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diff --git a/35510-8.txt b/35510-8.txt new file mode 100644 index 0000000..2e3e6d8 --- /dev/null +++ b/35510-8.txt @@ -0,0 +1,12346 @@ +Project Gutenberg's The Preparation of Plantation Rubber, by Sidney Morgan + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Preparation of Plantation Rubber + +Author: Sidney Morgan + +Contributor: Henry P. Stevens + +Release Date: March 7, 2011 [EBook #35510] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK RUBBER *** + + + + +Produced by Chris Curnow, Harry Lamé, Robin Curnow and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + + + + + + + + + +----------------------------------------------------------------------+ + | TRANSCRIBER'S NOTES: | + | | + | * Minor typographical and lay-out errors have been corrected. | + | * Inconsistencies in spelling (e.g. hyphenated vs. non-hyphenated | + | words) have not been corrected. | + | * Italics are represented by underscores as in _text_. | + | * The original book uses a V symbol to describe V-shaped cuts. These | + | V symbols are represented as [V]. | + | * Changes made to original text: | + | * Table of Contents: | + | * "Early collection of latex transport" changed to "Early | + | collection of latex--Transport". | + | * "Roof brick built houses" changed to "Roof--Brick built | + | houses". | + | * The order of the sections under Chapters XII and XXII has been | + | changed slightly to reflect the order of the sections in the | + | text. | + | * "Tephrosia candiad" changed to "Tephrosia candida". | + | * "Archiev" changed to "Archief". | + | * "about 1/2 square" changed to "about 1/2 inch square". | + | * "asbesto-slate" changed to "asbestos-slate" as elsewhere. | + | * "Formaline" changed to "Formalin" as elsewhere. | + | * Footnotes moved to under the paragraph they belong to. | + | * Page 141: "The lengths of crepe were weighed carefully at 8 a.m. | + | and 4 a.m." should probably read "The lengths of crepe were weighed| + | carefully at 8 a.m. and 4 p.m." | + +----------------------------------------------------------------------+ + + + + + THE PREPARATION OF PLANTATION + RUBBER + + + + + THE PREPARATION + OF + PLANTATION RUBBER + + BY + + SIDNEY MORGAN, A.R.C.S. + + VISITING AGENT FOR ESTATES IN THE EAST; FORMERLY SENIOR SCIENTIFIC OFFICER + AND NOW HONORARY ADVISER TO THE RUBBER GROWERS' ASSOCIATION + IN MALAYA + + WITH A PREFACE AND A CHAPTER ON VULCANIZATION + + BY + + HENRY P. STEVENS, M.A. (OXON.,) PH.D., F.I.C. + + CONSULTING CHEMIST TO THE RUBBER GROWERS' ASSOCIATION IN LONDON + + + CONSTABLE & CO. LTD. + LONDON : BOMBAY : SYDNEY + 1922 + + + PRINTED IN GREAT BRITAIN BY + BILLING AND SONS, LTD., GUILDFORD AND ESHER + + + + +PREFACE + + +Mr. Sidney Morgan's work on Plantation Rubber in the East is so well known +that he hardly needs introduction. + +An earlier book, published in 1914, by the Rubber Growers' Association, +entitled "The Preparation of Plantation Rubber," was well received and +widely read. This book dealt in a very practical manner with problems with +which the industry had to contend. A second edition was subsequently +published. Both editions are now out of print. The present opportunity was +therefore taken to revise the original work, with the result that it has +been enlarged and practically rewritten. The information given is brought +up-to-date, and covers the whole process of production, commencing with the +planting of the tree, passing on to the collection, coagulation, and curing +of the rubber, and concluding with the packing for export. In the course of +his work for the Association, Mr. Morgan carried out a great deal of +industrial research in rubber production, including lengthy experiments on +tapping, the use of different coagulants and different conditions of +coagulation, and also on varying modes of rolling, drying, and smoking +rubber. He also went very fully into the types of construction and details +of the machinery and buildings employed on estates. + +Much of this valuable work has escaped notice, owing to its having been +published in reports with limited circulation. Also a great deal of +information was supplied to planters in a quiet and unobtrusive fashion, in +interviews, visits to estates, and on other similar occasions. The +knowledge and experience thus accumulated has been embodied in the present +volume. The subject-matter should interest not only those actually engaged +in rubber planting, but those otherwise directly or indirectly connected +with the industry, such as importers, brokers, and particularly the rubber +manufacturers in this country and in America. My experience has been that +manufacturers as a whole have but a vague idea as to the methods employed +in the preparation of plantation rubber, and this work provides them with +the opportunity of obtaining an insight into the actual operations on the +estates. It is most desirable that a closer bond should unite the +plantation and manufacturing rubber industries. Such a result is best +promoted by a better understanding of the problems with which each is +confronted. Perhaps I may go so far as to suggest that some leading +scientific officer in the employment of one of the large manufacturing +concerns may take in hand a book which will give the planters the +equivalent of information in regard to the manufacturing industry which the +planters are now offering to the manufacturers. + +The photographs in the earlier part of the book will give the layman some +conception of the enormous amount of labour that must be expended in the +opening up, planting, trenching, and weeding the plantations which have +replaced the virgin jungle. The authors are indebted for most of these +photographs to Mr. H. Sutcliffe, one of the mycologists of the Rubber +Growers' Association. The pictures of spotless coagulating tanks and tiled +verandahs regularly hosed down will indicate the cleanliness necessary for +the preparation of the beautifully clean sheet and crepe rubber which +became available with the advent of plantation rubber. These results are +largely due to the work of Sidney Morgan and his colleagues, on whom the +planters have relied for technical guidance and advice. + +As regards my own contribution this is confined to a general outline of the +subject. I have, therefore, omitted reference to a number of matters which +would have been dealt with in detail had space permitted. The information +given is based on researches on vulcanisation carried out for the Rubber +Growers' Association by the writer over a period of nine or ten years. It +was not found practicable to give detailed references in all cases. The +reports on which the conclusions are based will, however, be found among +the regular quarterly reports made by the writer for the Association up to +June, 1919. Subsequent reports have been published in the Monthly Bulletin +of the Rubber Growers' Association. We are indebted to the Association for +permission to publish details from these reports, and also for the use made +of numerous earlier reports published both in London and in the East. + + + + +CONTENTS + + + PART I + _FIELD OPERATIONS_ + + PAGE + CHAPTER I + PLANTING + + Seeds--Seed selection--Strain improvement by bad propagation-- + Nurseries--Stumps--Seed at stake--Basket plants--Preparation + of land--Danger of disease--Clean clearing--Loss of top-soil-- + Silt-trenches on slopes 1 + + CHAPTER II + FIELD MAINTENANCE + + Clean weeding--Selective weeding--Loss of top-soil--Grass + ridges--Lallang eradication--_Mimosa gigantea_ (_M. + invisa_)--Green cover-plants--Connection between weeding, + soil conservation, and soil improvement 13 + + CHAPTER III + THINNING OF AREAS + + Original planting per acre--Ultimate stand per acre--Close- + planting _versus_ wide-planting--When to commence + thinning operations--How to select in preliminary rounds-- + Later selections based on yields of individuals--Yields per + tree, present and future--Trees per acre 19 + + CHAPTER IV + TAPPING SYSTEMS + + Former methods--Former systems--Tendency to reduce number of + tapping cuts and frequency of tapping--Period allowed for + bark-renewal--Modern systems--Superimposed cuts--Single cuts, + etc.--Tapping experiments--R.G.A. experiment--Alternate-daily + _versus_ daily tapping 28 + + CHAPTER V + TAPPING AND COLLECTING + + Tapping knives--Personal equation in use of knives--Choice of + latex cups--Cleaning of cups--Water in cups--Premature + (spontaneous) coagulation--Prevention of spontaneous + coagulation--The use of anti-coagulants in the field-- + Collecting pails--Payment by result--Methods for calculation + of yields per coolie--Tree-scrap, oxidation of--Prevention of + oxidation--Bark-shavings--Collection and storage of shavings-- + Treatment of shavings--Collection of earth-scrap 38 + + CHAPTER VI + TRANSPORT OF LATEX AND COAGULUM + + Percentages of "first" latex and other grades--Early + collection of latex--Transport, nature of--Light railways-- + Motor-lorries--Bullock-carts--Care of transport vessels--Use + of an anti-coagulant during transport--Transport by coolie-- + Coagulation centres (stations)--Transport of coagulum 59 + + + PART II + _FACTORY OPERATIONS_ + + CHAPTER VII + PRELIMINARY TREATMENT OF LATEX + + Reception at store--Receptacles--Jars--Tanks--Necessity for + close supervision--Need for utmost cleanliness--Straining of + latex--Strainers--Facilitation of straining--Bulking of latex + --Standardised dilution of latex--Facilities for receiving and + handling latex--Reception verandahs--Receiving vessels--Types + of installations 65 + + CHAPTER VIII + COAGULATION + + Choice of coagulant--Strength of acid solution--Making stock + solution--Quantity for use--Quantities under modern + requirements--Care in mixing--Method of mixing with latex--Use + of sodium bisulphite as an anti-oxidant--Quantities for use-- + Formulæ--Abuse of the chemical--Residual traces in the dry + rubber--Use of sodium sulphite as an anti-coagulant, + quantities for use--Formulæ--Use of Formalin as anti-coagulant + --Formulæ for use 74 + + CHAPTER IX + PREPARATION OF SHEET RUBBER + + Pale (air-dried) sheets--Uniformity of product--Pans _versus_ + tanks--The ideal tank--Modern installations--Care of tanks-- + Standardised dilution of latex--Variation in dimensions and + density of coagulum--Standardising instruments--Method of + using--Skimming latex--Style of sheets--Standard sheets-- + Rolling and marking--When to work the coagulum--Hand-rolling-- + Power smooth-rolling--Marking rolls--Preparation for smoke- + curing--Caution against accumulation of wet sheets--Hot-water + treatment--Dripping in the open air--When to place in smoke- + house 89 + + CHAPTER X + PREPARATION OF CREPE RUBBER + + First consideration, fine pale crepe--Standardised dilution of + latex--Coagulation and coagulant--Quantities of coagulant-- + Colour of rubber--Sodium bisulphite (use of)--Evaluation and + deterioration of the bisulphite and sulphite of sodium--To + distinguish between these two chemicals--Care of sodium + bisulphite--Mixing solution with latex--Former methods of + making pale rubber--Working the coagulum--Lower grades of + crepe--Naturally coagulated lump--Skimmings and washings-- + Tree-scrap--Bark-shavings--Earth-scrap--Fibrous matter in low- + grade rubbers--Scrap-washers--Compound crepes--Increased care + with lower grades--Block rubber from crepe--Smoked crepe + _versus_ sheet clippings 110 + + CHAPTER XI + DRYING OF RUBBER + + Air-drying of crepes--Artificial driers for crepes--Vacuum + drying--Hot-air driers--Michie-Golledge system--Rate of air- + drying--When drying takes place--Increase in weight of drying + crepe--Differences in weight--Aids to normal drying--Smoke- + curing of sheet rubber--Instruments for recording temperature + --Temperatures of smoke-house--Period of drying--Fuels for + smoking--Sun-drying of sheet rubber--Artificial driers for + sheet rubber 132 + + CHAPTER XII + SORTING, GRADING, AND PACKING + + Reducing number of grades--Reduction carried too far--R.G.A. + recommendations--Care in sorting--Choice of packing cases-- + Bags--Bales--Folding of crepe--Mechanical folders--Care in + assembling--Methods of packing--Weight of contents--Short + weights 150 + + + PART III + _MACHINERY AND BUILDINGS_ + + CHAPTER XIII + MACHINES + + Quality of metal in rolls--Nature of roll-bearings--Brass + liners--Liners of alloy or of cast-iron--Adequacy of machines + --Arrangement of battery--Speed of machines--Gear ratios-- + Grooving of rolls--Heating of rolls--Sheeting machines-- + Lubrication--Trays--Position of battery--Drainage of battery-- + Access to back of machines--Engines--Power 159 + + CHAPTER XIV + FACTORIES + + General construction--Plenty of light--Floors--Drainage of-- + How many storeys--Verandahs--Tanks, situation of--Designs and + lay-out--Drains--Water supply 172 + + CHAPTER XV + OTHER BUILDINGS + + Drying-houses for crepe rubber--How many storeys--Ventilation + --Windows--Effect of light--Effect of direct sun-rays--Hot-air + houses--Smoke-houses--Various types--Ordinary smoke-houses-- + General ventilation--Windows--Racks of supports--Floors-- + Furnaces in general--Pit-fires--Pot-fires--Iron stoves-- + Horizontal drum-furnaces--Rate of combustion--Brick stoves-- + Pataling type of--Consumption of fuel--Floor of furnace room-- + Roof--Brick built houses--"Third Mile" type--Jackson cabinet-- + Devon type--Detailed description of--Barker patent design 178 + + CHAPTER XVI + OTHER BUILDINGS (_continued_), AND SITUATION OF BUILDINGS + + Sorting-room--Packing room--Store rooms--Storage of rubber-- + Need for special accommodation--Floor of store room--Local + conditions--Temperature and humidity--Incidence of moulds-- + Effect upon smoked sheets--Tool-sheds and stores--Situation of + buildings--Position with respect to points of the compass-- + Choosing a factory site--Centralisation--Decentralisation 211 + + + PART IV + _THE FINISHED RUBBER_ + + CHAPTER XVII + DEFECTS IN CREPE RUBBERS + + General style of finish--Dirty edges--Iron-stains--Rust-stains + --Oil-marks--Trays--Dirt--Holes--Greenish and tacky streaks-- + Not due to oil _per se_--Tackiness and copper--Cotton and + other fibre--Bark and grit--Sand--Oxidation streaks--Yellow + streaks--Bisulphite streaks--Spot disease--Cause of--Influence + of rate of drying--Percentage of moisture--Humidity of + atmosphere--Prevention of disease--Infection by contact-- + Outbreak of dormant spores--Rules to be observed--Surface + moulds or mildew--Tackiness in general--Full discussion of-- + Experimental reproduction--Lack of uniformity in colour-- + Defects in block rubber 223 + + CHAPTER XVIII + DEFECTS IN SHEET RUBBER + + Defective coagulation--Coloured surface blotches--General + darkening of surface--Soft coagulum--Spongy underface--Tearing + --"Pitting" of surface--Thick ends or edges--Mis-shapen sheets + --Thick patches--Torn sheets--"Dog-ears"--Creases--Greasiness + of surface before smoking--Surface blemishes--Uneven + appearance--Variation due to oxidation--Colour when dry-- + Surface gloss--Dull surface--Moist glaze and greasiness-- + Virgin spots--Surface moulds or mildew--Black streaks or spots + --White or grey streaks--Rust--Theories on formation of-- + Prevention of--Two methods--Other views on causation--Bubbles + --Causes of formation--In the field--In the factory--Blisters + --"Spot" disease in sheet rubber--Support marks--Stickiness-- + Surface pattern--Sheet clippings--Other infrequent defects-- + Dirt--Ash--Bark--Splinters 249 + + PART V + _GENERAL_ + + CHAPTER XIX + CHOICE OF COAGULANT + + Acetic acid in general use--Is a coagulant necessary?--Acetic + acid--Formic acid--Citric acid--Tartaric acid--Oxalic acid-- + Sulphuric acid--Hydrochloric and nitric acids--Hydrofluoric + acid--Alum--Pyroligneous acid--Smoked water--Chinese vinegar-- + Sulphurous acid--Sugars--Various salts--Proprietary compounds + --Carbonic acid gas--Alcohol--Vegetable extracts 278 + + CHAPTER XX + SPECIAL METHODS OF PREPARATION + + Da Costa process--Byrne curing process--Freezing process-- + Wickham process--Derry process--Spontaneous coagulation-- + Definition of--Discussion of types--Ærobic--Anærobic-- + Organisms--Maude-Crosse patent--Method of operation-- + Accelerating action of sugars--Accelerating action of soluble + calcium salts--Ilcken-Down process--Slab rubber 290 + + + PART VI + _VULCANISATION_ + + CHAPTER XXI + INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION + + Wild rubber contrasted with plantation rubber--Milling and + mixing--Preparation for vulcanising--Vulcanising 301 + + CHAPTER XXII + TESTING OF PLANTATION RUBBER + + Tests on raw rubber--Breaking strain--Behaviour of rubber + during milling, etc.--Preparation for testing--Tests on + vulcanised rubber--Choice of a formula--Physical tests 309 + + CHAPTER XXIII + THE PROPERTIES OF RUBBER + + Raw rubber--Physical tests--Vulcanised rubber--"Inner + qualities" of raw rubber--Defects of crepe and sheet-- + Variation in physical properties--Rate of cure--Influence of + various factors in raw rubber on rate of cure--Other types of + plantation rubber--Fine para 313 + + INDEX 327 + + + + +LIST OF ILLUSTRATIONS + + + PAGE + SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING 2 + FELLING LIGHT (SECONDARY) JUNGLE 3 + SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED 4 + NEW CLEARING 5 + TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON + VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING 6 + LIGHT JUNGLE 7 + DENSE JUNGLE 8 + CLEARING READY FOR PLANTING 9 + NEW CLEARING: SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING + DRAINED 11 + TYPICAL YOUNG CLEARING, WITH TIMBER 15 + TYPICAL YOUNG CLEARING, WITH TIMBER 17 + TYPICAL YOUNG PLANTED AREA 20 + ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA 21 + WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO + TAPPING 24 + FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED + TOO LONG 25 + TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE 31 + THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE AND + ON RENEWED BARK 33 + SINGLE CUT ON HALF CIRCUMFERENCE (HALF-SPIRAL) 35 + A [V]-CUT ON HALF THE CIRCUMFERENCE 37 + SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE 41 + EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING 44 + ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING 45 + 1. SHOWING EFFECT OF "WINTERING" 48 + 2. NEW GROWTH OF YOUNG LEAF ON SAME TREE 49 + EFFECTS OF DISEASE--"MOULDY ROT" 50 + EFFECTS OF DISEASE--"MOULDY ROT" 51 + EFFECTS OF DISEASE--"MOULDY ROT" 52 + EFFECTS OF DISEASE--"MOULDY ROT" 53 + RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED WITH + FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER + COOLIE" BY SAMPLING OF LATEX 66 + END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD + FOR RECEIVING LATEX AND FILLING TANK 70 + RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX 71 + ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH 72 + TWO VIEWS OF DILUTION AND MIXING TANKS 81 + UNIT MODERN COAGULATING TANK (TWO VIEWS) 91 + ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON THE + RIGHT 92 + CLOSER VIEW OF FOREGOING 93 + ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF + GRAVITATING LATEX 95 + A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION 96 + A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION + TANKS, RAISED, ON THE LEFT 97 + THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN THE + FACTORY 108 + THE NEWER METHOD OF HANGING IN THE OPEN AIR 109 + THREE GRADES OF CREPE RUBBER 111 + A WASHING SHED 112 + DRYING GRAPH. PALE CREPE (THIN) 140 + A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT 155 + ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT 157 + A BATTERY OF MACHINES 165 + "THIRD MILE" TYPE; HORIZONTAL DRUM 190 + "THIRD MILE" TYPE OF FURNACE, USED IN CONJUNCTION WITH "THIRD + MILE" SMOKE-HOUSE 190 + SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE) 193 + PATALING TYPE OF FURNACE 193 + LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED + VENTILATORS PERMANENTLY OPEN 194 + BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE + BUILDING, BUT FED FROM OUTSIDE 195 + GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES 196 + NEAR VIEW OF SHELTER 197 + "THIRD MILE" TYPE OF SMOKE-HOUSE 199 + GENERAL VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE 201 + GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND FACTORY + BUILDINGS 202 + VIEW OF PLATFORM OF "DEVON" SMOKE-HOUSE; DOORS OF COMPARTMENTS + OPEN, AND ONE RACK PARTIALLY WITHDRAWN 203 + DOUBLE "DEVON" SMOKE-HOUSE OF BRICK, WITH ROOF OF CHINESE + TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM + SMOKING CHAMBERS 204 + SIDE-VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL + ARRANGEMENT FOR STOKING FURNACES 205 + FRONT VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE 206 + SIDE-VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE 207 + THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT 210 + SUGGESTED ARRANGEMENT OF BUILDING 218 + THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM "SPOT" + DISEASE 237 + + + + +THE PREPARATION OF PLANTATION RUBBER + + + + +PART I + +FIELD OPERATIONS + + + + +CHAPTER I + +_PLANTING_ + + +To criticise the methods of the pioneer planters of _Hevea Brasiliensis_ +presents no difficulty in the light of present comparative knowledge, and +to be "wise after the event" is a failing which is not confined to those +interested in modern planting methods. Looking at the matter broadly, +however, it must be acknowledged that the pioneers, wrong though they may +have been on some points, did remarkably well, considering that there +existed no real knowledge on the subject and that the methods employed were +perforce of an empirical nature. Although we know a little more concerning +the scientific aspects of rubber planting, the sum total of that knowledge +does not justify any drastic criticism of the methods employed by our +predecessors. In fact, although we may be of opinion that on general lines +there is little now to be learned regarding the planting of _Hevea +Brasiliensis_, our present knowledge does not preclude the possibility that +future investigations may bring against us charges similar to those +sometimes levelled at the earlier planters. + +The main theme of the present volume is that of the preparation of rubber +for the market. Hence it is not proposed to deal in detail with the work +attaching to the opening and development of rubber estates. For this the +reader is referred to the literature dealing specifically with rubber +planting. Certain points in connection with planting may advantageously be +treated in a general way according to modern knowledge, and of these it is +proposed to discuss a few in the following pages. + +[Illustration: SEEDS, SHOWING VARIABLE SIZE, SHAPE, AND MARKING.] + +SEEDS.--The view is now generally held that many areas were planted from +seed which was not collected in a discriminate manner; and that probably +the comparatively low yields obtained on areas of some estates may be due +to the employment of seed from a poor strain. To be able to decide whether +such explanation fits the case demands a full knowledge of all the possible +factors governing the question of yields. It may, or may not, be a fact +that seed from a poor strain is wholly or partially accountable for low +yields; but whatever the degree in which the seed influences the result, it +is an axiom that to obtain the best results in all planting industries a +most judicious selection of seed should be made. In short, seed obtained +from good-yielding specimens by selective treatment will eventually produce +progeny of good-yielding strain. + +[Illustration: FELLING LIGHT (SECONDARY) JUNGLE.] + +The recognition of these principles as applied to the planting of _H. +Brasiliensis_ has focussed recent attention upon the desirability of +planting nurseries with seeds obtained from those trees which are known to +be good producers of latex of normal consistency. It does not follow that +the tree of most rapid growth and development is necessarily the best +yielder; such is often not the case. In the matter of selection, therefore, +one has to take other standards than that of size; and the issue is +narrowed chiefly to a consideration of the yields of latex given by +individual trees. It has been found by various experimenters that there is +no necessity to proceed to such a refinement as the determination of the +actual weight of rubber yielded. The dry rubber content of latices from the +same trees is found to be so comparatively regular, allowing for climatic +changes, that it is sufficient for the purposes of selection to measure the +volumes of latex yielded by individual trees. + +[Illustration: SEEDLING, SHOWING ROOT-SYSTEM WITH SEED STILL ATTACHED.] + +Unfortunately the industry is so young that the question of seed selection +yet awaits study. The task presents certain practical difficulties, and +would be by no means so easy to control as in the case of seed selection +from other plants. It will be obvious that several generations of trees +raised from selected seed would have to be under observation before any +sound deductions could be made from statistics obtained in the course of +the work. Thus the problem of seed-selection as it concerns the +establishment of a high-yielding strain would involve many years of +observation on the part of a trained man. Unfortunately neither the man nor +the facilities for such experimental work exist at the present moment in +the Federated Malay States. On the scientific side the industry is +incommensurably staffed, and most of the workers' time is occupied with +routine work connected with estate practice. + +[Illustration: NEW CLEARING. + +In the middle distance, felled trees awaiting burning; in the foreground, a +flat and wet area with main drainage outlined. + +(_By courtesy of the manager of Membakut Estate, British North Borneo._)] + +[Illustration: TYPICAL YOUNG CLEARING, AGED ABOUT THREE YEARS, PLANTED ON +VIRGIN SOIL. ORIGINAL JUNGLE TIMBER SLOWLY ROTTING.] + +SELECTION.--It is possible, however, that the question of strain +improvement will be solved in another manner than that of successive +breeding from the seeds of high-yielding trees. Such investigatory work is +now occupying the attention of scientific organisations in the East, and +credit is due to the stations in Java which have begun experimental work in +this direction. In brief, the scheme may be outlined as follows. Trees +known to be uniformly good yielders are kept under observation, and the +seeds gathered carefully. These seeds are germinated in a special nursery, +and the best-grown seedlings are selected for further operations. At a +certain stage a bud is taken from a high-yielding parent tree and grafted +upon the stem of the seedling. When this has "struck" the original head of +the seedling is removed. This ensures that one has in the seedling both the +stem and future branch system of the same strain as the parent +high-yielding trees. It is possible to go a step farther, and by certain +processes induce a new root system to grow above the existing roots, which +are then removed. One is then able to guarantee that the roots, stem, and +branches will be of the original high-yielding strain. An objection +sometimes made against the third operation of inducing a new root system is +that the original tap-root is removed and that the subsequent system +consists only of laterals. Against this argument may be quoted the observed +fact that in actual development any one of the laterals may under such +circumstances function eventually as a tap-root. + +[Illustration: LIGHT JUNGLE.] + +On the whole, this system of propagation receives the approval of +investigators, and removes the objections which may be advanced against the +development of a scheme entirely founded upon successive breedings from +selected seed. The course of the investigations, also, are thereby +shortened considerably. Care must be exercised in the work of obtaining and +grafting the buds, but it has now been proved that by exercising reasonable +precautions which are not beyond the intelligence and ability of +subordinates, an extremely high percentage of success can be attained. + +[Illustration: DENSE JUNGLE.] + +Until such time as this process becomes practicable the inception of a +planted area must follow the lines usually adopted. + +NURSERIES.--The usual practice is to obtain seeds from some estate which +has a reputation for good yields and for exercising care in the gathering +and shipping of seeds. The seed is planted in specially prepared beds, and +the percentage of germination noted for future reference. The plants should +be tended carefully, and close observation made for the detection of +disease or pests. It is not uncommon to find that owing to lack of care in +the preparation of the seed-bed, the young plants are attacked by disease. + +[Illustration: CLEARING READY FOR PLANTING. + +Surface timber removed, but stumps remaining.] + +STUMPS.--At a stage, varying according to the requirements of the estate, +when the plants are from twelve to eighteen months old, they are lifted +from the earth. The roots and head are cut off, and the "stump" is ready +for immediate planting in the field. Naturally any appreciable delay in +planting, or unfavourable weather conditions, will militate against the +chances of successful "striking"; and it is not uncommon to find that a +certain number of "supplies" will be necessary. + +SEED AT STAKE.--A method sometimes adopted is to put out seed in the field, +in prepared holes which indicate the exact position of the future trees. +Usually three seeds are placed in each hole, and if two or three germinate, +the plant having the healthiest appearance is retained, and the others +removed. The possible objections to this method of planting are obvious to +those acquainted with field conditions, but in actual practice planting +seed "at stake" has often proved highly successful. Naturally the results +obtained must depend upon the selection of good seeds, the care exercised +in the preparation of the "holes," weather conditions, and the +discrimination exercised in the selection of the plants to be +retained--apart from such disabilities as the depredations of rats and +other pests. + +BASKET PLANTS.--Yet another and perhaps the most popular method at present +is the germination and growth of seedlings in baskets specially constructed +for the purpose. These plants are kept under observation until of the +required age and growth. They are then conveyed to the field, and the +baskets are planted in prepared holes. The baskets, being of vegetable +material, are liable to be attacked by various diseases while in the +nursery or after planting. It is considered advisable, therefore, to treat +them by dipping into some disinfectant such as tar, or a mixture of tar and +one of the common proprietary disinfectants. Otherwise a disease may be +conveyed from the basket to the seedling. + +PREPARATION FOR PLANTING.--There can be no other opinion than that ideally +all land required for planting should be perfectly clear of timber of every +description. After felling and burning, under ordinary conditions a certain +amount of clearing is effected, but in actual practice this amounts to +comparatively little. Big logs and stumps are left because the cost of +clean clearing is judged to be prohibitive and non-economic. Surface timber +is gradually cleared in the course of development, and usually large stumps +are the last to be tackled. The objection to this procedure is really not +strong, but unfortunately an important point is generally overlooked. +Granted that most of the dreaded diseases travel beneath the surface of the +ground by means of buried timber, it is plain that as far as stumps are +concerned, the chief source of danger lies in the existence of the roots. +If these were carefully exposed and removed, the isolated stumps would then +not be such potential infection points. It follows from this argument that +the importance of removing buried timber cannot be too strongly insisted +upon. It is not uncommon to find that some years after the opening of an +estate, and after surface timber has been removed, a large number of trees +are affected with _Fomes lignosus_ (formerly known as _Fomes semitostus_). +Such cases are directly attributable to the existence of buried timber, and +no local treatment will be successful unless the whole of the area is dug +over carefully, and all pieces of timber removed. + +[Illustration: NEW CLEARING; SLOPES "HOLED" FOR PLANTING; FLAT AREA BEING +DRAINED. + +(_By courtesy of manager, Membakut Estate, British North Borneo._)] + +SILT CATCHMENT TRENCHES.--Granted the ultimate necessity of clean clearing, +it becomes necessary to take some precautions to prevent loss of soil by +"wash" in young areas planted on sloping land. An argument often used in +extenuation of the practice of allowing large surface timber to remain +until it becomes rotten is that it is an aid in preventing loss of soil by +wash. Its removal necessitates the institution of some method of preventing +"wash." The establishment of terraces on steep slopes tends to the +achievement of the desired result, but this method is not extended to more +moderate slopes where loss by wash is still considerable. It is the opinion +of the writers and others that the general case calls for the institution +of silt catchment trenches, which, as the name denotes, fulfil the duty of +catching any surface soil and of retaining rainwater. These trenches are +usually laid out on contour, and do not exceed a length of 20 feet. They +are usually from 18 inches to 2 feet wide and deep, and are so arranged on +the slope that they occupy overlapping positions. The actual number of +trenches required will depend upon the angle of slope; the steeper the +slope the greater the number required--_i.e._, the shorter will be the +length of slope between any two trenches. Given a clean area, it is obvious +that the momentum acquired by running water (and hence the amount of soil +removed) on any one slope will depend upon the distance travelled. It is +advisable, therefore, to place a larger proportion of the trenches on the +upper part of the slope than on the lower, so as to guard against the +breaking down of the trench system under an abnormal downpour of rain. + +On land thus prepared the writer has seen areas successfully planted, +which, under ordinary conditions, were condemned as being too steep for +planting. It is true that these trenches necessitate continual upkeep until +the soil becomes well shaded by trees, but the actual amount of work +demanded in cleaning and maintaining the trenches will depend largely upon +the thoroughness with which the original work was planned and executed. +Whatever may be the weaknesses exposed as a result of providing an +insufficient number of trenches of inadequate dimensions, there can be no +question that they are a necessity. + + + + +CHAPTER II + +_FIELD MAINTENANCE_ + + +CLEAN WEEDING.--Intimately connected with the growth and development of the +rubber tree one has to consider the conditions under which it is allowed to +mature. The argument has been used that, since the habitat of _Hevea +Brasiliensis_ is in the jungle, we should be proceeding against nature by +introducing conditions unlike those under which the "wild" rubber tree +grows. It is difficult to treat such an argument seriously, as by quoting +parallel instances in arboriculture it could be shown that growth, +development, and yields are improved by cultivation of "wild" plants. + +It needs small experience with rubber-tree plantations to be convinced of +the necessity for dealing with other growths, which would otherwise soon +surround and overshadow young rubber trees. + +Apart from checking and preventing woody undergrowths it is considered +advisable to keep the ground more or less free from light vegetable +growths, which are roughly grouped under the heading of "weeds." + +Naturally, if these weeds are allowed to flourish and seed, their eventual +eradication may be a matter of extreme difficulty and expense. It is the +aim, therefore, of properly conducted estates generally to institute such a +system of work that the weeding-gangs cover the whole estate at regular +intervals; and, as a general rule, it may be accepted that the shorter the +interval between successive visits by the gang to any particular area, the +easier it is to keep weeds in check, and the cheaper the work will +eventually be done. This procedure defines roughly what is implied by the +term "clean weeding," and it is the policy adopted by most estates. + +Strict adherence to this practice in rubber cultivation has been inculcated +by the older school of planters who obtained their experience in the +cultivation of other crops such as tea, coffee, tobacco, etc. + +In latter years the wisdom of scrupulous clean weeding under all conditions +has been questioned; and there can be no doubt that under certain special +conditions a continuation of the policy of clean weeding is calculated to +produce, in course of time, more harm than benefit. As an instance, the +case might be cited of steep slopes on poor land. Continual clean weeding +on such areas will lead eventually to a great loss of the surface soil, +unless some precautions are adopted for catching and retaining the fine +silt particles. It is to be noted that such a type of soil and slope, when +the shade is appreciable, often produces no weeds heavier in growth than a +very light grass. It is urged that the necessity for strict clean weeding +on such soils does not exist, and, in fact, that it would be an injurious +policy. Such arguments appear to be well founded in experience, and the +writers are in thorough agreement that such special cases deserve special +consideration. Rigid adherence to a policy of clean weeding, without regard +to special conditions, would be most inadvisable. + +Nevertheless, such exceptional cases do not detract from the wisdom of +clean weeding in general. Every planter of experience realises how easily +fields become infested with weeds if the regular work is suspended or +delayed. It is probably quite true that the harm due to the presence of +some weeds on an occasion is negligible; but apart from this debatable +point, there is the solid fact that if once an area is allowed to become +weedy it may soon demand a much greater expenditure to bring it back to +normal condition than if it had been regularly weeded. This is common +experience, and for that reason alone a general policy of clean weeding is +thoroughly sound; especially if combined with some system of +silt-retention. + +GRASS SQUARES.--On some estates the practice of clean weeding is undertaken +in combination with a system of silt-retention, which depends upon the +development and maintenance of ridges. These are built up from the débris +of weeding in the form of hollow squares. Grass is allowed to sprout and +grow in these ridges, and when it attains a certain height it is trimmed +down so as to keep it within bounds. The soil within the hollow square is +clean weeded; and it is maintained that loss of soil by wash is avoided. +Under certain conditions there is a great deal to be said in favour of the +method, but in the opinion of the writers it should be regarded only as a +method of expediency. It is not to be preferred to the more thorough +practice of soil-retention by means of silt-trenches, although the latter +method may be slightly more expensive in the end. + +[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER. + +Planted "rubber-stump" in foreground.] + +"LALLANG" ERADICATION.--The greatest bugbear of the planter in connection +with weeding is the incidence of lallang. Many proposals have been put +forward at various times for the complete eradication of this pest; but at +present, under ordinary circumstances, there would seem to be no better +method than by heavy and deep digging, followed by regular attention. The +method is acknowledged to be expensive, but any half-hearted measure +otherwise taken will eventually prove to be even more costly. + +One has to differentiate, of course, between the incidence of lallang +attributable to negligence on the estate itself, and the occasional +outbreaks near boundaries, due to seeds having been wind-borne from patches +of lallang outside the boundaries But, in general, it would be safe to +remark that the appearance of lallang could be taken as evidence of a +failure to cover the area at sufficiently short intervals. + +As already intimated, the usual method of eradication of areas of lallang +is by thorough digging, and the exposure of the strong root system to the +sun. As a matter of interest it may be noted that recently some success has +been obtained by another method[1] on areas which one may have in view for +planting at some future date. + +[1] "Eradication of Lallang," W. P. Handover, _The Planter_, Vol. I., No. +1, August, 1920. + +It consists in the employment of _Mimosa gigantea_, which eventually +smothers the growth of lallang. + +The seeds are sown broadcast, in drills, or in pockets, amongst the +lallang. In the course of about three months it overtops the grass and +proceeds to travel. At this stage the whole mass is pressed down, and the +pressing is repeated at regular intervals. Under favourable conditions, in +about twelve months, an impenetrable mat has been formed, which gradually +forms a good mulch. When it is desired to remove the Mimosa, the mass +(pressed down) is cut and rolled up like a carpet. Cleared in this manner, +the area then needs regular weeding, in order to check the development of +any stray lallang shoots. In actual practice it was found that the cost of +this method was approximately two-thirds that of the usual digging method. + +GREEN COVER PLANTS.--Some years ago it was quite common to find green +cover-plants employed on estates with the primary idea of minimising +weeding costs. With most of these it was found later that their value was +not real, and that they harboured diseases, and pests. Moreover, when they +were removed, it was often found that an abundant crop of lallang and +weeds resulted. + +There can be no question that certain plants can be employed with +advantage, not only in the control of weeds, but also by reason of benefit +to the soil in which they are established. These plants are leguminous, and +their use is restricted almost entirely to young areas, inasmuch as they +will not continue to grow when shade becomes marked. Of those best known in +modern practice might be mentioned _Tephrosia candida_ (Boga bean), +_Centrosema Plumerii_, and _Dolichos Hoseii_ (Sarawak bean). + +[Illustration: TYPICAL YOUNG CLEARING, WITH TIMBER. + +Young rubber plants in foreground. Two of these are easily distinguishable, +both with small crowns of leaves.] + +It is wrong to imagine, however, that the establishment of such leguminous +cover-plants obviates weeding. So far is this from being the case, that in +practice it is found that the weeding "rounds" must be conducted at first +with the same regularity as in ordinary working, but that naturally there +is much less work to be done. + +As the plants develop, they can be pruned or dug into the soil, as the case +may be. The addition of the green material to the soil, either by digging +or by burying in open trenches, is calculated to cause improvement in the +condition of the soil. There may thus be a close connection between +weeding, soil conservation, and soil improvement. + + + + +CHAPTER III + +_THINNING OF AREAS_ + + +On this subject there is unanimity regarding the necessity for the +operation. Divergence of opinion exists only as to a matter of degree. + +On the one hand there is the school of planters who would advocate the +advisability of planting up to, say, 200 trees per acre, with subsequent +thinning out by selection. At the other extreme there is the opinion that +we should plant only a few more trees per acre than it is intended +eventually to maintain, the argument being that by this method the growth +and development of individual trees will be so much greater than in close +planting that the necessity for drastic thinning out will not arise. + +Unfortunately for the latter school, a very important point is +overlooked--viz., that size and general development are not criteria of +yielding capacity. It might thus follow that a stand of ninety well-grown +trees per acre might give very disappointing yields per acre. In a few +instances this has been noted with 30 by 30 feet planting, but it is +doubtful whether the factor influencing such results has been appreciated. + +The apostles of close-planting have this in their favour: that if the trees +to be removed are selected on proper lines, it is possible to have all +remaining trees of comparatively high-yielding strain. This is a very sound +argument, but its practicability is limited very largely by the question of +early growth and development. It would seem the sane course in any event +not to plant more trees per acre than may grow normally, and without branch +or root interference up to the fifth year (the normal first year of +tapping). + +Before this stage has been reached, stunted or deformed trees will have +been noted and removed, so that in the first year of tapping thinning +proper can be commenced. In the past this has been effected wholly by +selection of trees according to their general appearance and situation; but +it is now safe to predict that future operations will be based upon sounder +and more scientific lines. + +Trees will be selected for removal according to their individual yields, a +standard which we have been advocating for years without much practical +success. In Java and Sumatra much good work has been done in this +direction, and recently a commencement has been made in the F.M.S. + +[Illustration: TYPICAL YOUNG PLANTED AREA. + +Heavy original jungle timber.] + +It is within the daily observation of all planters that certain trees +regularly give greater yields than others, and that such trees are not to +be distinguished by size or general development. Moreover, with slight +variations, it has been found that a good yielding tree is consistently a +good yielder, and the converse holds true. + +If, therefore, measurements of individual yields are taken at intervals, +and the results recorded during the first year of tapping of an area, an +excellent guide is obtained for the first round of thinning. It is found +in actual practice that five, or even three, readings during the year are +sufficient to give the indication required. It is not essential that +simultaneous readings should be taken over a large area; in fact, such a +step is really impracticable at first. The simplest method is to employ +either-- + +(_a_) A small uniform vessel in which the latex is measured by means of a +thin slip of bamboo upon which graduations are marked. + +(_b_) A glass measure graduated regularly. + +[Illustration: ANOTHER EXAMPLE OF A RECENTLY PLANTED AREA.] + +In both cases it is immaterial what units are represented by the +graduations--whether cubic centimetres, quarter ounces, half-ounces, or +ounces, as long as the unit is not too large. It is preferable to employ a +fairly small unit, so that in taking readings from young trees a wider +range may be obtained between poor yields and good yields. In the case of +older trees a larger unit may be taken. + +The first stage in the operations is to number all trees in the field to +be tested, and to prepare a rough register, with three or five vacant +columns opposite each tree number. + +It is not advisable to commence the record of yields until the panel of +bark has been under tapping for a month or two. It is found that an +intelligent coolie can be taught the method of measuring and rough +recording. The latter is accomplished by means of marks made upon the +virgin bark of the tree above the tapped area. The marks may be made with a +tapping knife, by means of paint, or with a lead pencil. The simplest form +of record consists in putting one mark for each graduation of reading. + +In practice it is found that, commencing about an hour after the first tree +has been tapped (in the case of young trees) and following the course taken +by the tapper, the measurer of yields is able to do about 2 full tasks (650 +to 750 trees) per diem. Each day progress is made through the field. + +Obviously on such a small scale and utilising only one measuring coolie the +comparison is restricted very much; but in any case this is immaterial as, +owing to the personal equation of the tapper, comparison strictly should be +limited and internal--_i.e._, it should really be confined to one task only +at a time. In this way the worst trees in any task are indicated. + +The keeping of the records may be entrusted to a field clerk, but is better +placed in the hands of a European. The register is taken into the field and +the rough records found on the trees are noted in the columns against the +tree number. + +Most planters are aware in a general way of the disparity between the +yields of individual trees, but they would probably be surprised if they +undertook the institution of such records. + +The following figures must not be taken as typical. They represent the +average results from several tasks in a young field from which all +ill-grown and deformed trees had been removed. It is immaterial what the +units represent, as they are purely arbitrary and were selected for the +purpose of obtaining a fairly wide range. + +Any trees which failed to yield sufficient latex to reach the first mark +were registered at zero. The following percentages were obtained: + + Zero 3 per cent. + Above mark 1 6 " + " " 2 16 " + " " 3 42 " + " " 4 12 " + " " 5 14 " + " " 6 6 " + " " 7 0 " + " " 8 1 " + " " 9 0 " + --- + 100 " + +It may be remarked that, judging by ordinary standards, it was impossible +to discriminate between good yielders and others, and if thinning were to +be done on the usual lines it is quite possible that some of the best +yielding trees would be removed. + +Taking the mark No. 5 as the datum line, it will be noted that 79 per cent. +of the trees come below and 21 per cent. above. In the latter proportion +the majority lie close to the datum line. It will be seen that there are +outstanding yielders even amongst these young trees, and that it would be +possible to mark about 10 per cent. of the stand per acre at once for +removal in the first round of thinning. + +In the case of old trees it is possible that one would encounter greater +extremes of yields than those shown in the foregoing table, especially if a +certain amount of thinning had been done previously on empirical lines. +Sufficient has been written to show that the only reasonable basis for +selection of trees in thinning is that of yields; and it is obvious that if +the method be adopted the future yield per acre of any area is bound to be +in excess of the same area as thinned on rule-of-thumb lines. + +YIELDS PER TREE.--A great feature is made in estate reports of the figure +showing the average yield per tree per annum. Assuming an area to be +yielding at the average high rate of 540 lbs. per acre per annum, with an +average stand of ninety trees per acre, the yield per tree per annum +averaged over all trees is 6 lbs. Keeping in mind the test-figures on a +previous page, it will be obvious that some of these trees may have given +very much more than 6 lbs. during the year, and some less. In view of +present information it would not be surprising to find that a few might +have been yielding upwards of 15 lbs. per annum. Unfortunately this +information is only to be obtained by individual tests, and under normal +estate conditions the facts escape notice. Cases are known in which +out-standing individual trees have been known to yield at the rate of 25 +lbs. and more per annum. + +[Illustration: WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO +TAPPING.] + +[Illustration: FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED +TOO LONG. + +Note height and comparative lack of girth.] + +FUTURE YIELDS PER TREE.--It has been shown that by selective methods based +on yields, poor trees can be eliminated. Whether by a process of +seed-selection or by means of propagation based on bud-grafting and +marcotting, it needs no great stretch of imagination to forecast future +conditions under which trees may be bred which will be capable eventually +of giving an average yield of 25 lbs. per annum over any given area. +Yields of 1,000 lbs. per acre per annum should be obtained easily. + +TREES PER ACRE.--This brings us to the question as to how many trees one +should leave to the acre after thinning operations. Figures have been given +by various authorities, but it appears to the writer at the present time to +be impossible to lay down a general rule. So much depends upon conditions. +In certain cases where the soil is admittedly poor, the average growth +below normal, and thinning has been postponed too long, the writer has been +forced to the conclusion that it would be most inadvisable, and +commercially unsound, to reduce the stand of trees below 120 per acre. In +such instances the average yield per tree equalled only 3 lbs. per annum, +and although the trees were upwards of nine or ten years old the crowns +were small and sparse. It is doubtful whether such trees will ever exhibit +any further development, and to thin them further would probably lead only +to a diminution in the crop per acre. + +Under normal conditions of growth an arbitrary figure of eighty trees per +acre has been selected as a standard by many estates. In these cases it +would probably be correct to state that thinning was undertaken on almost +purely empirical lines--_i.e._, that trees were not selected by tests of +individual yields. As far as such a method retained the apparently most +vigorous trees it was successful; but in view of what has been written it +might explain some of the disappointing results which have followed upon +such a system of thinning. + +It will be clear that any decision regarding the number of trees to be +retained must be derived from a study of the detailed results of individual +tests. If the large majority of the trees appear to be fairly uniform in +yields the first thinning must be confined to comparatively few trees. +Where there is, on the other hand, a good percentage of high-yielding trees +the final stand per acre may be appreciably less. Unless and until such +information is available, one cannot give any definite opinion as to the +requisite number of trees to be retained per acre. + +Similarly, intelligence must be displayed in deciding which of several +uniformly-yielding trees should be removed. In the average sense of this +consideration one must pay no attention to symmetry of spacing, but when +dealing with trees of fairly uniform yields one needs to study the +characteristic development of the trees individually, in order to retain +those which would appear to be most favourably situated with regard to +surrounding trees. + + + + +CHAPTER IV + +_TAPPING SYSTEMS_ + + +Broadly there are only two methods employed in obtaining the latex from +_Hevea Brasiliensis_. The first is that employed in South America, where +incisions are made by means of a light axe. The other is the system of +excision, or paring, of the bark practised on plantations in the East. + +In the early days of the plantation industry, the South American method +seems to have been employed, and the writer has knowledge of trees on one +of our best-known estates in Malaya which still exhibit the outward and +visible signs of that method. At a comparatively early stage, however, the +method of excision was introduced. Curiously enough there appears to be no +record of its inception or of the individual who was responsible for the +substitution of this method. We have been so accustomed to regard it as one +of the ordinary facts of estate procedure, that this point seems to have +escaped notice and enquiry. + +As a variant of these two main methods, a slight vogue was for a short +while obtained by the operation known as "pricking." This was generally +combined with excision of bark, and was then known as the "paring and +pricking" method; but the simple operation of pricking alone had its +adherents, and various forms of instruments were designed to achieve the +object. As a means for obtaining a flow of latex, pricking may have been +effective, but the general difficulties attaching to the collection of the +latex was such as to put the method out of favour. + +In the employment of "paring and pricking," a thin shaving of bark was +excised on one occasion. At the next tapping no bark was excised, but a +pricking instrument was used along the previously cut surface. It was not +proved that any advantage was gained by this method, which was more +commonly employed in Ceylon than elsewhere, and it would be surprising to +find it in use at the present day. + +In the ordinary way the method of excision is practised in such a manner +that the "cut" gradually descends to the base of the tree. + +Planters with original views, and of an enquiring nature, often query the +common practice; and it has been suggested that "as the latex descends by +the force of gravity," one's paring should be done in an upward direction, +thus obtaining a greater pressure of latex--and hence a greater flow. It +will be obvious that it would be no simple matter to collect effectively +the latex thus obtained from the under edge of a sloping cut, but apart +from this the argument would appear to be founded upon what is now accepted +to be a fallacy--viz., that the latex _per se_ is manufactured in the +leaves and gravitates down the tree. + +FORMER SYSTEMS OF TAPPING.