inches to 18 inches face.
+
+ROLLS RUNNING HOT OR "FREE."--If the rolls are found to become hot, work on
+that machine should be stopped, and an examination made, otherwise there
+is the possibility of the crepe becoming sticky and "tacky" when dry.
+
+Although comparatively cold water may be flowing upon the rubber and the
+rolls, little alleviation may be noticed, inasmuch as the source of heat
+lies generally at the bearing ends of the rolls. This may be tested by
+placing the hand on the top of the "standard" of the machine. The
+development of the heat may be due to lack of lubrication, worn bearings,
+or sometimes faulty setting-up of the machines.
+
+Allusion has been made to the necessity for avoiding the running "free" of
+rolls--_i.e._, in the absence of rubber. The grinding of the rolls, when
+working close together, produces a fine powder, which causes a more or less
+pronounced deposit on pale crepe. When the rolls have been in action for
+some time and become slightly worn, this deposit may be confined only to
+the edges of the rubber.
+
+SHEETING MACHINES.--The foregoing paragraphs have dealt entirely with
+machines for crepe preparation. Concerning machines for use in
+sheet-making, the ground has been mainly covered in Chapter IX.
+
+Where both crepe and sheet are made, it is permissible and advantageous to
+use the heavy smooth rolls for the rolling of the sheets, and it is only
+necessary to instal one or two light machines for placing a pattern on the
+rubber.
+
+Where a heavy battery does not exist, light machines with smooth rolls may
+be employed satisfactorily. Even engine-power is not necessary for the
+preparation of excellent sheets, but the output is limited where hand-power
+only is employed. Estates are known on which upwards of 1,000 lbs of sheet
+rubber are made daily with hand-power machinery in one station. Beyond this
+figure, it is deemed advisable to instal a small engine, say of 7-9
+horse-power. This is ample to drive a battery of three smooth-roll machines
+and two markers, and yet have sufficient reserve to actuate a small pump
+for the water supply.
+
+LUBRICATION OF MACHINES.--It must always appear to those inexperienced in
+engineering matters that existing methods for lubricating rubber machinery
+are distinctly crude, when one considers the delicacy of the material to
+be prepared. Many existing machines are still lubricated with oil, which
+has to be administered in generous quantities. Generally, such machines
+have been so designed that the excess of oil may find an easy passage into
+the tray which receives the rubber. If not, it drops just outside the tray
+to the floor, and is washed away in great gouts. Even where grease-cap
+lubricators are fitted it is common to find that the excess can often be
+transferred from the bearings to the trays and so to the rubber. One would
+have expected from the attention which is being given to machinery for
+rubber estates that some improvement in lubrication methods would have been
+devised.
+
+It is probable, however, that a great deal of the disabilities attaching to
+present methods of lubrication might be obviated if closer attention were
+given to the actual operation of the lubricators. Coolies should not be
+allowed to handle them, and the responsibility should be placed upon a
+foreman or the engine-driver.
+
+TRAYS.--The most unsuitable and damage-causing part of the vast majority of
+machines, without doubt, is the tray. On nearly all machines the tray is
+wider than the effective portion of the rolls, so that any excess of
+lubricant may drop into it. On others, not only is the tray wider than the
+rolls, but its edge either is in contact with the shaft of a roll or just a
+small distance away. The edge of the tray is thus favourably situated for
+acting as a "wipe," and the lubricant is transferred to the inside of the
+tray. Considering that the effective portion of rolls is about two-thirds
+of their length, it must be unnecessary to have trays wider than the length
+of the rolls. For the preparation of fine crepe trays are quite
+superfluous, and their place can be taken by a narrow piece of board if
+required. If the bed of the machines has been covered with glazed tiles,
+even a piece of board is not necessary. Where trays have been removed from
+the fine-crepe rolls on a number of estates, a marked decrease in the
+number of spoiled pieces of rubber has resulted.
+
+It must be recorded that the foregoing paragraph appeared in our 1913
+publication. After a lapse of over seven years, the remarks remain as true
+as when originally written. One of us is continually meeting with cases in
+which the defects are plainly attributable to the cause indicated above,
+and the fault often lies with the management of estates. On most machines
+the trays are not fixtures, and could be removed if desired.
+
+ARRANGEMENT OF MACHINES.--In considering the future arrangement of
+machines, the first care should be to see that machines and windows are to
+be found together.[16] Of all the factory operations, rolling of rubber
+should be given the maximum light. At the same time it would not be
+advisable always to choose a southern aspect, unless outside shades were
+supplied. The best position for setting up machines, therefore, is along a
+wall having a number of windows. This is extremely convenient also from the
+view of power transmission, and gives the maximum free floor space to the
+factory. In setting up machines, foresight must be displayed, otherwise one
+may find, when future extensions are made, that the extra machines may
+obstruct an entry or exit.
+
+[16] Windows imply the existence of walls. Such is the conventional design
+of factories. It may be pointed out that walls are not necessary. The roof
+may be supported on pillars between which expanded metal of large size may
+be placed. This fulfils all requirements and gives the maximum of light and
+air. Many new factories have been erected to such a design.
+
+For the actual erection of machines, no labour should be accepted without
+European supervision. At present there are machines which are practically
+useless owing to faulty workmanship, and on many machines bearings run hot
+for no apparent or explicable reason. Whether the fault lies with the
+turning of the rolls or the setting of the machine cannot be decided; but
+at any rate too much care cannot be expended on the supervision of setting
+up machines.
+
+There is no reason why everything in a factory should not be made as easy
+to clean as possible. For this desirable condition all machines should have
+the beds faced with tiles. A word of caution should be given against using
+marble slabs under the machines, as they would be eroded in time by the
+slight amount of acid washed out of the rubber. There would be no such
+objection against the use of white glazed tiles, if they are well set.
+
+ACCESS TO BACK OF MACHINE.--In a few factories it has been noticed that the
+drainage of water from the machines runs to the front of them. This means
+that the coolies are put to unnecessary inconvenience and discomfort, and
+they often suffer from sore feet. All water should drain to the back of the
+machines. The necessity for seeing that these drains are kept clear might
+then induce those in charge to examine the back of the machines. It is
+often the case that, while the front of the rolls and tray are kept clean,
+little attempt is made to cleanse those parts which are not visible or
+accessible from the front. There should be no need to point out that any
+labour expended in such "front-window" work is rendered useless by the
+contamination from accumulations of old rubber and grease at the back of
+the machines. In the course of visiting factories one of us has many times
+seen great surprise exhibited by the manager or assistants on being shown
+the state of affairs at the back of the machines. There should have been no
+occasion for such surprise, for the back of the machines is quite as
+accessible to them as to the visitor.
+
+In conclusion it might be said that the manager needing advice as to the
+best machines cannot go far wrong in purchasing any of the better-known
+makes, such as Shaw's, Bridge's, Robinson's, Bertram's, Walker's, Carter's,
+Iddon's, etc. This list does not include local manufacturers such as the
+"United Engineers." It must not be imagined that their machines are not
+recommended. As a matter of fact, their machines compare well with those
+made at Home. It would be well to judge in the final decision upon--
+
+     1. Cost.
+
+     2. The experience of those already using the machines.
+
+     3. Simplicity of parts.
+
+     4. Lubrication system.
+
+     5. Mode of adjusting rolls.
+
+     6. Fitting of trays.
+
+ENGINES.--It is not intended here to discuss particular makes of engines,
+or even to attempt to lay down definite statements with regard to the type
+of engine. Without a full knowledge of local circumstances, it is not
+possible to recommend whether the engine shall be oil-driven, gas-driven,
+or steam-driven.
+
+Assuming a copious supply of very cheap timber, there could be no objection
+to the employment of a steam-engine; but for most estates such a choice is
+out of the question.
+
+Again, in deciding between oil and gas, local economic factors must be
+considered. Suction-gas plants are now made, in which a wonderful variety
+of refuse can be consumed in the production of gas, whereas ordinarily
+estates are restricted to the use of either charcoal or anthracite coal.
+Both oil and gas driven engines are eminently suitable for the purpose of a
+rubber factory, and the results obtained on different estates with either
+are often discussed in favour of one or the other. The selection ultimately
+narrows itself down to one of cost of running, in which availability of
+supplies becomes an essential feature.
+
+POWER.--No matter what type is selected, there should be made an ample
+allowance for margin of power. The general experience of estates has been
+that when the first portion of the estate comes into bearing, there is a
+desire to avoid great outlay, which should really have been secured in the
+original capital. The result has been that as later the estate expands, the
+original power unit is found to be inadequate, and a larger engine has to
+be purchased. In a short while the original engine is found to be
+unsuitable even as a "stand-by," inasmuch as it is incapable of doing more
+than a portion of the work required. This means eventually that another
+large engine is required. Had sufficient margin of power been allowed
+originally, only two engines would have been bought, as against the three
+indicated above. Without going into finer details, it is usual to allow a
+rate of 10 horse-power per heavy machine used for crepe preparation. In
+actual practice, when a battery is working under full load, the power
+demanded is about 6 horse-power per machine. Thus a 50 horse-power engine
+running six machines and a scrap-washer is really running with only a small
+margin of power, and if large pieces of hard coagulum are placed in the
+washer or the macerator there may be a sudden stoppage. Assuming an average
+estate commences with only three machines for crepe-making, on an expanding
+programme, allowance of power should be made for six machines and a
+scrap-washer, if the purchase of larger power units is to be avoided
+later.
+
+
+
+
+CHAPTER XIV
+
+_FACTORIES_
+
+
+GENERAL CONSTRUCTION.--On the question of general construction there is
+little to be said, except that buildings are now being properly designed in
+more permanent form than were some of the earlier buildings. On the whole
+there is little fault to be found with factories in general, except in so
+far as the output has outgrown the accommodation.
+
+Most factories are now erected in iron, but there are a few which are built
+of bricks. It should be premised that a factory in which rubber is to be
+prepared should be as light and airy as possible. In this respect quite a
+number of the older factories are lacking, and they seem to have been
+designed to exclude as much air and light as possible. Under these
+circumstances, the building is always dark, there is always an air of
+dampness, dirt may accumulate, and there is usually a bad smell. Rubber
+prepared under these conditions is always liable to be below the high
+standard which should be attained, and the general tone of the factory is
+depressing.
+
+PLENTY OF LIGHT.--The old idea that light must be excluded is now known to
+be erroneous; so that in designing a factory, provision should be made for
+ample light and air. It should not be forgotten that in tropical climates,
+iron buildings may become uncomfortably hot, as most of our older factories
+are. Usually it will be found that the ventilation is imperfect. There is a
+lack of window space, and the roof is imperfectly ventilated. The ridge of
+the roof should be opened up by means of a "jack-roof," so that the warm
+air rising naturally may escape at the highest point of the building. These
+are defects which should be remedied in old buildings.
+
+As a rule no rubber remains in the factory at night-time, except in the
+form of coagulum, the loss of any of which would be noted with ease. The
+conventional idea of enclosing the factory with walls of galvanised
+sheeting, wood, or brick, is not strictly necessary. In modern buildings
+these walls are replaced by large-mesh expanded metal, thus making the
+machine-room perfectly light and plentifully ventilated. Under such
+conditions, dirt cannot accumulate unseen, and the general tone of the work
+is raised.
+
+THE FLOOR.--The floor should be of thick concrete, and have a good surface
+layer of cement. Preparations are now advertised for which claims are made
+that their employment renders the surface of such floors waterproof and
+dustproof. If these claims can be substantiated when the use is applied to
+the floors of rubber factories, the employment of a preparation of this
+nature should result in a considerable saving of expense and trouble.
+Preferably the floor should not be flat, but should slope slightly from the
+longitudinal middle of the building to the sides on either hand. If the
+floor is level it usually results in accumulation of water, the cement
+breaks in patches, and the factory always appears to be dirty.
+
+POSITION OF MACHINES.--All machines should be arranged adjacent to and
+parallel with one of the long sides of the building, and should be raised
+about 6 inches above the floor, so that water may escape easily. Tanks for
+the reception of latex, scrap rubber, etc., should be placed along the
+opposite wall to the machines, and the intermediate length of the building
+should be entirely free from fixtures. It was not uncommon in older
+factories to find the engine situated in the middle of the floor, so that
+what with the space occupied by the engine, and the space rendered
+unavailable by the belt-drive, the real accommodation of the factory was
+sadly diminished. In no modern factory should the engines be brought into
+the main room. They should always be accommodated in a special compartment,
+situated outside the wall, along the inside of which machines are placed.
+In this way considerable floor space is left available, and the machines
+may be worked by direct drive. Not only so; but if a suction-gas plant is
+worked, there can then be no excuse for particles of coal or charcoal dust
+being found in the factory.
+
+POSITION OF ENGINES.--It scarcely need be pointed out that if the engines
+are placed outside the wall which is opposite the machines, a long
+belt-drive would be necessitated, and that the presence of the belt would
+prevent the use of end doors. It is presumed in these arguments that two
+engines are to be installed. One can hardly imagine a modern factory in
+full working being equipped with only one engine, which might possibly have
+an excess of power necessary to drive all the machines. In the case of
+breakdown, which sometimes happens in the best supervised factories, it
+would be small consolation to know that this excess of power was present
+theoretically.
+
+HOW MANY STOREYS.--There can be no doubt that, taking all things into
+consideration, the best type of factory is that consisting only of one
+floor. The factory should be quite separate from all other buildings, and
+if attempts are made to conserve ground space by putting a drying-room over
+the factory, much trouble will ensue, especially if pale crepes are to be
+made. In the first place, the factory is made very much darker, and hence
+more difficult to keep clean; secondly, the ventilation of the factory is
+seriously interfered with; and thirdly, it is manifestly prejudicing the
+drying of rubber to place it directly over a room which is always more or
+less awash with water. At night such a building would reek with a
+moisture-laden atmosphere, and little drying could be expected to take
+place in that interval. From actual experience it has been shown that
+rubber hung to dry in such a room, situated over a damp factory, is very
+liable to attacks of "spot" diseases, since the presence of perpetual
+moisture is favourable to the development of these diseases. If a
+double-storey building has to be worked, it will be readily seen that no
+first-grade rubber should be allowed to dry in it. The accommodation over
+the factory may be restricted to the purpose of receiving lower grade
+rubber which is not so liable to "spot" diseases, and possibly does not
+take so long to dry as first-grade rubbers of equal thickness. It is
+evident, therefore, that the erection of double-storey factories is false
+economy, as separate drying-houses have to be built eventually. This
+conclusion does not apply with the same force to factories worked in
+conjunction with smoke-houses for preparing sheet rubber, but,
+nevertheless, such a factory should not have another floor above the
+work-room.
+
+VERANDAHS.--One of the worst features in many factories is the necessity
+for coolies to bring latex into the factory. As already mentioned, the
+floors of factories are usually running with water (or should be), and it
+can be imagined that the passage to and fro of scores of coolies must bring
+in a great quantity of dirt. Not only so; the very presence of the coolies
+is a hindrance to the efficient working of the factory, and considerable
+floor-space and time are wasted.
+
+This feature in factory working is all the more annoying because the
+necessity for it could so easily be obviated. All that is necessary is the
+erection of a wide, open verandah outside the wall of the factory. Here all
+latex could be received and strained, scrap-rubbers could be received and
+passed through an opening into tanks placed in convenient position. Water
+could be laid on in this verandah so that coolies might wash their buckets,
+and the whole verandah might be enclosed only with expanded metal so as to
+avoid interference with the lighting of the factory. In this way it would
+be quite unnecessary for any field coolie to enter the factory proper, and
+this would facilitate cleanliness. Such an arrangement has been discussed
+by the writers many times during the last few years, but the number of
+estates which have made such provision is still in the minority, and the
+same slipshod and dirt-making procession of coolies continues to walk
+through the factories, and the same piles of bark-shavings and scrap-rubber
+continue to accumulate and ferment in a few instances.
+
+An indication of types of verandahs is given in Chapters VII. and IX. These
+are not intended to be representative of a universal design, but may be
+suggestive in the planning of others according to local conditions.
+
+SITUATION OF TANKS.--It will be noted that these verandahs are raised from
+the ground-level to a height of about 3 feet in order that latex may be
+gravitated, with a slight fall, into the coagulating tanks which are within
+the factory. There exists a real necessity for this practice, inasmuch as
+otherwise to obtain gravitation of latex (which is quicker and cheaper
+than handling) the coagulating tanks would have to be either placed on the
+floor or sunk beneath the level. The risk of contamination of latex or
+coagulum under such circumstances would be appreciable. Apart from this, it
+is advisable to have the coagulating tanks raised to a height of between 2
+and 3 feet, to secure the advantage of ease of working in the processes of
+coagulation and the handling of coagulum--a not inconsiderable factor.
+
+In some modern designs it is proposed to place the coagulating tanks in a
+separate building. This would seem to be an unnecessary refinement in a new
+building, if observance is given to the suggestions made in previous
+paragraphs.
+
+DESIGNS AND "LAY-OUT."--In a previous publication[17] comment was made upon
+grievous errors in designs prepared by those inexperienced in the
+requirements of the tropics. There is little ground now for complaint, and
+local engineering firms are fully capable of advising upon, and
+constructing, suitable buildings.
+
+[17] "Preparation of Plantation Rubber," Morgan, 1913.
+
+In considering the first installation of a factory and equipment one always
+has to weigh the question of prime cost against the probability of future
+expansion of crop. If it should be decided at first merely to cater for
+contemporary requirements, the fullest consideration should be given in
+discussing design of building and lay-out of machinery to the
+practicability of later extension. The site should be large enough for the
+eventual group of buildings, the building should be easily capable of
+extension with the least cost, and the same forethought should govern the
+lay-out of the machinery.
+
+DRAINS.--Lastly, there is the question of drains. Generally speaking, all
+factories are well provided with drains, and the only difficulty is that of
+getting an adequate fall for efficient drainage. But there is a certain
+amount of laxity exhibited in the matter of providing sieves in drains. To
+anyone acquainted with factory working, it must be apparent that quite a
+lot of small pieces of rubber are washed into the drains. This rubber
+should be collected at intervals during the day; but in many instances
+that collected is only a fraction of what escapes. Wherever possible the
+drainings of a factory should be carried as far as is practicable from the
+buildings by means of cement drains. Too often these are short, and lead
+into earthen drains. Even if no pieces of rubber are present, the serum
+from the coagulum is subject to decomposition, the effluvium from which is
+objectionable.
+
+WATER SUPPLY.--It is essential that a good supply of water should be
+available. This should be distributed by pipes all round the building, so
+that a hose may be used in every part for the thorough cleansing of the
+factory at intervals during the hours of working.
+
+Summing up, it might be said that a good factory, therefore, should have
+the following features:
+
+     1. Plenty of windows, or walls of expanded metal.
+
+     2. A jack-roof in the ridge, and hence a good system of ventilation.
+
+     3. Engines in compartments outside the walls of the factory.
+
+     4. Machines close to and parallel with the wall outside of which the
+     engines are placed.
+
+     5. Latex tanks and other fixtures along the wall opposite the
+     machines.
+
+     6. A long middle free space, at either end of which a large double
+     door should be placed in the end walls.
+
+     7. A good concrete and cement floor sloping slightly from the middle
+     towards each long wall.
+
+     8. An abundant water supply, and several lengths of hose.
+
+     9. The building should be of only one floor, and have ample head room.
+
+     10. There should be an outside, open verandah upon which latex may be
+     received, etc.; preferably outside the wall which is opposite to the
+     machines.
+
+     11. The system of drainage should be thorough, and the drains should
+     be adequately screened, so that all particles of rubber may be
+     collected.
+
+
+
+
+CHAPTER XV
+
+_OTHER BUILDINGS_
+
+
+DRYING-HOUSES FOR CREPE.--It has already been shown in the previous chapter
+that one type of drying-houses--viz., that over a factory--stands
+condemned, except for the drying of low-grade rubbers. Generally speaking,
+a great advance has been made in the design of crepe drying-houses during
+recent years, and it has been possible even to improve older ones so as to
+bring them into line with the more modern buildings. Houses for drying
+crepe rubber may be of one floor, two floors, or even three floors.
+Doubtless those built with three floors were designed with a view to
+economising the available site for factory buildings, and as long as the
+ventilation is good there can be no very great objection to them. It might
+be pointed out, however, that even with the best of ventilation the air
+passing successively through three layers of rubber must be fairly
+saturated with moisture by the time it leaves the building. The effect of
+this upon the rate of drying in the uppermost chamber will not be so marked
+as it will be in the middle floor, as the temperature of the top floor must
+be many degrees higher than that of the other two rooms. It would be
+expected, therefore, that the rate of drying in the middle storey would be
+slower than that in either of the other two.
+
+In houses of two floors this objection would not have to be met, and
+drying-houses of this type are successful and common.
+
+HOW MANY STOREYS?--Again nothing could be urged against a building of two
+or three storeys in which the ground floor was occupied as a packing-room,
+except that, by negligence in not allowing wet crepe a preliminary dripping
+period, water might fall upon the packed rubber below.
+
+As a matter of experience, such a house is, taking all into consideration,
+the cheapest and most suitable type for any estate with an increase in
+output. Even at the outset there should be a separate room in which sorting
+and packing is undertaken. This is conveniently the lower room of a
+drying-house. The only stipulation to be made for a house with two storeys
+is that the floor of the upper room should be of an open pattern, so that
+the air may circulate right through the building. This is usually and very
+successfully attained by laying down wide slats of wood, with spaces of an
+inch or more between them. It is not advisable to have spaces wider than
+1-1/2 inches, otherwise there is a certain amount of danger to the limbs of
+individuals who have to work or supervise in the building. In any case, it
+is very convenient to have pathways of planks running the whole length of
+the floor, so that the supervision is made more convenient. If this is
+done, there can be no objection to the custom of suspending the rubber of a
+lower chamber from the slats of the floor of the upper room. At present, in
+some drying-houses, this means of suspension is used, but no planks are
+laid down, and it becomes necessary to walk over the drying rubber. This is
+a detail, but it is one which does not make for the improvement of rubber,
+and the expenditure of a small sum would be sufficient to rectify the
+matter.
+
+From every point of view, it would be desirable to have the floor of the
+packing-shed (or the packing-room in a combined house) raised from the
+ground, to a height of, say, 3 feet; or the height of a bullock-cart or
+motor-lorry. Not only is ventilation improved, but there would be a great
+saving in labour. Packed cases could be wheeled directly on a level with
+the cart or lorry.
+
+A great many estates favour drying-houses of one storey. These are
+eminently suitable, provided that the site is suitable, and that the
+relative dimensions of the house are favourable to efficient ventilation.
+It is a common mistake to find buildings of which the breadth is out of
+proportion to the height. Obviously, if the height is not considerably in
+excess of the breadth, ventilation will be defective. For a single-storey
+drying-house, the maximum height should bear the ratio to the breadth of
+3:2, and in a house of this type specially long pieces of crepe can be
+utilised. Naturally, in a house of two storeys, this factor is not likely
+to be neglected, and if the lower room is used for packing purposes the
+rate of drying should be rapid. Again, when a single-storey building is
+contemplated, it is well to make strict examination of local conditions. If
+the site is low-lying and surrounded by trees it will be clear that tall
+buildings are required, and that a house of more than one floor is to be
+preferred. Considerations of this nature would have prevented the erection
+of some dry-sheds which do not give a satisfactory rate of drying.
+
+VENTILATION.--No matter how many floors there may be in a drying-house, the
+greatest attention should be given to the question of ventilation. It is an
+elementary point in the study of ventilation problems that the best system
+of natural ventilation is obtained by admitting cool air near or through
+the floor and providing an exit for the warmer air at the highest point in
+the building. It is not often that such a rule is infringed in the
+ventilation of rubber drying-houses, but several of the older buildings
+erred in this respect. In a good modern house there is a space (about 2
+feet in height) all round the base of the walls merely closed with expanded
+metal; this admits cool air. An exit for warm air is provided in the ridge
+of the roof by either ventilation chimneys or by a jack-roof. The latter is
+preferable, as it provides for a more free and uniform escape.
+
+In some drying-houses, besides the ridge openings, the space along the
+eaves is left open. This would seem to be undesirable, as it provides for
+the entrance of outer air, which might combat the ascending warm air and so
+interfere with the natural upward currents. Provided that a jack-roof or
+other suitable openings have been installed, there is, therefore, no
+necessity for the existence of open spaces at the eaves, and they probably
+do more harm than good.
+
+In the tropics, on days of sunshine, there must always be an upward current
+of air in well-designed houses. Temperatures of 105 deg. F. are easily recorded
+in the ridge space of a building, while the temperature in the lower part
+of the house may be at least 15 deg. F. lower. On the floor of an upper room a
+temperature of 90 deg. F. is commonly noted, and in buildings with three
+storeys the usual day temperature of the top room is about or over 100 deg. F.
+Even, therefore, when there is no trace of a breeze, there must be a
+displacement of air in an upward direction, though it may not be detected
+without tests being applied.
+
+It is often asked whether a temperature of 100 deg. F., such as is obtained in
+the upper room, is calculated to injure the quality of the rubber. There
+need be no fear on this ground; the experience of many estates goes to show
+not only that no harm results, but also that the drying of the rubber is
+expedited. There would seem to be no reason why crepe rubber should not be
+dried at a temperature of 100 deg. F. It must be understood, however, that
+higher temperatures for crepe rubber are not recommended, as it has been
+proved that the rubber is affected. The fact becomes obvious with continued
+treatment at temperatures much above 100 deg. F., for the rubber stretches and
+breaks across the support.
+
+WINDOWS.--Concerning the subject of window space in a drying-house, there
+has been much discussion at various times. Years ago it was common to find
+windows widely open with the sunshine streaming in. Naturally, tackiness
+developed in some of the rubber, and care was then taken to keep the
+windows closed. Thus the rooms were darkened and air excluded. There
+followed a period in which windows were fitted with ruby-coloured glass to
+keep out the actinic rays of the sun, which were responsible for tackiness,
+and excess of light, which was supposed to be responsible for the rapid
+oxidation of rubber. Unless special precautions were observed in the
+processes of coagulation and preparation, it was not proved that the
+exclusion of light prevented or lessened the natural oxidation of crepe
+rubber. Since the introduction of sodium bisulphite for the prevention of
+oxidation, there has been no cause to worry as to the possible effect of
+light, as no perceptible darkening of the rubber takes place. It follows,
+therefore, that no trouble need be taken to exclude light, although the
+necessity for excluding direct sunshine still exists. Windows may be left
+open as long as the sun does not reach them. This can usually be arranged
+in a drying-house by manipulating the windows at intervals during the day,
+so that those in the shady side of a building are always open, while those
+on the sunny side are always closed. If it is thought that this
+manipulation cannot be entrusted with success to the store coolies, the
+case may be met by having all windows constructed on the louvre pattern, so
+that, although the windows are closed all day, air and light are not
+excluded. Should it be desired to retain the existing type of windows,
+which open outwards, and to keep them open all day, a simple arrangement of
+ruby-coloured cloth on an outstanding wooden frame may be placed within the
+walls of the building, or the shutters of the windows may be hinged at the
+top to open outwards. Unless there is a pronounced breeze, or it is
+required to examine the rubber closely, there is no necessity to have
+windows open, except in the case of a house in which the bottom floor is
+used as a packing-room. The windows of this chamber may remain open during
+the day, to advantage in sorting and packing, and also to the proper
+ventilation of the building. Thus the direct rays of the sun are rendered
+harmless, while air and light are allowed to enter.
+
+HOT-AIR DRYING-HOUSES.--Mention has already been made of the existence of a
+system of drying in which hot air is forced into a drying-house by means of
+a powerful fan. Provided that the temperature of the hot air could be so
+regulated as not to exceed 100 deg. F., there would be merit in the system.
+Such matter of regulation could be solved by having a duct in the main air
+passage, through which cool air could be admitted in such proportion as to
+modify the temperature of the hot air. As the process is worked at present,
+the temperature attained is often well above 100 deg. F., and there is a danger
+of thin crepe placed in this house over-night being found upon the floor in
+the morning. Unless the crepe is prepared thick and cut into fairly short
+lengths, it will not bear its own weight at higher temperatures; and if it
+is made thick, drying is impracticably prolonged. It is probable that, with
+a temperature of 100 deg. F., and a steady current of air, average thin crepe
+would dry in such a drying-house within six or seven days. This would be
+an improvement upon the usual rate of drying in most factories, although
+several ordinary drying-houses are known in which thin crepe will dry
+naturally in that period.
+
+SMOKE-HOUSES.--No discussion of theoretical considerations regarding the
+process of smoke-curing will be attempted here. We are concerned only with
+the necessity for supplying a demand for smoke-cured sheet rubber. Broadly,
+the process is akin to the smoke-curing of herrings, and the objects are
+much the same--viz., (1) drying, (2) preservation--except that while
+herrings are only dried partially, rubber should be dried perfectly.
+
+On a small scale a primitive smoke-house could be built easily and cheaply,
+and such a building might be fully as efficacious as the most elaborate and
+expensive installation. In the early days of estates it was not uncommon to
+see temporary smoke-houses constructed of wood, and roofed with "attaps"
+(palm leaves). Some of the best rubber in the market has come from wooden
+buildings, but naturally the risk of destruction by fire is considerable.
+
+For imperative reasons it may be sometimes found necessary to smoke rubber
+when the only available building is a single-storey one. As a temporary
+measure, the building may be converted into a smoke-house by placing the
+fires in pits sunk deeply into the ground, and effectively screened above
+by iron baffle plates. But it is not advisable that smoking be continued in
+such a single-storey building, as the best effects are not obtained, and
+the risk of fire is far too great.
+
+USUAL TYPES.--At first sight it would appear that the best type of
+smoke-house would be one consisting of a tall building, covering a
+comparatively small superficial area, and having a number of superimposed
+chambers in which the rubber could be hung to dry. In practice there are
+several solid objections which limit the height and the number of floors.
+Chief among these is the question of temperature. If smoke-curing is to be
+effective, a certain temperature must be attained and maintained. To obtain
+such results in a house of excessive height would be difficult, if not
+impossible, under normal conditions. It would be found that the chamber
+immediately above the furnace-room would be overheated if the temperature
+in the upper rooms was within the desired range, etc.
+
+Until recent years smoke-houses could be classed as belonging to one of two
+types:
+
+     (1) Those having external furnaces.
+
+     (2) Those having internal furnaces.
+
+The number of the former existing at the present time must be very small,
+as it has been shown that the arrangement of the furnace outside the house
+is unsatisfactory in comparison with the other type of house. In discussing
+the question of smoke-houses, therefore, it will be understood that the
+standard type accepted is that having an internal furnace. In its original
+form it was known as a "Kent" drier, and consisted of a tall two-storey
+wooden building. The walls of the lower chamber had the form of an inverted
+and truncated pyramid. By this arrangement it was possible to obtain from a
+comparatively small fire sufficient smoke and heat to cure the product
+placed in the room above. This is the principle upon which many
+smoke-houses in Malaya are designed. On a very large scale it is not
+claimed that the sloping sides of the lower chamber lead to economy in the
+number of fires, but merely divert the smoke in an upward direction. It is
+acknowledged that vertical lower walls are quite effective, and it is an
+easier matter to fit in doors.
+
+It may be noted that the usual type of smoke-house now in general use
+consists of a building of two storeys, in the lower of which are situated
+the furnaces, while rubber is hung on racks in the upper room. Sometimes
+there may be a third storey, also used as a drying (curing) chamber. As a
+rule the drying-room is one long unit, as also is the furnace chamber; but
+in some cases they are subdivided by vertical partitions into smaller
+chambers, for ease of working and better control. This applies with some
+force in the case of very long houses standing in an open space. It is
+sometimes found in such cases that at certain seasons the prevailing winds
+have the effect of making drying and curing uneven in parts of the
+building.
+
+With these exceptions, the ordinary type of smoke-house functions very
+efficiently, and is capable of drying average sheet (from standardised
+latex) in a period ranging from seven to eleven days. Should the building
+not be capable of such performance, in spite of the strict observance of
+all rules laid down for the processes of preparation, then there is some
+defect in ventilation or in the distribution of heat.
+
+GENERAL VENTILATION.--The ordinary rules of ventilation in drying-houses
+apply equally to a smoke-house. There should be a slow current of air and
+smoke from the lowest point to the highest point in the building.
+
+In spite of all that has been written on this subject, it is by no means
+uncommon to encounter the idea that a smoke-house should be perfectly
+closed in order to get good results. As to what must become of the (say) 25
+per cent. of moisture which the rubber contains there is no knowledge. In
+dozens of cases, when complaints regarding slowness of drying have been
+investigated, it has been necessary to point out the need for providing a
+rational system of ventilation.
+
+Naturally only a slow current of air and smoke is required. The creation of
+an appreciable draught would have the effect of increasing the fuel
+consumption of the furnaces, raising dust from the ash, and of causing a
+temperature higher than that which is known to be desirable. It will be
+clear, therefore, that if there are to be any openings at the base of the
+walls they should be small in area, and should have some device by means of
+which the current of air can be efficiently regulated. In the usual case
+the construction of the building is not calculated to render it air-tight,
+and the necessity for providing special air inlets does not arise.
+
+WINDOWS.--Windows are not strictly necessary, and are only intended to be
+of service during the time in which coolies are at work within the
+building. The operations of examining rubber, turning sheets, removing dry
+rubber, cleaning racks and floors, and putting wet rubber into position,
+usually occupy some hours daily. During this interval the windows should be
+widely opened if the weather is favourable, and should remain so until the
+fires have been lighted. It should not be forgotten that during the heat
+of the day quite an appreciable degree of drying is possible. Advantage can
+be taken of this; but there is no necessity to extend the interval unduly,
+and it is of greater advantage to proceed with smoke-curing when the work
+in the drying-chambers has ceased.
+
+RACKS OF SUPPORTS.--Still referring to the usual type of smoke-house, it
+may be remarked that in the upper room bays of racks run at right angles to
+a central passage down the length of the building. Narrower passages run
+between the bays of the racks to facilitate ease in handling and
+inspection. The wooden supports may be placed about 3 inches apart
+horizontally, and 15 or 18 inches apart vertically. A full bay of racks
+should contain nine or more lines of support in each of the planes which
+are 15 or 18 inches apart vertically. The number of these planes is
+governed only by the height of the room, measured from the floor to eaves.
+The supports should be of smooth timber, and need not exceed 1-1/2 inches
+square in section.
+
+It is usual and advisable to smooth off the rectangular edges of the
+supports or bars, to avoid the incidence of splinters of wood adhering to
+the rubber. The bars should not be fixtures, but may either be accommodated
+in slots, or may rest _between_ two nails, so that it is possible to give
+them a rotary motion by turning the projecting ends. This practice is
+followed in smoke-houses, the idea being to move the drying sheets slightly
+each day, with a view to the prevention of a pronounced mark across the
+sheets.
+
+Care should be taken to see that the vacant racks are thoroughly cleaned
+before fresh rubber is placed upon them, otherwise a distinct dirty mark is
+caused across the middle of the sheet. This mark usually cannot be removed,
+even by scrubbing with water. Where this mark occurs regularly in all
+sheets, attention should be turned to the openings beneath the bays of
+racks, if open fire furnaces are employed. It will generally be found that
+gauze of too wide mesh has been fitted. This should be removed or covered
+with a finer gauze.
+
+A more effective way of dealing with the trouble, provided other
+precautions have been taken, is to have plenty of spare wooden bars. It
+should be a rule stringently enforced that, as soon as racks are emptied,
+the bars should be removed to the factory to be cleansed thoroughly. A
+spare set should enter the smoke-house with each batch of fresh rubber. The
+actual number of spare sets required could be limited to a two days'
+supply, and the extra cost would be recouped easily.
+
+FLOOR OF DRYING-CHAMBER.--The floor of the chamber is usually of planks,
+except that the space under each bay of racks should be filled with
+expanded metal. With the use of wood fires there is always a large amount
+of light ash formed, which may find its way into the upper chamber. To
+counteract this, screens of fine mesh gauze are laid over the expanded
+metal. This gauze may be fitted into a movable wooden frame, so that when
+it becomes necessary to clean it the whole may be removed.
