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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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