--To hark back ten years in the plantation rubber +industry is equivalent to delving into history, since development has been +so rapid. It was then thought necessary to place upon the trees a number of +simultaneous cuts which the modern planter would judge to be inconceivably +excessive. Were it not for evidence in the shape of photographs extant, it +would be difficult to convince a young planter that such systems were +employed. + +It was not uncommon for trees to have from six to ten cuts, sometimes all +placed on one half of the tree in a herring-bone fashion, and sometimes +divided into two portions, each of which tapped the opposite quarter panel +of the tree's circumference. Such superimposed cuts were spaced from 1 foot +to 18 inches apart. + +On other occasions, a spiral cut was employed, commencing at a height of, +say, 5 feet, and gradually descending to the cup at the base of the tree. + +Later systems varied from several cuts on a half-circumference, or on a +quarter of the tree, tapped either daily, or on alternate days, to cases in +which one-third or one-fifth of the tree was employed. Also popular were +the systems of the [V] and half-spiral cuts on half the circumference. + +It did not take long to be recognised that with all these systems demanding +a number of simultaneous parings from the same panel of bark, the rate of +excision was so heavy that the period available for the renewal of bark was +insufficient for continuous tapping. + +As a result most of the systems specified have fallen into desuetude, and +the tendency has since been to reduce the number of cuts, or the +periodicity of tapping, so as to allow for increasing periods of bark +renewal. + +In the earlier days, a period of four years was thought to be an extremely +generous allowance, whereas six years is now becoming recognised as a +minimum necessity. Eight years is not regarded as extravagant, while with +older bark on some estates periods of ten and twelve years have to be +allowed for full renewal. Even so no finality has been reached, and no +general rule can be laid down. Local conditions of planting and growth +exercise great influence, and the writers have in mind instances in which a +period of eight years has proved to be insufficient even for a first +renewal after the excision of virgin bark. + +In the main the most popular systems of tapping are: + + (_a_) One cut on a quarter of the tree, tapped daily. + + (_b_) One cut on a third of the tree, tapped daily. + + (_c_) One cut on half the circumference, tapped on alternate days. + + (_d_) A [V] cut on half the circumference, tapped on alternate days. + +Variants and extremes are: + + (1) One cut on a quarter, tapped on alternate days. + + (2) One cut on a half, tapped daily. + +Superficially viewed the latter is four times as strenuous as the former, +and the relative position seems to be inexplicable. It may be explained +that as a rule the former system is practised on old trees with poorly +renewed bark, in order to allow for adequate bark renewal; and the latter +is employed in opening young trees just brought into tapping, when the rate +of bark renewal is at a maximum. + +[Illustration: TWO CUTS ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE.] + +A few estates in this country still continue to tap trees by means of two +superimposed cuts on a quarter of the tree. This was a very popular system +some four or five years ago, but it has come to be recognised by practical +experience that any system employing superimposed cuts leads to a high +consumption of bark without proportionate increase in yield. For instance, +if one compares the system of two cuts on a quarter tapped daily with a +similar system employing only one cut, one finds that the major quantity of +latex is yielded by the lower cut, and that the single-cut system which +excises approximately half the amount of bark gives about 80 per cent. of +the yield obtained by the tapping of two superimposed cuts. + +Of experiments to test the relative values of different systems of tapping +there have been many. Most of them suffered from the initial handicap that +they dealt with systems which were then popular. In order to obtain any +valid result they had to be undertaken over a long period. Meantime there +was a progressive movement in actual estate practice towards a greater +conservatism in bark removal, and hence the experiments as originally +planned lost value. + +Moreover, in Malaya it was difficult for experimenters to obtain practical +support in the form of areas of trees suitable for experiment. As a result +experiments were often confined to small blocks of trees, and a small +number of blocks, from which any conclusions derived were subject to +considerable errors of experiment. Often comparisons were made between only +two blocks, and no allowance was made for varying factors, such as initial +differences in yielding capacities of the trees, soil conditions, or the +personal equation of the tappers. As a general rule, therefore, the results +were vitiated to a very appreciable extent. + +All these factors were later taken into consideration in an experiment +undertaken on behalf of the Rubber Growers' Association. In this instance +unique facilities were provided by the London Asiatic Rubber Company on +their property at Semenyih Estate, and it is only fitting that the company +should receive the recognition which its enterprise deserves. + +It would have been a great advantage to have included in that experiment +other features which have since come into prominence, but the original +scope of the experiment had to be confined to the point of comparing yields +obtained in making comparative tests based on one system of tapping with +different frequencies. Such data were required as a check upon a Ceylon +tapping experiment which had attracted much attention. In that experiment +trees were tapped at intervals ranging from one day to seven days; and it +was concluded that after a period of three and a half years trees tapped +with greater intervals gave yields equalling or exceeding those obtained +from trees tapped with shorter intervals. + +[Illustration: THE SINGLE CUT ON A QUARTER CIRCUMFERENCE, ON AN OLD TREE +AND ON RENEWED BARK.] + +In the Semenyih experiment the system chosen was that which had the +greatest contemporary vogue--viz., two superimposed cuts on a quarter of +the tree. The various blocks were tapped respectively every day, every +second day, and every third day. + +It was found that the conclusions drawn from the Ceylon experiment were not +confirmed. After a period of three and a half years' continuous tapping +neither the alternate-day system nor the third-day system gave results in +any way approximating to the yield of the daily system. + +The actual average yields from these systems over the whole period were in +the order of-- + + _Daily._ _Two Days._ _Three Days._ + 100 per cent. 60 per cent. 45 per cent.; + +and throughout the course of the experiment neither of the other sections +showed any appreciable improvement in position relative to the daily +section. + +In actual yields "per tapping" over the whole period the alternate-day and +the third-day divisions showed advantages of 20 and 35 per cent. +respectively over the daily portion. + +At the beginning of the second year of experiment another section of blocks +was opened with a single cut on a quarter, tapped daily. This enabled +direct comparison between the values of one cut and two cuts on a quarter +in daily tappings and between a daily single cut and two cuts tapped +alternate daily. + +It appeared that the daily single cut yielded over the period of experiment +80 per cent. of that obtained by tapping two cuts daily; and that in the +comparison between two cuts tapped alternate-daily and a single cut tapped +daily the latter had an advantage of about 40 per cent. in yield. + +This result has been used by advocates of daily tapping generally, but it +does not constitute a fair argument, inasmuch as the single cut was tapped +twice as often, and its position was always relatively low on the hole of +the tree. It has been shown in the comparison between the daily single cut +and the two cuts daily that the influence on yields of the superimposed cut +is relatively small. A fairer comparison would have been obtained if the +two cuts tapped alternate-daily had been either amalgamated to form one +long cut on half the tree or to form a [V] on half the tree, thus placing +the cuts in the opposing sections on the same level. With the knowledge +that the yield obtained from cuts is _always greater per tapping_ by using +the alternate-daily system, it would appear to be plain that the one long +cut on half the tree would at least equal the yield of the single short cut +tapped daily on a quarter tree. + +[Illustration: SINGLE CUT ON HALF CIRCUMFERENCE (HALF SPIRAL). + +_Note._--In this particular instance the cut is changed to the opposite +half of the tree every half-year.] + +Unfortunately no opportunity has been afforded up to the present of +definitely proving this point by prolonged experiment under strict +conditions. It is true that the view is held strongly in some quarters as a +result of the experience of managers, chiefly on their own estates, that +alternate-daily tapping generally gives better yields than daily tapping. + +In a number of instances this view is probably correct, and the writers are +in agreement; but it is necessary to clear away some misconceptions which +confuse the issue. In the main there are two schools, one of which plumps +for alternate-daily tapping, while the other adheres strongly to daily +excision. Great confusion exists, inasmuch as in many instances the +disciples of these schools are really discussing different matters. In the +case of managers who argue for alternate-daily tapping their experience is +gained, with very few exceptions, from systems in which the excision covers +half the circumference of the tree; whereas in almost all cases daily +tapping is confined to a single cut on a quarter of the girth. Bearing on +such a comparison there are, as far as the writers are aware, no reliable +published experimental results. To compare the results obtained from one +system practised on one estate with the results of the other system +established on another estate is not strictly permissible, as we know that +conditions generally may vary to an enormous degree. + +The controversy has raged, however, to such an extent that many who are not +directly engaged in estate practice have obtained confused impressions. For +instance, it appears to be the belief in some quarters that alternate-daily +tapping, when applied to a single cut on a quarter of the tree, will yield +more than an exactly similar cut tapped daily. In support of such a +statement there does not appear to be any confirmation under normal +conditions; although such a result might be obtained in the case of old +trees which have been heavily over-tapped in the past, and on which the +rate of bark renewal has been appreciably retarded. It might also be the +case eventually when trees with the opposing frequencies have been tapped +for a period extending into many years; but it is the opinion of the +writers that under normal conditions such a result would be extremely +doubtful. + +When we come, however, to a comparison of daily tapping on a single cut on +a quarter with double the length of that cut on half the circumference, at +the same height, tapped alternate-daily--whether in the form of one long +cut or in the form of a [V]--we arrive at a contrast which gives a clear +issue. As already stated, facts and figures of reliable experiment are +wanting; but it is the opinion and experience of the writers that the +alternate-daily system at least suffers no disadvantage on the point of +yields, and in other respects, such as conservation of labour and costs, is +superior to the daily system. + +[Illustration: A [V]-CUT ON HALF THE CIRCUMFERENCE.] + + + + +CHAPTER V + +_TAPPING AND COLLECTING_ + + +TAPPING KNIVES.--The choice of a tapping knife is a subject upon which +there is much divergence of opinion. This must be so because no known knife +has such apparent outstanding superior features or claims as would enable +one to settle the point. Moreover, the personal factor is so large that, as +far as the knives in common use are concerned, it appears to exert the +greatest influence. The possibility of obtaining the ideal knife, which +will go to sufficient depth into barks of varying thickness to yield the +maximum quantity of latex without wounding, is quite as remote at the +present time as it was some years ago. Meanwhile the search for that ideal +knife continues, and occasionally one learns of the alleged merits of some +new instrument which, it is said, fulfils all requirements. It is only to +be regretted, both for the sake of the inventor and for the expectant +buyers, that the claims always fail in some one or more particulars. + +In Malaya probably the number of different types of tapping knives may +amount to a half-dozen, but those most commonly in use are: + + (1) The gouge--straight or bent. + + (2) The ordinary farrier's knife. + + (3) Modifications of the farrier's knife, such as the "Jebong." + +Argument on the respective merits of knives is popular, and discussion +seems endless. It is claimed for the bent gouge that it is superior to the +straight instrument, because, the leverage being downwards on the handle, +the tendency is to lift the cutting edge upwards and out of the bark, +whereas with a straight gouge the tendency is to push the knife downwards +into the bark. It is claimed, therefore, that the average shavings taken +off by the bent gouge should be thinner than those obtained by the use of +the straight instrument. + +For similar reasons it is asserted that the "Jebong" and other +modifications are superior to the original form of the farrier's knife. +These points are generally accepted without great argument, but when +comparisons are made between the gouge and the farrier's knife (with its +modifications) the opinions of planters are so varied and conflicting as to +be almost irreconcilable. Two opinions based on experience with both types +of knives are often wholly contradictory. + +There can be no doubt that the likes and dislikes of operative coolies have +a considerable influence in determining the measure of success obtained +with any one knife. Should coolies have been accustomed to the use of a +particular form of instrument they become quite expert, and any proposed +change creates in the minds of coolies a prejudice which is considerable in +effect on the quality of the handicraft. Such prejudice may be overcome in +course of time, but in the interval not a little damage may have been done +in the shape of tapping wounds. So considerable is this question of +personal favour that even on estates where a standard pattern of knife is +issued coolies often modify that knife slightly on their own accord. Such +alteration is ignored by the superintendents as long as the quality of the +tapper's work is maintained at a high standard. + +Naturally there is a limit to such leniency, and this limit is soon reached +in the case of knives having adjustable parts controlled by screws, or nuts +and bolts, etc. Some knives of this description really merit a much wider +use than is afforded them at present; but in view of the potential damage +which might be done as a result of adjustments made by the coolies these +knives do not become popular. + +It is not proposed here to enter into a description of even recent +instruments for which strong claims are being made by their inventors or +vendors. If they possess the merits attributed to them they will soon find +favour, as managers are always keen on studying the points of any new knife +which will lead to a conservation of bark and a reduction in the number of +wounds. On the whole, it may be advanced that the best general results are +obtained by the adoption of a simple non-adjustable knife and the retention +of its use. + +THE CHOICE OF LATEX CUPS.--It has come to be recognised that the maximum +possible cleanliness is essential in all details of estate work, and the +younger generation of planters could scarcely be aware that a few years ago +it was deemed sufficient to use coco-nut shells for the reception of latex +on individual trees. + +Terne-plate cups ousted the coco-nut shell, and they had the merit of being +cheap. The interior coating of tin did not last long if the cups were +properly cleaned. The iron being exposed, with a minutely roughened +surface, each microscopic projection served as a point around which latex +coagulated. Scrapping the film of interior rubber became more and more +difficult, and often the cups were burnt in order to get rid of the +accumulation of rubber. The last state of such cups was worse than the +preceding one. On some estates fairly successful attempts were made to keep +these cups clean by making the coolies bring them into the store each day. +Terne-plate cups are not now in common use. + +Aluminium cups have their advocates, but much the same argument applies to +the difficulty of keeping them clean as was used in the foregoing +paragraph. On many estates, however, they are used with success, the usual +method of treatment being to make the coolies bring them into the store and +clean them there. Owing to the comparative lightness of the material such a +scheme is more feasible than was the case with terne-plate cups. + +The cups now most in general use are either of glass or white-ware, and +probably those of glass are the most extensively employed. There are many +details to be studied in the choice between these two types of +cups--_e.g._, percentage of breakage in transport and in the field, price +when breakage is taken into account, etc.; but these apart the glass cups +have one advantage--namely, the ability of the superintendents to see +whether the cups have been properly cleaned. In the case of white-ware cups +this means an inspection and handling of individual cups, whereas in the +case of glass the point is settled by visual examination at a comparative +distance. + +[Illustration: SINGLE CUT ON TWO-FIFTHS OF CIRCUMFERENCE. + +The opening cut covers two-fifths. Subsequent cuts occupy one-fifth of +circumference.] + +Glass cups are made in two patterns, one having a flat bottom and the other +a conical base. The latter is convenient for use when wire supports are +employed, the cup fitting into a loop placed beneath the spout. Used on the +ground its shape is an obvious disadvantage, as, unless a hole is scooped +for its reception, it has to be propped up with sticks or stones. Often a +touch is sufficient to upset the balance, and latex is lost. + +The flat-bottomed cup, on the other hand, may be used with success equally +on a wire support or on the ground. It is sometimes said that owing to its +shape the ease of cleaning, as compared with the half-spherical cup, is +diminished, and that if the cups when not in use are kept inverted upon +sticks placed near the foot of the tree the breakage is apt to be high. +This latter objection is being rapidly removed as the practice of using +these sticks is losing vogue for various reasons, and wire cup-holders will +be in general use as soon as the cost of material becomes normal. + +There are on the market, and in fairly wide use, cups of Chinese and +Japanese manufacture. These generally consist of brown earthenware with an +interior glass finish. These are cheap in comparison with glass and +white-ware cups, but it is a pity that the glass does not extend over the +whole of the cup. The outer surface has a tendency to collect rubber and +dirt. On some few estates small china bowls or saucers are still used and +are quite satisfactory, except for the favour with which they are regarded +by natives on the outskirts of the estates. + +CLEANING CUPS.--The question of cup-cleaning would appear to be a very +simple one; but in practice it is quite a source of worry to managers, +especially where a mixed labour force is employed. Tamil coolies can be +made to clean their cups in the day's task and at odd times. Chinese +coolies, more often than not, either refuse to give the necessary attention +or else demand extra pay for the work. + +The method of cup-cleaning employed more popularly within recent years was +that of daily washing. The tapper carried two buckets, one for receiving +the latex and the other containing water. Pouring the latex in the bucket +the coolie then added a little water to the cup and added these rinsings to +the latex collected. The cup was next washed hastily in the bucket of water +and replaced. By the time the coolie has emptied and washed some 200 cups +(about half the task generally) the water has the consistency of dilute +latex, and the wet cup when replaced becomes coated with a thin film of +rubber. If the latex is always collected in one direction it will be clear +that, while the cups at one end of the task are comparatively clean, those +at the other end have the chance of being correspondingly dirty. + +Controversy has raged respecting this question of cup-washing, and many +estates have abandoned it as a daily practice. Coolies have not to carry an +extra bucket of water. The contents of the cups are poured into the +latex-bucket, and the bulk of the latex film remaining is also removed by +the aid of a finger. The cup is then replaced, a thin skin of rubber +forming on the interior surface. As a general rule this is easily removed +on the next occasion, except perhaps in dry weather. It is the custom on +most estates employing this practice to have all cups receive special +attention at regular intervals. + +There are certain economic factors entering into the difference of opinion +regarding the two broad methods employed. In some cases--_e.g._, on old +areas--it would be practically impossible to follow the older method of +daily cup-washing, as the tappers have to employ two buckets for the +collection of the latex. The employment of special coolies for cup-washing +would be necessitated, such as may be seen sometimes on estates working +Chinese "squatter" labour--where the man taps, a child assists in +collecting, and another child, or the mother, washes the cups. It may be +pointed out that in such instances the helpers are not paid by the estate. +Their services merely mean a saving in time which is spent in the +squatter's garden, and perhaps the permission to the tapper to work a +larger number of trees than would be allotted ordinarily to a task. + +Again, on some estates, the tappers, while not being required to carry a +bucket of water for cup-washing, are given an increased number of trees to +tap. Furthermore, on hilly areas under tapping, it is often manifestly +unfair to expect the tapper to be able to carry two buckets during +collection, when the slope is such, as to make the manipulation of even one +bucket a matter of difficulty. + +It will be seen, therefore, that there is no clear issue for argument +concerning the two methods, and that the point must be decided on the +economic factors peculiar to each estate or district. + +[Illustration: EFFECTS UPON RENEWED BARK OF PREVIOUS TAPPING. + +Note uneven surface and callosities.] + +[Illustration: ANOTHER EXAMPLE SHOWING THE EFFECTS OF PREVIOUS TAPPING.] + +WATER IN CUPS.--Much discussion used to take place regarding the necessity +or otherwise for placing a small quantity of water in the cups when +tapping. It was recognised that the permission to use water (with the idea +of preventing coagulation) led to much abuse, apart from the question as to +the utility of the method. Dirty water was often used, although clean water +may have been placed in the buckets when coolies left the muster-ground. +The small quantity of water often exceeded the actual yield of pure latex +by hundreds per cent., with the result that on arrival at the factory the +diluted latex was below the standard desirable for the preparation of a +good sheet-rubber. + +PREMATURE COAGULATION.--Other opinion to the contrary it is now generally +acknowledged that the possibility of premature coagulation in the cup or +bucket is at least not diminished by the addition of even clean water. The +use of water often obtained from estate drains clearly led to increased +trouble. The extent to which such premature coagulation takes place varies +greatly under the influence of many factors--_e.g._: + + (_a_) Cleanliness of cups and spouts (the latter an important item + often overlooked, and involving the presence of certain organisms + which effect coagulation). + + (_b_) Climatic conditions. + + (_c_) Rate and volume of flow of latex. + + (_d_) Size of tappers' tasks (involving the length of interval between + tapping, and the collection of latex). + + (_e_) Distance to be traversed between the site of the task and the + store. + + (_f_) Care in collecting, to exclude extraneous matter. + + (_g_) Nature of transport; agitation of the latex to be reduced to a + minimum. + + (_h_) Nature of the soil, and situation of the estate. + +The last mentioned factor is of great importance. As a general rule it is +noted that premature coagulation is less marked on estates situated on +comparatively hilly land. The greatest effect is remarked on estates +situated on the flat lands of the coastal area where peaty soils are a +feature. On many such estates, in spite of the observance of all ordinary +precautions, it is not possible to receive the latex at the factory without +a large percentage of prematurely coagulated rubber being found in the +transport vessels. + +ANTI-COAGULANTS.--For this reason on these (and other) estates, the use of +small quantities of anti-coagulants is common. The effect of these is to +keep the latex liquid and thus render possible the preparation of a higher +percentage of first-grade rubber than would be otherwise obtained. + +Among the better known agents which have such an effect upon latex, +formalin and sodium sulphite (not bisulphite) are the chief. The latter is +the more popular as it is slightly cheaper and much more stable. As now +used, it is in the form of an easily soluble powder (anhydrous sodium +sulphite). The ordinary crystalline form of sodium sulphite as used in +photography is not recommended, on account of its comparative lack of power +and its poor keeping qualities. + +It will be obvious that, given two equal quantities of different latices, +different amounts of an anti-coagulant may be required to produce the same +effect. Hence it should be remembered that a formula which suits the needs +of one field or one estate will not necessarily prove suitable in the case +of another field or estate. Unless this point is appreciated trouble may +ensue. On some estates it has been the custom to give equal quantities of +sodium sulphite solution to all coolies irrespective of the ages of the +trees in the fields to be tapped. Thus it happened that the latex from one +field was found to have insufficient anti-coagulant present, while that +from another field could only be coagulated by the addition of an excess of +acid. In this matter the experience of the preliminary trials should have +caused some discrimination to be exercised as to the quantities of solution +to be issued in each field or division. It has been found sometimes that a +moist glossiness in the smoked sheet could be attributed to the use of an +excess of sodium sulphite. Traces of the salt remained in the rubber, and +as the substance is hygroscopic, moisture was being absorbed from the air, +to cause a surface deposit which often returned even after the sheets were +surface-washed and re-dried. + +If sodium sulphite is to be used in the field, the following formula, which +is in wide use, may serve as a basis for trials. + + +_Formula for Use of Sodium Sulphite in the Field._ + + (_a_) Dissolve anhydrous sodium sulphite in water at the rate of 1 + pound to 3 gallons. + + (_b_) Of this solution each coolie is given about 3/4 pint. This is + usually sufficient for a task of 350 trees. The solution is used by + shaking a few drops into the cup or, diluted with an equal volume of + water, it is run down the main channel when the latex flows. + +[Illustration: 1. SHOWING EFFECT OF "WINTERING."] + +On some estates it is found either unnecessary or impracticable to use the +solution in this manner. Instead the anti-coagulant is placed in the bottom +of the bucket prior to the commencement of collection. The solution is made +as in (_a_) above, and roughly half an ordinary latex-cupful is placed in +each bucket. + +[Illustration: 2. NEW GROWTH OF YOUNG LEAF ON SAME TREE.] + +COLLECTING PAILS.--All vessels intended for the transport of latex should +have a smooth and curved interior, so that cleansing may be easy. +Preferably the interior and exterior surfaces should be glazed, but it is +often found that the enamel chips easily, and that the handles are too +frail in construction. The shoulder-pieces, to which the handles are +joined, are often too lightly attached to the bucket. Something stouter in +the shape of enamelled ware is required, without an appreciable increase in +weight. Until such a utensil is available, the heavily galvanised and +brass-bound milk-pails used on some estates are as good as anything at +present in vogue, providing they are kept scrupulously clean. + +[Illustration: EFFECTS OF DISEASE--"MOULDY ROT." + +(_a_) Note on right hand the panel next in order for tapping; a hopeless +position.] + +[Illustration: EFFECTS OF DISEASE--"MOULDY ROT." + +(_b_) The present cut badly infected; above there is no renewal of bark.] + +The collecting pails should be kept under cover, when not in use, either at +the muster grounds or at the factory. On some estates coolies are allowed +to take them to their quarters, where they are used for various purposes. +Curious effects of this practice have sometimes been noticed. As an +example might be quoted an instance in which premature coagulation was +found to take place to a surprising degree. It was discovered eventually +that the coolies (Javanese in this case) were in the habit of utilising the +buckets for the preparation of their food. A liquid extract of a popular +fruit was often made. This extract was very markedly acid in character, +and as the buckets were not afterwards thoroughly cleansed, the latex of +the following day suffered. + +[Illustration: EFFECTS OF DISEASE--"MOULDY ROT." + +(_c_) As in (_b_); another tree.] + +Preferably all buckets should have a lid of slightly funnel shape. This is +inverted during collection, and thus prevents much dirt falling into the +latex. + +[Illustration: EFFECTS OF DISEASE--"MOULDY ROT." + +(_d_) At close quarters. Note wounds due, apparently, to bad tapping, but +really caused by the disease.] + +PAYMENT BY RESULT.--The arguments for and against the institution of this +practice are many. In actual result there can be no question that a higher +yield is obtained by the adoption of a scheme under which the coolie is +either given a bonus based on result or is paid at a definite rate per +pound. It is fully recognised, both by advocates and opponents of payment +by result, that the personal equation of the tapper is a very important +factor. A good skilled tapper will always obtain a higher yield than an +ordinary individual from the same task of trees, and without any more +injury to the trees. It is argued, therefore, that such an operative should +be given the benefit of his skill. Apart from this, it is claimed that even +the average tapper does not do his best work if he knows that he will get +his daily wage, no matter what his yield may be, as long as he does not +injure the trees by wounding. It is claimed that this sense of security +leads to shallow tapping which, while it has an agreeable appearance, does +not produce the available amount of rubber. + +On the other hand, it is advanced in opposition that under a scheme of +payment by result the tappers' only consideration is the matter of +obtaining rubber, and that considerable damage in the form of wounds is +done by over-deep tapping. That there is a great deal of truth in these +statements is not to be doubted. Much, of course, depends upon the amount +and quality of the supervision possible, and upon the standard demanded. It +is a notable fact, however, that on estates which first introduced the +system some years ago the quality of the tapping compares favourably with +that of average estates, and in a few instances within the experience of +the writer the tapping is of a high standard. Possibly these are +exceptional instances, and there can be no doubt that the opposition of +many managers of considerable experience is founded upon the deterioration +in the standard of tapping which often follows the institution of payment +of tappers by result. + +It will be recognised by planters that apart from the personal factor in +tapping, the worker might be so unfortunate as to be placed in an area from +which the yield is naturally low, either by reason of its youth or from +other natural causes. Obviously such individuals are entitled to special +consideration in respect of the rate per pound paid for the rubber +obtained. Again, on very hilly land it may be not humanly possible for a +worker to tap the usual number of trees. Hence to place him on a parity +with other tappers, as far as wage-earning capacity is concerned, a higher +rate than ordinary must be given. It will be plain, therefore, that on any +one estate it is generally impossible to set a standard rate per pound for +payment by result; the rate may vary, for example, from, say, 3 cents per +pound in old and high-yielding tasks to 12 cents or more per pound on young +areas of the same estate. + +Naturally the actual rates paid will primarily depend upon the average +yield per tree or yield per acre, and the lower the average yield the +higher the rates to be paid per pound. Thus, on low-yielding properties +where the natural conditions render a high yield impossible the rate per +pound may reach a figure of 22 cents (approximately 6d.). + +The methods of arriving at the yield of rubber brought in by individual +tappers vary, but broadly they fall into two classes: + + (_a_) That in which the volume of latex is ascertained (either by + measuring or by weighing), a sample is drawn, and the final + calculation made from the weight of the more or less dry sample. + + (_b_) That in which, after noting the volume, the calculation is based + upon a reading of the dry rubber content of the latex, obtained by + means of an instrument such as the "Metrolac," or any other instrument + working on the same principle. + +Quite a number of estates which have not adopted the full system of payment +by result yet employed some such method of checking the yields of +individual coolies, as the observed results act as a great deterrent +against various malpractices, such as neglecting to tap trees, adulteration +of the latex, etc. + +TREE-SCRAP.--The thin film of latex which coagulates naturally upon the +surface of the tapping cut after the latex has ceased to flow is known as +"tree-scrap." Normally it is collected on all estates, but the method of +collection varies according to the class of labour employed. On most +estates, where the labour is Tamil or Javanese, it is supposed to be +removed as fully as possible before the tapping cut is reopened. The narrow +strips are then placed in a bag or basket carried by the tapper. Chinese +tappers usually decline to follow this practice of first peeling off the +scrap, and remove it by the operation of tapping, with the result that the +scrap when brought into the store has adhering to it various shavings of +bark. Unless these can be thoroughly cleaned off the scrap cannot truly be +classed as "tree-scrap." + +OXIDATION OF TREE-SCRAP.--It is often noted that some scrap is dark in +colour, and in this condition it is generally spoken of as "oxidised" +scrap. The oxidation is probably due to an enzyme, and also to the presence +of chemical substances of a phenolic nature. In the course of laboratory +experiments with normal latex, it was found possible to reproduce this +darkening due to oxidation by the addition of very small quantities of +various phenols used in general chemical processes, and the rapidity with +which the darkening was effected depended upon the quantity of the phenol +added. If this rapidly oxidising latex be mixed with normal latex, it would +seem that the whole bulk of the latex is affected by this tendency to rapid +oxidation. It is observed that this condition under which any tree may +yield rapidly oxidising latex is not a permanent one. + +CARE OF TREE-SCRAP.--As these scraps eventually give a grade of rubber +which compares well with other and better-looking grades care should be +exercised in collection and treatment so that its quality is not impaired +in any way. + +TO PREVENT OXIDATION.--As a rule the scraps are picked over, and heavily +oxidised pieces are sorted out; otherwise the crepe rubber prepared +exhibits black streaks. The scraps should not be allowed to remain in the +sun (which induces "tackiness"), and if they have to be kept over night +they may be placed in a weak solution (1 per cent.) of sodium bisulphite to +arrest oxidation. It should be recognised that such a solution will not +"bleach" already darkened scrap-rubber, and the nature of its action is +only anti-oxidant. + +BARK SHAVINGS.--In the matter of collecting bark-shavings much depends upon +the organisation and nature of the labour force. Probably, on the majority +of estates bark-shavings are collected systematically, but on quite a +number considerable laxity in this respect has been noted. This may arise +from lack of adequate supervision or from the peculiar systems of working +which seem to pertain to Chinese labour. Granted that the trees are well +"scrapped," and that the percentage of rubber obtained from shavings under +such circumstances would be extremely small (say 2 per cent. by weight on +the total output), it does not need much calculation to see that annually +the loss of rubber to the estate must be considerable. It would also seem +to follow that, if the adult labour declines to pick up bark-shavings +carefully, it might pay to employ children for the purpose. Or, as is done +in some places, the adult labour might find it advantageous to collect +bark-shavings at low rates per pound. + +It is a well-known fact that if bark-shavings be allowed to accumulate in a +heap for any but a short period, a fermentative and heating action is set +up. The heat developed in these piles of shavings is so considerable that +it is impossible to keep the hand in a heap for more than a second or two. +Should this be allowed to persist, as would happen in the case of a +breakdown of engine or machines, it usually results in the final crepe +rubber becoming tacky when approaching dryness. + +To avoid this heating effect it is necessary to have spare jars or proper +tanks in which the shavings may be soaked in water. In this condition +bark-shavings may be kept for many days. + +For the same reason (_i.e._, the heating effect and consequent tackiness) +the custom followed on some estates of allowing coolies to keep +bark-shavings in their "lines" until they have accumulated a fair quantity +cannot be commended, quite apart from the possibility of actual loss by +theft, which is thus rendered easy. + +It will be clear that where the trees are scrapped efficiently before +tapping, the amount of rubber to be obtained from the treatment of pure dry +shavings would be almost nil, and would scarcely repay the cost of +collection and working. In actual practice, however, it is not possible to +guarantee that the shavings are free from some scrap-rubber. Shavings +brought in by Tamils and Javanese carry only a small amount of rubber, +whereas where Chinese tappers are employed the yield of rubber may be as +high as 35 to 40 per cent. upon the total weight of the material treated. + +Few estates now are not equipped with "scrap-washers"--machines specially +designed for removing the bark from the rubber--and if they function +efficiently the resulting crepe should be free from bark-particles. + +COLLECTION OF EARTH-SCRAP.--This, the lowest grade of rubber, is found at +the base of the tree. Theoretically, if proper precautions are observed, +the amount should be comparatively small, but in actual practice it may be +very appreciable. The usual contributory causes are: + + (_a_) Failure to replace cups beneath the spouts of trees which + continue to drip latex after collection. + + (_b_) Collection of latex at too early a stage. + + (_c_) Failure on the part of the tapper to ensure the flow of latex, + by means of the spout, into the cup. + + (_d_) Flowing of latex over the edge of the cut before it reaches the + vertical channel. + + (_e_) "Wash-cuts" on wet days, when the volume of rainwater down the + tree is sufficient to wash the latex out of the cup. + +The amount of earth-scrap collected on any estate will depend, all other +things being equal, upon the labour expended in its collection. Certainly +on well-organised estates, having ample labour, the amounts collected are +huge in comparison with other estates. The ground at the base of the tree +below the latex-spout is systematically turned over with pointed sticks and +large clots of rubber are often picked up. Here, again, it is advised that +the collected earth-scrap should not be allowed to remain in heaps upon the +floor of the factory. It should be placed in suitable tanks containing +water, and quite a considerable portion of the cleansing work is thus taken +from the machines. + + + + +CHAPTER VI + +_TRANSPORT OF LATEX AND COAGULUM_ + + +PERCENTAGE OF FIRST LATEX AND OTHER GRADES.--One of the problems +confronting any manager is the question of the percentage of first-grade +rubber calculated upon the whole output. Inquiries are constantly being +received for advice as to what the various percentages of each grade of +rubber should be. This is a question to which no definite list of figures +can apply. There are so many little factors influencing the result. Some +estates are not particularly careful in collecting tree-scrap. Hence quite +a quantity of tree-scrap finds its way into the crepe made from +bark-shavings. On the other hand, bark-shavings are not collected +systematically on some estates, and the total output is thereby diminished. +In consequence the first-grade rubber shows a higher percentage than it +would otherwise. Again, if the earth-rubber is not regularly collected the +percentages of the best grades are higher than they should be. In comparing +the percentages of each grade of rubber from any two estates, therefore, +one should have all the information possible as to the various working +details of the estates. Without wishing to lay down any definite +proportions which can be applied to all estates it might be said that, +taking averages over a large number of estates, the percentages to be aimed +at are: + + First-grade latex 75 per cent. to 80 per cent. + Other grades 20 " " 25 " + +For these figures one promises that all lower grades are collected and +accounted for carefully and regularly. The distribution of the lower grades +will depend upon the field practices of the particular estate, but the +following list might be given for an estate keeping all lower grades +distinctly separate: + + First-grade latex 75 per cent. + Cup-washings } + Coagulated lump, etc. } 10 " + Tree-scrap 9 " + Bark-shavings 4 " + Earth rubber 2 " + --- + 100 " + +Emphasis is again laid on the statement that these figures must not be +accepted as a standard. Nevertheless, they may prove of some service to +managers in giving an idea of what the general line of percentages may be. +There are special circumstances, such as distance of transport and the +nature of the land, which at present would render the attainment of more +than 75 per cent. first-grade rubber impossible on some estates. Still the +fact remains that if the percentage is low through distance of transport, +etc., some method will have to be discovered by means of which the +difficulty maybe overcome. On a few estates the percentage of first-grade +rubber obtained sometimes reaches 85, but these results are rather out of +the ordinary. An estate which collects all lower grades properly is doing +well if the percentage of first-grade rubber is 75 or over. + +EARLY COLLECTION.--As already noted in the preceding chapter, one of the +factors influencing premature coagulation is that of the interval elapsing +between the commencement of tapping and the collection of latex. It will be +seen that this ordinarily would depend, in turn, upon such considerations +as the size of the tappers' tasks, the spacing of the trees, and the +natural conformation of the land over which the tappers have to perform +their tasks. In general it need only be remarked that every possible +consideration should be given to this question, and that any delay should +be avoided. + +TRANSPORT.--Wherever possible it is endeavoured to convey latex from field +to factory by man-power. Tamil coolies, as a rule, place the bucket on the +head; Chinese and Javanese coolies like to use a balanced carrying-pole. +Where distance renders these methods too costly in time and labour, it is +usual to have field centres where the latex is collected and dispatched to +the factory generally (_a_) by means of vessels conveyed on light railways; +(_b_) in large cans placed on motor-lorries; (_c_) in cylindrical +galvanised drums supported on two wheels and drawn by bullocks. There may +be variants, but these are the chief means of transport in bulk over a +distance. + +Where possible, the best system is that employing a trolley-line, as great +agitation of the latex is avoided, and the time in transit is much reduced. + +The usual method of transport by bullock power is slow, and as estate roads +(and even Government roads) are often below the standard expected in this +country, the jolting undergone by the latex is, to say the least, not +calculated to afford a high yield of first-grade rubber. The late Mr. F. W. +F. Day advocated the use of a circular perforated wooden grid, to be +floated on the latex, in order to moderate the wave effect produced by +jolting. + +Whatever the means of bulk-transport employed, it should be the care of +those in charge to see that vessels are not allowed to remain in the sun +longer than is necessary. Even during the journey they should be shaded in +the best possible manner. + +These large transport vessels usually receive what is really only +perfunctory attention in the matter of cleaning. They should receive the +same care as would be exercised in dealing with milk cans in other +countries. Ordinary sluicing with water is not sufficient, and if they +cannot be sterilised by means of boiling water, they should be treated, +after ordinary washing, with a 5 per cent. solution of sodium bisulphite +every day. + +ANTI-COAGULANT FOR TRANSPORT.--When anti-coagulants are not used in the +cups or buckets, it is advisable to use them in the bulk-transport vessels. +Either formalin or sodium sulphite is of service, but the great objection +advanced against the former is its loss due to evaporation while the carts +are going to the fields or waiting at the centres. For this reason sodium +sulphite is now generally employed. + + +_Formula for Use of Sodium Sulphite in Transport._ + + (_a_) Dissolve 1 pound of powder in 3 gallons of water. + + (_b_) Of this solution, place half a gallon in the vessel for every 30 + to 40 gallons of latex. + +TRANSPORT BY COOLIE.--As already pointed out, the extent to which man-power +can be used in transport of latex is generally limited. On small estates it +is an easy matter for coolies to carry the latex to the factory, but on +larger estates many difficulties may arise, which may also militate against +the successful use of other means of transport. It is not uncommon to find, +therefore, that a policy of decentralisation has been adopted. + +COAGULATION CENTRES.--Divisions of the estate have their own small stations +at which latex is received and coagulated. In this way it is possible to +receive latex without much delay, and with benefit to the resultant rubber, +especially if prepared in sheet form. Much controversy has arisen regarding +these decentralised establishments, but the fact remains that on large +estates, which are efficiently controlled, the scheme has been highly +successful from all points of view. On the other hand, it is alleged that +this method of working increases costs, and often gives an unsatisfactory +quality of rubber. Concerning the latter point it seems to be reasonable to +expect that the European in charge of any division should be conversant +with the method of preparation required, and should be capable of seeing +that no mistakes are made. Given uniform equipment in all stations, and +uniform rules for treatment of the latex, there does not appear to be any +valid reason why the product of one station should be inferior to that of +the others. Neither is it so in the case of several estates which might be +quoted. + +In the matter of costs of working the writer has had to investigate several +cases regarding which there was dissatisfaction. In some instances it was +found that the stations had not been placed advantageously with respect to +a water-supply; and instead of one or two coolies pumping for an hour or +two, a larger number had to be employed for hours in the carriage of water +from the nearest available source. This meant that, as the coolies were on +daily wage, the force appeared to be much bigger than that usually +required. In other cases there were too many store coolies, when often the +place of some could have been taken for the necessary period by tappers +arriving early from the nearer fields. Sometimes costs were increased by +reason of the use of an excess of chemicals, owing to the lack of uniform +rules throughout the several stations. In spite of all that has been +written, and the verbal instructions that have been given, it was not +uncommon to find unstable chemicals such as sodium bisulphite exposed to +the moist air. In this way not only was there waste of material, but also +the probability of inferior rubber being made. + +TRANSPORT OF COAGULUM.--On the whole if it is a question between the +transport of latex and the transport of coagulum, the writer would always +favour the latter, for reasons which have possibly been made clear in the +preceding paragraphs. In effect, it should be recognised that the less +handling and transport the latex receives the better the general result. + +If proper precautions are taken, the transport of coagulum intended for the +preparation of crepe should present no difficulty, and should have no +injurious effect upon the quality of the resultant rubber. It is only too +common, nevertheless, to note defects, in the finished crepes, which can +only be attributed to a failure to observe reasonable care in the transport +of the coagulum. For example, it has been observed that a mass of coagulum +from a coagulation station has been conveyed on the floor of a +bullock-cart, or motor-lorry, previously used in the carriage of other +materials. Unless the boards have been most scrupulously cleansed, the +coagulum is found to be contaminated, often to a marked degree. Again, +although the cart may be clean, it may have to travel some distance on +roads carrying a fair amount of motor traffic. Even should the cart have a +canopy, road-dust is often whirled through the open sides of the cart; and +in the districts where red laterite roads are common, the stain of such +dust often persists in the finished crepe. It scarcely need be remarked +that coagulum should be transported in closed wooden boxes or in galvanised +iron drums fitted with lids; and that preferably sufficient water should +be present in these receptacles to allow the coagulum to float. All such +containers should receive the same scrupulous attention as the vessels +employed in the transport of latex. + +The successful transport of coagulum for sheet-making is fraught with much +greater disabilities, and it is usual to note on most estates that the +resulting sheets from out-stations are always inferior, in final result, to +those coagulated and prepared at the central factory. If the flat pieces of +coagulum are placed in piles of any height it is common to find, on arrival +at the factory, that much adhesion has been caused. There is great +difficulty in separating the pieces, and often the successful operation is +impossible. It is usual to hand-roll the coagulum before transport, but it +is often found that by the time the rubber reaches the factory it has +become too hard for subsequent good results. + +One of the strong arguments in favour of the establishment of divisional +stations is to be found in the preceding paragraph. Sheet-making, as it +necessitates the employment of only light machines suitable for hand-power, +is a feasible proposition in a field station. There is no reason for sheets +made thus to be in any way inferior to those made at a central factory; in +fact, they are often better, as the latex has the chance of being treated +when comparatively fresh. + +If it is found necessary to transport sheet-coagulum, every possible +precaution should be taken against piling the pieces. + +After hand-rolling some estates bring the rubber from the field-stations to +the central factory in drums of water, others in shallow boxes containing +not more than half a dozen sheets in a pile. A method proposed long ago, +but not in practice, was to have a number of shallow trays subdivided so +that each compartment held one sheet only. If these trays were properly +made and carefully fitted there appeared to be no reason why they should +not form sliding parts of a large box, in which squeezing and adhesion of +the pieces of coagulum would be avoided. Naturally any such device would +increase appreciably the weight to be transported, and on this ground would +not find popular favour except where motor-power is used for road +transport. + + + + +PART II + +FACTORY OPERATIONS + + + + +CHAPTER VII + +_PRELIMINARY TREATMENT OF LATEX_ + + +RECEPTION OF LATEX AT THE STORE.--Bearing in mind the remarks in Chapter +VI. on the conditions under which latex is transported, it follows that +nothing but the very best and most suitable vessels should be used in the +store. A point to which adequate attention is not given in many factories +might be mentioned here. Considering the importance attached to colour in +the dry rubber by brokers and consumers, and knowing how extremely trivial +are the causes which may mar the colour, it is rather surprising that +better provision is not made for the reception and handling of latex in +factories. Too often the receiving vessels are placed on the floor of the +store close to the entrance. Coolies bringing in latex cannot avoid +bringing with them quite a considerable amount of dirt. Presuming that a +hose-pipe has been installed, and that the floor is constantly being +sluiced down with water, no great harm will result. But would it not be +ever so much better if the dirt were kept out? In how many factories is +provision made for this? Such an arrangement is not difficult to make, and +is already in practice on a few estates. A verandah is built outside the +wall of the factory and all latex is received there. In another place open +chutes are provided which terminate in the straining sieves. The coolie +thus stands on the verandah where he removes coagulated lump and impurities +from the latex, which is then poured down the chute, passing through the +sieve into large coagulating jars or tanks. + +Too often it would appear, from the writers' observation, there is a lack +of adequate supervision on the arrival of latex at the store. Much can be +learned from an inspection of the coolies' buckets, and the cause of small +defects in the finished rubber can often be thus traced. Leaves, stems, +bark-shavings, and dirt appear in the buckets, and it is a source of +constant surprise to imagine how even unintelligent coolies can allow such +things to happen. These objects are removed before or during straining, but +still they ought not to be there in the first place, and the fact that such +a state of things exists is evidence of neglect on the part of the coolies +or lack of supervision. Efforts are made in a large number of cases to cope +with these troubles, but on some estates things are allowed to proceed in +the same slipshod way, and too much responsibility is thrown on the +straining process. + +[Illustration: RAISED VERANDAH FOR RECEPTION OF LATEX; LIKEWISE EQUIPPED +WITH FACILITIES FOR CALCULATING INDIVIDUAL DAILY "YIELD PER COOLIE" BY +SAMPLING OF LATEX.] + +It is suggested that it should be the business of a European to supervise +the reception of latex every day. This is at present quite impossible on +some estates, but it does not alter the fact that this supervision should +be provided, and is extremely necessary. + +It is surprising how the point is overlooked in many factories--not that +they are in a dirty state, but they fall short of being classed as clean +factories for want of the little that makes the difference. Possibly those +in charge do not believe that all this fuss need be made, but the writers +can assure them, from a practical knowledge of a very large number of +factories, that cleanliness does pay. + +It might not be credited to Tamil coolies, but yet it is probably true, +that the moral effect of working under the cleanest and best conditions has +an influence upon the store coolies, and that their work is better in +consequence. Everything which will tend to simplify the cleansing of the +factory should therefore be installed. Hose-pipes, glazed tiles, clean +floors, plenty of light and air are not fads or fancies, but considerable +factors in determining the final quality of the rubber. There is +considerable truth in the suggestion that the coagulating room and machine +room should be as "spick and span" as a modern home dairy. + +STRAINING OF LATEX.--This is a most necessary process, and one which +usually entails much trouble and time which one could wish avoided. It will +be admitted that the trouble could be reduced greatly if the regulation of +field processes could be made more stringent. In spite of knowledge that +impurities must not be allowed to enter the cups, coolies will ignore the +rule that the cup must not be placed in position until the bark shaving has +been cut. The result is that pieces of bark fall into the cups, and coolies +are generally too careless or too hurried to remove them. + +Again, when cups are placed on the ground, it is easy to see that dirt may +adhere to them. In the collection of latex some of this dirt may fall into +the bucket. Since the introduction of cup-holders on many estates the +trouble from this source has decreased considerably, but, nevertheless, it +may be taken for granted that even under the best of conditions all latex +requires straining. + +The best type of strainer has yet to be evolved. Usually it consists in +principle of a piece of fine brass mesh contained in some form of holder. +Theoretically such a strainer should work well, but in actual practice +nearly all strainers are a source of continual worry. Undiluted latex, as +received at the factory, is of a rich consistency, containing very fine +particles of dirt and often minute particles of prematurely coagulated +rubber. The latter soon clog a fine mesh strainer, while the former may +pass through. When the flow through the strainer becomes slow, the coolie +in charge generally rubs the top surface of the sieve with a piece of +coagulum, thus forcing material through the mesh. He then rubs the +under-surface, with the result that undesirable matter falls into the +strained latex. In theory it seems a simple matter to have a number of +sieves ready so that a clean one may be substituted for a clogged one, +which should be cleansed at once with water. In practice the factory coolie +will probably only carry out instructions when the eye of the +superintendent is alert. As a result of the rubbing and consequent strain, +the brass mesh usually breaks away from its support and the fracture may +not be detected for some time, during which irreparable damage may have +been done to the resultant rubber. + +In view of the presence of the fine particles of dirt, to which allusion +has been made, fine sieving of the latex appears to be essential, +especially when sheet-rubber is to be prepared. The fine sieves are +generally of the type known as "60 mesh," and they do not usually give +thoroughly satisfactory results even when the gauze is supported and +strengthened by means of cross-wires placed underneath. The general fault +with these strainers is that a sufficiently wide "selvage" is not allowed +in the clamped edges of the gauze, or that the edges of the support are so +sharp and abrupt that the strands of the gauze are soon severed by the +strain imposed in vigorous cleaning. + +Many estates use two strainers; the first a more robust one containing "30 +mesh" gauze, and the second the fine "60 mesh." Even this device does not +bring about the desired immunity from trouble. Relief could be obtained if +the latex were always in a more freely fluid form. Estates employing +anti-coagulants in the field benefit in this respect. Other estates, +although finally using the finest of mesh, experience far less trouble than +most estates by reason of a difference in method of working. This can be +explained by an outline of the system adopted on a particular estate: + + (_a_) On arrival of the rich latex at the store, all visible + coagulated lumps and other extraneous matter are removed by the + tapper. + + (_b_) Each tapper's latex is diluted with a quantity of water. + + (_c_) The diluted latex passes through two sieves, one above the + other. The top sieve is of stout perforated zinc sheet, with 10 + circular holes to the inch. This removes all large particles. The + lower is of "30 mesh" brass gauze, and practically no rubbing is + required. The latex is now in glazed-tile tanks, in which it is + further diluted to the required standard by means of a recording + instrument. + + (_d_) The latex flows by means of a chute into the coagulating tanks, + passing through a large "60 mesh" sieve. + +It is not guaranteed that this method will furnish a complete absence of +very fine particles of dirt in sheet rubber, as the human element enters so +largely into the question; but it can be stated that no complaints have +been received on the point of "specks of dirt" since this system was +inaugurated. + +On the same estate fine sieving in the preparation of pale crepe has been +abandoned as an unnecessary refinement. The two coarse sieves mentioned +above are employed only, and it is to be acknowledged that the results +justify the procedure. + +BULKING OF LATEX.--Not long ago advanced estates used to combine all latex +before coagulation, in order to obtain uniformity of product. Previously it +had been the custom to deal only with comparatively small separate volumes +of latex, with obviously great disadvantage. + +Since the introduction of instruments such as the "Metrolac," by means of +which any volume and all volumes of latex may be reduced to a common +standard of dry rubber content, the necessity for "bulking" has passed. It +is not now necessary to keep latex standing, perhaps for two hours, +awaiting the arrival of other latex from distant fields. + +STANDARDISATION OF LATEX.--In modern practice, as already pointed out, it +is possible now to handle any volume of latex with a view to its reduction +to any required standard of dilution for the purpose of obtaining a +uniform product. For the reception and subsequent handling of the latex +various schemes have been devised, and they are usually planned in +connection with coagulating tanks used in the preparation chiefly of sheet +rubber. + +[Illustration: END-SECTION SKETCH OF VERANDAH, ETC., SHOWING A GOOD METHOD +FOR RECEIVING LATEX AND FILLING TANK. + +T, Sheet coagulation tank; C, cylinder for reception and dilution of latex; +GG, gutter; PP, raised platform on verandah; SS, steps leading to platform; +W, dwarf wall; EE, expanded metal partition; OO, open.] + +In the successful working of a tank it is necessary, in order to obtain the +best results, to standardise all latex. This cannot be effected properly in +the tank itself, and hence it is the practice to dilute each lot of latex +to standard before it is run into the tank. In the ordinary way this would +entail a great deal of labour in handling the diluted latex. To obviate +this, the scheme outlined in the accompanying sketch has been suggested on +several occasions and in various quarters. Such a scheme or modification of +it has been put into successful practice on several estates. Although the +drawing was made some considerable time ago when estates were not then +prepared to go so far in this direction, subsequent modifications show only +minor differences which, while leaving the original principle intact, +testify to a fertility of resource in adapting the idea to existing +circumstances and buildings. The drawing is _in toto_ almost a replica of +the original installation now in successful use on the Kinrara Estate of +the Ledbury Rubber Company. On this company's Ledbury Estate likewise a +similar system is employed, except that the reception verandah is part of a +natural formation and needed no such direct raising. Several other estates +have now adopted the scheme, which has been proved to be of practical +value. The writers make no claim to originality in the idea, which might +have occurred to many independently on the introduction of coagulating +tanks. + +[Illustration: RAISED VERANDAH FOR RECEPTION AND HANDLING OF LATEX.] + +VERANDAH.--In reproducing the drawing it is believed that the sketch will +convey practically all the information required. It may be explained that +the coolies are allowed to enter only the outer part of the verandah. The +buckets are handed across the low wall into the care of factory coolies, +who strain the latex through gauze sieves into the latex cylinders. + +LATEX RECEPTION VESSELS.--These cylinders may be similar to the tanks +commonly used for transport of latex from distant fields to the factory. An +80-gallon cylinder is easily mounted by its trunnions on a suitable iron +framework which is superimposed on a skeleton truck. + +[Illustration: ANOTHER SET OF DILUTION TANKS ON RAISED VERANDAH.] + +The latex is diluted down to standard in the cylinders, the truck is moved +opposite the compartment to be filled, and a light movable gutter is placed +beneath the vent of the outlet pipe. This pipe is fixed in the bottom of +the cylinder, and is provided with a large stop-cock which is operated by a +spanner key. The stop-cock should be of the simplest type, capable of being +taken apart and assembled in a minute or so. The orifices should be large +enough for a coolie to insert at least two or three fingers so as to +facilitate cleaning, and the pipe should have no right-angle bends. + +On the inside of the cylinder a scale of gallons may be painted, so that +one may possess a knowledge of the quantities run into, or required for the +completion of, any compartment. + +A SCREW PLUG UNSATISFACTORY.--It may be of benefit to managers who +contemplate such an installation to know that the adoption of a stop-cock +in the vent pipe of the cylinder is the outcome of experience. In one +instance the vent pipe as designed was fitted with a screw plug at the end. +Unfortunately with this arrangement the flow could not be regulated, and +owing to the "head" of the latex it dashed violently down the gutter, +struck the bottom of the coagulating tank, and thence was scattered over +the factory. + +ANOTHER INSTALLATION.--In another type of installation, in place of the +vessels travelling upon a raised verandah platform, the standardised latex +is conveyed to the coagulating tanks by means of drums supported by hooks +to a chain-block and pulley which travels on an overhead gantry. This +method is practicable, but may be regarded as less satisfactory in general +working than the verandah method of treatment. + +A MODERN INSTALLATION.--In the most recent scheme for dealing with the +reception of latex, its standardisation, and conveyance to the coagulating +tank, the main principle of the first system outlined is retained; but the +receptacles are not mobile. Glazed-tile tanks are employed, the capacity of +each being approximately equivalent to that of each unit coagulating tank. + +The accompanying illustrations show the general arrangement and some +details of the system of reception tanks employed on the well-known +Pataling Estate. + + + + +CHAPTER VIII + +_COAGULATION_ + + +Whether it is necessary to employ any coagulant, or whether latex should be +allowed to coagulate naturally, will not be discussed at this stage. +Neither will mention be made of any patent processes of coagulation which +employ other than acid mediums. These subjects will be treated in a +subsequent section of the book. + +CHOICE OF COAGULANTS.