+
+The difficulty is that with furnaces of the "open-fire" type the rise of
+dust is so great that the gauze screens soon become clogged, especially as
+the slight tarry matter in the smoke condenses on the gauze, causing the
+dust to adhere. With the better types of furnaces, the employment of gauze
+screens is not necessary, as there should be very little rise of dust. It
+is sufficient to use only expanded metal, to prevent any displaced pieces
+of rubber falling into the furnace chamber.
+
+FURNACES GENERALLY.--The crudest and dirtiest method of fuel consumption in
+the preparation of smoked-sheet rubber is that of making a fire on the
+ground. This is still a common practice, and should be condemned as being
+both wasteful and harmful. Under prevailing conditions coolies will, in
+spite of instructions, heap up a pile of logs in order to save themselves
+the trouble of stoking the fire in small quantity and at regular intervals.
+A small supply of water is kept at hand with which to quench the fire
+somewhat if it threatens to cause trouble. Naturally a large quantity of
+fine ash is thus thrown up, and the rubber above receives the deposit. If
+the coolie does not happen to be sufficiently awake, of course a house
+burns occasionally.
+
+From this primitive type of furnace, others have been evolved. These
+usually take the form of more or less shallow trucks, the majority of
+which are similar in principle to the fire on the ground, except that the
+container can be withdrawn from the house for the purpose of removing the
+ash. Sometimes they are even more objectionable than the ground fire,
+inasmuch as, being raised above the ground level, an under-draught through
+fire-bars is caused, and consumption of fuel is so much the more rapid.
+
+PITS.--It is clear that large fires are not desirable, and that combustion
+should be slow, provided that the necessary temperature can be maintained.
+The lines along which the development of furnaces needed to extend are
+therefore plain. The simplest device adopted was the digging of pits in the
+ground. Sometimes these pits received the addition of an iron truncated
+cone which was movable. Naturally the combustion was slow, but sufficient
+heat was obtained if the pits were large enough or in sufficient number. An
+objection was that the ash had to be cleared _in situ_, and in the process
+the earthen pits gradually increased in size. In all cases it was necessary
+to suspend an iron baffle-plate above the furnaces to distribute smoke and
+arrest any sparks.
+
+"POT" FURNACES.--The next development was the employment of "pot-furnaces."
+These consist of iron drums, sometimes merely resting on the ground, and
+sometimes mounted on trucks for easy withdrawal. These drums radiate
+sufficient heat if present in sufficient numbers, and the fuel consumption
+is low. They are usually manipulated by starting a fire in the bottom and
+packing in logs cut to the necessary length. Some have no lids, while
+others are fitted with perforated caps.
+
+It was considered necessary in some instances to punch a few small holes
+near the base of the drum in order to ensure a very slight upward draught.
+In a few cases this perforation has been exaggerated to the form of a
+hinged door. Unless this can be closed with ease, and is closed according
+to instructions, part of the object of this type of furnace is defeated;
+fuel consumption is rapid, and the temperature is too high. In the original
+form "pot-furnaces" have been found to be effective on many estates, and
+are still employed with satisfaction.
+
+IRON STOVES.--Working on exactly the same principle, on some estates one
+finds small iron stoves in use. Sometimes broad pipes are attached for the
+better distribution of the smoke; if this is the case it should be noted
+that the pipes should have a slight downward slope, and that the "bend" at
+the end should be turned downwards. In this way condensed moisture and
+creosotic matter falls to the ground, and does not lodge in the pipe. The
+life of the conduit is thus prolonged. Usually such stoves are in use where
+the "head-room" of a smoking chamber is insufficient for other types, or
+where the nature of the site does not permit of sunken furnaces being
+installed. They are of value likewise on occasions where the fuel supply is
+limited to a rich timber such as mangrove-logs ("bakau"), when it is
+necessary to ensure a low combustion with low cost of fuel.
+
+HORIZONTAL DRUM-FURNACES.--To overcome difficulties inherent to drums or
+"pot-furnaces," the next development was that in which the drum was made to
+assume a horizontal position, and adapted ingeniously to a simple system of
+working from the outside of the building. Reference to the drawings given
+will explain how this is effected. In the first illustration (No. 2) it
+will be noted that the drum is supported upon brick pillars, with one end
+projecting through the wall of the building. At the other end a short
+chimney is mounted, having within it a "damper" which is adjustable from
+the outside. Over this chimney is suspended a simple baffle-plate, made
+from a Chinese iron cooking-pan. The outer end of the drum is furnished
+with a hinged and latched door, in which a small air-regulator is
+accommodated.
+
+In the second set of drawings (No. 1) the drum is increased in size and
+fitted in a special manner for incorporation with a distinct type of
+building. Such a scheme was first put into effect by Mr. R. C. Sherar, the
+manager of Third Mile Estate, Seremban, F.M.S., and for ease of reference
+the house and furnace will hereafter be mentioned when necessary as the
+"Third Mile" type.
+
+[Illustration: "THIRD MILE" TYPE; HORIZONTAL DRUM.
+
+This type of furnace is suitable for adapting to existing buildings with
+perpendicular lower walls.]
+
+[Illustration: "THIRD MILE" TYPE OF FURNACE, USED IN CONJUNCTION WITH
+"THIRD MILE" SMOKE-HOUSE.]
+
+It will be seen that the furnace has at the farther end a door for the
+removal of ash. As this, if badly fitting, may result in too great a
+draught, it is well to insist upon good workmanship. Other adjustable
+air-inlets are provided, and the drum is enclosed in a brick chamber.
+
+RATE OF COMBUSTION.--However successful this furnace may have proved in the
+hands of trained coolies, one must feel that with such a number of
+air-inlets (whether accidental or designed) there would always be present
+the possibility of obtaining too rapid a combustion. In the original forms
+of drums or pot-furnaces of various kinds, a very slow rate of combustion
+was attained. Naturally a relatively larger proportion of carbon remained
+unconsumed, and there was a small proportion of ash. In these respects the
+furnaces resembled charcoal-burners. In point of fact, some estates used
+this principle for the dual purpose of smoke-curing the rubber, and at the
+same time obtaining a supply of charcoal to provide fuel for their
+suction-gas engines. This is a consideration in times when managers are
+desirous of discovering any devices which tend towards reduction of costs.
+
+It will be clear that, under ordinary circumstances, the condition of what
+remains after the combustion of the fuel gives an indication of the rate at
+which the wood has burned, and this test should apply to all furnaces. That
+in which there is the most ash and the least charcoal is the one least to
+be desired. In direct connection with this consideration, one must
+recognise that a fire which is sunk below the level of the ground exposes
+the least surface from which heat may radiate; and hence, in order to
+obtain the maximum benefit of heat from a slow-combustion furnace, it
+should be above ground-level, or should have a superstructure from which
+the heat may be dissipated.
+
+Simple drum furnaces, with slow combustion, have the further advantages
+that a "charge" of fuel will need no attention for possibly eight to ten
+hours, and practically no ash is found to be ejected. These advantages have
+great practical importance. The first minimises any disabilities arising
+from neglect on the part of coolies, and the second makes for increased
+cleanliness in the drying-chamber. While these advantages would appeal to
+most estates, there would appear to be a further advantage to small
+estates which have only temporary timber smoke-houses. With a slow rate of
+combustion in a furnace of this type, danger from fire is diminished
+considerably.
+
+Bearing in mind the slow rate of combustion, and hence the comparatively
+low temperature obtained, it will be plain that drum furnaces should be
+employed in larger number than ordinary open-hearth fires; and the drums
+can be so placed as to ensure the best possible uniform distribution of
+heat and smoke.
+
+Large furnaces are sometimes seen, with flues of brickwork. In view of the
+foregoing remarks, it will be obvious that these tend to large fires and a
+rapid combustion, and hence must be classed as undesirable.
+
+BRICK STOVES.--Developing from "drum" furnaces, another type comes into
+existence. In principle it consists of an enclosed brick furnace, with
+feeding door, and a low conical dome surmounted by an adjustable cap or
+spark-arrester. The rate of combustion can be influenced by a suitable
+movement of the cap, which is operated by a screw. This type of furnace has
+been installed on several estates by the engineering department of Messrs.
+Harrisons and Crosfield, and is understood to give satisfaction.
+
+PATALING TYPE.--With the exception of the "Third Mile" type already
+mentioned, all the furnaces described are open to a strong objection, in
+that the coolies have to enter a room, usually filled with hot smoke, in
+order to attend to the fires. The mere opening of the door of the building
+is sufficient to fan most fires into a blaze and to raise sparks. Apart
+from these points, it is natural for coolies to avoid entering too often,
+with the result that they generally stoke with the maximum load of timber.
+Even should they not sleep the danger is clearly great.
+
+[Illustration: SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE).]
+
+[Illustration: PATALING TYPE OF FURNACE.]
+
+To obviate these drawbacks, furnaces which are fed from the outside of the
+building were designed. There have been various forms, but as they were
+first installed on Pataling Estate, in the present form, they may be known
+under the description of the Pataling type of furnace. They are eminently
+satisfactory, and have a low rate of fuel consumption. They are very
+safe, and in fact, if worked with average intelligence in supervision, can
+be regarded as being fool-proof. There is practically no ejection of fine
+ash, and no fine-mesh screens need be employed. They can be adapted to any
+building having either vertical or sloping walls of galvanised iron.
+
+[Illustration: LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED
+VENTILATORS PERMANENTLY OPEN.
+
+In foreground, movable folding racks on which sheets "drip" in the open
+air. This smoke-house is equipped with brick furnaces fed from the outside
+(Pataling Estate).]
+
+In essential the furnace consists of a shallow pit below ground-level,
+lined with brick, and having a square brick superstructure rising 4 feet
+above the floor of the building. On top of the brick walls rests a sheet of
+boiler-plate perforated with small holes. The hearth being below
+ground-level, and with the extra 4 feet of height above the floor, it
+follows that if ash is disturbed it is confined.
+
+From the drawings it may be seen that the pit is prolonged to the side wall
+of the building, with steps leading up to the ground-level. The top and
+sides of the opening are made with galvanised sheeting, forming a kind of
+short tunnel in which the coolie may stand upright. The outer face of the
+brick furnace forms the inner end of the tunnel, and accommodates the door
+of the furnace. The bottom of the pit is filled up with clay and stones
+almost to the level of the bottom of the door. This ensures a very shallow
+hearth, and guards against an unduly large fire. Obviously it is not
+desirable or necessary to make the hearth of fire-bars, as was done in one
+instance, with the provision of a door below for removing the ash. This
+would lead only to a strong draught being created, with a high rate of fuel
+consumption.
+
+[Illustration: BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE
+BUILDING, BUT FED FROM OUTSIDE.
+
+On the top of the superstructure rests a sheet of perforated boiler-plate.
+The actual fire-pit is below ground-level, and to the left may be seen
+parts of the sides and top of the downward approach, from the outside, to
+the door of the fire-pit.]
+
+The openings can be screened by a narrow sloping lean-to, which serves to
+keep out rain, and provides shelter for the stock of fuel and the coolie.
+The iron furnace-door should be well made, with an easily worked latch; but
+it is not necessary that it should be perfectly fitting. Any slight
+aperture will serve to provide the necessary air-inlet, but in any case it
+should not be more than slight.
+
+CONSUMPTION OF FUEL.--Regarding this furnace, it may be said in conclusion
+that it is more satisfactory in general working than any other furnaces yet
+encountered. Obtaining information from over sixty estates, on the question
+of fuel consumption compared with output of rubber, it was found that, as
+far as ordinary smoke-houses were concerned, the Pataling type of furnace
+showed the lowest unit consumption of fuel.
+
+[Illustration: GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES.]
+
+This was at the rate of slightly less than 1 lb of fuel per 1 lb of
+thoroughly cured sheet rubber. The figure on some estates mounted as high
+as 4-1/2 lbs. of fuel per lb. of rubber. Naturally this factor may have
+been affected by failure to utilise the drying space to its fullest
+capacity, but in the main the high rate of consumption could be attributed
+solely to the deficiencies of the furnaces.
+
+FLOOR OF FURNACE-ROOM.--As a rule no attempt is made to improve the natural
+earthen floor. Whether open-hearth fires, truck furnaces, or drums are
+employed, it is usual to find a floor with an inch or two of dust upon it.
+Where all endeavours are directed in other directions towards cleanliness,
+it appears strange that this should be overlooked. In contrast, houses
+employing the Pataling type of furnace (or others) have concrete and cement
+floors, which can be kept quite clean. Cleanliness should be as zealously
+attempted in the smoke-house as in other departments.
+
+[Illustration: NEAR VIEW OF SHELTER.
+
+Steps lead downwards where the wall of the smoke-house has been removed.]
+
+ROOF.--In any type of smoke-house, the roof should fit tightly at the
+eaves, and the only vent should be in or near the roof-ridge.
+
+In an ordinary smoke-house, the opening should take the form either of a
+low jack-roof or of squat chimneys protected against rain. If a jack-roof
+is chosen, it may be so low as to need no scheme of adjustment, or
+otherwise adjustable swing shutters must be provided. The chimneys may be
+made with such low fitting between the cap and the body that no interior
+swinging flaps are required.
+
+During the operation of smoke-curing the smoke vents must remain open to a
+degree which is arrived at by experience. Failure to provide a
+comparatively free egress for smoke and moisture will bring trouble in its
+train. After a house has been in use for some time, it will be noted that
+the timber becomes covered with a shiny tarry coating deposited by the
+smoke. If the rubber remained in the house for an equal period, it would
+take on the same appearance. During the interval between the entry and the
+exit of the rubber some amount of deposit does take place, and it is this
+mixture of creosotic substances which plays a part in fitting the rubber to
+withstand growths of mildew which would otherwise form.
+
+If proper smoke-vents are not provided, the moisture evaporating from the
+sheets is unable to escape quickly enough, with the result that a great
+deal condenses at night-time upon the inner surface of the comparatively
+cool roof, and falls back upon the rubber in unsightly black "drips," which
+leave a distinct mark on the sheet. Even if vents are open, this may happen
+during seasons of rain. The temperature of the moist smoke in the
+roof-ridge may be as high as 130 deg. to 140 deg. F., while the outer atmosphere
+may have been cooled by rain to 70 deg. F. Such a difference on the two
+surfaces of the roof must lead to condensation within the house, with
+consequent "dripping." It used to be the custom to drape sacking material
+above the bays of racks in order to prevent the drops of liquid falling
+upon the rubber; but often for want of renewal the last state was worse
+than the first. Modern houses have often an inner lining, a few inches
+below the roof. This is made of soft wood which receives any product of
+condensation and absorbs it.
+
+OTHER TYPES OF SMOKE-HOUSE.--So far we have confined the arguments to
+smoke-houses of the usual type. There are others which vary in either
+design and method of working, or in the material of the structure. Mention
+may be made of the most prominent of these.
+
+BRICK HOUSES.--Some houses are constructed of brick, and may have one or
+two storeys above the furnace chamber. The floors are sometimes made of
+ferro-concrete, and the furnaces may also be of this material. These brick
+houses give satisfaction, but there would seem to be some difficulty in
+obtaining and maintaining the desired temperature, although it is not quite
+plain why this should be so. The principle of these buildings is the same
+as that of the ordinary iron house, and the suggestions made in previous
+paragraphs apply with equal force.
+
+"THIRD MILE" TYPE.--Reference has been made to the "Third Mile" type of
+furnace. This is an integral part of a smoke-house, which for clearness of
+distinction may be known as the "Third Mile" type of smoke-house, the
+original of which was erected on the Third Mile Estate, Seremban, F.M.S.
+
+[Illustration: "THIRD MILE" TYPE OF SMOKE-HOUSE.]
+
+In essence the design consists of a building, having two storeys for
+rubber-drying, and a shallow inverted pyramidal base, ending on the ground
+in "Third Mile" furnace, already described and illustrated.
+
+It will be seen that the principles of ventilation employed are those
+indicated for an ordinary house--viz., air-inlet near the ground (with
+little draught), and smoke-vent at the roof-ridge. The windows shown in the
+drawing are only for purposes of inspection of the rubber during the day,
+and form no part of the scheme of ventilation during the hours of smoking.
+
+It is claimed that the efficiency of the house is high. Certainly the work
+of attending to the furnaces is simplified, and there should be small
+ground for excuse if negligence is displayed.
+
+JACKSON HOUSE.--This was brought into notice under the description of the
+"Jackson Cabinet," and it was claimed that average sheets could be dried in
+a few days. It consisted of a small house of one storey, having several
+tiers of racks. Smoke and heat were generated in a small stove placed
+outside the wall. A smoke vent was provided in the roof. These cabinets had
+a certain vogue as part of a small unit installation, with a fair degree of
+success. It is not clear, however, that such speed in drying is required.
+(This point will receive further attention in a subsequent chapter.)
+
+"DEVON" TYPE.--In its full original design this type owes its origin to Mr.
+H. E. Nixon, General Manager of the Devon Estates, Malacca, where it forms
+part of unit divisional installations worked under a scheme of
+decentralisation.
+
+The original units consisted of a building erected with an iron framework
+covered with sheets of asbestos-slate, and a roof of galvanised iron.
+
+The novelty in design lies in the utilisation of external platforms upon
+which the racks of bars supporting the sheets of rubber may be drawn out of
+the smoking chambers, and on which the racks are loaded and unloaded. By
+this device it is possible to remove the contents of any compartment bodily
+without interfering with the continuity of curing in the other
+compartments. That is to say, smoking in such a house can proceed day and
+night if necessary, and yet the rubber in any part of the house can be
+examined, can be removed, or can be replaced without cessation of smoking.
+
+It will be seen from the illustrations that the house is more or less of
+the same general design as the "Third Mile" type, with the addition of
+external platforms. It has two storeys for the reception of rubber; and a
+basal furnace-room with sloping sides converging downwards into a pit
+containing a large drum-furnace. This is mounted on a low truck, and
+travels on a short length of railway.
+
+[Illustration: GENERAL VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE.
+
+The platforms are common to both units. Building of brick with iron roof
+(Batu Caves Estate).]
+
+Each of the curing-rooms is divided into four compartments (making eight
+compartments in all). These are closed by swing doors, each of which is the
+full width of a compartment, and has a slight overlapping edge. Through
+these doors light railways run into the house and out upon the platforms.
+On the rails "bays" of racks run, and when fully loaded they are easily
+moved. The racks were designed with a frame of stout hard wood, but light
+angle-iron could be utilised.
+
+[Illustration: GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND FACTORY
+BUILDINGS.
+
+Timber in foreground cut to length for stoking. Note water-tower and engine
+cooling-tanks adjacent to factory.]
+
+The chimney style of smoke-vent has an internal butterfly flap, which is
+controlled by means of a wire from the outside. In the ordinary course of
+smoke-curing, it is advised that this flap should be permanently open so as
+to reduce the possibility of internal condensation of moisture and
+creosotic matter. The exact degree to which it should be open must be found
+by experience.
+
+[Illustration: VIEW OF PLATFORM OF "DEVON" SMOKE-HOUSE; DOORS OF
+COMPARTMENTS OPEN, AND ONE RACK PARTIALLY WITHDRAWN.
+
+Note below each rack opening through which smoke rises, covered with wire
+netting.]
+
+Although reference has been made several times to compartments, it should
+be understood that the chambers are not subdivided internally by means of
+partitions. There exists only the external effect of compartments in the
+form of the eight swinging doors which allow for the withdrawal of, or
+insertion of, any one unit of racks at any time without interference with
+the bulk of the rubber.
+
+[Illustration: DOUBLE "DEVON" SMOKE-HOUSE OF BRICK, WITH ROOF OF CHINESE
+TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM SMOKING
+CHAMBERS.
+
+Federated Engineering Co., Ltd., Kuala Lumpur.]
+
+[Illustration: SIDE VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL
+ARRANGEMENT FOR STOKING FURNACES.
+
+Federated Engineering Co., Ltd., Kuala Lumpur.]
+
+DETAILED DESCRIPTION.--As enquiries are often received it is permissible to
+reproduce the following detailed description of the original house. This
+appeared in the Fourth Local Report (Malaya) 1916, issued to subscribers by
+the Rubber Growers' Association.
+
+     "The house has a steel frame-work, 22 feet long, 16 feet wide, and 22
+     feet high. Of the length, 14 feet is occupied by the platforms, and 8
+     feet by the chambers. These measurements can be varied. The whole of
+     the width (16 feet) is occupied by compartments of which one series is
+     placed above the other.
+
+     [Illustration: FRONT VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE.
+
+     Glenmarie Estate: Batu Tiga Co.]
+
+     "_Platforms._--The loading verandahs or platforms are of ordinary
+     'seriah' timber.
+
+     "_Compartments and Furnace Chamber._--These are enclosed with Bell's
+     'Poilite' sheets, each of which measures 8 feet by 4 feet by 3/16
+     inch. The sheets are affixed to the steel stanchions, doors, etc., by
+     galvanised bolts (1 inch by 1/4 inch) which pass through iron flats
+     measuring 8 feet by 2 inches by 3/8 inch (about). These iron flats
+     hold the sheets at the edges. The dimensions of the compartments are 8
+     feet by 8 feet by 4 feet.
+
+     "_Racks._--These are eight in number, and measure just under 8 feet by
+     8 feet by 4 feet. The capacity of each is roughly about 450 lbs., of
+     dry sheet rubber. The racks are mounted on 6-inch iron wheels, running
+     on rails of stock size, 'T' iron (1-3/4 inches by 1-3/4 inches by 1/4
+     inch).
+
+     "The sheets are hung on split bamboos. To prevent these projecting
+     over the edge of the rack and catching in the doors when the rack is
+     moved in or out, a thin strip of wood, about 1/2 inch high, is nailed
+     along the sides of the rack.
+
+     [Illustration: SIDE VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE.
+
+     Building constructed of galvanised iron. Shows door to furnace
+     chamber, and ventilator.]
+
+     "_Furnace._--This is of the type that aims at slow combustion. It
+     consists of a cast-iron cylinder, 3 feet in diameter and 4 feet high,
+     carried on a truck made of a sheet of boiler-plate, and mounted on
+     small wheels, so that the whole can be moved easily out of, and into,
+     the furnace chamber for easy cleaning and stoking.
+
+     "The furnace chamber is a pit lined with concrete, just wide enough
+     to take the trolley, and about 12 feet long. The top of the furnace,
+     which is almost flush with the ground-level, consists of a sheet of
+     zinc or galvanised iron with numerous holes about 3 inches in
+     diameter. Over these holes are strips of mosquito gauze, as flame and
+     dust arresters (see note below). There are no holes in the sides or
+     bottom of the cylinder.
+
+     "Over the furnace is hung a baffle-plate, measuring 4 feet by 4 feet.
+     Above this, on the first floor-level, the bottom of the compartments
+     is covered with wire netting, to prevent any rubber dropping
+     accidentally into the furnace chamber. The furnace chamber is fitted
+     with an iron-frame door, swinging on perpendicular hinges.
+
+     "_Method of Stoking._--The timber used is a mixture of jungle wood and
+     rubber-tree wood, cut to lengths of about 1-1/2 feet. In the ordinary
+     way the furnace is charged at 6 p.m., and at six-hour intervals a
+     little more fuel is added, but a new charge is not necessary. During
+     the daytime, when the heat of the sun is sufficient to raise the
+     temperature appreciably, a smaller fire is maintained.
+
+     "_Temperature._--There is no difficulty in maintaining a temperature
+     of 120 deg. F. By continuous smoking, average sheets prepared from
+     standardised latex can be fully cured in five days. This represents
+     110 hours of smoke-curing, which is at least equal to ten days'
+     intermittent smoking in an ordinary house.
+
+     "_Capacity._--There are eight racks, each accommodating 450 lbs. of
+     standardised sheet rubber. The loading capacity of the house,
+     therefore, is 3,600 lbs. As each charge is cured in five days, the
+     monthly output may be 21,000 lbs.
+
+     "The cubic capacity is 2,048 cubic feet. As there are no gangways,
+     etc., this is fully utilised. This gives a rate of monthly output
+     capacity to over 10-1/4 lbs. dry rubber per cubic foot of drying
+     space; an excellent figure much in advance of values obtained in the
+     great majority of ordinary smoke-houses."[18]
+
+[18] Since the above was written, it has been found possible to eliminate
+the gauze. A mild steel top has been made, perforated with 2-inch holes.
+Practically no dust is ejected from the furnace, and there are no flames.
+
+Owing to shortage of supplies during the War, similar buildings have been
+erected with frames of well-seasoned hard wood, which was protected by
+strips of asbestos-slate or galvanised iron. The latter material was also
+substituted in the covering walls. Later, houses were erected of brick,
+with other minor modifications. As a natural development, the latest
+buildings consist of two of the original houses face to face, under a
+common roof, and served by common platforms.
+
+As originally designed, the house was intended to meet the needs of a small
+estate, or a division of an estate, having a maximum output of about 20,000
+lbs. of sheet rubber per month. The possibility of an extension of this
+idea has been shown to be great.
+
+The furnace has been described as situated in a pit. Situated on a bank or
+on sloping ground, it was easy to arrange for withdrawal of the furnace. In
+some cases this has not been possible, and various modifications have been
+effected. The most satisfactory yet encountered is that in which a shallow
+brick pit is surmounted by an iron cone, about 4 feet in height. This is
+fitted with a cap having small perforations. The fire burns in the pit, and
+the heat is radiated by the cone. It would have been more effective to have
+allowed greater height in the furnace chamber, and to have employed the
+travelling drum-furnace as in the original design.
+
+In order to avoid interference in draught by a space between the bottom of
+the doors of the compartments and the platform (due to the presence of
+rails), the floor of the platform is laid level with the top of the rails;
+or to the bottom of the doors is attached a swinging flap, notched for
+accommodating the rails when in position.
+
+       *       *       *       *       *
+
+There are in use houses of other designs, which all more or less vary only
+in some modifications from the types described. Hence they do not call for
+special comment. Recently a rather distinct departure has been noted in a
+structure designated the "Barker" smoke-house.
+
+BARKER PATENT.--In essential this consists of a long narrow structure
+erected with an appreciable slope from one end to the other. At the lower
+end is a small furnace enclosed in a brick compartment. The smoke from this
+furnace travels up the slope to the other end, at which the rubber enters.
+The sheets are hung on bars which are attached to a unit framework. This
+frame slides, by its own weight, upon timber side supports. A sufficient
+number of these units occupies the full effective length of the structure.
+The removal of "stops" at the lower end enables the foremost frame to be
+removed, and the succeeding frames slide into a new position. Thus the
+freshly prepared sheets, entering at the higher end, gradually and
+automatically move towards the furnace as the frames of dry rubber are
+removed from the lower end.
+
+[Illustration: THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT.
+
+The racks slide automatically from top to bottom on withdrawal of the lower
+frames through door at front. The furnace is contained in the brick
+compartment at the lower (front) end.]
+
+Thus far only small units have been seen. It is claimed that, properly
+prepared, sheet rubber can be smoke-cured in about five or six days, and it
+is stated that installations have been in successful working for
+sufficiently long periods to prove their efficacy. The device is better
+known in Java and Sumatra than in Malaya. The capacity of a unit building
+is stated to be 7,000 lbs. per month, calculating on a six days' cycle of
+working. In a more recent design provision is made at the lower end for a
+water tank, into which all rubber can be discharged in case of fire.
+
+
+
+
+CHAPTER XVI
+
+_OTHER BUILDINGS (continued) AND SITUATION OF BUILDINGS_
+
+
+SORTING-ROOM AND PACKING-ROOM.--It is in these departments that most
+factory installations are lacking. More often than one cares to
+acknowledge, sorting and packing are done under conditions which place a
+premium upon poor work. As a consequence, consignments of rubber are often
+marred by the inclusion of defective specimens. The result is that
+shipments may be rejected when tendered against contracts, or that
+allowances in price have to be made. In many instances it would not be fair
+to lay the blame upon the manager or an assistant, as it is obviously
+impossible for an individual to inspect every piece of rubber. Neither
+would it be strictly fair in some cases to ascribe the fault to pure
+carelessness on the part of the coolies.
+
+Often the only provision made for this important work is the lower room of
+a drying-shed, which may also contain hanging rubber. Under these
+circumstances, space is cramped, and the light often poor. Small defects
+may pass unnoticed, and the general surroundings do not conduce to keen
+work.
+
+Where, for economic reasons, the sorting and packing operations are
+conducted in the drying-shed, there should be ample space free from hanging
+rubber, and it should not be possible for wet rubber placed in the upper
+room to drip upon the dry rubber below or upon packed cases. There should
+be plenty of light, and for this reason windows should be ample. Usually
+the window-frames are fitted with wooden shutters, which are preferably
+hung on horizontal hinges from the top of the frame. By this device it is
+not necessary to close all windows during a shower of rain, and rubber may
+be stacked near a window with reasonable chance that direct sunlight will
+not be allowed to fall upon it.
+
+In dealing with smoked sheet, it is advised that the rubber to be examined
+should be placed upon tables facing the windows, so that each piece may be
+scrutinised in a strong light.
+
+Crepe rubber also is best examined in a strong light, but preferably with
+one's back towards the source of light or at an angle to it. For this work
+coolies usually are most efficient when sitting on the floor.
+
+It will be clear from the foregoing remarks that the best conditions would
+be secured in a separate building especially constructed. A single room
+would be all that is required; at one end sorting could be undertaken,
+while packing could be done at the other end. No hanging rubber should be
+allowed in the room.
+
+The floor should be of hard timber, and raised from the ground, to the
+height approximately of a bullock-cart or motor-lorry, as the case may be.
+The boxes of rubber could thus be transported by small hand-trucks on a
+level with the transport vehicle, reducing labour to the minimum.
+
+The ventilation of the building should be good, especially if cases of
+rubber are to be stored therein; and the entire structure should be
+weather-proof.
+
+STORE-ROOMS FOR RUBBER AND STORAGE.--The question of storage of rubber in
+factory buildings has always possessed importance, but has demanded
+increased consideration recently.
+
+From experience in this country, it is clear that cement floors for
+store-rooms or packing-sheds are the least suitable. They are often visibly
+damp, especially in the early morning. To allow rubber, packed or unpacked,
+to remain upon a cement floor in the tropics, is to court trouble from
+moulds, external or internal. If the employment of a cement floor is
+unavoidable, the rubber and boxes should be raised on wooden supports,
+giving a clearance of at least 3 or 4 inches, and there should be clear
+ventilation space between tiers of boxes.
+
+Experience indicates that the best type of floor is that already advised
+for sorting and packing rooms--_i.e._, a good hard timber floor raised at
+least 3 feet above ground-level. Apart from the advantage in labour
+specified in the previous paragraphs, this provision of ample ventilation
+space below the floor is a great consideration in the preservation of the
+timber. Raised store-rooms become essential in low-lying districts which
+are at all subject to flooding, yet the writer has seen many boxes of
+rubber damaged by flood-water entering a packing-room situated on the
+level.
+
+The question has often been raised recently as to the length of the period
+during which rubber may be safely stored in this country. The answer can be
+only supplied by experience, of which up to the present we have none
+possible of being classed as reliable. Whatever storage may have been done
+in the past has been influenced greatly by the unsuitability of the storage
+accommodation, and the fact that often the rubber was not prepared with a
+view to prolonged storage.
+
+While the market demand was strong, rubber was being shipped and passed
+into circulation, at a rate which did not demand investigation of the
+subject of local storage. In the year 1918 conditions were such as to bring
+the matter into prominence, and we were able to tender advice on the lines
+given in this chapter. The necessity passed, but has again arisen.
+
+Our experience goes to prove that if rubber is properly prepared and
+thoroughly dried before packing, it will remain in good condition for a
+period of a year or more in this country. How much beyond a year it may be
+kept remains to be determined. The assumption of "proper preparation"
+leaves great room for reservations.
+
+In the case of crepe rubbers, there is no great difficulty, provided that
+the recognised methods and formulae are employed, and that the rubber is
+packed only when perfectly dry. Under those conditions, the higher grades
+of crepe remain apparently unaffected on storing. Any appreciable
+deterioration may be attributed to defective preparation or external
+causes, such as accidental damage by water.
+
+The prolonged storage of lower grade rubbers is attended by more risk,
+especially in the case of the lowest grade (earth-scrap) from estates which
+neglect the practice of regular and frequent collection of the raw product.
+The same reservation applies to crepes made from tree-scrap which is not
+collected daily. In these types of crepe rubber "tackiness" may be
+initially present only in small degree, but the final damage may be
+immensely greater by close contact of the folded rubber during prolonged
+storage.
+
+When we come to discuss the possibility of storage of smoked sheets, the
+difficulties become immensely greater. We have yet no reliable experience
+as to the keeping properties of this grade when properly prepared, fully
+cured, correctly packed, and stored under the best of local conditions. It
+is understood, of course, that in the qualification by the term "local"
+conditions, we assume it to be more difficult to store rubber generally in
+Malaya than in a temperate climate. The average temperature and humidity of
+the atmosphere are here much more favourable to the development of mould
+growths than would be the case, say, in Great Britain.
+
+In discussing this question, as far as it refers to the preservation by
+storing of smoked sheet rubber, it is not fair to draw conclusions as to
+the likely behaviour of packed rubber from data based upon observation of
+loose specimens. We have samples of smoked sheets prepared in 1910, and
+these, superficially, appear to have remained unchanged. No mould is
+present and, as far as intermittent observation enables us to judge, moulds
+have never been incident. Whether such rubber would have been preserved in
+this condition had it formed part of a packed case, is a point upon which
+we have no experience; neither can we give any opinion. It seems true,
+however, that loose specimens "keep" better than bulk samples of the same
+preparation.
+
+It cannot be argued that the present good condition of these old specimens
+may be due to correct preparation. In those days methods and formulae were
+rather haphazard, especially in view of the fact that the daily variability
+of dry rubber content of latices was not then recognised.
+
+One would rather submit the factor of adequate smoke-curing as the chief
+influence in the superficial preservation of smoked sheets. Ten or eleven
+years ago it was considered advisable to allow the rubber to remain in the
+smoke-house for a period extending well beyond that necessary for ordinary
+drying. As a result, very dark rubber was produced, which was thoroughly
+impregnated with the products of wood combustion. There would seem to be
+little doubt that this procedure was responsible for the prolonged freedom
+from mould growths.
+
+Market standards have varied to some degree since, with a tendency to
+prefer a paler product than that in vogue, say, six or seven years ago.
+Moreover, standardised methods of preparation have been introduced, with
+the result that sheets of a desirably high standard can be produced in from
+ten to fourteen days, when smoke-curing is conducted only during night
+hours. Some estates are equipped with smoke-houses which, by continuity of
+working day and night, provide smoke-dried rubber in from five to six days;
+but the actual hours of smoke-curing are approximately equal to those of
+the ordinary type of house.
+
+This tendency towards the production of sheets paler in colour than the old
+standard is probably largely responsible in the present for the commonly
+observed incidence of surface moulds on stored smoked sheets, and also for
+some complaints of "under-curing," where the term specifically refers to a
+failure to dry and cure the rubber thoroughly. Boxes of smoked sheets,
+which had been stored for varying periods up to five months, were recently
+inspected, and, in the majority of instances, surface moulds were found to
+be plentiful. In all cases it was observed that the trouble was intensified
+where boxes of rubber were stored in contact with cement floors.
+
+This "under-curing" is not a question solely of the duration of
+smoke-drying, although probably the modern practice of curtailing the
+period has exerted a great influence. To make this clear, it may be stated
+that, given two batches of uniformly prepared wet sheets, it would be
+possible to smoke-cure them for equal periods in different houses, so as to
+produce one batch very much paler in colour than the other, although the
+total hours of actual smoke-curing would be identical. In order to produce
+such effects, all that is necessary is to employ different timbers for fuel
+or different types of furnaces. In the one case there would be produced
+heat and very little smoke, while in the other the necessary heat would be
+obtained plus plenty of smoke. The best results naturally are obtained by
+the employment of the happy medium, and if smoked sheets have to be stored,
+the ordinary period of smoke-curing should be prolonged to an interval
+consistent with the capacity of the smoke-house.