--It is not proposed here to enter into a discussion +as to the merits of the dozens of known coagulants. Suffice it to state +that acetic acid, although the oldest general coagulant, still remains the +best and safest at the present time. There is a deal to be said in favour +of the use of another organic acid, formic acid. It is equally as safe as +acetic acid, and quite efficacious; the only drawback is that, taking all +things into consideration, it is very slightly more expensive. Acetic acid, +therefore, will always be implied in this chapter when the word "acid" is +used. + +STRENGTH OF ACID SOLUTION.--In the old days it was the rule rather than the +exception to find pure, undiluted acid used in coagulation. In many cases +no harm resulted, for the simple reason that, owing to the large proportion +of water in the latex, the acid was thereby very much diluted. The estates +had to thank the over-dilution of the latex for the non-injury of the +resulting rubber. + +Some estates make up a stock solution of 1 part acid to 20 of water, and +use this with success because of the fair amount of added water present in +the latex. + +It must be understood that what is being referred to now is not the +absolute quantity necessary for coagulation, but the proportions--_i.e._, +the respective volumes of acid and water in the solution of acid made up +every day. That the strength of the acid solution, as well as the quantity +used, has an effect upon coagulation can be easily demonstrated in the +following way: + +Take separate and equal lots of the same latex, and to each add the same +quantity of pure acid, but in each case diluted with varying quantities of +water. It will be found that coagulation is quickest where pure acid is +employed, and slowest where the acid is most dilute. It will also be found +that, providing the quantity of acid employed was sufficient for +coagulation, the best and most uniform coagulation is obtained from the use +of the most dilute acid, within limits. It will often be found that where +pure acid has been employed coagulation is local--_i.e._, we have lumpy +coagulation, and often a very milky remaining liquor. This is due to the +fact that, as coagulation is immediate upon the spot which is first touched +by the pure acid, a deal of the acid is enclosed within the rubber at that +spot, and hence other portions of the latex are deprived of acid. It is in +such cases that most air-bubbles are enclosed. + +As the dilution of the acid solution is increased the mixing is more +thorough and uniform. Coagulation is slower, and air-bubbles can escape to +the surface. + +METHOD OF MAKING STOCK SOLUTION.--Experiments have been repeatedly made in +the laboratory with acid solutions of varying dilution, from pure acid down +to 1 part of acid in 500 parts of water. While it has been found that a 1 +in 5 solution can be used where the latex is very dilute (say, 1 part of +latex to 5 parts of water), and a 1 in 20 solution may be used in fairly +dilute latex (for crepe-making), it is undoubtedly a fact that for latex as +generally "standardised" on estates a much more dilute solution of acid +should be used--_e.g._, 1 in 100, or even 1 in 200, of water. It must be +borne in mind that the quantity of acid necessary for coagulation is not +changed, but merely the dilution. Let us take a concrete case to illustrate +the point: + + On an estate at present the stock solution is made up by diluting 1 + pint of acid with 20 pints of water, and 1 gallon of this is necessary + to coagulate 50 gallons of pure latex. + + It is desired to use a stock solution of 1 pint of acid to 100 pints + of water. Evidently, therefore, 5 gallons of this stock solution + contain only the same quantity of pure acid as 1 gallon of the old + solution contained, and it will be necessary to add 5 gallons for + every 50 gallons of pure latex. Thus: + + 1 to 20; 1 gallon necessary for 50 gallons pure latex. + 1 to 100; 5 gallons necessary for 50 gallons pure latex. + +It may be pointed out that the quantities worked out in the foregoing +examples are not absolutely and mathematically correct, but they are quite +close enough for all practical purposes. + +It may be advanced by someone that if a dilute solution of acid, such as 1 +in 100, is used the bulk of this stock solution (5 gallons to 50 gallons of +latex) is very great, and might be injurious to the quality of the +resulting rubber. A moment's consideration will show that, after all, the +volume of acid solution is only one-tenth that of the volume of latex. This +can have no effect upon the quality of the rubber. Even dilution of the +pure latex with half its bulk of water in the factory will have no effect +upon the quality of the resulting rubber. It is to be remembered that, +except in cases where the proportion of added water to latex is absurdly +large, the main argument against putting water into the latex-cups is +against the possible poor quality of the water rather than against the +actual small quantity theoretically added. It is acknowledged that, where +the water to be put into the cups can be guaranteed to be of good quality, +no great objection would be raised against placing the smallest possible +quantity of such water in the cups. But how many estates have such good +water easily available to the coolies, and how many estates can be sure +that only that smallest possible quantity would be used? It is a notorious +fact that, even on estates where the quantity of water used was supposed to +be a minimum, the proportion of water to latex in some cups often exceeded +even three or four to one. In any case it may be stated as an elementary +truism that the absence of water is more to be desired than water of +doubtful quality. + +QUANTITY OF ACID.--As a result of repeated experimental work it has been +found that, for pure average latex, the quantity of acid necessary for +complete coagulation, reckoned in parts of pure acid to parts of latex, is: + + 1 part pure acid; 1,000 parts average latex. + +Where the latex is rather richer than average (above 30 per cent. dry +rubber) probably a little more acid would be required, and similarly if the +dry rubber content is lower the quantity of acid must be less. + +It used to be a common belief that the more dilute the latex the greater +the quantity of acid necessary, but this would only apply to cases of +extreme dilution of latex. + +As a matter of fact, up to certain limits of added water, the reverse is +actually the case--_i.e._, the more water in the latex the less acid must +be added, assuming that for pure latex the proportion of pure acid to latex +is taken as 1 part to 1,000 parts. This was found to be the case up to +dilutions of three or four times the volume of latex. To take concrete +examples which will perhaps make the truth more clear: + + Assuming we commence by making up our stock solution of acid by adding + 100 parts of water to 1 part of pure acid, this gives us a mixture of + 1 to 100. For 1 gallon of pure latex it would be necessary to add + one-tenth of its volume of the above mixture--_i.e._, 16 ozs. + + Suppose we take a gallon of pure latex and add a gallon of water, we + now have 2 gallons of so-called latex. But we still have only 1 gallon + of real latex present in the diluted latex, and it is only necessary + to add sufficient acid to coagulate this gallon--_i.e._, 16 ozs. + + Further, if 1 gallon of latex be diluted with 2, 3, or even 4 gallons + of water it is still only necessary to add 16 ozs. of the acid + mixture. + + At dilutions beyond this limit, however, it is necessary to add a + little more acid to obtain complete coagulation. + +In the process of preparing sheet rubber it is very necessary to see that +the minimum quantity of acid is used, otherwise visible defects are caused. +But in coagulating latex intended for preparing crepe, where the rubber +undergoes protracted washing on the machines, the presence of a slight +excess of acid in coagulation is not calculated to cause any deterioration +in the quality of the rubber. Advantage must not be taken of this statement +to argue that more than a slight excess may be used without injury to the +rubber, as it can be shown that the use of a large excess of acid results +in an inferior rubber. + +QUANTITIES NECESSARY FOR MODERN REQUIREMENTS.--It may be commended to the +notice of the beginner that any further experimental work as to the +quantity of acetic acid necessary for complete coagulation would only +involve a waste of time and energy. + +The general figure given in a preceding paragraph (1 part pure acid to +1,000 parts of latex) may be accepted as the rough basis for working. In +modern practice, however, undiluted latex is usually diluted to a standard +which may vary on different estates from 1-1/4 lbs. to 1-1/2 lbs. dry +rubber per gallon. + +Latices of these strengths can be coagulated at a ratio of 1 part pure acid +to 1,200 parts of standardised latex; and this quantity need not be +exceeded, except in cases where an appreciable amount of some +anti-coagulant is present in the latex. The proportion may then be raised +to 1 in 1,000. + +If considered advisable the acid may be used in a 1/2 per cent. solution +for sheet preparation; but in any case it is advised for the sake of +uniformity that a 1 per cent. solution should be employed in the +preparation of both sheet rubber and crepe rubber. In most modern +factories, measuring vessels of various capacities are to be found, and it +is always more satisfactory to have the solution made up in approximately +correct strength at the rate of 1 oz. of pure acid to 5 pints of water. +Often, however, on some estates European supervision of this work is not +possible, and the preparation of the acid solution has to be left in the +hands of a (more or less) skilled coolie. It is thus necessary to find some +less fine, but still approximately correct, method of procedure. In the +East the kerosene tin is in universal favour for the carriage of water, and +there is no reason why it should not be utilised as a standard measure for +preparing the dilute acid solution, _providing it is not allowed to become +rusty_. The capacity of the tin is 4 gallons (640 fluid ozs.), so that a +one-hundredth part would be approximately 6-1/2 ozs. It is suggested that +this quantity should be measured out by means of a glass graduated vessel, +and then that an aluminium cup should be cut down so as to hold the exact +quantity. + +This would reduce the making of a solution, sufficiently approximate to 1 +per cent. strength for all practical purposes, into a simple operation of +mixing pure acid and water in the ratio of one cupful of acid to 1 kerosene +tin of water. + +The actual quantity of solution required for the coagulation of any volume +of standardised latex can be calculated easily from the ratio 1:1,200. As +the strength of solution is 1:100 it will be seen that the quantity to be +taken is _always one-twelfth_ that of the volume of latex--_e.g._: + + (_a_) If the latex tank holds 90 gallons of standardised latex, 7-1/2 + gallons of dilute acid solution are required. + + (_b_) A tank containing 120 gallons of latex would need 10 gallons of + the 1 per cent. acid solution. + +It is assumed that all estates, not only in the preparation of sheet +rubber, but also in the making of crepe rubber, always employ the system of +standardising latex in order to obtain uniformity. They are ill-advised if +they do not follow this practice; but in case average undiluted latex is +treated in coagulation, the quantity of acetic acid to be used should be +calculated from the ratio 1:1,000. + +If the acid solution is to be employed in 1 per cent. strength, _one-tenth_ +of the volume of latex to be treated will indicate the required quantity of +solution necessary for complete coagulation unless anti-coagulants have +been used, when the quantity must be increased as experience directs. It +will be recognised, of course, that undiluted latex may only be used in any +case for the preparation of crepe rubber; or in some exceptional case, such +as the special preparation of "slab" rubber. + +CARE IN MIXING.--It is essential that the mixture of dilute acid and latex +should be thoroughly intimate. This can only be attained by careful +manipulation, especially in the case of sheet preparation. Where crepe +rubber is to be made it may be permissible to employ a solution stronger +than 1 per cent., but it is not advised. The acid should be poured into +the latex while stirring, and the agitation should continue for such a +period as to ensure thorough mixing in all parts. + +It will be appreciated that in the preparation of sheet rubber this period +may not be unduly prolonged, otherwise the latex will have begun to +coagulate before skimming and the placing of the partitions in their +respective slots can be effected. Furthermore, while in the preliminary +treatment for crepe rubber, the formation of enclosed bubbles and surface +froth is immaterial. For sheet preparation it is essential that the +stirring shall be done so carefully as to try to avoid internal bubbles and +to reduce surface froth to a minimum. For crepe-making a perforated board, +with handle attached at right angles to the face of the board, may be used; +but in shallow sheet-coagulating tanks, broad paddles (which may or may not +be perforated) give good results as long as there is a sufficient number +used to cover the area of the tank in reasonable time. Obviously also, +where the area of any tank or compartment is of any appreciable size, the +dilute acid solution should be poured in from various points so as to +obtain a good even distribution. In some cases the acid is distributed from +a sprinkling can, but this is a refinement which experience shows to be +unnecessary. In actual practice, working on a tank measuring 12 ft. by 4 +ft., no difficulty is found if coolies pour in acid solution from four +points. The degree of success depends entirely upon experience and +efficient supervision. This remark applies equally to the use of various +devices, such as rakes with broad teeth, used as stirring implements. There +is room for display of ingenuity in this direction, and it is found often +that, while they are used successfully on one estate, they may be condemned +on another. + +[Illustration: TWO VIEWS OF DILUTION AND MIXING TANKS. + +Below, on the right, coagulating tanks. At the far end strainers. Each +dilution tank is of equal capacity to the corresponding coagulating tank.] + +USE OF SODIUM BISULPHITE.--Some few years ago a demand for pale crepe +rubbers sprang up, and this demand has been maintained. The total quantity +of pale rubber put on the market previously could only have amounted to +very little, and that little was obtained by luck and various tricks in +manipulation. It must be premised that if coagulation is allowed to take +place, either naturally or with the aid of acetic acid, the resulting +rubber will almost inevitably oxidise on the surface, except in the cases +of very dilute or young latices. Even supposing that this darkening of the +surface does not take place in the wet stage, it is often found that a +rubber expected to dry to a pale colour does not fulfil expectations, and a +dull neutral shade results. This darkening of crepe rubber may be +attributed to a slow process of oxidation, which continues until the rubber +is dry. From these remarks it will be seen that the process of oxidation is +a natural one, and that any pale rubber formerly shipped was the outcome of +circumstances outside the control of the estate, except in such cases where +boiling of the coagulum, etc., was resorted to. The fact that one rubber +happened to be a shade darker than another was absolutely no criterion as +to the value of the rubber, but apparently the market thought, and still +thinks, otherwise, although the actual necessities of manufacturers for a +pale crepe to be employed in special processes must be comparatively small. + +The prevention of this natural oxidation was a problem which exercised the +minds of all responsible for the preparation of pale rubbers, and much time +and thought were expended upon it. Various theories were propounded, and +the chief conclusion arrived at was that the darkening of rubber was to be +prevented by excluding all the light possible from the drying houses. To +this end windows were to be kept shut, or else they were provided with +ruby-coloured glass, which incidentally kept out the air. In spite of these +precautions, little success attended the expenditure of so much energy and +thought. It was absolutely necessary that some chemical agent should be +discovered which would make the preparation of pale crepe possible for any +estate. This chemical would have to fulfil several requirements before it +could become popular: + + 1. It must be a simple substance capable of being easily handled. + + 2. It must be very soluble, so that solutions could easily be made up + by inexpert workers. + + 3. It must be cheap. + + 4. It must be quite innocent of any harmful effect upon the quality of + the rubber. + +After months of investigation into the properties of other chemicals the +writers decided that the only one which satisfactorily answered all +requirements was sodium bisulphite. The writers make no pretension to any +claim of having discovered the properties of this substance, which was a +common chemical, and widely known. Even its action on latex was suspected +before they engaged upon the work. These matters are only mentioned because +the credit, if any, should be given to the laboratories of the Rubber +Growers' Association. + +As soon as it began to be known on the market that sodium bisulphite was +being used in the preparation of pale crepe, a great outcry was made, and +estates were warned that no more rubber prepared in this way would be +accepted. It was said that the chemical would destroy the "nerve" of the +rubber,[2] and it was definitely stated that rubber prepared with this +chemical was brittle. It must be remembered that brokers had some +legitimate excuse in raising objections to the introduction of new and +strange chemicals for preparing rubber, as they were quite without means of +judging whether the rubber had suffered harm or not. Still, on the other +hand, private tests had been made in conjunction with Messrs. Beadle and +Stevens for fully eight months before the name of the chemical was +mentioned in reports, and they had decided from the results of +vulcanisation tests that the chemical was quite innocuous. Then, and only +then, did we consider it advisable to recommend the use of sodium +bisulphite in general estate practice. Owing to the initial prejudice +against rubber prepared with sodium bisulphite, the results of our +preliminary work were published by permission of the Rubber Growers' +Association.[3] The original instructions to estates regarding the proper +employment of this chemical were given in the private reports issued by the +Rubber Growers' Association in 1911. At the present time it is probably +accurate to state that it is now used by all estates preparing fine crepes. +Representatives of manufacturers have sometimes given us to understand +that the question of paleness of colour in such rubber is of no such +importance as is impressed upon us as producers. While we are prepared to +believe, we can only plead that from our point of view the supply arises +from the demand. Such are the conditions governing the sale of rubber that, +irrespective of the requirements of the ultimate user, we have to market +rubber which is valued almost completely upon its appearance at the time of +sale. + +[2] Williams, International Rubber and Allied Congress, London, 1914. + +[3] "The Employment of Sodium Bisulphite in the Preparation of Plantation +Rubber," Beadle, Stevens, and Morgan, _India-rubber Journal_, August 2, +1913. + +As long as such conditions prevail estates must continue to adopt any +device of proved harmlessness, in order to obtain the best possible price +for their product, and not because we desire to continue a practice which +some assure us to be unnecessary, and which, moreover, adds somewhat to the +cost of production. + +QUANTITIES OF SODIUM BISULPHITE.--It must be premised that, although sodium +bisulphite is employed on some few estates in the preparation of sheet +rubber, we do not advise the practice. It is unnecessary, and may lead to +some little trouble and delay in drying. In any case, sodium sulphite gives +the results desired for sheet rubber (see following). It must be +understood, therefore, that we are concerned here, in the case of sodium +bisulphite, with its employment in the preparation of fine pale crepe only. + +As the dry rubber contents of latices vary with the age of the trees, the +general health of the trees, the seasons and general climatic conditions, +the relative strain imposed by depletion of reserves through tapping, etc., +it will be clear that the effect produced by a definite quantity of sodium +bisulphite in any given volume of latex will also vary--_i.e._, the effect +depends upon the potential amount of rubber present. A dilute latex needs +less sodium bisulphite than a richer latex to produce the same effect in +colour.[4] + +[4] Incidentally there are certain occasions, as in the opening of areas of +bark rested for long periods, when the latex is of a rich yellow colour. +Sodium bisulphite will not "bleach" this colour, and it is well to remark +again at this stage that the action of the chemical is only to avoid or +arrest oxidation (darkening). + +Hence it follows that if in any factory uniform quantities of the solution +are used for any given volume of undiluted latices from different areas of +the estate, the effect upon the dry rubbers will vary. This explains why +some estates obtain different shades of rubber in their fine pale crepes. + +The remedy obviously is to reduce the variation in latices by diluting them +all to a standard rubber content as is done in sheet preparation. One is +thus assured that the prescribed quantities of sodium bisulphite will meet +requirements in every case, and that waste will be avoided. + +Working with a standard of 1-1/2 lbs. dry rubber per gallon the following +formula should serve as a _maximum_: + + +_Formula for Use of Sodium Bisulphite._ + + (_a_) Dissolve sodium bisulphite in water at the rate of 1 lb. to 10 + gallons. + + (_b_) Of this solution use 1 gallon to every 10 gallons of latex. + +MAKING A SOLUTION.--The making of a solution of the chemical would seem to +be a simple matter, but to judge by the ill-effects sometimes observed in +the dry rubber the simplicity of the operation appears to have been +overrated. Great care must be exercised in preparing the solution, and the +work should not be left to the few minutes preceding its actual +requirement; such has been found to be the case in several factories, so +that it is not surprising if the rubber is defective. + +The powder should be added gradually to water with thorough stirring, which +should be continued for five minutes at least. Even then there may often be +seen at the bottom undissolved particles, sand, and other impurity. It is +necessary, therefore, in such cases to decant the solution through a piece +of cotton cloth before using. No solid particles should be allowed to enter +the latex. + +ABUSE OF SODIUM BISULPHITE.--It is now generally recognised that the abuse +of sodium bisulphite, in the form of an excess, leads mainly to delay in +the period of drying and the production of an overpale rubber.[5] It is +probable that few estates, if any, now experience trouble due to this +non-observance of the rules and quantities laid down for use. + +[5] "The Preparation of Plantation Rubber," Morgan, 1913, p. 74. + +RESIDUAL TRACES OF SODIUM BISULPHITE.--The prolongation of the drying +period was attributed to the fact that traces of substances caused by the +decomposition of sodium bisulphite remained in the rubber if the rubber +were not sufficiently worked and washed on the rolls. These traces must +have been very minute, but they were sufficient to retard the progress of +drying. That much depended on the care exercised in washing is evident from +the fact that samples prepared with varying quantities of the chemical show +varying results on extraction. These samples were tested for the presence +of sulphates. Of the series tested that sample prepared with bisulphite in +the proportion of 1 part to 600 parts latex showed only a trace of sulphate +present; while the one prepared 1:2,400 gave an equal quantity. +Intermediate samples contained no trace of sulphate. On the whole, +therefore, the presence of sulphate in crepe rubber is adventitious, and +properly washed crepe prepared with moderate quantities of bisulphite may +be taken as free from any residual quantities. Meanwhile there cannot +possibly be any doubt of the advantages gained by the use of sodium +bisulphite, and it would not be very wide of the mark if the statement were +made that, in the event of this chemical being discarded, most contracts +for pale crepe could not be fulfilled. + +SODIUM SULPHITE.--It would not be amiss to insist upon the point that while +the nature of sodium _bisulphite_, as employed in the preparation of +rubber, is anti-oxidant, sodium sulphite is employed chiefly for its +anti-coagulant property. It is not used, therefore, in the making of crepe +rubber, but is of service in the preparation of sheet rubber, where the aim +is to keep the latex in good fluid condition as long as is necessary, and +to retard coagulation slightly so that enclosed bubbles of gas or air may +escape. Formulæ have been given for its use in the field when required. On +some estates this practice is not found necessary, but a quantity of +solution is always placed in the bottom of the reception vessels prior to +the straining of latex into them. Only a small quantity is used, and as a +working basis the following formula may be adopted: + + +_Sodium Sulphite: For Use in the Factory._ + + (_a_) Dissolve 2 ozs. of anhydrous sodium sulphite in a gallon of + water. + + (_b_) The gallon of solution, placed in the bottom of the reception + jar or tank, is sufficient for the treatment of 40 gallons of + standardised latex (1-1/2 lbs. dry rubber per gallon). + +The warning previously given regarding the necessity for thoroughness in +the preparation of solutions is here reiterated. Stirring should be +thorough, say for five minutes, and if there is any sediment or undissolved +matter the solution should be strained through cloth before using. + +Where uniform jars or tanks are in use, the majority of which will contain +uniform quantities of latex daily, the practice of using the chemical can +be made almost fool-proof even in the hands of coolies. A calculation is +made of the quantity of powder required for each vessel daily. The +necessary number of lots is weighed out each morning and each placed in an +envelope. The process is thus simplified by the fact that the contents of +an envelope, neither more nor less, are required for each unit reception +vessel. Even the weighing can be done by a coolie if he is given a +counterpoise (of lead, for example) equivalent to the required weight. + +It will not be found necessary to do any vigorous stirring of the solution +with the latex, as the latter is strained into the solution and the +continued addition of successive quantities is sufficient to give a good +mixture. + +USE OF FORMALIN.--Few estates now use formalin (formaldehyde) as an +anti-coagulant. It must be acknowledged that when not abused there are +points in favour of its employment in preference to sodium sulphite, but +these are outbalanced by certain disadvantages. The argument may be stated +thus: + + _Points for_: (1) If made up freshly it is an effective + anti-coagulant. + + (2) Formalin being the solution of a gas in water, there is no + residual substance left in the rubber to delay drying. + + (3) Its use gives a bright clear rubber. + + _Points against_: (1) Its cost at all times is greater than that of + sodium sulphite. + + (2) If the jar is not sealed there is loss by evaporation, thus + increasing the cost. + + (3) Its effect upon the rubber is uncertain. Even in normal quantity + it is said to cause "brittleness" or "shortness." + +Certain few estates, however, have continued its use, and no trouble is +claimed to ensue. The following formula is stated to give satisfactory +results in the preparation of sheet rubber, when applied as in the +preceding paragraphs bearing on the employment of sodium sulphite: + + +_Formula for Use of Formalin (Formaldehyde)._ + + (_a_) 1 pint of formalin is diluted with 5 gallons of water. + + (_b_) Of this solution 1 gallon is required for 50 gallons of + standardised latex. + +In noting this formula the writer gives no recommendation regarding its +use. Whatever may be the actual facts regarding the effect of formalin upon +the vulcanisation of rubber, when used in minimum proportions, there can be +no question concerning its injurious effect if used in excess. Beyond this +the factors of cost and loss militate against its wider employment. + + + + +CHAPTER IX + +_PREPARATION OF SHEET RUBBER_ + + +PALE SHEET.--The first form in which plantation rubber was prepared was as +"biscuits" or sheets. This form remained in favour for some years. The +first biscuits or sheets were rather dark in colour owing to the natural +oxidation which followed. Then it was discovered that by diluting the latex +the degree of oxidation was diminished, and later it was found that if the +soft coagulum were placed in almost boiling water for a short time the +resulting rubber was pale. Thus there arose gradually a demand for pale +sheet. With our present knowledge we are in a position to state that the +pale biscuits were not in any way superior to the darker ones, and they +were in most cases actually inferior. + +It was found also as time progressed that sheet rubber, on air-drying, +became covered with external surface moulds, and that, more often than not, +the smell of the drying rubber was the reverse of pleasant. Even when dry +the sheets had to be continually brushed free from moulds, and by the time +the rubber reached the market it was again usually mouldy. Such are, even +now, the handicaps under which those who prepare pale sheets have to +labour. Few, however, are the estates making pale sheets, and they are +confined almost entirely to native holdings. + +To those accustomed only to the preparation of crepe rubber, where +coagulation can be effected in large batches, the preparation of sheet +rubber always seems to demand much more labour. As a matter of fact, +although the preliminary operations certainly do demand more care and +labour than in crepe-making, there are compensating advantages in the +machining stage. For the preparation of sheet of the highest quality on any +but the largest scale, elaborate installations of machinery are quite +superfluous, as equal results can be obtained with pairs of rolls worked by +hand. + +UNIFORMITY OF PRODUCT.--There will be no need to enter again into a +discussion of the preliminary operations of receiving and straining latex +for sheet-making. They have been fully dealt with in Chapter VII. It used +to be the general custom to mix the acid and latex in each individual dish, +and in some small or non-progressive factories that is still the procedure. +Quite apart from the question of labour entailed, the process is quite +unnecessary. Even if comparatively small volumes of latex are handled, +standardisation by dilution should be the rule, and the acid solution +should be added to the bulk. It is possible to stir in the acid and to +ladle out uniform quantities in each pan or dish from a bulk volume of up +to 40 gallons if the organisation is efficient. + +On any but a small scale the labour entailed in the handling and cleaning +of pans is excessive, and shallow tanks are now employed on most estates. +The reception and standardisation of latex by dilution has already been +discussed in Chapter VII. The combination of this practice with the +employment of shallow coagulating tanks has simplified working and reduced +the cost of labour. It is not intended to enter into any lengthy discussion +relative to the merits of sheets made in pans as against those made in +tanks. It is granted that it is possible to make a "pan" sheet superior in +appearance to the general average of "tank" sheets; but from an economic +standpoint the introduction of the use of tanks into all but the smallest +factories is only a matter of time, if the demand for this class of rubber +persists. + +THE IDEAL TANK.--Even the most modern installations of sheet-coagulating +tanks must be regarded as merely temporary devices, as, given facilities, +the room for improvement is so wide. + +The first tanks made erred in being too large, and as the result of +experience the size of units has now been reduced to a maximum of 12 feet +by 4 feet by 1 foot deep. + +[Illustration: UNIT MODERN COAGULATING TANK (TWO VIEWS). + +Construction of brick and cement with lining of glazed tiles. Note slots +incorporated in side tiles. Partition boards in piles in the background.] + +Tanks are at present constructed either of hard timber or of brick and +cement faced with glazed tiles; both types have inherent drawbacks. The +wooden tanks are difficult to keep clean and in "sweet" condition. The +glazed tiles, unless extremely well laid, allow the acid serum (from which +the rubber is removed) to percolate between the interstices. Thus "pockets" +of liquid collect beneath the tiles, and in process of the decomposition of +certain constituents dissolved in the serum evil-smelling gases are set +free. + +[Illustration: ANOTHER BATTERY OF TANKS, WITH DILUTION TANKS, RAISED, ON +THE RIGHT. + +Note drainage cocks, chute, and sieve in position.] + +It should not be a matter of difficulty for manufacturers to make sheets of +thick glass sufficiently large to form the bed-plate and side-pieces +necessary in the lining of a tank. If such adjuncts could be secured, the +disabilities indicated above would be perhaps wholly removed. Unless there +is a demand from estates, however, it is idle to expect a supply to be +forthcoming. + +An even greater improvement would take the form of unit tanks cast in +glazed white-ware with the necessary slots incorporated in the sides. At +present no known firm makes such tanks of sufficient size. A unit could +measure (internally) 6 feet by 4 feet by 1 foot deep, with slots 1-1/2 +inches apart, and 3/8 inch in width. The tanks might be reinforced with +iron bars, so that they could either be used alone or embedded in the usual +brick structure. The junctions of the bed-plate and side-pieces could be +finely rounded so as to facilitate cleaning, and at one end a draining-hole +could be made, say, 1 inch in diameter. + +[Illustration: CLOSER VIEW OF FOREGOING. + +Note partitions in position and coagulum being removed.] + +Meantime both the hard-wood tanks and those of glazed tiles find their +particular applications. The former is generally employed in smaller +factories, or where future large increases of crop preclude the present +installation of a fixed system. The latter find use in large factories, or +where no new areas remain to come into bearing. + +MODERN INSTALLATION.--As an example of a modern installation of coagulating +tanks, we can do no better than offer reproductions of the system now in +use on Pataling Estate. + +A warning must be given against employing all tanks of stone-ware or cement +unless well glazed. Almost without exception, irrespective of the material +used in the construction of coagulating tanks, wooden partitions are +employed. In the few exceptional cases the partitions are either of glass +or of aluminium. The former would appear to be the ideal substance, were it +not for initial cost and loss by breakage. These disabilities may possibly +be overcome in course of time. + +CARE OF TANKS.--The use of aluminium would have been wider had it not been +for lack of supplies and the question of cost during the War. A novel +method of employing aluminium partitions was introduced in the factory of +Tremelbye Estate. There were no slots in the sides of the glazed-tile +tanks, but the necessary slots were very ingeniously created by means of +aluminium "distance-pieces," the two long edges of which were turned at +right angles to the face of each piece to a depth of about 1/4 inch. The +ends of the thin aluminium partition moved in the slot thus formed between +two adjacent "distance-pieces." The friction between the surfaces was +sufficient to allow all the partitions, when in position, to be raised well +above the floor of the tank, so that a uniform level of latex was obtained. +Slight hand-pressure only was then required to push the partitions down. + +Naturally the cleansing of glass or aluminium partitions presents no +difficulty, but in the case of wood failure to ensure thorough cleanliness +leads to possible defects in the finished dry rubber. Provided the wood +could be made waterproof, no trouble would ensue, and hence various +measures have been tried with that object in view. When new the boards have +been surface-waxed or varnished, and the treatment has been repeated on +occasions. But in course of time the surface film of waterproof material +has disappeared, partially or wholly, and the trouble recurs. When +partitions become sodden with serum, the surfaces are liable to be coated +with a slime, consisting largely of organic growths which have an effect +upon the latex, causing "pitting" on the surface of the coagulum and +enclosed bubbles within. + +[Illustration: ANOTHER BATTERY OF TANKS, WITHOUT DILUTION TANKS OR MEANS OF +GRAVITATING LATEX.] + +It is recommended, therefore, that wooden tanks, after ordinary cleansing +daily, should be swabbed out with a 5 per cent. solution of sodium +bisulphite. Wooden partitions should receive the same treatment, and once a +week at least (or every day if possible) they should be placed in the sun +for an hour or two, care being taken that both sides of a partition are +exposed in turn. Before being placed in the latex, all wooden partitions +should be made wet on the surfaces. + +Some years ago the writers had made a partition of vulcanite, which +apparently would have proved of great service but for the initial cost. The +advent of the War put the matter out of the question, but it is possible +now that such a material would be worthy of extended trial. Except in the +matter of cost, it would appear to have advantages over any substance yet +tried; and if it were possible for estates to supply their own lower grade +rubbers direct, the cost might be reduced considerably. + +[Illustration: A SHEETING TANK CONTAINING COAGULUM FOR CREPE PREPARATION. + +Behind wall in background are the tanks in which latex is standardized. +Note vent, to the left, through which latex flows and wooden "stopper" on +edge of tank.] + +STANDARD LATEX.--Enough has been written (see Chapter VII.) to familiarise +the reader with the use of this term for the description of latex diluted +daily to a level of dry rubber content. Whatever may be the practice +elsewhere, it is now fairly general on estates in Malaya to reduce all +latices to a uniform "strength" for the preparation of sheet rubber. It is +claimed that only in this manner can uniformity of product be achieved. + +The selection of a standard has been the outcome of general experience. It +has been found that if too high a standard is taken difficulties arise, +such as (1) unsatisfactory and uneven coagulation, (2) too thick a coagulum +for easy working in general, (3) too extended a period of drying and +smoke-curing, and hence too dark a colour in the finished rubber. + +[Illustration: A "BATTERY" OF SHEETING TANKS (PATALING ESTATE). DILUTION +TANKS, RAISED, ON THE LEFT.] + +On the other hand, too low a standard also brings trouble in its train. The +coagulum is too porous, will not stand handling, and the resultant sheet is +too thin unless an abnormal thickness of coagulum is prepared. Furthermore, +over-dilution means an increase in the number of tanks required for any +original volume of latex. This involves an increase in floor area, and +perhaps in the size of the building. The soft sheets, when rolled, may +spread to such a width as to cause the edges to be squeezed under the +cheek-blocks of the machines, etc. + +For all practical purposes, whether sheets are prepared in pans or in +tanks, it has been found that the optimum results are obtained by the +adoption of a standard approximating and not exceeding 1-1/2 lbs. dry +rubber per gallon. Primarily this standard has a direct connection and +interdependence with the distance between the partitions (or between the +slots) in coagulating tanks. The distance found most practicable is 1-1/2 +inches. This thickness of coagulum, when prepared from latex not exceeding +a standard of 1-1/2 lbs. dry rubber per gallon, is found to yield a very +satisfactory sheet in all respects. + +It will be seen that we have two possible main factors of variation: + + (_a_) Distance between partitions, causing visible differences in + thickness of coagulum. + + (_b_) Dry rubber content of latex, causing differences in the density + (_e.g._, hardness or softness) of the coagulum. + +The effect of variation in (_a_) will be clear. Even when latex of a +standard of 1-1/2 lbs. per gallon is employed the resulting sheet may be +either too thin or too thick. + +Similarly, as already argued, the use of too low or too high a standard of +dilution (when the factor of distance between partitions is not allowed to +vary) is capable of causing much difficulty. While this is correct, +broadly, it is found in the experience of some estates that their +requirements are satisfied by a slightly lower standard than 1-1/2 lbs. per +gallon. Thus it is not uncommon to note the adoption of a standard +equivalent to 1 lb. 4 ozs. or 1 lb. 6 ozs. dry rubber per gallon. +Experience dictates, however, that for the recognised standard measurements +of modern tanks the practical limits of satisfactory density of latex lie +between 1-1/4 lbs. and 1-1/2 lbs. per gallon. + +STANDARDISING INSTRUMENTS.--For standardising latex by dilution all that is +required is an instrument which will preserve a perpendicular position +while floating in latex, will be sufficiently sensitive to indicate fairly +small differences in density of latex, and has one mark on its aerial +portion accurately indicating a density corresponding to the required +standard. On scientific grounds it can be demonstrated that such an +instrument as employed in common practice would not be strictly +accurate.[6] It is not proposed, in this section of the book, to discuss +such considerations. + +[6] De Vries, "Archief voor de Rubbercultuur." + +Instruments of this nature are represented by the "Metrolac" (originating +from the Rubber Growers' Association) and other similar recorders. They +generally consist of a submersible bulb with a projecting stem which is +graduated. The "Metrolac" differs from others in that the bulb is of +torpedo form (thus reducing "skin friction"), and the graduations on the +stem indicate actual weight of dry rubber per gallon instead of the +ordinary specific gravity figures. + +Theoretical considerations to the contrary, it is found in actual practice +in Malaya and Ceylon that, although such instruments are naturally delicate +and require careful manipulation, they are of considerable practical value +and satisfy a definite requirement. Until an instrument of greater accuracy +and equal simplicity can be discovered all estates should regard the +possession of a few "Metrolacs" as essential. + +The nature of their construction and the average conditions under which +they are used (and abused) make it impossible to rely upon their accuracy +indefinitely or for any long period. It is always recommended, therefore, +that there should be at least two instruments available, one of which may +be in daily use, while the other is kept in safe custody and only employed, +say, once a week for purposes of checking the accuracy or degree of +inaccuracy of the other. This can be done with reasonable approximity by +placing both instruments in a tall vessel containing well-mixed and diluted +latex. Instruments showing a marked degree of inaccuracy should not be +preserved; but in cases of necessity "Metrolacs" from estates belonging to +company members of the Rubber Growers' Association may be sent to the +laboratories for repair and adjustment.[7] + +[7] This applies to the gilt brass instruments. As the result of experiment +the Rubber Growers' Association are now introducing glass instruments. +These are necessarily more fragile, but while unbroken can be relied on to +give correct readings. + +Where field coagulating stations have been instituted on estates, it is +strictly necessary that instruments should be provided in all cases; and it +should be a rule that these are tested and corrected weekly by a standard +instrument employed for that purpose only. This need was well recognised by +many estates when, during the War and the consequent shortage of supply of +"Metrolacs," a demand arose which was met in some degree by crude +instruments of local manufacture, such as that commonly known as the +"Castlefield bobber," contrived and made by the enterprising manager of the +estate of that name. The demand for the more accurate instruments can now +be met. + +METHODS OF USING THE INSTRUMENTS.--The "Metrolac" was devised and +introduced by the writers on behalf of the Rubber Growers' Association, and +directions for its use were given. Tables were prepared by means of which +simple calculations for the dilution of any given latex could be made. +These did not find an extended application, inasmuch as in the majority of +cases native workers only were in charge of the processes of rubber +preparation. In point of fact, such calculations are not strictly +necessary, as the operation of standardising the latex can be done quite +simply and skilfully by a trained native. Latex as it reaches the store in +average weather from any particular division or field does not vary greatly +in density. The trained coolie or foreman, basing his practice on +experience, adds to the latex a quantity of water, and then makes a first +test with the standardising instrument. Several additions of water (with +thorough stirring) may have to be made before a test indicates that the +correct density has been obtained, but it is surprising how quickly a +skilled worker will arrive at the desired standard. Extreme or absolute +accuracy is not insisted upon or desired, as avoidable delay is to be +deprecated, and the result in any case is sufficiently exact for practical +purposes. + +SKIMMING.--During the gravitation of the latex from the reception vessels +(in which the standardising of the latex is effected) to the coagulating +tanks, much surface froth is usually caused. This is best removed by means +of a thin board of a width slightly less than the breadth of the tank. The +skimmings are sometimes placed in pans and subsequently made into a second +grade of sheet rubber, or they receive treatment with a small proportion of +sodium bisulphite and eventually appear as fine pale crepe. The practice +varies usually according to the form in which the general No. 1 grade is +prepared. + +On some estates a great deal of the frothing is avoided by placing in +position at the receiving end of the tank a perforated partition. This +partition may be made of wood, or of stout zinc (or aluminium) carrying ten +circular holes to the inch. Through this the latex percolates, while the +froth is retained on a small area. The froth is removed prior to the +addition of the acid. After stirring in the acid solution most estates +again skim the surface of the latex; but if the stirring has been performed +properly there should be little froth. This, when it collapses, in any case +will appear only on the upper edge of the strip of coagulum, and after +rolling should not be visible. It would appear, therefore, that the second +skimming is not necessary. + +STYLE OF SHEET.--Within the last few years the custom of making plain +sheet--_i.e._, sheet having a plain surface--has gradually given place to +the preparation of ribbed sheet--_i.e._, sheet having a pattern marked on +the surface. It would probably be correct to say that plain (smooth) sheet +is now only prepared by natives or by some estates just come into bearing. +Even in the latter case there is no reason why smooth sheet should be made, +as hand machines are sold which will do all the work required. It will be +evident to anyone acquainted with rubber preparation that in the matter of +actual quality of rubber the question of smoothness or a pattern can have +no bearing on the result. One advantage claimed for ribbed sheet which may +entirely justify the preference exhibited by consumers, relates to the +question of packing. When rubber arrives at home it is frequently found to +be in an almost solid block, due to the pressure of the sheets superimposed +in the case. The smoother the surfaces of the rubber in contact the greater +the adhesion and the denser will be the mass, and consequently the greater +the difficulty in separating individual pieces. Under such circumstances it +is plain that the difficulty is diminished if the sheets have a raised +pattern on them. It is noted also that the liability to mildew-growth is +greater the smoother the surfaces of the rubber. + +On these grounds the "marking" of sheet rubber is to be commended. These +reasons apart, it is really astonishing the difference made in the +appearance of the sheets by impressing upon them a ribbed pattern, and it +is highly probable that the market value of the rubber is slightly +increased. It is not our duty to attempt to reason why this simple +operation should increase the market value of sheet rubber; it is +sufficient to recognise that it is so, and that money may be thrown away by +neglecting to cater for the taste of the market. Of the patterns impressed +upon sheet rubber there is a variety, but the general style is that known +as the "spirally close-cut ribbing." + +STANDARD SHEET.--Leaving for the present the question of pattern of mark, +one cannot do better by way of introduction than to reproduce the +instructions[8] given generally to estates. + +[8] "Handbook on Preparation of Rubber," Rubber Growers' Association, May, +1917, p. 28. + +ROLLING AND MARKING OF SHEET RUBBER.--Working with standard latex it is +found that strips of coagulum 1-1/2 inches in thickness require little +rolling to produce sheets of desirable thickness. + + (1) The sheets or strips are first given a preliminary rolling with a + heavy hand-roller made of hard wood. The roller is passed once in one + direction, and once in the reverse direction. + + (2) The coagulum is then passed through smooth machines twice, once + with the rolls fairly open, and once with a narrower space. It is not + found advisable to close the smooth rolls so tightly that the rubber + is made too hard. + + (3) The sheets or strips are then passed once through a pair of + marking rollers. Various types of patterns are used, but the one which + appears to give the most satisfactory results is that known as the + "close-cut spiral." This produces the semblance of a small diamond + pattern on the rubber. The surface of the sheet is raised in + well-defined ridges, which appear to present the maximum drying + surface exposed to the atmosphere of the smoke-house. Thus, not only + is the appearance of the sheet rendered attractive, but also the + period of drying is reduced. Starting with standard latex and + following the procedure here described for rolling and marking, sheets + should be ready for packing in ten or eleven days. If the period is + longer, it is possible that the design or structure of the smoke-house + is at fault. + +WHEN TO WORK THE COAGULUM.--Before proceeding to discuss other points the +question remains to be settled as to how long it may be necessary or +advisable to allow the coagulum to remain in the serum before rolling it. +For reasons of practical economy in factory working, it is usual to allow +sheet rubber to remain over night, and the coagulum receives attention +early next morning. During the interval (averaging about eighteen hours), +the coagulum consolidates, leaving an almost clear serum if the correct +quantity of acid has been added to the latex. Any but the very slightest +trace of milkiness in the serum indicates an insufficiency of coagulant. If +the serum is always definitely clear, there may be grounds for believing +that an excess is being used. If the quantity of coagulant has been +calculated to an average nicety, the serum should be just dubiously free +from milkiness. + +The firmness gained by the coagulum on standing in the serum overnight +should enable it to be handled next morning without any marked stretching, +and in some estates the rubber is put direct through the first pair of +smooth rolls without a preliminary consolidation by means of hand-rolling. + +Some estates prefer to handle the coagulum while rather softer, as it is +claimed: + + (_a_) That the coagulum is easier to work, and sheets of improved + appearance can be made. + + (_b_) That there is greater freedom from "bubbles." + + (_c_) That the incidence of "rust" is lessened. + + These claims are substantiated in practice; but in the case of the + third, it only holds provided that the rubber can be finished and + placed in the smoke-house almost as soon as the last sheet has been + machined. + +In such cases all latex must reach the store comparatively early in the +day--_e.g._, before noon. Three hours is allowed for coagulation, and the +working of the rubber is then commenced. As a general rule this means that +the operations of rolling and marking must be completed, a short interval +given for dripping, weighing must be done, and the rubber placed in the +smoke-house before night falls (as a rule about 6.30 p.m.). + +Unless factories dealing with a large crop are well equipped with +artificial light, such a course is not open to them; in any case it remains +true that night work should be avoided if possible. If, however, it can be +arranged without increasing the cost of production, there would appear to +be no objection to the early working of the coagulum as described above. + +HAND-ROLLING.--As already indicated, some few estates do not give the +strips of coagulum any preliminary hand-rolling, as the rubber is +considered to be sufficiently firm to be handled into the first machine. + +On most estates hand-rolling is found necessary, owing to the tendency of +the long strips to stretch unduly, giving badly shaped sheets. This +hand-rolling should be done carefully, and is best effected on a specially +constructed table. This consists essentially of an inch-thick hard-wood +plank about 2 inches wider, and 4 or 5 feet longer, than the strip of +coagulum. Along the edges of the plank, and at right angles to its upper +flat surface, may be fastened strips of wood about 1/2 inch square in +section, thus forming a shallow tray open at either end. These strips serve +two purposes: + + (_a_) As the wooden roller is wider than the plank, they prevent the + coagulum being rolled too thin and too firm. + + (_b_) They prevent the coagulum being squashed too wide, and tend to + keep the edges straight. + +To avoid "thick ends" it is sometimes considered advisable to insert, at +either end of the rolling table, shallow wedges about 6 inches long, of the +same width as the table (between the edge-strips), and with the sharp end +of the wedge pointing in the direction of the length of the table. The ends +of the coagulum are drawn up and finished on these inclined planes. + +These points may appear to be extreme refinements, but as long as rubber is +valued on such grounds we must endeavour to meet the system imposed upon +us. + +SMOOTH-ROLLING.--It is advised that, after hand-rolling, the coagulum +should be passed through at least two machines having smooth-rolls. On some +estates three such machines are employed. The purpose of this procedure is +to reduce the thickness of the coagulum gradually. The same could be +effected, of course, on one machine; but obviously the distance between the +rolls would have to be readjusted at each operation and for each piece of +coagulum. Apart from the time thus wasted, there is the certainty, in view +of the rough adjustment of the machines, that the chances of obtaining +uniformly thick sheets would be slight. + +The machines should be arranged as a battery, with the marking rolls at one +end, so that the operations are consecutive. It is erroneous to imagine +that heavy machines (such as those used in crepe preparation) are required. +Light machinery only is necessary for sheet-making; but any available heavy +smooth-roll machines in a crepeing battery may serve admirably for the +purpose. + +MARKING.--Heavy machines are unnecessary for the purpose of putting a +pattern on sheet rubber. If the rubber has been properly prepared a light +pair of rolls is capable of exerting sufficient pressure to cause a good +upstanding pattern. + +Rolls are cut in various designs: some with "diamond" grooves on both +rolls; some with grooves of varying width and depth encircling the +circumference of the rolls, thus creating a "stripe" effect on the rubber; +and some with diagonally-cut spiral grooves placed closely together. The +last has the greatest vogue at present, while the first has almost gone out +of favour. An objection lodged against the second design is that the edges +of the grooves sometimes cut through the rubber, so that the dried sheet +divides in strips. It would appear in such instances that either the +coagulum was too thin and soft, or that the grooves had been cut too deeply +and sharply. In any case the choice of a design is an arbitrary matter, and +should depend upon the effect produced on the rate of drying and the +general appearance. + +The popular "close-cut spiral" roll is machined with varying measurements, +but the usual design has grooves 1/8 inch wide by 1/8 inch deep and 3/16 +inch apart. + +Many estates have a particular "brand" cut in the middle of the rolls for +purposes of identification. If this is done it is advised that the main +grooving of the rolls be carried into the "branding" strip; otherwise grip +will be lacking on this portion, and a certain amount of "cockling" of the +sheets will result. + +Sheets are often seen in which the potential effect of the grooving is +reduced to a comparatively flat pattern in place of the desired ridges. The +fault is generally attributed to the shortcomings of the marking rolls. +While it is true that the grooving often deteriorates by friction-wear when +the rolls are running "free," experience generally decides that the +deficiency in the appearance of the rubber should be attributed to faulty +previous preparation rather than to the marking rolls. Sets of rolls have +been changed often without justification or an improved result. It would +always be well to be certain first that the trouble did not emanate from +the fact that the coagulum had been previously rolled so thin and hard that +the rubber could not be squeezed so as to fill the grooves. This has been +found to be a common fault, and the general effect is to delay drying in +spite of the thinness of the rubber. + +Again, the trouble may have been due to an incorrect standardisation of the +latex, generally in the direction of too heavy a density (too rich a latex) +being employed. The original thickness of the coagulum would be normal, but +owing to the abnormal rubber-content the effect of passing through the +smooth rolls would be the production of a strip thicker and firmer than +ordinary. If this firmness is appreciable the resistance of the rubber to +the squeezing action of the marking rolls will result in a flat +pattern--_i.e._, the grooves cannot be filled, and the ridges are low. + +It is advised that all rolls used in the preparation of sheet rubber should +be at least 18 inches wide, in order to avoid the appearance of thickened +edges which delay drying. + +Working with the correct standard of dilution of latex, and following the +procedure indicated in the foregoing paragraphs, the dry sheet should not +exceed an average thickness (over ridges and depressions) of 1/8 inch. + +PREPARATION FOR SMOKE-CURING.--It used to be the custom to allow sheet +rubber to air-dry first for periods varying from one to several days. +Naturally moulds were soon formed, and when the sheets were quite +smoke-cured a mass of the dead moulds could be seen, if not over the whole +sheet, at least in the corners of each diamond mark. It has been +demonstrated in practice that there is no advantage in allowing sheets to +air-dry partially before smoking. In fact, to obtain the greatest benefit +from smoke-curing, sheet rubber should be placed in the smoke-house as soon +as possible. The same effect of mould-growth may be noted if the wet sheets +are placed in a smoke-house insufficiently heated. + +Other defects may arise which can be traced to faulty treatment of the +marked coagulum prior to hanging in the smoke-house and subsequent to +rolling. These will be enlarged upon in a subsequent section of the book, +and at present it will suffice to indicate the procedure which experience +directs as likely to give the best results. + +When the lengths of coagulum leave the marking machine they are usually +laid in piles containing two dozen or more strips. The piles are then cut +into the required lengths, the exact length generally being determined by +the available perpendicular distance between the supports in the +smoke-house. It is necessary to remark that the piles of sheets should not +be allowed to accumulate, but should be dealt with in subsequent treatment +progressively. If for some reason this is not possible, then all piles of +sheets should be turned on edge so as to assist the draining away of the +serum or "mother-liquor," which continues to ooze from the rubber for some +time after the squeezing in the machines. + +Where hot water is available the freshly cut sheets should be passed into +it as soon as possible, and given a thoroughly good swilling. The caution +must be given that the hot water should be changed very frequently and, if +possible, after every batch, say, of a hundred sheets. + +The sheets should then be carried immediately to racks on which they are +hung to drip. Generally these racks are situated under cover, but there is +no reason why they should not be placed in the open air without cover or +shade. From continued experience of this practice over a period of years it +is found advantageous and to be preferred to the usual method of allowing +sheets to drip under cover. + +While the sheets are fresh and loaded with internal moisture, the effect of +sun-heat upon the surface, when exposed for, say, two hours, is nil; and +the safety of the process can be guaranteed, provided the stated limit is +not exceeded to an appreciable extent. + +[Illustration: THE OLD METHOD OF "DRIPPING" FRESHLY ROLLED SHEETS WITHIN +THE FACTORY.] + +After dripping for an hour or so, the sheets should be placed in the +smoke-house. If it is a bright sunny day, no extra precautions need be +taken; but on cool, dull days it would be advisable to light the fires +earlier than usual, consistent with the work required to be done in the +house--_e.g._, in the removal of dry rubber. There would appear to be no +reason why the dry sheets should not be first removed, so that on dull or +wet days smoking can be commenced as soon as the wet rubber has been hung. + +On a few estates where the smoke-houses are worked continuously, except for +a few hours in the morning, a portion of the building is separated by a +partition for the reception of the wet rubber. The sheets are taken +directly from the marking rolls and placed in the chamber, beneath which a +fire is started. The sheets thus drip in a warm and smoke-laden atmosphere +until next morning, when they are weighed and removed to the smoke-house +proper. It is claimed that freedom from "rust" is thus obtained. + +It will be clear that in the treatment of the rubber preparatory to smoking +the whole process should be continuous, and delay should be avoided if the +best results are to be obtained. + +[Illustration: THE NEWER METHOD OF HANGING IN THE OPEN AIR.] + +SMOKING OF RUBBER.--The assumption may have been noted above that the sheet +is to be smoked. As far as our knowledge extends, none but small native +estates now prepare sheet rubber of any other type, with the exception of +certain patent processes. Air-dried sheets are generally made on +small-holdings, and are bought in the market chiefly for the purpose of +macerating and making into blanket crepe. We have no intention, therefore, +of discussing the possibilities or qualities of air-dried sheets, as the +output of sheet-rubber from our estates is always in smoked form. The +drying (or, properly, smoking) stage will be discussed in Chapter XI. + + + + +CHAPTER X + +_PREPARATION OF CREPE RUBBER_ + + +NO. 1, OR FINE PALE CREPE.--Considering first the preparation of the +highest grade, fine pale crepe, it must be stated that the difficulties +attached to the process are generally not sufficiently appreciated. In this +pale rubber minor blemishes are so plainly apparent that their importance +is highly exaggerated, and what would worthily escape notice in smoked +rubber assumes disproportionate prominence in pale crepes. The very fact +that such a delicate material as colourless coagulum has to be manipulated +in coarse iron rollers, with the attendant oil and grease worries, should +be sufficient to deter one from criticising too harshly the occasional +lapses of an estate struggling to give of its best to the market. At the +same time there can be no doubt that if precautions are taken to attend to +all likely sources of contamination, defects in pale crepe may be avoided +to a wonderful extent; and on some estates the observance of elementary +rules enables the preparation of the finest pale crepe to be made almost +mechanically. + +STANDARDISATION OF LATEX.--The question of the standardisation of latex has +been dealt with in a general way in Chapter VII., and the reader is now +familiar with the trend of the argument in its favour. It will be +recognised that the necessity for standardisation exists to the same degree +in the correct preparation of pale crepe as in the case of smoked sheet. +Unless the dry rubber content is invariable, and the quantities of +chemicals fixed, the colour of the crepe may vary appreciably. + +It may be pointed out that it is not _essential_ to adopt the same standard +of dilution as for sheet preparation. Given that latices from all fields or +divisions are fairly uniform, and of high rubber content, the standard may +be taken at a figure equivalent, for example, to 2 lbs., or 2-1/2 lbs., or +even 3 lbs. per gallon. It is wise, nevertheless, to take a lower standard +for several reasons. For instance: + + (_a_) The average dry rubber content varies with climatic conditions, + position of the cut on the tree, general health of the tree, etc. On a + rainy day the dry rubber content may be lowered too greatly by + adventitious circumstances. + + (_b_) Recording instruments often fail to give even approximately + correct readings in rich latex. Errors may thus be made easily. + + (_c_) A fairly soft coagulum means easier working on the machines, + less labour, and proportionately cheaper costs. + +[Illustration: THREE GRADES OF CREPE RUBBER. + +Left to right: fine pale crepe; second quality pale crepe; compound crepe.] + +It is advised, therefore, that for general purposes the same standard as +that found suitable for sheet rubber should be taken--viz., 1-1/2 lbs. dry +rubber per gallon. At all events the standard should not exceed 2 lbs. per +gallon. + +COAGULATION AND COAGULANT.--Coagulation may be undertaken without any +special arrangement of tanks, and is usually effected in the ordinary +"Shanghai" glazed earthenware jars containing about 45 gallons. Given +reasonable care, and a fairly fool-proof system of calculation for the +quantities of chemicals required, no difficulty need be experienced. + +[Illustration: A WASHING SHED. + +Sheets are soaked in hot water in tanks in the background, and then +scrubbed under a spray of cold water.] + +On a larger scale it is advised that proper reception tanks, in which +standardisation can be effected, should be installed. Where both sheet +rubber and fine crepe are being prepared, the whole system of +sheet-coagulating tanks may be employed with considerable advantage, even +to the insertion of the partitions. + +If ordinary jars are used, and the coagulum is left until the following +morning, the mass of rubber has to be cut up into pieces of a size suitable +for the machines. The knives or saws are sometimes rusty, and the colour of +the coagulum is affected. The coolies often feed into the machines lumps +which are too large, with the result that portions are thrust under the +cheek-blocks and become stained. + +When a sheet-coagulating tank is used all labour of cutting the coagulum is +obviated. The long strips are handled and fed into the rolls easily. It may +be seen, likewise, that actual work is thus saved in machining. + +QUANTITY OF COAGULANT.--For a general discussion on the coagulant and +quantities employed, the reader is referred to Chapter VIII. It is there +recommended that for latex standardised to a level of 1-1/2 lbs. per +gallon, the proportion of pure acetic acid should be in the ratio of +1:1,200. Directions are there given for the making of the solution, and the +calculation of the quantity required for any given volume of latex. + +It is pointed out that for average _undiluted_ latex the basis of +calculation, for quantities of acetic acid required, should be taken on the +ratio 1:1,000. Where latex exceeds a dry rubber content of 3 lbs. per +gallon, it may be necessary to increase the quantity of acid to 1:800. + +If a standard of 2 lbs. per gallon is adopted, the formula given for the +1-1/2 lbs. standard will not give full satisfaction, and the quantity of +acid solution must be increased slightly in order to obtain complete +coagulation. Assuming that the original solution is prepared in 1 per cent. +strength, the following difference would be noted: + + (_a_) One part pure acetic acid to 100 parts water (theoretically 99 + parts). + + (_b_) _1-1/2 lbs. per gallon._ | _2 lbs. per gallon._ + | + Of the above solution use 1 gallon | Of the above solution use 1 + to every 12 gallons of standardised| gallon to every 10 or 11 + latex. | gallons of standardised latex. + +It is not possible to lay down an exact figure governing all cases, as so +much depends upon the treatment undergone by the latex before it reaches +the store. + +Some estates continue to use solutions of greater strength, generally 5 per +cent., in crepe preparation. While such solutions may be effectively +stirred in when the latex is dilute, it is advised that for intimate +mixture the solution need not be stronger than 1 per cent. + +In estimating the quantities of acetic acid required much depends upon the +interval which is to elapse between the addition of acid and the time of +working of the coagulum. If the rubber is to remain until next morning, the +average formulæ will be found suitable; but if it is required to work the +coagulum with an interval of less than three hours, an excess of acid must +be employed. The excess need be comparatively small, unless the interval is +much reduced. For instance, it is the practice on some few estates to begin +the machining of the coagulum about half an hour after coagulation +commences; in which case it is usual to add from a quarter to a half of the +normal quantity in excess. It need scarcely be pointed out that unless this +procedure is strictly unavoidable it should be discouraged on account of +the waste of coagulant involved. Incidentally, the use of strong solutions +of acid under such circumstances may lead to increased deterioration of the +rolls. + +COLOUR OF FINE CREPE.--We are sometimes assured that manufacturers do not +pay the attention to the question of colour which sale conditions would +lead one to believe. As far as we are concerned, and as long as there is no +direct traffic between producer and consumer, it must be recognised that in +the vast majority of cases we are forced to concern ourselves only with the +standards set up in the markets. This, in spite of the knowledge that, all +other things being equal, the arbitrary distinctions in colour afford no +indication of the intrinsic value of the rubber. Under present +circumstances it is plain that if paleness is demanded it has to be +supplied. + +Probably without exception all estates employ sodium bisulphite as the +agent for the prevention of that darkening (oxidation) which is natural in +drying rubber. + +SODIUM BISULPHITE.--A formula for use of this chemical is given in Chapter +VIII., and is applicable to latex standardised to 1-1/2 lbs. dry rubber per +gallon. If a higher standard is chosen the quantity calculated as in (_b_) +of that formula may be increased slightly, and the exact requirements found +by experience. The caution must again be given that the employment of an +excess of sodium bisulphite will lead to the production of an over-pale +rubber, and a prolongation of the drying period. If thick crepes are made, +an excess of the chemical is sometimes made visible by a greyish powder +deposited on the edges of the strips of dry rubber. + +It must be emphasised that the formula in Chapter VIII. indicates the +_maximum_ quantities required for use with standard latex. Many estates +will find it expedient to use less of the chemical; and if it is found that +the desired result is not obtained from normal proportions, attention +should be directed to the points discussed in the following paragraph. + +EVALUATION AND DETERIORATION OF SODIUM BISULPHITE AND SODIUM +SULPHITE.--Sodium bisulphite and sodium sulphite are both bought for our +purpose in the form of a fine crystalline powder, and on analysis good +specimens should contain over 90 per cent. pure substance, when packed in +well-sealed vessels. + +It has often happened that shippers or local sellers, by inadvertence, have +supplied the one chemical in place of the other--to the detriment of the +rubber and the discomfiture of managers of estates. The error, as a rule, +has not been detected for some time, and then perhaps only as a result of +complaints or enquiries reaching the laboratories. To the layman, and +certainly to the native who usually has charge of these substances, it is +not a simple matter to distinguish between them without special knowledge. +There are certain elementary tests, however, which can be applied on all +estates serving to make the distinction, but affording no information +regarding the actual quality of the chemicals. They are given in a +comparative form on page 116. Samples of doubtful specimens may be sent to +the laboratories for analysis, but the bulk of the chemical should not be +used. + +During the War some very poor shipments were received, and much trouble was +caused. Under normal conditions there can be no question that it is to the +interests of chemical manufacturers to supply the best article; and it is +anticipated that in future there should be no difficulty in procuring +shipments of a high degree of purity. + + _Sodium Bisulphite._ | _Sodium Sulphite._ + | + 1. If in good condition it | 1. It has no perceptible + has a powerful odour of | odour. + sulphur dioxide.[9] | + | + 2. In solution it should turn | 2. In solution it should turn + a blue litmus-paper red. | a red litmus-paper blue. + | + 3. It exhibits a marked tendency | 3. The tendency to "cake" + to "cake" if the | is less marked than in + drum is allowed to | the case of the bisulphite. + remain open. | + +[9] High-grade sodium bisulphite has very little odour, but by the time it +reaches the estate, and as a result of short exposure to the moist +atmosphere of the tropics, a little decomposition sets in and a strong +odour of sulphur dioxide gas is noticeable. + +It will be evident that, as sodium bisulphite under normal conditions gives +off a gas when exposed to the atmosphere, it deteriorates in quality +continuously. It is the potential presence of this gas which makes the +powder effective as an anti-oxidant and disinfectant. It is within the +experience of all accustomed to the handling of this chemical, that in +addition to the loss of gas, the powder cakes into a hard mass on exposure. +If only the top layer is caked, the remainder may be in fair condition; but +no caked portions should be used, as they cannot be of good quality. They +may, however, be used for the treatment of scrap rubber, to be discussed +later. + +CARE OF SODIUM BISULPHITE.--The ready tendency of sodium bisulphite to +deteriorate on exposure should give sufficient indication regarding its +treatment in storage. It should be bought only in drums (or other air-tight +containers), and should be stored in a dry place. No drum should be opened +until required, and the common practice of keeping an open drum on the +floor of the factory should be avoided. + +Drums are of two sizes, generally containing 1/4 or 1/2 cwt. respectively. +It will be obvious that, although the prime cost may be cheaper with the +larger quantity, it would always be preferable to secure the smaller +drums, as the loss on exposure will be less. + +Most commonly the 56 lb. drum is purchased. It should not be difficult to +calculate the period during which the contents will be consumed, on the +basis of a maximum of 1 lb. per 100 gallons of latex. A 56 lb. drum, +assuming no loss or waste, should be sufficient to treat _at least_ 5,600 +gallons of latex (say, 8,500 lbs. of rubber)--if the bisulphite is of +first-class quality, and the use is applied only to the preparation of fine +pale crepe. + +Where the quantity used per diem is small, it is advised that precautions +should be taken to preserve the quality of the chemical when a drum is +opened. It might be of advantage to place the contents of the drum in +smaller sealed tins, or to have made a special container (with a closely +fitting lid) into which the powder can be placed as soon as the drum has +been opened. + +MIXING SOLUTION WITH LATEX.--Emphasis has been laid, in Chapter VIII., upon +the necessity for care in the preparation of the solution. Equal regard +must be given to the mixture of the solution with the latex. + +On a few estates it used to be the practice to add the powder to the +solution of acid, with stirring. Obviously this led at least to a great +loss of efficiency, owing to the rapid escape of the gas which was evolved. + +The solution of sodium bisulphite should be poured into the latex in as +uniform a distribution as possible. The mixture of solution and latex +should be thoroughly stirred, and if only natives are in charge a minimum +period of five minutes should be prescribed before the addition of the +coagulant. A thorough stirring should again follow the advent of the acid. + +If these elementary rules are not observed faithfully, the deficiency will +most probably be manifested in the dry rubber in the shape of streaks of +varying shades of colour. + +Finally it may be insisted upon that deteriorated sodium bisulphite should +not be used. In order to obtain an effect double the quantity may be +required, and the residual salts left in the rubber on evaporation of the +moisture will be responsible for prolonged drying, surface deposits, and +possibly "spot disease." + +FORMER METHODS OF MAKING PALE RUBBER.--Merely as a matter of historic +interest it may be mentioned that previous to the introduction of sodium +bisulphite pale crepes were made in comparatively small quantity by various +devices, among which the following might be quoted: + + (_a_) Use of excessive quantities of strong acetic acid. + + (_b_) Extreme dilution of latex in conjunction with excessive + quantities of acid. + + (_c_) Extreme dilution in conjunction with steaming and excess of + acid. + + (_d_) Extreme dilution of latex in conjunction with excess of acid and + subsequent heating of the coagulum in hot water. + + (_e_) The use of excess of a mineral acid such as sulphuric acid. + + (_f_) The skimmings and very dilute latex, coagulated with excess of + acid. + +WORKING THE COAGULUM.--Description of the details of necessary machinery +for crepe-making is relegated to Section III. of this book. Here we shall +treat only of the matter in general. + +In the preparation of crepe rubber heavy machinery is necessary, and ample +engine-power must be available. The machines should comprise three types: + + (_a_) With rolls cut in such fashion, and run at such different + speeds, as to have a macerating effect upon the coagulum. Such + machines or rolls will be referred to as "macerators." + + (_b_) Intermediate rolls, grooved in varying designs and geared + differentially. These reduce the thick rough crepe obtained from the + macerators into a form suitable for passing to the rolls described in + (_c_). They are sometimes called "crepers," but as this term may be + applied equally to the macerating rolls, they will be termed the + "intermediate" rolls. + + (_c_) Smooth rolls usually run at approximately even speeds and, as + their name denotes, devoid of any grooving. They are called "smooth" + rolls or "finishers." + +Without such equipment it is not possible to prepare the grade which is +known as "fine pale crepe." In the common acceptation of this term crepe of +No. 1 quality generally connotes fineness and paleness with a thin crepe +which has a good, smooth, and fairly well-knit texture. + +It is, of course, possible to make a thick pale crepe, using only the +macerators and intermediates, but the "finish" will be that typical of the +particular grooving of the intermediate rolls. For the preparation of crepe +ordinarily, the possession of smooth rolls is a _sine qua non_. + +For reasons which will be explained more fully in the chapter dealing with +the defects of crepe rubber, the practice of preparing thick crepes direct +from the coagulum is now very uncommon. Thick crepes are generally made by +reworking dry rubber, either in the form of thin crepes or from air-dried +sheets. The market for the latter in Malaya is confined almost entirely to +Singapore, where factories buy native rubber and re-work it into thick +crepe. + +The bulk of the output of No. 1 crepe from estates is in the form of thin +"fine pale crepe." The artificial standard set up by buyers and brokers +necessitates this thin crepe being of even texture and fairly free from +small holes ("looseness"). What difference the small holes are to make in +the vulcanising properties of the rubber is beyond our knowledge; but such +being the standard, it must be attained if the full price is to be +obtained. + +In order to secure the desired effect the coagulum must be passed +consecutively through the three types of rolls, and undergoes a varying +degree of working in each. + +Given the necessary equipment of machines, it is possible to make a good +specimen of thin pale crepe if the coagulum passes through all the rolls a +total of twelve times (or even less in exceptional cases). There is no +intention of suggesting that this is possible on all estates. Clearly the +number of times the rubber passes through the rolls will depend upon the +total efficiency of the machines. This in turn involves such factors as +(_a_) the size of the rolls, (_b_) the number of machines of each type, +(_c_) the gearing of the pinions, (_d_) the speed of the drive, etc. Again, +much depends upon the nature of the coagulum worked. A fairly soft coagulum +will offer less resistance, and conversely a dense coagulum will require +more machining. + +It has been shown by the writers in previous publications that over-working +of the coagulum has an effect on the vulcanisation of the rubber; and this +has been confirmed by others.[10] Apart from this point, it should be +recognised that over-working, beyond that necessary to produce a thin crepe +of even texture, is to be deprecated, on the ground of economy, in working. + +[10] Bulletin No. 27, Department of Agriculture F.M.S., April, 1918, +"Preparation and Vulcanisation of Plantation Para Rubber," Eaton, Grantham +and Day. + +Owing to the existing differences in equipment and speed of drive, etc., +the regular practice of any one estate may be unsuitable for another. It +remains, therefore, a matter of study for each estate to discover the +minimum number of times which rubber should pass through the machines, +consistent with the factors indicated above. In any case it may be assumed +that if any factory cannot prepare a good crepe by passing the rubber, say, +twelve times through the rolls, there is some deficiency in the machines, +or of speed; the coagulum may be too hard, or the rolls may be badly worn. + +LOWER GRADES OF CREPE RUBBER.--Even a few years ago it was plain that the +lower grades of crepe (_i.e._, all grades lower than first latex rubber) +were not sufficiently appreciated in the market. There was often a marked +difference in price between a first-grade crepe and crepe made from +naturally coagulated lump. This arose chiefly from lack of knowledge. It +has since been recognised in some measure that no reason exists for such a +wide difference in price, and more recently the margin between even the +first-grade rubber and the lowest grade of scrap rubber has been a +gradually diminishing one. Providing sufficient care is exercised in the +preparation of the lower grades, one would expect to see but very small +difference in prices between any two grades. It is true that adequate +attention has been given to the preparation of the scrap grades only in +comparatively recent years, and it is acknowledged that when high prices +were ruling for first-grade rubbers sufficient attention was not generally +given to the subject of the preparation of the lower grades. + +NATURALLY COAGULATED LUMP RUBBER.--The grade of rubber made from the +naturally coagulated lump which forms in buckets and carts is usually of a +mixed colour, due to the fact that the lumps oxidise very quickly. When +they are allowed to remain overnight before being machined, it can be +imagined that the colour of the dry crepe would be very dark, or would +contain very dark streaks. Such is ordinarily the case, unless special +precautions are taken. + +Providing that the coagulated lump is free from bark, leaves, and +leaf-stems, and certain other precautions taken, the difference in price +between coagulated-lump crepes and first-grade crepes should be very +slight. Too often, however, not sufficient supervision is given to the +coagulated-lump rubber, and it is common to see it come into the factory +containing leaves and bark. These should be picked out before the latex is +strained, but obviously it would be better to ensure that they did not +enter the buckets in the first place. + +It would seem reasonable to suppose that if some means could be employed +for preventing or checking the surface oxidation of naturally-coagulated +lump rubber, there would be a corresponding improvement in the colour of +the dry crepe. That such a method is practicable has been demonstrated on +many estates. The lump when lifted out of the latex is allowed to drain for +a few minutes, and is then (without squeezing) placed in a dilute solution +of sodium bisulphite. A 1 per cent. solution is sufficiently powerful. It +is not to be thought for a moment that by the use of sodium bisulphite any +previous oxidation will be counteracted; all that is claimed for the +treatment is that any further surface oxidation will be checked, and the +rubber may be allowed to remain until the next day, for working, if it is +so desired. It will probably be found that quite a quantity of latex has +been expressed from the lumps by contraction, and acid may be added to +obtain the rubber from this. On other estates the lump rubber is worked on +the machines as it is received, and the resulting crepe is submerged in a +weak solution of sodium bisulphite over-night. It is then rinsed in water +and hung to drip before weighing and placing in the drying house. Under +certain conditions some of the lump rubber darkens rapidly during transport +to the store, and any such oxidised portions must be rejected if a uniform +colour is to be expected in the crepe. + +Following the procedure indicated above, some estates find it possible to +prepare from naturally coagulated lump rubber a crepe which can be classed +as No. 1 grade. + +SKIMMINGS AND WASHINGS.--The skimmings of tanks, as already shown, may be +prepared sometimes as a second quality of smoked sheet; but generally they +are amalgamated with the rinsings of cups and buckets, treated with sodium +bisulphite and acid, and made into crepe form. + +The cup-washings, as they arrive at the store, represent a very dilute +latex, the rubber from which is generally of a greyish colour. + +Bucket-washings should yield a good type of pale rubber if they are +obtained properly. To obtain the maximum quantity of good rubber the +buckets should first be rinsed. A gang should be taken, a small quantity +(say a quart) of water poured into the first bucket, and this dilute latex +used progressively in all the buckets of that gang of tappers. The result +is a fair latex which can be added to the bulk of No. 1 latex, provided it +is free from dirt. Where sheet rubber is being prepared, carefully strained +cup-washings or bucket-washings may be utilised in the dilution of the +latex to the required standard, thus increasing slightly the percentage of +first-grade rubber. + +TREE-SCRAP.--As tree-scrap is a naturally coagulated rubber, it should be +expected to show up well in quality. This is usually the case; but from +what has been said of the effect of sun-heat it will be understood that if +trees are not regularly "scrapped," there is a danger that the crepes may +be found to contain tacky streaks due to the inclusion of old scrap which +has been sun-baked. In hot dry weather, on widely planted areas tapped on +alternate days, it has been noticed that scrap remaining for two days often +exhibits a resinous appearance, and feels sticky to the touch. + +If tree-scrap is to be made as a separate grade, as used to be the general +custom, care should be taken to see that it is free from bark and dirt. On +some estates where scrap-rubber is paid for per pound collected, it is +usually the rule to insist that scrap shall be washed free from dirt and +picked free of bark. This course is to be commended, but might probably +prove impracticable to the majority of estates. Theoretically, of course, +the operation of machining should rid the scrap of all traces of bark; but +in practice it does not do so. + +Some proportion of the tree-scrap is usually found to be heavily oxidised, +and naturally if a crepe of uniform colour is to be obtained these dark +scraps must be rejected, otherwise dark streaks will be formed. Coolies +should be instructed to sort out the dark pieces before arriving at the +store. + +BARK-SHAVINGS.--It has been intimated in a previous section that the method +of obtaining and collecting bark-shavings varies with the type of labour +employed. + +Where the scrap is removed from the edge of the bark on each occasion +before tapping, the amount of rubber to be extracted from the dry shavings +is very small--so small, in fact, that when the price of rubber is low, it +is doubtful whether it pays to collect and work the material. + +On the other hand, where trees are not "scrapped" before tapping, the +bark-shavings and tree-scrap are collected together, and the amount of +rubber derived from the mixture may be 30 to 40 per cent. upon the gross +weight--depending chiefly upon the quality of the tapping (_i.e._, in this +case, the thickness of the paring). Another factor influencing this figure +would be the effect of using an anti-coagulant on the cuts. + +Bark-shavings entail such wear upon the ordinary machines during working, +especially if fairly free from rubber, that unless the factory is equipped +with a special "scrap-washer" it is advised that this material should be +sent for working to a factory having the necessary equipment. Whenever +possible, bark-shavings should receive treatment on the day of collection. + +It used to be quite common to see heaps of bark-shavings accumulating on +the floor of a factory, and generating excessive heat. Yet these heaps were +allowed to stand about for a day or days. Is it any wonder then that +tackiness was found to develop when the rubber was dry? It is here +definitely laid down that no heaps of bark-shavings should be accumulated +even for half a day. Tanks should be provided in which the shavings should +be submerged in water. + +EARTH-SCRAP.--Of all grades of crepe this is the one most liable to become +tacky in transit. This tackiness to a large extent cannot be avoided, as +old pieces of earth-scrap may be brought in amongst the bulk. Probably +these old pieces have been exposed to the sun for days, and have become +quite resinous. It would be practically impossible to go through all +earth-scrap in order to find these odd pieces, but unless this were done +one could not guarantee that the earth-rubber would always be free from +tackiness. The difficulty does not appear, however, on estates where +earth-rubber is collected systematically at very frequent intervals. + +FIBROUS MATTER IN LOW-GRADE RUBBERS.--It is sometimes found in this and +other lower grade rubbers that pieces of cloth or cotton-waste are +concealed. Coolies may have used them for cleaning cups, or the store +coolies may have been at fault. Earth-scraps especially should be examined, +before working, for such extraneous matter. + +SCRAP-WASHERS.--These are heavy machines specially devised for the +treatment of lower grade rubbers. In these the raw rubber is well +masticated and freed from impurities, if the machine functions efficiently. + +There are several types of these machines, all of which are efficient. That +best known is the "Universal" washer, made by Joseph Baker, Sons, and +Perkins, Ltd. (formerly Perkins Engineering Company). Coming into local +favour during the War, the "U.E." scrap-washer, made by the United +Engineering Company (Singapore), gives very good service. The "C.C.C." +washer, made by the Colombo Commercial Company, is suitable for the +purposes of an average estate. There are others, less well known. Most of +these machines are made in varying sizes to meet the requirements of small, +medium, or large estates; and if funds are available, a scrap-washer should +be regarded as an essential item in the machinery of any estate employing +engine power. + +The rate of output of scrap-washers will depend mainly upon the speed at +which they are driven, and when ordering the equipment it would be +advisable to state the ordinary speed of the back-shaft, length of drive, +etc. It does not follow that the larger the rate of output, the greater is +the efficiency of the washer. The point is not as to what quantity of +rubber can be taken out per hour, but what quantity is actually freed from +impurities. + +It is advisable for the superintendent to obtain a thorough knowledge of +the general construction and principles of the particular scrap-washer +employed. In the past it was not uncommon to find superintendents innocent +of the fact that a certain type of washer possessed movable parts upon +which the efficiency of the cleansing largely depended. It was often found +that these parts, which were intended to be removed and cleaned at +intervals, had become firmly fixed and could not be removed for inspection. + +It must be recognised also that the machines are liable to considerable +damage if extraneous substances are allowed to enter--for example, +tapping-knives, stones, pieces of iron, spouts, etc., which are sometimes +present in the loose scraps of rubber or shavings, owing to the +carelessness of coolies. Under the best regulated-system, such accidents +occasionally occur, but a great deal of trouble could be avoided by having +it understood that each charge must be sorted over before entering the +washer. + +Again a deal of extra work, and much wear and tear, is caused by the +_abuse_ of the scrap-washer--_e.g._, in the cleansing of earth-scrap. As +this reaches the factory it often contains a quantity of internal or +adhering earth. Before entering the washer a good proportion of the +external soil could be removed if the scraps were thrown into a tank and +given a thorough soaking and stirring. In a similar manner dry +bark-shavings, which have been allowed to accumulate, could be softened. + +In the actual working of scrap-washers instructions are generally given by +the makers. These sometimes advise the introduction of warm water (or of +steam into the cold water supply) for an interval during the working of +each charge. Where possible, such instructions should be followed, as by +this means the individual pieces of rubber are massed together, in the +final stage, into a "sausage" form which is easy to transport and to +manipulate in the ordinary crepeing battery. + +COMPOUND CREPES.--The attitude of both buyers and sellers with regard to +the types of lower grade rubbers appears to be changing. In the past, from +any one estate there might be obtained as many as six grades of crepe below +No. I. These comprised: + + (1) A pale rubber (often streaked) obtained from coagulation of cup + washings and bucket rinsings. + + (2) A pale rubber (often streaked) obtained by coagulation of the + skimmings from the surface of the No. 1 latex. + + (3) A streaked and dull rubber prepared from naturally-coagulated + clots found in cups, buckets, and latex carts. + + (4) A streaked rubber prepared from scrap which had coagulated upon + the face of the cut bark. + + (5) A brownish and streaked rubber made by maceration of bark-shavings + to which pieces of tree-scrap adhered. + + (6) A dark rubber, often tacky, prepared from scrap found in or on the + ground near the base of the trees. As it is often a matter of weeks + between any two regular collections, it is easy to understand why the + dry rubber was more liable to be "tacky" than any other grade of + crepe. + +It will have been evident to all who have acquaintance with these grades, +as shipped from many different estates, that the diversity in the various +shipments must have been rather bewildering. There appeared to be a +regrettable lack of uniformity, even in the appearance of, say, a bark +scrap rubber from any two estates. When, in addition to these variations, +the further complication of condition of cleanliness is introduced, one may +realise the difficulty attaching to the evaluation of these rubbers as they +appeared upon the market. + +Although the foregoing paragraph is written in the past tense, it should be +pointed out that within certain limits the trouble continues to exist with +respect to the output of a great number of estates. + +In the case of many, it has been realised that the manufacturer does not +want to buy a large number of "parcels," all differing in some respect. It +is probably correct to state that what a manufacturer requires is a big +"parcel" uniform in appearance and treatment, even though the colour may +not be so light as that of many smaller lots. This statement is modified +with the proviso that the rubber, no matter what its colour or appearance +may be, must be free from dirt, grit, and bark. + +The difficulty of making a uniform product from several types of lower +grade rubbers has been successfully solved on several estates by the +preparation of a "compound" crepe composed of a mixture of the best lower +grades in approximately definite proportions daily. Naturally the shade of +colour of this compound crepe will depend largely upon the types of rubber +employed, but as a rule it is somewhat darker than the highest of the types +employed in the mixture. To the writers this seems immaterial as long as +the manufacturer is offered a larger and more uniform lot which can be +given uniform treatment in vulcanisation processes. Neither would it appear +that the seller suffers any monetary loss. In point of fact it will be +found probably that the reverse is the case. For instance, supposing it +were decided to mix for a compound crepe-- + + (_a_) Naturally coagulated lump rubber. + + (_b_) Tree-scrap. + + (_c_) Bark-shavings scrap. + +The product would be darker in colour than (_a_) and slightly better than +(_b_). Let it be granted that there might be a monetary loss on (_a_), it +is probable that there would be a slight gain in comparison with the usual +prices obtained for (_b_) and (_c_). Now, as a general rule, the actual +percentage of crop made into (_b_) is appreciably less than that made into +(_c_) and still less than (_b_) and (_c_) together. Apparently, therefore, +there would be a margin of profit on the whole by making a compound crepe. +It may be pointed out, on the other hand, that there might be expended on +the manufacture of this crepe more time and labour, but as against this the +labour of sorting and grading would be simplified. + +Unfortunately this process is not open to estates which do not possess a +scrap-washer. _It is essential that the rubber should be free from grit, +sand, and bark particles._ In the absence of a scrap-washer for the +cleansing of the bark-shavings, it would be futile to attempt to make a +compound crepe containing that type of rubber, as one would run the risk of +spoiling the whole. It seems certain that in course of time a scrap-washer +will be considered as necessary a piece of machinery as an ordinary +crepeing machine in the factories of estates having sufficient means. Until +that time the preparation of compound crepes must be the privilege only of +well-equipped estates, unless other estates can send their lower grade +rubbers for treatment in a scrap-washer to their more fortunate neighbours. + +In previous publications a diminution in the number of grades of crepe +rubber has been advocated, and it is gratifying to find that in many cases +the amending grades suggested have been improved upon. Many estates now +make only three grades of crepe--viz.: + + (_a_) No. 1. From latex coagulated in the store. + + (_b_) No. 2. Compound. + + (_c_) No. 3. Earth-rubber. + +It will be seen that the compound crepe includes all types between fine +pale crepe and earth-rubber. Naturally one could not safely recommend the +inclusion of earth-rubber in any compound crepe, as the risk of possible +"tackiness" in the whole would be serious. In the case of the bark-shavings +rubber to be incorporated, it is first cleaned alone in the scrap-washer. +Then all types are mixed together again in the scrap-washer in proportions +ruled by the experience of the usual average percentages of each grade of +the crop. + +Besides the estates having only three grades, there are others which make +four--viz.: + + (_a_) No. 1. From latex coagulated in the store. + + (_b_) No. 2. Compound, from cup washings, etc., skimmings, and + naturally coagulated lump. + + (_c_) No. 3. Compound, from tree-scrap and bark-shavings rubber. + + (_d_) No. 4. Earth-scrap. + + Other variations are possible, but their number is limited, and they + all conduce to simplification of working, and a supply to the market + of rubber having greater uniformity. + +NEED FOR INCREASED CARE WITH LOWER GRADE RUBBER.--In the ordinary procedure +of estate-working there appears to be an undesirable variety in the style +of lower grade crepes. On some estates an examination of these rubbers +would appear to suggest that there need be no expenditure of care in the +preparation or the form in which it is made. This is a great mistake. With +the exception of the lowest grade (earth-rubber), it would not be unfair to +state that the quality of the rubbers on testing should be very little +inferior to the No. 1 product. Often, as in the case of naturally +coagulated rubbers, they are superior in some respects to ordinary fine +pale crepe. Doubtless manufacturers are aware of these facts, but what +course is open to them if they find the rubber spoiled for their purpose by +the presence of particles of sand, grit, or bark? The possible injury +caused by these ingredients cannot be insisted upon too strongly, and it +must be evident that great care should be exercised in the preparation of +the lower grades of crepe. + +As to the particular form of the lower grade crepe rubber, one may apply +the remarks made under the section dealing with the best grades. It is +common to find thin crepes, medium crepes, and "blanket" crepes. More often +than otherwise, the medium and thicker crepes are prepared direct in those +forms. It follows that they are liable to attacks of "spot" disease, which, +however, is not easily visible in the lowest grades, owing to the dark +colour of the rubber. Furthermore, it is not possible to cleanse the rubber +so thoroughly if thick crepes are made. + +BLOCK RUBBER.--Few estates now prepare block rubber, which is essentially +crepe rubber pressed into blocks. In the ordinary process the fresh +coagulum is lightly rolled into thin crepe, which is then vacuum-dried. +There are slight variations in the subsequent procedure. Sometimes the +rubber as it comes from the vacuum drier is merely allowed to remain on +racks overnight before blocking. In other instances, the sticky rubber from +the vacuum drier is passed once or twice through wet, smooth rolls and hung +to dry for some days. The dry crepe is then folded into the pressing box or +cut to suit the size of the box. Pressure is applied for some time, and +finally the rubber is taken out in one homogeneous mass. Naturally the +appearance of the block depends upon the quality of the parent crepe. Some +block rubber is made up thick; other is made in slabs about 3 inches or 4 +inches in thickness. With the latter, it should be possible, when held up +to the light, to see the shape of a hand held between it and the source of +light. + +It is possible that an erroneous idea of the strength of block rubber has +been formed. It should only be necessary to point out that essentially +block rubber is merely pressed crepe rubber. It is inconceivable that the +mere action of pressing layers of crepe together would increase the +physical quality of the rubber. + +The advantages which block rubber possesses are the compactness of the +output, its ease of packing, and a saving in freight; but there is the +disadvantage, from the consumer's point of view, that extra labour is +involved in the preparatory work of cutting up the blocks. + +SMOKED CREPE AND SHEET CLIPPINGS.--There appears to be no certain demand +for any grade of smoked crepe, and probably all which is put into the +market is really comprised of (1) clippings obtained from the ends of +sheets, (2) sheets which have been malformed in machining, or (3) sheets +showing the presence of many "bubbles." + +As to the first class it might be explained that through defective rolling, +thick ends or edges may be caused. These show signs of contained moisture +when the bulk of the sheet is perfectly dry, and as undue delay would +otherwise result these moist strips are trimmed and either returned to the +smoke-house, or machined to form crepe. + +Similarly a torn or otherwise badly formed sheet, when brought from the +smoke-house, may be made into crepe, rather than it should prejudice the +selling price of the bulk under ruling conditions. + +In the same manner, although "bubbles" have no influence upon the quality +of the rubber on vulcanisation, sheets thus affected are generally made +into crepe. + +It cannot possibly be argued that rubber of this description would be in +any way inferior to the best smoked sheet for manufacturing purposes, but +owing to the prevailing system of evaluation for market purposes, it is +necessary to resort to the expedients indicated above. + +On some estates the rubber specified in the three classes mentioned is not +made into crepe, but cut up into small pieces and shipped as "sheet +clippings" or "sheet trimmings"--a procedure which would appear to be +justified by a steady demand. In point of fact, the buyers are really +obtaining a first-class article (except in superficial appearance) at a +reduced price. + + + + +CHAPTER XI + +_DRYING OF RUBBER_ + + +AIR-DRYING OF CREPE.--It is still the prevailing custom to air-dry crepe +rubbers. A few estates, it is true, have artificial driers installed, and +in some necessary cases others will be erected. But in the majority of +cases where money has been expended in building air-drying sheds, as long +as it is only possible to ship rubber regularly air-drying is likely to +remain in favour. + +The great drawback to air-drying is that one is so dependent upon the +weather conditions. In favourable weather the rubber dries well, but in a +long period of wet weather rubber may accumulate at an alarming rate, and +the accommodation is sometimes severely taxed. Of course, the rate of +drying under the best conditions is mainly dependent on the thickness of +the crepe, and every endeavour should be made to maintain a thin style of +preparation. If this precaution is not taken, the rubber is liable to +recurrent attacks of "spot" disease, and one's troubles are very much +augmented. This is a disability to which rubber treated in artificial +driers is not liable. Still, air-dried rubber can be made equal, if not +superior, in appearance to pale rubbers prepared by other processes. + +For the lowest grades of crepe air-drying is always likely to remain the +only method, as it would be extremely unsafe to submit them to heat. + +It is noted in ordinary practice that the rate of drying on different +estates, for the same type of rubber, may vary widely. Naturally the +construction of the house has a great effect, and this subject will receive +attention in a subsequent chapter. + +Similarly the position of the drying-shed exerts an important influence, +and the erection of the building in low-lying surroundings is always +calculated to prolong the drying period appreciably. Incidentally this +means that the building must be larger than a normal rate of drying would +otherwise demand. + +The combination of a poor type of drying-house, a low-lying situation, and +a prolonged wet season, might render it advisable to abandon the air-drying +of high grade crepes in favour of artificial drying. + +ARTIFICIAL DRIERS FOR CREPE.--It is more common to find artificial driers +in use in Ceylon than in Malaya, possibly because these driers have been in +use in Ceylon for other products. Some time ago the question of installing +artificial driers received the serious attention of a number of estates in +this country, chiefly on account of the incidence of fungoid and bacterial +diseases in crepe rubber. The simple treatment for the prevention of these +diseases is to get the rubber dry in the shortest possible space of time. +In most cases it is found sufficient to roll crepe thin for air-drying in +order to prevent the appearance of coloured spots. It is found, however, +that some drying-houses are so badly planned and constructed, that quick +drying under even the best of conditions is a practical impossibility. +Cases have been known in which the disease may disappear almost entirely +during a period of freedom from rain, only to recur as soon as wet weather +sets in again. There can be no doubt that, on the whole, the number of +cases of "spot" disease is on the decline; but equally it is certain that a +very few estates will always be liable to outbreaks as long as drying is +attempted in existing houses. For these reasons it is a poor policy to +temporise, and the only sound policy in extreme cases would be to give up +ordinary air-drying in favour of some method of artificial drying. As +regards the majority of estates preparing pale crepe for various reasons, +it is not expected that any will instal artificial driers. Money has been +expended in elaborate buildings which certainly do the work for which they +were designed. As long, therefore, as the accommodation is sufficient, and +regular shipments are the rule, it is expected that ordinary air-drying +will still remain the general practice. + +Of the better-known artificial driers, there are only three which merit +serious consideration in these pages. They are the vacuum driers, the +Colombo Commercial Company's hot-air drier, and the Michie-Golledge +process. + +VACUUM DRIERS.--The vacuum drier is so well known that only a brief +description need be given. It consists of a chamber heated by steam pipes +and capable of having the contained air and moisture withdrawn by a pump. +This description sounds very simple, and in practice the operation of +vacuum drying is really a simple one, and can well be entrusted to an +intelligent coolie under efficient supervision. Indicators are fitted which +show the vacuum pressure and the pressure of steam in the heating pipes +which travel underneath horizontal slabs upon which trays may be placed. +Still, in spite of the apparent simplicity of the process, there would +appear to be a number of little details which, if overlooked, prove to be +factors influencing the result to a considerable degree. Thus it is not +uncommon to find complaints that the rubber is not dry when packed. The +writers have seen rubber taken from a vacuum drier still containing a +visible quantity of moisture. One would have imagined that continuous +working of the drier would give the experience necessary to obtain dry +rubber, but, apparently, such is not the case in a number of instances. +Elaborate instructions are given by the makers, but often they are more +honoured in the breach than in the observance. Really, there are only two +points to bear in mind: + + (1) That the rubber must be fairly thin. + + (2) That the temperature be not allowed to rise too high. Some makers + advise 140° F. as a maximum, but no harm results from a temperature of + 150° to 160° as long as the interval is not prolonged.[11] + +[11] These figures refer to temperatures recorded by thermometers placed in +the folds of the rubber. + +These two points presume that the vacuum drier is true to its name, and +that one can obtain a maximum steady pressure. The machines are so well +made now that no drier should be taken over from those responsible for its +erection unless it can show a vacuum pressure of 28 inches within fifteen +minutes of starting the pump; and with the pump stopped, there should not +be a greater fall in pressure than 1 inch within ten minutes after stopping +the pump. + +One of the most frequent sources of error is the control of steam pressure +which is responsible for the temperature of the drier. It is quite +unnecessary and unwise to maintain any steam pressure once the drying is +well under way. All that is necessary is to heat the chamber well, with a +steam pressure of 5 lbs., before inserting the rubber. As soon as the +maximum vacuum pressure has been obtained, steam should be shut off from +the heating pipes, and it will be found that the temperature is well +maintained throughout the operation with a rise of ten to twenty degrees at +the end. If the drier is working at a vacuum pressure of 28 inches, and if +the crepe has been prepared thin enough, the rubber should be quite dry +within two hours. Should the operation have to be extended to two and a +half hours at 28 inches vacuum pressure, it is a sign that the crepe is too +thick. On such occasions it is often noticed that these thicker crepes are +not thoroughly dry, having moist spots enclosed in them. On re-rolling, +these moist patches become easily visible, and are a source of great +annoyance, inasmuch as they take quite a long time to dry out. + +As mentioned before, the crepe for vacuum drying should be thin. There is +no necessity to give it a superfine finish, and the presence of small holes +is quite permissible, as they disappear on subsequent re-rolling. The thin +crepe may be folded loosely to the length (or breadth) of the tray several +times, but in no other way can the drier be expected to perform its work +satisfactorily. A case was noted in which thin crepe was excellently +prepared, and four or five layers were rolled together for vacuum drying. +Naturally this mode of procedure does not give the drier a fair chance, and +it would be ridiculous to judge vacuum drying on the results. After two and +a half hours at a temperature of 145° F. the rubber appeared to be only +about three parts dry, and the subsequent air-drying extended well into a +fortnight. + +It is the common practice to screw up the door of the chamber as tightly as +possible. As a rule it is found in course of time that the obtainable +maximum vacuum pressure decreases. This may be attributed solely to the +forcible screwing up of the door. Around the inside edges of the door are +strips of rubber compound, the function of which is to form a tight joint. +Should the door be screwed up too tightly, these strips become deformed in +course of time, and slight leaks occur. It should be pointed out that it is +only necessary to screw up the door at the beginning of the operation. When +the vacuum has been obtained, the screw pressure may be released, as the +atmospheric pressure outside the chamber is more than ample to keep the +door in a close fitting position. This will be obvious from the fact that +the difference in pressure between the inside and the outside of the door +amounts to, say, 28 inches atmospheric pressure--_i.e._, nearly 14 lbs. per +square foot. By slackening the screw handles, therefore, as soon as the +indicator shows the maximum working vacuum pressure, the life of the door +joints may be prolonged, and the drier will remain efficient for a longer +time. + +A careful consideration of the question of temperature leads one to the +conclusion that the practice of placing a thermometer through the roof of +the chamber does not enable one to determine the temperature correctly. In +the same way a thermometer suspended behind the observation window cannot +indicate the temperature of the rubber, as in both of these positions the +thermometer must be influenced by radiation from the walls of the chamber. +The only position in which the correct temperature could be indicated is +between the folds of crepe. This can be arranged easily so as to enable one +to read the temperature from the observation window. + +COLOMBO COMMERCIAL COMPANY'S DRIER.--The drier of the Colombo Commercial +Company consists in principle of a number of small chambers or units in +which crepe rubber is placed, and through which hot air is passed. As in +the case of vacuum drying, a great deal depends upon the preliminary +treatment of the rubber. If the crepe is not rolled thin enough drying will +be unduly prolonged, with a possibility that the rubber will become tacky. +The temperature usually obtained is about 150° F., and if the rubber is +thin the production of an installation of two chambers should be at the +rate of 1 lb. of dry rubber per minute. The usual period of drying is +under two hours. One advantage which this drier has over the vacuum drier +is that the chamber can be opened at any time for a short period to +withdraw or insert trays. The thin crepe is folded several times, as in the +case of vacuum-drying. + +Figures obtained from the actual working of a drier in Ceylon are given +below: + + -------------------------------------------------+----------------------- + CHAMBER 1.--TEMPERATURE 160°-180°F. | + -------------------------------------------------|CHAMBER 2.--TEMPERATURE + _NO. OF | _DRYING | _WEIGHT OF | _WEIGHT OF | 150°-165°F. + Tray._ | Period._ | Wet Rubber._ | Dry Rubber._ | + --------+----------+--------------+--------------+----------------------- + |Hrs. Mins.| Lbs. | Lbs. | + 1 | 1 22 | 7-1/2 | 6 |Worked similarly + 2 | 1 42 | 7-1/2 | 6 |to No. 1. Yielded + 3 | 1 57 | 7-1/2 | 6 |in 2 hrs. 23 mins. + 4 | 1 57 | 7-1/2 | 6 |70-3/4 lbs. dry rubber, + 5 | 1 57 | 7 | 5-3/4 |from 87-1/2 lbs. wet + 6 | 1 57 | 7-1/2 | 6 |rubber. + 7 | 2 0 | 7-1/2 | 6 | + 8 | 2 0 | 7-1/2 | 6 | + 9 | 2 11 | 6-1/2 | 5 | + 10 | 2 11 | 7-1/2 | 6 | + 11 | 2 11 | 7-1/2 | 6 | + 12 | 2 18 | 7-1/2 | 6 | + --------+----------+--------------+--------------+----------------------- + | | 88-1/2 | 70-3/4 | + --------+----------+--------------+--------------+----------------------- + +It will be seen, therefore, that the drier had an output in 2 hrs. 23 mins. +of 141-1/2 lbs., which is at the rate of 1 lb. per minute approximately. + +As the rubber leaves the driers it resembles vacuum-dried rubber in being +surface-sticky. This stickiness is only temporary, and is got rid of by +passing the crepe through wet rolls. Opinions differ as to when this +rolling should be given. On some estates the rubber is only allowed to cool +a little before passing through the rolls; on others it is given a day or +so before rolling. The methods of rolling also differ. In some factories +the rubber has been cut to lengths before drying, and these lengths are +merely rolled together by simple pressure. Other estates prefer to +re-macerate the crepe while still fairly warm and soft. It is probable that +little harm, if any, results from this re-maceration while the rubber is +soft, as it is more easily worked in this condition. The thick rubber is +then generally hung for a few days to air-dry before packing. As most of +the moisture taken up by the dry rubber is surface moisture, three or four +days is usually found ample for air-drying. + +MICHIE-GOLLEDGE SYSTEM.--The Michie-Golledge system comprises a process of +preparation and drying. The latex is diluted with two, three, or four +volumes of water and coagulated with acid in a vessel which is rotated with +a churning motion. In this cylinder there are curved and fixed blades. The +revolving cylinder and its ribs force the latex against the curved blades +so as to cause an eddy in the middle of the machine. Here the rubber +coagulates and accumulates, the remaining liquor whirling round outside the +blades. It can be imagined that with such dilute latex, the coagulum is +very soft and spongy. This soft mass is passed through a machine which cuts +it into "worms" about 3/16 inch in section. These are placed upon wire +trays and dried by means of hot air. The "worms" when dry are re-macerated +and built up into medium and thick crepes. The colour of the rubber +prepared by this process is usually very good. When treated in a Colombo +drier the "worms" usually require about two hours to dry, so that crepe +rubber may be packed at latest on the fourth or fifth day, as in the case +of vacuum-dried rubber. + +RATE OF AIR-DRYING OF CREPE RUBBER.--In spite of the facts that some +estates have been making thin pale crepes for years, and that so much has +been written concerning the preparation of this grade of rubber, one +occasionally meets with a case in which an estate seems to be unable to +prepare thin pale crepe, or if it does the period of drying is much longer +than obtains on most estates. + +Again, when cases of infection by spot disease in fairly thin crepes are +submitted, it is usually found that the particular crepes are of that type +which, though fairly thin, show whitish spots of moisture when the bulk of +the rubber is nearly dry. This type of crepe is to be noted for the +excessive period of drying in comparison with other crepes of equal +thinness. It has been advanced elsewhere[12] that a factor of the most +considerable importance in the rate of drying of crepe rubber is the type +of drying-house and its situation. This accounts very largely for observed +differences in the rate of drying of thin crepes on different estates. Yet +even where two drying-houses may be of the same type, and the situations +may be comparable, one still observes that one thin crepe dries more +quickly than another. It has been remarked also that a thin crepe in one +old drying-house dries in a shorter period than a similar crepe in another +more modern house, although the methods of coagulation and preparation +exhibit no apparent diversity. In all these conflicting cases allowance is +made for the weather conditions, and the observed differences seem to be +inexplicable. It has always been the opinion of the writers that the actual +rolling of the rubber plays an important part in determining the rate of +drying of crepe, apart from the question of thinness; and it seemed +possible that this factor would account for the discrepancies noted above, +either partially or wholly. + +[12] "Preparation of Plantation Rubber," Morgan, 1913, chapters xii. and +xiii. + +With a view to determining to what degree the drying of crepe rubber was +hastened by the extent to which the rubber was rolled, experiments were +made. It was hoped, also, that some idea would be gained of the particular +stage in crepe rolling which had the greatest effect upon the rate of +drying. In preparing crepe in the estate in the ordinary way the coagulum +is passed through three sets of rollers, and the stages may be described +as: + + (1) Rough rolling. + + (2) Medium rolling. + + (3) Smooth rolling. + +In the first the coagulum is broken down by passing through the machines +until a thick rough crepe is formed. This passes to the intermediate +rollers, where it is worked down to a medium crepe. The rubber finally goes +to the smooth running at approximately even speeds. Passing through these a +number of times it emerges as a thin uniform crepe, free from "lumpiness" +and free from holes, which should dry in from ten to twelve days. + +In the experiment the rubber was passed through the machines with varying +frequency, the number of times in each machine being progressively +increased, while the working on the other machines remained constant. + +It was determined that the rate of drying was affected only by the extent +to which the crepe was worked in the smooth rolls. The less often the +rubber passed through these rolls, the slower the rate of drying. Beyond a +limit in the other direction, increased rolling did not reduce the period +of drying. It follows, therefore, that crepes which have a good thin finish +should dry in a minimum period. + +[Illustration: DRYING GRAPH. PALE CREPE (THIN).] + +WHEN DOES AIR-DRYING TAKE PLACE?