+
+All precautions taken in preparation and curing can be nullified, as
+already indicated, by unsuitable storage conditions.
+
+TOOL-SHEDS AND STORE-ROOMS.--In some factories it is the rule to see lime,
+cement, spare rolls, sieves, and a general heterogeneous assortment
+occupying part of the rubber-drying rooms. The inconvenience is often
+great; and it certainly seems that these stores and tools are of sufficient
+value to be accommodated in suitable buildings.
+
+SITUATION OF FACTORY BUILDINGS.--There can be no doubt that a great deal of
+the "spot" disease trouble, and the general slowness of drying, can be
+attributed in many factories to the unsuitability of the site chosen.
+Probably the idea which actuated those responsible for the choice of site
+generally was proximity to a water supply. This would account for the fact
+that a number of factories are situated in valleys or near swamps. More
+often than not, also, the actual clear space is very limited, and rubber
+trees grow close up to the walls of the buildings. Under such
+circumstances, it is difficult to see how these buildings can be anything
+but dark and damp, and it is not difficult to understand the slow rate of
+drying. In a few cases the sites chosen proved to be so unsuitable that the
+estates were confronted with a very serious problem, the solution to which
+was, either the erection of another complete set of buildings in a more
+suitable spot or the installation of artificial driers.
+
+It must be laid down as an axiom that the first essential in a suitable
+site is that water may be brought to it easily, but, as already indicated,
+this does not mean that the buildings need be placed in actual proximity to
+the water-supply. The mistakes made by pioneers in this work are not likely
+to be repeated, and it is common now to note well-designed and
+comprehensive schemes in which the water is pumped to a reservoir placed at
+a suitable elevation, whence the supply is gravitated to bungalows, coolie
+lines, and the factory. The importance of securing a plentiful supply of
+good water for factory purposes cannot be exaggerated, and it is a point
+which is only thoroughly appreciated on estates where smoke-sheet rubber
+has to be prepared.
+
+The second essential, but of equal importance, is that there shall be an
+ample open space on which the sun may shine all day. There must be no trees
+too near the buildings, and there should be no adjacent swamps. Preferably,
+the site should be on a raised position, so that it will be impossible for
+surrounding trees to cut off sunshine, even when they are fully grown. From
+such an arrangement it will follow that the factory will be light and airy,
+and the drying-houses will receive the maximum of benefit to drying from
+direct sunshine on the roof and walls. There can be little doubt that these
+considerations play a most important part in determining the rate of drying
+of the rubber, and where comparisons are made between the rates of drying
+in various drying-houses all these factors enter into the question and
+contribute to the total result. Presuming that the thin crepes made in two
+factories are equal in thickness, it is not uncommon to find that in a
+drying-house, situated in a wide open space, the period of drying may be as
+low as six or seven days; while in another drying-house, situated near a
+swamp and surrounded by trees, the period may be as high as eighteen days
+to twenty-one days. The figures quoted are not fictitious, but are facts
+actually noted in the course of the writers' experience.
+
+A great deal also depends upon the exact position of buildings. Thus, to
+obtain the maximum of light in a factory, it will be obviously beneficial
+to erect it with the long sides running east and west, so that the windows
+face the north and south, and the large end doors face the east and west
+respectively. At first sight it would appear that the best position for the
+machines would be on the north side of the building where no sun can enter;
+but a moment's consideration shows that the south side would give the best
+results. By the time the sun has come round to the south, it is usually
+high in the heavens, and the direct sunshine does not fall very far into
+the room. Even should it play upon the machines for an hour or two during
+the day, no harm could result to the rubber which was being worked, as no
+piece would remain there a sufficiently long time to be injured in the
+slightest degree. Placed in this position, the maximum benefit of light
+would be obtained, whereas if the length of the building ran east and west,
+the machines would have only either the morning or afternoon light.
+
+[Illustration: SUGGESTED ARRANGEMENT OF BUILDING.]
+
+While it is advisable to erect a factory running east and west, the
+drying-houses should run north and south. In this position the maximum wall
+area will be exposed to the sun during the day, and it will be possible to
+manipulate the windows of the drying-rooms so that those along one side are
+open, and it will never be necessary to close all the windows at any time
+of the day. Thus the windows facing east will be closed, and those facing
+west will be open until after midday; then _vice versa_. With such an
+arrangement a more uniform temperature may be obtained than by any other
+arrangement of the buildings. If the building ran east and west, the
+windows on the north side could remain open all day, while those facing
+south would have to remain closed practically all day. The south side of
+the house would be heated by the sun, while the north side would remain
+cool, and the rates of drying would be correspondingly unequal. The total
+wall area heated by the sun at any time of the day would be less in this
+position than if the house ran north and south.
+
+Similarly, to obtain the best drying effect during the daytime in a
+smoke-house the building should run north and south. By this means the
+temperature will be maintained to the maximum possible by sun heat, and the
+rate of drying will correspond.
+
+
+_References to Sketch Plan._
+
+Drying-house No. 2 should be of two storeys, and unless a separate sorting
+and packing room is to be built, No. 1 should also have two floors (see
+previous notes on packing-rooms).
+
+In the factory--
+
+     _V_ shows the position of the verandah, which may be quite open and
+     only divided from the inner room by
+
+     _S_, a wall composed of very strong expanded metal, which allows light
+     and air to enter the factory.
+
+     _T,T_ are the glazed tile tanks for the reception of latex, scrap
+     rubbers, and bark-shavings.
+
+     _M_ shows the position of the machines on the south side of the
+     factory, with the direction of extensions, and
+
+     _E,E_ the compartments in which the engines are bedded. In these
+     positions it is possible to obtain direct drive to the machines.
+
+     _D,D_ are large double swing or sliding doors (the latter for
+     preference always). These, while suiting transport of rubber, provide
+     also for a free draught of air.
+
+If possible the scrap-washing machine should be placed outside the wall of
+the factory, and tanks for the reception of scrap rubbers may then be
+situated in convenient proximity.
+
+Economy of labour is obtained by grouping all factory buildings as closely
+as possible, but it should be borne in mind that smoke-houses should be
+regarded as a possible source of danger from fire. This point has a
+practical bearing upon rates of insurance, and it is essential that the
+smoke-house should be situated at a minimum of 50 feet from any other
+building or group of buildings. In this connection, also, it may be noted,
+as being of further practical interest, that, in the insurance of
+smoke-houses, preferential rates are given to those having a good type of
+slow-combustion furnace.
+
+CHOOSING A FACTORY SITE.--Sufficient has been written to make it clear that
+the choice of a site for factory buildings is a matter demanding weighty
+consideration. Much, of course, depends upon the planted area, and the rate
+at which it comes into bearing. Under certain circumstances which will be
+obvious, it is permissible to instal first a group of buildings of a
+temporary nature only, the future site and permanent buildings to be chosen
+later when the main portion of the estate comes into bearing. Often,
+however, one finds that, from lack of forethought, the estate has been
+committed to considerable expense in the establishment of equipment, which
+later is proved to be unfavourably situated with regard to the majority of
+the area in ultimate bearing. In such case, transport of latex is fraught
+with difficulties and may be expensive.
+
+In the instance of an estate which will gradually come into bearing, it is
+not easy to decide whether a temporary installation shall first be
+provided, or whether, in anticipation of future demands, a complete
+equipment shall be erected. So much depends upon the financial aspect of
+the question, and upon the rate at which areas will come into bearing. As
+far as is possible, the best policy would be that of a compromise under
+which the site would suit later requirements, and the factory would be so
+planned as to be capable of future easy extensions both of buildings and
+machinery.
+
+It is not possible to lay down any definite data as regards requirements
+based on acreage, or to make comparisons between any two estates of similar
+acreage. The important factors determining such requirements are:
+
+     (_a_) Area.
+
+     (_b_) Shape of the estate.
+
+     (_c_) Topography of the estate.
+
+     (_d_) Available supplies of water.
+
+Naturally the ideal site for factory buildings would lie in a central
+position, given other favourable conditions.
+
+CENTRALISATION OR DECENTRALISATION.--It is the experience of a number of
+estates that, all other conditions being favourable, there is a limit
+beyond which the centralisation of factory work leads to an unwieldy
+position. We are not here concerned with the few extremely large estates
+running into tens of thousands of acres. In those cases the total area
+would be divided into economic sections. The argument there would resolve
+itself into a discussion on the size of an economic section. This, in turn,
+would be dependent upon the type of main product, involving the question of
+transport of latex or coagulum, and the possible provision of batteries of
+heavy machinery.
+
+The differentiation between the transport of latex and coagulum,
+respectively, is a most important one, and has a powerful influence in
+determination of the maximum of centralisation possible. Whereas properly
+prepared coagulum may be safely transported by bullock-cart, light-railway,
+or motor vehicle for many miles, latex, on the other hand, demands very
+careful treatment. Anti-coagulants may be employed to preserve fluidity,
+but only within certain limits. Even under these conditions, other factors
+(chiefly climatic) exert an influence which renders the transport of latex
+for any distance a matter of anxiety.
+
+It will be plain, therefore, that the limits of centralisation of factory
+work are much narrower for the preparation of sheet rubber than is the case
+when crepe rubber is to be made. In actual experience the preparation of a
+high standard and a high percentage of smoked sheet is attended with
+considerable difficulty in those cases where the factory processes have
+been ultra-centralised. Apart from the difficulties inherent to the
+transport of latex in a state of good preservation, there is the added
+difficulty of dealing quickly with large volumes of latex brought from
+various quarters. None of these should be allowed to remain standing if the
+best results are to be secured; but obviously there must at times be some
+congestion. Even on a small scale it is often found that the latest batches
+of latex are unfit for the preparation of good sheet rubber, and the
+trouble may be easily exaggerated when working on a large scale.
+
+The centralisation of work on crepe preparation, therefore, is limited only
+to a comparatively slight degree by distance of transport, and in the main
+only by the size of the necessary equipment of machinery and drying
+accommodation.
+
+The successful preparation of sheet rubber is, on the contrary, governed
+chiefly by the factor of transport. With this consideration in view,
+several large estates, preparing sheet rubber as the chief grade, have
+found it necessary to decentralise the factory work, with very satisfactory
+results. Outlying sections are given uniform and complete equipments of
+necessary buildings on a small scale, and hand-driven light machines.
+Uniform coagulating tanks are installed, and the methods and quantities of
+chemicals employed are carefully standardised. Experience has shown that
+often the best sheet rubber coming to the market has been prepared on small
+estates; and the same applies to the product of these decentralised
+stations on large estates. There is no _a priori_ reason why the product
+from one station should differ in the smallest particular from that of
+another, apart from minor fluctuations which are due to variable weather
+conditions affecting the latex. If the contrary is found to be the case, it
+indicates failure on the part of the person responsible to follow the
+regular rules and methods.
+
+In the natural scheme of development of a large estate, it would be
+necessary, of course, to have a comparatively small centrally situated
+factory, equipped with power and heavy machinery for working scrap rubbers
+in the preparation of crepe grades below No. 1 in quality. As the yield per
+acre increases, or the area in bearing expands, it would be advisable later
+to increase the size of the central factory and buildings so as to permit
+of the preparation of a proportion of the crop in the form of No. 1 crepe
+rubber, in order to be able to comply with prevailing market demands under
+which preferential rates fluctuate between pale crepe and smoked sheet.
+
+
+
+
+PART IV
+
+THE FINISHED RUBBER
+
+
+
+
+CHAPTER XVII
+
+_DEFECTS IN CREPE RUBBERS_
+
+
+GENERAL STYLE OF FINISH.--Broadly, there is no single and definite style of
+finish, but on the whole it may be stated that the greater proportion of
+crepe rubbers are prepared in a thin form and with a close-knit texture or
+finish.
+
+Very little thick or blanket crepe is now made on estates in Malaya, so
+that beyond the mention of that type little need be written. A fair amount
+of blanket crepe is sold in the Singapore market, but it should generally
+be regarded as re-made rubber--_i.e._, it may have been prepared from thin
+crepes, or from native pale sheets, in local rubber-washing factories. In
+appearance these crepes have a rough finish, and vary in colour according
+to the crude material employed.
+
+The general preference of the market at present is for a thin,
+smooth-finished crepe, with a close-knitted surface--_i.e._, free from what
+is described as "laciness." What effect this looseness of finish can
+possibly have upon the quality of the rubber is not understood, but the
+standard type set up by the market must be comparatively free from small
+holes.
+
+Under existing conditions governing the sale and purchase of rubber,
+various "standards" are set up. These really have no bearing upon the
+intrinsic qualities of the rubber, and are concerned almost entirely with
+superficial attributes. They are necessary in the absence of any proper
+scheme of evaluation for the establishment of certain standards of
+comparison, which imply that the rubber is apparently clean, free from
+certain recognised defects, and has been carefully prepared--as far as can
+be determined by a superficial examination. Thus the question of "finish"
+has attained disproportionate importance, but must be respected when
+preparing rubber for sale.
+
+Under ordinary conditions, thin crepe rubber, as it leaves the finishing
+machines, has what may be termed "deckled" edges. On many estates, in order
+to comply with market conditions, the edges of the wet crepe are trimmed,
+and the trimmings re-made into lengths of crepe. This is done under the
+impression that the market price is influenced by the evenness of the edges
+of crepe rubbers.
+
+Again, it sometimes happens that, owing to "wear" of the rolls, the
+finished dry crepe may show a faint but distinct pattern of mark--a diamond
+or a horizontal bar. Since these are not accepted under the "standard"
+comparisons, rubber exhibiting these characteristics does not obtain the
+top market price. In other words, these innocent and innocuous marks are
+regarded as defects and penalised accordingly.
+
+Enough has been written to show how very important becomes the question of
+finish. It will be acknowledged that the superficial qualities demanded in
+the "standard" market type can be reproduced by any estate having adequate
+machinery and ample facilities for drying and handling the rubber.
+
+Methods of preparation and formulae for the employment of chemicals are so
+well laid down that, up to the stage of machining, no difficulty need be
+encountered. But the standard type of finish in the dry crepes cannot be
+obtained unless the estate factory is fully equipped with the three types
+of rolls necessary--_i.e._, macerators, intermediate crepers, and smooth
+finishing-rolls. This subject has received full discussion in Chapter
+XIII., and is here only mentioned with the view of emphasising the point
+that no estate can be blamed for a lack of "finish" in crepe rubbers if the
+equipment of machinery is inadequate or in poor condition.
+
+If, on the other hand, the factory has ample machinery for requirements,
+and a good finish cannot be obtained on the thin crepe, then it is time the
+rolls were attended to and changed, or that the ratios of the driving
+pinions were altered.
+
+DIRTY EDGES.--It seems to be almost impossible to keep old machines clean,
+and it is equally difficult to keep the edges of crepe free from oil and
+dirt. Usually these dark edges are to be found on crepe which is rather
+wide, and it will be noticed that where wide crepe is made, unless special
+precautions are taken, the edges of the rubber often pass under the edges
+of the hopper and so pick up dirt and oil. On most machines it is a great
+mistake to attempt the preparation of wide crepe; nothing but narrow crepe
+must be made. To obtain this it is necessary to decrease the width of the
+hopper placed above the rolls. This can easily be effected by blocks of
+heavy hard wood, cut to shape and fastened in position.
+
+Sometimes the dark edges of crepe are due to another cause. Rolls may be
+gradually worn in the middle, so that to obtain a good finish it becomes
+increasingly necessary to tighten up the screws which regulate the distance
+between the rolls. It thus happens that just at, and beyond, the edges of
+the rubber the rolls grind upon each other, and fine particles of iron and
+graphite are transferred to the rubber. In such a case it is evident that
+either the rolls must be "turned" or that a new pair of rolls must be
+substituted.
+
+IRON-STAINS.--One of the causes of iron-stain on rubber has been mentioned
+in the preceding paragraph. This particular kind of iron-stain must not be
+confounded with rust-stain, and gives a dark dirty colour. It results from
+the grinding together of the rolls, and is usually noticed in the finishing
+of fine pale crepe. For this operation it is necessary to screw up the
+rolls tightly, and it will be plain that, whenever the rolls are vacant of
+rubber, there is a tendency for them to grind upon each other, thus setting
+free fine particles of iron and graphite. In order to avoid this, one must
+be careful to see that between the working of each length of fine crepe the
+rolls should be occupied with another piece of rubber, which may be kept
+for the purpose. In some factories this trouble apparently does not exist,
+while in others the amount of wear on the rolls is surprisingly great, and
+the damage done to the rubber is excessive. The only way in which this
+difference can be accounted for is that there must be a great difference
+in the quality of the roll material. Some rolls seem to be excessively
+soft, and from these contamination by iron-stain is great. For this reason
+rolls are sometimes rejected, and there would appear to be an objection to
+any but chilled steel rolls for the final stage of finishing crepe rubbers.
+
+RUST-STAINS.--Rust-stains, on the other hand, throw the responsibility
+entirely upon the labour and supervision of the factory. Rust is formed
+upon the rolls when they are at rest, and any one passing pale rubber
+between the rolls before they have been thoroughly cleaned is guilty of
+culpable negligence. Even when apparently clean, a piece of lower grade
+rubber should be passed through the rolls several times so as to remove any
+slight trace of rust remaining.
+
+Rust-stains have also been caused in a few cases by the large knives which
+are used to cut up lumps of coagulum, or by allowing freshly coagulated
+rubber to come into contact with iron vessels in the factory.
+
+A similar appearance has been traced in a few instances to contamination of
+the coagulum in transit by the dust of the reddish rock (laterite) employed
+in localities for road-making.
+
+OIL-MARKS.--The origin of oil-marks in crepe has already been described in
+Chapter XIII. The whole question resolves itself into one of cleanliness,
+moderation in lubrication, and supervision. The machines should be
+inspected every day, and once a week rolls may be swabbed down with a 10
+per cent. solution of caustic soda applied by means of a piece of cloth
+fastened round the end of a stick. Immediately after this operation water
+should be turned on and the rolls set in motion, so that all traces of
+caustic soda are thoroughly removed. If possible, lubrication by oil should
+be substituted by grease lubrication through screw caps.
+
+Particular attention should be paid to the back of the machines. None but
+the individual in charge of engines should be allowed to lubricate the
+machines, and he should be held responsible for any excess of lubricant.
+
+As a rule oil-marks are restricted to the edges or the proximity of the
+edges of crepe, but sometimes the streak is to be found in the middle of
+the length. In such a case it is almost certain that the oil or grease has
+been picked up by the rubber in the tray. It sometimes happens, if the
+"liners" of the bearings are eccentrically worn, that a few drops of dirty
+oil or a particle of grease are squirted out to some distance. These
+usually find a resting-place in the tray, and the contamination may then
+appear in any part of the rubber.
+
+It will be clear, therefore, that all trays beneath machines should be
+examined as the probable source of danger from contamination by oil and
+dirt. If the trays are as wide as or wider than the effective portion of
+the rolls, they should be discarded. In their place (except sometimes in
+the case of the macerating machine) all that is necessary is a movable
+piece of board, in width not less than from 4 to 6 inches shorter than the
+width of the rolls. Any oil or grease ejected from the bearings will thus
+be allowed to fall clear of the board; and defects due to oil streaks,
+etc., will be very much diminished, if not entirely obviated.
+
+This point in connection with the damage possible by the existence of wide
+trays is commended to the notice of manufacturers of machines for
+plantations, as it is common to find that trays are made which contravene
+the rule prescribed by experience. In fact, trays on some machines have
+been so designed as to act as "traps" for all dirty matter exuding from the
+bearings. Not only so; they are sometimes made of such a shape and height
+that oil or grease lodging upon the edges act as a "wipe" to the rolls,
+thus increasing the possibility of contamination. Until this defect was
+investigated, it was common to note continued contamination of pale crepes
+in spite of all precautions taken in cleaning the rolls at frequent
+intervals. The trouble due to this cause is intensified when the same
+machines are employed for the preparation of scrap-rubber crepes and No. 1
+crepe. Small pieces of scrap find their way towards the bearings and lodge
+on the edges of the trays. Unless a thorough inspection is made before
+proceeding with the working of the No. 1 (pale) grade, contamination may be
+continuous.
+
+DIRT.--Streaks due to the presence of dirt (as apart from oil or grease
+contamination, or that due to pieces of oxidised scrap) are unusual, and
+when they do appear their origin seems to be somewhat of a mystery. It
+could scarcely be advanced that the dirt was picked up on the machines, as
+it is difficult to imagine where such dirt could come from. In one or two
+instances there has been fairly clear evidence that the dirt was contained
+in the coagulum, and the only explanation fitting the case is that it fell
+into the latex after straining and during the course of coagulation. On
+cutting open lumps of coagulum brought in from the field division, it has
+sometimes been noticed that dirt is included, and the foregoing explanation
+is the only reasonable one. How it was possible for dirt to get into the
+latex must be left for explanation to those better acquainted with the
+conditions under which the latex was coagulated.
+
+HOLES.--On some estates it would seem impossible, with the existing
+machines, to make really good crepe. The complaint is that, if thin crepe
+is attempted, it is invariably found to be "full of holes"; and as,
+apparently, the presence or absence of small holes in crepe rubber is a
+factor which influences buyers, this defect must be avoided at all costs.
+Why this matter of small holes in thin crepe should weigh so heavily with
+buyers is a matter which the writers are not in a position to explain. As a
+matter of fact, the presence of small holes is most generally an indication
+that the rubber has received the minimum amount of working on the rolls
+consistent with good washing. Further working would only be undertaken with
+the idea of so consolidating the rubber as to get rid of holes in order to
+meet the market scheme of valuation.
+
+This is usually achieved by making a very thin crepe and rolling together
+two lengths when wet. The resulting crepe may be slightly thicker than
+ordinary, and the method employed may be usually detected by the appearance
+of the edges unless these are trimmed.
+
+GREENISH AND TACKY STREAKS.--Occasionally one meets cases in which pale
+crepe exhibits streaks varying in colour from a decided green to an almost
+black in which the greenish tinge is scarcely perceptible. Experience
+indicates that these streaks are much more dangerous than they appear
+superficially, inasmuch as they contain traces of brass from the "liners"
+of the bearings. The presence of the copper in brass is responsible for a
+gradual disintegration of the rubber, commonly recognised as "tackiness."
+In fact, copper may be said to be a "poison" to rubber, and every effort
+should be made to avoid possible sources of contamination. The effect may
+be proved easily and perceptibly by fastening together several pieces of
+crepe rubber by means of a brass "paper-fastener." In course of time a salt
+of copper, green in colour, will be formed, and it will be found that the
+portions of rubber in contact with the fastener have "perished" and become
+tacky.
+
+This contamination of crepe rubber may take place in two ways:
+
+     (1) By the ejection of actual particles of brass from the bearings of
+     machines, due to eccentric grinding of the "standards" of the rolls
+     upon the brass "bushes." These particles are carried by exuded oil or
+     grease into trays, and thence to the rubber.
+
+     (2) By the action of an acid lubricant upon the brass, with the
+     formation of a metallic soap which has a decided green colour, unless
+     obscured by the dark colour of the oil or grease. It is transferred to
+     the crepe rubber in the manner indicated above.
+
+The inevitable effect, apart from the superficial defect, is incipient
+tackiness. The extent to which this may develop will depend upon the amount
+of the copper compound present, but it should be remembered that an
+exceedingly small trace is capable of causing a disproportionately large
+amount of damage. This effect is further magnified if the "tacky" piece of
+rubber is packed in close contact with previously unaffected rubber.
+
+When the defect is discovered, the affected portions should be cut out, and
+the cuttings should be burned. To mix them with the lowest scrap grades, as
+may be done thoughtlessly, is only inviting further trouble.
+
+Besides the source of danger already indicated, it may be found, but far
+less frequently, that contamination may arise from the presence in the
+rubber of small pieces of the brass mesh which is generally used for
+straining latex.
+
+The view appears to be held in some quarters that these tacky streaks and
+patches in crepe rubber may arise from contamination with oil or grease
+alone. This does not agree with our experience. An experiment was made to
+test the point using fresh oil and grease drawn from drums in stock,
+specimens of the same lubricants to which traces of a copper salt were
+added, and samples of lubricants taken from the bearings of several
+machines. The treated pieces of rubber were placed in contact with
+untreated pieces of crepe which served as "blanks."
+
+Notes were made at intervals extending over a period of two years. The
+conclusions arrived at were:
+
+     (1) Although there was surface discoloration, no tackiness had been
+     caused by fresh (unadulterated) lubricant; neither were the "blanks"
+     affected.
+
+     (2) In the majority of specimens upon which had been smeared a small
+     streak of lubricant taken from the bearings of machines, tackiness had
+     supervened, and had developed likewise in the contact "blanks."
+
+     (3) In all cases where a trace of copper salt had been used to
+     adulterate the fresh lubricant, tackiness was to be noted in the
+     course of a short period (a week upwards) after the rubber was dry.
+     Development was slow, but progressive, over the full period of
+     experiment, and the "blanks" in contact were affected. The degree of
+     affection was determined by the proportion of copper salt employed. In
+     the worst cases the affected strip of rubber had deteriorated and
+     disintegrated to such a degree as to cause a distinct longitudinal
+     gap, the edges of which appeared to consist of a moist gummy substance
+     of a deep syrup colour. The adjacent blanks in some cases exhibited a
+     similar appearance in lesser degree, or were merely affected by a
+     characteristic brownish stain.
+
+These observations regarding the possibility of damage to crepe rubbers
+from the existence of brass "liners" or "bushes" in the bearings of the
+machines lead to the natural query as to whether the use of brass is
+necessary. Experience shows that it is not necessary. Machines in use for
+years have been running with plain bearings of iron or other metallic
+substances. Satisfaction is obtained without the use of brass.
+
+COTTON AND OTHER FIBRE.--One of the most frequent complaints made against
+low grade crepes is the presence of fibre--generally classed in a wholesale
+fashion as "cotton-waste."
+
+It is true that some years ago most of the complaints were genuine in
+referring the cause to cotton-waste. The defect arose chiefly owing to the
+careless use of this material in the factory. Lumps of waste when discarded
+were often thrown to the ground, and became mixed with the heaps of scrap
+rubber and bark-shavings awaiting attention. The fault was one of sheer
+negligence, and nothing can be advanced in extenuation. Even when the
+soiled waste was thrown into the external drains, it often returned to the
+factory mixed up with the scraps of rubber recovered by means of the
+drain-screens.
+
+As far as the complaint concerns itself with cotton-waste only, the remedy
+is plain, and lies in the power of the management by reason of the ability
+to restrict the use of "waste" only to the engine-drivers and mechanics.
+
+In the vast majority of cases, however, the defect arises from
+circumstances beyond the direct control of the factory, and under
+conditions which make it difficult to check the evil. Although against
+instructions, and for the purpose of fulfilling other orders, some coolies
+persist in using pieces of cloth for cleaning cups. In course of time,
+unless the practice is detected, this cloth becomes coated with rubber.
+Careless coolies throw it away, when it may be collected by the individuals
+who gather earth-scrap; or it may be brought into the factory in the
+tappers' scrap-bag.
+
+Cases have been known in which the fibrous matter observed in the dry crepe
+rubber was of such a nature as to indicate that the source might be
+attributed to leaf-stalks which had passed through the scrap-washer. It is
+an easy matter to condemn the sorting as being careless, but it is another
+matter to instil into the mind of factory coolies such a respect for easy
+and sane precautions that the practice of them will be continued when the
+eye of the supervisor is not fixed upon the workers.
+
+It will be clear that contamination by fibrous matter should be limited
+practically to the lowest grades of rubber.
+
+The appearance of cotton-waste in high-grade crepes must be most unusual,
+and the writers have not yet seen a case in a drying-house. That it does
+occur, however, seems to be evident from brokers' reports. It is extremely
+difficult to imagine how the waste enters the rubber. One possible
+explanation is that a coolie may have been cleaning the rolls
+surreptitiously with waste, which may have passed later into the rolls
+together with rubber. Another explanation was offered in one factory by the
+observed fact that coolies engaged in cutting up coagulum, ready for
+passing into the machines, kept a wad of waste for the purpose of keeping
+the knife-blade clean. This may have found its way into the rolls. It must
+be recorded that in the course of many years of experience no case has been
+seen in any drying-house of contamination of the higher grades of crepe by
+fibrous matter.
+
+BARK AND GRIT.--With ordinary machines and the usual process of working, it
+would seem impossible to wash and macerate some of the scrap rubbers
+sufficiently to free them entirely from bark. This applies specially to the
+grade of rubber prepared from bark-shavings. Specimens have been handled in
+which it was practically impossible to detect bark, but in such instances
+the amount of working necessary would be such as to interfere seriously
+with the regular working of the factory. Even with the employment of
+special scrap-washing machines, complaints of the presence of bark in dry
+crepe have been received, but it is certain that this mode of operation
+reduces the quantity of bark to a minimum. While fully realising that the
+amount of working it is possible to give in proportion to the existing
+machinery and the output per day is limited, it must be recognised that the
+working of lower grades of rubber is usually insufficient, and that where
+possible it is the duty of estates to pay more attention to these lower
+grades. A considerable improvement in this direction has been noticed of
+recent years. It is not uncommon to encounter managers who fail to
+appreciate that complaints regarding the presence of bark in the lower
+grades are founded on legitimate grounds, and that they are not frivolous
+objections put forward for the purpose of depressing the price of the
+article. The sooner such an idea is jettisoned the better. There would
+appear to be a good future demand for the lower grades, and it is only
+natural that consumers will be willing to pay the best price only for an
+article which is clean.
+
+The same arguments apply to the complaints regarding the presence of sand
+and grit. The quantity of the latter found in low-grade crepes from some
+estates is surprisingly high. Its presence can often be shown by the simple
+device of spreading a piece of crepe over the upturned and hollowed palm of
+one hand, while striking the rubber with the other hand.
+
+The incidence of bark in higher grades of crepe may be due to inadvertence
+or to gross negligence. In the former class one might put those occasions
+on which pieces of bark are embedded in lumps of naturally coagulated
+rubber. A piece of bark-shaving may fall unnoticed into latex and be
+partially responsible for the coagulation which takes place. This piece of
+coagulated lump may be massed with others, and hence, unless each small
+piece is cut up, the bark is not perceived. Or again, by some unknown
+means, a piece of shaving may drop into a jar of latex, and so become
+embedded in the coagulum. Sometimes this becomes evident on cutting up the
+rubber, but it is quite as likely to pass unseen. On the whole, the
+presence of bark in first-grade rubber is most unusual, and should be seen
+before the rubber is packed.
+
+In the class due to negligence may be included cases in which careless
+coolies place the cup upon the ground before tapping. Pieces of shavings
+fall into the cup, and coolies are too lazy to pick them out. More often
+than not coagulation in the cup is caused. As it is impossible for the
+European staff to supervise each individual tree tapped, some cases must
+continue to pass unheeded. Sometimes bark-shavings are brought in with the
+latex, and if a broken sieve is being used, these, with other impurities,
+pass into the jar, and are embedded in the coagulated rubber. This must be
+classified as negligence, for no manager would willingly allow the use of a
+broken sieve. Again, naturally coagulated lump rubber on arrival at the
+factory sometimes contains evident pieces of bark, leaves, and stems of
+leaves. For lack of supervision the average coolie would not think of
+picking out these obvious impurities, and would pass the whole mass into
+the machines.
+
+OXIDATION STREAKS.--Since the introduction of sodium bisulphite defects due
+to streaks, caused by portions of the coagulum becoming oxidised, have
+practically ceased to exist. In the usual course, and without the use of an
+antiseptic agent, the freshly coagulated rubber has a surface darkened by
+oxidation. Unless this dark surface were carefully cut off, there would
+result a crepe containing dark streaks caused by the mixture of the
+oxidised surface portion with the bulk of the paler coagulum. The presence
+of oxidation streaks in No. 1 crepes, now being made, would imply either
+that no anti-oxidant substance was in use, or that the quantity necessary
+to prevent this surface oxidation is exceedingly small. Although the price
+obtained would appear to be influenced by the presence of oxidation
+streaks, no evidence can be obtained that the actual quality of the rubber
+suffers to the same degree as does the appearance--_i.e._, there is no
+evidence to show that a pale rubber, in which surface oxidation has been
+inhibited, is intrinsically superior to one in which slight natural
+oxidation has been incident.
+
+"YELLOW LATEX" STREAKS.--This appearance of "yellow-latex" streaks in not
+common, and may be accounted for by incomplete mixture of two different
+latices. It is a fact of common observation that, when a new portion of
+bark is being tapped for the first time, there is a distinct yellow tinge
+in the latex excluded. As tapping progresses, this colour vanishes; usually
+it may persist for a period varying from two weeks to more than a month.
+Should this latex be poured into ordinary latex without thorough mixing, it
+is sometimes found that, when the crepe rubber is dry, there are distinct
+yellow streaks. It should be remembered that, as the rubber content of the
+latex from first tappings is high, this latex is lighter than latex which
+is more dilute, so that the mixed latices must be well stirred with a broad
+paddle to obtain intimate mixture. It would be much better to keep yellow
+latex apart, and coagulate it separately, if at all possible. In such case
+the resultant crepe may be of a distinct canary yellow in tint.
+
+In scrap-crepes of the higher grade this distinct yellow colour is often
+visible in streaks which indicate the presence of tree-scrap, etc.,
+obtained from recently opened tapping areas.
+
+BISULPHITE STREAKS.--These, again, arise from defective mixing. In the dry
+rubber it is seen that there are streaks of colourless rubber in a general
+mass, which may be of varying shades of yellow; or, a length of exceedingly
+pale rubber is apparently streaked in patches with a darker shade of
+colour. A solution of sodium bisulphite is heavier than latex, and there
+would be a tendency, therefore, for the chemical to sink in the large
+mixing jar. Unless stirring is thorough it is possible that portions of the
+latex would not be in contact with sodium bisulphite while others receive
+more than a fair share. Especially would this effect be seen where
+coagulation takes place quickly, and experience bears out the truth of the
+suggestion. Another factor which has some bearing on the point is the
+strength of solution in which sodium bisulphite is used. In the ordinary
+course of working, the acid coagulant is added immediately after sodium
+bisulphite has been stirred in. Should a strong solution of the bisulphite
+be used, and if coagulation takes place quickly, it is easy to see that the
+possibilities of obtaining a uniform and intimate mixture are small.
+Probably in no factory is the sodium bisulphite now added to latex in
+powder form, but it has been found that if care is not taken to see that
+all the bisulphite has dissolved before the solution is added to latex
+streaks may result in the dry rubber. The undissolved particles sink to the
+bottom of the coagulating jar or tank, and there slowly dissolve, forming
+local strong solutions. The effect upon the rubber in the vicinity of these
+strong solutions is much more marked than in the bulk of the coagulum, and
+hence lighter streaks or patches appear in the dry rubber. In spite of
+apparently complete mixture by good stirring, it will be seen that it is
+possible, therefore, to have failed in this direction if any undissolved
+powder remains in the solution of sodium bisulphite.
+
+"SPOT" DISEASE.--Few managers of estates preparing pale crepe rubbers are
+unacquainted with this defect. It is manifested by the appearance of small
+coloured spots varying in density (_i.e._, number to a unit area) and
+differing in hue. The most common colours are black and orange, but "spots"
+of brick-red, yellow, violet and ruby and green tints have been noted, the
+last named very seldom. Sometimes in place of definite "spots," or
+colonies, the colour is spread over practically the whole surface of the
+rubber as a "flush."
+
+These coloured spots, or "flushes," indicate infection by minute fungi,
+which are present in the latex prior to coagulation. The infection of the
+latex takes place in the field by means of spores, which are only visible
+with a microscope.
+
+It is not feasible to discuss any method of preventing this infection of
+latex by air-borne spores, as the eventual preventive measures are so
+simple. But it may be believed that under ordinary weather conditions most
+latices are infected before reaching the factory. It is likewise true that
+even fine pale crepes shipped in perfect condition may contain
+possibilities of trouble in the form of "dormant" spores, the development
+of which may commence and continue if favourable conditions arise.
+
+The subject of "'Spot' Diseases" has been treated fully in previous
+publications,[19] and it is not proposed here to enter into any lengthy
+discussion.
+
+[19] "Preparation of Plantation Rubber," Sidney Morgan, 1913. "Spotting of
+Plantation Rubber," Keith Bancroft, 1913; Bulletin No. 16, F.M.S.
+Department of Agriculture. "Spotting of Prepared Plantation Rubber," A.
+Sharpies, 1914; Bulletin No. 19, F.M.S. Department of Agriculture.
+
+If any reader is desirous of producing the defect experimentally, all that
+is necessary is to prepare a piece of crepe rubber of rather more than
+ordinary thickness, roll it up while wet, and place aside for some days.
+
+This experiment reproduces the conditions favourable for the development of
+the spores, and spots of various colours may result. It will be clear that
+the chief factor influencing the result is the continued presence of plenty
+of moisture.
+
+This condition may be created inadvertently in the course of factory
+practice, if piles of crepe rubber are allowed to remain for any
+appreciable period before hanging to dry. For this reason batches of wet
+crepe should always be placed on edge, to allow free drainage of surface
+moisture, if the rubber cannot be taken at once to the drying-sheds.
+
+[Illustration: THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM "SPOT"
+DISEASE.]
+
+The condition also is provided if the thickness of the crepe is
+excessive. In some factories, having no smooth-roll finishing machines, the
+crepes may have a distinct raised pattern upon them. It is usual to note
+that if "spot" disease appears in such crepes, it is incident to much
+greater degree in the thicker portions of the rubber--_i.e._, upon the
+raised pattern.
+
+The direct connection between the rate of drying and the appearance of
+coloured spots or flushes is thus established, and it only remains to adopt
+precautionary measures which will lead to an avoidance of delay (1) between
+machining and hanging, (2) in drying.
+
+It is indicated, therefore, that, if spot disease is to be avoided, the
+prime consideration is the preparation of a thin crepe which will dry
+quickly under average conditions. It may sometimes happen that even very
+thin crepes will sometimes be found affected on some estates. In such
+instances, it will be found that the design or situation of the
+drying-house is at fault, and that specially favourable conditions for the
+development of the fungi have been created by excessively wet weather.
+Should the trouble persist in spite of the preparation of the thinnest
+crepe, it would be advisable either to abandon this form of No. 1 product
+or to consider the installation of artificial aids to drying.
+
+We have not yet encountered any case in which it was found necessary to
+treat the latex with an antiseptic or disinfectant substance for the
+prevention of "spot" disease. There appears to be an idea held in some
+quarters that sodium bisulphite may be so employed as a fungicide. This
+does not agree with our experience, which is confirmed by Sharpies
+(Bulletin No. 19, F.M.S. Department of Agriculture).
+
+In 1913 experiments with chinosol were undertaken at the Pataling
+Laboratory of the Rubber Growers' Association, and an account of the method
+of treatment was given in a printed report issued to subscribers. Dr. P.
+Arens,[20] of the Malang Experimental Station (Java), has also recommended
+the use of chinosol. The substance is expensive, but is effective in very
+small quantity. On the whole, given average conditions in factory practice,
+such aids should not be necessary, and where keen supervision is not
+available may lead to other difficulties.
+
+[20] "Guide to the Preparation of Rubber," Arens, 1918; Communications from
+the Experimental Station (Malang, Java).
+
+It has already been remarked that it is possible for "spot" disease to
+develop in dry rubber which previously gave no evidence of the presence of
+fungi. The condition necessary to such an occurrence is supplied by the
+presence of moisture. Thus, to state instances which are by no means
+uncommon, if a box of rubber is allowed to remain exposed to rain, or is
+damaged by flood-water, or by sea-water during transit, or (sometimes) if
+the rubber is packed in a damp case, the crepe on arrival at its
+destination may be found to be affected to a degree dependent upon the
+extent of wetting and the duration of the wetting period.
+
+No means are known by which these coloured spots, due to the growth of
+chromogenic organisms, can be removed from the rubber. Naturally, although
+they may be present in the darker lower grades of crepe, they are not so
+easily visible as in pale crepe. It follows, therefore, that every possible
+precautionary measure must be taken when pale crepe has to be prepared.
+
+We are often asked whether it is possible for an infected piece of rubber
+to affect sound rubber hanging in the same building; and whether, in case
+of "spot" disease appearing, it is necessary to disinfect the drying-house.
+
+In a general sense, the answer to both queries is in the negative. It has
+not been proved possible to transmit the disease from one piece of crepe to
+another, except by the closest possible contact and in the presence of an
+abundance of moisture.
+
+A dry crepe, even when in close contact with an infected dry specimen, has
+not been found to be affected.
+
+Unless, therefore, pieces of rubber are pressed together, under favourable
+conditions as to moisture, there has been observed no transfer of disease.
+
+Similarly it has not been found that the presence of spotted rubber in one
+part of the drying-house has been responsible for an outbreak of disease
+in another part of the same building. Furthermore, after the removal of
+diseased rubber from the drying-shed, freshly prepared rubber may be hung
+on the same supports without becoming affected, and without any
+intermediate treatment of the wooden bars, providing the crepe is thin and
+weather conditions are good. In our experience, no case has been observed
+in which the disease has been communicated to freshly prepared rubber by
+reason of the previous presence of affected rubber. In our opinion,
+therefore, any scheme for disinfecting the interior of a drying-house, as a
+preventive measure against the spread of "spot" disease, is unnecessary.
+
+All other things being equal, it is plain that much will depend, as to the
+incidence of coloured spots, upon the design and situation of the
+drying-house. Sufficient has been written in previous chapters to indicate
+the importance of these points as affecting the rate of drying, upon which
+hinges the possibility of the appearance of "spot" disease.
+
+In conclusion, the chief points in any discussion of this subject may be
+summarised thus:
+
+     1. No coagulum should be left without working for longer than the
+     ordinary period. Otherwise, the prevailing conditions are very
+     favourable for the development of the disease.
+
+     2. Thin crepe only should be made. The quicker the rate of drying the
+     less possibility is there of the coloured spots appearing.
+
+     3. Crepe should never be allowed to remain folded overnight, and
+     batches of folded wet crepe should be placed on edge to drain off
+     surface moisture. The rubber should be hung to dry as soon as
+     possible.
+
+     4. Several species of fungi causing coloured spots have been
+     recognised, and it has been proved conclusively that it is possible to
+     infect latex and also fresh coagulum.
+
+     5. As far as our present knowledge goes, it appears that infection
+     takes place chiefly, if not entirely, by means of the latex in the
+     field-vessels. It may take place during transport also, or even during
+     coagulation.
+
+     6. While it is certain that infection can be caused by contact, it has
+     not yet been shown that infection of the finished wet rubber takes
+     place in the drying-houses by means of air-borne spores--at least,
+     under ordinary drying conditions.
+
+     7. There is reason to believe that no further infection takes place
+     once the rubber is well into the drying stage, and that dry rubber is
+     not infected even by contact. From this one might infer that, as long
+     as rubber remains dry, infection cannot take place during the voyage
+     to the port of consignment.
+
+     8. Coloured spots do not appear until the rubber is about half dry,
+     because that period is necessary for the development of the fungus to
+     that stage in its life-history when it excretes colouring matter. The
+     fungus in its earlier and colourless stage may have been present from
+     the time the latex entered the cup.
+
+     9. The natural habitat of the fungi would appear to be decaying
+     vegetable matter in the field.
+
+     10. Finally, if it is found impossible to be rid of fungoid-spot
+     disease after having exercised all care and observed all known
+     precautions, nothing remains but to supersede the ordinary drying
+     process by some system of quick drying, such as the vacuum-drying
+     process or a hot-air draught system, in which the rubber dries so
+     quickly that any possibility of appearance of "spots" is entirely
+     removed.
+
+SURFACE MOULDS OR MILDEWS ON CREPE RUBBER.--Defects of this nature are most
+uncommon in the higher grades of crepe rubber, but cases of affection in
+the lower grades are not rare.
+
+It will be evident from all previous discussions that the incidence of
+these moulds must be due to an extremely slow rate of drying. The necessary
+conditions would be supplied by one or more of the following causes:
+
+     (_a_) Making the crepe too thick.
+
+     (_b_) Hanging the crepe in a badly ventilated or badly situated
+     building.
+
+     (_c_) Occasionally by abnormally wet weather.
+
+     (_d_) Allowing piles of crepe to remain too long before hanging.
+
+     (_e_) Using excessive quantities of deteriorated sodium bisulphite. In
+     short, any factor contributing towards a retarded rate of drying may
+     be responsible for the appearance of surface mildews. The last
+     mentioned cause is of not infrequent occurrence. Knowing the chemical
+     to be of poor quality, relatively more is used to produce the desired
+     anti-oxidant effect. Unless the rubber is particularly well washed on
+     the rolls, there remains within it a residue of sodium _bisulphate_,
+     an oxidation product of the bisulphite. This is hygroscopic to some
+     degree--_i.e._, it takes up moisture from the atmosphere. Hence
+     drying is delayed, and even should mildews not develop the chemical
+     may sometimes be seen on the surface of the rubber as a whitish
+     "bloom."
+
+The enumeration of the possible causes of mildews on crepe rubber is
+sufficient to indicate the necessary precautions to be taken, and the
+discussion will not be extended further.
+
+TACKINESS IN RUBBER.--"Tackiness" is a term used to denote a deterioration
+of rubber which renders it sticky, and, beyond this, implies that some
+physical and chemical change in the nature of the substance has taken
+place. In fact, it is no longer "rubber," but an oxidation product
+containing much resinous matter. It does not behave as rubber, and hence
+its value is much depreciated.
+
+With modern ideas of erection of factories to guard against the
+introduction of direct sunlight, it was hoped that this defect had
+practically ceased to exist. In one grade of rubber it would be expected
+that tackiness would continue to appear. Earth-rubber, often exposed to
+direct sunlight for a week, would naturally become tacky, and this
+tackiness cannot be avoided unless the earth-scrap is to be collected more
+frequently. But in many cases even the higher grades of rubber show signs
+of tackiness. Experiments have been carried out at various times and in
+various places to determine the cause of tackiness. For some time the
+theory of bacterial origin was in favour, but none of the experimental
+results was convincing. Bacteria may be present in tacky rubber; but, on
+the other hand, many cases of bacteria in rubber have been observed in
+which there was no tackiness. Experiments were made by one of us some years
+ago with a view to testing the bacterial theory by inoculating latex with
+small pieces of tacky rubber. In opposition to the results which were
+stated to have been obtained, there was no spread of tackiness. Other
+investigators have obtained similar results. One writer proposed to explain
+tackiness as caused by excess of moisture. This perfectly simple
+explanation unfortunately displays only a profound ignorance of the
+subject, and does not take into account the fact that tackiness is incident
+in rubber after dryness has been reached. It need not be pointed out to
+planters in Malaya that wet sheets of rubber are often exposed to direct
+sunlight by workers of native holdings, with no resulting harm as long as
+plenty of moisture is present in the rubber.
+
+TACKINESS THE RESULT OF A SLOW PROCESS OF CHANGE.--As stated above,
+tackiness does not appear until the rubber is dry, and even then it is to
+be noted that it is possible for tackiness to appear in rubber arriving in
+London, which showed no indications of tackiness when packed for shipment.
+
+TACKINESS CAUSED BY TRACES OF COPPER SALTS.--Spence, as the result of
+investigations, has pointed out that none of the various theories put
+forward to account for tackiness--viz., the action of bacteria, premature
+putrefaction, oxidation, excess of moisture, the action of enzymes,
+etc.--have any basis in scientific proof, and believes that the cause of
+tackiness cannot be directly attributed to bacteria. It has been stated
+that the only known way of causing rubber to become tacky is to expose it
+to sunlight or heat. While agreeing that in the ordinary way this statement
+is correct as far as one rules out the employment of chemical substances,
+it must be pointed out that tackiness of the worst degree may be caused by
+the presence of traces of copper or copper salts. This point has already
+been touched upon in a preceding paragraph dealing with the defect of
+"green streaks" in pale crepe rubber.
+
+In the course of laboratory experiments tackiness has often been induced by
+the use of traces of copper salts. The rate at which tackiness is induced
+appears to be dependent upon the amount of copper salt used, but once it
+begins, the rubber molecule is very rapidly broken down, and resins are
+formed. As the formation of resins is accompanied by the inclusion of
+oxygen in the chemical constitution, it would be expected that dry rubber
+becoming tacky should increase in weight. This is found to be the case, and
+to give an idea of how this weight increases with the progress of
+tackiness, the results below may be studied.
+
+It will be seen that the maximum quantity of copper sulphate used amounted
+to 0.025 per cent, (approx.) upon the weight of latex taken. Now it is
+highly probable that only a fraction of this quantity was retained in the
+rubber on coagulation, the remainder being in solution in the serum.
+Furthermore, as the rubber was well washed and worked down to thin crepe,
+_the total quantity of copper salt remaining in the dry crepe must have
+been exceedingly small_. Yet the effect is most marked and should impress
+upon all managers the necessity for guarding against any possible
+contamination caused by brass or copper.
+
+  ----------+-----------------+--------------------------------------------
+  _Sample._ |                 |             _Weight of Rubber._
+     +------+                 +------+--------+--------+--------+----------
+     |                        |      | After  |Further |Further | Percent-
+     |_Amount of Copper Salt._| When |Interval|Interval|Interval|age in In-
+     |                        | Dry. |of Four |of Seven|of Three|crease in
+     |                        |      | Weeks. | Weeks. | Weeks. | Weight.
+  ---+------------------------+------+--------+--------+--------+----------
+     |                        | Grms.| Grms.  | Grms.  |  Grms. |
+   1 |0.02 grms. copper       |      |        |        |        |
+     |sulphate per 100 c.c.   | 430  |  441   |  482   |  488   |   13.5
+     |latex                   |      |        |        |        |
+   2 | Ditto                  | 428  |  439   |  481   |  486   |   13.55
+   3 |0.01 grms. copper     } |      |        |        |        |
+     |sulphate, per 100 c.c.} |      |        |        |        |
+     |latex                 } | 962  |  987   | 1035   | 1036   |    7.7
+     |0.01 grms. copper     } |      |        |        |        |
+     |acetate, per 100 c.c. } |      |        |        |        |
+     |latex                 } |      |        |        |        |
+   4 |0.025 grms. copper      |      |        |        |        |
+     |sulphate, per 100 c.c.  | 502  |  513   |  558   |  560   |   11.5
+     |latex                   |      |        |        |        |
+  ---+------------------------+------+--------+--------+--------+----------
+
+In view of the effect thus produced by the addition of traces to latex of a
+copper salt, and the observed effect on rubber of contact with copper
+salts, one may imagine the result produced some years ago when on an estate
+smoked sheets were washed with a solution of copper sulphate as a remedy
+for surface moulds!
+
+With the exception of this chemical action we know of no other means by
+which tackiness is produced, beyond those of direct sunshine and heat.
+Cases governed by these two causes are common on estates. They are confined
+chiefly to the lowest grades of scrap rubber, when the component raw
+materials have been exposed to the sun for a period before being brought to
+the factory.
+
+It is now comparatively rare to find cases of tackiness in the higher
+grades of crepe, and when they occur, one may look for evidence of gross
+carelessness in the admission of direct sunshine. Usually this means the
+failure of some individual to regulate window shutters according to the
+position of the sun in the sky. More rarely does it happen that tackiness
+may have been induced by placing thin crepe rubber too near the iron roof
+of the drying-shed.
+
+Regarding the question as to whether tackiness may be communicated by
+direct contact, opinion appears to be divided. It has been stated that
+sound rubber left in contact with tacky specimens was found to be
+unaffected after two years. On the other hand, it is claimed that tackiness
+has been induced in a sound rubber by infecting it with small pieces which
+were tacky. In a preliminary article on the effect of copper and copper
+salts upon pieces of dried and sound crepe[21] it was noted, after one
+year, that tackiness had been communicated from the treated portion to the
+"blank" in contact. There is sufficient evidence to warrant the injunction
+that tacky rubber should be excluded from contact with sound rubber. If
+shipped it should be packed separately.
+
+[21] Report I., 1916 (Sidney Morgan), Rubber Growers' Association (Malaya).
+
+Compounds have been put upon the market which assumedly claim to be cures
+for tackiness. These are merely palliatives, consisting of starch, talc, or
+chalk powders, which counteract stickiness.
+
+NO CURE FOR TACKINESS.--At the present stage of our knowledge, there
+appears to be no cure for tackiness. Neither do we see the necessity for a
+cure when the phenomenon may be avoided by taking simple precautions, which
+may be briefly summarised thus:
+
+     (1) Any permanent openings through which it is possible for direct
+     sunlight to enter, whether large or small, should either be totally
+     closed or provided with some substance which cuts off the direct
+     effect of the sunlight--_e.g._, ruby glass or ruby glazed cloth.
+
+     (2) Rubber should under no circumstances be placed near any source of
+     heat.
+
+     (3) No rubber should be hung in a drying-room in such a position
+     adjacent to a window or door that it is possible for sunshine to reach
+     it, even should coolies neglect to obey rules.
+
+     (4) Instruments or vessels of copper or brass should not be used where
+     acids are employed.
+
+LACK OF UNIFORMITY IN COLOUR.--The complaint is far less real than it was
+a few years ago. The introduction by the Rubber Growers' Association of the
+"Metrolac" led to uniform dilution of latices varying in rubber content.
+Previously the only known method of obtaining uniformity in colour and
+appearance was that by which latices from all fields were mixed together in
+bulk. Even so the uniformity applied only to the one bulking operation, and
+any other day's results might show considerable variation from the first
+standard.
+
+This does not take into account any observed differences in shade of colour
+attributable to natural oxidation which might vary in intensity from day to
+day. The introduction of sodium bisulphite as an anti-oxidant exerted a
+great influence upon the colour of pale crepes generally; but considerable
+variation would still have been notable but for the adoption of the scheme
+for uniform dilution, in addition to the use of small quantities of
+anti-oxidant.
+
+On most estates it is now possible, with slight exceptions due to abnormal
+conditions, so to treat the latex that the pale crepes prepared on any one
+day differ in no perceptible degree from the product of any other day.
+Where this is not the case it must be suspected that there has been some
+carelessness in manipulating the latex or the chemicals. Attention has been
+drawn to the fact that there may be exceptional cases, when the determining
+factors lie beyond the control of factory processes--_e.g._, heavy rains
+causing over-dilution of latex, the yielding of "yellow" latex from newly
+opened areas, etc. But on the whole there is now no reason why the general
+average product from any estate should not be uniform in colour and
+appearance. Furthermore, it should be possible for large groups of estates,
+by the adoption of uniform methods, to produce similar rubber from all the
+plantations. Moreover, apart from some differences caused by factors which
+still need determination, the total product in a general sense should not
+only be uniform in appearance but uniform in physical and chemical
+properties.
+
+BLOCK RUBBER.--This mode of preparation is employed only in comparatively
+few instances. The block is prepared from crepe rubber, which has been
+dried either in a hot-air drier or in a vacuum chamber.
+
+There is another type of block which is made by placing layers of dry crepe
+under considerable pressure. This is not the true type of block, and the
+layers are quite distinct--_i.e._, they do not amalgamate. Usually this
+pressed rubber consists of lower grades of crepe, and it should not be
+popular, inasmuch as it leaves too wide an opportunity for the inclusion of
+dirt, bark particles, and other impurities, which cannot be seen generally
+on account of the protective colour of the rubber.
+
+In the true type of block, the layers are in a plastic condition, due to
+heat, when they leave the drying-chamber; and being immediately submitted
+to great pressure the result is a homogeneous mass in which the layers
+disappear by amalgamation. Only the best grade of crepe is employed, and
+given the absence of defects in the layers there should be no complaint
+regarding the final block.
+
+Prepared in slabs which are three or four inches in thickness, the product
+is easily handled, and should be sufficiently translucent to make it
+possible to distinguish the shape of the hand when held between the block
+and the light. This is not possible when blocks are made of greater
+thickness.
+
+The only complaints which it should be possible to lodge against block
+rubbers are:
+
+     (_a_) The inclusion of dirt and other matter.
+
+     (_b_) The use of layers of crepe which have some defect.
+
+     (_c_) The inclusion of air-bubbles.
+
+The remedy for (_a_) and (_b_) lies in the hands of the factory
+superintendent. The last ground of complaint is dependent upon the style of
+preparation of the original layers of crepe.
+
+When layers of crepe are placed one upon the other, and submitted to great
+pressure, it is natural to suppose that air would be contained in spaces,
+and would be unable to escape. To guard against this, it would seem
+necessary to prepare the crepe thin and with a fairly good surface finish.
+
+It must be obvious to all acquainted with the processes involved in the
+preparation of block rubber, that no possibility exists for the presence
+of air-bells actually enclosed _in_ thin crepe. When the vacuum-dried crepe
+is folded preparatory to the blocking process it is apparent that between
+the layers there must always be a considerable volume of air, a small
+proportion of which is bound to be retained owing to the nature of the
+surface of crepe rubber.
+
+That this has always been true of the preparation of block rubber cannot be
+denied. It is possible, of course, for one type of block to show the
+presence of air-bells more than another type, the proportion of air
+enclosed in blocking depending upon the nature of the crepe of which the
+block is composed. A block built up of layers of smooth, fine crepe would
+be expected to contain less air-bells than a block composed of layers of a
+rough crepe.
+
+Block rubber has been seen which was free from air-bells, but this was the
+thin variety of block prepared for show purposes with far greater care,
+probably, than would be expended in commercial preparations.
+
+
+
+
+CHAPTER XVIII
+
+_DEFECTS IN SHEET RUBBER_
+
+
+Before proceeding to deal with defects in the rubber as it is put upon the
+market a brief account will be given of faults which may be noted in the
+preparatory stages.
+
+MILKY RESIDUE OR SERUM.--If the serum is not clear after the ordinary
+period allowed for coagulation, it indicates one of the following possible
+causes:
+
+     (_a_) Failure to obtain complete mixture by thorough stirring.
+
+     (_b_) Insufficiency of acid solution. This may be real or indirectly
+     due to the presence of an excess of anti-coagulant such as formalin or
+     sodium sulphite.
+
+     (_c_) In cases where other coagulants than acetic or formic acids have
+     been employed the failure may be due to an excess of, or an
+     unsuitable, coagulant--_e.g._, hydrochloric acid.
+
+COLOURED SURFACE BLOTCHES AND UNPLEASANT ODOUR.--Sometimes the surface of
+the coagulum exhibits yellowish or bluish streaks and patches. It will be
+found generally that the yellowish colour is possessed by a slimy
+substance, of offensive odour, which may be scraped from the surface.
+Either insufficient acid has been used, or the mixing of latex and
+coagulant has been at fault.
+
+DARK DISCOLORATION OF THE RUBBER.--This may be stated to be a natural
+process when fresh rubber is exposed to the atmosphere. It is usually
+described as "oxidation," and it will be noted to be absent, or to occur to
+less degree, on those portions of the rubber which are protected from the
+atmosphere by being below the surface of the remaining liquid. This surface
+change may be prevented (see Chapters VIII. and IX.) by the use of small
+quantities of sodium sulphite (for preference) or bisulphite.
+
+SOFT COAGULUM, SPONGY UNDER-SURFACE, TEARING OF COAGULUM.--If the whole
+mass of coagulum is too soft, while coagulation appears to be complete,
+over-dilution of the latex has occurred. This may apply also to the case in
+which the under-surface only is spongy and soft. If coagulating-tanks are
+employed, the upper edge may be comparatively hard, while the lower is soft
+and weak. Often the spongy portion may adhere to the partitions. This
+prevents the natural rise of the coagulum, due to retraction, as the mass
+"sets." The pull between the free upper portion and the adhering lower edge
+causes splitting and tearing of the coagulum, with marked porosity (spongy
+appearance). The two factors to receive attention are the standard of
+dilution and the condition of the surfaces of the partitions. If these have
+minute cracks into which latex can penetrate, and in which coagulation
+takes place, the boards should be discarded. Given the conditions indicated
+above, the tearing and splitting of rubber in coagulating tanks is
+sometimes augmented by the practice of flooding the tanks when coagulation
+is judged to be complete. The surface water finds its way downwards between
+strips of coagulum and the partitions, thus increasing the upward tension
+between the free and adhering portions. The main idea governing the
+practice of flooding the tanks is to prevent "oxidation" (darkening) of the
+upper edges. If a small quantity of sodium sulphite is employed as an
+anti-oxidant and to retard coagulation, it is not necessary to flood tanks.
+
+"PITTING" OF SURFACES.--In pan coagulation this "pitted" appearance is
+usually limited to the under-surface, while coagulum prepared in tanks may
+exhibit the defect on both faces. The existence of these numerous "pits,"
+or small depressions, points to the presence of bubbles of gas which have
+been unable to escape freely. As the formation and retention of gas-bubbles
+is not a normal occurrence in coagulation, we are led to infer that some
+special conditions must have arisen. These may be supplied by one or more
+of the following contributory causes:
+
+     (_a_) The latex had begun to "sour" before arrival at the factory or
+     while waiting to be treated. This premature coagulation is usually
+     checked or diminished by the employment of anti-coagulants (see
+     Chapters VIII. and IX.). It is generally accompanied by the
+     appearance of enclosed gas-bubbles in the dry rubber.
+
+     (_b_) There may have been a slight insufficiency of coagulant, or the
+     admixture was not thorough, thus allowing a slow putrefactive change
+     to take place in the incompletely coagulated areas.
+
+     (_c_) The wooden partitions may not have been effectively cleansed.
+     The existence of a thin slime, of bacterial origin, is sometimes
+     noted. This is accountable for putrefactive effects in the surfaces of
+     the coagulum, or in the serum, giving rise to the formation of gases.
+     If these cannot escape freely, by reason of adhesion between the
+     coagulum and the partitions, "pitting" occurs.
+
+THICKENED ENDS OR EDGES, AFTER ROLLING.--As a rule these defects may be
+ascribed to the employment of too rich a latex, or faulty manipulation.
+Even if the standard of dilution should be correct it sometimes happens
+that, in the preliminary rolling of a long strip of rubber, coolies begin
+in the middle, rolling with a forward pressure and tension towards the ends
+of the strip. This is generally not so much the fault of the coolie as
+being due to the lack of proper facilities for preliminary rolling. The
+table should be about 3 feet in height, so that ease of working is obtained
+merely by natural pressure due to the position in which the worker stands.
+The use of a heavy wooden roller would contribute towards this result,
+inasmuch as it obviates the use of force, and the pressure is almost
+entirely in a vertical direction.
+
+MIS-SHAPEN SHEETS.--It is sometimes noted that sheets may be wider and
+thicker at the ends than in the middle. Manipulation alone, as indicated
+above, is not solely responsible. The primary cause is to be traced to
+over-dilution of latex, giving a very soft coagulum which responds too
+readily to tension and pressure. Faulty treatment in rolling exaggerates
+the tendency for the strip of sheet to become narrow and thin in the
+middle, wider and thicker at the ends.
+
+THICKENED PATCHES, TORN SHEETS, "DOG-EARS," CREASES.--These elementary
+defects are all due to careless working. While occasional errors cannot be
+avoided, there is no real excuse for the continuance of trouble to any
+degree, under average supervision.
+
+Thickened patches are often caused in conjunction with torn sheets, and
+the trouble may be ascribed to faulty practice in allowing too heavy a pile
+of wet strips to accumulate before machining. Or a comparatively small pile
+may have been transported some distance. It is difficult to separate the
+strip, and occasionally the separation is only effected at the expense of
+two sheets, one of which is torn and the other has a portion of the first
+strip adhering to it.
+
+"Dog-ears" due to the folding over of corners of the sheets, and creases
+due to the rumpling of the coagulum, are generally the result of haste and
+lack of average care. Machine coolies, more often than not, will not be at
+any pains to straighten out folds before passing the coagulum through the
+rolls.
+
+GREASINESS BEFORE SMOKING.--Under ordinary methods of working this should
+never be encountered. It may be taken to show that the machined rubber has
+been allowed to remain, either hanging or in piles, far too long before
+entering the smoke-house. The appearance is most marked if the rubber has
+remained in a cool and moist atmosphere--_e.g._, if it has been hanging
+over-night in a closed and badly-ventilated factory. In a marked degree
+this is to be observed in the preparation of air-dried sheets, unless they
+are exposed, when freshly prepared, to the action of the sun for a period.
+This period, in the case of rubber prepared on native small-holdings,
+generally extends over several days--until the sheets are more than half
+dry.
+
+In the preparation of smoked sheet, the greasy appearance and the cause
+outlined contribute to a defect which is eventually described as
+"stretching rusty."
+
+SURFACE BLEMISHES.--The coagulum, during coagulation and subsequently, can
+be contaminated in various ways. In most cases a little intelligence or
+increased care would prevent the occurrence of these defects.
+
+When the coagulum remains over-night, in the absence of a cover, it is not
+uncommon to note the presence of dirt (from the roof above, or blown in
+from the outside), the droppings of mice and rats, flies and small insects.
+In theory these should be seen and removed by the factory hands. In
+practice, except while under immediate supervision, the extraneous matter
+is often rolled into the soft coagulum.
+
+A fairly common cause of this surface contamination is the exhaust from the
+power-unit; generally the worst offender is a steam-engine. Grit and smuts
+continually find their way into the factory, alighting on the tables, in
+the latex, in the water, and on the freshly prepared rubber. They are
+rolled into the soft rubber and lead to marked depreciation in the selling
+value. The radical remedy seems obvious, but is often beset with many
+difficulties not unconnected with financial considerations.
+
+Other superficial blemishes, such as those due to the presence of rust
+marks, oil or grease patches, etc., are self-explanatory, if a little
+thought is brought to bear upon them; and it is not proposed here to
+discuss such defects more fully.
+
+       *       *       *       *       *
+
+Having now dealt with certain defects which are visible in wet rubber, we
+come to the discussion of others which are only perceptible either during
+or after the drying period. As far as is known no plantations of any size
+now prepare sheets other than in the form of smoke-dried rubber, with the
+exception of a few which make a special form of thick and partially
+air-dried product known as "slab" rubber.
+
+It is not proposed, therefore, to treat in any detail with air-dried sheet
+rubber. Certain obvious defects are common to both air-dried and
+smoke-cured sheets, and these will be first discussed.
+
+UNEVENNESS OF APPEARANCE.--This lack of uniformity may refer either to size
+or colour, or to both. Apart from any other contributory causes, this
+variation is due, in pan sheet, to a neglect to standardise the dilution of
+all latices, or to lack of uniformity in the quantity of standardised latex
+placed in each receptacle.
+
+Where tanks are employed all sheets from the same tank should be of the
+same size before rolling, and any subsequent disparity in thickness and
+length must be attributed to some alteration in the width of the gap
+between the rolls of the machines.
+
+Unless all latices are standardised by means of an instrument, it is of
+course probable that the content of one tank may be found to differ from
+that of another.
+
+In a general sense, whether air-dried or smoke-cured sheets are considered,
+a thin strip will dry more quickly than a thick one, and should be paler in
+colour when viewed by transmitted light--_i.e._, when the rubber is held
+between the eye and the source of light.
+
+It is necessary, therefore, to guard against the possibility of variations
+in thickness caused by faulty manipulation. The distance between the
+squeezing rolls (smooth) and between the marking rolls (patterned) should
+be adjusted and should remain set until the conclusion of work. In a
+factory having nothing beyond average requirements in equipment of machines
+it should not be necessary to have to interrupt the work of the smooth
+rolls or "markers" by having to make adjustments. This is, however,
+inevitable if there is only one smooth-roll machine, as it is always
+desirable to reduce the thickness of the coagulum by at least two stages
+through even-speed smooth rolls. In some factories there are three light
+power-driven smooth-roll machines, the gaps between pairs of rolls being
+set so as to obtain a gradual thinning effect upon the fresh coagulum,
+which is then passed once between patterned rolls. With such equipment it
+is found possible, in some cases, to omit the preliminary hand-rolling, and
+the strips of coagulum from the tank are passed direct through rolls set
+with a wide gap. This work demands much care, as it is necessary to avoid
+any distortion of the coagulum which may be caused by its own weight and
+length.
+
+VARIATION DUE TO OXIDATION.--The subject of oxidation has been mentioned in
+the opening paragraphs of this chapter. It will have been learned that
+oxidation is a natural process, and that it may be prevented by the
+employment of anti-oxidants such as the sulphite or bisulphite of soda. In
+earlier days it was sometimes prevented by steeping the thin rubber in very
+hot water.
+
+In the absence of an anti-oxidant the degree of oxidation may vary daily
+and in different batches of latex on any one day, so that there is always
+the possibility of a lack of uniformity due to oxidation effects. This
+would be more evident in air-dried sheets than in smoke-cured rubber, as in
+the latter case the darkening of the surface would be masked by the colour
+induced by the smoke-drying process.
+
+To obviate this variation anti-oxidants are used on most estates, but the
+accidental or misinformed abuse of these chemicals may lead to further lack
+of uniformity. Hence it is necessary to follow carefully the formulae
+prescribed by experience.
+
+COLOUR OF SMOKED SHEETS.--It may be of interest to note that the effect
+known as oxidation is attributed to the presence of micro-organisms called
+enzymes (ferments) in the latex. It can also be produced artificially in
+various ways--_e.g._, by the use of the crude product of wood-distillation
+(pyroligneous acid) as a coagulant, or by the addition to the latex of
+small quantities of a phenol such as carbolic acid. It is thus possible to
+prepare in sheet form a rubber which has the appearance of having been
+smoke-cured, although it may never have been in a smoke-house.
+
+It will be clear, therefore, that apart from other causes, the colour of
+the cured sheets may be influenced by oxidation of the fresh coagulation,
+and by the constituents of the smoke. It follows that the smoke from
+timbers which are richer than others in certain chemical bodies set free by
+combustion will produce a rubber darker in colour.
+
+There is thus no real connection between colour and period of cure,
+although in a general sense the longer the interval the darker the colour.
+
+Similarly it is now plain that when anti-oxidants are employed in excess
+the paleness of the rubber is in no degree truly indicative of the period
+during which the rubber has been smoke-cured.
+
+The influence of the effect of the hypsical condition of the wet rubber
+upon the final colour must be thoroughly grasped. One may take two sheets
+of apparently the same thickness, and smoke-cure them in juxtaposition
+within the same house, only to find that one dries much more rapidly than
+the other. As a consequence, the first, when fully cured, will be of a
+medium golden brown colour; while the other, owing to protracted smoking,
+will be dark. Evidently there must be some distinct difference between the
+two in physical condition prior to the smoking. Here the factor involved is
+the rubber-content of the latex. Given two pieces of coagulum of identical
+thickness, but prepared from latices of different dry rubber content, it
+will be obvious that to reduce them to similar thickness, more pressure
+will be necessary in one case--_i.e._, that piece of coagulum will be much
+more dense (more consolidated)--while the other will be comparatively soft
+and porous. Into the latter warm smoke can penetrate much more easily, and
+the internal moisture can escape more rapidly. The full cure may be made,
+say, within twelve days, while the tougher sheet may demand up to twenty
+days.
+
+To attain uniformity in colour, therefore, the following points must be
+studied and controlled as far as is possible:
+
+     (_a_) Uniform dilution of all latices.
+
+     (_b_) Uniform dimensions of coagulating receptacles.
+
+     (_c_) Uniform volumes of standardised latex.
+
+     (_d_) Uniform quality and quantities of chemicals.
+
+     (_e_) Uniform methods of manipulating the coagulum.
+
+     (_f_) Uniform conditions of fuel and accommodation during
+     smoke-curing.
+
+SURFACE GLOSS.--In the choice of fuel there is room for control if one has
+good timber available. This point opens up a discussion on the vexed
+question of "over-smoking," as the term is sometimes applied to a
+pronounced dry glossy appearance of the surface of sheets.
+
+Three main factors are involved:
+
+     (1) The nature of the fuel.
+
+     (2) The ratio between furnace capacity and the capacity of the
+     smoke-house.
+
+     (3) The rate of combustion.
+
+     Obviously any fuel which yields an excessive quantity of tarry matter
+     or creosotic substance would conduce to the formation of a heavy glaze
+     on the rubber. Such fuel, therefore, should at most only be employed
+     as the smaller portion in a mixture with "dead" timber.