--Experiments[13] were conducted with a +view to discovering, if possible, the rate at which crepe rubber dries, and +the extent of drying during the night under weather conditions such as +prevail ordinarily in Malaya. It is to be remembered that, during the day, +most drying-houses are fairly open and that the temperature ranges from +about 88° F. in the lower rooms to over 100° in the upper rooms (near the +roof) when the sun shines. At night, however, there is usually a decided +drop in the temperature, and unless it is a very clear night the air is +generally saturated with moisture. In addition the drying-house is closed +as thoroughly as possible, and we should expect the atmosphere of the house +to be laden with moisture from the wet and drying rubber. It would be a +just inference, therefore, that the rate of drying during the night would +be much less than the rate of drying during the day, and the results of +experiments confirm this very fully. One was hardly prepared, however, to +find that, under certain circumstances and at a certain stage, the amount +of drying is nil; not only so, but it was found under certain conditions +that the amount of drying which took place was negative--_i.e._, the rubber +weighed slightly more when taken out in the morning than it had weighed the +previous afternoon. + +[13] Rubber Growers' Association, Malaya Local Report, No. 2, 1914. + +CREPE MAY INCREASE IN WEIGHT.--As an instance of the kind of result +obtained a graph is here given of the rate of drying of a batch of pale +crepe. This was hung to dry in the top room of a drying-house in which +rubber ordinarily dries quickly. The rubber was hung in a good position, +with the bulk of output, near a window which was open for some time during +the day. In order to restrict the day interval of drying to the actual +period in which the sun was likely to be in evidence, the day was taken to +begin at 8 a.m. and end at 4 p.m., the night interval covering the +remaining sixteen hours. Thus the night interval was twice as long as the +period of day drying. The lengths of crepe were weighed carefully at 8 a.m. +and 4 a.m., and the average of the several weights was plotted in a graph. + +The weights are placed vertically and the duration of drying horizontally. +It will be seen that the rubber was quite dry and fit for packing on the +sixth day, as far as could be judged in the usual way by casual inspection. +Peculiarly enough at this time it weighed slightly more than had been +registered on the fourth and fifth days, but the difference did not amount +to more than about 0·4 per cent. In examining the graph it should be borne +in mind that the steeper the slope of the curve downwards the quicker the +rate of drying, and that when the curve takes an upward direction there is +an addition of moisture instead of abstraction. It will be noted that when +drying takes place the slopes more nearly approximating the vertical +represent the extent of day drying, and that often the night drying is +represented either by a very flat curve or even by an upward curve which +shows the addition of moisture. A striking feature of the experiment is +shown by the rapidity with which drying takes place during the first few +days and the comparative slowness with which the remaining moisture is got +rid of. Thus, from the graph, it may be calculated that about 80 per cent. +of the total moisture content was lost in the first two days, and over 93 +per cent. in two and a half days. Yet three days had to elapse before the +remaining 7 per cent. of total moisture was lost--_i.e._, before the rubber +was judged to be ready for packing. It will be seen that after this stage +had been reached the rubber alternately lost and gained in weight, with a +tendency to increase. This increase was attributed to the presence of +surface moisture after hanging overnight, when the rains had become +frequent. Some light is thus shed upon a subject which has puzzled both +shippers and receivers of crepe rubber. + +DIFFERENCES IN WEIGHT.--It will be obvious that if rubber is allowed to +hang after becoming dry, and is taken down, packed, and weighed in the +early morning, it will weigh more than when it reaches a drier climate. The +loss in weight under such circumstances might amount to even 1 per cent. It +may seem to some an unnecessary refinement to introduce, but it would +appear from the graph that rubber should be packed for preference in the +afternoon if the weights are to be more nearly correct. + +It is extremely singular to note how quickly the curve changes its slope +after the major portion of the moisture has evaporated, and it will be very +plain that in the last stages any decrease in weight during the day would +appear to be counterbalanced, or more than counterbalanced, by the addition +of moisture during the night. It may be pointed out, however, that this +increase in weight during the later stages of drying of pale crepe is +mainly, if not altogether, due to surface moisture. The chief point of +interest is the fact that in the case of thin pale crepe, quite 80 per +cent. of the total moisture content is lost during the first two or three +days, and that, owing to the negative influence of the night atmosphere, +the final drying is delayed. It will be understood that the foregoing +results applied to thin pale crepe. Thin lower-grade crepes appeared to dry +at more uniform rates, but the differences between the rates of drying at +night and during the day were similarly notable. + +AIDS TO NORMAL AIR-DRYING.--These experiments were undertaken in a +drying-house, favourably situated for rapid drying, in which the average +period of drying for thin crepes is nine days. It is easy to imagine that +the condition of affairs as revealed would be much exaggerated in a +drying-house situated on low-lying ground and surrounded by trees. In +extreme cases of this nature the use of large fans and heating pipes has +been advocated. It is believed that in some cases these installations have +given satisfaction, but that in others the degree of improvement obtained +has not been in economic proportion to the outlay incurred. + +SMOKE-CURING OF SHEET RUBBER.--It will have been evident that one of the +disadvantages of air-drying sheet is the incidence of moulds. Now it is +found that moulds should not develop in smoke-curing; and if they do, then +the smoke-curing has been insufficient or inefficient. The difference in +the drying period also is a strong argument in favour of smoke-curing, so +that all-round it is seen that there are many valuable advantages to be +gained by smoke-curing sheet in comparison with air-drying, and no +disadvantages. + +The manipulation of the rubber, after it leaves the marking rolls and +preparatory to smoke-curing, has been discussed in Chapter IX. It is +sufficient only to allow adequate time for furnace water to drip from the +sheets before transferring them to the smoke-house. As it is the general +rule to roll sheet rubber in the morning, this arrangement fits in very +well. The furnaces of the smoke-house are usually extinguished as soon as +the sun is well risen, and the rest of the day is occupied in sorting dry +sheets, etc. Towards noon the day's wet sheets should have been admitted, +and smoking may be commenced as soon as the sun is well in the west--say, +at half-past four o'clock or earlier. + +It used to be the custom on a few estates to smoke during the daytime and +to discontinue smoking at night. As the night-air in Malaya is usually +heavily laden with moisture, it will be plain that such a policy was a +topsy-turvy one. It is vastly more reasonable to smoke-cure at night; +usually the heat of the sun during the day is quite sufficient in itself to +promote the drying of rubber; but there is no reason why smoking should not +be carried on in the daytime in wet weather, should it be found expedient +to do so. + +RECORDING INSTRUMENTS.--During the night the care of the smoke-houses is +usually in the hands of natives, except for occasional surprise visits from +a European superintendent. To all acquainted with the ways of the native it +must be plain that means must be provided for the checking of the +temperatures attained in the smoke-house. Ordinary thermometers are quite +unsuitable, and even thermometers registering maximum and minimum +temperatures are of little avail, inasmuch as they record only the degree +of heat attained at a particular moment, and do not indicate any period +during which a particular temperature was maintained. + +It is evident that something more informative is required. There are many +types of suitable recording instruments or "pyrometers," some of which can +be electrically connected, so as to cause the ringing of a bell, placed in +the superintendent's office or house, on the attainment of a certain +temperature. The type best known in estate practice is that named the +"Thermograph," in which a pen traces a curve or graph on a plotted piece of +paper carried by a rotating cylinder which is actuated by clockwork. Such +instruments can be purchased through most of the local firms dealing in +estate supplies. From experience it can be asserted that, given intelligent +attention, these instruments yield very satisfactory results. The apparatus +should not be placed always in one position in the smoke-house, but should +be moved frequently so as to obtain information regarding the distribution +of heat. + +TEMPERATURE OF SMOKE-CURING.--In the question of temperature of drying, it +is well to be as strict as possible; not that any great harm will result +from a rise of 10° above that recommended, but because the higher the +temperature recorded the larger the fires must have been, and consequently +the more real danger there was of the store becoming ignited. It has been +shown[14] that the temperature giving the maximum benefit of drying and +quality was found experimentally to be rather above the temperature usually +prescribed for smoke-houses, but in the experimental work there was no +danger from fire. + +[14] "Preparation of Plantation Rubber," Morgan, 1913, chapter x. + +The figure given in previous publications as a maximum working temperature +for smoke-houses was 110° F., but certainly the temperature may be as high +as 130° if it is considered safe to allow fires to be so arranged. One or +two estates are known to work at temperatures of 130° F. and over, in spite +of the recommendations of the writers. If those estates care to risk it +they may do so, with increased rapidity of drying; but no responsibility +can be taken for whatever may happen in smoke-houses where the temperature +is allowed to remain, as in one case, at 160° F. Naturally the range of +temperature is strictly limited by the properties of the substance to be +treated, and with a substance such as rubber it would be far better to err +on the side of caution than to risk damage to such a commodity, apart from +the consideration of the possible destruction of the building. + +PERIOD OF DRYING.--Considerable differences are noted in the periods of +drying on various estates; but, as there is more than one factor +influencing the results, it is not easy at first to find why these +differences should exist. Really there are three factors: + + (1) Relative thickness of rubber. + + (2) Extent and quality of rolling. + + (3) Temperature of drying. + +It is presumed that the smoke-houses are identical in type and efficiency, +and that smoking is in force for the same length of time each day. There +need be no discussion of these points; the effect of each is so obvious. +The thinner the sheet, the quicker the rate of drying; the better the sheet +has been rolled, the shorter the period of drying; the higher the +temperature, the more rapid the drying. + +It has been shown in Chapter IX. that the condition of the sheet after +rolling depends primarily upon the standard of dilution of the latex and +the original thickness of the coagulum. If these factors are correctly +controlled, the rolling should give a sheet which is fairly soft and +porous--_i.e._, it should not have been subjected to such pressure as to +make it both thin and hard. An average sheet of rubber which has been well +rolled should be smoke-dried at a temperature of 120° F. in about ten days. +If sheets take appreciably longer to dry, then the three foregoing factors +must be examined. + +On the other hand, it is often found that thin sheets made from very dilute +latex dry so quickly that they are considered to be fully smoke-cured in +from five to seven days. It frequently happens in such cases, however, that +the smoking is insufficient, and by the time the rubber reaches home it has +begun to show signs of surface moulds. It is evident, therefore, from this +discussion that: + + (1) If smoked sheet develops surface moulds within a short period + after smoking, the duration of curing has been insufficient, or the + quality of the smoking is at fault. + + (2) The actual time taken to smoke-dry rubber may be insufficient to + smoke-cure it. + + (3) The rate of drying of smoked sheet depends upon-- + + (_a_) The relative thickness of the rubber. + + (_b_) The preliminary treatment of rolling. + + (_c_) The temperature of the smoke-house, and + + (_d_) The type of smoke-house used. This point will be treated + in a subsequent chapter. + +FUELS FOR SMOKING.--The general idea formerly held was that the beneficial +effects of smoking were to be attributed to the constituents of the smoke, +and chiefly the creosotic substances. This is not now the opinion of the +writers, who attribute the effect largely to the temperature of drying and +constituents of the smoke other than creosotic substances. There can be no +doubt that the presence of creosotic bodies is responsible largely for the +absence of moulds and the existence of the typical odour, but it is +becoming increasingly known that the employment of substances rich in +creosote is not required or desirable. + +Estates used to be put to considerable expense in the purchase of "bakau" +(a mangrove timber rich in creosote and creating much heat), under the idea +that it was the best material and almost indispensable. Most estates now +restrict themselves to the consumption of timber obtained from their own +areas. Thinning-out programmes are largely responsible for the supply, but +the local authorities are much concerned regarding future supplies; and +consideration has been given in some quarters to the question of the +development of quick-growing trees on estates with a view to safeguarding +the future. This seems to be desirable, as it is difficult to imagine that +the place of timber can be taken by any other material in the smoke-curing +of rubber. Unless some such precautions are taken it is not difficult to +predict that, in course of time, some estates will be able to continue the +preparation of smoked sheets only at considerable expense in obtaining +suitable fuel from a distance. + +It is not true that _any kind of timber_ is suitable as a fuel to be used +in a smoke-house. All timbers are suitable, either alone or in mixture with +others, provided that the wood is not too green. + +Naturally an absolutely dead and crumbling wood will smoulder, but does not +develop sufficient smoke. A green timber will give an acrid and moist +smoke, but demands the consumption of a certain amount of dry timber in +addition if it is to be used. + +Rubber-tree prunings and sawn rubber trees obtained by thinning-out may be +used in mixture with dead wood, provided the logs are stacked to dry in the +sun for some weeks before use. If the timber is too green, steam is formed +as well as smoke, and the sheets of rubber may have a moist surface glaze. + +SUN-DRYING SHEET RUBBER.--Among the first curious sights which impress the +visitor or newcomer to this country is the spectacle of sheet rubber +hanging in the sun on native holdings. From what one has learned of the +extraordinary care which must be exercised in all the processes of rubber +preparation, one fails to understand how such rubber reaches the market +without becoming tacky. That some of it does become slightly tacky is +certain, but on the whole native rubber, though crudely prepared, is +usually sound. The native idea of giving sheet rubber a preliminary drying +in the sun is to hasten the total period of drying. That the period is +curtailed would seem to be the case, but it is open to doubt, as the effect +of sun-drying, if unduly prolonged, is to create a thin surface film of dry +rubber which retards the drying of the rubber below the surface. Working +with wet crepe rubber, the writer found that, to all external appearances, +there was no effect upon the rubber when it was allowed to sun-dry for four +or five hours. With periods of from six to ten hours the crepe becomes +slightly sticky, chiefly on that portion across the support. When removed +to the air-drying house this tackiness developed further, and the rubber, +on the line of support, became so weak that it stretched and broke. + +Reasoning by analogy, it would appear that no apparent harm would result to +sheet rubber from sun-drying for periods up to four or five hours. From +experience (see Chapter IX.), not the slightest ill-effect is found to +result from the short interval of preliminary drying or dripping practised +on many estates preparatory to smoke-curing. + +ARTIFICIAL DRIERS FOR SHEET RUBBER.--It is understood that when vacuum +driers were first applied to the drying of rubber it was thought possible +to dry sheet rubber in this way. The practice was found to be impossible, +as the length of time required and the temperature were responsible for the +destruction of the form of the rubber; it became tacky and semi-liquid. + +THE "CHULA" DRIER.--Although several suggestions of devices for +artificially drying sheet have been made, only one is known to be in use at +the present time. In the original form this was used for drying other +tropical products. It consists of a large iron chamber, in which are +several compartments divided by means of baffle-plates. At one end there is +a small furnace and, by means of a fan, smoke and hot air are drawn +through the compartments. Owing to the temperature attained (140° to 160° +F.) sheet rubber cannot be completely dried in the chambers, and is, as a +rule, only treated in this manner for one or two days. Drying is then +completed in an ordinary air-drying house. It is claimed that drying is +expedited, and that the rubber can be packed in ten days. + +In the more recent modification, the smoke and hot air which leave the +Chula drier pass through a large room in which may be hung either sheet or +crepe rubber. It would seem that all sources of danger have not been +eliminated from the process, as on one estate a wooden room containing +rubber was ignited by a spark which passed through the drier. + +Yet another form exists in which the furnace is outside the main building, +and in the ordinary course of working only heats a series of open pipes +through which air is drawn by a powerful fan. By means of a valve it is +possible to allow smoke from the furnace to pass into the room with the hot +air for the preparation of smoked rubber. The hot air or smoke is +distributed in the lower room by means of main and branch pipes, and passes +through an open floor to the room above. With such an arrangement it is +possible, therefore, to prepare either air-dried or smoke-cured rubber. If +the method could be successfully applied to the drying of crepe it would be +of great assistance on some estates. There would seem to be a difficulty in +working it for the drying of sheer rubber and crepe together, as the +temperature suitable for the one is excessive for the other. Given an +efficient control over the temperature of the hot air, the house should be +successful in the drying of crepe, provided the rubber is not hung in folds +of too great length. For smoke-curing sheet rubber the period is said to be +reduced by several days in comparison with the time occupied in an ordinary +smoke-house, but it is not clear that such a system would have any +advantage over a modern smoke-house, in types of which rubber can be fully +cured in periods ranging from five to ten days. + + + + +CHAPTER XII + +_SORTING, GRADING, AND PACKING_ + + +The question of standardising the output of our plantations is one which +has occupied attention for some years, with a not inconsiderable degree of +success. + +Meanwhile opinion is growing in favour of proceeding along the line of +reducing the number of plantation grades to a minimum. At present some +confusion exists. Some estates make up tree-scrap and bark-shavings +together; one estate puts tree-scrap, earth-scrap, and bark-shavings into +one uniform crepe; other estates have three or more separate scrap +grades--_e.g._, lump-rubber and "washings," tree-scrap, earth-scrap, and +bark-shavings scrap. There is a movement on foot at present to try to +restrict plantation rubber to three grades: + +CREPES--1. _First Quality Latex._--_I.e._, crepe made from the true +coagulum obtained from the regulated coagulation of strained latex. This is +a pale rubber, and may be prepared satisfactorily if the directions given +in preceding chapters are followed. Naturally there must be, in all +factories, some defective rubber of this grade. For various reasons the +crepe may be of inferior colour, or is slightly contaminated with dirt or +traces of oil and grease, etc. This defective rubber should be placed aside +most rigorously and plainly marked as "off-quality." + +If a proper scheme of standardisation of latex and chemicals is followed, +there should not be any such variety in shades of colour, such as was +common in No. 1 crepe in the past. + +Comparatively few estates in Malaya now prepare thick (or blanket) crepes +in the No. 1 grade, but in such cases the same rules must be applied as +govern the sorting of thin fine pale crepes. + +2. _Compound Crepe, No. 1._--In this it is proposed to include +cup-coagulated lumps, coagulated lumps from transport vessels, skimmings, +bucket rinsings, cup-washings, and tree-scrap. It has been shown in Chapter +X. that strict care is necessary to eliminate all oxidised (dark) scraps. +These are relegated to a lower grade. The possession of a "scrap-washer" is +necessary if the best results are to be obtained. + +On some estates the ingredients of this compound crepe, while fresh, are +placed in a common jar or tank to which a quantity of sodium bisulphite (1 +per cent. solution) and acid are added. The resulting conglomerate mass is +cut up for working. + +3. _Compound Crepe, No. 2._--This grade would include the remaining lower +grades--viz., bark-shavings, scrap, and earth-rubber scrap. + +REDUCTION CARRIED TOO FAR.--However desirable it may be to diminish the +number of grades, it must be pointed out that diminution and simplification +are not necessarily synonymous terms in this matter. It is well known that +on estates where the earth-rubber is only brought in at lengthy intervals, +say of a week, the resulting crepe is sometimes very tacky. This is only +natural, and is due to the prolonged exposure to the sun's rays. With the +improved machinery now at our disposal, and with the increasing attention +which will be given to the lower grades in the future, it is possible to +prepare from average bark-shavings crepe free from bark, and of quite a +good colour. Where trees are not "scrapped" before tapping, there would +seem to be no objection to amalgamating the rubber obtained from the +bark-shavings with the No. 1 Compound crepe; and it would be a distinct +danger and possible loss if this good rubber were to be mixed with earth +rubber. The liability of the latter to become tacky is well recognised; and +if possible it should be maintained as a separate grade, in which it would +be permissible to mix only rubber obtained from actually dry shavings from +"scrapped" trees, or heavily-oxidised scraps which have been rejected from +other grades. + +SHEETS.--Broadly there are no fine distinctions to be made at present in +the grading of smoked-sheet rubber; it is either No. 1, or if any +so-called defect is visible the sheets must be rejected and plainly marked +as "off-quality." + +Clippings (trimmings) may either be made into crepe or shipped under their +own description. + +RUBBER GROWERS' ASSOCIATION'S RECOMMENDATIONS.--Taking the foregoing +arguments into full consideration, it would seem that, strictly speaking, +the number of grades cannot be reduced to less than four at present without +producing some amount of confusion. + +In its handbook,[15] the Rubber Growers' Association remarks: + +[15] "Preparation of Plantation Rubber," 1917. + + "The fewer grades the better, and regularity of each grade is most + important. + + "The grading should be as follows: + + "(No. 1) Fine crepe (or No. 1 sheet), made from the free or + liquid latex. + + "(No. 2) Clean light brown crepe, made from lumps and skimmings. + + "(No. 3) Scrap crepe, made from tree-scrap. + + "(No. 4) Dark crepe, made from bark-shavings, earth rubber, and + the lower quality of scrap. + + "Tacky rubber should be packed separately. + +"_Compound Scrap Crepe._--Estates using scrap-washers should make a +compound crepe of grades Nos. 2 and 3, which will make one compound free +from bark and specks. All rubber intended for No. 4 should be most +thoroughly washed." + +Concerning these recommendations the remarks in preceding paragraphs should +be studied. + +CARE IN SORTING.--Whether dealing with smoked-sheet, pale crepe, or lower +grades, the strictest care is necessary in sorting and grading. This work +must of necessity be relegated to coolies, and they should be trained men. +Instructions must be definite, and doubtful specimens of rubber should +always be placed aside for the decision of the European superintendent. Any +pieces showing unmistakable signs of what are regarded as defects should be +stringently rejected. In the case of pale crepe, when the defect is +confined only to a small area it is permissible to cut out the affected +portion. Similarly there can be no objection, in the case of smoked sheets, +to an occasional sheet being treated in this manner. On the majority of +estates these rules are observed carefully, but some estates yet have to +learn that defective pieces of rubber may not be concealed in a bulk of +otherwise good quality. Samplers have often an uncanny knack of hitting +upon the defective specimens, and it is entirely the fault of the estate's +sorters if these pieces are submitted as being representative of the mass. + +CHOICE OF CASES.--Consumers complain justly of the presence of chips, +splinters, and wood-dust. It will be evident, therefore, that whatever the +type of case employed the interior surfaces should be smooth, there should +be no cracks or gaps in the timber, and the cases should be cleaned out +before using. There remains great room for improvement in the means and +method of packing, and in spite of suggested alternatives we are at present +restricted to the use of wooden cases. + +From comparisons of actual quality and fulfilment of the requirements +indicated above, there can be no question that cases made of three-ply +wood, such as the "Venesta," are in every respect superior to the ordinary +wooden cases of "Momi" type. The consideration of cost and available +supplies, of course, enters largely into the question, and three-ply cases +are not at present so largely employed as they deserve to be. + +A new type of case was recently exhibited in Singapore. It emanates from +the U.S.A. and is made of a fibrous material, resembling in appearance a +very stout cardboard. The complete case when assembled consists really of +two boxes, one of which is inverted and slides down over the other. Packing +is completed by means of stout wire, which is strained by a simple ratchet +arrangement. It is claimed that from 225 to 250 lbs. of rubber can be +contained. Other claims made amount to the statement that the case is +practically indestructible under normal conditions of handling and +shipping. A demonstration given certainly appeared to substantiate the +statement fully. Rubber packed in cases of various and average type was +allowed to fall from a height of about twenty feet. In all instances the +wooden cases of every type were either smashed or badly burst, whereas the +fibre cases were merely dented. These cases are obtained in flat sections, +which, in assembling, are folded and clamped by means of copper rivets in +a special but simple machine. It was pointed out that objection might be +lodged against the use of copper for this purpose. + +More recently there is announced a new packing case which is stated to be +made from low-grade rubbers, but information is rather vague. + +BAGS.--There are in local use stout canvas bags which have the advantage of +being used many times, as long as they are waterproof and kept in good dry +condition. Their employment for the conveyance of smoked-sheets would +appear to be permitted, but crepe rubbers sent in them are often reported +upon as being "massed" at the edges, and hence difficult to "sample." + +BALES.--Attempts to bale rubber for the market have been frequent, but no +success seems to have attended the efforts. In some quarters the failure +has been ascribed to prejudice on the part of buyers, but it is the opinion +of the writers that the objections to baling are, or could be, +well-founded. Massed rubber often cannot be inspected properly, and hence +is always open to suspicion that internally there may be unsuitable +portions. + +There have been several schemes put forward for winding crepe rubber on +spindles so as to form a cylindrical package complete in itself. We have +seen the process, and certainly the method had much which appeared +commendable. Apart from other objections which might be raised, there is +always the one prominent objection mentioned in the preceding paragraph. + +While baling of rubber is thus not likely to suit the general market, there +is no reason why, as in one or two instances, it should not be practised by +agreement between producer and consumer. It is believed that "slab" rubber +is shipped in bales from Sumatra to the U.S.A. + +Quite recently a proposal has been put forward to revert to a simple form +of baling for ordinary plantation rubber. Under this scheme wooden cases +are discarded, the packing material being composed of scrap-grade crepe +rubber which, it is claimed, could be put to use by the manufacturer. An +obvious drawback would be evident if these bales happened to be exposed to +direct sunlight or a continuous high temperature. The tackiness which might +supervene would make the handling of such bales unpleasant, even if it did +not affect the internal rubber. + +FOLDING FOR PACKING.--In the packing of smoked sheets it would appear to be +advisable to avoid, if possible, the folding of any pieces, as the +objection is made that such rubber is difficult to "sample" on arrival, +especially in cold weather. Sheets should be prepared or cut to such length +that they occupy the full superficial area of the box, either singly or +side by side. + +[Illustration: A SHIPMENT OF RUBBER, PACKED AND READY FOR TRANSPORT.] + +The same remark applies to the packing of crepe rubbers, except that here +we deal with units of folded rubber. Crepes are generally folded by hand, +and coolies usually work to a certain dimension by means of a standard +stick. The work is slow, but often gives employment, at a cheap rate of +pay, to women and weak coolies. + +Several machines have been invented to replace this labour. The best of +these yet seen has a simple device by means of which the length of the fold +is adjustable to suit the size of any packing case. It is called the +"Senang" folder, and is made by the General Engineering Company (Radcliffe) +Ltd., Radcliffe, near Manchester. + +CARE IN ASSEMBLING.--Whatever the type of case employed, great care must be +given to the assembling of parts and the final fastening. It is not +uncommon to find in the operation of putting on the "strapping" that nails +have been driven into the rubber. Extra bands of strapping are sometimes +advised, and where these bands pass over the sides (not edges) of the case +only specially short nails should be used. + +All wood should be planed, and in cases other than three-ply should be of +stout wood, not less than 5/8 inch in thickness. All timber used should be +of uniform type and thickness. + +METHODS OF PACKING.--The usual method of packing crepe is to fold the +lengths to some measure of the dimensions of the case. This is done in a +haphazard fashion on some estates, with the result that either space is +lost or the packing is badly arranged. + +Some ingenuity can be displayed in the packing of sheet rubber in order to +avoid folding the sheets, which, besides increasing the difficulty of +sampling, leads to loss of space. Endeavours are being continually made on +estates to prepare sheet of such a size as to obtain the maximum benefit of +space both in smoke-house accommodation and in packing. A few estates +employ tanks of such calculated dimensions as will yield uniform sheets +which pack flat and fill the superficial area of the case. + +In view of the contamination which sometimes characterises the employment +of wooden cases it is sometimes advised that the interior should be lined +with sheets, or pieces of crepe, the ends of which are later folded over +the top of the mass. In this manner it is stated that contamination is +confined only to the exterior of the contents of the case. + +WEIGHT OF CONTENTS.--The dimensions of average cases are 19 inches by 19 +inches by 24 inches, giving a capacity of 5 cubic feet. + +In these it is possible to pack 150 lbs. of crepe rubber and 200 lbs. of +sheet rubber (about 5 per cent. more in cases of three-ply wood). It may +be noted that boxes arrive in better condition when fully packed. The +foregoing figures are not adhered to strictly. For example, some estates +find it expedient to ship rubber in actual ton lots, and for this purpose +pack only 140 lbs. of crepe per case, giving sixteen cases to the ton. +Other estates, using presses, pack more per case than the quantities noted +above. At present there does not appear to be any definite regularity in +practice. + +[Illustration: ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT.] + +In all instances it should be the invariable rule that the rubber should be +weighed before packing, and that all cases should contain uniform nett +quantities of any particular type of rubber. Invoicing, etc., will thus be +greatly facilitated. If these practices are followed, and the rubber always +weighed on the same scales (assuming it to be perfectly dry when packed) +complaints of "short-weight" should be infrequent. + +"SHORT" WEIGHTS.--In some cases the occurrence of "short" weights on +arrival at ports would appear to be inexplicable. It often happens that the +constituent parts of wooden cases have been in stock for a considerable +period. If for no other reason than that indicated below, all cases, +either before or after assembling, should be thoroughly dried in the sun. +"Short" weight could be accounted for to some degree by a lack of +observance of this elementary rule, as it is most probable that there would +be a perceptible difference in weight of the wooden case in a drier +atmosphere. + + (_a_) If rubber is weighed in the box, and the average tare of the + case deducted from the gross weight (in order to obtain the nett + weight), any loss in the weight of the timber would appear as a + deficiency of rubber at the distant port. + + (_b_) Whether the same effect would be produced eventually in the case + of rubber which is weighed before packing will depend upon the method + of weighing at the warehouse. If the rubber is weighed in the box, any + observed deficiency would be attributed to a loss of weight in the + rubber. + + + + +PART III + +MACHINERY AND BUILDINGS + + + + +CHAPTER XIII + +_MACHINES_ + + +The number of manufacturers of machines for preparing rubber would seem to +be on the increase, and there can be little doubt that this competition +will result in a continued improvement in the design of machines. It cannot +be denied that there has been room for such improvement, and it is believed +that manufacturers will display judgment in putting only their best quality +into the work. While design and finish are very excellent in their way, it +is to be regretted that in a number of cases in the past the material of +rolls has been found to be of inferior quality. Generally, the complaint +seemed to be that the rolls were too soft, and that the "grinding" effect +was far too great. The damage to pale rubber in such cases is considerable, +as it is impossible to keep the rolls free from fine dark powder. The +effect is generally noticed more in the smooth rolls with which a finish is +put upon the crepe. + +Cases have occurred frequently in which rolls have been returned, because +of the injury caused to pale rubber, and there can be little doubt that the +life of quite a large number of rolls is even now far too short in +comparison with the expense involved. + +It is a moot point, however, in many instances how far the quality of the +rolls is actually responsible for the damage done to the rubber. In the +experience of the writers it is certain that complaints regarding the rolls +were unjustifiable, and that the injury had been caused by carelessness in +the "feeding" of the machine. Especially in the case of smooth finishing +rolls, it is clear that if the rolls are allowed to run idle for more than +the briefest possible interval grinding must take place. + +The complaints apply not only to the rolls themselves, but also to the +brass linings for shaft-bearings. Cases are known in which a brass "liner" +was so worn within a few weeks as to be quite useless. If the matter ended +there it would not be so bad; but there is always the possibility of +particles of brass finding their way into trays, and so into the rubber. +The damage which ensues to the rubber is quite irreparable. This particular +defect arising from the presence of brass will be dealt with in a later +chapter. But here again it is necessary to point out that such wear on +brass liners may be caused by the standards (ends) of the rolls being +eccentric; and the case may be analogous to the placing of "new wine in old +bottles." + +_En passant_ it may be remarked that in any case brass liners are not +strictly necessary. White-metal alloys are in use on rubber machines, and +cast-iron bearings have been employed satisfactorily for years. + +It would be well for managers to remember, therefore, that when machines +have to be ordered, nothing but the best is good enough, and that the +difference between good machinery and passable machinery is probably +immensely greater in effect than any saving in expenditure would warrant. + +ADEQUACY OF MACHINES.--In general, the factories which prepare sheet rubber +are usually equipped with adequate machinery. This arises from the fact +that machines are necessary for preparing all grades below the first, even +if they are not necessary for the making of sheet. Thus all the necessary +macerators and finishing machines are installed, but the major part of the +output is in sheet form. For the preparation of sheet, no heavy machinery +is required; all that is necessary are light machines for rolling the +sheets and expressing as much moisture as possible. To obtain a pattern on +the sheet, another light machine may be used. It may be imagined, then, +that the work of rolling sheet rubber by power machines is small, and that +a large quantity of rubber can be worked off in a comparatively short time. +It follows, therefore, that the preparation of the lower crepe grades can +be proceeded with at once, and that the whole work of the factory is +expedited. + +The case of factories which have to prepare all first-grade rubber in crepe +form is quite different, especially when thin rubber has to be made. The +care which has to be exercised in preparing pale crepe rubber is very great +in comparison with what is demanded by sheet rubber. The rubber has to go +first through the uneven-speed macerators, from there to the intermediate +rollers, thence to the finishing rollers. Considerable ingenuity has to be +displayed in the arrangement of the machines, so that one section will not +work faster or slower than another. More often than not, the attempt to +arrive at such a desirable arrangement fails, owing to an insufficiency of +machines. Such a statement will probably read strangely to the uninitiated; +but an example will make it plain. A factory may have a battery of six +machines, one only of which is a finishing machine (smooth rolls). With +five macerators and intermediate machines working continuously, it will be +more than the work of one finishing pair of rolls to keep pace, especially +as so much more care has to be exercised in finishing than in rough +crepe-making. The obvious course to adopt is to substitute a pair of smooth +rolls, with suitable gear ratio, for a pair of macerators or +"intermediates." + +If, however, the macerators and intermediates are already fully occupied +the whole of the time, any such change would be of small benefit. What is +really needed in this case is more machinery. + +It might be pertinently asked what constitutes an adequate equipment of +machines for crepe-making. The writers cannot give a number, but have no +hesitation in stating that if a factory cannot complete its whole day's +work before dark, it is inadequately equipped. No work should be done after +dark, if possible, as it cannot receive the supervision which crepe-making +demands. To make comparison between the number of machines in any two +factories and their respective outputs is not sound argument, as the +out-turn of two similar machines will depend upon the speed at which the +rolls travel--_i.e._, the gearing between the machines and the engines. +Thus, while one machine will out-turn 40 lbs. of crepe per hour, another +may only have an output of 30 lbs., although the machines may be identical +in pattern. To make calculations based on a rate per hour for any known +make of machine, and to apply those calculations to the existing machinery +in any factory, in an attempt to judge whether there is a sufficient number +of machines, would be a mistake, unless one were also supplied with the +relative speeds at which the rolls work. + +Finally, on the question of adequacy of machines, it must be pointed out +that an insufficient number of machines must result in a poor product, +since all rolls have to be used for all grades. Even with the greatest +possible care it happens that pale crepe is sometimes spoiled because it is +contaminated with foreign matter, resulting from the working of lower +grades on the same machines. This is one of the great arguments in another +direction for the installation of a scrap-washer. + +In conclusion, the writers can only give their opinion that one must not +decide the question of adequacy by the number of existing machines, but by +the time taken each day in working off the rubber, providing one can be +satisfied that the best arrangement of the existing machines has been made. + +IDEAL ARRANGEMENT.--As to what this best arrangement may be, guidance can +be obtained from the results of experience here given. It must be premised +that the output of any factory preparing fine pale crepe is limited by the +output of the smooth finishing rolls. Broadly, it will be recognised that +if there is any excess of capacity in a battery it should be found in the +smooth-roll machines. This sufficiency, or excess of capacity, may +sometimes be attained by an alteration in the gearing of the drive of the +rolls from the back-shaft, or by an addition to the number of machines. In +the former case, there are practicable limits of speed, beyond which the +second alternative measure must be adopted. + +SPEED.--The usual speed at which the back-shaft travels ranges from 60 to +70 revolutions per minute. Taking first the macerating machines, the +intermediate gearing between the shaft and the rolls should give a driving +speed of about 20 revolutions per minute on the faster-travelling roll. +This is equivalent, with a 15-inch diameter roll, to a peripheral speed of +about 60 to 65 feet per minute. + +The intermediate and smooth rolls can be arranged to travel more quickly, +but the maximum comfortable speed for proper feeding and control appears to +be about 25 revolutions per minute on even-speed rolls. In view of the fact +that the rubber at each successive machine becomes longer and thinner, it +will be seen that a smooth-roll machine could not cope with the output of a +macerator in the same period of time. If, therefore, the macerator is fully +occupied for the greater part of the time, an additional smooth-roll +machine must be installed, even though the existing one has been "speeded +up" to practicable limits. + +For the information of the uninitiated it might be explained that in the +macerating and intermediate machines the cog-wheels driving the two rolls +are of different sizes (_i.e._, differentially geared), as opposed to the +smooth rolls on which the cog-wheels are usually of the same size (_i.e._, +even speed). The idea in the one case is to exert a "working" influence +upon the rubber while it is being washed by the stream of water coming from +above; in the smooth rolls a squeezing action only is effected. + +To give an idea of the ratio of the speeds of the rolls in each machine in +a typical working battery, the following particulars may be noted: + +GEAR RATIOS.-- + + _Machine._ _Differential Ratio._ + + 1. Macerator 32-17 + 2. Intermediate (coarse grooved) 32-17 + 3. " (fine grooved) 30-19 + 4. Smooth (uneven speed) 30-19 + 5. " (finishing) 25-24 + 6. " ( " ) 25-24 + +It will be seen that the so-called "even-speed" smooth rolls run at +approximately the same rate. + +It is advised that in all cases the gear wheels should be cut helically. +Those who have experience of the noise of some batteries after they are +slightly worn will appreciate such a remark. + +GROOVING OF ROLLS.--Concerning the choice of grooving, there is divergence +of opinion, some managers preferring one type, which others reject in +favour of another type. Provided any particular type can be shown to be as +effective as required, no necessity for laying down hard-and-fast rules +seems to exist. + +The following particulars serve to describe a battery well known to the +writers, and accustomed to produce the finest quality of thin pale crepe +and lower grades: + + -----------------+-----------------------------------+------------- + | |_No. of Times + _Machine._ | _Grooving._ |Rubber passes + | | through._ + -----------------+-----------------------------------+------------- + 1. Macerator | Deep horizontal grooves; | + | square-cut, 5/16 inch × 5/16 inch | + | × 5/8 inch spaces | 3 + 2. Intermediate | Horizontal grooves; 3/16 inch | + | × 3/16 inch × 3/8 inch spaces | 2 + 3. " | Fine spiral grooves; 1/8 inch | + | × 1/8 inch × 1/4 inch spaces | 2 + 4. Geared smooth | Nil | 1 + 5. "Even" smooth | " | 1 + 6. " " | " | 1 + -----------------+-----------------------------------+------------- + | Total | 10 times + -----------------+-----------------------------------+------------- + +The actual rate of output of this installation is the capacity of the last +smooth machine. This is about 180 lbs. per hour, while the output of the +macerator is approximately double this amount. Thus the macerator only +works for about half the time. This applies also to the two intermediate +machines. After a study of the preliminary remarks, it would not be +difficult to suggest methods for improving the condition of affairs. It +would appear that, in order to obtain a uniform rate of working in such a +battery, the relative peripheral speeds of the several machines should +be--(1), (2), and (3) 100; (4) 150; (5) and (6) 200. The remarks on the +practical limits of speed should be borne in mind. In this case the smooth +rolls travelled at 23 revolutions per minute. + +As already stated, it is not intended to lay down definitely that, _e.g._, +horizontal grooving alone should be cut on macerating rolls. Some estates +employ with satisfaction a deep square-cut spiral 1/4 inch by 1/4 inch by +1/4 inch or 1/2 inch spacing; others use a large diamond pattern. Similarly +various types of grooving are cut in the intermediate rolls. + +[Illustration: A BATTERY OF MACHINES. + +On the left, light marking rolls for sheet rubber; on the right, heavy +machines for crepe preparation. In the middle background, "scrap-washing" +machines outside the main building.] + +It has been remarked in the chapter dealing with crepe preparation that +much depends upon the condition of the coagulum. There is no necessity, or +desirability, for having a standard higher than 2 lbs. dry rubber per +gallon, and it has been argued that it would be better to select a standard +of 1-1/2 lbs. The tougher the coagulum, the more the power required, and +the slower the rate of output of the leading machines. + +In ordering machines for crepe-making, only large rolls should be +considered--_e.g._, rolls having a diameter of 12 inches to 18 inches and +from 15 inches to 18 inches face. + +ROLLS RUNNING HOT OR "FREE."--If the rolls are found to become hot, work on +that machine should be stopped, and an examination made, otherwise there +is the possibility of the crepe becoming sticky and "tacky" when dry. + +Although comparatively cold water may be flowing upon the rubber and the +rolls, little alleviation may be noticed, inasmuch as the source of heat +lies generally at the bearing ends of the rolls. This may be tested by +placing the hand on the top of the "standard" of the machine. The +development of the heat may be due to lack of lubrication, worn bearings, +or sometimes faulty setting-up of the machines. + +Allusion has been made to the necessity for avoiding the running "free" of +rolls--_i.e._, in the absence of rubber. The grinding of the rolls, when +working close together, produces a fine powder, which causes a more or less +pronounced deposit on pale crepe. When the rolls have been in action for +some time and become slightly worn, this deposit may be confined only to +the edges of the rubber. + +SHEETING MACHINES.--The foregoing paragraphs have dealt entirely with +machines for crepe preparation. Concerning machines for use in +sheet-making, the ground has been mainly covered in Chapter IX. + +Where both crepe and sheet are made, it is permissible and advantageous to +use the heavy smooth rolls for the rolling of the sheets, and it is only +necessary to instal one or two light machines for placing a pattern on the +rubber. + +Where a heavy battery does not exist, light machines with smooth rolls may +be employed satisfactorily. Even engine-power is not necessary for the +preparation of excellent sheets, but the output is limited where hand-power +only is employed. Estates are known on which upwards of 1,000 lbs of sheet +rubber are made daily with hand-power machinery in one station. Beyond this +figure, it is deemed advisable to instal a small engine, say of 7-9 +horse-power. This is ample to drive a battery of three smooth-roll machines +and two markers, and yet have sufficient reserve to actuate a small pump +for the water supply. + +LUBRICATION OF MACHINES.--It must always appear to those inexperienced in +engineering matters that existing methods for lubricating rubber machinery +are distinctly crude, when one considers the delicacy of the material to +be prepared. Many existing machines are still lubricated with oil, which +has to be administered in generous quantities. Generally, such machines +have been so designed that the excess of oil may find an easy passage into +the tray which receives the rubber. If not, it drops just outside the tray +to the floor, and is washed away in great gouts. Even where grease-cap +lubricators are fitted it is common to find that the excess can often be +transferred from the bearings to the trays and so to the rubber. One would +have expected from the attention which is being given to machinery for +rubber estates that some improvement in lubrication methods would have been +devised. + +It is probable, however, that a great deal of the disabilities attaching to +present methods of lubrication might be obviated if closer attention were +given to the actual operation of the lubricators. Coolies should not be +allowed to handle them, and the responsibility should be placed upon a +foreman or the engine-driver. + +TRAYS.--The most unsuitable and damage-causing part of the vast majority of +machines, without doubt, is the tray. On nearly all machines the tray is +wider than the effective portion of the rolls, so that any excess of +lubricant may drop into it. On others, not only is the tray wider than the +rolls, but its edge either is in contact with the shaft of a roll or just a +small distance away. The edge of the tray is thus favourably situated for +acting as a "wipe," and the lubricant is transferred to the inside of the +tray. Considering that the effective portion of rolls is about two-thirds +of their length, it must be unnecessary to have trays wider than the length +of the rolls. For the preparation of fine crepe trays are quite +superfluous, and their place can be taken by a narrow piece of board if +required. If the bed of the machines has been covered with glazed tiles, +even a piece of board is not necessary. Where trays have been removed from +the fine-crepe rolls on a number of estates, a marked decrease in the +number of spoiled pieces of rubber has resulted. + +It must be recorded that the foregoing paragraph appeared in our 1913 +publication. After a lapse of over seven years, the remarks remain as true +as when originally written. One of us is continually meeting with cases in +which the defects are plainly attributable to the cause indicated above, +and the fault often lies with the management of estates. On most machines +the trays are not fixtures, and could be removed if desired. + +ARRANGEMENT OF MACHINES.--In considering the future arrangement of +machines, the first care should be to see that machines and windows are to +be found together.[16] Of all the factory operations, rolling of rubber +should be given the maximum light. At the same time it would not be +advisable always to choose a southern aspect, unless outside shades were +supplied. The best position for setting up machines, therefore, is along a +wall having a number of windows. This is extremely convenient also from the +view of power transmission, and gives the maximum free floor space to the +factory. In setting up machines, foresight must be displayed, otherwise one +may find, when future extensions are made, that the extra machines may +obstruct an entry or exit. + +[16] Windows imply the existence of walls. Such is the conventional design +of factories. It may be pointed out that walls are not necessary. The roof +may be supported on pillars between which expanded metal of large size may +be placed. This fulfils all requirements and gives the maximum of light and +air. Many new factories have been erected to such a design. + +For the actual erection of machines, no labour should be accepted without +European supervision. At present there are machines which are practically +useless owing to faulty workmanship, and on many machines bearings run hot +for no apparent or explicable reason. Whether the fault lies with the +turning of the rolls or the setting of the machine cannot be decided; but +at any rate too much care cannot be expended on the supervision of setting +up machines. + +There is no reason why everything in a factory should not be made as easy +to clean as possible. For this desirable condition all machines should have +the beds faced with tiles. A word of caution should be given against using +marble slabs under the machines, as they would be eroded in time by the +slight amount of acid washed out of the rubber. There would be no such +objection against the use of white glazed tiles, if they are well set. + +ACCESS TO BACK OF MACHINE.--In a few factories it has been noticed that the +drainage of water from the machines runs to the front of them. This means +that the coolies are put to unnecessary inconvenience and discomfort, and +they often suffer from sore feet. All water should drain to the back of the +machines. The necessity for seeing that these drains are kept clear might +then induce those in charge to examine the back of the machines. It is +often the case that, while the front of the rolls and tray are kept clean, +little attempt is made to cleanse those parts which are not visible or +accessible from the front. There should be no need to point out that any +labour expended in such "front-window" work is rendered useless by the +contamination from accumulations of old rubber and grease at the back of +the machines. In the course of visiting factories one of us has many times +seen great surprise exhibited by the manager or assistants on being shown +the state of affairs at the back of the machines. There should have been no +occasion for such surprise, for the back of the machines is quite as +accessible to them as to the visitor. + +In conclusion it might be said that the manager needing advice as to the +best machines cannot go far wrong in purchasing any of the better-known +makes, such as Shaw's, Bridge's, Robinson's, Bertram's, Walker's, Carter's, +Iddon's, etc. This list does not include local manufacturers such as the +"United Engineers." It must not be imagined that their machines are not +recommended. As a matter of fact, their machines compare well with those +made at Home. It would be well to judge in the final decision upon-- + + 1. Cost. + + 2. The experience of those already using the machines. + + 3. Simplicity of parts. + + 4. Lubrication system. + + 5. Mode of adjusting rolls. + + 6. Fitting of trays. + +ENGINES.--It is not intended here to discuss particular makes of engines, +or even to attempt to lay down definite statements with regard to the type +of engine. Without a full knowledge of local circumstances, it is not +possible to recommend whether the engine shall be oil-driven, gas-driven, +or steam-driven. + +Assuming a copious supply of very cheap timber, there could be no objection +to the employment of a steam-engine; but for most estates such a choice is +out of the question. + +Again, in deciding between oil and gas, local economic factors must be +considered. Suction-gas plants are now made, in which a wonderful variety +of refuse can be consumed in the production of gas, whereas ordinarily +estates are restricted to the use of either charcoal or anthracite coal. +Both oil and gas driven engines are eminently suitable for the purpose of a +rubber factory, and the results obtained on different estates with either +are often discussed in favour of one or the other. The selection ultimately +narrows itself down to one of cost of running, in which availability of +supplies becomes an essential feature. + +POWER.--No matter what type is selected, there should be made an ample +allowance for margin of power. The general experience of estates has been +that when the first portion of the estate comes into bearing, there is a +desire to avoid great outlay, which should really have been secured in the +original capital. The result has been that as later the estate expands, the +original power unit is found to be inadequate, and a larger engine has to +be purchased. In a short while the original engine is found to be +unsuitable even as a "stand-by," inasmuch as it is incapable of doing more +than a portion of the work required. This means eventually that another +large engine is required. Had sufficient margin of power been allowed +originally, only two engines would have been bought, as against the three +indicated above. Without going into finer details, it is usual to allow a +rate of 10 horse-power per heavy machine used for crepe preparation. In +actual practice, when a battery is working under full load, the power +demanded is about 6 horse-power per machine. Thus a 50 horse-power engine +running six machines and a scrap-washer is really running with only a small +margin of power, and if large pieces of hard coagulum are placed in the +washer or the macerator there may be a sudden stoppage. Assuming an average +estate commences with only three machines for crepe-making, on an expanding +programme, allowance of power should be made for six machines and a +scrap-washer, if the purchase of larger power units is to be avoided +later. + + + + +CHAPTER XIV + +_FACTORIES_ + + +GENERAL CONSTRUCTION.--On the question of general construction there is +little to be said, except that buildings are now being properly designed in +more permanent form than were some of the earlier buildings. On the whole +there is little fault to be found with factories in general, except in so +far as the output has outgrown the accommodation. + +Most factories are now erected in iron, but there are a few which are built +of bricks. It should be premised that a factory in which rubber is to be +prepared should be as light and airy as possible. In this respect quite a +number of the older factories are lacking, and they seem to have been +designed to exclude as much air and light as possible. Under these +circumstances, the building is always dark, there is always an air of +dampness, dirt may accumulate, and there is usually a bad smell. Rubber +prepared under these conditions is always liable to be below the high +standard which should be attained, and the general tone of the factory is +depressing. + +PLENTY OF LIGHT.--The old idea that light must be excluded is now known to +be erroneous; so that in designing a factory, provision should be made for +ample light and air. It should not be forgotten that in tropical climates, +iron buildings may become uncomfortably hot, as most of our older factories +are. Usually it will be found that the ventilation is imperfect. There is a +lack of window space, and the roof is imperfectly ventilated. The ridge of +the roof should be opened up by means of a "jack-roof," so that the warm +air rising naturally may escape at the highest point of the building. These +are defects which should be remedied in old buildings. + +As a rule no rubber remains in the factory at night-time, except in the +form of coagulum, the loss of any of which would be noted with ease. The +conventional idea of enclosing the factory with walls of galvanised +sheeting, wood, or brick, is not strictly necessary. In modern buildings +these walls are replaced by large-mesh expanded metal, thus making the +machine-room perfectly light and plentifully ventilated. Under such +conditions, dirt cannot accumulate unseen, and the general tone of the work +is raised. + +THE FLOOR.--The floor should be of thick concrete, and have a good surface +layer of cement. Preparations are now advertised for which claims are made +that their employment renders the surface of such floors waterproof and +dustproof. If these claims can be substantiated when the use is applied to +the floors of rubber factories, the employment of a preparation of this +nature should result in a considerable saving of expense and trouble. +Preferably the floor should not be flat, but should slope slightly from the +longitudinal middle of the building to the sides on either hand. If the +floor is level it usually results in accumulation of water, the cement +breaks in patches, and the factory always appears to be dirty. + +POSITION OF MACHINES.