+
+It is impossible to lay down any general rules for the guidance of estates,
+as the timber available varies so widely in nature. Experience must be the
+only guide, and it should not be difficult to obviate the defect. Even so,
+there must be minor differences between the results obtained on estates, so
+that it is not possible to make strict estimations of the smoke-curing
+period by an examination of the surface appearance of rubber, even under
+the best of conditions. Some estates find that the rubber has a distinct
+gloss in ten days, while others may smoke-cure for twice that period
+without difficulty. Evidently, therefore, the question of available fuel is
+of prime importance. It may be remarked that very satisfactory results are
+always obtained from the use of fairly dry timber obtained from thinned
+rubber trees, mixed with the "dead" timber of old logs and stumps found on
+the estates.
+
+Obviously if a smoke-house has a superabundance of furnaces, producing more
+heat and smoke than is required, glazing will result. The point is tested
+by the average temperature maintained and the average rate of drying. The
+result of a high temperature would be the possibility of volatile tarry
+matter being driven in excess to the upper chamber. That this effect is
+eventually produced even at optimal temperatures is evident from an
+examination of the wood-work within the upper room.
+
+It is clear, also, that the rate of combustion exerts an influence. In a
+general sense a rapid consumption of fuel would augment the quantity of
+tarry matter passing into the upper chamber over any given period, and the
+possibility of glazing would be increased.
+
+On the other hand, it is possible that a surface glaze might be formed if
+the temperature were uniformly too low, especially if the rubber were
+rather thick. The rate of drying would be so slow, that if a timber rich in
+tarry matter were employed, the rubber might be exceedingly glossy.
+
+In order to guard against the appearance of a heavy glaze, then, the
+following points must be observed:
+
+     1. The fuel must be carefully selected by experience.
+
+     2. The sheets must not be thick. No sheets should be thicker than 1/8
+     inch measured in average section across the ribs.
+
+     3. The temperature must not be too high. An average working
+     temperature of 120 deg. to 125 deg. F. should be ample.
+
+     4. If the sheets are fairly thick, a low average temperature should be
+     avoided. No lower average than 110 deg. F. should be allowed.
+
+DULL, BLACK SURFACE.--This is the opposite of the previous case, and
+generally is accompanied by a fairly heavy darkening of the surface due to
+"oxidation" effects. The fuel used is too "dead," and needs the addition of
+some substance containing a fair amount of creosotic matter. The appearance
+of the rubber does not justify the assumption that it has been over-smoked.
+As a matter of fact, this type of rubber often becomes affected by mildew
+fairly rapidly, thus showing that the smoking has been inefficient.
+
+It may happen that an estate is in the habit of using a fuel which gives
+even to a thin sheet a heavy glaze in a comparatively brief period. The
+general custom is to soak such sheets in cold water, and then to scrub the
+surfaces, sometimes using soap, in order to cleanse the rubber and free it
+from the glaze. This operation may be done too well, in which case the
+rubber will have a dull appearance, and may be rather more liable to
+develop surface mildew after a time.
+
+MOIST GLAZE, GREASINESS OF SURFACE.--This describes the condition of sheet
+rubber when taken from the smoke-house. Sometimes the greasiness does not
+develop until the rubber has been out of the smoke-house for a day or two.
+
+As far as experience shows at present it may be due to two causes:
+
+     (_a_) The use of an excess of sodium bisulphite or sodium sulphite.
+     The use of sodium bisulphite is not recommended generally for
+     sheet-making. It may cause the rubber to be too pale in colour, and
+     the abuse of it may delay the drying unduly. In the latter case, a
+     trace of the salt may remain within the rubber or upon the surface. If
+     so, as the substance remaining is fairly hygroscopic, it will take up
+     moisture from the atmosphere and may cause the surface of the sheets
+     to have a moist and shiny appearance. The moist surface deposit comes
+     away upon the hand when the sheets are touched, and is difficult to
+     remove entirely. On some estates a very small quantity of the
+     bisulphite is employed, as it is found to be of service in the
+     prevention of bubbles, but in unskilled hands the method is open to
+     abuse, and is, therefore, not recommended for general use.
+
+     A large number of estates now use sodium sulphite in very small
+     quantities as an anti-coagulant and a preservative for latex in the
+     field. The abuse of this very useful substance carries its own
+     penalty. The substance is hygroscopic; and if an excess is present the
+     drying period will be protracted, and the sheets will have a very
+     moist surface film.
+
+     It may be found sometimes that only some of the sheets are affected.
+     This indicates that, whereas uniform quantities of a solution of
+     sodium sulphite have been served out in all fields, the proportion may
+     have been excessive in the case of fields giving a latex of
+     comparatively low rubber content. What suits the latex from old trees
+     may be excessive probably for the latex of younger trees. This is not
+     an infallible rule, as in the case of older fields in which immature
+     bark is being tapped, it is to be noted that the dry rubber content of
+     latex may be less than that of latex obtained from younger trees.
+
+     This type of moist glaze is not easy to remove. Ordinary surface
+     washing had but a temporary effect, and the trouble recurs. The only
+     way of dealing with the difficulty is to soak the sheets for days in
+     running water (or in successive changes of water) and to re-smoke
+     until dry.
+
+     (_b_) The second type of moist glaze is not so difficult to deal with,
+     and may be removed as a rule by washing the sheets when the rubber is
+     otherwise apparently dry.
+
+     It appears to be mainly a matter of unsuitable fuel for smoking and of
+     failure to provide adequate ventilation. A large number of estates
+     have been "thinning-out" or are doing so systematically. The logs thus
+     obtained are often used as fuel in the very green stage. The smoke
+     thus generated must be moist, and if the building is entirely closed,
+     this moisture must be deposited eventually upon the rubber and racks.
+     Some estates have surmounted the difficulty by opening up the
+     roof-ridge slightly so as to allow the moisture to escape with some of
+     the smoke; but if the logs from rubber-trees are to be used, they
+     should be stacked in the sun for some time. Even then, preferably,
+     they should not be used alone. A judicious admixture of dead and
+     rotting jungle-timber appears to give very satisfactory results.
+
+VIRGIN SPOTS AND PATCHES.--If the description really indicates the defect
+it simply means that portions of the sheets are not dry. When cut they
+exhibit the typical whitish, opaque appearance described as "virgin." It is
+doubtful whether any rubber put upon the market as No. 1 product nowadays
+can have this complaint levelled at it. In the extreme case it points to
+gross negligence on the part of the packer.
+
+Sometimes what are taken to be small spots of "virgin" are really patches
+of tiny air or gas bubbles. The point can be easily determined by cutting
+through the patch and examining the cut edges.
+
+SURFACE MOULDS OR MILDEW.--During the last two years, complaints regarding
+the incidence of "mouldy rubber" (_i.e._, relating chiefly to the presence
+of mildews on the surface) have become increasingly common.
+
+To judge by the comments of producers, who as a rule never again see their
+rubber after it leaves the estate, one would infer that the defect is
+imaginary, and that the complaints are made solely with a view to
+repudiation of contracts or the general cheapening of an article of
+commerce. They can often point out, with a certain amount of truth, that
+there has been no change in the methods of preparation or curing, and that
+previously there were no complaints.
+
+It is forgotten, however, that in former years the smaller output of rubber
+was taken into consumption more rapidly than of recent years. That is to
+say, the interval between smoke-curing and the employment of the rubber in
+the manufacture of goods did not demand such a long period of storage.
+Hence the effects of smoke-curing are now more likely to vanish.
+
+Going still further back in the history of plantation rubber, we can point
+to the time when smoked sheets were allowed, or had, to remain in the
+curing-sheds for very extended periods. Loose specimens of rubber prepared
+during that decade still exhibit no signs of mildew growth.
+
+In later years a demand arose for sheets paler in colour than the old type,
+and in order to meet that demand, a change had to be made in methods. This
+led to a system of working whereby it was possible to smoke-dry sheets
+thoroughly in from twelve to fourteen days. This interval was further
+reduced on many estates, until some were producing rubber which appeared to
+satisfy all requirements after only five or six days' curing. This does not
+refer to the case of estates having smoke-houses of "continuous-working"
+type, but to those on which smoking was confined practically to the hours
+of night. Under former conditions of rate of production and consumption,
+this short period of smoke-curing would possibly have been ample; but even
+this is very doubtful, as often the rubber would not stand the relatively
+short journey from the estate to Singapore without mildew-growth being
+incipient. We have often received specimens of rubber sent from estates for
+criticism, and have noted that within a comparatively brief period mildew
+was to be seen.
+
+The whole matter resolves itself into a question of thorough efficiency of
+smoking. This is not dependent on duration of smoking alone, but involves
+other factors, such as the kind of fuel employed, the rate of combustion of
+fuel, the average temperature sustained, the ventilation of the
+smoke-house, and the situation of the building. Other occasional
+contributory factors are contemporary adverse climatic conditions and the
+possible abuse of an anti-coagulant such as sodium sulphite.
+
+It has been shown that after a time, given suitable conditions involving
+the presence of moisture, moulds may appear on sheets which were apparently
+fully smoke-cured, and that under the same conditions other and older
+samples were unaffected. It is argued that the latter sheets had evidently
+been smoked more efficiently than the others. Hence it is fair to assume
+that, except under very special conditions, which do not apply to the
+ordinary procedure in the shipping, storage, and sale of rubber, moulds
+will not develop upon sheets which have been properly smoked. The term
+"properly smoked" signifies efficient smoking for all practical purposes
+under ordinary procedure, and implies or includes all the advantageous
+factors which have been discussed or alluded to in preceding paragraphs.
+
+Without discussing in wearisome detail conditions which may give rise to
+the incidence of mildew on properly smoked rubber, it may be pointed out
+that the following are favourable to the growth of moulds:
+
+     (_a_) Storing sheets in a damp place before packing.
+
+     (_b_) Packing sheets in wooden cases which are not thoroughly dry.
+
+     (_c_) Piling up cases of rubber in a badly ventilated store-room.
+
+     (_d_) Placing the cases on a cement floor.
+
+     (_e_) Wetting of cases by sea-water or by rain during transport, etc.
+
+BLACK STREAKS, SPOTS OR PATCHES.--The origin of these is not difficult to
+trace. They are caused by drippings from the roof, and contain condensation
+products from smoke plus moisture. The ventilation of the roof-ridge should
+receive attention, and if the trouble persists it will be necessary to
+place some absorbent screen below the sloping roof. Sackcloth is sometimes
+used, but leads to a worse state of affairs unless changed frequently. In
+most modern smoke-houses having an iron roof there is an inner lining of
+soft timber.
+
+There scarcely seems a necessity to discuss the case in which an iron roof
+has become perforated by the action of smoke. The remedy is too obvious to
+describe.
+
+WHITISH OR GREY STREAKS.--This is a very uncommon defect, and is generally
+to be traced to a building in which fairly new galvanised sheets have been
+employed. The zinc surface becomes oxidised, and the whitish powder which
+is formed "flakes," or is carried away by drops of moisture condensing on
+the surface of the iron sheets.
+
+RUST.--Sometimes if a sheet is stretched forcibly and allowed to retract
+quickly, the hitherto clear surface will be seen to be marred by a "rusty"
+deposit. The rubber is then described as "stretching rusty," and its value
+is depreciated.
+
+This defect has caused more trouble during recent years than any other. It
+is not proposed here to argue the question as to whether the presence of
+this film, which appears when some rubbers are stretched, is detrimental to
+the physical qualities of the product on vulcanisation. With the mere
+statement of opinion that it could do no apparent harm, we may pass to the
+aspect of the case as it affects the buyer and consumer. If one were to
+judge by the attention drawn to the appearance of smoke sheet-rubber after
+it has been stretched and allowed to retract, one would imagine the defect
+to be of comparatively sudden and recent incidence. This is not so. The
+peculiarity must have existed for years, and perhaps became more marked as
+so many estates abandoned the former common practice of allowing varying
+quantities of water to be placed in the collecting cups. As the substances
+which cause the defect to be visible are partially soluble in water, it
+would follow that when working with the very dilute latices which were
+characteristic of the earlier years of the plantation industry, the
+remaining liquid in the pan after coagulation would contain an appreciable
+quantity of soluble substances which would otherwise have been retained in
+the coagulum.
+
+Conversely, the richer the latex, the greater the percentage of protein
+matter retained in the coagulum. In the case of very rich latex, it must be
+within the knowledge of every manager that the quantity of remaining liquid
+in the pans would be almost nil. We may assume that the greater part of
+these soluble proteins would be enclosed in the structure of the rubber,
+but as the fresh coagulum must retain a quantity of liquid amounting to
+from 60 to 70 per cent. by weight (we are now referring to rich latices),
+it follows that some of the soluble protein matter must be removed when the
+coagulum is placed under pressure. Even after the pressure is released more
+of the contained liquid will exude from the surface of the rubber; and from
+experience it is easy to imagine that this exudation, becoming
+progressively feebler, will continue until the rubber begins to dry. Then,
+with the evaporation of the surface moisture, the protein matter, either in
+original form or as a degradation product, remains on the surface of the
+rubber as a thin, solid film or crust. As drying continues, the interior
+moisture escaping through the pores of the rubber evaporates, leaving
+behind the substances hitherto held in solution. Should, however, the sheet
+be thick and/or the temperature of drying low, the rubber may dry first on
+the outside, forming a thin skin of dry rubber, which delays further drying
+indefinitely.
+
+It will be seen, therefore, that sheets which have been prepared from rich
+latex or from too deep a layer of comparatively dilute latex will have a
+surface film of dry protein matter. Moreover, these sheets will be slow in
+drying, and in all probability will have a surface gloss and a dark colour.
+Hence it is not difficult to understand that some brokers regarded the
+presence of the so-called "rust" as an indication of over-smoking.
+
+To show that this is not so, and further that the presence of rust has
+nothing whatever to do with smoke-curing, it may be stated that _the
+presence of this protein film may be seen on unsmoked sheets_ which have
+been prepared from rich latex, from too deep a layer of more dilute latex,
+or from some thick sheets which have been rolled only very lightly. In
+fact, the presence of the protein film was noted on unsmoked sheet in 1910,
+when it was seen to resemble a thin yellowish glaze which could be scraped
+off with a pen-knife. Later, sufficient of this substance was removed from
+some very thick air-dried sheets, or thin slabs, to fill a small test-tube.
+
+When the sheets were bent or twisted, the apparent surface of the rubber
+(_i.e._, the protein glaze) cracked in all directions. In the case of
+sheets prepared from less rich latex, the surface film naturally is
+extremely thin, and no cracking is observed.
+
+If the fresh sheets are placed in a smoke-house, the drying film will take
+up colour from the constituents of the smoke, and it will be invisible.
+Somewhat analogous to the instance of a transparent glass giving a visible
+and opaque powder when crushed, so the transparent film on stretching
+breaks up into a visible powder which is lighter in colour than the rubber
+on which it is superimposed.
+
+It will be noted that since the introduction of standard methods of
+preparation, involving uniform dilution of latex, say, to a content of
+1-1/4 or 1-1/2 lbs. dry rubber per gallon, complaints as to "rust" have
+decreased considerably.
+
+It is to be further noted as a peculiar fact that while two estates may be
+apparently working on identical lines, both as regards manipulation of
+latex and subsequent treatment of the coagulum, the rubber of the one may
+always be free from rust, while that of the other is often, if not always,
+condemned for the alleged defect. Obviously, in such a case, there must be
+an initial difference between the two latices as regards the percentage of
+proteins present; or there must be some small unrecognised difference at
+some stage of working.
+
+It will now be clear that "rust" is caused by a film of matter which is
+formed on the surface of the pressed coagulum, being there deposited by the
+exudations from within the rubber and through the pores. It is, therefore,
+necessary to avoid any conditions which will favour the formation of this
+deposit--_e.g._, allowing sheets to remain too long in a moist atmosphere
+before placing in the smoke-house.
+
+At present there would seem to be only two methods which are successful in
+the prevention of a "rusty" appearance in the dry rubber. Singularly
+enough, the two methods appear to be directly opposed in principle. They
+are:
+
+     A. THE HOT-WATER TREATMENT.--This method has been in constant use on
+     estates which have old trees giving rich latices. These latices are
+     always diluted to a uniform standard daily. Some estates which
+     formerly suffered from the defect now experience no difficulty, and in
+     other instances, where no complaint has yet been received, the
+     treatment has been followed consistently.
+
+     (1) After the sheets have been through the marking rolls, it is the
+     general custom to allow them to drip for about three hours. This
+     interval is really excessive for the mere draining away of the surface
+     water, but as a rule it is just sufficient to allow a portion of the
+     liquid retained in the rubber to exude. It has been shown that this
+     liquid may contain some protein matter in solution. Sometimes in the
+     case of thick sheets which have been subjected to pressure so much of
+     this matter is exuded as to form a thin surface slime which is
+     distinctly evident to the touch. If the sheets are allowed to hang
+     overnight, the presence of the exuded matter may be detected also by
+     its odour.
+
+     (2) Obviously, any method which will remove this surface film should
+     be of great benefit. It is found that the best results are obtained by
+     allowing sheets to drip for about two hours, and then placing them in
+     hot water for five or ten minutes. The water should be hot as the hand
+     can conveniently bear, and it need hardly be pointed out that the same
+     water should not be used for the whole day's output. For preference
+     there should be three or four vessels, each capable of holding a fair
+     proportion of the total number of sheets, and frequent changes of hot
+     water.
+
+     (3) After remaining in the hot water for the period mentioned, the
+     sheets are removed singly, each one being surface washed or swilled as
+     it is taken out.
+
+     (4) _It is important to see that the sheets are now well washed or
+     scrubbed under running cold water, or in frequent changes of water._
+     The reason for this procedure is plain. If the sheets are merely hung
+     again to drip after removing from the hot water, some moisture is
+     bound to remain on the surface of the sheet. As this surface moisture
+     contains some protein matter in solution, it is evident that, as the
+     water evaporates, the solid protein is again deposited on the surface
+     of the rubber. This would explain why some estates were unsuccessful
+     with the hot-water treatment. It is not essential that the running
+     water should be cold; it may be conveniently lukewarm if drawn from
+     the cooling tanks of the engines. But it is essential for the best
+     results that there should be running water, so that the substance in
+     solution is carried away. If the sheets are merely washed in a large
+     vessel, which has been filled with clean water, it must be obvious
+     that, by the time some scores of sheets have been washed, the protein
+     matter in solution on the surface of the sheets has been transferred
+     to the washing water, so that the later sheets of the batch are liable
+     to show the defect again on drying.
+
+     B. The second method is much more simple, and entails no extra labour
+     such as is demanded by the first method. A successful issue, however,
+     is rather more uncertain, and the method appears to give the best
+     results with sheet-rubber prepared on young estates or from more
+     dilute latex.
+
+     In this method, the sheets after rolling are allowed to drip for a
+     very short interval, so that the surface water is mainly removed. The
+     sheets are then placed in the smoke-house, and smoking is commenced at
+     once. In some cases where the defect had appeared continuously for a
+     long period, it was found to vanish entirely as soon as the method was
+     adopted; but when tried on some of the older estates, the results were
+     very doubtful, and a return was made to the hot-water treatment.
+
+     The explanation of the action which takes place is rather obscure, but
+     two theories may be advanced.
+
+     (_a_) It may be assumed that the interval given for dripping is too
+     brief to allow for the exudation of the internal moisture containing
+     dissolved protein matter.
+
+     In such case, the rubber is still in a highly porous condition, and it
+     might be advanced that the heat of the smoke may help to maintain that
+     condition. Thus the contained liquid might evaporate so quickly as to
+     leave behind the dissolved substances in the minute cellular structure
+     of the rubber. In other words, instead of the internal moisture
+     exuding slowly to the surface in liquid form, it may leave the
+     rubber, even in the first stages, in an evaporated condition, just as
+     it does in the subsequent stages of drying. Thus no dissolved protein
+     matter would be brought to the surface of the sheet and be deposited
+     there.
+
+     (_b_) The other theory also demands the first assumption propounded in
+     the preceding theory, but subsequently perhaps is less feasible as it
+     assumes a chemical action of which we have no definite knowledge.
+
+     The idea is that as the rubber is in a porous condition, and is placed
+     quickly in an atmosphere of smoke, the heat may maintain that
+     condition to such a degree, that some constituents of the smoke may
+     enter the rubber and cause the precipitation _in situ_ of the protein
+     matter held in solution by the contained water or other liquid. The
+     contained liquid would be water which has in solution possibly a very
+     slight trace of the coagulant employed, of sugars, of protein matter,
+     and of inorganic salts. Of these the substances which would evaporate
+     would be probably the water and the coagulant in most cases. If a salt
+     had been used as a coagulant, the dissolved trace would be deposited
+     within the rubber in this case, whereas if a rich latex had been
+     employed or a thicker sheet made from more dilute latex, some of the
+     salt would be brought to the surface and there deposited together with
+     the protein matter. This has actually been experienced in practice,
+     and it has been possible to remove minute crystals from the edges of
+     the rubber so prepared.
+
+It will be evident that in order for either theory to contain an element of
+probability, the rubber must be soft (porous) when placed in the
+smoke-house, and must also be fairly thin. It is observed in all cases
+where the method has been successfully employed that both these conditions
+are generally fulfilled--at all events the rubber is fairly thin. When
+thicker sheets are made, either from rich latex or from a deeper layer of
+comparatively dilute latex, the method is not uniformly successful.
+
+OTHER VIEWS ON "RUST" CAUSATION.--Later experimental work on "rust"
+formation by Hellendoorn[22] leads to the observation that "rustiness" is
+caused, not actually by the deposition of original serum-substances, but by
+the decomposition thereof, under the action of aerobic micro-organisms.
+
+[22] "The Cause of Rustiness in Sheet-Rubber," H. J. Hellendoorn, Archief
+voor de Rubbercultuur, October, 1919 (Communication from the Central Rubber
+Station, Buitenzorg, Java).
+
+Without going into a full discussion of the subject, the following points
+noted in the experimental work may be quoted:
+
+     1. Rustiness could apparently be produced at any time merely by
+     keeping freshly rolled sheets for periods varying from twenty-four to
+     forty-eight hours in a moist atmosphere.
+
+     2. Sheets placed immediately in a temperature of, say, 110 deg. to 130 deg. F.
+     never showed "rust"; but if air-dried at ordinary room temperature,
+     "rust" might appear.
+
+     3. "Rust" can be prevented by soaking freshly prepared sheets in
+     dilute solutions of disinfectants--_e.g._, formalin, sodium
+     bisulphite, or chinosol.
+
+     If subsequently the sheets are hung for any length of time in a moist
+     atmosphere, the protective effect of the disinfectant gradually
+     vanishes and "rustiness" may be produced.
+
+     The same disinfecting effect may be obtained by the use of steam or
+     hot water. It was found that there was less liability to the formation
+     of "rust" when sheets were immersed in water at a temperature of 95 deg.
+     to 120 deg. F., whilst steeping at 140 deg. F. gave complete freedom.
+
+     4. It was shown that the micro-organisms which cause decomposition of
+     the serum-products flourish only in the presence of air--_i.e._, they
+     are aerobic in character. It is not uncommon to find, therefore, that
+     "rust" may be incident only on those parts of a sheet which have been
+     exposed for some time to air and moisture before being placed in a
+     warm smoke-room.
+
+     5. The optimal temperature for development of the particular organisms
+     appeared to be about 100 deg. F., in a moist atmosphere.
+
+     6. Soaking the sheets in water (except the short immersion in hot
+     water, which we recommend), even for a period extending over a week,
+     does not hinder the formation of "rust."
+
+     7. Rustiness may be prevented by placing the sheets in a sufficiently
+     warmed smoke-house as long as there is adequate ventilation and a
+     moist atmosphere does not persist.
+
+     The simplest means of prevention is to soak the sheets first for a
+     short period in water, and then to hang them to drip for a few hours
+     in a well-ventilated place, outside the factory and under cover.[23]
+
+[23] We advise and practise hanging sheets in the open, without shade or
+cover.
+
+It will be gathered that, although there may be a slight difference between
+our previous views and those advanced by Hellendoorn as to the exact cause
+of formation of the "rusty" film, the general conclusions are identical
+with those given by us in preceding paragraphs and previously advised in
+the Malayan reports of the Rubber Growers' Association.
+
+BUBBLES.--The presence of bubbles in sheet-rubber has for years been the
+bane of some managers' existence, and the bone of contention between
+sellers and buyers. Taking the argument down to bed-rock, producers urge
+that the presence of bubbles has no influence upon the ultimate quality of
+the rubber on vulcanisation. They assert that the alleged defect is merely
+a peg upon which to hang an unreal grievance, serving the purpose of the
+buyer under the existing conditions of sale. All this may be true, but as
+long as the present system continues, it must be recognised that "kicking
+against the pricks" is a futile recreation.
+
+The sympathy of the writers is certainly on the side of the producers,
+inasmuch as they realise how extremely difficult, and even impossible at
+times, it is for the most careful individual to prepare sheet-rubber free
+from this blemish.
+
+Much has been written, and many have been the discussions, on this vexed
+subject; and it is recognised that sometimes, in spite of all precautions,
+there may suddenly be an incidence of bubbles in rubber which is ordinarily
+free from them. It must be allowed that climatic conditions and
+physiological variations affecting the metabolic functions of the trees
+exert an influence which is difficult at times to combat, and often beyond
+human control.
+
+The contributory causes are many and varied. It should be premised that,
+although the defect is described as "air-bubbles," it is seldom that the
+appellation is strictly correct. Rarely do the bubbles contain air. In the
+vast majority of cases they contain gases in minute quantity. These gases
+may be considered to arise, broadly, from some decomposition of substances
+(other than rubber), contained either in the coagulum or in the serum. In a
+general way, if this decomposition is evidenced by an unpleasant odour, it
+is described under the term of "putrefaction." We are not concerned here
+with the question as to how far such decomposition may be ascribed to a
+purely chemical action, or to the indirect result of the presence of
+certain bacteria or other micro-organisms. Suffice it to state that, at
+least as far as field operations influence the result, the decomposition is
+generally to be attributed to the work of micro-organisms. Conditions
+favourable to the incidence and development of these are to be found when
+absolute cleanliness in all details is not aimed at.
+
+With this preamble we may proceed to classify possible causes of the
+formation of bubbles into two groups:
+
+     (_a_) Those originating in field operations.
+
+     (_b_) Others which may arise after the arrival of the latex at the
+     factory.
+
+IN THE FIELD.--Decomposition may be caused by:
+
+     (1) Spouts, buckets, and cups being dirty. Regular cleaning is
+     necessary. If the buckets are allowed to be taken to the lines by
+     tappers, trouble may ensue. Within the writers' experience it has been
+     shown that an otherwise baffling case of premature flocculation of
+     latex was traced to the presence of acid substances in the buckets,
+     which had been used by coolies for preparing their food.
+
+     (2) Delay in commencing work. This means similar delay in collecting
+     the latex which is exposed to greater heat than under ordinary
+     circumstances.
+
+     (3) Exposure to the sun's rays. The heating of the latex may provide
+     improved conditions favourable to the development and action of
+     micro-organisms.
+
+     (4) Allowing latex to stand too long before collection. This usually
+     is the result of giving tappers too great a task.
+
+     (5) The addition of water to the latex, either purposely or
+     accidentally, in the form of rain. The water may be slightly acid in
+     character, or it may carry micro-organisms from the bark into the
+     latex.
+
+     (6) Tapping trees at too great a height. The latex generally has an
+     abnormal distance to travel before reaching the cup.
+
+     (7) Sometimes the latex from old trees, or from trees after wintering
+     (just prior to full renewal of leaf), contains more than the usual
+     proportion of substances (_e.g._, sugars), which are capable of
+     effecting flocculation or coagulation.
+
+     (8) Too great a distance for transport. The trouble arising from this
+     cause is likely to be much increased if the journey has to be made
+     over bad roads. In such case the physical action augments the effect
+     likely to be produced by long standing.
+
+The foregoing do not include all possible causes, but serve to indicate the
+directions from which trouble may be mainly anticipated. It will be plain
+that any latex which exhibits symptoms of premature coagulation (or minute
+flocculation) should be regarded as a potential source of bubbles in
+sheet-rubber.
+
+It will be equally obvious that the employment in the field of any harmless
+substance of an anti-coagulant nature is to be encouraged. This point is
+discussed in detail in Chapter V.
+
+IN THE FACTORY.--As a general rule it may be understood that the mischief
+has been done before the latex is handled at the factory. Sometimes it is
+perceptible from the peculiar appearance of the latex, and in such case the
+batch should not be used for the preparation of sheet-rubber. Often it is
+found that only the last to arrive at the store is visibly affected. This
+should not be mixed with other apparently normal latex, as it is capable of
+acting as a "leaven" to the bulk.
+
+Contributory factors in the store are:
+
+     (1) Lack of cleanliness of utensils, particularly of coagulating
+     dishes or tanks.
+
+     The trouble becomes acute sometimes where wooden tanks are employed.
+     Unless the tank and the partitions are thoroughly and regularly
+     cleansed, the wood may become coated with a bacterial slime, which is
+     capable of causing what may be termed "fermentation" of the latex
+     layers in contact.
+
+     The tank should be thoroughly cleaned occasionally with a weak (5 per
+     cent.) solution of sodium bisulphite. The partitions should be
+     scrubbed and placed in the sun twice or three times a week.
+
+     (2) Allowing latex to stand too long before treatment. This point
+     needs no further expansion.
+
+     (3) The use of a latex of too high a rubber content. Such latices are
+     difficult to handle in order to secure uniform mixture with the
+     coagulant.
+
+     (4) The use of too concentrated a solution of coagulant. In
+     conjunction with (3) there may be a rapid and irregular coagulation,
+     giving rise not only to decomposition in parts (and subsequent
+     formation of gas), but also to the formation of true "air-bubbles" by
+     inclusion of air during stirring.
+
+     (5) The use of insufficient coagulant. Coagulation is slow and
+     incomplete.
+
+     (6) Defective straining and skimming. Small flocculated particles of
+     rubber may pass, or be rubbed through, the strainer. If allowed to
+     remain, they act as local points of danger.
+
+     (7) The proximity of the coagulating latex to some source of heat, or
+     exposure to sunlight.
+
+     (8) Any delay of drying in the preliminary stages, either before or
+     after the rubber enters the smoke-house.
+
+BLISTERS.--This description aptly fits the case in which sheet-rubber in
+the smoke-house exhibits large bubbles of gas which distend the surface of
+the rubber. When subjected to pressure, small "balloons" are formed, which
+burst with a perceptible report. It was formerly the belief that this
+defect was occasioned solely by an abnormally high temperature. That such
+is not the case can be shown by the experience of estates which have had
+only the rubber of a particular day or short period affected under normal
+factory conditions.
+
+At the same time it is not disputed that the heat of the smoke-house exerts
+an influence (causing expansion and distension), but it is advanced that
+the gases had begun to form before the rubber entered the house.
+
+The view held is that decomposition had supervened or was taking
+place--probably from one or more of the causes enumerated in the preceding
+paragraphs. The heat of the smoke-house only serves to exaggerate the
+effect. It is acknowledged that the degree of decomposition must be
+initially greater than in the ordinary incidence of "bubbles."
+
+Beyond this point we are not in a position to put forward any definite
+supposition as to the apparently haphazard occurrence of the phenomenon.
+
+It is to be noted, fortunately, that the defect is comparatively rare, and
+seldom appears on estates which employ an anti-coagulant in the field.
+While we have examined persistent cases, one of which led to a temporary
+discontinuance of the preparation of smoked sheet rubber, we have not yet
+been able to arrive at any satisfactory idea of the exact conditions
+governing the incidence of "blisters." Our investigations only lead us to
+two observations:
+
+     (_a_) That blisters have appeared on the rubber of some estates after
+     wintering, and during the period of new leaf-development.
+
+     (_b_) That the defect has been noted on other estates during a period
+     when there were frequent but not heavy rains, and when there was a
+     comparatively low average temperature.
+
+In either case, as the factors are beyond human control, it would be
+expected that without any change being made in estate procedure, the
+trouble would vanish as mysteriously as it appeared. This is our
+experience; but as showing the possible intensive effect of a high
+temperature in the smoke-house, it may be remarked that very infrequently,
+in a batch of sheets exhibiting ordinary bubbles, a few hanging directly
+above the furnaces show signs of a slight blistering effect.
+
+"SPOT" DISEASE IN SHEET RUBBER.--That "spot" disease may appear in
+air-dried sheets was evident at the beginning of the outbreak in the spring
+of 1911. The first cases noticed took the form of pink and bluish "blushes"
+spreading over the whole of the sheets. Later, fungoid spots began to
+appear. These mainly took the form of red or black blotches, and were very
+unsightly. As "spot" disease cannot develop in smoked rubber, the obvious
+and simple course to adopt was to smoke-cure the sheets. When it is stated
+that "spots" do not develop in smoke-cured rubber, it is understood that
+the smoke-curing must be efficient and must commence as soon as the rubber
+has been rolled, and the surface water has drained away. If the sheets are
+allowed to air-dry for a few days, the disease may develop, and then
+smoke-curing will not get rid of the coloured patches. The operation of
+smoke-curing will not get rid of the coloured patches. The operation of
+smoke-curing may tone down the colour, but the spots would still remain
+evident.
+
+SUPPORT MARKS.--It frequently occurs that one sees across the middle of
+smoked sheets a wide mark. This is where the wooden support in the
+smoking-chamber has been. As a rule, even in the most careful cases a faint
+mark may always be seen, but in many instances this mark is exaggerated to
+such an extent as to point to lack of care on the part of the store
+supervision. If bays of racks remain empty over-night, they may possibly
+become covered with a light sprinkling of fine wood-ash and tarry deposit.
+Wet rubber placed upon these racks will pick up and retain the impurities,
+and more often than not they cannot be washed out. It is incumbent upon the
+manager to see that empty racks are thoroughly cleansed before placing wet
+rubber upon them. The better plan is to arrange that the bars can be
+removed easily from sockets. There should be in stock sufficient "spares"
+for, say, two days' rubber. When the dry rubber is removed, the bars should
+likewise be taken away, to be cleansed and kept in the factory until again
+required. This will ensure that fresh rubber always rests upon a clean
+support.
+
+On some estates, in order to guard against a pronounced "bar-mark," sheets
+are moved and turned daily.
+
+In other smoke-houses the upper surface of the bar is chiselled in concave
+form, so as to admit of the passage of smoke below the surface resting on
+the bar.
+
+STICKINESS.--This is not to be confounded with "tackiness," from which the
+rubber does not recover. Stickiness is only temporary, and may be remedied.
+As a general rule, it is due to packing sheets, which have not a good
+raised "ribbing," and which may have been coated with light tarry deposits
+(see Glaze). This surface film may be removed by washing the sheets, or
+scrubbing them, with cold water. Usually a further two days' air-drying
+will make the rubber fit for packing; and if the smoke-curing has been
+efficient, there should be no need to anticipate trouble from mildew. Some
+estates adopt this practice daily with success, as a form of insurance
+against complaints of surface deposits.
+
+RIBBING, SURFACE PATTERN.--While we know that the passing of sheets of
+rubber between rolls, causing a particular raised pattern to appear, has no
+effect upon the actual quality of the rubber, there is a great deal of
+practical advantage gained.
+
+The practice ensures an increase of superficial area which is an aid in
+drying, improves the appearance of the rubber for selling purposes, and is
+of distinct advantage in enabling the rubber when packed to travel in
+better condition. Sheets do not become so closely packed; sampling and
+general handling are easier on delivery.
+
+As long as the plane surfaces are sufficiently and regularly distorted,
+there would seem to be no limits to the type of pattern or "mark" which may
+be placed upon the rubber. But in actual practice the variety is small. The
+most popular type of "ribbing" is that best described as a small diamond
+effect, produced by a pair of rolls cut with closely placed narrow grooves
+running spirally. The spirals travel in the same direction on both rolls,
+producing close-cut ribbing running in opposite directions on the surfaces
+of the sheet. On sheets of standard thickness, the result approaches a
+diamond effect.