--All machines should be arranged adjacent to and +parallel with one of the long sides of the building, and should be raised +about 6 inches above the floor, so that water may escape easily. Tanks for +the reception of latex, scrap rubber, etc., should be placed along the +opposite wall to the machines, and the intermediate length of the building +should be entirely free from fixtures. It was not uncommon in older +factories to find the engine situated in the middle of the floor, so that +what with the space occupied by the engine, and the space rendered +unavailable by the belt-drive, the real accommodation of the factory was +sadly diminished. In no modern factory should the engines be brought into +the main room. They should always be accommodated in a special compartment, +situated outside the wall, along the inside of which machines are placed. +In this way considerable floor space is left available, and the machines +may be worked by direct drive. Not only so; but if a suction-gas plant is +worked, there can then be no excuse for particles of coal or charcoal dust +being found in the factory. + +POSITION OF ENGINES.--It scarcely need be pointed out that if the engines +are placed outside the wall which is opposite the machines, a long +belt-drive would be necessitated, and that the presence of the belt would +prevent the use of end doors. It is presumed in these arguments that two +engines are to be installed. One can hardly imagine a modern factory in +full working being equipped with only one engine, which might possibly have +an excess of power necessary to drive all the machines. In the case of +breakdown, which sometimes happens in the best supervised factories, it +would be small consolation to know that this excess of power was present +theoretically. + +HOW MANY STOREYS.--There can be no doubt that, taking all things into +consideration, the best type of factory is that consisting only of one +floor. The factory should be quite separate from all other buildings, and +if attempts are made to conserve ground space by putting a drying-room over +the factory, much trouble will ensue, especially if pale crepes are to be +made. In the first place, the factory is made very much darker, and hence +more difficult to keep clean; secondly, the ventilation of the factory is +seriously interfered with; and thirdly, it is manifestly prejudicing the +drying of rubber to place it directly over a room which is always more or +less awash with water. At night such a building would reek with a +moisture-laden atmosphere, and little drying could be expected to take +place in that interval. From actual experience it has been shown that +rubber hung to dry in such a room, situated over a damp factory, is very +liable to attacks of "spot" diseases, since the presence of perpetual +moisture is favourable to the development of these diseases. If a +double-storey building has to be worked, it will be readily seen that no +first-grade rubber should be allowed to dry in it. The accommodation over +the factory may be restricted to the purpose of receiving lower grade +rubber which is not so liable to "spot" diseases, and possibly does not +take so long to dry as first-grade rubbers of equal thickness. It is +evident, therefore, that the erection of double-storey factories is false +economy, as separate drying-houses have to be built eventually. This +conclusion does not apply with the same force to factories worked in +conjunction with smoke-houses for preparing sheet rubber, but, +nevertheless, such a factory should not have another floor above the +work-room. + +VERANDAHS.--One of the worst features in many factories is the necessity +for coolies to bring latex into the factory. As already mentioned, the +floors of factories are usually running with water (or should be), and it +can be imagined that the passage to and fro of scores of coolies must bring +in a great quantity of dirt. Not only so; the very presence of the coolies +is a hindrance to the efficient working of the factory, and considerable +floor-space and time are wasted. + +This feature in factory working is all the more annoying because the +necessity for it could so easily be obviated. All that is necessary is the +erection of a wide, open verandah outside the wall of the factory. Here all +latex could be received and strained, scrap-rubbers could be received and +passed through an opening into tanks placed in convenient position. Water +could be laid on in this verandah so that coolies might wash their buckets, +and the whole verandah might be enclosed only with expanded metal so as to +avoid interference with the lighting of the factory. In this way it would +be quite unnecessary for any field coolie to enter the factory proper, and +this would facilitate cleanliness. Such an arrangement has been discussed +by the writers many times during the last few years, but the number of +estates which have made such provision is still in the minority, and the +same slipshod and dirt-making procession of coolies continues to walk +through the factories, and the same piles of bark-shavings and scrap-rubber +continue to accumulate and ferment in a few instances. + +An indication of types of verandahs is given in Chapters VII. and IX. These +are not intended to be representative of a universal design, but may be +suggestive in the planning of others according to local conditions. + +SITUATION OF TANKS.--It will be noted that these verandahs are raised from +the ground-level to a height of about 3 feet in order that latex may be +gravitated, with a slight fall, into the coagulating tanks which are within +the factory. There exists a real necessity for this practice, inasmuch as +otherwise to obtain gravitation of latex (which is quicker and cheaper +than handling) the coagulating tanks would have to be either placed on the +floor or sunk beneath the level. The risk of contamination of latex or +coagulum under such circumstances would be appreciable. Apart from this, it +is advisable to have the coagulating tanks raised to a height of between 2 +and 3 feet, to secure the advantage of ease of working in the processes of +coagulation and the handling of coagulum--a not inconsiderable factor. + +In some modern designs it is proposed to place the coagulating tanks in a +separate building. This would seem to be an unnecessary refinement in a new +building, if observance is given to the suggestions made in previous +paragraphs. + +DESIGNS AND "LAY-OUT."--In a previous publication[17] comment was made upon +grievous errors in designs prepared by those inexperienced in the +requirements of the tropics. There is little ground now for complaint, and +local engineering firms are fully capable of advising upon, and +constructing, suitable buildings. + +[17] "Preparation of Plantation Rubber," Morgan, 1913. + +In considering the first installation of a factory and equipment one always +has to weigh the question of prime cost against the probability of future +expansion of crop. If it should be decided at first merely to cater for +contemporary requirements, the fullest consideration should be given in +discussing design of building and lay-out of machinery to the +practicability of later extension. The site should be large enough for the +eventual group of buildings, the building should be easily capable of +extension with the least cost, and the same forethought should govern the +lay-out of the machinery. + +DRAINS.--Lastly, there is the question of drains. Generally speaking, all +factories are well provided with drains, and the only difficulty is that of +getting an adequate fall for efficient drainage. But there is a certain +amount of laxity exhibited in the matter of providing sieves in drains. To +anyone acquainted with factory working, it must be apparent that quite a +lot of small pieces of rubber are washed into the drains. This rubber +should be collected at intervals during the day; but in many instances +that collected is only a fraction of what escapes. Wherever possible the +drainings of a factory should be carried as far as is practicable from the +buildings by means of cement drains. Too often these are short, and lead +into earthen drains. Even if no pieces of rubber are present, the serum +from the coagulum is subject to decomposition, the effluvium from which is +objectionable. + +WATER SUPPLY.--It is essential that a good supply of water should be +available. This should be distributed by pipes all round the building, so +that a hose may be used in every part for the thorough cleansing of the +factory at intervals during the hours of working. + +Summing up, it might be said that a good factory, therefore, should have +the following features: + + 1. Plenty of windows, or walls of expanded metal. + + 2. A jack-roof in the ridge, and hence a good system of ventilation. + + 3. Engines in compartments outside the walls of the factory. + + 4. Machines close to and parallel with the wall outside of which the + engines are placed. + + 5. Latex tanks and other fixtures along the wall opposite the + machines. + + 6. A long middle free space, at either end of which a large double + door should be placed in the end walls. + + 7. A good concrete and cement floor sloping slightly from the middle + towards each long wall. + + 8. An abundant water supply, and several lengths of hose. + + 9. The building should be of only one floor, and have ample head room. + + 10. There should be an outside, open verandah upon which latex may be + received, etc.; preferably outside the wall which is opposite to the + machines. + + 11. The system of drainage should be thorough, and the drains should + be adequately screened, so that all particles of rubber may be + collected. + + + + +CHAPTER XV + +_OTHER BUILDINGS_ + + +DRYING-HOUSES FOR CREPE.--It has already been shown in the previous chapter +that one type of drying-houses--viz., that over a factory--stands +condemned, except for the drying of low-grade rubbers. Generally speaking, +a great advance has been made in the design of crepe drying-houses during +recent years, and it has been possible even to improve older ones so as to +bring them into line with the more modern buildings. Houses for drying +crepe rubber may be of one floor, two floors, or even three floors. +Doubtless those built with three floors were designed with a view to +economising the available site for factory buildings, and as long as the +ventilation is good there can be no very great objection to them. It might +be pointed out, however, that even with the best of ventilation the air +passing successively through three layers of rubber must be fairly +saturated with moisture by the time it leaves the building. The effect of +this upon the rate of drying in the uppermost chamber will not be so marked +as it will be in the middle floor, as the temperature of the top floor must +be many degrees higher than that of the other two rooms. It would be +expected, therefore, that the rate of drying in the middle storey would be +slower than that in either of the other two. + +In houses of two floors this objection would not have to be met, and +drying-houses of this type are successful and common. + +HOW MANY STOREYS?--Again nothing could be urged against a building of two +or three storeys in which the ground floor was occupied as a packing-room, +except that, by negligence in not allowing wet crepe a preliminary dripping +period, water might fall upon the packed rubber below. + +As a matter of experience, such a house is, taking all into consideration, +the cheapest and most suitable type for any estate with an increase in +output. Even at the outset there should be a separate room in which sorting +and packing is undertaken. This is conveniently the lower room of a +drying-house. The only stipulation to be made for a house with two storeys +is that the floor of the upper room should be of an open pattern, so that +the air may circulate right through the building. This is usually and very +successfully attained by laying down wide slats of wood, with spaces of an +inch or more between them. It is not advisable to have spaces wider than +1-1/2 inches, otherwise there is a certain amount of danger to the limbs of +individuals who have to work or supervise in the building. In any case, it +is very convenient to have pathways of planks running the whole length of +the floor, so that the supervision is made more convenient. If this is +done, there can be no objection to the custom of suspending the rubber of a +lower chamber from the slats of the floor of the upper room. At present, in +some drying-houses, this means of suspension is used, but no planks are +laid down, and it becomes necessary to walk over the drying rubber. This is +a detail, but it is one which does not make for the improvement of rubber, +and the expenditure of a small sum would be sufficient to rectify the +matter. + +From every point of view, it would be desirable to have the floor of the +packing-shed (or the packing-room in a combined house) raised from the +ground, to a height of, say, 3 feet; or the height of a bullock-cart or +motor-lorry. Not only is ventilation improved, but there would be a great +saving in labour. Packed cases could be wheeled directly on a level with +the cart or lorry. + +A great many estates favour drying-houses of one storey. These are +eminently suitable, provided that the site is suitable, and that the +relative dimensions of the house are favourable to efficient ventilation. +It is a common mistake to find buildings of which the breadth is out of +proportion to the height. Obviously, if the height is not considerably in +excess of the breadth, ventilation will be defective. For a single-storey +drying-house, the maximum height should bear the ratio to the breadth of +3:2, and in a house of this type specially long pieces of crepe can be +utilised. Naturally, in a house of two storeys, this factor is not likely +to be neglected, and if the lower room is used for packing purposes the +rate of drying should be rapid. Again, when a single-storey building is +contemplated, it is well to make strict examination of local conditions. If +the site is low-lying and surrounded by trees it will be clear that tall +buildings are required, and that a house of more than one floor is to be +preferred. Considerations of this nature would have prevented the erection +of some dry-sheds which do not give a satisfactory rate of drying. + +VENTILATION.--No matter how many floors there may be in a drying-house, the +greatest attention should be given to the question of ventilation. It is an +elementary point in the study of ventilation problems that the best system +of natural ventilation is obtained by admitting cool air near or through +the floor and providing an exit for the warmer air at the highest point in +the building. It is not often that such a rule is infringed in the +ventilation of rubber drying-houses, but several of the older buildings +erred in this respect. In a good modern house there is a space (about 2 +feet in height) all round the base of the walls merely closed with expanded +metal; this admits cool air. An exit for warm air is provided in the ridge +of the roof by either ventilation chimneys or by a jack-roof. The latter is +preferable, as it provides for a more free and uniform escape. + +In some drying-houses, besides the ridge openings, the space along the +eaves is left open. This would seem to be undesirable, as it provides for +the entrance of outer air, which might combat the ascending warm air and so +interfere with the natural upward currents. Provided that a jack-roof or +other suitable openings have been installed, there is, therefore, no +necessity for the existence of open spaces at the eaves, and they probably +do more harm than good. + +In the tropics, on days of sunshine, there must always be an upward current +of air in well-designed houses. Temperatures of 105° F. are easily recorded +in the ridge space of a building, while the temperature in the lower part +of the house may be at least 15° F. lower. On the floor of an upper room a +temperature of 90° F. is commonly noted, and in buildings with three +storeys the usual day temperature of the top room is about or over 100° F. +Even, therefore, when there is no trace of a breeze, there must be a +displacement of air in an upward direction, though it may not be detected +without tests being applied. + +It is often asked whether a temperature of 100° F., such as is obtained in +the upper room, is calculated to injure the quality of the rubber. There +need be no fear on this ground; the experience of many estates goes to show +not only that no harm results, but also that the drying of the rubber is +expedited. There would seem to be no reason why crepe rubber should not be +dried at a temperature of 100° F. It must be understood, however, that +higher temperatures for crepe rubber are not recommended, as it has been +proved that the rubber is affected. The fact becomes obvious with continued +treatment at temperatures much above 100° F., for the rubber stretches and +breaks across the support. + +WINDOWS.--Concerning the subject of window space in a drying-house, there +has been much discussion at various times. Years ago it was common to find +windows widely open with the sunshine streaming in. Naturally, tackiness +developed in some of the rubber, and care was then taken to keep the +windows closed. Thus the rooms were darkened and air excluded. There +followed a period in which windows were fitted with ruby-coloured glass to +keep out the actinic rays of the sun, which were responsible for tackiness, +and excess of light, which was supposed to be responsible for the rapid +oxidation of rubber. Unless special precautions were observed in the +processes of coagulation and preparation, it was not proved that the +exclusion of light prevented or lessened the natural oxidation of crepe +rubber. Since the introduction of sodium bisulphite for the prevention of +oxidation, there has been no cause to worry as to the possible effect of +light, as no perceptible darkening of the rubber takes place. It follows, +therefore, that no trouble need be taken to exclude light, although the +necessity for excluding direct sunshine still exists. Windows may be left +open as long as the sun does not reach them. This can usually be arranged +in a drying-house by manipulating the windows at intervals during the day, +so that those in the shady side of a building are always open, while those +on the sunny side are always closed. If it is thought that this +manipulation cannot be entrusted with success to the store coolies, the +case may be met by having all windows constructed on the louvre pattern, so +that, although the windows are closed all day, air and light are not +excluded. Should it be desired to retain the existing type of windows, +which open outwards, and to keep them open all day, a simple arrangement of +ruby-coloured cloth on an outstanding wooden frame may be placed within the +walls of the building, or the shutters of the windows may be hinged at the +top to open outwards. Unless there is a pronounced breeze, or it is +required to examine the rubber closely, there is no necessity to have +windows open, except in the case of a house in which the bottom floor is +used as a packing-room. The windows of this chamber may remain open during +the day, to advantage in sorting and packing, and also to the proper +ventilation of the building. Thus the direct rays of the sun are rendered +harmless, while air and light are allowed to enter. + +HOT-AIR DRYING-HOUSES.--Mention has already been made of the existence of a +system of drying in which hot air is forced into a drying-house by means of +a powerful fan. Provided that the temperature of the hot air could be so +regulated as not to exceed 100° F., there would be merit in the system. +Such matter of regulation could be solved by having a duct in the main air +passage, through which cool air could be admitted in such proportion as to +modify the temperature of the hot air. As the process is worked at present, +the temperature attained is often well above 100° F., and there is a danger +of thin crepe placed in this house over-night being found upon the floor in +the morning. Unless the crepe is prepared thick and cut into fairly short +lengths, it will not bear its own weight at higher temperatures; and if it +is made thick, drying is impracticably prolonged. It is probable that, with +a temperature of 100° F., and a steady current of air, average thin crepe +would dry in such a drying-house within six or seven days. This would be +an improvement upon the usual rate of drying in most factories, although +several ordinary drying-houses are known in which thin crepe will dry +naturally in that period. + +SMOKE-HOUSES.--No discussion of theoretical considerations regarding the +process of smoke-curing will be attempted here. We are concerned only with +the necessity for supplying a demand for smoke-cured sheet rubber. Broadly, +the process is akin to the smoke-curing of herrings, and the objects are +much the same--viz., (1) drying, (2) preservation--except that while +herrings are only dried partially, rubber should be dried perfectly. + +On a small scale a primitive smoke-house could be built easily and cheaply, +and such a building might be fully as efficacious as the most elaborate and +expensive installation. In the early days of estates it was not uncommon to +see temporary smoke-houses constructed of wood, and roofed with "attaps" +(palm leaves). Some of the best rubber in the market has come from wooden +buildings, but naturally the risk of destruction by fire is considerable. + +For imperative reasons it may be sometimes found necessary to smoke rubber +when the only available building is a single-storey one. As a temporary +measure, the building may be converted into a smoke-house by placing the +fires in pits sunk deeply into the ground, and effectively screened above +by iron baffle plates. But it is not advisable that smoking be continued in +such a single-storey building, as the best effects are not obtained, and +the risk of fire is far too great. + +USUAL TYPES.--At first sight it would appear that the best type of +smoke-house would be one consisting of a tall building, covering a +comparatively small superficial area, and having a number of superimposed +chambers in which the rubber could be hung to dry. In practice there are +several solid objections which limit the height and the number of floors. +Chief among these is the question of temperature. If smoke-curing is to be +effective, a certain temperature must be attained and maintained. To obtain +such results in a house of excessive height would be difficult, if not +impossible, under normal conditions. It would be found that the chamber +immediately above the furnace-room would be overheated if the temperature +in the upper rooms was within the desired range, etc. + +Until recent years smoke-houses could be classed as belonging to one of two +types: + + (1) Those having external furnaces. + + (2) Those having internal furnaces. + +The number of the former existing at the present time must be very small, +as it has been shown that the arrangement of the furnace outside the house +is unsatisfactory in comparison with the other type of house. In discussing +the question of smoke-houses, therefore, it will be understood that the +standard type accepted is that having an internal furnace. In its original +form it was known as a "Kent" drier, and consisted of a tall two-storey +wooden building. The walls of the lower chamber had the form of an inverted +and truncated pyramid. By this arrangement it was possible to obtain from a +comparatively small fire sufficient smoke and heat to cure the product +placed in the room above. This is the principle upon which many +smoke-houses in Malaya are designed. On a very large scale it is not +claimed that the sloping sides of the lower chamber lead to economy in the +number of fires, but merely divert the smoke in an upward direction. It is +acknowledged that vertical lower walls are quite effective, and it is an +easier matter to fit in doors. + +It may be noted that the usual type of smoke-house now in general use +consists of a building of two storeys, in the lower of which are situated +the furnaces, while rubber is hung on racks in the upper room. Sometimes +there may be a third storey, also used as a drying (curing) chamber. As a +rule the drying-room is one long unit, as also is the furnace chamber; but +in some cases they are subdivided by vertical partitions into smaller +chambers, for ease of working and better control. This applies with some +force in the case of very long houses standing in an open space. It is +sometimes found in such cases that at certain seasons the prevailing winds +have the effect of making drying and curing uneven in parts of the +building. + +With these exceptions, the ordinary type of smoke-house functions very +efficiently, and is capable of drying average sheet (from standardised +latex) in a period ranging from seven to eleven days. Should the building +not be capable of such performance, in spite of the strict observance of +all rules laid down for the processes of preparation, then there is some +defect in ventilation or in the distribution of heat. + +GENERAL VENTILATION.--The ordinary rules of ventilation in drying-houses +apply equally to a smoke-house. There should be a slow current of air and +smoke from the lowest point to the highest point in the building. + +In spite of all that has been written on this subject, it is by no means +uncommon to encounter the idea that a smoke-house should be perfectly +closed in order to get good results. As to what must become of the (say) 25 +per cent. of moisture which the rubber contains there is no knowledge. In +dozens of cases, when complaints regarding slowness of drying have been +investigated, it has been necessary to point out the need for providing a +rational system of ventilation. + +Naturally only a slow current of air and smoke is required. The creation of +an appreciable draught would have the effect of increasing the fuel +consumption of the furnaces, raising dust from the ash, and of causing a +temperature higher than that which is known to be desirable. It will be +clear, therefore, that if there are to be any openings at the base of the +walls they should be small in area, and should have some device by means of +which the current of air can be efficiently regulated. In the usual case +the construction of the building is not calculated to render it air-tight, +and the necessity for providing special air inlets does not arise. + +WINDOWS.--Windows are not strictly necessary, and are only intended to be +of service during the time in which coolies are at work within the +building. The operations of examining rubber, turning sheets, removing dry +rubber, cleaning racks and floors, and putting wet rubber into position, +usually occupy some hours daily. During this interval the windows should be +widely opened if the weather is favourable, and should remain so until the +fires have been lighted. It should not be forgotten that during the heat +of the day quite an appreciable degree of drying is possible. Advantage can +be taken of this; but there is no necessity to extend the interval unduly, +and it is of greater advantage to proceed with smoke-curing when the work +in the drying-chambers has ceased. + +RACKS OF SUPPORTS.--Still referring to the usual type of smoke-house, it +may be remarked that in the upper room bays of racks run at right angles to +a central passage down the length of the building. Narrower passages run +between the bays of the racks to facilitate ease in handling and +inspection. The wooden supports may be placed about 3 inches apart +horizontally, and 15 or 18 inches apart vertically. A full bay of racks +should contain nine or more lines of support in each of the planes which +are 15 or 18 inches apart vertically. The number of these planes is +governed only by the height of the room, measured from the floor to eaves. +The supports should be of smooth timber, and need not exceed 1-1/2 inches +square in section. + +It is usual and advisable to smooth off the rectangular edges of the +supports or bars, to avoid the incidence of splinters of wood adhering to +the rubber. The bars should not be fixtures, but may either be accommodated +in slots, or may rest _between_ two nails, so that it is possible to give +them a rotary motion by turning the projecting ends. This practice is +followed in smoke-houses, the idea being to move the drying sheets slightly +each day, with a view to the prevention of a pronounced mark across the +sheets. + +Care should be taken to see that the vacant racks are thoroughly cleaned +before fresh rubber is placed upon them, otherwise a distinct dirty mark is +caused across the middle of the sheet. This mark usually cannot be removed, +even by scrubbing with water. Where this mark occurs regularly in all +sheets, attention should be turned to the openings beneath the bays of +racks, if open fire furnaces are employed. It will generally be found that +gauze of too wide mesh has been fitted. This should be removed or covered +with a finer gauze. + +A more effective way of dealing with the trouble, provided other +precautions have been taken, is to have plenty of spare wooden bars. It +should be a rule stringently enforced that, as soon as racks are emptied, +the bars should be removed to the factory to be cleansed thoroughly. A +spare set should enter the smoke-house with each batch of fresh rubber. The +actual number of spare sets required could be limited to a two days' +supply, and the extra cost would be recouped easily. + +FLOOR OF DRYING-CHAMBER.--The floor of the chamber is usually of planks, +except that the space under each bay of racks should be filled with +expanded metal. With the use of wood fires there is always a large amount +of light ash formed, which may find its way into the upper chamber. To +counteract this, screens of fine mesh gauze are laid over the expanded +metal. This gauze may be fitted into a movable wooden frame, so that when +it becomes necessary to clean it the whole may be removed. + +The difficulty is that with furnaces of the "open-fire" type the rise of +dust is so great that the gauze screens soon become clogged, especially as +the slight tarry matter in the smoke condenses on the gauze, causing the +dust to adhere. With the better types of furnaces, the employment of gauze +screens is not necessary, as there should be very little rise of dust. It +is sufficient to use only expanded metal, to prevent any displaced pieces +of rubber falling into the furnace chamber. + +FURNACES GENERALLY.--The crudest and dirtiest method of fuel consumption in +the preparation of smoked-sheet rubber is that of making a fire on the +ground. This is still a common practice, and should be condemned as being +both wasteful and harmful. Under prevailing conditions coolies will, in +spite of instructions, heap up a pile of logs in order to save themselves +the trouble of stoking the fire in small quantity and at regular intervals. +A small supply of water is kept at hand with which to quench the fire +somewhat if it threatens to cause trouble. Naturally a large quantity of +fine ash is thus thrown up, and the rubber above receives the deposit. If +the coolie does not happen to be sufficiently awake, of course a house +burns occasionally. + +From this primitive type of furnace, others have been evolved. These +usually take the form of more or less shallow trucks, the majority of +which are similar in principle to the fire on the ground, except that the +container can be withdrawn from the house for the purpose of removing the +ash. Sometimes they are even more objectionable than the ground fire, +inasmuch as, being raised above the ground level, an under-draught through +fire-bars is caused, and consumption of fuel is so much the more rapid. + +PITS.--It is clear that large fires are not desirable, and that combustion +should be slow, provided that the necessary temperature can be maintained. +The lines along which the development of furnaces needed to extend are +therefore plain. The simplest device adopted was the digging of pits in the +ground. Sometimes these pits received the addition of an iron truncated +cone which was movable. Naturally the combustion was slow, but sufficient +heat was obtained if the pits were large enough or in sufficient number. An +objection was that the ash had to be cleared _in situ_, and in the process +the earthen pits gradually increased in size. In all cases it was necessary +to suspend an iron baffle-plate above the furnaces to distribute smoke and +arrest any sparks. + +"POT" FURNACES.--The next development was the employment of "pot-furnaces." +These consist of iron drums, sometimes merely resting on the ground, and +sometimes mounted on trucks for easy withdrawal. These drums radiate +sufficient heat if present in sufficient numbers, and the fuel consumption +is low. They are usually manipulated by starting a fire in the bottom and +packing in logs cut to the necessary length. Some have no lids, while +others are fitted with perforated caps. + +It was considered necessary in some instances to punch a few small holes +near the base of the drum in order to ensure a very slight upward draught. +In a few cases this perforation has been exaggerated to the form of a +hinged door. Unless this can be closed with ease, and is closed according +to instructions, part of the object of this type of furnace is defeated; +fuel consumption is rapid, and the temperature is too high. In the original +form "pot-furnaces" have been found to be effective on many estates, and +are still employed with satisfaction. + +IRON STOVES.--Working on exactly the same principle, on some estates one +finds small iron stoves in use. Sometimes broad pipes are attached for the +better distribution of the smoke; if this is the case it should be noted +that the pipes should have a slight downward slope, and that the "bend" at +the end should be turned downwards. In this way condensed moisture and +creosotic matter falls to the ground, and does not lodge in the pipe. The +life of the conduit is thus prolonged. Usually such stoves are in use where +the "head-room" of a smoking chamber is insufficient for other types, or +where the nature of the site does not permit of sunken furnaces being +installed. They are of value likewise on occasions where the fuel supply is +limited to a rich timber such as mangrove-logs ("bakau"), when it is +necessary to ensure a low combustion with low cost of fuel. + +HORIZONTAL DRUM-FURNACES.--To overcome difficulties inherent to drums or +"pot-furnaces," the next development was that in which the drum was made to +assume a horizontal position, and adapted ingeniously to a simple system of +working from the outside of the building. Reference to the drawings given +will explain how this is effected. In the first illustration (No. 2) it +will be noted that the drum is supported upon brick pillars, with one end +projecting through the wall of the building. At the other end a short +chimney is mounted, having within it a "damper" which is adjustable from +the outside. Over this chimney is suspended a simple baffle-plate, made +from a Chinese iron cooking-pan. The outer end of the drum is furnished +with a hinged and latched door, in which a small air-regulator is +accommodated. + +In the second set of drawings (No. 1) the drum is increased in size and +fitted in a special manner for incorporation with a distinct type of +building. Such a scheme was first put into effect by Mr. R. C. Sherar, the +manager of Third Mile Estate, Seremban, F.M.S., and for ease of reference +the house and furnace will hereafter be mentioned when necessary as the +"Third Mile" type. + +[Illustration: "THIRD MILE" TYPE; HORIZONTAL DRUM. + +This type of furnace is suitable for adapting to existing buildings with +perpendicular lower walls.] + +[Illustration: "THIRD MILE" TYPE OF FURNACE, USED IN CONJUNCTION WITH +"THIRD MILE" SMOKE-HOUSE.] + +It will be seen that the furnace has at the farther end a door for the +removal of ash. As this, if badly fitting, may result in too great a +draught, it is well to insist upon good workmanship. Other adjustable +air-inlets are provided, and the drum is enclosed in a brick chamber. + +RATE OF COMBUSTION.--However successful this furnace may have proved in the +hands of trained coolies, one must feel that with such a number of +air-inlets (whether accidental or designed) there would always be present +the possibility of obtaining too rapid a combustion. In the original forms +of drums or pot-furnaces of various kinds, a very slow rate of combustion +was attained. Naturally a relatively larger proportion of carbon remained +unconsumed, and there was a small proportion of ash. In these respects the +furnaces resembled charcoal-burners. In point of fact, some estates used +this principle for the dual purpose of smoke-curing the rubber, and at the +same time obtaining a supply of charcoal to provide fuel for their +suction-gas engines. This is a consideration in times when managers are +desirous of discovering any devices which tend towards reduction of costs. + +It will be clear that, under ordinary circumstances, the condition of what +remains after the combustion of the fuel gives an indication of the rate at +which the wood has burned, and this test should apply to all furnaces. That +in which there is the most ash and the least charcoal is the one least to +be desired. In direct connection with this consideration, one must +recognise that a fire which is sunk below the level of the ground exposes +the least surface from which heat may radiate; and hence, in order to +obtain the maximum benefit of heat from a slow-combustion furnace, it +should be above ground-level, or should have a superstructure from which +the heat may be dissipated. + +Simple drum furnaces, with slow combustion, have the further advantages +that a "charge" of fuel will need no attention for possibly eight to ten +hours, and practically no ash is found to be ejected. These advantages have +great practical importance. The first minimises any disabilities arising +from neglect on the part of coolies, and the second makes for increased +cleanliness in the drying-chamber. While these advantages would appeal to +most estates, there would appear to be a further advantage to small +estates which have only temporary timber smoke-houses. With a slow rate of +combustion in a furnace of this type, danger from fire is diminished +considerably. + +Bearing in mind the slow rate of combustion, and hence the comparatively +low temperature obtained, it will be plain that drum furnaces should be +employed in larger number than ordinary open-hearth fires; and the drums +can be so placed as to ensure the best possible uniform distribution of +heat and smoke. + +Large furnaces are sometimes seen, with flues of brickwork. In view of the +foregoing remarks, it will be obvious that these tend to large fires and a +rapid combustion, and hence must be classed as undesirable. + +BRICK STOVES.--Developing from "drum" furnaces, another type comes into +existence. In principle it consists of an enclosed brick furnace, with +feeding door, and a low conical dome surmounted by an adjustable cap or +spark-arrester. The rate of combustion can be influenced by a suitable +movement of the cap, which is operated by a screw. This type of furnace has +been installed on several estates by the engineering department of Messrs. +Harrisons and Crosfield, and is understood to give satisfaction. + +PATALING TYPE.--With the exception of the "Third Mile" type already +mentioned, all the furnaces described are open to a strong objection, in +that the coolies have to enter a room, usually filled with hot smoke, in +order to attend to the fires. The mere opening of the door of the building +is sufficient to fan most fires into a blaze and to raise sparks. Apart +from these points, it is natural for coolies to avoid entering too often, +with the result that they generally stoke with the maximum load of timber. +Even should they not sleep the danger is clearly great. + +[Illustration: SIDE SECTIONAL ELEVATION (PATALING TYPE OF FURNACE).] + +[Illustration: PATALING TYPE OF FURNACE.] + +To obviate these drawbacks, furnaces which are fed from the outside of the +building were designed. There have been various forms, but as they were +first installed on Pataling Estate, in the present form, they may be known +under the description of the Pataling type of furnace. They are eminently +satisfactory, and have a low rate of fuel consumption. They are very +safe, and in fact, if worked with average intelligence in supervision, can +be regarded as being fool-proof. There is practically no ejection of fine +ash, and no fine-mesh screens need be employed. They can be adapted to any +building having either vertical or sloping walls of galvanised iron. + +[Illustration: LARGE SMOKE-HOUSE OF ORDINARY CONSTRUCTION, WITH SHIELDED +VENTILATORS PERMANENTLY OPEN. + +In foreground, movable folding racks on which sheets "drip" in the open +air. This smoke-house is equipped with brick furnaces fed from the outside +(Pataling Estate).] + +In essential the furnace consists of a shallow pit below ground-level, +lined with brick, and having a square brick superstructure rising 4 feet +above the floor of the building. On top of the brick walls rests a sheet of +boiler-plate perforated with small holes. The hearth being below +ground-level, and with the extra 4 feet of height above the floor, it +follows that if ash is disturbed it is confined. + +From the drawings it may be seen that the pit is prolonged to the side wall +of the building, with steps leading up to the ground-level. The top and +sides of the opening are made with galvanised sheeting, forming a kind of +short tunnel in which the coolie may stand upright. The outer face of the +brick furnace forms the inner end of the tunnel, and accommodates the door +of the furnace. The bottom of the pit is filled up with clay and stones +almost to the level of the bottom of the door. This ensures a very shallow +hearth, and guards against an unduly large fire. Obviously it is not +desirable or necessary to make the hearth of fire-bars, as was done in one +instance, with the provision of a door below for removing the ash. This +would lead only to a strong draught being created, with a high rate of fuel +consumption. + +[Illustration: BRICK AND CEMENT SUPERSTRUCTURE OF FURNACE INSIDE THE +BUILDING, BUT FED FROM OUTSIDE. + +On the top of the superstructure rests a sheet of perforated boiler-plate. +The actual fire-pit is below ground-level, and to the left may be seen +parts of the sides and top of the downward approach, from the outside, to +the door of the fire-pit.] + +The openings can be screened by a narrow sloping lean-to, which serves to +keep out rain, and provides shelter for the stock of fuel and the coolie. +The iron furnace-door should be well made, with an easily worked latch; but +it is not necessary that it should be perfectly fitting. Any slight +aperture will serve to provide the necessary air-inlet, but in any case it +should not be more than slight. + +CONSUMPTION OF FUEL.--Regarding this furnace, it may be said in conclusion +that it is more satisfactory in general working than any other furnaces yet +encountered. Obtaining information from over sixty estates, on the question +of fuel consumption compared with output of rubber, it was found that, as +far as ordinary smoke-houses were concerned, the Pataling type of furnace +showed the lowest unit consumption of fuel. + +[Illustration: GENERAL VIEW OF SHELTERS COVERING APPROACHES TO FURNACES.] + +This was at the rate of slightly less than 1 lb of fuel per 1 lb of +thoroughly cured sheet rubber. The figure on some estates mounted as high +as 4-1/2 lbs. of fuel per lb. of rubber. Naturally this factor may have +been affected by failure to utilise the drying space to its fullest +capacity, but in the main the high rate of consumption could be attributed +solely to the deficiencies of the furnaces. + +FLOOR OF FURNACE-ROOM.--As a rule no attempt is made to improve the natural +earthen floor. Whether open-hearth fires, truck furnaces, or drums are +employed, it is usual to find a floor with an inch or two of dust upon it. +Where all endeavours are directed in other directions towards cleanliness, +it appears strange that this should be overlooked. In contrast, houses +employing the Pataling type of furnace (or others) have concrete and cement +floors, which can be kept quite clean. Cleanliness should be as zealously +attempted in the smoke-house as in other departments. + +[Illustration: NEAR VIEW OF SHELTER. + +Steps lead downwards where the wall of the smoke-house has been removed.] + +ROOF.--In any type of smoke-house, the roof should fit tightly at the +eaves, and the only vent should be in or near the roof-ridge. + +In an ordinary smoke-house, the opening should take the form either of a +low jack-roof or of squat chimneys protected against rain. If a jack-roof +is chosen, it may be so low as to need no scheme of adjustment, or +otherwise adjustable swing shutters must be provided. The chimneys may be +made with such low fitting between the cap and the body that no interior +swinging flaps are required. + +During the operation of smoke-curing the smoke vents must remain open to a +degree which is arrived at by experience. Failure to provide a +comparatively free egress for smoke and moisture will bring trouble in its +train. After a house has been in use for some time, it will be noted that +the timber becomes covered with a shiny tarry coating deposited by the +smoke. If the rubber remained in the house for an equal period, it would +take on the same appearance. During the interval between the entry and the +exit of the rubber some amount of deposit does take place, and it is this +mixture of creosotic substances which plays a part in fitting the rubber to +withstand growths of mildew which would otherwise form. + +If proper smoke-vents are not provided, the moisture evaporating from the +sheets is unable to escape quickly enough, with the result that a great +deal condenses at night-time upon the inner surface of the comparatively +cool roof, and falls back upon the rubber in unsightly black "drips," which +leave a distinct mark on the sheet. Even if vents are open, this may happen +during seasons of rain. The temperature of the moist smoke in the +roof-ridge may be as high as 130° to 140° F., while the outer atmosphere +may have been cooled by rain to 70° F. Such a difference on the two +surfaces of the roof must lead to condensation within the house, with +consequent "dripping." It used to be the custom to drape sacking material +above the bays of racks in order to prevent the drops of liquid falling +upon the rubber; but often for want of renewal the last state was worse +than the first. Modern houses have often an inner lining, a few inches +below the roof. This is made of soft wood which receives any product of +condensation and absorbs it. + +OTHER TYPES OF SMOKE-HOUSE.--So far we have confined the arguments to +smoke-houses of the usual type. There are others which vary in either +design and method of working, or in the material of the structure. Mention +may be made of the most prominent of these. + +BRICK HOUSES.--Some houses are constructed of brick, and may have one or +two storeys above the furnace chamber. The floors are sometimes made of +ferro-concrete, and the furnaces may also be of this material. These brick +houses give satisfaction, but there would seem to be some difficulty in +obtaining and maintaining the desired temperature, although it is not quite +plain why this should be so. The principle of these buildings is the same +as that of the ordinary iron house, and the suggestions made in previous +paragraphs apply with equal force. + +"THIRD MILE" TYPE.--Reference has been made to the "Third Mile" type of +furnace. This is an integral part of a smoke-house, which for clearness of +distinction may be known as the "Third Mile" type of smoke-house, the +original of which was erected on the Third Mile Estate, Seremban, F.M.S. + +[Illustration: "THIRD MILE" TYPE OF SMOKE-HOUSE.] + +In essence the design consists of a building, having two storeys for +rubber-drying, and a shallow inverted pyramidal base, ending on the ground +in "Third Mile" furnace, already described and illustrated. + +It will be seen that the principles of ventilation employed are those +indicated for an ordinary house--viz., air-inlet near the ground (with +little draught), and smoke-vent at the roof-ridge. The windows shown in the +drawing are only for purposes of inspection of the rubber during the day, +and form no part of the scheme of ventilation during the hours of smoking. + +It is claimed that the efficiency of the house is high. Certainly the work +of attending to the furnaces is simplified, and there should be small +ground for excuse if negligence is displayed. + +JACKSON HOUSE.--This was brought into notice under the description of the +"Jackson Cabinet," and it was claimed that average sheets could be dried in +a few days. It consisted of a small house of one storey, having several +tiers of racks. Smoke and heat were generated in a small stove placed +outside the wall. A smoke vent was provided in the roof. These cabinets had +a certain vogue as part of a small unit installation, with a fair degree of +success. It is not clear, however, that such speed in drying is required. +(This point will receive further attention in a subsequent chapter.) + +"DEVON" TYPE.--In its full original design this type owes its origin to Mr. +H. E. Nixon, General Manager of the Devon Estates, Malacca, where it forms +part of unit divisional installations worked under a scheme of +decentralisation. + +The original units consisted of a building erected with an iron framework +covered with sheets of asbestos-slate, and a roof of galvanised iron. + +The novelty in design lies in the utilisation of external platforms upon +which the racks of bars supporting the sheets of rubber may be drawn out of +the smoking chambers, and on which the racks are loaded and unloaded. By +this device it is possible to remove the contents of any compartment bodily +without interfering with the continuity of curing in the other +compartments. That is to say, smoking in such a house can proceed day and +night if necessary, and yet the rubber in any part of the house can be +examined, can be removed, or can be replaced without cessation of smoking. + +It will be seen from the illustrations that the house is more or less of +the same general design as the "Third Mile" type, with the addition of +external platforms. It has two storeys for the reception of rubber; and a +basal furnace-room with sloping sides converging downwards into a pit +containing a large drum-furnace. This is mounted on a low truck, and +travels on a short length of railway. + +[Illustration: GENERAL VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE. + +The platforms are common to both units. Building of brick with iron roof +(Batu Caves Estate).] + +Each of the curing-rooms is divided into four compartments (making eight +compartments in all). These are closed by swing doors, each of which is the +full width of a compartment, and has a slight overlapping edge. Through +these doors light railways run into the house and out upon the platforms. +On the rails "bays" of racks run, and when fully loaded they are easily +moved. The racks were designed with a frame of stout hard wood, but light +angle-iron could be utilised. + +[Illustration: GENERAL VIEW OF DOUBLE "DEVON" SMOKE-HOUSE AND FACTORY +BUILDINGS. + +Timber in foreground cut to length for stoking. Note water-tower and engine +cooling-tanks adjacent to factory.] + +The chimney style of smoke-vent has an internal butterfly flap, which is +controlled by means of a wire from the outside. In the ordinary course of +smoke-curing, it is advised that this flap should be permanently open so as +to reduce the possibility of internal condensation of moisture and +creosotic matter. The exact degree to which it should be open must be found +by experience. + +[Illustration: VIEW OF PLATFORM OF "DEVON" SMOKE-HOUSE; DOORS OF +COMPARTMENTS OPEN, AND ONE RACK PARTIALLY WITHDRAWN. + +Note below each rack opening through which smoke rises, covered with wire +netting.] + +Although reference has been made several times to compartments, it should +be understood that the chambers are not subdivided internally by means of +partitions. There exists only the external effect of compartments in the +form of the eight swinging doors which allow for the withdrawal of, or +insertion of, any one unit of racks at any time without interference with +the bulk of the rubber. + +[Illustration: DOUBLE "DEVON" SMOKE-HOUSE OF BRICK, WITH ROOF OF CHINESE +TILES, SHOWING LOADING PLATFORMS WITH RACKS WITHDRAWN FROM SMOKING +CHAMBERS. + +Federated Engineering Co., Ltd., Kuala Lumpur.] + +[Illustration: SIDE VIEW OF PRECEDING PHOTOGRAPH, SHOWING EXTERNAL +ARRANGEMENT FOR STOKING FURNACES. + +Federated Engineering Co., Ltd., Kuala Lumpur.] + +DETAILED DESCRIPTION.--As enquiries are often received it is permissible to +reproduce the following detailed description of the original house. This +appeared in the Fourth Local Report (Malaya) 1916, issued to subscribers by +the Rubber Growers' Association. + + "The house has a steel frame-work, 22 feet long, 16 feet wide, and 22 + feet high. Of the length, 14 feet is occupied by the platforms, and 8 + feet by the chambers. These measurements can be varied. The whole of + the width (16 feet) is occupied by compartments of which one series is + placed above the other. + + [Illustration: FRONT VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE. + + Glenmarie Estate: Batu Tiga Co.] + + "_Platforms._--The loading verandahs or platforms are of ordinary + 'seriah' timber. + + "_Compartments and Furnace Chamber._--These are enclosed with Bell's + 'Poilite' sheets, each of which measures 8 feet by 4 feet by 3/16 + inch. The sheets are affixed to the steel stanchions, doors, etc., by + galvanised bolts (1 inch by 1/4 inch) which pass through iron flats + measuring 8 feet by 2 inches by 3/8 inch (about). These iron flats + hold the sheets at the edges. The dimensions of the compartments are 8 + feet by 8 feet by 4 feet. + + "_Racks._--These are eight in number, and measure just under 8 feet by + 8 feet by 4 feet. The capacity of each is roughly about 450 lbs., of + dry sheet rubber. The racks are mounted on 6-inch iron wheels, running + on rails of stock size, 'T' iron (1-3/4 inches by 1-3/4 inches by 1/4 + inch). + + "The sheets are hung on split bamboos. To prevent these projecting + over the edge of the rack and catching in the doors when the rack is + moved in or out, a thin strip of wood, about 1/2 inch high, is nailed + along the sides of the rack. + + [Illustration: SIDE VIEW OF DOUBLE "DEVON" TYPE OF SMOKE-HOUSE. + + Building constructed of galvanised iron. Shows door to furnace + chamber, and ventilator.] + + "_Furnace._--This is of the type that aims at slow combustion. It + consists of a cast-iron cylinder, 3 feet in diameter and 4 feet high, + carried on a truck made of a sheet of boiler-plate, and mounted on + small wheels, so that the whole can be moved easily out of, and into, + the furnace chamber for easy cleaning and stoking. + + "The furnace chamber is a pit lined with concrete, just wide enough + to take the trolley, and about 12 feet long. The top of the furnace, + which is almost flush with the ground-level, consists of a sheet of + zinc or galvanised iron with numerous holes about 3 inches in + diameter. Over these holes are strips of mosquito gauze, as flame and + dust arresters (see note below). There are no holes in the sides or + bottom of the cylinder. + + "Over the furnace is hung a baffle-plate, measuring 4 feet by 4 feet. + Above this, on the first floor-level, the bottom of the compartments + is covered with wire netting, to prevent any rubber dropping + accidentally into the furnace chamber. The furnace chamber is fitted + with an iron-frame door, swinging on perpendicular hinges. + + "_Method of Stoking._--The timber used is a mixture of jungle wood and + rubber-tree wood, cut to lengths of about 1-1/2 feet. In the ordinary + way the furnace is charged at 6 p.m., and at six-hour intervals a + little more fuel is added, but a new charge is not necessary. During + the daytime, when the heat of the sun is sufficient to raise the + temperature appreciably, a smaller fire is maintained. + + "_Temperature._--There is no difficulty in maintaining a temperature + of 120° F. By continuous smoking, average sheets prepared from + standardised latex can be fully cured in five days. This represents + 110 hours of smoke-curing, which is at least equal to ten days' + intermittent smoking in an ordinary house. + + "_Capacity._--There are eight racks, each accommodating 450 lbs. of + standardised sheet rubber. The loading capacity of the house, + therefore, is 3,600 lbs. As each charge is cured in five days, the + monthly output may be 21,000 lbs. + + "The cubic capacity is 2,048 cubic feet. As there are no gangways, + etc., this is fully utilised. This gives a rate of monthly output + capacity to over 10-1/4 lbs. dry rubber per cubic foot of drying + space; an excellent figure much in advance of values obtained in the + great majority of ordinary smoke-houses."[18] + +[18] Since the above was written, it has been found possible to eliminate +the gauze. A mild steel top has been made, perforated with 2-inch holes. +Practically no dust is ejected from the furnace, and there are no flames. + +Owing to shortage of supplies during the War, similar buildings have been +erected with frames of well-seasoned hard wood, which was protected by +strips of asbestos-slate or galvanised iron. The latter material was also +substituted in the covering walls. Later, houses were erected of brick, +with other minor modifications. As a natural development, the latest +buildings consist of two of the original houses face to face, under a +common roof, and served by common platforms. + +As originally designed, the house was intended to meet the needs of a small +estate, or a division of an estate, having a maximum output of about 20,000 +lbs. of sheet rubber per month. The possibility of an extension of this +idea has been shown to be great. + +The furnace has been described as situated in a pit. Situated on a bank or +on sloping ground, it was easy to arrange for withdrawal of the furnace. In +some cases this has not been possible, and various modifications have been +effected. The most satisfactory yet encountered is that in which a shallow +brick pit is surmounted by an iron cone, about 4 feet in height. This is +fitted with a cap having small perforations. The fire burns in the pit, and +the heat is radiated by the cone. It would have been more effective to have +allowed greater height in the furnace chamber, and to have employed the +travelling drum-furnace as in the original design. + +In order to avoid interference in draught by a space between the bottom of +the doors of the compartments and the platform (due to the presence of +rails), the floor of the platform is laid level with the top of the rails; +or to the bottom of the doors is attached a swinging flap, notched for +accommodating the rails when in position. + + * * * * * + +There are in use houses of other designs, which all more or less vary only +in some modifications from the types described. Hence they do not call for +special comment. Recently a rather distinct departure has been noted in a +structure designated the "Barker" smoke-house. + +BARKER PATENT.--In essential this consists of a long narrow structure +erected with an appreciable slope from one end to the other. At the lower +end is a small furnace enclosed in a brick compartment. The smoke from this +furnace travels up the slope to the other end, at which the rubber enters. +The sheets are hung on bars which are attached to a unit framework. This +frame slides, by its own weight, upon timber side supports. A sufficient +number of these units occupies the full effective length of the structure. +The removal of "stops" at the lower end enables the foremost frame to be +removed, and the succeeding frames slide into a new position. Thus the +freshly prepared sheets, entering at the higher end, gradually and +automatically move towards the furnace as the frames of dry rubber are +removed from the lower end. + +[Illustration: THE NEW "BARKER" TYPE OF SMOKE-HOUSE: A SMALL UNIT. + +The racks slide automatically from top to bottom on withdrawal of the lower +frames through door at front. The furnace is contained in the brick +compartment at the lower (front) end.] + +Thus far only small units have been seen. It is claimed that, properly +prepared, sheet rubber can be smoke-cured in about five or six days, and it +is stated that installations have been in successful working for +sufficiently long periods to prove their efficacy. The device is better +known in Java and Sumatra than in Malaya. The capacity of a unit building +is stated to be 7,000 lbs. per month, calculating on a six days' cycle of +working. In a more recent design provision is made at the lower end for a +water tank, into which all rubber can be discharged in case of fire. + + + + +CHAPTER XVI + +_OTHER BUILDINGS (continued) AND SITUATION OF BUILDINGS_ + + +SORTING-ROOM AND PACKING-ROOM.--It is in these departments that most +factory installations are lacking. More often than one cares to +acknowledge, sorting and packing are done under conditions which place a +premium upon poor work. As a consequence, consignments of rubber are often +marred by the inclusion of defective specimens. The result is that +shipments may be rejected when tendered against contracts, or that +allowances in price have to be made. In many instances it would not be fair +to lay the blame upon the manager or an assistant, as it is obviously +impossible for an individual to inspect every piece of rubber. Neither +would it be strictly fair in some cases to ascribe the fault to pure +carelessness on the part of the coolies. + +Often the only provision made for this important work is the lower room of +a drying-shed, which may also contain hanging rubber. Under these +circumstances, space is cramped, and the light often poor. Small defects +may pass unnoticed, and the general surroundings do not conduce to keen +work. + +Where, for economic reasons, the sorting and packing operations are +conducted in the drying-shed, there should be ample space free from hanging +rubber, and it should not be possible for wet rubber placed in the upper +room to drip upon the dry rubber below or upon packed cases. There should +be plenty of light, and for this reason windows should be ample. Usually +the window-frames are fitted with wooden shutters, which are preferably +hung on horizontal hinges from the top of the frame. By this device it is +not necessary to close all windows during a shower of rain, and rubber may +be stacked near a window with reasonable chance that direct sunlight will +not be allowed to fall upon it. + +In dealing with smoked sheet, it is advised that the rubber to be examined +should be placed upon tables facing the windows, so that each piece may be +scrutinised in a strong light. + +Crepe rubber also is best examined in a strong light, but preferably with +one's back towards the source of light or at an angle to it. For this work +coolies usually are most efficient when sitting on the floor. + +It will be clear from the foregoing remarks that the best conditions would +be secured in a separate building especially constructed. A single room +would be all that is required; at one end sorting could be undertaken, +while packing could be done at the other end. No hanging rubber should be +allowed in the room. + +The floor should be of hard timber, and raised from the ground, to the +height approximately of a bullock-cart or motor-lorry, as the case may be. +The boxes of rubber could thus be transported by small hand-trucks on a +level with the transport vehicle, reducing labour to the minimum. + +The ventilation of the building should be good, especially if cases of +rubber are to be stored therein; and the entire structure should be +weather-proof. + +STORE-ROOMS FOR RUBBER AND STORAGE.