+
+A few other patterns are employed, notably that producing longitudinal
+stripes of varying thickness. On the whole, the type of pattern would seem
+to be immaterial, if the points already indicated are achieved.
+
+It is seldom one encounters a case nowadays in which the "marking" is
+unsuitable, but a few estates may be using an old type of patterned roll on
+which the full diamond grooving is cut. As this appears on both sides of
+the sheet of rubber, and as the ribbing does not coincide, a blurred effect
+is seen when the sheet is viewed against the light.
+
+THICK ENDS, "SHEET CLIPPINGS."--It rarely happens, even with good equipment
+and average supervision, that the preparation of smoked sheet is
+unaccompanied by slight defects. For instance, in spite of rules and
+regulations regarding manipulation of the coagulum, it is not uncommon to
+find that some sheets, after rolling, have slightly thickened ends. In the
+ordinary course of events these might delay drying considerably. It is the
+practice on some estates to cut off these thickened ends while the rubber
+is still wet. The pieces are then machined into crepe form, but as no
+sodium bisulphite may have been used, the resulting rubber cannot be
+classed as No. 1 Standard Crepe.
+
+The other alternative is to trim the ends when the bulk of the rubber is
+thoroughly smoke-dried. The moisture containing portions are then returned
+to the smoke-house until dry, and are subsequently packed without further
+treatment as "smoked-sheet clippings." It will be plain that, except in the
+particularity of form, these clippings differ in no degree from the
+original sheets; and, owing to extra smoke-curing, may arrive in even
+better condition. One must be prepared, however, to find that a slightly
+lower price is offered. Whether the price obtained would be comparable with
+that commanded by the crepe made from wet sheet slipping would depend upon
+general ruling market conditions, and the degree of care exercised in
+guarding against the inclusion of any inferior pieces of rubber. In
+ordinary factory practice, there could be no room for abuse under the
+latter clause.
+
+OTHER INFREQUENT DEFECTS.--This chapter will be closed with a reference to
+other small defects which, although infrequent, cannot be classed as minor
+complaints. In point of fact, when they occur, they assume an importance,
+in the eyes of the consumer, which is not, perhaps, sufficiently
+appreciated by producers.
+
+DIRT.--Trouble from this source should be absent, but carelessness on the
+part of packing coolies may be responsible for occasional complaints. How
+the dirt is incident may remain a mystery, but it has been noted that
+sheets have at times been thrown upon a cement floor. A certain amount of
+loose dust may thus adhere to the rubber.
+
+ASH.--The source of this surface deposit scarcely needs indication. Where
+open-hearth furnaces are employed, and the wire-mesh floor screens are not
+perfectly sound, fine ash may find its way into the upper chamber. If this
+trouble is persistent in spite of precautions, the sheets should be
+surface-washed and air-dried before packing.
+
+BARK.--Complaints of the presence of particles of bark in sheet rubber used
+to be fairly frequent, but are now less common. The trouble may be traced
+to the use of defective straining sieves when the latex is being handled.
+
+SPLINTERS.--The use of packing-cases of unplaned soft timber is responsible
+for complaints of this nature on delivery. Without here discussing the
+larger question of the ideal packing case, it is sufficient to emphasise
+that the interior surfaces of wooden chests should be planed. The cases are
+often so damaged in transit, that splinters of wood may be found throughout
+the contents. The device adopted on some estates may go far to prevent
+this. The cases are first lined with loose sheets, and finally other sheets
+are arranged to overlap at the top of the case. The bulk is thus enclosed
+in a wrapping of sheets, and any splinters or other deleterious substances
+are confined to the surface of the mass.
+
+
+
+
+PART V
+
+GENERAL
+
+
+
+
+CHAPTER XIX
+
+_CHOICE OF COAGULANT_
+
+
+Almost without exception, the agent employed in the coagulation of
+plantation (_Hevea_) rubber is acetic acid, or in some cases formic acid.
+Under ordinary trade conditions supplies are always obtainable at
+reasonable prices, but during the recent War the question of possible
+substitutes was brought greatly to the fore. Fortunately the subject of
+coagulation and coagulants had been previously studied to such effect in
+laboratory practice, that there would have been small difficulty in
+prescribing agents other than acetic acid in cases of expediency. As far as
+our knowledge extends, all the possible substances which have the power of
+coagulating latex have been tested. They include mineral acids, organic
+acids, compounds known chemically under the general term of "salts,"
+alcohols, sugars, etc.
+
+The heading of this chapter must be seen to "beg the question," inasmuch as
+it leads to the assumption that a coagulant (in the popular sense) is
+necessary to secure coagulation. In point of fact, methods are sometimes
+employed which depend upon no artificial coagulant to produce the desired
+effect. To these methods reference will be made later.
+
+In this section it is proposed to describe briefly the more important
+agents which are used, or might be used, in effecting coagulation. In the
+class of those which are not in common use some could be used as
+expedients, while others are only of scientific interest.
+
+ACETIC ACID.--There is no need to enter into a discussion of the merits of
+this agent. In practice it remains the cheapest and safest coagulant known
+at present.
+
+FORMIC ACID.--This agent is equally as safe to use as acetic acid, and as
+easy to handle. Bulk for bulk its coagulative power is higher than that of
+acetic acid. Its pre-war shipping price, when taken in conjunction with its
+coagulative power, was slightly below that of acetic acid, but local prices
+put the balance in favour of the latter. If prevailing costs put it on
+terms of parity with acetic acid, there would appear to be no reason why
+formic acid should not have a widely-extended use on plantations.
+
+CITRIC ACID, TARTARIC ACID.--The acids of the extracted juices of most
+tropical fruits consist, to a large degree, of citric or tartaric acids.
+These can be used in place of acetic acid as satisfactory coagulants in
+case of emergency; but the questions of availability of supplies and of
+costs preclude their more general adoption.
+
+OXALIC ACID.--This is a satisfactory coagulant as far as observed effect is
+concerned. It produces a rubber paler than ordinary coagulants (without the
+use of sodium bisulphite), as it has the nature of an anti-oxidant.
+
+It would not be a safe agent in the hands of coolies, as it is classed as a
+poison.
+
+SULPHURIC ACID.--During the War, in a period of shortage of acetic acid and
+of high prices, this agent was used with success on some estates.
+
+It scarcely need be remarked that it is a dangerous substance to handle,
+and that its employment must be accompanied by close European supervision.
+
+At prevailing prices during the War it was very much cheaper than acetic
+acid, and even at the present reduced cost of the latter the advantage
+still lies with sulphuric acid.
+
+It must be emphasised, however, that the abuse of this agent to any but the
+slightest degree is harmful to the resultant rubber. Hence its use would be
+sanctioned _only in the absence of the commoner, and much safer,
+coagulants_.
+
+In view of the possible incidence of such an emergency, the following
+notes are given. It is impressed that strict adherence to the rules must be
+given.
+
+HANDLING SULPHURIC ACID.--(_a_) Always use glass or glazed earthenware
+vessels.
+
+(_b_) Pour slowly and avoid splashing. Drops finding their way to clothing
+or other fibrous material will destroy it locally; and if thrown upon any
+part of the body may cause painful burns.
+
+(_c_) When diluting this agent always remember to pour the acid into the
+water (_i.e._, the lesser into the greater), and never _vice versa_. Pour
+the acid carefully and slowly down the side of the vessel, and stir well.
+
+(_d_) Should strong acid be spilled, do not throw water upon it. A supply
+of sand or dry earth should be kept close at hand. Throw this upon the
+acid.
+
+STORING SULPHURIC ACID.--(_a_) Jars or cases should be handled as seldom,
+and as carefully, as possible. If the acid is contained in a case, the top
+should be plainly indicated.
+
+(_b_) Stocks should be stored in a detached building which should not be
+damp. Jars or cases should not stand on a wooden floor if possible.
+
+(_c_) See (_d_) above.
+
+BUYING SULPHURIC ACID.--(_a_) Commercial acid of specific gravity 1.84 is
+the best of its kind. It contains impurities which are non-injurious to
+rubber preparation.
+
+(_b_) It is always advisable, if possible, to buy the acid in small jars
+containing not more than 100 lbs. each. Smaller jars, with a content not
+exceeding 50 lbs., would be preferable.
+
+(_c_) If the acid is bought in jars, it should be stipulated that the
+stoppers be covered with a plaster head, and that the containing crate or
+case should have prominent labels or marks indicating the top of the case.
+
+FORMULA FOR USE OF SULPHURIC ACID.--It will be understood that as this
+formula has been calculated for working with latex, having a consistency of
+1-1/2 lbs. dry rubber per gallon, it applies in a strict degree only to
+such latex. In other cases, where the dilution of the latex is not known,
+the formula will serve as a basis for experiment until the correct quantity
+has been discovered.
+
+(Sulphuric acid of specific gravity 1.84.)
+
+     NOTE.--The directions must be followed carefully, and glass measuring
+     vessels should be used if procurable.
+
+     (_a_) Measure out 1 pint of strong acid, and pour it carefully and
+     slowly _down the inner surface_ of a jar containing 20 gallons of
+     water. Do not pour it directly into the water.
+
+     The heavy acid will sink to the bottom of the jar, and a good mixture
+     must be obtained by stirring well.
+
+     (_b_) Of this solution (which is approximately 1 per cent. by weight),
+     use 1 gallon to 20 gallons of latex.
+
+Readers are doubtless now well aware of the corrosive action of strong
+sulphuric acid, and we scarcely need point out that even the dilute acid
+should not be kept in contact with the usual iron vessels found in
+factories. The mixing of solutions should be done in one of the glazed
+earthenware jars commonly in use.
+
+The formula given above works out at approximately 1 part strong acid to
+2,000 parts of latex (of dry rubber content 1-1/2 lbs. per gallon). The
+formula for using acetic acid with the same latex works out at about 1:
+1,200. It will be apparent, therefore, that relatively sulphuric acid is a
+more powerful coagulant than acetic acid. In terms of dry rubber obtained
+from latex of the consistency indicated above--
+
+     1 lb. sulphuric acid will produce 300 lbs. dry rubber. 1 lb. acetic
+     acid will produce 180 lbs. dry rubber.
+
+With both acids selling at the same rate, sulphuric acid would be more
+economical in use; when its cost is less than that of acetic acid, which is
+the normal condition, the economic advantage in favour of sulphuric acid is
+augmented still further.
+
+It may be found that the standard formula for sulphuric acid will not
+always give a perfectly clear remaining serum, even though an attempt is
+made daily to work to a uniform consistency for all latices. It is
+inevitable that the manipulation of the latices should be slightly in error
+on occasions, or that a small mistake might occur in preparing the solution
+of acid. Hence a clear remaining serum after coagulation may be secured
+less often than a slightly turbid serum. This is as it should be. The
+minimum quantity of acid may be adjusted so closely as to give such
+results. If a clear serum is obtained always, that should be an indication
+of continual excess of coagulant. Naturally, if a milky serum is always
+obtained, the reverse is the case.
+
+As a last word on the subject, it may again be emphasised that the use of
+sulphuric acid is not advised, except in an emergency; and that the
+greatest possible care must be exercised in the observance of the strict
+formula for use.
+
+HYDROCHLORIC ACID, NITRIC ACID.--These mineral acids would prove more
+expensive than sulphuric acid. In addition they are much more uncertain in
+action. For example, the use of a certain excess of hydrochloric acid would
+not hasten coagulation, but would prevent it. Above all their effect, in
+excess, is deleterious to the rubber.
+
+HYDROFLUORIC ACID.--This has a strong corrosive action on porcelain or
+glass. Hence it has to be contained in bottles of gutta-percha or lead. It
+is mentioned here merely because some years ago it found a use as a
+coagulant, chiefly in Ceylon. It was sold in the form of a 10 per cent.
+solution under the name of "Purub," and was the subject of a patent.
+
+It is effective as a coagulant, and has also an anti-oxidant action, which
+was its chief recommendation when cheap and harmless anti-oxidants were not
+commonly known. It is comparatively expensive, and, as indicated above,
+difficult to handle and store. In short, it has nothing to commend it, in
+comparison with acetic or formic acids.
+
+ALUM.--This substance has been used for years by native rubber producers as
+a coagulant. It fulfils the desired purpose, and its popularity was
+maintained because of the ease with which it could be stored and handled.
+Unfortunately, this facility often led to the use of an excess, and native
+sheets were often criticised as being brittle. Investigations have shown
+that alum, even in minimum proportions, has an appreciably harmful effect
+upon the quality of the rubber prepared by its use as a coagulating agent.
+Its employment by native rubber producers has now been largely superseded
+by acetic acid in some form.
+
+PYROLIGNEOUS ACID.--This is otherwise known under the names of "crude
+acetic acid" and "crude wood vinegar." Owing to the shortage of acetic acid
+during the War, attention was directed towards the possibility of making an
+effective coagulant locally by what is termed the "dry distillation of
+wood"--_i.e._, the wood is not burned but heated in a retort. The enquiries
+could be placed in two classes:
+
+     1. Those which aimed at making the pure, strong acid of commerce.
+
+     2. Those which sought information concerning a crude coagulant
+     (pyroligneous acid) on estates.
+
+Regarding the first class, we can do no better than reproduce our remarks
+published in the April local report of the Rubber Growers' Association for
+1916--with the reservation that, on account of a threatened shortage of
+timber, a local scheme might not now be feasible:
+
+     "Probably the most common enquiry encountered since the rise in the
+     price of acetic acid is concerned with the possibility of making
+     acetic acid in this country. It may be stated that the proposition is
+     a feasible one, even on a fairly large scale. We have the essentials
+     necessary for such a scheme in:
+
+          "1. A good supply of suitable timbers, the most valuable of
+          which, possibly, is mangrove timber, locally known as 'bakau.'
+          Other suitable timbers are known, but as far as preliminary
+          experiments show mangrove timber gives the best yield. At present
+          this timber is in great demand as a fuel for steam plants, but
+          with the extension of the local coal industry the timber may
+          become cheaper.
+
+          "2. There would appear to be less valuable timber which would be
+          suitable for heating the retorts. Or, local coal might be used.
+
+          "3. Supplies of lime at reasonable rates are available, as the
+          limestone formation in the peninsula is quite considerable in
+          extent.
+
+          "4. Supplies of sulphuric acid are available from Japan,
+          Australia, Burma, etc., even at the present time, although
+          naturally rates are higher than normal. Under ordinary
+          conditions, supplies from England and parts of Europe would be
+          much cheaper than at current rates.
+
+          "For the benefit of many readers perhaps a brief and nontechnical
+          description of the preparation of acetic acid would not be amiss,
+          and would explain the necessity for the essentials indicated
+          above. In brief, the process is as follows:
+
+          "(_a_) A suitable timber is heated in a closed retort. This is
+          termed 'dry distillation,' and results eventually in the
+          carbonisation of the wood--_i.e._, charcoal is obtained in the
+          retort.
+
+          "(_b_) Tar, vapours and gases are distilled over during the
+          carbonisation of the wood. These liquors and gases pass through
+          condensers. The gases pass away, while the condensed liquors
+          separate out into (1) wood tar, (2) a watery liquor called
+          pyroligneous acid or crude wood vinegar.
+
+          "(_c_) The pyroligneous acid is separated from the tar, and again
+          distilled to obtain the acetic acid present.
+
+          "(_d_) This crude acid is steam-heated with milk of lime, which
+          fixes the acid, forming calcium acetate (or acetate of lime).
+
+          "(_e_) Eventually the calcium acetate is taken out in the form of
+          a thick paste, which is spread to dry. When dry this 'grey
+          acetate' is the main source of all glacial acetic acid now made.
+
+          "(_f_) The acetic acid is released from the 'acetate of lime' by
+          the action of sulphuric acid. It is then distilled several times,
+          and under various conditions, in order to increase its strength.
+          In the past copper tubes were used for this purpose, but owing to
+          the fact that traces of copper were found to be injurious to
+          rubber, some works instal tubes of glazed earthenware for the
+          distillation.
+
+     "Such is the process in outline, and it will be seen that no proposal
+     to manufacture _glacial acetic acid_ on an estate could be considered
+     feasible, although it would not present any great difficulty on a
+     large scale and under skilled direction. Furthermore, the cost of the
+     plant would be far too great for any estate."
+
+Although it is clear that pure acetic acid is beyond the scope of an
+estate, crude pyroligneous acid has been produced on a varying scale in
+this country and in Ceylon. In the latter country some success was obtained
+by the distillation of coconut shells with comparatively inexpensive plant.
+In this country, wood-distillation was practised on a few estates, but
+improved facilities for obtaining pure acetic led to a termination of the
+experiments, although sufficient crude acid could then be made at a
+reasonable cost.
+
+The pyroligneous acid obtained, is generally clear, after nitration, and of
+a dark brown colour. It has a peculiar odour reminiscent of smoked
+sheet-rubber, or of creosotic substances in general.
+
+Its acid content depends chiefly upon:
+
+     (_a_) The kind of timber heated in the retort.
+
+     (_b_) The efficiency of the apparatus.
+
+     (_c_) Condition of the timber as to moisture.
+
+     (_d_) The temperature employed, and rate of working.
+
+     (_e_) The point at which distillation ceases (_i.e._, the duration of
+     interval between commencement of heating and cessation of collection).
+
+Samples received from estates for testing purposes were found to contain
+equivalents varying from 2 per cent. to 10 per cent. of acetic acid.
+
+They were all suitable coagulants when used in quantity calculated from the
+discovered acidity, but produced rubber darker than ordinary when
+air-dried. This effect was not of much importance in the preparation of
+smoked sheets, but to produce a pale crepe it was necessary to employ
+sodium bisulphite as an anti-oxidant.
+
+This darkening in colour is to be ascribed to the presence of traces of
+phenols,[24] which are stated to exert an effect upon the rubber during and
+after vulcanisation.[25] This subject will be discussed in another section.
+
+[24] Whitby, _Journal Soc. Chem. Industry_, vol. xxxv., No. 9, 1916.
+
+[25] See also "Preparation and Vulcanisation of Plantation Rubber" (Eaton,
+Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture,
+April, 1918.
+
+With this provision the crude pyroligneous acid which can be produced on
+estates, could be employed as a coagulant until such time as the price of
+glacial acetic acid was so low as to make the production of the crude acid
+non-profitable. This point would be determined from a knowledge of the cost
+of production per gallon, and the percentage of acetic acid per unit. For
+example, if the cost of production (including cost of timber for
+distillation, cost of fuel for heating the retort, cost of labour, etc.)
+was 60 cents per gallon of crude acid containing 9 per cent. of acetic
+acid, that would be equivalent approximately to buying glacial acetic acid
+at $30 per demijohn of 44 lbs.
+
+SMOKED WATER.--A weak solution of pyroligneous acid may also be obtained
+by passing smoke through water. With this object in view, a machine was
+designed by the Federated Engineering Company of Kuala Lumpur. In this the
+principle of retorting was not employed. Smoke was produced by ordinary
+combustion in a compartment of the apparatus, and was drawn through water
+by the action of a high-speed fan worked by hand. A solution, equivalent in
+effect to a 2 per cent. solution of acetic acid, could be obtained at a
+comparatively cheaper cost than crude pyroligneous acid produced by dry
+distillation as it was then being practised. This was chiefly because of
+the wasteful methods of fuel combustion, in the latter process, in the
+heating of the retort.
+
+CHINESE VINEGAR.--This agent was found to be a satisfactory coagulant, and,
+_a priori_, there is no reason why it should not be suitable, as it is
+essentially a dilute solution of acetic acid.
+
+The qualities sold were generally colourless, and were probably the result
+of acetic fermentation of rice.
+
+Samples tested showed a varying content of acetic acid, ranging roughly
+from 3 per cent. to 8 per cent.; but on this basis of valuation it was
+found generally that the price bore no relation to the degree of
+efficiency.
+
+It was advanced not only that the vinegar was an efficient substitute for
+glacial acetic acid, but that it was also cheaper. This latter claim was
+proved to have no foundation in fact, even at the high price of acetic acid
+prevailing during the period of stress. It is not likely, therefore, that
+vinegar can displace acetic acid, except as an expedient.
+
+SULPHUROUS ACID.--The anti-oxidant effect of sodium bisulphite and sodium
+sulphite is due to the liberation of the gas, sulphur dioxide. This gas
+dissolves easily in water, forming an acid solution called sulphurous acid.
+
+This acid solution is an effective coagulant in fairly small quantity. Not
+only so, but it produces, in addition, the anti-oxidant effect noted in the
+employment of sodium bisulphite. It is thus possible to produce rubber
+varying in shade of paleness by means of a single solution.
+
+In the event of sulphurous acid being used, it would be necessary to
+import cylinders of sulphur dioxide from which the solution could be
+prepared in factories each day. There would be no insurmountable difficulty
+in this, as it is only necessary to pass the gas through a series of closed
+vessels containing water. Enough solution could be prepared at one time for
+three or four days, but preferably the solutions should be as fresh as
+possible. Altogether there would seem to be possibilities in the use of
+sulphurous acid for preparing pale crepe rubbers, providing the cost is
+within comparable limits with the commoner coagulants at present in use,
+and that no adverse effect on the rubber can be shown to result. If the
+cost did not exceed the combined cost of acetic acid and sodium bisulphite,
+the employment of sulphurous acid solution might be worthy of
+consideration. There is one drawback to the use of sulphurous acid
+solution, and that lies in the proximity of the limits of the quantities
+necessary for coagulation and that which is in excess, and prevents
+coagulation. Thus, with ordinary field latex having about 20 per cent. dry
+rubber content, the minimum necessary for coagulation per 100 c.c. of latex
+is about 8 c.c. of a 1 per cent. solution. The maximum quantity possible
+for use is about 15 c.c. of a 1 per cent, solution, so that great care
+would have to be exercised in avoiding an excess of coagulant, otherwise
+coagulation would be effectually prevented.
+
+It is believed that the preparation of rubber by this method is the subject
+of a patent secured by Messrs. Boake, Roberts, and Co., London.
+
+SUGARS.--Coagulation may be effected by the addition of small quantities of
+sugars.[26] These are assumed to be effective by fermentative conversion
+into lactic and acetic acids. The presence of lactic acid is supposed to
+have a twofold effect:
+
+[26] "Preparation and Vulcanisation of Plantation Para Rubber" (Eaton,
+Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture;
+Gorter and Swart, Bulletin No. 6, West Java Expt. Station.
+
+     (_a_) As a direct coagulant.
+
+     (_b_) In its action upon certain organisms which, in the ordinary
+     course of events, would delay or prevent coagulation. Although work on
+     an experimental scale has been done, as far as we know no practical
+     application has been made of the employment of sugars as coagulating
+     agents.
+
+VARIOUS SALTS.--Of experimental interest only it may be recorded that
+coagulation has been effected by means of various chemical "salts"--_e.g._,
+calcium chloride, barium chloride, magnesium chloride, sodium chloride,
+aluminium sulphate, magnesium sulphate, sodium sulphate, etc. None of these
+has been found to have any practical application, except, perhaps, calcium
+chloride, which is used in small quantity as an accelerating agent in a
+special process of anaerobic coagulation, which will receive mention in the
+following chapter.
+
+At one period during the War and the dearth of acetic acid, it was found
+that there were available in England large supplies of the acid sulphate of
+sodium (sodium hydrogen sulphate), which proved to be an effective
+coagulant. Experimental work gave satisfactory results, but no practical
+application resulted when supplies of acetic acid were again obtainable.
+
+VARIOUS PROPRIETARY COMPOUNDS.--We have seen many proprietary coagulants
+advertised and pass into the limbo of forgotten things. They can generally
+be divided into two classes. The first embraces those founded upon a
+woefully incomplete knowledge of requirements. The second covers those
+which meet requirements, but for which exaggerated claims are made and
+excessive prices charged.
+
+As as instance of a substance which fell under both classifications might
+be mentioned the case of "Coagulatex." Pretentious claims were made, and it
+was emphasised that the liquid contained no _vegetable acids_. Acetic and
+formic acids might be quoted as examples of vegetable acids, and as these
+have been shown to be the most satisfactory coagulants now employed one
+fails to imagine where lay the value of the guarantee given by the
+advertisers of "Coagulatex."
+
+On analysis the liquid was found to consist mainly of sulphuric acid,
+against the indiscriminate use of which warnings have been given. Thus it
+was a dangerous substance for common use.
+
+Furthermore, comparing the value with its sulphuric acid content, it was
+found that the price required for "Coagulatex" was roughly four times the
+contemporary cost of commercial sulphuric acid in the Federated Malay
+States.
+
+Those in charge of estates should realise, therefore, that no proprietary
+coagulants should be adopted until a proper report of tests, and a
+comparative valuation, has been obtained from one of the research
+laboratories.
+
+CARBONIC ACID GAS, CARBON DIOXIDE.--Now of only scientific interest, it may
+be noted that some years ago great claims were made for the use of carbon
+dioxide gas as a coagulant. In actual practice we were unable to effect
+coagulation by passing the dry gas into latex. It was suggested that the
+original investigators were misled by failure to secure a dry and clean
+gas. It would appear that probably the gas was prepared by the action of
+hydrochloric acid upon marble or limestone. Unless intervening "washers"
+and "driers" were used, the liberated gas, when passed into latex, would
+carry with it traces of hydrochloric acid, which would effect coagulation.
+
+ALCOHOL.--In the cheap form of methylated spirit, alcohol has been employed
+by us as a speedy coagulant for many years. Latex run slowly into alcohol
+coagulates instantaneously. The method has been in common laboratory use.
+
+The employment of alcohol has also been made the part-subject of a patent
+process of coagulation, to which reference will be made in the succeeding
+chapter.
+
+VEGETABLE EXTRACTS.--At various times experimental work has been directed
+towards the use of liquids of purely vegetable origin, such as the juices
+of tropical fruits, and of a waste product of tropical industry--the
+so-called "milk" (or water) of ripe coconuts.
+
+In the former class there is usually a natural acidity, but in coconut
+water the acidity is chiefly the result of fermentation of the carbohydrate
+(sugar) constituents.
+
+These substances were all found to effect a more or less satisfactory
+coagulation, but it is unlikely that they would be suitable for practical
+application on a large scale.
+
+As being more directly related to the subject of coagulation in general
+than to coagulants in particular, a discussion of several special processes
+will be relegated to the ensuing chapter.
+
+
+
+
+CHAPTER XX
+
+_SPECIAL METHODS OF PREPARATION_
+
+
+Every year appears to bring forth some new ideas in the mode of rubber
+preparation. Some of them are based in principle upon the oldest known
+method--_i.e._, the native Brazilian process of making "Hard Para." Others
+strike a new note, and in a few cases the claims put forward are
+substantially confirmed by results. In other instances the claims are too
+pretentious, and discredit may be brought upon schemes which, although
+lacking in comparative success, are yet commendable for the ingenuity
+manifested.
+
+To the present not one of these new methods has been able to compete to any
+marked degree in general practice with the established methods of ordinary
+preparation. A few continue to find local application, but most have either
+been abandoned or are gradually falling into desuetude.
+
+We do not propose to discuss in fine detail all the various claims made on
+behalf of these special processes, or to enter into controversies. The aim
+is to present to the reader an outline embodying the main principles and
+advantages claimed.
+
+DA COSTA PROCESS.--Briefly, this was a method by which coagulation was
+effected with smoke. The smoke was generated by the combustion of wood in a
+special compartment, and was forced into latex by means of a jet of steam.
+It was really only applied to the preparation of coagulum intended for
+crepe form. The exact degree of coagulation effected was uncertain, and the
+final colour of the rubber precluded it from being classed as a modern No.
+1 product.
+
+"BYRNE CURING" PROCESS.--This is a process for treating coagulum obtained
+by ordinary methods.
+
+It was the subject of a patent obtained by Messrs. E. J. and F. A. Byrne,
+and at one time had a considerable vogue on estates. The chief claim
+advanced was that the rubber produced was in all respects equal to Fine
+Hard Para, and could be shipped while still moist without detriment to the
+physical qualities.
+
+The principle of the process was the treatment of coagulum, in either sheet
+or thick crepe form, with vapours produced by the volatilisation of two
+special fluids. This treatment was undertaken in comparatively small wooden
+sheds, in which the coagulum was placed. The "smoke" was conducted into the
+curing sheds from furnaces outside the building. The sheds were covered
+externally with "felt" material to prevent leakage of the vapours, and a
+very dense smoke was obtained.
+
+The furnaces were specially designed, and consisted essentially of a
+"hot-plate" heated by a powerful kerosene blast-flame. On top of the
+machine were two reservoirs controlled by taps. In these were placed the
+special fluids which were released in definite proportion. The composition
+of the fluids was not divulged, but it is assumed that the principal
+ingredients were (_a_) wood tar products, (_b_) crude pyroligneous or
+acetic acid. The mixture of these, dropping on the hot plate at the correct
+temperature, spontaneously volatilised, to form dense whitish fumes, having
+an intense and not disagreeable odour of wood combustion. A duct led from
+the back of the machine into the curing-shed, where the vapours were
+distributed through perforations in the pipe.
+
+The coagulum usually remained under treatment in the shed for three to four
+hours, and then was removed for ordinary air-drying. When taken from the
+curing-shed it had a pinkish colour, which later developed into a dark
+brown by a natural process of oxidation. The exterior of the rubber, on
+shipment, resembled the appearance of smoked sheets; while the interior, on
+cutting, was seen to be still white. As packed for shipping, the rubber
+contained from 10 to 15 per cent. of original moisture, for the usual sheet
+form, and even more when "slab" rubber was prepared.
+
+Originally either crepe or sheet rubber was made, but later the preparation
+of the crepe form was displaced largely by "slab" rubber. These "slabs"
+were really very thick sheets, which had been subject to only slight
+pressure.
+
+Still later the preparation of the "slab" form was displaced by "loaf"
+rubber. This form was built up by winding together ordinary thin sheets
+which had been subject to the "cure." Only slight tension was needed,
+during the operation of winding, to cause close adhesion of the component
+wet layers, and the final result was a "loaf" or roll dark in colour, and
+apparently dry when examined superficially. On being cut, even after an
+interval of months, the middle portion was still so moist as to be quite
+white.
+
+In course of time it was discovered that all the claims made for the
+process could not be substantiated, and for various reasons (which need not
+be detailed) most of the estates which had adopted the scheme reverted to
+ordinary methods of preparation. At the time of writing few, if any,
+continue to work the process. It appears to be agreed, as the result of
+investigations, that in no degree does the process yield advantage over
+ordinary methods.
+
+FREEZING PROCESS.--A patent was secured a few years ago to cover a process
+whereby coagulation was effected by refrigeration.
+
+Latex remained for several hours in the refrigerating chambers of an
+ordinary ice-making plant. The resulting solid mass, on being thawed,
+yielded a coagulum appearing in no way to differ from that obtained by
+ordinary methods of coagulation.
+
+Provided the process exerted no influence for good or evil upon the quality
+of the resulting dry rubber, the value of it would appear to depend upon
+the relative cost of working, plus considerations of capital expenditure
+and depreciation on the plant. At the present time it would be difficult to
+imagine that the cost of preparation alone would compare favourably with
+that sustained by ordinary coagulative methods.
+
+Furthermore, beyond the expensive refrigerating plant, the usual machinery
+of a factory would still be required if the ordinary market demands are to
+be met.
+
+Finally, it has not been found[27] that any advantage in the final physical
+qualities of the rubber is obtained by the employment of this process.
+
+[27] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture.
+
+WICKHAM PROCESS.--This process, invented by Sir Henry Wickham, aimed at the
+production of a rubber resembling Fine Hard Para. The principle employed
+was that underlying the preparation of the best rubber in Brazil--viz.,
+coagulation of superimposed thin layers of latex by the action of smoke and
+heat.
+
+In essential the machine employed consisted of a rotating drum into which
+latex and smoke entered. The result was the formation of thin "skins" of
+rubber which, coagulating _in situ_, formed a mass corresponding to "Fine
+Hard."
+
+That the rubber was fully satisfactory as to quality is acknowledged, but
+economically and in practical utility the process was unsuccessful, the
+rate of output being so low.
+
+DERRY PROCESS.--The invention of Mr. R. Derry, late of the Singapore
+Botanic Gardens, this in principle resembled the Wickham and other
+processes. It aimed at a mechanical imitation of the native method of
+producing Fine Hard Para.
+
+In place of the rotating drum, an endless belt was used. This travelled
+over pulleys, more or less horizontally placed. The upper of these could be
+raised to varying height above the level of the other, and likewise could
+be so adjusted as to tighten the belt.
+
+The under layer of the belt impinged, in its travel, upon the surface of a
+layer of latex contained in a shallow tray. The belt was operated by
+hand-power, and the height of the latex trays was adjustable.
+
+The trays of latex were situated at the lower end of the machine which lay
+outside the smoking-chamber. It will be understood that the vastly major
+part of the total length of belt was always within the chamber.
+
+Smoke was generated by combustion of wood in an external structure, was
+brought into the chamber by a wide duct, and was then distributed below
+the belt by means of perforated pipes.
+
+The thin film of latex picked up by the belt was coagulated partly by the
+action of smoke constituents by evaporation due to heat. Assuming (1) that
+the belt was of adequate length, (2) that the rate of travel was not
+excessive, (3) that the latex was not too dilute, (4) that the temperature
+of the smoke was sufficiently high, (5) that the smoke was sufficiently
+dense and not too damp--then the process should be a continuous one.
+
+It will be clear that success could only be obtained by a careful
+adjustment of all these factors. The latex must, necessarily, be of a
+fairly rich consistency (at least 2-1/2 lbs. dry rubber per gallon), but
+unfortunately there is considerable difficulty in maintaining such latex in
+a state of fluidity for the period demanded by this process, without loss
+of latex. Naturally, the addition of an anti-coagulant would retard the
+rate of output of the machine to a marked degree.
+
+The layer of rubber thus formed on the belt was stripped off, and hung for
+further air-drying, as it still contained a fair percentage of moisture.
+
+As a really practicable method for treating plantation latex, the process
+failed by reason of its low rate of output over a given interval. This
+alone was sufficient to condemn it, apart from the facts (1) that it was
+not shown to be a cheaper method than coagulation by acetic acid, (2) that
+the resulting rubber was not proved to be of superior intrinsic value to
+rubber prepared by ordinary methods.
+
+SPONTANEOUS COAGULATION.--All readers will be aware of the phenomenon of
+the curdling or souring of milk. The behaviour of _Hevea_ latex, under
+certain conditions, may be taken to be analogous. Difficulty is experienced
+in maintaining fluidity--a difficulty which appears to vary in great degree
+according to locality, nature of soil, age of trees, the relative demand
+made upon the trees by the system of tapping employed, etc.
+
+It is sometimes found, before the latex reaches the store, that it may
+exhibit one of various stages of premature (spontaneous) coagulation:
+
+     (_a_) To all appearances it may be quite fluid, but a close
+     examination shows it to consist mainly of a serum containing very
+     minute particles of rubber in suspension (microscopic coagulation).
+
+     (_b_) In a later stage these particles coalesce to form larger
+     "flocks" (macroscopic coagulation).
+
+     (_c_) The whole, or practically the whole, of the latex may have
+     coagulated, forming one mass of rubber with a milky residual serum.
+
+Passing from this aspect of the question, it may be noted as peculiar facts
+that:
+
+     (1) A shallow layer of latex is less likely to coagulate spontaneously
+     (_i.e._, without the addition of a coagulant) than a deeper volume.
+
+     (2) The shallow layer, and also the surface of the deeper volume
+     (where exposed to air), on standing will be found to develop a
+     superficial film of finely coagulated particles, yellowish in colour,
+     and having an offensive odour due to decomposition of protein matter.
+
+     (3) While this partial coagulation is confined only to the surface of
+     a shallow layer of latex, it will be found that below the surface film
+     of the deeper volume a much more definite coagulation has taken place.
+     The coagulation will be practically complete, and the coagulum, apart
+     from a spongy appearance, is normal in character. This coagulum is
+     free from the offensive odour noted above.