--The question of storage of rubber in +factory buildings has always possessed importance, but has demanded +increased consideration recently. + +From experience in this country, it is clear that cement floors for +store-rooms or packing-sheds are the least suitable. They are often visibly +damp, especially in the early morning. To allow rubber, packed or unpacked, +to remain upon a cement floor in the tropics, is to court trouble from +moulds, external or internal. If the employment of a cement floor is +unavoidable, the rubber and boxes should be raised on wooden supports, +giving a clearance of at least 3 or 4 inches, and there should be clear +ventilation space between tiers of boxes. + +Experience indicates that the best type of floor is that already advised +for sorting and packing rooms--_i.e._, a good hard timber floor raised at +least 3 feet above ground-level. Apart from the advantage in labour +specified in the previous paragraphs, this provision of ample ventilation +space below the floor is a great consideration in the preservation of the +timber. Raised store-rooms become essential in low-lying districts which +are at all subject to flooding, yet the writer has seen many boxes of +rubber damaged by flood-water entering a packing-room situated on the +level. + +The question has often been raised recently as to the length of the period +during which rubber may be safely stored in this country. The answer can be +only supplied by experience, of which up to the present we have none +possible of being classed as reliable. Whatever storage may have been done +in the past has been influenced greatly by the unsuitability of the storage +accommodation, and the fact that often the rubber was not prepared with a +view to prolonged storage. + +While the market demand was strong, rubber was being shipped and passed +into circulation, at a rate which did not demand investigation of the +subject of local storage. In the year 1918 conditions were such as to bring +the matter into prominence, and we were able to tender advice on the lines +given in this chapter. The necessity passed, but has again arisen. + +Our experience goes to prove that if rubber is properly prepared and +thoroughly dried before packing, it will remain in good condition for a +period of a year or more in this country. How much beyond a year it may be +kept remains to be determined. The assumption of "proper preparation" +leaves great room for reservations. + +In the case of crepe rubbers, there is no great difficulty, provided that +the recognised methods and formulæ are employed, and that the rubber is +packed only when perfectly dry. Under those conditions, the higher grades +of crepe remain apparently unaffected on storing. Any appreciable +deterioration may be attributed to defective preparation or external +causes, such as accidental damage by water. + +The prolonged storage of lower grade rubbers is attended by more risk, +especially in the case of the lowest grade (earth-scrap) from estates which +neglect the practice of regular and frequent collection of the raw product. +The same reservation applies to crepes made from tree-scrap which is not +collected daily. In these types of crepe rubber "tackiness" may be +initially present only in small degree, but the final damage may be +immensely greater by close contact of the folded rubber during prolonged +storage. + +When we come to discuss the possibility of storage of smoked sheets, the +difficulties become immensely greater. We have yet no reliable experience +as to the keeping properties of this grade when properly prepared, fully +cured, correctly packed, and stored under the best of local conditions. It +is understood, of course, that in the qualification by the term "local" +conditions, we assume it to be more difficult to store rubber generally in +Malaya than in a temperate climate. The average temperature and humidity of +the atmosphere are here much more favourable to the development of mould +growths than would be the case, say, in Great Britain. + +In discussing this question, as far as it refers to the preservation by +storing of smoked sheet rubber, it is not fair to draw conclusions as to +the likely behaviour of packed rubber from data based upon observation of +loose specimens. We have samples of smoked sheets prepared in 1910, and +these, superficially, appear to have remained unchanged. No mould is +present and, as far as intermittent observation enables us to judge, moulds +have never been incident. Whether such rubber would have been preserved in +this condition had it formed part of a packed case, is a point upon which +we have no experience; neither can we give any opinion. It seems true, +however, that loose specimens "keep" better than bulk samples of the same +preparation. + +It cannot be argued that the present good condition of these old specimens +may be due to correct preparation. In those days methods and formulæ were +rather haphazard, especially in view of the fact that the daily variability +of dry rubber content of latices was not then recognised. + +One would rather submit the factor of adequate smoke-curing as the chief +influence in the superficial preservation of smoked sheets. Ten or eleven +years ago it was considered advisable to allow the rubber to remain in the +smoke-house for a period extending well beyond that necessary for ordinary +drying. As a result, very dark rubber was produced, which was thoroughly +impregnated with the products of wood combustion. There would seem to be +little doubt that this procedure was responsible for the prolonged freedom +from mould growths. + +Market standards have varied to some degree since, with a tendency to +prefer a paler product than that in vogue, say, six or seven years ago. +Moreover, standardised methods of preparation have been introduced, with +the result that sheets of a desirably high standard can be produced in from +ten to fourteen days, when smoke-curing is conducted only during night +hours. Some estates are equipped with smoke-houses which, by continuity of +working day and night, provide smoke-dried rubber in from five to six days; +but the actual hours of smoke-curing are approximately equal to those of +the ordinary type of house. + +This tendency towards the production of sheets paler in colour than the old +standard is probably largely responsible in the present for the commonly +observed incidence of surface moulds on stored smoked sheets, and also for +some complaints of "under-curing," where the term specifically refers to a +failure to dry and cure the rubber thoroughly. Boxes of smoked sheets, +which had been stored for varying periods up to five months, were recently +inspected, and, in the majority of instances, surface moulds were found to +be plentiful. In all cases it was observed that the trouble was intensified +where boxes of rubber were stored in contact with cement floors. + +This "under-curing" is not a question solely of the duration of +smoke-drying, although probably the modern practice of curtailing the +period has exerted a great influence. To make this clear, it may be stated +that, given two batches of uniformly prepared wet sheets, it would be +possible to smoke-cure them for equal periods in different houses, so as to +produce one batch very much paler in colour than the other, although the +total hours of actual smoke-curing would be identical. In order to produce +such effects, all that is necessary is to employ different timbers for fuel +or different types of furnaces. In the one case there would be produced +heat and very little smoke, while in the other the necessary heat would be +obtained plus plenty of smoke. The best results naturally are obtained by +the employment of the happy medium, and if smoked sheets have to be stored, +the ordinary period of smoke-curing should be prolonged to an interval +consistent with the capacity of the smoke-house. + +All precautions taken in preparation and curing can be nullified, as +already indicated, by unsuitable storage conditions. + +TOOL-SHEDS AND STORE-ROOMS.--In some factories it is the rule to see lime, +cement, spare rolls, sieves, and a general heterogeneous assortment +occupying part of the rubber-drying rooms. The inconvenience is often +great; and it certainly seems that these stores and tools are of sufficient +value to be accommodated in suitable buildings. + +SITUATION OF FACTORY BUILDINGS.--There can be no doubt that a great deal of +the "spot" disease trouble, and the general slowness of drying, can be +attributed in many factories to the unsuitability of the site chosen. +Probably the idea which actuated those responsible for the choice of site +generally was proximity to a water supply. This would account for the fact +that a number of factories are situated in valleys or near swamps. More +often than not, also, the actual clear space is very limited, and rubber +trees grow close up to the walls of the buildings. Under such +circumstances, it is difficult to see how these buildings can be anything +but dark and damp, and it is not difficult to understand the slow rate of +drying. In a few cases the sites chosen proved to be so unsuitable that the +estates were confronted with a very serious problem, the solution to which +was, either the erection of another complete set of buildings in a more +suitable spot or the installation of artificial driers. + +It must be laid down as an axiom that the first essential in a suitable +site is that water may be brought to it easily, but, as already indicated, +this does not mean that the buildings need be placed in actual proximity to +the water-supply. The mistakes made by pioneers in this work are not likely +to be repeated, and it is common now to note well-designed and +comprehensive schemes in which the water is pumped to a reservoir placed at +a suitable elevation, whence the supply is gravitated to bungalows, coolie +lines, and the factory. The importance of securing a plentiful supply of +good water for factory purposes cannot be exaggerated, and it is a point +which is only thoroughly appreciated on estates where smoke-sheet rubber +has to be prepared. + +The second essential, but of equal importance, is that there shall be an +ample open space on which the sun may shine all day. There must be no trees +too near the buildings, and there should be no adjacent swamps. Preferably, +the site should be on a raised position, so that it will be impossible for +surrounding trees to cut off sunshine, even when they are fully grown. From +such an arrangement it will follow that the factory will be light and airy, +and the drying-houses will receive the maximum of benefit to drying from +direct sunshine on the roof and walls. There can be little doubt that these +considerations play a most important part in determining the rate of drying +of the rubber, and where comparisons are made between the rates of drying +in various drying-houses all these factors enter into the question and +contribute to the total result. Presuming that the thin crepes made in two +factories are equal in thickness, it is not uncommon to find that in a +drying-house, situated in a wide open space, the period of drying may be as +low as six or seven days; while in another drying-house, situated near a +swamp and surrounded by trees, the period may be as high as eighteen days +to twenty-one days. The figures quoted are not fictitious, but are facts +actually noted in the course of the writers' experience. + +A great deal also depends upon the exact position of buildings. Thus, to +obtain the maximum of light in a factory, it will be obviously beneficial +to erect it with the long sides running east and west, so that the windows +face the north and south, and the large end doors face the east and west +respectively. At first sight it would appear that the best position for the +machines would be on the north side of the building where no sun can enter; +but a moment's consideration shows that the south side would give the best +results. By the time the sun has come round to the south, it is usually +high in the heavens, and the direct sunshine does not fall very far into +the room. Even should it play upon the machines for an hour or two during +the day, no harm could result to the rubber which was being worked, as no +piece would remain there a sufficiently long time to be injured in the +slightest degree. Placed in this position, the maximum benefit of light +would be obtained, whereas if the length of the building ran east and west, +the machines would have only either the morning or afternoon light. + +[Illustration: SUGGESTED ARRANGEMENT OF BUILDING.] + +While it is advisable to erect a factory running east and west, the +drying-houses should run north and south. In this position the maximum wall +area will be exposed to the sun during the day, and it will be possible to +manipulate the windows of the drying-rooms so that those along one side are +open, and it will never be necessary to close all the windows at any time +of the day. Thus the windows facing east will be closed, and those facing +west will be open until after midday; then _vice versa_. With such an +arrangement a more uniform temperature may be obtained than by any other +arrangement of the buildings. If the building ran east and west, the +windows on the north side could remain open all day, while those facing +south would have to remain closed practically all day. The south side of +the house would be heated by the sun, while the north side would remain +cool, and the rates of drying would be correspondingly unequal. The total +wall area heated by the sun at any time of the day would be less in this +position than if the house ran north and south. + +Similarly, to obtain the best drying effect during the daytime in a +smoke-house the building should run north and south. By this means the +temperature will be maintained to the maximum possible by sun heat, and the +rate of drying will correspond. + + +_References to Sketch Plan._ + +Drying-house No. 2 should be of two storeys, and unless a separate sorting +and packing room is to be built, No. 1 should also have two floors (see +previous notes on packing-rooms). + +In the factory-- + + _V_ shows the position of the verandah, which may be quite open and + only divided from the inner room by + + _S_, a wall composed of very strong expanded metal, which allows light + and air to enter the factory. + + _T,T_ are the glazed tile tanks for the reception of latex, scrap + rubbers, and bark-shavings. + + _M_ shows the position of the machines on the south side of the + factory, with the direction of extensions, and + + _E,E_ the compartments in which the engines are bedded. In these + positions it is possible to obtain direct drive to the machines. + + _D,D_ are large double swing or sliding doors (the latter for + preference always). These, while suiting transport of rubber, provide + also for a free draught of air. + +If possible the scrap-washing machine should be placed outside the wall of +the factory, and tanks for the reception of scrap rubbers may then be +situated in convenient proximity. + +Economy of labour is obtained by grouping all factory buildings as closely +as possible, but it should be borne in mind that smoke-houses should be +regarded as a possible source of danger from fire. This point has a +practical bearing upon rates of insurance, and it is essential that the +smoke-house should be situated at a minimum of 50 feet from any other +building or group of buildings. In this connection, also, it may be noted, +as being of further practical interest, that, in the insurance of +smoke-houses, preferential rates are given to those having a good type of +slow-combustion furnace. + +CHOOSING A FACTORY SITE.--Sufficient has been written to make it clear that +the choice of a site for factory buildings is a matter demanding weighty +consideration. Much, of course, depends upon the planted area, and the rate +at which it comes into bearing. Under certain circumstances which will be +obvious, it is permissible to instal first a group of buildings of a +temporary nature only, the future site and permanent buildings to be chosen +later when the main portion of the estate comes into bearing. Often, +however, one finds that, from lack of forethought, the estate has been +committed to considerable expense in the establishment of equipment, which +later is proved to be unfavourably situated with regard to the majority of +the area in ultimate bearing. In such case, transport of latex is fraught +with difficulties and may be expensive. + +In the instance of an estate which will gradually come into bearing, it is +not easy to decide whether a temporary installation shall first be +provided, or whether, in anticipation of future demands, a complete +equipment shall be erected. So much depends upon the financial aspect of +the question, and upon the rate at which areas will come into bearing. As +far as is possible, the best policy would be that of a compromise under +which the site would suit later requirements, and the factory would be so +planned as to be capable of future easy extensions both of buildings and +machinery. + +It is not possible to lay down any definite data as regards requirements +based on acreage, or to make comparisons between any two estates of similar +acreage. The important factors determining such requirements are: + + (_a_) Area. + + (_b_) Shape of the estate. + + (_c_) Topography of the estate. + + (_d_) Available supplies of water. + +Naturally the ideal site for factory buildings would lie in a central +position, given other favourable conditions. + +CENTRALISATION OR DECENTRALISATION.--It is the experience of a number of +estates that, all other conditions being favourable, there is a limit +beyond which the centralisation of factory work leads to an unwieldy +position. We are not here concerned with the few extremely large estates +running into tens of thousands of acres. In those cases the total area +would be divided into economic sections. The argument there would resolve +itself into a discussion on the size of an economic section. This, in turn, +would be dependent upon the type of main product, involving the question of +transport of latex or coagulum, and the possible provision of batteries of +heavy machinery. + +The differentiation between the transport of latex and coagulum, +respectively, is a most important one, and has a powerful influence in +determination of the maximum of centralisation possible. Whereas properly +prepared coagulum may be safely transported by bullock-cart, light-railway, +or motor vehicle for many miles, latex, on the other hand, demands very +careful treatment. Anti-coagulants may be employed to preserve fluidity, +but only within certain limits. Even under these conditions, other factors +(chiefly climatic) exert an influence which renders the transport of latex +for any distance a matter of anxiety. + +It will be plain, therefore, that the limits of centralisation of factory +work are much narrower for the preparation of sheet rubber than is the case +when crepe rubber is to be made. In actual experience the preparation of a +high standard and a high percentage of smoked sheet is attended with +considerable difficulty in those cases where the factory processes have +been ultra-centralised. Apart from the difficulties inherent to the +transport of latex in a state of good preservation, there is the added +difficulty of dealing quickly with large volumes of latex brought from +various quarters. None of these should be allowed to remain standing if the +best results are to be secured; but obviously there must at times be some +congestion. Even on a small scale it is often found that the latest batches +of latex are unfit for the preparation of good sheet rubber, and the +trouble may be easily exaggerated when working on a large scale. + +The centralisation of work on crepe preparation, therefore, is limited only +to a comparatively slight degree by distance of transport, and in the main +only by the size of the necessary equipment of machinery and drying +accommodation. + +The successful preparation of sheet rubber is, on the contrary, governed +chiefly by the factor of transport. With this consideration in view, +several large estates, preparing sheet rubber as the chief grade, have +found it necessary to decentralise the factory work, with very satisfactory +results. Outlying sections are given uniform and complete equipments of +necessary buildings on a small scale, and hand-driven light machines. +Uniform coagulating tanks are installed, and the methods and quantities of +chemicals employed are carefully standardised. Experience has shown that +often the best sheet rubber coming to the market has been prepared on small +estates; and the same applies to the product of these decentralised +stations on large estates. There is no _a priori_ reason why the product +from one station should differ in the smallest particular from that of +another, apart from minor fluctuations which are due to variable weather +conditions affecting the latex. If the contrary is found to be the case, it +indicates failure on the part of the person responsible to follow the +regular rules and methods. + +In the natural scheme of development of a large estate, it would be +necessary, of course, to have a comparatively small centrally situated +factory, equipped with power and heavy machinery for working scrap rubbers +in the preparation of crepe grades below No. 1 in quality. As the yield per +acre increases, or the area in bearing expands, it would be advisable later +to increase the size of the central factory and buildings so as to permit +of the preparation of a proportion of the crop in the form of No. 1 crepe +rubber, in order to be able to comply with prevailing market demands under +which preferential rates fluctuate between pale crepe and smoked sheet. + + + + +PART IV + +THE FINISHED RUBBER + + + + +CHAPTER XVII + +_DEFECTS IN CREPE RUBBERS_ + + +GENERAL STYLE OF FINISH.--Broadly, there is no single and definite style of +finish, but on the whole it may be stated that the greater proportion of +crepe rubbers are prepared in a thin form and with a close-knit texture or +finish. + +Very little thick or blanket crepe is now made on estates in Malaya, so +that beyond the mention of that type little need be written. A fair amount +of blanket crepe is sold in the Singapore market, but it should generally +be regarded as re-made rubber--_i.e._, it may have been prepared from thin +crepes, or from native pale sheets, in local rubber-washing factories. In +appearance these crepes have a rough finish, and vary in colour according +to the crude material employed. + +The general preference of the market at present is for a thin, +smooth-finished crepe, with a close-knitted surface--_i.e._, free from what +is described as "laciness." What effect this looseness of finish can +possibly have upon the quality of the rubber is not understood, but the +standard type set up by the market must be comparatively free from small +holes. + +Under existing conditions governing the sale and purchase of rubber, +various "standards" are set up. These really have no bearing upon the +intrinsic qualities of the rubber, and are concerned almost entirely with +superficial attributes. They are necessary in the absence of any proper +scheme of evaluation for the establishment of certain standards of +comparison, which imply that the rubber is apparently clean, free from +certain recognised defects, and has been carefully prepared--as far as can +be determined by a superficial examination. Thus the question of "finish" +has attained disproportionate importance, but must be respected when +preparing rubber for sale. + +Under ordinary conditions, thin crepe rubber, as it leaves the finishing +machines, has what may be termed "deckled" edges. On many estates, in order +to comply with market conditions, the edges of the wet crepe are trimmed, +and the trimmings re-made into lengths of crepe. This is done under the +impression that the market price is influenced by the evenness of the edges +of crepe rubbers. + +Again, it sometimes happens that, owing to "wear" of the rolls, the +finished dry crepe may show a faint but distinct pattern of mark--a diamond +or a horizontal bar. Since these are not accepted under the "standard" +comparisons, rubber exhibiting these characteristics does not obtain the +top market price. In other words, these innocent and innocuous marks are +regarded as defects and penalised accordingly. + +Enough has been written to show how very important becomes the question of +finish. It will be acknowledged that the superficial qualities demanded in +the "standard" market type can be reproduced by any estate having adequate +machinery and ample facilities for drying and handling the rubber. + +Methods of preparation and formulæ for the employment of chemicals are so +well laid down that, up to the stage of machining, no difficulty need be +encountered. But the standard type of finish in the dry crepes cannot be +obtained unless the estate factory is fully equipped with the three types +of rolls necessary--_i.e._, macerators, intermediate crepers, and smooth +finishing-rolls. This subject has received full discussion in Chapter +XIII., and is here only mentioned with the view of emphasising the point +that no estate can be blamed for a lack of "finish" in crepe rubbers if the +equipment of machinery is inadequate or in poor condition. + +If, on the other hand, the factory has ample machinery for requirements, +and a good finish cannot be obtained on the thin crepe, then it is time the +rolls were attended to and changed, or that the ratios of the driving +pinions were altered. + +DIRTY EDGES.--It seems to be almost impossible to keep old machines clean, +and it is equally difficult to keep the edges of crepe free from oil and +dirt. Usually these dark edges are to be found on crepe which is rather +wide, and it will be noticed that where wide crepe is made, unless special +precautions are taken, the edges of the rubber often pass under the edges +of the hopper and so pick up dirt and oil. On most machines it is a great +mistake to attempt the preparation of wide crepe; nothing but narrow crepe +must be made. To obtain this it is necessary to decrease the width of the +hopper placed above the rolls. This can easily be effected by blocks of +heavy hard wood, cut to shape and fastened in position. + +Sometimes the dark edges of crepe are due to another cause. Rolls may be +gradually worn in the middle, so that to obtain a good finish it becomes +increasingly necessary to tighten up the screws which regulate the distance +between the rolls. It thus happens that just at, and beyond, the edges of +the rubber the rolls grind upon each other, and fine particles of iron and +graphite are transferred to the rubber. In such a case it is evident that +either the rolls must be "turned" or that a new pair of rolls must be +substituted. + +IRON-STAINS.--One of the causes of iron-stain on rubber has been mentioned +in the preceding paragraph. This particular kind of iron-stain must not be +confounded with rust-stain, and gives a dark dirty colour. It results from +the grinding together of the rolls, and is usually noticed in the finishing +of fine pale crepe. For this operation it is necessary to screw up the +rolls tightly, and it will be plain that, whenever the rolls are vacant of +rubber, there is a tendency for them to grind upon each other, thus setting +free fine particles of iron and graphite. In order to avoid this, one must +be careful to see that between the working of each length of fine crepe the +rolls should be occupied with another piece of rubber, which may be kept +for the purpose. In some factories this trouble apparently does not exist, +while in others the amount of wear on the rolls is surprisingly great, and +the damage done to the rubber is excessive. The only way in which this +difference can be accounted for is that there must be a great difference +in the quality of the roll material. Some rolls seem to be excessively +soft, and from these contamination by iron-stain is great. For this reason +rolls are sometimes rejected, and there would appear to be an objection to +any but chilled steel rolls for the final stage of finishing crepe rubbers. + +RUST-STAINS.--Rust-stains, on the other hand, throw the responsibility +entirely upon the labour and supervision of the factory. Rust is formed +upon the rolls when they are at rest, and any one passing pale rubber +between the rolls before they have been thoroughly cleaned is guilty of +culpable negligence. Even when apparently clean, a piece of lower grade +rubber should be passed through the rolls several times so as to remove any +slight trace of rust remaining. + +Rust-stains have also been caused in a few cases by the large knives which +are used to cut up lumps of coagulum, or by allowing freshly coagulated +rubber to come into contact with iron vessels in the factory. + +A similar appearance has been traced in a few instances to contamination of +the coagulum in transit by the dust of the reddish rock (laterite) employed +in localities for road-making. + +OIL-MARKS.--The origin of oil-marks in crepe has already been described in +Chapter XIII. The whole question resolves itself into one of cleanliness, +moderation in lubrication, and supervision. The machines should be +inspected every day, and once a week rolls may be swabbed down with a 10 +per cent. solution of caustic soda applied by means of a piece of cloth +fastened round the end of a stick. Immediately after this operation water +should be turned on and the rolls set in motion, so that all traces of +caustic soda are thoroughly removed. If possible, lubrication by oil should +be substituted by grease lubrication through screw caps. + +Particular attention should be paid to the back of the machines. None but +the individual in charge of engines should be allowed to lubricate the +machines, and he should be held responsible for any excess of lubricant. + +As a rule oil-marks are restricted to the edges or the proximity of the +edges of crepe, but sometimes the streak is to be found in the middle of +the length. In such a case it is almost certain that the oil or grease has +been picked up by the rubber in the tray. It sometimes happens, if the +"liners" of the bearings are eccentrically worn, that a few drops of dirty +oil or a particle of grease are squirted out to some distance. These +usually find a resting-place in the tray, and the contamination may then +appear in any part of the rubber. + +It will be clear, therefore, that all trays beneath machines should be +examined as the probable source of danger from contamination by oil and +dirt. If the trays are as wide as or wider than the effective portion of +the rolls, they should be discarded. In their place (except sometimes in +the case of the macerating machine) all that is necessary is a movable +piece of board, in width not less than from 4 to 6 inches shorter than the +width of the rolls. Any oil or grease ejected from the bearings will thus +be allowed to fall clear of the board; and defects due to oil streaks, +etc., will be very much diminished, if not entirely obviated. + +This point in connection with the damage possible by the existence of wide +trays is commended to the notice of manufacturers of machines for +plantations, as it is common to find that trays are made which contravene +the rule prescribed by experience. In fact, trays on some machines have +been so designed as to act as "traps" for all dirty matter exuding from the +bearings. Not only so; they are sometimes made of such a shape and height +that oil or grease lodging upon the edges act as a "wipe" to the rolls, +thus increasing the possibility of contamination. Until this defect was +investigated, it was common to note continued contamination of pale crepes +in spite of all precautions taken in cleaning the rolls at frequent +intervals. The trouble due to this cause is intensified when the same +machines are employed for the preparation of scrap-rubber crepes and No. 1 +crepe. Small pieces of scrap find their way towards the bearings and lodge +on the edges of the trays. Unless a thorough inspection is made before +proceeding with the working of the No. 1 (pale) grade, contamination may be +continuous. + +DIRT.--Streaks due to the presence of dirt (as apart from oil or grease +contamination, or that due to pieces of oxidised scrap) are unusual, and +when they do appear their origin seems to be somewhat of a mystery. It +could scarcely be advanced that the dirt was picked up on the machines, as +it is difficult to imagine where such dirt could come from. In one or two +instances there has been fairly clear evidence that the dirt was contained +in the coagulum, and the only explanation fitting the case is that it fell +into the latex after straining and during the course of coagulation. On +cutting open lumps of coagulum brought in from the field division, it has +sometimes been noticed that dirt is included, and the foregoing explanation +is the only reasonable one. How it was possible for dirt to get into the +latex must be left for explanation to those better acquainted with the +conditions under which the latex was coagulated. + +HOLES.--On some estates it would seem impossible, with the existing +machines, to make really good crepe. The complaint is that, if thin crepe +is attempted, it is invariably found to be "full of holes"; and as, +apparently, the presence or absence of small holes in crepe rubber is a +factor which influences buyers, this defect must be avoided at all costs. +Why this matter of small holes in thin crepe should weigh so heavily with +buyers is a matter which the writers are not in a position to explain. As a +matter of fact, the presence of small holes is most generally an indication +that the rubber has received the minimum amount of working on the rolls +consistent with good washing. Further working would only be undertaken with +the idea of so consolidating the rubber as to get rid of holes in order to +meet the market scheme of valuation. + +This is usually achieved by making a very thin crepe and rolling together +two lengths when wet. The resulting crepe may be slightly thicker than +ordinary, and the method employed may be usually detected by the appearance +of the edges unless these are trimmed. + +GREENISH AND TACKY STREAKS.--Occasionally one meets cases in which pale +crepe exhibits streaks varying in colour from a decided green to an almost +black in which the greenish tinge is scarcely perceptible. Experience +indicates that these streaks are much more dangerous than they appear +superficially, inasmuch as they contain traces of brass from the "liners" +of the bearings. The presence of the copper in brass is responsible for a +gradual disintegration of the rubber, commonly recognised as "tackiness." +In fact, copper may be said to be a "poison" to rubber, and every effort +should be made to avoid possible sources of contamination. The effect may +be proved easily and perceptibly by fastening together several pieces of +crepe rubber by means of a brass "paper-fastener." In course of time a salt +of copper, green in colour, will be formed, and it will be found that the +portions of rubber in contact with the fastener have "perished" and become +tacky. + +This contamination of crepe rubber may take place in two ways: + + (1) By the ejection of actual particles of brass from the bearings of + machines, due to eccentric grinding of the "standards" of the rolls + upon the brass "bushes." These particles are carried by exuded oil or + grease into trays, and thence to the rubber. + + (2) By the action of an acid lubricant upon the brass, with the + formation of a metallic soap which has a decided green colour, unless + obscured by the dark colour of the oil or grease. It is transferred to + the crepe rubber in the manner indicated above. + +The inevitable effect, apart from the superficial defect, is incipient +tackiness. The extent to which this may develop will depend upon the amount +of the copper compound present, but it should be remembered that an +exceedingly small trace is capable of causing a disproportionately large +amount of damage. This effect is further magnified if the "tacky" piece of +rubber is packed in close contact with previously unaffected rubber. + +When the defect is discovered, the affected portions should be cut out, and +the cuttings should be burned. To mix them with the lowest scrap grades, as +may be done thoughtlessly, is only inviting further trouble. + +Besides the source of danger already indicated, it may be found, but far +less frequently, that contamination may arise from the presence in the +rubber of small pieces of the brass mesh which is generally used for +straining latex. + +The view appears to be held in some quarters that these tacky streaks and +patches in crepe rubber may arise from contamination with oil or grease +alone. This does not agree with our experience. An experiment was made to +test the point using fresh oil and grease drawn from drums in stock, +specimens of the same lubricants to which traces of a copper salt were +added, and samples of lubricants taken from the bearings of several +machines. The treated pieces of rubber were placed in contact with +untreated pieces of crepe which served as "blanks." + +Notes were made at intervals extending over a period of two years. The +conclusions arrived at were: + + (1) Although there was surface discoloration, no tackiness had been + caused by fresh (unadulterated) lubricant; neither were the "blanks" + affected. + + (2) In the majority of specimens upon which had been smeared a small + streak of lubricant taken from the bearings of machines, tackiness had + supervened, and had developed likewise in the contact "blanks." + + (3) In all cases where a trace of copper salt had been used to + adulterate the fresh lubricant, tackiness was to be noted in the + course of a short period (a week upwards) after the rubber was dry. + Development was slow, but progressive, over the full period of + experiment, and the "blanks" in contact were affected. The degree of + affection was determined by the proportion of copper salt employed. In + the worst cases the affected strip of rubber had deteriorated and + disintegrated to such a degree as to cause a distinct longitudinal + gap, the edges of which appeared to consist of a moist gummy substance + of a deep syrup colour. The adjacent blanks in some cases exhibited a + similar appearance in lesser degree, or were merely affected by a + characteristic brownish stain. + +These observations regarding the possibility of damage to crepe rubbers +from the existence of brass "liners" or "bushes" in the bearings of the +machines lead to the natural query as to whether the use of brass is +necessary. Experience shows that it is not necessary. Machines in use for +years have been running with plain bearings of iron or other metallic +substances. Satisfaction is obtained without the use of brass. + +COTTON AND OTHER FIBRE.--One of the most frequent complaints made against +low grade crepes is the presence of fibre--generally classed in a wholesale +fashion as "cotton-waste." + +It is true that some years ago most of the complaints were genuine in +referring the cause to cotton-waste. The defect arose chiefly owing to the +careless use of this material in the factory. Lumps of waste when discarded +were often thrown to the ground, and became mixed with the heaps of scrap +rubber and bark-shavings awaiting attention. The fault was one of sheer +negligence, and nothing can be advanced in extenuation. Even when the +soiled waste was thrown into the external drains, it often returned to the +factory mixed up with the scraps of rubber recovered by means of the +drain-screens. + +As far as the complaint concerns itself with cotton-waste only, the remedy +is plain, and lies in the power of the management by reason of the ability +to restrict the use of "waste" only to the engine-drivers and mechanics. + +In the vast majority of cases, however, the defect arises from +circumstances beyond the direct control of the factory, and under +conditions which make it difficult to check the evil. Although against +instructions, and for the purpose of fulfilling other orders, some coolies +persist in using pieces of cloth for cleaning cups. In course of time, +unless the practice is detected, this cloth becomes coated with rubber. +Careless coolies throw it away, when it may be collected by the individuals +who gather earth-scrap; or it may be brought into the factory in the +tappers' scrap-bag. + +Cases have been known in which the fibrous matter observed in the dry crepe +rubber was of such a nature as to indicate that the source might be +attributed to leaf-stalks which had passed through the scrap-washer. It is +an easy matter to condemn the sorting as being careless, but it is another +matter to instil into the mind of factory coolies such a respect for easy +and sane precautions that the practice of them will be continued when the +eye of the supervisor is not fixed upon the workers. + +It will be clear that contamination by fibrous matter should be limited +practically to the lowest grades of rubber. + +The appearance of cotton-waste in high-grade crepes must be most unusual, +and the writers have not yet seen a case in a drying-house. That it does +occur, however, seems to be evident from brokers' reports. It is extremely +difficult to imagine how the waste enters the rubber. One possible +explanation is that a coolie may have been cleaning the rolls +surreptitiously with waste, which may have passed later into the rolls +together with rubber. Another explanation was offered in one factory by the +observed fact that coolies engaged in cutting up coagulum, ready for +passing into the machines, kept a wad of waste for the purpose of keeping +the knife-blade clean. This may have found its way into the rolls. It must +be recorded that in the course of many years of experience no case has been +seen in any drying-house of contamination of the higher grades of crepe by +fibrous matter. + +BARK AND GRIT.--With ordinary machines and the usual process of working, it +would seem impossible to wash and macerate some of the scrap rubbers +sufficiently to free them entirely from bark. This applies specially to the +grade of rubber prepared from bark-shavings. Specimens have been handled in +which it was practically impossible to detect bark, but in such instances +the amount of working necessary would be such as to interfere seriously +with the regular working of the factory. Even with the employment of +special scrap-washing machines, complaints of the presence of bark in dry +crepe have been received, but it is certain that this mode of operation +reduces the quantity of bark to a minimum. While fully realising that the +amount of working it is possible to give in proportion to the existing +machinery and the output per day is limited, it must be recognised that the +working of lower grades of rubber is usually insufficient, and that where +possible it is the duty of estates to pay more attention to these lower +grades. A considerable improvement in this direction has been noticed of +recent years. It is not uncommon to encounter managers who fail to +appreciate that complaints regarding the presence of bark in the lower +grades are founded on legitimate grounds, and that they are not frivolous +objections put forward for the purpose of depressing the price of the +article. The sooner such an idea is jettisoned the better. There would +appear to be a good future demand for the lower grades, and it is only +natural that consumers will be willing to pay the best price only for an +article which is clean. + +The same arguments apply to the complaints regarding the presence of sand +and grit. The quantity of the latter found in low-grade crepes from some +estates is surprisingly high. Its presence can often be shown by the simple +device of spreading a piece of crepe over the upturned and hollowed palm of +one hand, while striking the rubber with the other hand. + +The incidence of bark in higher grades of crepe may be due to inadvertence +or to gross negligence. In the former class one might put those occasions +on which pieces of bark are embedded in lumps of naturally coagulated +rubber. A piece of bark-shaving may fall unnoticed into latex and be +partially responsible for the coagulation which takes place. This piece of +coagulated lump may be massed with others, and hence, unless each small +piece is cut up, the bark is not perceived. Or again, by some unknown +means, a piece of shaving may drop into a jar of latex, and so become +embedded in the coagulum. Sometimes this becomes evident on cutting up the +rubber, but it is quite as likely to pass unseen. On the whole, the +presence of bark in first-grade rubber is most unusual, and should be seen +before the rubber is packed. + +In the class due to negligence may be included cases in which careless +coolies place the cup upon the ground before tapping. Pieces of shavings +fall into the cup, and coolies are too lazy to pick them out. More often +than not coagulation in the cup is caused. As it is impossible for the +European staff to supervise each individual tree tapped, some cases must +continue to pass unheeded. Sometimes bark-shavings are brought in with the +latex, and if a broken sieve is being used, these, with other impurities, +pass into the jar, and are embedded in the coagulated rubber. This must be +classified as negligence, for no manager would willingly allow the use of a +broken sieve. Again, naturally coagulated lump rubber on arrival at the +factory sometimes contains evident pieces of bark, leaves, and stems of +leaves. For lack of supervision the average coolie would not think of +picking out these obvious impurities, and would pass the whole mass into +the machines. + +OXIDATION STREAKS.--Since the introduction of sodium bisulphite defects due +to streaks, caused by portions of the coagulum becoming oxidised, have +practically ceased to exist. In the usual course, and without the use of an +antiseptic agent, the freshly coagulated rubber has a surface darkened by +oxidation. Unless this dark surface were carefully cut off, there would +result a crepe containing dark streaks caused by the mixture of the +oxidised surface portion with the bulk of the paler coagulum. The presence +of oxidation streaks in No. 1 crepes, now being made, would imply either +that no anti-oxidant substance was in use, or that the quantity necessary +to prevent this surface oxidation is exceedingly small. Although the price +obtained would appear to be influenced by the presence of oxidation +streaks, no evidence can be obtained that the actual quality of the rubber +suffers to the same degree as does the appearance--_i.e._, there is no +evidence to show that a pale rubber, in which surface oxidation has been +inhibited, is intrinsically superior to one in which slight natural +oxidation has been incident. + +"YELLOW LATEX" STREAKS.--This appearance of "yellow-latex" streaks in not +common, and may be accounted for by incomplete mixture of two different +latices. It is a fact of common observation that, when a new portion of +bark is being tapped for the first time, there is a distinct yellow tinge +in the latex excluded. As tapping progresses, this colour vanishes; usually +it may persist for a period varying from two weeks to more than a month. +Should this latex be poured into ordinary latex without thorough mixing, it +is sometimes found that, when the crepe rubber is dry, there are distinct +yellow streaks. It should be remembered that, as the rubber content of the +latex from first tappings is high, this latex is lighter than latex which +is more dilute, so that the mixed latices must be well stirred with a broad +paddle to obtain intimate mixture. It would be much better to keep yellow +latex apart, and coagulate it separately, if at all possible. In such case +the resultant crepe may be of a distinct canary yellow in tint. + +In scrap-crepes of the higher grade this distinct yellow colour is often +visible in streaks which indicate the presence of tree-scrap, etc., +obtained from recently opened tapping areas. + +BISULPHITE STREAKS.--These, again, arise from defective mixing. In the dry +rubber it is seen that there are streaks of colourless rubber in a general +mass, which may be of varying shades of yellow; or, a length of exceedingly +pale rubber is apparently streaked in patches with a darker shade of +colour. A solution of sodium bisulphite is heavier than latex, and there +would be a tendency, therefore, for the chemical to sink in the large +mixing jar. Unless stirring is thorough it is possible that portions of the +latex would not be in contact with sodium bisulphite while others receive +more than a fair share. Especially would this effect be seen where +coagulation takes place quickly, and experience bears out the truth of the +suggestion. Another factor which has some bearing on the point is the +strength of solution in which sodium bisulphite is used. In the ordinary +course of working, the acid coagulant is added immediately after sodium +bisulphite has been stirred in. Should a strong solution of the bisulphite +be used, and if coagulation takes place quickly, it is easy to see that the +possibilities of obtaining a uniform and intimate mixture are small. +Probably in no factory is the sodium bisulphite now added to latex in +powder form, but it has been found that if care is not taken to see that +all the bisulphite has dissolved before the solution is added to latex +streaks may result in the dry rubber. The undissolved particles sink to the +bottom of the coagulating jar or tank, and there slowly dissolve, forming +local strong solutions. The effect upon the rubber in the vicinity of these +strong solutions is much more marked than in the bulk of the coagulum, and +hence lighter streaks or patches appear in the dry rubber. In spite of +apparently complete mixture by good stirring, it will be seen that it is +possible, therefore, to have failed in this direction if any undissolved +powder remains in the solution of sodium bisulphite. + +"SPOT" DISEASE.--Few managers of estates preparing pale crepe rubbers are +unacquainted with this defect. It is manifested by the appearance of small +coloured spots varying in density (_i.e._, number to a unit area) and +differing in hue. The most common colours are black and orange, but "spots" +of brick-red, yellow, violet and ruby and green tints have been noted, the +last named very seldom. Sometimes in place of definite "spots," or +colonies, the colour is spread over practically the whole surface of the +rubber as a "flush." + +These coloured spots, or "flushes," indicate infection by minute fungi, +which are present in the latex prior to coagulation. The infection of the +latex takes place in the field by means of spores, which are only visible +with a microscope. + +It is not feasible to discuss any method of preventing this infection of +latex by air-borne spores, as the eventual preventive measures are so +simple. But it may be believed that under ordinary weather conditions most +latices are infected before reaching the factory. It is likewise true that +even fine pale crepes shipped in perfect condition may contain +possibilities of trouble in the form of "dormant" spores, the development +of which may commence and continue if favourable conditions arise. + +The subject of "'Spot' Diseases" has been treated fully in previous +publications,[19] and it is not proposed here to enter into any lengthy +discussion. + +[19] "Preparation of Plantation Rubber," Sidney Morgan, 1913. "Spotting of +Plantation Rubber," Keith Bancroft, 1913; Bulletin No. 16, F.M.S. +Department of Agriculture. "Spotting of Prepared Plantation Rubber," A. +Sharpies, 1914; Bulletin No. 19, F.M.S. Department of Agriculture. + +If any reader is desirous of producing the defect experimentally, all that +is necessary is to prepare a piece of crepe rubber of rather more than +ordinary thickness, roll it up while wet, and place aside for some days. + +This experiment reproduces the conditions favourable for the development of +the spores, and spots of various colours may result. It will be clear that +the chief factor influencing the result is the continued presence of plenty +of moisture. + +This condition may be created inadvertently in the course of factory +practice, if piles of crepe rubber are allowed to remain for any +appreciable period before hanging to dry. For this reason batches of wet +crepe should always be placed on edge, to allow free drainage of surface +moisture, if the rubber cannot be taken at once to the drying-sheds. + +[Illustration: THREE SPECIMENS OF FINE PALE CREPE SUFFERING FROM "SPOT" +DISEASE.] + +The condition also is provided if the thickness of the crepe is +excessive. In some factories, having no smooth-roll finishing machines, the +crepes may have a distinct raised pattern upon them. It is usual to note +that if "spot" disease appears in such crepes, it is incident to much +greater degree in the thicker portions of the rubber--_i.e._, upon the +raised pattern. + +The direct connection between the rate of drying and the appearance of +coloured spots or flushes is thus established, and it only remains to adopt +precautionary measures which will lead to an avoidance of delay (1) between +machining and hanging, (2) in drying. + +It is indicated, therefore, that, if spot disease is to be avoided, the +prime consideration is the preparation of a thin crepe which will dry +quickly under average conditions. It may sometimes happen that even very +thin crepes will sometimes be found affected on some estates. In such +instances, it will be found that the design or situation of the +drying-house is at fault, and that specially favourable conditions for the +development of the fungi have been created by excessively wet weather. +Should the trouble persist in spite of the preparation of the thinnest +crepe, it would be advisable either to abandon this form of No. 1 product +or to consider the installation of artificial aids to drying. + +We have not yet encountered any case in which it was found necessary to +treat the latex with an antiseptic or disinfectant substance for the +prevention of "spot" disease. There appears to be an idea held in some +quarters that sodium bisulphite may be so employed as a fungicide. This +does not agree with our experience, which is confirmed by Sharpies +(Bulletin No. 19, F.M.S. Department of Agriculture). + +In 1913 experiments with chinosol were undertaken at the Pataling +Laboratory of the Rubber Growers' Association, and an account of the method +of treatment was given in a printed report issued to subscribers. Dr. P. +Arens,[20] of the Malang Experimental Station (Java), has also recommended +the use of chinosol. The substance is expensive, but is effective in very +small quantity. On the whole, given average conditions in factory practice, +such aids should not be necessary, and where keen supervision is not +available may lead to other difficulties. + +[20] "Guide to the Preparation of Rubber," Arens, 1918; Communications from +the Experimental Station (Malang, Java). + +It has already been remarked that it is possible for "spot" disease to +develop in dry rubber which previously gave no evidence of the presence of +fungi. The condition necessary to such an occurrence is supplied by the +presence of moisture. Thus, to state instances which are by no means +uncommon, if a box of rubber is allowed to remain exposed to rain, or is +damaged by flood-water, or by sea-water during transit, or (sometimes) if +the rubber is packed in a damp case, the crepe on arrival at its +destination may be found to be affected to a degree dependent upon the +extent of wetting and the duration of the wetting period. + +No means are known by which these coloured spots, due to the growth of +chromogenic organisms, can be removed from the rubber. Naturally, although +they may be present in the darker lower grades of crepe, they are not so +easily visible as in pale crepe. It follows, therefore, that every possible +precautionary measure must be taken when pale crepe has to be prepared. + +We are often asked whether it is possible for an infected piece of rubber +to affect sound rubber hanging in the same building; and whether, in case +of "spot" disease appearing, it is necessary to disinfect the drying-house. + +In a general sense, the answer to both queries is in the negative. It has +not been proved possible to transmit the disease from one piece of crepe to +another, except by the closest possible contact and in the presence of an +abundance of moisture. + +A dry crepe, even when in close contact with an infected dry specimen, has +not been found to be affected. + +Unless, therefore, pieces of rubber are pressed together, under favourable +conditions as to moisture, there has been observed no transfer of disease. + +Similarly it has not been found that the presence of spotted rubber in one +part of the drying-house has been responsible for an outbreak of disease +in another part of the same building. Furthermore, after the removal of +diseased rubber from the drying-shed, freshly prepared rubber may be hung +on the same supports without becoming affected, and without any +intermediate treatment of the wooden bars, providing the crepe is thin and +weather conditions are good. In our experience, no case has been observed +in which the disease has been communicated to freshly prepared rubber by +reason of the previous presence of affected rubber. In our opinion, +therefore, any scheme for disinfecting the interior of a drying-house, as a +preventive measure against the spread of "spot" disease, is unnecessary. + +All other things being equal, it is plain that much will depend, as to the +incidence of coloured spots, upon the design and situation of the +drying-house. Sufficient has been written in previous chapters to indicate +the importance of these points as affecting the rate of drying, upon which +hinges the possibility of the appearance of "spot" disease. + +In conclusion, the chief points in any discussion of this subject may be +summarised thus: + + 1. No coagulum should be left without working for longer than the + ordinary period. Otherwise, the prevailing conditions are very + favourable for the development of the disease. + + 2. Thin crepe only should be made. The quicker the rate of drying the + less possibility is there of the coloured spots appearing. + + 3. Crepe should never be allowed to remain folded overnight, and + batches of folded wet crepe should be placed on edge to drain off + surface moisture. The rubber should be hung to dry as soon as + possible. + + 4. Several species of fungi causing coloured spots have been + recognised, and it has been proved conclusively that it is possible to + infect latex and also fresh coagulum. + + 5. As far as our present knowledge goes, it appears that infection + takes place chiefly, if not entirely, by means of the latex in the + field-vessels. It may take place during transport also, or even during + coagulation. + + 6. While it is certain that infection can be caused by contact, it has + not yet been shown that infection of the finished wet rubber takes + place in the drying-houses by means of air-borne spores--at least, + under ordinary drying conditions. + + 7. There is reason to believe that no further infection takes place + once the rubber is well into the drying stage, and that dry rubber is + not infected even by contact. From this one might infer that, as long + as rubber remains dry, infection cannot take place during the voyage + to the port of consignment. + + 8. Coloured spots do not appear until the rubber is about half dry, + because that period is necessary for the development of the fungus to + that stage in its life-history when it excretes colouring matter. The + fungus in its earlier and colourless stage may have been present from + the time the latex entered the cup. + + 9. The natural habitat of the fungi would appear to be decaying + vegetable matter in the field. + + 10. Finally, if it is found impossible to be rid of fungoid-spot + disease after having exercised all care and observed all known + precautions, nothing remains but to supersede the ordinary drying + process by some system of quick drying, such as the vacuum-drying + process or a hot-air draught system, in which the rubber dries so + quickly that any possibility of appearance of "spots" is entirely + removed. + +SURFACE MOULDS OR MILDEWS ON CREPE RUBBER.--Defects of this nature are most +uncommon in the higher grades of crepe rubber, but cases of affection in +the lower grades are not rare. + +It will be evident from all previous discussions that the incidence of +these moulds must be due to an extremely slow rate of drying. The necessary +conditions would be supplied by one or more of the following causes: + + (_a_) Making the crepe too thick. + + (_b_) Hanging the crepe in a badly ventilated or badly situated + building. + + (_c_) Occasionally by abnormally wet weather. + + (_d_) Allowing piles of crepe to remain too long before hanging. + + (_e_) Using excessive quantities of deteriorated sodium bisulphite. In + short, any factor contributing towards a retarded rate of drying may + be responsible for the appearance of surface mildews. The last + mentioned cause is of not infrequent occurrence. Knowing the chemical + to be of poor quality, relatively more is used to produce the desired + anti-oxidant effect. Unless the rubber is particularly well washed on + the rolls, there remains within it a residue of sodium _bisulphate_, + an oxidation product of the bisulphite. This is hygroscopic to some + degree--_i.e._, it takes up moisture from the atmosphere. Hence + drying is delayed, and even should mildews not develop the chemical + may sometimes be seen on the surface of the rubber as a whitish + "bloom." + +The enumeration of the possible causes of mildews on crepe rubber is +sufficient to indicate the necessary precautions to be taken, and the +discussion will not be extended further. + +TACKINESS IN RUBBER.--"Tackiness" is a term used to denote a deterioration +of rubber which renders it sticky, and, beyond this, implies that some +physical and chemical change in the nature of the substance has taken +place. In fact, it is no longer "rubber," but an oxidation product +containing much resinous matter. It does not behave as rubber, and hence +its value is much depreciated. + +With modern ideas of erection of factories to guard against the +introduction of direct sunlight, it was hoped that this defect had +practically ceased to exist. In one grade of rubber it would be expected +that tackiness would continue to appear. Earth-rubber, often exposed to +direct sunlight for a week, would naturally become tacky, and this +tackiness cannot be avoided unless the earth-scrap is to be collected more +frequently. But in many cases even the higher grades of rubber show signs +of tackiness. Experiments have been carried out at various times and in +various places to determine the cause of tackiness. For some time the +theory of bacterial origin was in favour, but none of the experimental +results was convincing. Bacteria may be present in tacky rubber; but, on +the other hand, many cases of bacteria in rubber have been observed in +which there was no tackiness. Experiments were made by one of us some years +ago with a view to testing the bacterial theory by inoculating latex with +small pieces of tacky rubber. In opposition to the results which were +stated to have been obtained, there was no spread of tackiness. Other +investigators have obtained similar results. One writer proposed to explain +tackiness as caused by excess of moisture. This perfectly simple +explanation unfortunately displays only a profound ignorance of the +subject, and does not take into account the fact that tackiness is incident +in rubber after dryness has been reached. It need not be pointed out to +planters in Malaya that wet sheets of rubber are often exposed to direct +sunlight by workers of native holdings, with no resulting harm as long as +plenty of moisture is present in the rubber. + +TACKINESS THE RESULT OF A SLOW PROCESS OF CHANGE.