+
+     (4) On testing the surface film of both the shallow layer and the
+     deeper volume, it will be found to be _alkaline_ in character; whilst
+     the lower liquid surrounding the main portion of the coagulum in the
+     deeper volume of latex is of an _acid_ nature.
+
+These observed facts are sufficient to indicate that there are apparently
+_two distinct types of spontaneous coagulation_, and that the latter takes
+place particularly where the latex is more or less out of contact with the
+atmosphere. We may, therefore, differentiate thus:
+
+     (_a_) _In contact with air (aerobic)_: incomplete spontaneous
+     coagulation, accompanied by yellowish slime, offensive in odour and
+     alkaline in character.
+
+     (_b_) _Out of contact with air (Anaerobic)_: Practically or wholly
+     complete. There is no offensive odour under normal conditions and the
+     serum is acid in character.
+
+It is concluded[28] that there are present in latex, on collection in the
+field, two types of organisms. Those which work in contact with air
+(aerobic) show a tendency to _prevent_ coagulation and to form an alkaline
+yellow slime on the surface of the latex. The others, which work in the
+absence of air (anaerobic), may, under favourable conditions, cause
+complete coagulation unaccompanied by any decomposition or offensive odour
+within a normal period. If air is rigidly excluded, the coagulum obtained
+is quite satisfactory for all purposes.
+
+[28] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918; "De la
+Coagulation naturelle du Latex d'Hevea Brasiliensis" (Denier and Vernet),
+_Comptes Rendus l'Academie des Sciences_, No. 3, July, 1917.
+
+This type of coagulation, without the employment of a chemical coagulant,
+and under anaerobic conditions, was the subject of a patent granted in 1914
+to Messrs. Maude, Crosse and others. The process has been in use on Cicely
+Estate (Perak) for some years. With subsequent slight modifications the
+apparatus consisted in essential of a tank with a loose cover. The flanges
+of the cover were sufficiently long to dip into a water-seal surrounding
+the tank. Thus the cover may rise and fall without an inrush of air.
+
+Coagulation, in fact, can be effected thus in any kind of air-tight
+receptacle; and experimentally the reader can obtain a satisfactory result
+by filling completely with latex the bottle which has a loose stopper.
+
+Under the patent held the coagulum may be prepared either for crepe-making,
+or for sheets by a modification of the tank.
+
+The crepe when dry does not have the bright appearance of the ordinary
+"Fine Pale" standard prepared with the aid of the anti-oxidant sodium
+bisulphite.
+
+Unfortunately the addition of this substance to the latex in normal
+proportions is not possible under anaerobic conditions, as it is found to
+prevent coagulation, probably owing to its sterilising effect upon the
+anaerobic organisms.
+
+To prevent the oxidation of the rubber in actual practice, the freshly
+prepared crepe is soaked in a solution of sodium bisulphite before hanging
+to dry. The resulting colour of the rubber is quite good.
+
+It was shown by Eaton and Grantham that anaerobic coagulation is slightly
+uncertain in action. Owing probably to variations in the composition of the
+latices, or to the extent of infection by organisms, coagulation may one
+day be complete and on other days less satisfactory.
+
+They found further that, by the addition of small quantities of sugars,
+coagulation under both aerobic and anaerobic conditions was improved. The
+conclusion formed was that the addition of sugars created a medium
+favourable to the development of anaerobic organisms and unfavourable to
+those which cause decomposition of the natural nitrogenous constituents of
+latex.
+
+This work was confirmed by Gorter and Swart,[29] who attributed the action
+to the conversion of sugar to lactic, acetic, and succinic acids by
+fermentation.
+
+[29] Gorter and Swart, Bulletin No. 6, West Java Station.
+
+Denier and Vernet, whose work has already been mentioned, studied the
+presence of the organisms in latex, and succeeded in isolating one which,
+under anaerobic conditions, effects coagulation within twenty-four hours.
+Sometimes to produce complete coagulation it was found necessary to employ
+small quantities of sugars--_e.g._, 1 gramme per litre of latex (1:1,000).
+
+It is to be noted also that the addition of small quantities of soluble
+calcium (lime) salts to latex has much the same effect as the employment of
+sugars. Recent investigations[30] showed that the addition of 0.5 to 1
+gramme of calcium chloride per litre of latex caused complete coagulation
+in closed vessels within twenty-four hours, a result agreeing with the
+findings of Barrowcliff.
+
+[30] "Archief voor de Rubbercultuur," Nederlands Indies, 1920, 4, 273.
+
+On page 308 of the same publication, experiments on the effect of sugars
+are described, in connection with _aerobic_ coagulation. Observations from
+a further set of experiments tended to indicate a direct connection between
+the effects of tapping and spontaneous coagulation. It is suggested that
+heavy tapping causes a diminution in the latex of those substances which
+act in some way as accelerating agents in coagulation--_e.g._, sugars. The
+smaller the proportion of these substances, the slower and less complete is
+natural (spontaneous) coagulation.
+
+ILCKEN-DOWN PROCESS.--This process is the subject of patents granted in
+1915 to Messrs. Ilcken and Down. It has been in fair prominence, and has
+been tried experimentally on several estates and in public demonstration.
+
+It is a coagulating process, and, in the original specification, employed
+as agents a mixture of alcohol (in the form of methylated spirit) and
+benzene (petrol), or alcohol with petrol and coal-tar naphtha. The mixture
+was injected in the form of a fine spray into the latex, contained in a
+tank specially fitted with paddles.
+
+Later modifications covered the addition of a small quantity of glycerine;
+or, failing supplies of that substance, coconut oil.
+
+Many advantages are claimed for the process, but most of them cannot be
+substantiated. The two chief claims are:
+
+     1. The production of a uniform standard of rubber.
+
+     2. The obtainment from a unit volume of latex of a greater weight of
+     rubber than can be obtained from an equal volume of the same latex by
+     ordinary coagulation with acetic acid. It is to be inferred that the
+     agents employed have the power of adding to the coagulum some of the
+     substances which usually remain in solution in the clear serum.
+
+Regarding the first of these claims, it has been shown[31] that the rubber
+is not uniform in its behaviour on vulcanisation, and that its variability
+is similar to that of rubber prepared by other processes.
+
+[31] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918.
+
+The second claim has been the subject of much controversy. Experiments made
+on estates under the supervision of, or in the absence of, the patentees
+have given conflicting results. When varying factors have been eliminated,
+the general conclusion was that no increase in weight of rubber was
+obtained.
+
+Private laboratory investigations led to a similar verdict, and Eaton[32]
+records a confirmatory finding. More recently the claims made for the
+process were investigated in Java[33] under varying conditions. Three
+series of experiments were made:
+
+[32] _Ibid._
+
+[33] "Archief voor de Rubbercultuur" (De Vries and Spoon), Central Rubber
+Station, Java, May, 1921.
+
+     (1) During the rainy monsoon and at a height of 1,800 feet.
+
+     (2) During the dry monsoon on a low-country estate.
+
+     (3) In the experimental gardens at Buitenzorg during bright sunny
+     weather and the most favourable conditions.
+
+The agents used were (_a_) a mixture of alcohol and fusel oil, (_b_)
+alcohol and petrol (benzene).
+
+In these experiments no advantage in weight of rubber was obtained by the
+Ilcken-Down process, and it would thus appear that the principal claim
+fails to be substantiated.
+
+The general composition of the rubber was approximately the same as
+ordinary crepe obtained from undiluted latex. The rubber on vulcanisation
+was found to be normal in behaviour, and was similar to the controls.
+
+The coagulum ordinarily is affected by oxidation, and does not produce a
+fine pale crepe. To remedy this defect the freshly prepared crepe is soaked
+in a solution of sodium bisulphite and sulphuric acid.
+
+It may be noted that in the recent experiments coagulation was effected in
+vacuum in a specially designed wooden tank. From a study of the previous
+section on "Spontaneous Coagulation," the reader will perceive that results
+equal to those obtained by the Ilcken-Down process can be obtained
+_without_ the necessity of using such agents as alcohol, petrol, or fusel
+oil.
+
+SLAB RUBBER.--This type of preparation has been the subject of much
+discussion of recent years. There is nothing really special in the mode of
+preparation, and in its original form "slab" rubber is only a thick sheet
+which may be obtained by coagulation with acetic acid or other agents.
+
+The coagulum, when removed from the serum, is subjected to comparatively
+slight pressure, and the "slab" thus made is either placed to air-dry at
+once, or may be subject to treatment in other liquids before drying.
+
+The rubber is not allowed to remain until wholly dry, but is shipped while
+still containing an appreciable percentage of enclosed moisture.
+
+It is claimed[34] that the production of "slab" rubber by standardised
+methods eliminates to a great degree the variability which at present
+characterises plantation rubber, and that a fast-curing medium is obtained.
+These claims will be discussed in later chapters dealing with the
+vulcanisation of rubber, and demand no notice in this section.
+
+[34] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham,
+and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918.
+
+From the producers' point of view, it may be noted that the preparation of
+slab rubber is a simple process, but not altogether as pleasant probably as
+might be desired, when undertaken in crude form.
+
+The appearance of the partially dry slabs is unattractive, but that does
+not signify if the quality of the vulcanised product satisfies
+requirements.
+
+For the average producer, the difficulty lies in having to meet the demands
+of the general market. Even, therefore, if one assumes that the intrinsic
+qualities of slab rubber are all that the claims advance, it would be
+necessary for the producer to be assured of definite and regular sales.
+
+At present it would probably be fair to state that practically all the
+"slab" rubber being prepared is produced by those who are also consumers.
+They are thus in the enviable position of being able to satisfy their
+requirements as to the mode of preparation. Until such time, therefore, as
+there exists a regular demand for "slab" rubber in the general market, the
+vast majority of estates must proceed on ordinary lines of preparation.
+
+
+
+
+PART VI
+
+VULCANISATION
+
+(BY DR. H. P. STEVENS)
+
+
+
+
+CHAPTER XXI
+
+_INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION_
+
+
+In the foregoing chapters the methods of treating latex, coagulating,
+rolling and curing, or drying, have been described in great detail. These
+details will give the reader some idea of the precautions taken, and
+procedure necessary to produce rubber which will be acceptable to the
+market. The expressions "inferior rubber," "defective crepe," "poor quality
+sheets," etc., are frequently met with, but these expressions must not be
+taken to indicate any defect in the rubber for manufacturing purposes, but
+merely that the rubber is defective for selling purposes--that is to say,
+being unsightly, it will not fetch the full market price.
+
+Raw rubber, as produced on the plantations, is almost invariably subjected
+to the process of vulcanisation in the production of manufactured rubber
+articles as we know them. Previous to the advent of plantation rubber, the
+raw material was purchased by the manufacturer in a moist and impure
+condition; frequently the rubber was adulterated with sand, dirt, and even
+small stones. Consequently it was the invariable practice of the rubber
+manufacturer to wash the raw rubber and convert it into crepe, which was
+then hung and air-dried before use. The effect on the rubber, if of high
+grade, was more severe than the washing and crepeing process on the
+plantation, because the rubber was not a soft coagulum but generally dried
+on the surface and semi-hard. The power required was considerable, and the
+resulting crepe was consequently softer and more susceptible to heat than
+plantation first latex crepe. Much of the "wild" rubber was soft and tacky
+and inferior to "earth-scrap."
+
+Vulcanising in its simplest aspect consists in mixing the rubber with
+sulphur and heating the product under regulated conditions. The effect of
+heat on the inferior grades of "wild" rubber is very marked. A soft,
+sticky, and resinous material is transformed into a relatively tough and
+elastic product. The effect of vulcanising on the better grades is less
+marked, but immediately apparent. On the other hand, the effect of
+vulcanising is least apparent on first latex plantation grades, because in
+these we have a raw rubber prepared in a manner best suited to retain its
+natural characteristics.
+
+The need of vulcanising in the process of manufacturing rubber goods became
+an axiom in pre-plantation days, and it is only quite recently that
+attempts have been made to utilise raw rubber directly, without
+vulcanisation, particularly for shoe soles. For this purpose a thick dense
+crepe has been found satisfactory. Smoked sheet rubber is not generally
+suitable, apparently owing to its microphysical structure. It is possible
+that the process of rolling in the making of dense crepe compacts the
+rubber particles, yielding a harder and more resilient product. The rolling
+must not be carried too far, or the "working" of the rubber will
+approximate to a preliminary mastication, and the product will be weakened.
+
+The utilisation of crepe rubber directly has not yet been sufficiently
+tested to enable a definite conclusion to be reached as to its future
+scope, but it is obvious that for use in a raw state some modification in
+preparation may be advantageous. The present method--_e.g._, coagulation
+with acetic acid--does not yield the hardest and toughest rubber.
+
+Hardness and toughness are actual drawbacks in the utilisation of rubber
+which is required for vulcanising. When the output of plantation rubber
+began to increase and to displace the inferior wild sorts, manufacturers
+complained of the increased power consumption of their machines. The power
+was required mainly to "break down" or "mill" the rubber preliminary to the
+mixing with sulphur and other ingredients. It is obvious that a material
+such as raw rubber cannot be mixed with powders such as sulphur with a
+pestle and mortar, or in any simple form of mixing machine. This difficulty
+was overcome by the earlier experimenters by immersing the rubber in a bath
+of molten sulphur. The latter was gradually absorbed and "dissolved" in the
+rubber, and the heat of the bath caused the dissolved sulphur to combine
+with the rubber to produce vulcanised rubber. The limitations of such a
+process are apparent. Thus the vulcanised rubber retains the form in which
+it was originally shaped. Moreover, other ingredients, such as mineral
+matters, cannot be dissolved or absorbed by the rubber in this manner. The
+method eventually adopted consisted in "breaking down," "milling," or
+"masticating" the rubber by passing it continuously between differentially
+geared steam-heated rollers. By this means a high-grade rubber is converted
+into a soft, plastic mass, which will "take up" sulphur, mineral matter,
+and other ingredients as desired. The mixing operation may be carried
+through on the same roller machine as was used for breaking down the
+rubber, or separate machines of other designs may be adopted. Details of
+the process will be found in books dealing with rubber manufacturing.[35]
+It will suffice here to explain that when rubber is kneaded between two hot
+rollers moving at different speeds the rubber forms a continuous band
+around the slower moving roller, and if the distance between the rollers be
+adjusted the excess of rubber held back by the nip of the rollers will form
+a "bank" or moving wedge-shaped mass on the top of the nip. This closes the
+space between the rollers, so that sulphur and powder placed on the rubber
+pass round towards the nip, and are there driven into the rubber. In this
+manner it is easy to mix, say, 10 per cent. of sulphur into the rubber
+without a single particle falling through. In technical mixes where large
+quantities of powders require to be mixed there is always some caking, and
+part of the powder falls between the rollers into a tray underneath. This
+is swept up with a broom and put back on to the rollers, the process being
+repeated until the whole of the ingredients have been incorporated.
+
+[35] For instance, "India-Rubber and its Manufacture," by H. L. Terry.
+
+From this description it follows that, preliminary to mixing, it is
+necessary to thoroughly masticate or "plasticise" the raw rubber. Much of
+the "wild" rubber was of so inferior a quality that it very readily broke
+down, and but little mastication was necessary. It was soft and resinous,
+and readily took up the powders which were to be mixed with it. The better
+grades of wild rubber, such as Fine Para, were more difficult to break
+down, but not so difficult as most plantation rubber, because they had
+already received a preliminary "working" in the process of washing and
+crepeing, and we have already explained that such treatment takes more
+power than the crepeing of the soft moist coagulum on the plantations. The
+amount of "working" or "plasticising" produced in the rubber is connected
+with the power expended; the greater the expenditure of power, _caeteris
+paribus_, the greater the working effect on the rubber. Although the
+manufacturers possessed a relatively soft rubber in the form of washed Fine
+Para, it was customary in most cases to employ this rubber in conjunction
+with washed lower grades to produce a soft plastic material for further
+treatment. Now, however, the manufacturer has little else but plantation to
+deal with, and most of it more difficult to break down than washed Para
+crepe. This is the reason why a hard, tough rubber is no longer a
+desideratum with manufacturers, although originally taken as an indication
+of good quality. For the majority of purposes they want something which
+will break down easily. Hence if a rubber could be produced answering to
+these requirements, without loss of vulcanising quality, it would be
+preferred.
+
+Having incorporated sulphur and other ingredients, the plastic mass is
+sheeted and run between layers of calico to prevent the superimposed sheets
+from adhering. From this "calendered sheet" the article, whatever it may
+be, is built up. The calender rollers are heated so as to keep the rubber
+compound plastic. There is a limit to the thickness of the sheet which can
+be produced. It is a difficult operation to perform satisfactorily so as
+to yield a smooth surface and a sheet free from enclosed air. When cool the
+rubber hardens and is readily handled. The object to be manufactured is
+then built up from the calendered sheet. Thus in the manufacture of a motor
+tyre the tread is built up on the casing or carcase by laying the sheets on
+the canvas and rolling these with a hand or power operated roller, so that
+they adhere firmly, the first layer to the canvas of the casing and
+subsequent layers to one another. This rough description will suffice to
+illustrate how important it is that the rubber when mixed should be plastic
+enough to give a smooth sheet, and to allow the sheet to be manipulated in
+building up the article in process of manufacture. The testing of rubber in
+regard to its plasticity and power to absorb finely divided mineral matter
+will be discussed in a later chapter. We may, however, point out here, that
+the mineral matter is not generally added as an adulterant, but because of
+certain specific properties it confers on the product.
+
+To proceed with our outline of vulcanisation, we have now arrived at the
+stage at which the goods are built up and ready for vulcanising. For this
+purpose they are generally enclosed in some manner, either in metal moulds
+bolted together, or tightly wrapped in cloth, as, _e.g._, in the
+manufacture of inner tubes, hose, etc. In the latter case, you can detect
+the cloth mark on the finished product. Sometimes the rubber is
+spewed--that is, driven out of a barrel by means of an endless screw
+revolving in it. In this way rubber tubing, perambulator tyres, and such
+articles, may be made. More recently even tyre treads and the shaped rubber
+for band tyres (heavy solid tyres) have been extruded in this manner, for
+the process is much cheaper than building up a tyre from calendered sheet,
+and then cutting the mass to shape by hand. But for spewing the rubber mass
+must be very soft and plastic; this condition is not obtainable unless the
+raw rubber originally used can be made thoroughly plastic without damage.
+Nor can it be effected with a rubber mass containing much finely divided
+mineral matter, as this hardens the mixture.
+
+For other purposes the rubber is swollen in a solvent, such as coal-tar
+naphtha, and subsequently masticated; the soft dough is then shaped or
+spread on cloth, and vulcanised after allowing the solvent to evaporate.
+Here, again, the properties of the raw rubber are of immense importance.
+Thus, the more plastic the dough, the less solvent required, and the less
+there is to drive off before vulcanising. The plasticity of the dough will
+depend on the plasticity of the raw rubber, and so forth. It is evident
+that the physical properties of the raw rubber are of great importance.
+They directly affect the manufacturing operations up to the vulcanising
+stage, and indirectly affect the results obtained on vulcanising.
+
+The actual vulcanising consists of heating the mass of mixed rubber for
+a definite time and at a definite temperature, each "heat" being chosen
+to suit the particular mixture. These data are arrived at
+empirically--that is, by trying a number of "heats" and choosing that
+which appears the most suitable. The suitability will depend on the
+nature of the article, the service to which it is to be put, and the
+time it is intended to last. All vulcanised rubber goods, whatever the
+process, have a limited life or period during which they can be relied
+on to give useful service. After a time, vulcanised rubber tends to
+harden, cracks appear on the surface when the article is bent or
+stretched, and eventually the rubber becomes rotten and "perished." This
+tendency varies with the quality of the original raw rubber and the
+conditions of vulcanising. Before plantation rubber was available, the
+manufacturers were dependent on inferior wild grades for a great part of
+their output, and, consequently, the goods made from these inferior
+rubbers never showed very good mechanical properties and soon
+deteriorated. The severest critics of plantation rubber have admitted
+the advantages to the manufacturers of the replacement of the lower wild
+grades by plantation rubber.[36] But even the best grades give a
+vulcanised product which rapidly deteriorates if the vulcanisation is
+carried too far. This results from too long heating, or too high a
+temperature, and the product is termed "overvulcanised" or
+"overcured."[37] The appearance of the product is deceptive, as the
+physical properties are remarkably good if the overvulcanising is not
+more than 50 to 100 per cent. in excess of the normal cure. Only in the
+case of very much overvulcanised rubber do we obtain a product which is
+brittle from the beginning.
+
+[36] See Williams, "The Rubber Industry," 1914, p. 284. It must also be
+remembered that the inferior wild grades were derived from latices often
+containing a large proportion of "resinous" matter, and which could not
+yield a really high grade of vulcanised rubber whatever the care and skill
+employed in preparation.
+
+[37] The terms "curing" and "vulcanising" are generally employed as if
+synonymous. Twiss has suggested that the former be applied in regard to a
+change in physical properties, and the latter to the chemical change
+whereby sulphur is combined with the rubber. The term "curing" is also
+applied to the process of preparation of raw rubber. This must be kept in
+mind so as to avoid confusion.
+
+The degree of vulcanising will vary with the type of article to be
+produced, and where a long life is desired, the tendency will be to
+"undervulcanise"; but if the best mechanical properties are desired, the
+tendency will be towards "overvulcanising," or, more correctly, "fully"
+vulcanising. These considerations are aptly illustrated by reference to
+pneumatic tyres. The inner tube need not possess high tensile strength,
+provided that it is easily distensible, for the reason that, during use, it
+is protected by the casing of the tyre proper, which confines and supports
+it against the air-pressure applied. Inner tubes are therefore cured to
+give a long life without developing the maximal physical properties. On the
+other hand, the casing and tread of the tyre are required to withstand
+severe mechanical conditions--particularly the constant flexing of the
+cover, and the abrasion of the road surface. Tyres are not stored for any
+long period, and, when put into service, have a limited period of useful
+life. Consequently it is needful to develop maximal mechanical properties,
+and vulcanisation is therefore carried further than in the manufacture of
+inner tubes.
+
+The rate of cure is controlled by a number of factors in addition to the
+period and temperature of vulcanisation, in particular by the proportion
+and nature of the other ingredients, especially sulphur and accelerators,
+and also by the rubber itself. The main complaint as regards plantation
+rubber is that it varies excessively in this respect. This matter will not
+be discussed here, but is only introduced in order to explain the
+importance of a constant rate of vulcanising to the manufacturer.
+Plantation rubber should, therefore, be prepared so as to be as uniform as
+possible in this respect, and the earlier part of this book gives full
+details of the precautions advised, and in many cases adopted on the
+plantations. Unfortunately, it is impossible to secure uniformity of
+methods among all producers, even when they are Europeans, to say nothing
+of the native producers, who account for perhaps one-third of the output.
+Hence the importance of branding the rubber whenever possible, so that the
+manufacturer may identify the rubber he purchases. If found satisfactory,
+he can then secure further supplies from the same estate.
+
+
+
+
+CHAPTER XXII
+
+_TESTING OF PLANTATION RUBBER_
+
+
+This subject may be subdivided into (_a_) Tests on the raw rubber; (_b_)
+tests on the vulcanised rubber.
+
+The tests on the raw rubber may be carried out (1) on the sample of sheet
+and crepe as received. For this purpose the rubber is cut into a strip,
+which is clamped between grips and gradually stretched to breaking-point.
+The ring testing machine can be adapted for this purpose by replacing the
+rollers with clamps. As the thickness of the samples to be tested will
+vary, it is advisable to cut the strips of such a width that the
+cross-sectional area of all test pieces is the same--say, 40 sq. mm. The
+method is applicable to both sheet and crepe rubber. (2) Tests may be made
+as to the behaviour of the rubber during milling or mastication. Small
+batches are milled under uniform conditions, preferably in an enclosed
+masticator such as Baker and Perkins supply. The power taken (as measured
+by the current taken to drive the motor actuating the machine) and the time
+are recorded. A further test may be applied to the milled or masticated
+rubber, to ascertain the amount and the time taken to incorporate a finely
+divided mineral matter, such as carbon black, zinc oxide, or one of the
+refined clays.[38] The results are not very exact, and the difference in
+plasticity and dryness noted are usually less than found when working with
+full-sized machines in the factory. (3) The rubber, either raw or
+masticated, may be "dissolved" in a "solvent," such as benzene, and the
+viscosity of the "solution" measured. Generally speaking, the less viscous
+the solution, the more plastic the rubber.
+
+[38] Bulletin Rubber Growers' Association, January, 1921, p. 43; August,
+1921, p. 340.
+
+The testing of vulcanised rubber has been treated in such detail in the
+recent works of Whitby[39] and De Vries[40] that a few special points only
+will be dealt with here. The preparation of samples for testing involves
+first the sheeting of the mixture of rubber, sulphur, and other
+ingredients, if any. The sheets may be 1 to 2 mm. thick. They are soft and
+adherent, and must be kept between layers of calico to prevent adhesion. A
+sheet of rubber is then built up by laying three or four sheets evenly upon
+one another, and pressing together to form a sheet 5 mm. thick. The thick
+sheet is then roughly cut to shape and vulcanised in a mould by heating in
+steam under pressure. From the vulcanised sheet so obtained the rings for
+testing are cut (45 mm. internal diameter. 5 mm. face, and 4 mm. thick).
+Rings obtained in this manner will not vary in diameter or thickness
+(reckoned as sections of a tube), as these are controlled by the size of
+the punch, but will vary a little in the face, as this is controlled by the
+thickness of the sheet, which depends on the completeness with which the
+mould is closed. More recently smaller moulds have been adopted, one mould
+for each ring, and an annular space for moisture to develop a pressure
+during vulcanising and prevent porosity. The moulds are vulcanised in an
+oil bath, or oven of some description, in which a constant temperature is
+maintained. I have adopted for some years a third method. The principle is
+that used in the factory for making annular-shaped rubber articles, such as
+washers, rings, elastic bands, etc. An aluminium mandrel, 45 mm. external
+diameter, is taken, and the thin rubber sheet is wrapped round this, so as
+to build up a tube about 4 mm. thick, the surplus rubber is cut off, and
+the edge bevelled with a wet knife. The manipulation will vary somewhat
+with the type of compound to be treated; thus, in some cases, it is
+sufficient to well roll the tube with a hand roller to secure adhesion. In
+other cases it is better to wipe the sheet of compound with a rubber
+solvent previous to rolling. In the latter case time must be given for the
+solvent to evaporate before vulcanising. The tube is next tightly wrapped
+in wet cloth, and is then ready for the vulcaniser. Or the tube may be
+enclosed in moulds which form an outer circular shell and take the place of
+the cloth, but for most purposes, and in particular for the rubber-sulphur
+mixing usually employed, it is sufficient to use cloth to obtain even and
+regular tubes. The tube, after vulcanising, is slipped on to a wooden
+mandrel and cut into rings on a lathe. Of these rings the internal diameter
+is constant, for this is formed on the mandrel, also the face, which can be
+cut accurately in the lathe, but the external diameter, and consequently
+the thickness, may vary a little.
+
+[39] "Plantation Rubber and the Testing of Rubber."
+
+[40] "Estate Rubber."
+
+It appears, therefore, that all methods result in rings of approximately
+the correct size, and it is usual to check, and, if necessary, make an
+allowance for variation in dimensions. It is not possible to do this, even
+approximately, with soft rubbers, as the rubber gives under the pressure of
+the micrometer. No doubt a photographic method would give more accurate
+results, but would take too long. I have found that a very close
+approximation is obtainable by weighing the rings as the specific gravity
+of the standard rubber mix is known. It is not necessary to weigh each
+ring, but the whole five or ten taken for testing may be weighed together.
+
+The next point that arises is the choice of a formula for the test mix.
+Practically all the work to date has been carried out on mixtures of rubber
+with 7 to 10 per cent. of sulphur. For some purposes--_e.g._, detecting
+variation in rate of cure--this mixing is satisfactory, but for other
+purposes it is not. Nor is the behaviour of a rubber-sulphur mixing a sure
+guide to the behaviour of one containing other ingredients, such as
+litharge. Thus, two samples vulcanised satisfactorily when mixed with
+sulphur only, but one of them gave unsatisfactory results in the presence
+of litharge. It has long been recognised that mineral ingredients may
+modify the product when vulcanised, but the modification is not necessarily
+uniform. Consequently, tests should also be made, when practicable, with
+vulcanised rubber containing other ingredients in addition to sulphur.
+
+As regards physical tests on the vulcanised products, these usually involve
+determination of breaking load and elongation at rupture (usually recorded
+as final length--that is, including the original length reckoned either as
+unity or as 100 units). Simultaneously a load-stretch curve is recorded on
+an autographic attachment. The type of curve varies with (1) state of cure,
+or degree to which the rubber is vulcanised; (2) proportion of sulphur
+and/or other ingredients; (3) specific nature of the rubber used. The last
+factor is almost negligible compared with the two former--at any rate for
+average quality rubber. As (2) is kept constant for any batch of tests, or
+even for every test, it follows that the load-stretch curve is mainly
+dependent on the state of cure, and the degree of vulcanising may be
+measured by comparing either the elongation produced at a given load or the
+load produced at a given elongation. Either set of figures is readily
+determined by measuring up the load-stretch diagram.
+
+The peculiar type of the curves has long been a subject of comment and
+speculation. Special properties have been attributed to the "slope" or
+inclination of the upper and approximately straight portion of the curve.
+According to the writer's investigations, the "slope" is largely dependent
+on the degree of vulcanisation, so that it is difficult to "place" as an
+index of the specific nature of a rubber.[41] Moreover, it has recently
+been shown that the peculiar type of curve given by vulcanised rubber is
+the result of plotting the load against the sectional area of the
+unstretched test piece, whereas this area decreases progressively as the
+test piece stretches. If this decrease be allowed for, the curve obtained
+is an equilateral hyperbola.[42] Preliminary experiments with rubber
+compounded with large proportions of finely divided mineral matter, such as
+carbon black, show that the load-stretch curves obtained autographically
+are likewise reducible to equilateral hyperbolae.
+
+[41] Bulletin R.G.A., October, 1921, p. 397.
+
+[42] _Hatschek Journal Soc. Chem. Ind._ 1921; _Trans._, p. 251.
+
+
+
+
+CHAPTER XXIII
+
+_THE PROPERTIES OF RUBBER_
+
+
+This section, like the last, is divisible into two subsections. The first
+deals with raw rubber, the second with vulcanised rubber.
+
+We have already explained that, until recently, rubber was not used in the
+unvulcanised condition, but that the excellent physical properties of
+plantation rubber have made this possible. It is interesting to compare the
+physical properties of raw rubber with that vulcanised with sulphur. A
+compact sample of crepe as received from the East will give breaking strain
+of over 30 kilos per sq. cm. and over 300 per cent. elongation. When mixed
+with sulphur and vulcanised, a breaking strain of 150 kilos and elongation
+of 1,000 per cent. are not unusual. It is possible that crepe rubber would
+give higher figures if it could be prepared in the form of a compact ring,
+as used for tests on vulcanised rubber. In any case, the figures for
+vulcanised rubber are much in excess of those for raw crepe rubber. It must
+also be remembered that a breaking strain of 150 kilos is not permanent
+with vulcanised rubber, for reasons which will be explained later.[43] To
+obtain a reasonably permanent vulcanised product, the vulcanisation would
+not be carried further than to give a figure of 100 kilos. On the other
+hand, raw rubber is remarkable on account of its great permanency, although
+subject to some physical changes at ordinary atmospheric temperatures.
+Tensile tests, although valuable, do not tell us all about the physical
+properties of a sample of rubber. Abrasion tests, or tests designed to
+measure resistance to wear and tear, would be more valuable, but,
+unfortunately, these properties do not lend themselves to simple tests.
+There are grounds for believing that raw rubber is superior in some
+respects to fully vulcanised rubber, if prepared without the addition of
+finely divided mineral substances which exert a toughening effect.
+
+[43] _Journal Soc. Chem. Ind._, 1916, p. 872.
+
+Sheet rubber gives results in some ways inferior to compact crepe rubber
+when subjected to physical tests. Tensile strength seldom exceeds 15 kilos,
+but the elongation is usually higher--up to 600 or 700 per cent. That is to
+say, it stretches more, but breaks more easily. If, however, we take into
+consideration the diminution in sectional area of the test piece during
+stretching, it will be seen that crepe and sheet rubber have compensating
+properties.
+
+As this matter of sectional area reduction during stretching is important,
+both for raw and vulcanised rubber, it may be briefly referred to here.
+When rubber is stretched, the volume does not appreciably alter--at any
+rate, as regards uncompounded rubber. Hence the reduction of sectional area
+on stretching bears a simple relationship to the amount of stretching. If
+we double the length of the test piece, we halve the sectional area; if we
+treble the length, we reduce it to one-third, and so forth. Hence, if we
+multiply the breaking strain by the final length (_i.e._, length at break,
+taking the original length = 1), we obtain a figure, the "tensile product,"
+which embodies both breaking strain and stretching capacity. In effect it
+gives us the breaking strain calculated on the sectional area at the
+_moment of rupture_ of the test piece. Adopting this formula, we obtain for
+crepe--
+
+   _Tensile    _Final Length--i.e.,    _Tensile
+  Strength._     Elongation + 1._      Product._
+     30      x        4            =     120
+
+and for smoked sheet
+
+     15      x        8            =     120
+
+The difference in properties between crepe and sheet may probably be
+attributed to the heavier rolling of the crepe; which compacts the rubber.
+But if the crepe is rolled too much, the tensile strength falls, and there
+is no increased elongation to compensate. For the same reason, crepe which
+has been rerolled in this country is inferior to crepe as received direct
+from the plantation. At the most it is permissible to unite two or three
+layers of thin crepe to a thicker one by a single passage through even
+speed rollers, if the physical properties of the original rubber are to be
+conserved.[44]
+
+[44] Bulletin R.G.A., February, 1922, p. 64.
+
+Attempts to prepare crepe for use in a raw state, by rerolling uneven or
+irregular surfaced crepe in this country, only result in a rubber with
+inferior physical properties. Nor can sheet be rerolled to give crepe of
+good physical properties. The power required to break down the sheet and
+the heat developed, even on cold rollers, are an indication of physical
+properties destroyed. For subsequent vulcanisation this is not a matter of
+importance, because the vulcanising process restores to the rubber the
+properties which are lost in the process of rolling and milling or
+mastication.
+
+Raw rubber has been used to some extent for proofing purposes, as for the
+manufacture of material for hoods of motor-cars. In this case no attempt is
+made to preserve the physical properties. The rubber is masticated, mixed,
+taken up with solvent and spread on the cloth exactly as if it were to be
+vulcanised.
+
+VULCANISED RUBBER.--We have already explained that the properties of
+vulcanised rubber are dependent, to some extent, on the specific nature of
+the raw rubber, or what De Vries terms the "inner qualities." That is to
+say, differences appear on vulcanising which are not apparent from the
+tests made on the raw rubber. Indeed, no investigation or analysis of the
+raw rubber can enable one to foresee exactly how the rubber will behave on
+vulcanisation. This illustrates the deficiency in our knowledge of
+vulcanisation. When dealing with soft, resinous, or decomposed rubbers, it
+is safe to anticipate a weak vulcanised product; but when we come to deal
+with a number of samples of "standard" crepe or sheet--_i.e._, sheet or
+crepe passing a certain standard of appearance--it is found that
+differences in vulcanising properties cannot be foreseen. This matter is,
+however, not so great a drawback as might be imagined, for reasonably well
+prepared consignments of standard crepe or sheet differ but little from
+one another, and the difference is mainly in the ease with which they break
+down, or the rate or speed with which they vulcanise, and not with the
+properties of the vulcanised product. Many of the plantation scrap grades
+are equal to or nearly equal to "standard"; but some of these, as also the
+rubber produced by native holders, show appreciable variation, and are the
+source of most of the complaints which emanate from manufacturers. We shall
+consider in turn the different grades and the effect of the usual surface
+defects, such as mould, spots, etc.
+
+CREPE RUBBER.--Oil marks and tackiness are the most serious defects from
+the manufacturing standpoint. In the first part of this book we have shown
+that damage caused by the so-called oil marks is not due to the oil, but to
+traces of copper from the bearings of the machines. There are several
+metallic compounds which cause deterioration of rubber both raw and
+vulcanised, but copper is the most deadly, and rubber showing signs of
+deterioration is rightly rejected by the manufacturers.
+
+The only other defect of crepe rubber which has any bearing on its use in
+manufacture is mould. Crepe rubber very seldom shows the ordinary surface
+moulds not uncommon in sheet-rubber. There are, however, microscopic
+growths which cause the development of coloured spots referred to in detail
+in the earlier part of this book. The rubber hydrocarbon itself does not
+appear to be affected by the moulds, but some of the serum constituents are
+altered, with the result that the rubber vulcanises more slowly than it
+otherwise would do. For this reason, crepe rubber with coloured spots may
+give rise to trouble in the factory.
+
+SHEET RUBBER.--The commonest defect is mould.[45] This is usually of a
+light surface type, easily brushed off, and numbers of vulcanising tests
+failed to trace any reduction in rate of vulcanising or other defect due to
+this. In spite, however, of the harmlessness of light surface moulds, they
+are looked upon with suspicion by the manufacturer. Occasionally samples of
+smoked sheet are offered contaminated with a "heavy" type of mould. The
+sheet feels damp and "heavy" or flabby, and contains an excess of moisture;
+sometimes a moist exudation is noticeable on the surface, and "virgin"
+patches are present. Such sheet vulcanises more slowly than F.A.Q. samples,
+but does not necessarily show other defects after washing and drying.
+
+[45] Bulletin R.G.A., February, 1921, p. 97; April, 1921, p. 190; June,
+1921, p. 243; November, 1921, p. 472.
+
+"Stretching rusty," as already explained, is due to a dry film on the
+surface of the sheet, and according to a recent investigation, this film
+consists, not of serum substances, but of a microscopic mould growth, which
+presumably grows on the serum substances. A sample of sheet which stretches
+rusty gives the rubber a "dry" appearance, and for a long time
+manufacturers mistook the surface film for resin. On the assumption that
+such rubber was "resinous" they rejected it, and to this day it is regarded
+as a defect, although it has no influence on the vulcanising properties of
+the rubber.
+
+It is hardly necessary to point out that defective appearance, such as is
+due to thickened edges, faint markings, bubbles, and so forth, have no
+effect on the vulcanising properties of the rubber. They only point to some
+irregularity or carelessness in preparation. The only justification for
+distinguishing between rubber of good and bad appearance is that the former
+bears the impress of careful preparation, and is therefore more likely to
+be uniform in rate of vulcanising.
+
+Similar considerations apply to the colour of smoked sheet, which may vary
+from a pale yellow-brown, through various shades of red-brown to dark
+brown. There are various factors affecting the colour, but the buyer can
+see but one--viz., the "degree" of smoking--and the rubber, from his point
+of view, may be undersmoked or oversmoked. No doubt the degree of smoking
+affects the vulcanising properties, but to a less extent than was at one
+time imagined. In a recent paper[46] it has been shown that the average
+breaking strain and rate of cure of a number of samples of smoked sheets
+were practically the same for light as for dark sheets.
+
+[46] Bulletin R.G.A., December, 1921, p. 521.
+
+VARIATION IN PHYSICAL PROPERTIES.--A very large number of tests on
+vulcanised specimens of plantation rubber have been carried out. The
+rubber was almost invariably mixed with 7 to 10 per cent. of sulphur, and
+no other ingredient, and vulcanised to give the maximal breaking load.
+Unfortunately, this determination is subject to a very appreciable
+experimental error, so that a large number of determinations are necessary
+to give a reliable figure. It is quite impracticable to make a large number
+of determinations in routine testing, on account of the labour involved. It
+is usual to make five, or possibly ten, determinations, although some
+investigators have been content with two. It is generally conceded that any
+exceptionally low figures should be ignored, as probably caused by some
+flaw or irregularity in the test piece. On the other hand, a study of
+actual determinations shows an occasional excessively high figure, and it
+is questioned whether this also should be left out of account. Others
+ignore all except the highest figure, and take this to represent the true
+breaking strain. As a consequence, the figures published by different
+workers show considerable variation. De Vries has analysed a large number
+of the figures obtained in systematic examination of estate samples, and
+has constructed curves to illustrate the results.[47] It is open to
+question how far the variations shown are attributable to experimental
+error. The figures show, however, that the variation in breaking strain is
+relatively small, and not very different for crepe and sheet rubber. In our
+opinion, undue importance should not be attached to very high or
+exceptionally high figures for breaking strain, which are occasionally met
+with. Provided the figure does not fall much below the average, the sample
+may be regarded as satisfactory. It is very seldom that any sample of first
+latex estate rubber does not show satisfactory figures.
+
+[47] "Estate Rubber," p. 466.
+
+THE RATE OF CURE OR RATE OF VULCANISATION is subject to more exact
+measurement, whether this be based on the physical or the chemical
+properties of the rubber. If the testing machine be provided, as is usual,
+with an autographic attachment, the position of the curves traced on the
+recording paper gives a measurement of the rate of cure. These load-stretch
+curves, to which reference has already been made, take up a definite
+position in accordance with the physical properties; it is only the length
+of the curve, or the point where it terminates (which gives the breaking
+strain and elongation at break), which is largely fortuitous.
+
+As a measure of rate of cure we may take the actual measurements made on
+the record.[48] It is convenient to measure the elongation produced by a
+load of 130 kilos per sq. cm., as all fully vulcanised rings of soft rubber
+should give higher breaking load figures. For less cured or weaker samples
+a lower figure may be taken, such as 60 kilos. We have found that when
+fully vulcanised to give the maximal breaking strain, the elongation at a
+load of 130 kilos is in the neighbourhood of 850 per cent. (final length
+950 per cent.). This applies to ordinary samples of estate rubber under the
+conditions of testing indicated above. If, however, the proportion of
+sulphur be considerably reduced, or mineral ingredients in a fine state of
+division be added to the mixing, or accelerators, whether organic or
+inorganic, be employed, the above relationship no longer holds. Nor does it
+hold with regard to plantation rubber prepared in an exceptional manner,
+as, for instance, matured coagulum or "slab."
+
+[48] Bulletin R.G.A., June, 1921, p. 246.
+
+There is a second method of determining the rate of cure--namely, by
+analysing a vulcanisate produced under standard conditions, and determining
+the amount of sulphur which has entered into chemical combination with the
+rubber. For this purpose the weighed sample is cut thin or creped thin, and
+exhaustively extracted with acetone to remove any "free" sulphur--that is,
+sulphur not in combination with the rubber. The sulphur remaining is then
+determined and calculated as a percentage of the raw rubber contained in
+the sample taken. This gives the so-called coefficient of vulcanisation.
+
+If we compare the coefficient with the time of cure at a constant
+temperature for an ordinary sample of plantation rubber, they are found to
+be approximately proportional, so long as the sulphur is in sufficient
+excess. The amount of combined sulphur is, therefore, an index of the time
+vulcanisation has been in progress (under standard conditions of
+temperature, etc.), and, therefore, the coefficient is a measure of the
+rate of cure.
+
+The change in position of the load-stretch curve is not directly
+proportional to the time of heating, and it therefore follows that it is
+also not directly proportional to the coefficient. For ordinary samples of
+crepe and sheet the relationship is, however, not very far removed from
+proportionality. This applies particularly to sheet rubber. The
+relationship is readily seen on plotting one against the other and tracing
+the curves. For sheet we get an almost straight line; for crepe there is
+some curvature.[49] For ordinary estate samples of sheet and crepe rubber
+the maximal breaking strain is obtained when the coefficient reaches
+approximately five units, so that this corresponds to the elongation of 850
+per cent. at a load of 130 kilos.
+
+[49] Bulletin R.G.A., June, 1921, p. 246, October, 1921, p. 398.
+
+Either physical or chemical methods may, therefore, be used for determining
+the rate of cure of ordinary sheet or crepe rubber, but great care must be
+taken when interpreting the results obtained with rubber prepared in an
+unusual manner. The rate of cure may be expressed in terms of the time
+taken to vulcanise the rubber at a constant temperature (in our case 138 deg.
+C.), so as to give an elongation of 850 per cent. at a load of 130 kilos,
+or to give a coefficient of five units. The higher the figure so obtained,
+the slower curing the rubber. To express the results more directly as rate
+of cure, we have adopted the plan of taking an average crepe rubber,
+calling the rate of cure 100 units, and expressing the rate of cure of
+other samples in these terms. Thus, a sample which gave a coefficient of
+four only, in the time taken by the standard to give a coefficient of five,
+would have a rate of cure four-fifths of the standard, that is, 80; or if a
+sample takes only two hours to give an elongation of 850 per cent., whereas
+the standard takes three hours, the rate of cure of the sample will be 3/2
+of standard or 150.[50]
+
+[50] _Journal Soc. Chem. Ind._, 1918, p. 280.
+
+As stated, the coefficient is approximately directly proportional to the
+time of cure; it is also independent of the proportion of sulphur, if in
+fair excess, and in the presence of inert ingredients. It is also
+independent of the amount of mastication given to the original raw rubber,
+however great. On the other hand, the position of the load-stretch curve is
+variously modified by these factors--in some respects, therefore, the
+coefficient is a more reliable index. However, the coefficient is
+influenced by accelerators, so that here also great care must be exercised
+when interpreting results. For the purpose of detecting variations in rate
+of cure, it is best to choose a mixing which is particularly sensitive. In
+the first place, there must be an ample excess of sulphur; and in the
+second place, no ingredient should be added which will complicate the
+load-stretch curves, and no accelerators should be present which may
+possibly tend to obscure the vulcanising properties of the rubber itself.
+It has been found, therefore, that the best mixing to use consists of
+rubber with an excess of sulphur--say, in the proportion 9:1 without other
+ingredients. The rate of cure of a specimen of plantation rubber is
+attributed to the presence of certain natural vulcanising catalysts,
+because it is found that carefully purified raw rubber (that is, with the
+resinous and nitrogenous constituents removed) vulcanises very slowly or
+hardly at all, but that on replacing the extracted matter the rate of
+vulcanising is restored. The natural catalysts contained in the extracted
+matter are influenced to a varying degree by some of the common ingredients
+of manufactured rubber articles. This applies particularly to litharge
+(oxide of lead), to which reference has already been made. Thus, acetone
+extraction of raw rubber to remove resinous matter has but little effect on
+the vulcanising properties of a mixture of rubber and sulphur. But if
+litharge be a constituent, it is found that acetone-extracted rubber will
+hardly vulcanise at all. From this, it follows that a rubber giving a low
+acetone extract may be found to vulcanise exceptionally slowly in a mixing
+containing litharge, whereas it shows no such defect when compounded with
+sulphur only.[51] Litharge is used to a very large extent, as it has a
+balancing effect in a rubber compound--that is to say, it allows of
+appreciable variation in vulcanising conditions, without corresponding
+alteration in the state of cure.[52]
+
+[51] _Journal Soc. Chem. Ind._, 1916, p. 874.
+
+[52] _Ibid._, 1915, p. 524.
+
+INFLUENCE OF VARIOUS FACTORS IN RAW RUBBER PREPARATION ON THE "RATE OF
+CURE," OR "RATE OF VULCANISATION."--As the capacity of a rubber for
+vulcanisation depends on the presence of small quantities of accessory
+substances in the serum which act as catalysts, the rate of vulcanisation
+(or curing) will depend on the nature and quantity of such substances
+present in the rubber. A very small quantity of these substances has a
+considerable influence on rate of vulcanising, and as the substances are
+difficult to isolate and identify, our knowledge of their formation and
+chemical nature is not as definite as is desirable. Substances have been
+isolated having the characteristics of "simpler bases." Bodies of this
+class are formed by putrefaction of organic matter, and can be separated in
+much larger quantity from coagulated latex, which has been allowed to
+putrefy before working up than from such which has been worked up without
+giving time for an appreciable amount of putrefaction to take place.
+Further, rubber from putrefied coagulum vulcanised much faster than that
+ordinarily prepared, so that we are justified in connecting the
+putrefaction bases with the rate of vulcanisation. Moreover, it has been
+shown that any treatment of the latex or coagulum which inhibits the
+development of putrefactive organisms also prevents the rubber vulcanising
+as fast as would otherwise have been the case.[53] Also, the crude bases
+isolated from fast vulcanising rubber have the power of increasing the rate
+of vulcanisation when added to ordinary slow vulcanising rubber.[54]
+
+[53] Eaton and Co-workers: See Bulletin No. 27, F.M.S. Department of
+Agriculture.
+
+[54] _Journal Soc. Chem. Ind._, 1917, p. 365.
+
+On the other hand, there are one or two facts which are difficult although
+not impossible to fit in with theory. Thus, although the putrefaction bases
+are very easily soluble in water and acetone, they cannot be removed by
+washing on the creping rollers, or by acetone extraction. This may be due
+to the power of colloidal substances to retain other crystalloidal
+substances, such as the bases, which, in consequence, cannot be washed out.
+A parallel case is the retention of small quantities of water soluble
+substances in the soil. Also, the theory does not explain why rubber
+obtained by evaporation of latex at relatively high temperatures is fast
+vulcanising, although the possibility of putrefaction is excluded.
+
+As regards practical results, it follows that the rate of vulcanisation (or
+cure) of a sample of rubber will depend on the time allowed to elapse
+between the collection of the latex and treatment till the rubber is dry,
+as also on atmospheric conditions. Thus, slow drying will result in an
+increased rate of cure, for it gives an opportunity for putrefactive
+organisms to play a part. The results will, however, be influenced by the
+extent to which the rubber was washed previous to hanging, and so forth.
+Smoking is an antiseptic process and will, therefore, tend to inhibit the
+action of micro-organisms and produce a slower vulcanising rubber. On the
+other hand, sheet contains more serum than crepe, so that there is more
+food material for growth of micro-organisms. The net result is to give a
+rubber (sheet) which usually vulcanises a little faster than crepe.
+
+Among other factors controlling the rate of cure, special mention should be
+made of the nature and amount of coagulants. Weak "organic" acids, such as
+acetic, lactic, tartaric, etc., used in the minimal proportions (1 to 1,200
+of standardised latex in the case of acetic acid), give the fastest
+vulcanising rubber; "strong" mineral acids, such as sulphuric acid, even
+when used in the minimal proportions (1 to 2,000), yield slower vulcanising
+rubber. Acid salts, such as alum, are intermediate in effect. Increased
+proportions of coagulant cause a reduction in rate of vulcanising with all
+coagulants, and the effect is least noticeable in crepe rubber,
+intermediate in sheet rubber, and most pronounced in "slab" rubber
+(discussed below).[55]
+
+[55] Bulletin R.G.A., July, 1919, p. 39; September, 1920, p. 343; November,
+1920, p. 433; October, 1921, p. 393; March, 1922, p. 134.
+
+OTHER TYPES OF PLANTATION RUBBER.--We have up to now confined our attention
+to ordinary thin air-dried crepe and smoked sheet, as almost all plantation
+rubber is now marketed in one or other of these two forms. There are,
+however, other types, to which reference has been made. Of these, the most
+important is the thick blanket crepe, made chiefly in Ceylon by rolling
+together thin crepe, which has been artificially dried (Colombo drier or
+vacuum drier). The heat of the driers causes a surface stickiness, which is
+got rid of by rolling several thin layers together to give one thick one.
+This rubber vulcanises at about the same rate as ordinary thin crepe, for
+the relatively high temperature of drying does not appear to influence the
+rate of cure. The rubber is generally softer than air-dried crepe, and is
+easily "let down" in naphtha; it is, therefore, suitable for some solution
+work. Generally speaking, the properties of blanket crepe do not differ
+materially from ordinary thin crepe. Another type of rubber seldom met with
+is matured slab or crepe, prepared from it. This type of rubber is being
+made in small quantities on one or two estates, who supply direct to the
+manufacturer. The method of preparation has already been described. It is
+unsuitable for sale in the open market, as it contains a variable amount of
+moisture, has the various surface defects such as slime, mould, and "rust,"
+and there is the additional disadvantage that it is not easy to judge of
+its cleanliness or freedom from coarse impurities by inspection. If the
+slab rubber be creped and air-dried on the spot, the product is of
+satisfactory appearance, except that it is of low colour and may be
+streaked. As the crepe so produced vulcanises almost as fast as the
+original slab, the crepe embodies all the advantages of a fast curing
+rubber with few of the disadvantages of the slab itself. We have made
+experiments from time to time, and found that by a judicious use of sodium
+bisulphite it is possible to produce a fast vulcanising crepe rubber
+sufficiently even and light in colour to satisfy the Standards Committee.
+
+A fast curing raw rubber is not necessarily a desirable type for all
+manufacturing purposes. In the vulcanising of large masses of rubber, a
+slower rather than a faster vulcanising rubber may be desirable, so as to
+give ample time for the heat to penetrate and spread evenly throughout the
+mass. But for many purposes a fast curing rubber enables a larger output to
+be obtained, so that artificial organic accelerators are coming more and
+more into use. The addition of such accelerators might be obviated, if a
+suitable fast curing rubber were available, but it is essential that such
+rubber should be uniform. It is just in this respect that slab rubber or
+crepe made therefrom is found to be deficient.[56] The rate of cure depends
+on the functions of wild bacteria, which are naturally sensitive to changes
+of conditions, such as temperature, etc. The coagulated rubber depends on
+chance circumstances for infection, and, as a natural result, the activity
+of the bacteria and the nature and amounts of active vulcanising agent
+produced will vary and be difficult to control. Consequently, the rate of
+cure of slab rubber shows considerably greater variation than ordinary
+crepe or sheet.[57] This, in our opinion, is the main difficulty of
+utilising "slab," or crepe prepared from it. Experience in other
+industries, using micro-organisms, has shown that the only method of
+control has been to replace the wild growths by cultures of some particular
+strain, as, for instance, in yeasts for brewing. To control the rate of
+cure of slab, it might be possible to use a special culture for the
+purpose.
+
+[56] Bulletin R.G.A., January, 1920, p. 6; January, 1921, p. 47.
+
+[57] _Ibid._, January, 1920, p. 68.
+
+Other less usual methods of preparation, referred to in the earlier part of
+this book, do not call for particular mention, as the properties of the
+rubber do not differ much from ordinary sheet or crepe. It is mainly a
+matter of variation in rate of cure.
+
+This short account of the vulcanising properties of plantation rubber would
+not be complete without a reference to Fine Hard Para, the premier rubber
+of the Amazon. This rubber has come to be regarded as the standard
+high-grade product with which plantation rubber may be compared, and many
+manufacturers are still of the opinion that it is unsurpassed by any
+plantation product. Yet, when subjected to the ordinary vulcanising tests,
+we find that samples of Fine Hard Para give figures very similar to average
+plantation rubber; indeed, it is not difficult to find specimens of
+plantation rubber which give appreciably higher figures on testing. It is
+claimed, however, that Fine Para is more uniform than plantation rubber,
+and can be relied on always to give the same results. Yet tests on a series
+of Fine Hard Para specimens gave variations in rate of cure similar to
+those found for plantation. Some figures were published, which tended to
+show that the variation was smaller for Fine Para, but it turned out that
+each of the samples taken for examination consisted actually of a number of
+slices cut from different balls, so that greater uniformity was not
+unexpected.[58] The superiority of Fine Para is, therefore, somewhat of a
+mystery. It is probable that some manufacturers prefer to use it because
+they feel safer with it, and know actually how it will behave from long
+experience. In one respect Fine Para is possibly superior to most
+plantation rubber--that is, for the preparation of raw rubber solution for
+sticking the seams of waterproof garments, and for similar purposes. The
+method of preparation may well influence the strength of the raw rubber
+when used for this purpose. Plantation rubber has been prepared in the same
+manner as Brazilian Para, in particular on an estate in Java. The product
+resembles Brazilian Para in appearance. Vulcanising tests gave satisfactory
+figures, but, as already stated, this would not serve to show that the
+rubber was equal to Brazilian Para from the manufacturer's standpoint.
+
+[58] Bulletin R.G.A., September, 1920, p. 347.
+
+
+
+
+INDEX
+
+
+  Acetic acid, 74, 279
+
+  Acid, acetic, 74, 279
+  --, carbonic, gas, 289
+  --, formic, 279
+  --, hydrochloric, 282
+  --, hydrofluoric, 282
+  --, mixing, with latex, 79
+  --, nitric, 282
+  --, oxalic, 279
+  --, pyroligneous, 282
+  --, quantity of, 76
+  --, sulphuric, 279, 286
+
+  Acids for coagulation, effect of, on rate of cure, 323
+  --, quantities necessary for modern requirements, 78
+
+  Air-drying, aids to normal, 143
+  --, of crepe, rate of, 138
+  --, progress of, 140
+
+  Alcohol, coagulation with, 289
+
+  Alum, coagulation with, 282
+
+  Anti-coagulant for transport, 61
+
+  Anti-coagulants, 46
+
+  Artificial driers, 133, 148
+
+  Ash on sheet, 276
+
+  Assembling cases for shipment, 156
+
+
+  Bags for packing, 154
+
+  Bakau, 147
+
+  Bales for packing, 154
+
+  Bark in crepe, 232
+  -- -- shavings, 56, 123
+  -- -- sheet, 276
+
+  Bases in vulcanised rubber, 322
+
+  Basket plants, 10
+
+  Blanket crepe, properties of, 324
+
+  Blemishes of surface, 252
+
+  Blister in sheet, 272
+
+  Block rubber, 129, 246
+
+  Breaking down of rubber, 304
+  -- load of test piece, 311
+
+  Bubbles in sheet, 269
+
+  Buildings, 159
+
+  Bulking latex, 69
+
+  Byrne curing process, 270
+
+
+  Calendered sheet, 304
+
+  Carbon dioxide, 289
+
+  Carbonic acid gas, 289
+
+  Cases, choice of, for packing, 153
+
+  Catalysts, natural, in rubber, 312
+  --, vulcanising, 312
+
+  Centralisation of factories, 221
+
+  Chinese vinegar, 286
+
+  Chinosol, 238
+
+  "Chula" drier, 148
+
+  Clippings, sheet, 275
+
+  Coagulant, 111
+  --, choice of, 74, 278
+  --, quantity of, 113
+
+  Coagulation, 74, 111
+  -- centres, 62
+  --, premature, 46
+  --, spontaneous, 294
+  -- with alcohol, 289
+  -- -- sugars, 287
+  -- -- various salts, 288
+
+  Coagulum, soft, 249
+  --, spongy undersurface of, 249
+  --, tearing of, 249
+  --, transport of, 59, 63
+  --, working of, 103
+
+  Coefficient of vulcanisation, 319
+
+  Collecting latex, 38
+  -- pails, 48
+
+  Collection, advantages of early, 60
+
+  Combustion, rate of, in smoke house, 191
+
+  Compound crepes, 126
+  -- -- No. 1, 151
+  -- -- No. 2, 151
+
+  Contents of cases, weight of, 156
+
+  Copper salts, cause of tackiness, 243
+
+  Cotton fibre in crepe, 230
+
+  Creosotic substances, 146
+
+  Crepe, air-drying of, 132
+  --, bark in, 232
+  --, bearing of defects in, on manufacture, 316
+  --, bisulphite streaks in, 235
+  --, colour of fine, 114
+  --, dirt in, 227
+  --, dirty edges of, 225
+  --, drying houses for, 178
+  --, fibre in, 230
+  --, general style of finish, 223
+  --, grades of, 150
+  --, greenish, tacky streaks in, 228
+  --, iron stains on, 225
+
+  Crepe, No. 1 fine pale, 110
+  --, oil marks on, 226
+  --, oxidation streaks in, 234
+  --, rate of air-drying of, 138
+  --, rust stains on, 226
+  --, smoked, 130
+  --, surface moulds on, 241
+  --, weight increased in drying house, 141
+  --, yellow latex streaks in, 234
+  -- rubber, defects in, 223
+  -- --, lower grades of, 120
+  -- --, preparation of, 110
+  -- --, tensile strength of, 313
+
+  Cups, cleaning, 40
+  --, water in, 44
+
+  Cure, rate of, 318
+
+  Curing, 307
+
+
+  Da Costa process, 290
+
+  Decentralisation of factories, 221
+
+  Defects of sheet, infrequent, 276
+
+  Derry process, 293
+
+  Designs and "layout" of tanks, 176
+
+  Dirt in sheet, 276
+
+  Discoloration of rubber, dark, 249
+
+  Drains for tanks, 176
+
+  Drier, Colombo Commercial Company's, 136
+
+  Driers, artificial--for crepe rubber, 133
+  -- --, for sheet rubber, 148
+  --, "Chula," 148
+  --, vacuum, 134
+
+  Drum furnaces, horizontal, 189
+
+  Drying chamber, floor of, 187
+  -- --, arrangements of, 186
+  -- houses for crepe, 178
+  -- --, hot air, 182
+  -- --, ventilation of, 185
+  -- --, windows of, 185
+  -- of rubber, 132
+  --, period of, 145
+  --, rate of, effect on rate of cure, 323
+
+
+  Earth scrap, 124
+  -- --, collection of, 58
+
+  Edges, thickened, after rolling, 251
+
+  Elongation of test piece, 311
+
+  Ends, thickened, after rolling, 251
+
+  Engines, 170
+  --, position of, 174
+
+
+  Factories, 172
+  --, centralisation of, 221
+  --, decentralisation of, 221
+  --, number of floors, 174, 178
+  --, ventilation of, 180
+  --, windows of, 181
+
+  Factory buildings, situation of, 216
+  --, choosing site for, 220
+  --, ideal arrangement of, 162
+  -- operation, 65
+
+  Fibre cotton, in crepe, 230
+
+  Field maintenance, 13
+
+  Fine hard Para properties of, 325
+
+  First latex and other grades, percentage of, 59
+
+  Floor of drying chamber, 187
+  -- factories, 173
+  -- furnace room, 196
+
+  Formalin, 87
+
+  Formic acid, 74, 279
+
+  Formula for test mix, 311
+
+  Freezing (coagulation) process, 293
+
+  Fuel, consumption of, 196
+
+  Fuels for smoking, 146
+
+  Furnace room, floor of, 196
+  -- --, Petaling type of, 192
+
+  Furnaces, horizontal drum, 189
+  --, "pot," 188
+
+
+  Germination, 6
+
+  Grades, number of, 151
+
+  Grading, 150
+
+  Grafting, 8
+
+  Grass squares, 14
+
+  Greasiness before smoking, 252
+  -- of surface, 258
+
+  Grit in crepe, 232
+
+
+  Hand rolling sheets, 104
+
+  Hevea Brasiliensis, 1
+
+  Hot air drying houses, 182
+
+  Hydrochloric acid, 282
+
+  Hydrofluoric acid, 282
+
+
+  Ilcken-Down process, 298
+
+  Instruments, method of using, 100
+  --, recording, 144
+  --, standardising, 98
+
+
+  Lallang, eradication of, 15
+
+  Latex, bulking, 69
+  -- cups, choice of, 40
+  --, decomposition of, in the field, 270
+  --, first and other grades, percentage of, 59
+  --, first quality, 150
+  --, mixing acid with, 79
+  --, mixing sodium bisulphite solution with, 117
+  --, preliminary treatment of, 65
+  --, reception of, at the store, 65
+  --, standard, 96
+  --, standardisation of, 69, 110
+  --, straining, 67
+  --, transport of, 59
+
+  Light, importance of, in factories, 172
+
+  Litharge, 312
+
+  Load stretch curve, 312, 319, 320, 321
+
+  Low grade rubbers, fibrous matter in, 124
+
+  Lower grade rubber, care in manufacture, 129
+
+  Lubrication of machines, 166
+
+  Lump rubber, naturally coagulated, 120
+
+
+  Machinery, 159
+
+  Machines, access to, 169
+  --, adequacy of, 160
+  --, arrangement of, 168
+  --, lubrication of, 166
+  --, position of, 173
+  --, sheeting, 166
+  --, speed of, 162
+
+  Mangrove, 147
+
+  Marking sheets, 105
+
+  Metrolac, 98, 100
+
+  Michie-Golledge system, 138
+
+  Mildew on surface, 260
+
+  Milky residue on serum, 249
+
+  Mixing acid with latex, 79
+
+  Moist glaze of surface, 258
+
+  Mould on surface, 260
+
+  Moulds, surface, on crepe, 241
+
+
+  Natural catalysts, 312
+
+  Nitric acid, 282
+
+  Nurseries, 9
+
+
+  Overcured, 307
+
+  Overvulcanised, 306
+
+  Oxalic acid, 279
+
+  Oxidation, prevention of, 56
+  --, variation due to, 254
+
+
+  Packing, 150
+  --, bags for, 154
+  --, bales for, 154
+  --, cases, choice of, 153
+  --, folding for, 155
+  --, methods of, 156
+  --, rooms, 211
+
+  Pale crepe, No. 1 fine, 110
+  --, rubber, former methods of making, 118
+  --, sheet, 89
+
+  Patches, 259, 260
+  --, virgin, 259
+
+  Payment by result, 53
+
+  Perished rubber, 306
+
+  Physical properties of rubber, variation of, 317
+
+  Pits for smoke houses, 188
+
+  Pitting of surface, 250
+
+  Plantation rubber, testing of, 309
+
+  Planting, 1
+
+  Plasticising of rubber, 304
+
+  Plasticity of plantation rubber, 309
+
+  "Pot" furnaces, 188
+
+  Power units, 170
+
+  Premature coagulation, 46
+
+  Preparation, special methods of, 290
+
+  Pyroligneous acid, 282
+
+
+  Racks, 186
+
+  Rate of cure, 307
+
+  Raw rubber, physical properties of, 313
+  -- --, tests on, 309
+  -- --, uses of, 315
+
+  Recommendations, Rubber Growers' Association, 152
+
+  Recording instruments, 144
+
+  Ribbing of sheet, 274
+
+  Rolling, 251
+
+  Rolls, grooving of, 164
+  -- running hot, 165
+  -- -- "free," 165
+
+  Roof of smoke house, 197
+
+  Rubber, drying of, 132
+
+  Rubber Growers' Association, Recommendations, 152
+
+  Rubber, properties of, 313
+  --, smoking, 109
+
+  Rust, cause of, 267
+  -- on sheet, 262
+  --, treatment to prevent, 265
+
+
+  Scrap washers, 57, 124
+
+  Screw plug, unsatisfactory, 73
+
+  Seed at stake, 10
+
+  Seeds, 2
+
+  Selection, 5
+
+  Senang folder, 156
+
+  Serum, milky residue on, 249
+
+  Sheet, ash on, 276
+  --, bark in, 276
+  --, bearing of defects on, in manufacture, 316
+  --, blisters in, 272
+  --, bubbles in, 269
+  --, clippings, 130, 275
+  --, creases in, 251
+  --, dirt in, 276
+  --, "dog ears," 251
+  --, grades of, 151
+  --, infrequent defects of, 276
+  --, pale, 89
+  --, ribbing of, 274
+  -- rubber, artificial driers for, 148
+  -- --, defects in, 249
+  -- --, preparation of, 89
+
+  Sheet rubber, rolling and marking of, 102
+  -- --, tensile strength of, 313
+  --, rust on, 262
+  --, splinters in, 276
+  --, stickiness in, 274
+  --, style of, 101
+  --, support marks on, 273
+  --, surface pattern of, 274
+  --, thick ends of, 275
+
+  Sheeting machines, 166
+
+  Sheets, mis-shapen, 251
+  --, thickened patches in, 251
+  --, torn, 251
+  --, unevenness of appearance, 253
+
+  Short weights, 157
+
+  Skimming, 100
+
+  Skimmings, 122
+
+  Slab rubber, 299
+  -- --, properties of, 324
+
+  Slope, 312
+
+  Smoke curing of sheet rubber, 143
+  -- --, temperature of, 144
+  --, houses, 183
+  -- --, Barker patent, 209
+  -- --, Devon type, 200
+  -- --, iron stoves for, 189
+  -- --, Jackson type, 200
+  -- -- of brick, 198
+  -- -- rate of combustion in, 192
+  -- --, roof of, 197
+  -- --, "Third Mile" type, 199
+  -- --, types of, 198
+
+  Smoked crepe, 130
+  -- sheets, colour of, 255
+  -- water for coagulation, 286
+
+  Smoking, effect on rate of cure, 323
+  --, greasiness before, 252
+  -- rubber, 109
+
+  Smooth rolling of sheets, 104
+
+  Sodium bisulphite, 80, 114
+  -- --, abuse of, 85
+  -- --, care of, 116
+  -- --, deterioration of, 115
+  -- --, evaluation of, 115
+  -- --, making a solution of, 85
+  -- --, quantity of, 84
+  -- --, residual traces of, 86
+  -- -- solution, mixing, with latex, 117
+  -- sulphite, 86
+  -- --, deterioration of, 115
+  -- --, evaluation of, 115
+
+  Sorting, 150, 152
+  -- rooms, 211
+
+  Spewing, 305
+
+  Splinters in sheet, 276
+
+  Spontaneous coagulation, 294
+
+  Spot disease, 235
+  -- -- in sheet rubber, 273
+
+  Spots, 259, 262
+  --, virgin, 259
+
+  Standard latex, 96
+  -- sheet, 102
+
+  Standardising instruments, 98
+
+  Stickiness in sheet, 274
+
+  Stock solution, method of making, 75
+
+  Storage of rubber, 212, 216
+
+  Stoves, iron, for smoke houses, 189
+
+  Straining latex, 67
+
+  Streaks, 262
+
+  Stumps, 9
+
+  Sugars, coagulation with, 287
+
+  Sulphuric acid, 280, 286
+  -- --, buying, 280
+  -- --, formula for use of, 280
+  -- --, storing, 280
+
+  Sun-drying sheet rubber, 147
+
+  Support marks on sheet, 273
+
+  Surface blotches, coloured, 249
+  --, dull or black, 258
+  -- pattern of sheet, 274
+
+
+  Tackiness, cause of, 243
+  --, copper salts cause of, 243
+  -- in rubber, 242
+
+  Tanks, 90
+  --, care of, 94
+  --, designs and "layout," 176
+  --, drains for, 176
+  --, installation of, 93
+  --, situation of, 175
+  --, water-supply for, 177
+
+  Tapping, 38
+  --, former systems of, 29
+  -- knives, 38
+  -- systems, 38
+
+  Tartaric acid, 279
+
+  Tensile product, 314
+
+  Test mix, formula for, 311
+  -- pieces, making of, 310
+
+  Testing of plantation rubber, 307
+
+  Thick ends of sheet, 275
+
+  Thinning, 19
+
+  Timber for smoking, 147
+
+  Tool sheds, 216
+
+  Transport, 60
+  -- by coolie, 62
+  -- of coagulum, 59, 63
+  -- of latex, 59
+
+  Trays, 167
+
+  Treatment of rubber in the factory, 301
+  -- to prevent rust, 265
+
+  Tree scrap, 55, 122
+  -- --, care of, 56
+  -- --, oxidation of, 56
+
+  Trees per acre, 26
+
+  Trenches, silt catchment, 11
+
+
+  Uniformity, 90
+  -- in colour, lack of, 246
+
+
+  Vacuum driers, 134
+
+  Variation due to oxidation, 254
+
+  Vegetable extracts, 289
+
+  Ventilation of drying houses, 185
+  -- factories, 180
+
+  Verandas, 175
+
+  Virgin spots, 258
+
+  Viscosity of rubber solution, 309
+
+  Vulcanisation, 301
+  --, rate of, 318
+
+  Vulcanised rubber, 318
+  -- --, tests on, 309
+
+  Vulcanising, 307
+  -- catalysts, 312
+  --, "heat," 306
+
+
+  Washers, scrap, 57, 124
+
+  Washings, 122
+
+  Water-supply for tanks, 177
+
+  Weeding, clean, 13
+
+  Weights, "short," 157
+
+  Wickham process, 293
+
+  Windows of drying houses, 185
+  -- factories, 181
+
+  Working of rubber, 304
+
+
+  Yields, 23, 25
+
+
+
+
+
+End of the Project Gutenberg EBook of The Preparation of Plantation Rubber, by
+Sidney Morgan
+
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