--As stated above, +tackiness does not appear until the rubber is dry, and even then it is to +be noted that it is possible for tackiness to appear in rubber arriving in +London, which showed no indications of tackiness when packed for shipment. + +TACKINESS CAUSED BY TRACES OF COPPER SALTS.--Spence, as the result of +investigations, has pointed out that none of the various theories put +forward to account for tackiness--viz., the action of bacteria, premature +putrefaction, oxidation, excess of moisture, the action of enzymes, +etc.--have any basis in scientific proof, and believes that the cause of +tackiness cannot be directly attributed to bacteria. It has been stated +that the only known way of causing rubber to become tacky is to expose it +to sunlight or heat. While agreeing that in the ordinary way this statement +is correct as far as one rules out the employment of chemical substances, +it must be pointed out that tackiness of the worst degree may be caused by +the presence of traces of copper or copper salts. This point has already +been touched upon in a preceding paragraph dealing with the defect of +"green streaks" in pale crepe rubber. + +In the course of laboratory experiments tackiness has often been induced by +the use of traces of copper salts. The rate at which tackiness is induced +appears to be dependent upon the amount of copper salt used, but once it +begins, the rubber molecule is very rapidly broken down, and resins are +formed. As the formation of resins is accompanied by the inclusion of +oxygen in the chemical constitution, it would be expected that dry rubber +becoming tacky should increase in weight. This is found to be the case, and +to give an idea of how this weight increases with the progress of +tackiness, the results below may be studied. + +It will be seen that the maximum quantity of copper sulphate used amounted +to 0·025 per cent, (approx.) upon the weight of latex taken. Now it is +highly probable that only a fraction of this quantity was retained in the +rubber on coagulation, the remainder being in solution in the serum. +Furthermore, as the rubber was well washed and worked down to thin crepe, +_the total quantity of copper salt remaining in the dry crepe must have +been exceedingly small_. Yet the effect is most marked and should impress +upon all managers the necessity for guarding against any possible +contamination caused by brass or copper. + + ----------+-----------------+-------------------------------------------- + _Sample._ | | _Weight of Rubber._ + +------+ +------+--------+--------+--------+---------- + | | | After |Further |Further | Percent- + |_Amount of Copper Salt._| When |Interval|Interval|Interval|age in In- + | | Dry. |of Four |of Seven|of Three|crease in + | | | Weeks. | Weeks. | Weeks. | Weight. + ---+------------------------+------+--------+--------+--------+---------- + | | Grms.| Grms. | Grms. | Grms. | + 1 |0·02 grms. copper | | | | | + |sulphate per 100 c.c. | 430 | 441 | 482 | 488 | 13·5 + |latex | | | | | + 2 | Ditto | 428 | 439 | 481 | 486 | 13·55 + 3 |0·01 grms. copper } | | | | | + |sulphate, per 100 c.c.} | | | | | + |latex } | 962 | 987 | 1035 | 1036 | 7·7 + |0·01 grms. copper } | | | | | + |acetate, per 100 c.c. } | | | | | + |latex } | | | | | + 4 |0·025 grms. copper | | | | | + |sulphate, per 100 c.c. | 502 | 513 | 558 | 560 | 11·5 + |latex | | | | | + ---+------------------------+------+--------+--------+--------+---------- + +In view of the effect thus produced by the addition of traces to latex of a +copper salt, and the observed effect on rubber of contact with copper +salts, one may imagine the result produced some years ago when on an estate +smoked sheets were washed with a solution of copper sulphate as a remedy +for surface moulds! + +With the exception of this chemical action we know of no other means by +which tackiness is produced, beyond those of direct sunshine and heat. +Cases governed by these two causes are common on estates. They are confined +chiefly to the lowest grades of scrap rubber, when the component raw +materials have been exposed to the sun for a period before being brought to +the factory. + +It is now comparatively rare to find cases of tackiness in the higher +grades of crepe, and when they occur, one may look for evidence of gross +carelessness in the admission of direct sunshine. Usually this means the +failure of some individual to regulate window shutters according to the +position of the sun in the sky. More rarely does it happen that tackiness +may have been induced by placing thin crepe rubber too near the iron roof +of the drying-shed. + +Regarding the question as to whether tackiness may be communicated by +direct contact, opinion appears to be divided. It has been stated that +sound rubber left in contact with tacky specimens was found to be +unaffected after two years. On the other hand, it is claimed that tackiness +has been induced in a sound rubber by infecting it with small pieces which +were tacky. In a preliminary article on the effect of copper and copper +salts upon pieces of dried and sound crepe[21] it was noted, after one +year, that tackiness had been communicated from the treated portion to the +"blank" in contact. There is sufficient evidence to warrant the injunction +that tacky rubber should be excluded from contact with sound rubber. If +shipped it should be packed separately. + +[21] Report I., 1916 (Sidney Morgan), Rubber Growers' Association (Malaya). + +Compounds have been put upon the market which assumedly claim to be cures +for tackiness. These are merely palliatives, consisting of starch, talc, or +chalk powders, which counteract stickiness. + +NO CURE FOR TACKINESS.--At the present stage of our knowledge, there +appears to be no cure for tackiness. Neither do we see the necessity for a +cure when the phenomenon may be avoided by taking simple precautions, which +may be briefly summarised thus: + + (1) Any permanent openings through which it is possible for direct + sunlight to enter, whether large or small, should either be totally + closed or provided with some substance which cuts off the direct + effect of the sunlight--_e.g._, ruby glass or ruby glazed cloth. + + (2) Rubber should under no circumstances be placed near any source of + heat. + + (3) No rubber should be hung in a drying-room in such a position + adjacent to a window or door that it is possible for sunshine to reach + it, even should coolies neglect to obey rules. + + (4) Instruments or vessels of copper or brass should not be used where + acids are employed. + +LACK OF UNIFORMITY IN COLOUR.--The complaint is far less real than it was +a few years ago. The introduction by the Rubber Growers' Association of the +"Metrolac" led to uniform dilution of latices varying in rubber content. +Previously the only known method of obtaining uniformity in colour and +appearance was that by which latices from all fields were mixed together in +bulk. Even so the uniformity applied only to the one bulking operation, and +any other day's results might show considerable variation from the first +standard. + +This does not take into account any observed differences in shade of colour +attributable to natural oxidation which might vary in intensity from day to +day. The introduction of sodium bisulphite as an anti-oxidant exerted a +great influence upon the colour of pale crepes generally; but considerable +variation would still have been notable but for the adoption of the scheme +for uniform dilution, in addition to the use of small quantities of +anti-oxidant. + +On most estates it is now possible, with slight exceptions due to abnormal +conditions, so to treat the latex that the pale crepes prepared on any one +day differ in no perceptible degree from the product of any other day. +Where this is not the case it must be suspected that there has been some +carelessness in manipulating the latex or the chemicals. Attention has been +drawn to the fact that there may be exceptional cases, when the determining +factors lie beyond the control of factory processes--_e.g._, heavy rains +causing over-dilution of latex, the yielding of "yellow" latex from newly +opened areas, etc. But on the whole there is now no reason why the general +average product from any estate should not be uniform in colour and +appearance. Furthermore, it should be possible for large groups of estates, +by the adoption of uniform methods, to produce similar rubber from all the +plantations. Moreover, apart from some differences caused by factors which +still need determination, the total product in a general sense should not +only be uniform in appearance but uniform in physical and chemical +properties. + +BLOCK RUBBER.--This mode of preparation is employed only in comparatively +few instances. The block is prepared from crepe rubber, which has been +dried either in a hot-air drier or in a vacuum chamber. + +There is another type of block which is made by placing layers of dry crepe +under considerable pressure. This is not the true type of block, and the +layers are quite distinct--_i.e._, they do not amalgamate. Usually this +pressed rubber consists of lower grades of crepe, and it should not be +popular, inasmuch as it leaves too wide an opportunity for the inclusion of +dirt, bark particles, and other impurities, which cannot be seen generally +on account of the protective colour of the rubber. + +In the true type of block, the layers are in a plastic condition, due to +heat, when they leave the drying-chamber; and being immediately submitted +to great pressure the result is a homogeneous mass in which the layers +disappear by amalgamation. Only the best grade of crepe is employed, and +given the absence of defects in the layers there should be no complaint +regarding the final block. + +Prepared in slabs which are three or four inches in thickness, the product +is easily handled, and should be sufficiently translucent to make it +possible to distinguish the shape of the hand when held between the block +and the light. This is not possible when blocks are made of greater +thickness. + +The only complaints which it should be possible to lodge against block +rubbers are: + + (_a_) The inclusion of dirt and other matter. + + (_b_) The use of layers of crepe which have some defect. + + (_c_) The inclusion of air-bubbles. + +The remedy for (_a_) and (_b_) lies in the hands of the factory +superintendent. The last ground of complaint is dependent upon the style of +preparation of the original layers of crepe. + +When layers of crepe are placed one upon the other, and submitted to great +pressure, it is natural to suppose that air would be contained in spaces, +and would be unable to escape. To guard against this, it would seem +necessary to prepare the crepe thin and with a fairly good surface finish. + +It must be obvious to all acquainted with the processes involved in the +preparation of block rubber, that no possibility exists for the presence +of air-bells actually enclosed _in_ thin crepe. When the vacuum-dried crepe +is folded preparatory to the blocking process it is apparent that between +the layers there must always be a considerable volume of air, a small +proportion of which is bound to be retained owing to the nature of the +surface of crepe rubber. + +That this has always been true of the preparation of block rubber cannot be +denied. It is possible, of course, for one type of block to show the +presence of air-bells more than another type, the proportion of air +enclosed in blocking depending upon the nature of the crepe of which the +block is composed. A block built up of layers of smooth, fine crepe would +be expected to contain less air-bells than a block composed of layers of a +rough crepe. + +Block rubber has been seen which was free from air-bells, but this was the +thin variety of block prepared for show purposes with far greater care, +probably, than would be expended in commercial preparations. + + + + +CHAPTER XVIII + +_DEFECTS IN SHEET RUBBER_ + + +Before proceeding to deal with defects in the rubber as it is put upon the +market a brief account will be given of faults which may be noted in the +preparatory stages. + +MILKY RESIDUE OR SERUM.--If the serum is not clear after the ordinary +period allowed for coagulation, it indicates one of the following possible +causes: + + (_a_) Failure to obtain complete mixture by thorough stirring. + + (_b_) Insufficiency of acid solution. This may be real or indirectly + due to the presence of an excess of anti-coagulant such as formalin or + sodium sulphite. + + (_c_) In cases where other coagulants than acetic or formic acids have + been employed the failure may be due to an excess of, or an + unsuitable, coagulant--_e.g._, hydrochloric acid. + +COLOURED SURFACE BLOTCHES AND UNPLEASANT ODOUR.--Sometimes the surface of +the coagulum exhibits yellowish or bluish streaks and patches. It will be +found generally that the yellowish colour is possessed by a slimy +substance, of offensive odour, which may be scraped from the surface. +Either insufficient acid has been used, or the mixing of latex and +coagulant has been at fault. + +DARK DISCOLORATION OF THE RUBBER.--This may be stated to be a natural +process when fresh rubber is exposed to the atmosphere. It is usually +described as "oxidation," and it will be noted to be absent, or to occur to +less degree, on those portions of the rubber which are protected from the +atmosphere by being below the surface of the remaining liquid. This surface +change may be prevented (see Chapters VIII. and IX.) by the use of small +quantities of sodium sulphite (for preference) or bisulphite. + +SOFT COAGULUM, SPONGY UNDER-SURFACE, TEARING OF COAGULUM.--If the whole +mass of coagulum is too soft, while coagulation appears to be complete, +over-dilution of the latex has occurred. This may apply also to the case in +which the under-surface only is spongy and soft. If coagulating-tanks are +employed, the upper edge may be comparatively hard, while the lower is soft +and weak. Often the spongy portion may adhere to the partitions. This +prevents the natural rise of the coagulum, due to retraction, as the mass +"sets." The pull between the free upper portion and the adhering lower edge +causes splitting and tearing of the coagulum, with marked porosity (spongy +appearance). The two factors to receive attention are the standard of +dilution and the condition of the surfaces of the partitions. If these have +minute cracks into which latex can penetrate, and in which coagulation +takes place, the boards should be discarded. Given the conditions indicated +above, the tearing and splitting of rubber in coagulating tanks is +sometimes augmented by the practice of flooding the tanks when coagulation +is judged to be complete. The surface water finds its way downwards between +strips of coagulum and the partitions, thus increasing the upward tension +between the free and adhering portions. The main idea governing the +practice of flooding the tanks is to prevent "oxidation" (darkening) of the +upper edges. If a small quantity of sodium sulphite is employed as an +anti-oxidant and to retard coagulation, it is not necessary to flood tanks. + +"PITTING" OF SURFACES.--In pan coagulation this "pitted" appearance is +usually limited to the under-surface, while coagulum prepared in tanks may +exhibit the defect on both faces. The existence of these numerous "pits," +or small depressions, points to the presence of bubbles of gas which have +been unable to escape freely. As the formation and retention of gas-bubbles +is not a normal occurrence in coagulation, we are led to infer that some +special conditions must have arisen. These may be supplied by one or more +of the following contributory causes: + + (_a_) The latex had begun to "sour" before arrival at the factory or + while waiting to be treated. This premature coagulation is usually + checked or diminished by the employment of anti-coagulants (see + Chapters VIII. and IX.). It is generally accompanied by the + appearance of enclosed gas-bubbles in the dry rubber. + + (_b_) There may have been a slight insufficiency of coagulant, or the + admixture was not thorough, thus allowing a slow putrefactive change + to take place in the incompletely coagulated areas. + + (_c_) The wooden partitions may not have been effectively cleansed. + The existence of a thin slime, of bacterial origin, is sometimes + noted. This is accountable for putrefactive effects in the surfaces of + the coagulum, or in the serum, giving rise to the formation of gases. + If these cannot escape freely, by reason of adhesion between the + coagulum and the partitions, "pitting" occurs. + +THICKENED ENDS OR EDGES, AFTER ROLLING.--As a rule these defects may be +ascribed to the employment of too rich a latex, or faulty manipulation. +Even if the standard of dilution should be correct it sometimes happens +that, in the preliminary rolling of a long strip of rubber, coolies begin +in the middle, rolling with a forward pressure and tension towards the ends +of the strip. This is generally not so much the fault of the coolie as +being due to the lack of proper facilities for preliminary rolling. The +table should be about 3 feet in height, so that ease of working is obtained +merely by natural pressure due to the position in which the worker stands. +The use of a heavy wooden roller would contribute towards this result, +inasmuch as it obviates the use of force, and the pressure is almost +entirely in a vertical direction. + +MIS-SHAPEN SHEETS.--It is sometimes noted that sheets may be wider and +thicker at the ends than in the middle. Manipulation alone, as indicated +above, is not solely responsible. The primary cause is to be traced to +over-dilution of latex, giving a very soft coagulum which responds too +readily to tension and pressure. Faulty treatment in rolling exaggerates +the tendency for the strip of sheet to become narrow and thin in the +middle, wider and thicker at the ends. + +THICKENED PATCHES, TORN SHEETS, "DOG-EARS," CREASES.--These elementary +defects are all due to careless working. While occasional errors cannot be +avoided, there is no real excuse for the continuance of trouble to any +degree, under average supervision. + +Thickened patches are often caused in conjunction with torn sheets, and +the trouble may be ascribed to faulty practice in allowing too heavy a pile +of wet strips to accumulate before machining. Or a comparatively small pile +may have been transported some distance. It is difficult to separate the +strip, and occasionally the separation is only effected at the expense of +two sheets, one of which is torn and the other has a portion of the first +strip adhering to it. + +"Dog-ears" due to the folding over of corners of the sheets, and creases +due to the rumpling of the coagulum, are generally the result of haste and +lack of average care. Machine coolies, more often than not, will not be at +any pains to straighten out folds before passing the coagulum through the +rolls. + +GREASINESS BEFORE SMOKING.--Under ordinary methods of working this should +never be encountered. It may be taken to show that the machined rubber has +been allowed to remain, either hanging or in piles, far too long before +entering the smoke-house. The appearance is most marked if the rubber has +remained in a cool and moist atmosphere--_e.g._, if it has been hanging +over-night in a closed and badly-ventilated factory. In a marked degree +this is to be observed in the preparation of air-dried sheets, unless they +are exposed, when freshly prepared, to the action of the sun for a period. +This period, in the case of rubber prepared on native small-holdings, +generally extends over several days--until the sheets are more than half +dry. + +In the preparation of smoked sheet, the greasy appearance and the cause +outlined contribute to a defect which is eventually described as +"stretching rusty." + +SURFACE BLEMISHES.--The coagulum, during coagulation and subsequently, can +be contaminated in various ways. In most cases a little intelligence or +increased care would prevent the occurrence of these defects. + +When the coagulum remains over-night, in the absence of a cover, it is not +uncommon to note the presence of dirt (from the roof above, or blown in +from the outside), the droppings of mice and rats, flies and small insects. +In theory these should be seen and removed by the factory hands. In +practice, except while under immediate supervision, the extraneous matter +is often rolled into the soft coagulum. + +A fairly common cause of this surface contamination is the exhaust from the +power-unit; generally the worst offender is a steam-engine. Grit and smuts +continually find their way into the factory, alighting on the tables, in +the latex, in the water, and on the freshly prepared rubber. They are +rolled into the soft rubber and lead to marked depreciation in the selling +value. The radical remedy seems obvious, but is often beset with many +difficulties not unconnected with financial considerations. + +Other superficial blemishes, such as those due to the presence of rust +marks, oil or grease patches, etc., are self-explanatory, if a little +thought is brought to bear upon them; and it is not proposed here to +discuss such defects more fully. + + * * * * * + +Having now dealt with certain defects which are visible in wet rubber, we +come to the discussion of others which are only perceptible either during +or after the drying period. As far as is known no plantations of any size +now prepare sheets other than in the form of smoke-dried rubber, with the +exception of a few which make a special form of thick and partially +air-dried product known as "slab" rubber. + +It is not proposed, therefore, to treat in any detail with air-dried sheet +rubber. Certain obvious defects are common to both air-dried and +smoke-cured sheets, and these will be first discussed. + +UNEVENNESS OF APPEARANCE.--This lack of uniformity may refer either to size +or colour, or to both. Apart from any other contributory causes, this +variation is due, in pan sheet, to a neglect to standardise the dilution of +all latices, or to lack of uniformity in the quantity of standardised latex +placed in each receptacle. + +Where tanks are employed all sheets from the same tank should be of the +same size before rolling, and any subsequent disparity in thickness and +length must be attributed to some alteration in the width of the gap +between the rolls of the machines. + +Unless all latices are standardised by means of an instrument, it is of +course probable that the content of one tank may be found to differ from +that of another. + +In a general sense, whether air-dried or smoke-cured sheets are considered, +a thin strip will dry more quickly than a thick one, and should be paler in +colour when viewed by transmitted light--_i.e._, when the rubber is held +between the eye and the source of light. + +It is necessary, therefore, to guard against the possibility of variations +in thickness caused by faulty manipulation. The distance between the +squeezing rolls (smooth) and between the marking rolls (patterned) should +be adjusted and should remain set until the conclusion of work. In a +factory having nothing beyond average requirements in equipment of machines +it should not be necessary to have to interrupt the work of the smooth +rolls or "markers" by having to make adjustments. This is, however, +inevitable if there is only one smooth-roll machine, as it is always +desirable to reduce the thickness of the coagulum by at least two stages +through even-speed smooth rolls. In some factories there are three light +power-driven smooth-roll machines, the gaps between pairs of rolls being +set so as to obtain a gradual thinning effect upon the fresh coagulum, +which is then passed once between patterned rolls. With such equipment it +is found possible, in some cases, to omit the preliminary hand-rolling, and +the strips of coagulum from the tank are passed direct through rolls set +with a wide gap. This work demands much care, as it is necessary to avoid +any distortion of the coagulum which may be caused by its own weight and +length. + +VARIATION DUE TO OXIDATION.--The subject of oxidation has been mentioned in +the opening paragraphs of this chapter. It will have been learned that +oxidation is a natural process, and that it may be prevented by the +employment of anti-oxidants such as the sulphite or bisulphite of soda. In +earlier days it was sometimes prevented by steeping the thin rubber in very +hot water. + +In the absence of an anti-oxidant the degree of oxidation may vary daily +and in different batches of latex on any one day, so that there is always +the possibility of a lack of uniformity due to oxidation effects. This +would be more evident in air-dried sheets than in smoke-cured rubber, as in +the latter case the darkening of the surface would be masked by the colour +induced by the smoke-drying process. + +To obviate this variation anti-oxidants are used on most estates, but the +accidental or misinformed abuse of these chemicals may lead to further lack +of uniformity. Hence it is necessary to follow carefully the formulæ +prescribed by experience. + +COLOUR OF SMOKED SHEETS.--It may be of interest to note that the effect +known as oxidation is attributed to the presence of micro-organisms called +enzymes (ferments) in the latex. It can also be produced artificially in +various ways--_e.g._, by the use of the crude product of wood-distillation +(pyroligneous acid) as a coagulant, or by the addition to the latex of +small quantities of a phenol such as carbolic acid. It is thus possible to +prepare in sheet form a rubber which has the appearance of having been +smoke-cured, although it may never have been in a smoke-house. + +It will be clear, therefore, that apart from other causes, the colour of +the cured sheets may be influenced by oxidation of the fresh coagulation, +and by the constituents of the smoke. It follows that the smoke from +timbers which are richer than others in certain chemical bodies set free by +combustion will produce a rubber darker in colour. + +There is thus no real connection between colour and period of cure, +although in a general sense the longer the interval the darker the colour. + +Similarly it is now plain that when anti-oxidants are employed in excess +the paleness of the rubber is in no degree truly indicative of the period +during which the rubber has been smoke-cured. + +The influence of the effect of the hypsical condition of the wet rubber +upon the final colour must be thoroughly grasped. One may take two sheets +of apparently the same thickness, and smoke-cure them in juxtaposition +within the same house, only to find that one dries much more rapidly than +the other. As a consequence, the first, when fully cured, will be of a +medium golden brown colour; while the other, owing to protracted smoking, +will be dark. Evidently there must be some distinct difference between the +two in physical condition prior to the smoking. Here the factor involved is +the rubber-content of the latex. Given two pieces of coagulum of identical +thickness, but prepared from latices of different dry rubber content, it +will be obvious that to reduce them to similar thickness, more pressure +will be necessary in one case--_i.e._, that piece of coagulum will be much +more dense (more consolidated)--while the other will be comparatively soft +and porous. Into the latter warm smoke can penetrate much more easily, and +the internal moisture can escape more rapidly. The full cure may be made, +say, within twelve days, while the tougher sheet may demand up to twenty +days. + +To attain uniformity in colour, therefore, the following points must be +studied and controlled as far as is possible: + + (_a_) Uniform dilution of all latices. + + (_b_) Uniform dimensions of coagulating receptacles. + + (_c_) Uniform volumes of standardised latex. + + (_d_) Uniform quality and quantities of chemicals. + + (_e_) Uniform methods of manipulating the coagulum. + + (_f_) Uniform conditions of fuel and accommodation during + smoke-curing. + +SURFACE GLOSS.--In the choice of fuel there is room for control if one has +good timber available. This point opens up a discussion on the vexed +question of "over-smoking," as the term is sometimes applied to a +pronounced dry glossy appearance of the surface of sheets. + +Three main factors are involved: + + (1) The nature of the fuel. + + (2) The ratio between furnace capacity and the capacity of the + smoke-house. + + (3) The rate of combustion. + + Obviously any fuel which yields an excessive quantity of tarry matter + or creosotic substance would conduce to the formation of a heavy glaze + on the rubber. Such fuel, therefore, should at most only be employed + as the smaller portion in a mixture with "dead" timber. + +It is impossible to lay down any general rules for the guidance of estates, +as the timber available varies so widely in nature. Experience must be the +only guide, and it should not be difficult to obviate the defect. Even so, +there must be minor differences between the results obtained on estates, so +that it is not possible to make strict estimations of the smoke-curing +period by an examination of the surface appearance of rubber, even under +the best of conditions. Some estates find that the rubber has a distinct +gloss in ten days, while others may smoke-cure for twice that period +without difficulty. Evidently, therefore, the question of available fuel is +of prime importance. It may be remarked that very satisfactory results are +always obtained from the use of fairly dry timber obtained from thinned +rubber trees, mixed with the "dead" timber of old logs and stumps found on +the estates. + +Obviously if a smoke-house has a superabundance of furnaces, producing more +heat and smoke than is required, glazing will result. The point is tested +by the average temperature maintained and the average rate of drying. The +result of a high temperature would be the possibility of volatile tarry +matter being driven in excess to the upper chamber. That this effect is +eventually produced even at optimal temperatures is evident from an +examination of the wood-work within the upper room. + +It is clear, also, that the rate of combustion exerts an influence. In a +general sense a rapid consumption of fuel would augment the quantity of +tarry matter passing into the upper chamber over any given period, and the +possibility of glazing would be increased. + +On the other hand, it is possible that a surface glaze might be formed if +the temperature were uniformly too low, especially if the rubber were +rather thick. The rate of drying would be so slow, that if a timber rich in +tarry matter were employed, the rubber might be exceedingly glossy. + +In order to guard against the appearance of a heavy glaze, then, the +following points must be observed: + + 1. The fuel must be carefully selected by experience. + + 2. The sheets must not be thick. No sheets should be thicker than 1/8 + inch measured in average section across the ribs. + + 3. The temperature must not be too high. An average working + temperature of 120° to 125° F. should be ample. + + 4. If the sheets are fairly thick, a low average temperature should be + avoided. No lower average than 110° F. should be allowed. + +DULL, BLACK SURFACE.--This is the opposite of the previous case, and +generally is accompanied by a fairly heavy darkening of the surface due to +"oxidation" effects. The fuel used is too "dead," and needs the addition of +some substance containing a fair amount of creosotic matter. The appearance +of the rubber does not justify the assumption that it has been over-smoked. +As a matter of fact, this type of rubber often becomes affected by mildew +fairly rapidly, thus showing that the smoking has been inefficient. + +It may happen that an estate is in the habit of using a fuel which gives +even to a thin sheet a heavy glaze in a comparatively brief period. The +general custom is to soak such sheets in cold water, and then to scrub the +surfaces, sometimes using soap, in order to cleanse the rubber and free it +from the glaze. This operation may be done too well, in which case the +rubber will have a dull appearance, and may be rather more liable to +develop surface mildew after a time. + +MOIST GLAZE, GREASINESS OF SURFACE.--This describes the condition of sheet +rubber when taken from the smoke-house. Sometimes the greasiness does not +develop until the rubber has been out of the smoke-house for a day or two. + +As far as experience shows at present it may be due to two causes: + + (_a_) The use of an excess of sodium bisulphite or sodium sulphite. + The use of sodium bisulphite is not recommended generally for + sheet-making. It may cause the rubber to be too pale in colour, and + the abuse of it may delay the drying unduly. In the latter case, a + trace of the salt may remain within the rubber or upon the surface. If + so, as the substance remaining is fairly hygroscopic, it will take up + moisture from the atmosphere and may cause the surface of the sheets + to have a moist and shiny appearance. The moist surface deposit comes + away upon the hand when the sheets are touched, and is difficult to + remove entirely. On some estates a very small quantity of the + bisulphite is employed, as it is found to be of service in the + prevention of bubbles, but in unskilled hands the method is open to + abuse, and is, therefore, not recommended for general use. + + A large number of estates now use sodium sulphite in very small + quantities as an anti-coagulant and a preservative for latex in the + field. The abuse of this very useful substance carries its own + penalty. The substance is hygroscopic; and if an excess is present the + drying period will be protracted, and the sheets will have a very + moist surface film. + + It may be found sometimes that only some of the sheets are affected. + This indicates that, whereas uniform quantities of a solution of + sodium sulphite have been served out in all fields, the proportion may + have been excessive in the case of fields giving a latex of + comparatively low rubber content. What suits the latex from old trees + may be excessive probably for the latex of younger trees. This is not + an infallible rule, as in the case of older fields in which immature + bark is being tapped, it is to be noted that the dry rubber content of + latex may be less than that of latex obtained from younger trees. + + This type of moist glaze is not easy to remove. Ordinary surface + washing had but a temporary effect, and the trouble recurs. The only + way of dealing with the difficulty is to soak the sheets for days in + running water (or in successive changes of water) and to re-smoke + until dry. + + (_b_) The second type of moist glaze is not so difficult to deal with, + and may be removed as a rule by washing the sheets when the rubber is + otherwise apparently dry. + + It appears to be mainly a matter of unsuitable fuel for smoking and of + failure to provide adequate ventilation. A large number of estates + have been "thinning-out" or are doing so systematically. The logs thus + obtained are often used as fuel in the very green stage. The smoke + thus generated must be moist, and if the building is entirely closed, + this moisture must be deposited eventually upon the rubber and racks. + Some estates have surmounted the difficulty by opening up the + roof-ridge slightly so as to allow the moisture to escape with some of + the smoke; but if the logs from rubber-trees are to be used, they + should be stacked in the sun for some time. Even then, preferably, + they should not be used alone. A judicious admixture of dead and + rotting jungle-timber appears to give very satisfactory results. + +VIRGIN SPOTS AND PATCHES.--If the description really indicates the defect +it simply means that portions of the sheets are not dry. When cut they +exhibit the typical whitish, opaque appearance described as "virgin." It is +doubtful whether any rubber put upon the market as No. 1 product nowadays +can have this complaint levelled at it. In the extreme case it points to +gross negligence on the part of the packer. + +Sometimes what are taken to be small spots of "virgin" are really patches +of tiny air or gas bubbles. The point can be easily determined by cutting +through the patch and examining the cut edges. + +SURFACE MOULDS OR MILDEW.--During the last two years, complaints regarding +the incidence of "mouldy rubber" (_i.e._, relating chiefly to the presence +of mildews on the surface) have become increasingly common. + +To judge by the comments of producers, who as a rule never again see their +rubber after it leaves the estate, one would infer that the defect is +imaginary, and that the complaints are made solely with a view to +repudiation of contracts or the general cheapening of an article of +commerce. They can often point out, with a certain amount of truth, that +there has been no change in the methods of preparation or curing, and that +previously there were no complaints. + +It is forgotten, however, that in former years the smaller output of rubber +was taken into consumption more rapidly than of recent years. That is to +say, the interval between smoke-curing and the employment of the rubber in +the manufacture of goods did not demand such a long period of storage. +Hence the effects of smoke-curing are now more likely to vanish. + +Going still further back in the history of plantation rubber, we can point +to the time when smoked sheets were allowed, or had, to remain in the +curing-sheds for very extended periods. Loose specimens of rubber prepared +during that decade still exhibit no signs of mildew growth. + +In later years a demand arose for sheets paler in colour than the old type, +and in order to meet that demand, a change had to be made in methods. This +led to a system of working whereby it was possible to smoke-dry sheets +thoroughly in from twelve to fourteen days. This interval was further +reduced on many estates, until some were producing rubber which appeared to +satisfy all requirements after only five or six days' curing. This does not +refer to the case of estates having smoke-houses of "continuous-working" +type, but to those on which smoking was confined practically to the hours +of night. Under former conditions of rate of production and consumption, +this short period of smoke-curing would possibly have been ample; but even +this is very doubtful, as often the rubber would not stand the relatively +short journey from the estate to Singapore without mildew-growth being +incipient. We have often received specimens of rubber sent from estates for +criticism, and have noted that within a comparatively brief period mildew +was to be seen. + +The whole matter resolves itself into a question of thorough efficiency of +smoking. This is not dependent on duration of smoking alone, but involves +other factors, such as the kind of fuel employed, the rate of combustion of +fuel, the average temperature sustained, the ventilation of the +smoke-house, and the situation of the building. Other occasional +contributory factors are contemporary adverse climatic conditions and the +possible abuse of an anti-coagulant such as sodium sulphite. + +It has been shown that after a time, given suitable conditions involving +the presence of moisture, moulds may appear on sheets which were apparently +fully smoke-cured, and that under the same conditions other and older +samples were unaffected. It is argued that the latter sheets had evidently +been smoked more efficiently than the others. Hence it is fair to assume +that, except under very special conditions, which do not apply to the +ordinary procedure in the shipping, storage, and sale of rubber, moulds +will not develop upon sheets which have been properly smoked. The term +"properly smoked" signifies efficient smoking for all practical purposes +under ordinary procedure, and implies or includes all the advantageous +factors which have been discussed or alluded to in preceding paragraphs. + +Without discussing in wearisome detail conditions which may give rise to +the incidence of mildew on properly smoked rubber, it may be pointed out +that the following are favourable to the growth of moulds: + + (_a_) Storing sheets in a damp place before packing. + + (_b_) Packing sheets in wooden cases which are not thoroughly dry. + + (_c_) Piling up cases of rubber in a badly ventilated store-room. + + (_d_) Placing the cases on a cement floor. + + (_e_) Wetting of cases by sea-water or by rain during transport, etc. + +BLACK STREAKS, SPOTS OR PATCHES.--The origin of these is not difficult to +trace. They are caused by drippings from the roof, and contain condensation +products from smoke plus moisture. The ventilation of the roof-ridge should +receive attention, and if the trouble persists it will be necessary to +place some absorbent screen below the sloping roof. Sackcloth is sometimes +used, but leads to a worse state of affairs unless changed frequently. In +most modern smoke-houses having an iron roof there is an inner lining of +soft timber. + +There scarcely seems a necessity to discuss the case in which an iron roof +has become perforated by the action of smoke. The remedy is too obvious to +describe. + +WHITISH OR GREY STREAKS.--This is a very uncommon defect, and is generally +to be traced to a building in which fairly new galvanised sheets have been +employed. The zinc surface becomes oxidised, and the whitish powder which +is formed "flakes," or is carried away by drops of moisture condensing on +the surface of the iron sheets. + +RUST.--Sometimes if a sheet is stretched forcibly and allowed to retract +quickly, the hitherto clear surface will be seen to be marred by a "rusty" +deposit. The rubber is then described as "stretching rusty," and its value +is depreciated. + +This defect has caused more trouble during recent years than any other. It +is not proposed here to argue the question as to whether the presence of +this film, which appears when some rubbers are stretched, is detrimental to +the physical qualities of the product on vulcanisation. With the mere +statement of opinion that it could do no apparent harm, we may pass to the +aspect of the case as it affects the buyer and consumer. If one were to +judge by the attention drawn to the appearance of smoke sheet-rubber after +it has been stretched and allowed to retract, one would imagine the defect +to be of comparatively sudden and recent incidence. This is not so. The +peculiarity must have existed for years, and perhaps became more marked as +so many estates abandoned the former common practice of allowing varying +quantities of water to be placed in the collecting cups. As the substances +which cause the defect to be visible are partially soluble in water, it +would follow that when working with the very dilute latices which were +characteristic of the earlier years of the plantation industry, the +remaining liquid in the pan after coagulation would contain an appreciable +quantity of soluble substances which would otherwise have been retained in +the coagulum. + +Conversely, the richer the latex, the greater the percentage of protein +matter retained in the coagulum. In the case of very rich latex, it must be +within the knowledge of every manager that the quantity of remaining liquid +in the pans would be almost nil. We may assume that the greater part of +these soluble proteins would be enclosed in the structure of the rubber, +but as the fresh coagulum must retain a quantity of liquid amounting to +from 60 to 70 per cent. by weight (we are now referring to rich latices), +it follows that some of the soluble protein matter must be removed when the +coagulum is placed under pressure. Even after the pressure is released more +of the contained liquid will exude from the surface of the rubber; and from +experience it is easy to imagine that this exudation, becoming +progressively feebler, will continue until the rubber begins to dry. Then, +with the evaporation of the surface moisture, the protein matter, either in +original form or as a degradation product, remains on the surface of the +rubber as a thin, solid film or crust. As drying continues, the interior +moisture escaping through the pores of the rubber evaporates, leaving +behind the substances hitherto held in solution. Should, however, the sheet +be thick and/or the temperature of drying low, the rubber may dry first on +the outside, forming a thin skin of dry rubber, which delays further drying +indefinitely. + +It will be seen, therefore, that sheets which have been prepared from rich +latex or from too deep a layer of comparatively dilute latex will have a +surface film of dry protein matter. Moreover, these sheets will be slow in +drying, and in all probability will have a surface gloss and a dark colour. +Hence it is not difficult to understand that some brokers regarded the +presence of the so-called "rust" as an indication of over-smoking. + +To show that this is not so, and further that the presence of rust has +nothing whatever to do with smoke-curing, it may be stated that _the +presence of this protein film may be seen on unsmoked sheets_ which have +been prepared from rich latex, from too deep a layer of more dilute latex, +or from some thick sheets which have been rolled only very lightly. In +fact, the presence of the protein film was noted on unsmoked sheet in 1910, +when it was seen to resemble a thin yellowish glaze which could be scraped +off with a pen-knife. Later, sufficient of this substance was removed from +some very thick air-dried sheets, or thin slabs, to fill a small test-tube. + +When the sheets were bent or twisted, the apparent surface of the rubber +(_i.e._, the protein glaze) cracked in all directions. In the case of +sheets prepared from less rich latex, the surface film naturally is +extremely thin, and no cracking is observed. + +If the fresh sheets are placed in a smoke-house, the drying film will take +up colour from the constituents of the smoke, and it will be invisible. +Somewhat analogous to the instance of a transparent glass giving a visible +and opaque powder when crushed, so the transparent film on stretching +breaks up into a visible powder which is lighter in colour than the rubber +on which it is superimposed. + +It will be noted that since the introduction of standard methods of +preparation, involving uniform dilution of latex, say, to a content of +1-1/4 or 1-1/2 lbs. dry rubber per gallon, complaints as to "rust" have +decreased considerably. + +It is to be further noted as a peculiar fact that while two estates may be +apparently working on identical lines, both as regards manipulation of +latex and subsequent treatment of the coagulum, the rubber of the one may +always be free from rust, while that of the other is often, if not always, +condemned for the alleged defect. Obviously, in such a case, there must be +an initial difference between the two latices as regards the percentage of +proteins present; or there must be some small unrecognised difference at +some stage of working. + +It will now be clear that "rust" is caused by a film of matter which is +formed on the surface of the pressed coagulum, being there deposited by the +exudations from within the rubber and through the pores. It is, therefore, +necessary to avoid any conditions which will favour the formation of this +deposit--_e.g._, allowing sheets to remain too long in a moist atmosphere +before placing in the smoke-house. + +At present there would seem to be only two methods which are successful in +the prevention of a "rusty" appearance in the dry rubber. Singularly +enough, the two methods appear to be directly opposed in principle. They +are: + + A. THE HOT-WATER TREATMENT.--This method has been in constant use on + estates which have old trees giving rich latices. These latices are + always diluted to a uniform standard daily. Some estates which + formerly suffered from the defect now experience no difficulty, and in + other instances, where no complaint has yet been received, the + treatment has been followed consistently. + + (1) After the sheets have been through the marking rolls, it is the + general custom to allow them to drip for about three hours. This + interval is really excessive for the mere draining away of the surface + water, but as a rule it is just sufficient to allow a portion of the + liquid retained in the rubber to exude. It has been shown that this + liquid may contain some protein matter in solution. Sometimes in the + case of thick sheets which have been subjected to pressure so much of + this matter is exuded as to form a thin surface slime which is + distinctly evident to the touch. If the sheets are allowed to hang + overnight, the presence of the exuded matter may be detected also by + its odour. + + (2) Obviously, any method which will remove this surface film should + be of great benefit. It is found that the best results are obtained by + allowing sheets to drip for about two hours, and then placing them in + hot water for five or ten minutes. The water should be hot as the hand + can conveniently bear, and it need hardly be pointed out that the same + water should not be used for the whole day's output. For preference + there should be three or four vessels, each capable of holding a fair + proportion of the total number of sheets, and frequent changes of hot + water. + + (3) After remaining in the hot water for the period mentioned, the + sheets are removed singly, each one being surface washed or swilled as + it is taken out. + + (4) _It is important to see that the sheets are now well washed or + scrubbed under running cold water, or in frequent changes of water._ + The reason for this procedure is plain. If the sheets are merely hung + again to drip after removing from the hot water, some moisture is + bound to remain on the surface of the sheet. As this surface moisture + contains some protein matter in solution, it is evident that, as the + water evaporates, the solid protein is again deposited on the surface + of the rubber. This would explain why some estates were unsuccessful + with the hot-water treatment. It is not essential that the running + water should be cold; it may be conveniently lukewarm if drawn from + the cooling tanks of the engines. But it is essential for the best + results that there should be running water, so that the substance in + solution is carried away. If the sheets are merely washed in a large + vessel, which has been filled with clean water, it must be obvious + that, by the time some scores of sheets have been washed, the protein + matter in solution on the surface of the sheets has been transferred + to the washing water, so that the later sheets of the batch are liable + to show the defect again on drying. + + B. The second method is much more simple, and entails no extra labour + such as is demanded by the first method. A successful issue, however, + is rather more uncertain, and the method appears to give the best + results with sheet-rubber prepared on young estates or from more + dilute latex. + + In this method, the sheets after rolling are allowed to drip for a + very short interval, so that the surface water is mainly removed. The + sheets are then placed in the smoke-house, and smoking is commenced at + once. In some cases where the defect had appeared continuously for a + long period, it was found to vanish entirely as soon as the method was + adopted; but when tried on some of the older estates, the results were + very doubtful, and a return was made to the hot-water treatment. + + The explanation of the action which takes place is rather obscure, but + two theories may be advanced. + + (_a_) It may be assumed that the interval given for dripping is too + brief to allow for the exudation of the internal moisture containing + dissolved protein matter. + + In such case, the rubber is still in a highly porous condition, and it + might be advanced that the heat of the smoke may help to maintain that + condition. Thus the contained liquid might evaporate so quickly as to + leave behind the dissolved substances in the minute cellular structure + of the rubber. In other words, instead of the internal moisture + exuding slowly to the surface in liquid form, it may leave the + rubber, even in the first stages, in an evaporated condition, just as + it does in the subsequent stages of drying. Thus no dissolved protein + matter would be brought to the surface of the sheet and be deposited + there. + + (_b_) The other theory also demands the first assumption propounded in + the preceding theory, but subsequently perhaps is less feasible as it + assumes a chemical action of which we have no definite knowledge. + + The idea is that as the rubber is in a porous condition, and is placed + quickly in an atmosphere of smoke, the heat may maintain that + condition to such a degree, that some constituents of the smoke may + enter the rubber and cause the precipitation _in situ_ of the protein + matter held in solution by the contained water or other liquid. The + contained liquid would be water which has in solution possibly a very + slight trace of the coagulant employed, of sugars, of protein matter, + and of inorganic salts. Of these the substances which would evaporate + would be probably the water and the coagulant in most cases. If a salt + had been used as a coagulant, the dissolved trace would be deposited + within the rubber in this case, whereas if a rich latex had been + employed or a thicker sheet made from more dilute latex, some of the + salt would be brought to the surface and there deposited together with + the protein matter. This has actually been experienced in practice, + and it has been possible to remove minute crystals from the edges of + the rubber so prepared. + +It will be evident that in order for either theory to contain an element of +probability, the rubber must be soft (porous) when placed in the +smoke-house, and must also be fairly thin. It is observed in all cases +where the method has been successfully employed that both these conditions +are generally fulfilled--at all events the rubber is fairly thin. When +thicker sheets are made, either from rich latex or from a deeper layer of +comparatively dilute latex, the method is not uniformly successful. + +OTHER VIEWS ON "RUST" CAUSATION.--Later experimental work on "rust" +formation by Hellendoorn[22] leads to the observation that "rustiness" is +caused, not actually by the deposition of original serum-substances, but by +the decomposition thereof, under the action of aerobic micro-organisms. + +[22] "The Cause of Rustiness in Sheet-Rubber," H. J. Hellendoorn, Archief +voor de Rubbercultuur, October, 1919 (Communication from the Central Rubber +Station, Buitenzorg, Java). + +Without going into a full discussion of the subject, the following points +noted in the experimental work may be quoted: + + 1. Rustiness could apparently be produced at any time merely by + keeping freshly rolled sheets for periods varying from twenty-four to + forty-eight hours in a moist atmosphere. + + 2. Sheets placed immediately in a temperature of, say, 110° to 130° F. + never showed "rust"; but if air-dried at ordinary room temperature, + "rust" might appear. + + 3. "Rust" can be prevented by soaking freshly prepared sheets in + dilute solutions of disinfectants--_e.g._, formalin, sodium + bisulphite, or chinosol. + + If subsequently the sheets are hung for any length of time in a moist + atmosphere, the protective effect of the disinfectant gradually + vanishes and "rustiness" may be produced. + + The same disinfecting effect may be obtained by the use of steam or + hot water. It was found that there was less liability to the formation + of "rust" when sheets were immersed in water at a temperature of 95° + to 120° F., whilst steeping at 140° F. gave complete freedom. + + 4. It was shown that the micro-organisms which cause decomposition of + the serum-products flourish only in the presence of air--_i.e._, they + are aerobic in character. It is not uncommon to find, therefore, that + "rust" may be incident only on those parts of a sheet which have been + exposed for some time to air and moisture before being placed in a + warm smoke-room. + + 5. The optimal temperature for development of the particular organisms + appeared to be about 100° F., in a moist atmosphere. + + 6. Soaking the sheets in water (except the short immersion in hot + water, which we recommend), even for a period extending over a week, + does not hinder the formation of "rust." + + 7. Rustiness may be prevented by placing the sheets in a sufficiently + warmed smoke-house as long as there is adequate ventilation and a + moist atmosphere does not persist. + + The simplest means of prevention is to soak the sheets first for a + short period in water, and then to hang them to drip for a few hours + in a well-ventilated place, outside the factory and under cover.[23] + +[23] We advise and practise hanging sheets in the open, without shade or +cover. + +It will be gathered that, although there may be a slight difference between +our previous views and those advanced by Hellendoorn as to the exact cause +of formation of the "rusty" film, the general conclusions are identical +with those given by us in preceding paragraphs and previously advised in +the Malayan reports of the Rubber Growers' Association. + +BUBBLES.--The presence of bubbles in sheet-rubber has for years been the +bane of some managers' existence, and the bone of contention between +sellers and buyers. Taking the argument down to bed-rock, producers urge +that the presence of bubbles has no influence upon the ultimate quality of +the rubber on vulcanisation. They assert that the alleged defect is merely +a peg upon which to hang an unreal grievance, serving the purpose of the +buyer under the existing conditions of sale. All this may be true, but as +long as the present system continues, it must be recognised that "kicking +against the pricks" is a futile recreation. + +The sympathy of the writers is certainly on the side of the producers, +inasmuch as they realise how extremely difficult, and even impossible at +times, it is for the most careful individual to prepare sheet-rubber free +from this blemish. + +Much has been written, and many have been the discussions, on this vexed +subject; and it is recognised that sometimes, in spite of all precautions, +there may suddenly be an incidence of bubbles in rubber which is ordinarily +free from them. It must be allowed that climatic conditions and +physiological variations affecting the metabolic functions of the trees +exert an influence which is difficult at times to combat, and often beyond +human control. + +The contributory causes are many and varied. It should be premised that, +although the defect is described as "air-bubbles," it is seldom that the +appellation is strictly correct. Rarely do the bubbles contain air. In the +vast majority of cases they contain gases in minute quantity. These gases +may be considered to arise, broadly, from some decomposition of substances +(other than rubber), contained either in the coagulum or in the serum. In a +general way, if this decomposition is evidenced by an unpleasant odour, it +is described under the term of "putrefaction." We are not concerned here +with the question as to how far such decomposition may be ascribed to a +purely chemical action, or to the indirect result of the presence of +certain bacteria or other micro-organisms. Suffice it to state that, at +least as far as field operations influence the result, the decomposition is +generally to be attributed to the work of micro-organisms. Conditions +favourable to the incidence and development of these are to be found when +absolute cleanliness in all details is not aimed at. + +With this preamble we may proceed to classify possible causes of the +formation of bubbles into two groups: + + (_a_) Those originating in field operations. + + (_b_) Others which may arise after the arrival of the latex at the + factory. + +IN THE FIELD.--Decomposition may be caused by: + + (1) Spouts, buckets, and cups being dirty. Regular cleaning is + necessary. If the buckets are allowed to be taken to the lines by + tappers, trouble may ensue. Within the writers' experience it has been + shown that an otherwise baffling case of premature flocculation of + latex was traced to the presence of acid substances in the buckets, + which had been used by coolies for preparing their food. + + (2) Delay in commencing work. This means similar delay in collecting + the latex which is exposed to greater heat than under ordinary + circumstances. + + (3) Exposure to the sun's rays. The heating of the latex may provide + improved conditions favourable to the development and action of + micro-organisms. + + (4) Allowing latex to stand too long before collection. This usually + is the result of giving tappers too great a task. + + (5) The addition of water to the latex, either purposely or + accidentally, in the form of rain. The water may be slightly acid in + character, or it may carry micro-organisms from the bark into the + latex. + + (6) Tapping trees at too great a height. The latex generally has an + abnormal distance to travel before reaching the cup. + + (7) Sometimes the latex from old trees, or from trees after wintering + (just prior to full renewal of leaf), contains more than the usual + proportion of substances (_e.g._, sugars), which are capable of + effecting flocculation or coagulation. + + (8) Too great a distance for transport. The trouble arising from this + cause is likely to be much increased if the journey has to be made + over bad roads. In such case the physical action augments the effect + likely to be produced by long standing. + +The foregoing do not include all possible causes, but serve to indicate the +directions from which trouble may be mainly anticipated. It will be plain +that any latex which exhibits symptoms of premature coagulation (or minute +flocculation) should be regarded as a potential source of bubbles in +sheet-rubber. + +It will be equally obvious that the employment in the field of any harmless +substance of an anti-coagulant nature is to be encouraged. This point is +discussed in detail in Chapter V. + +IN THE FACTORY.--As a general rule it may be understood that the mischief +has been done before the latex is handled at the factory. Sometimes it is +perceptible from the peculiar appearance of the latex, and in such case the +batch should not be used for the preparation of sheet-rubber. Often it is +found that only the last to arrive at the store is visibly affected. This +should not be mixed with other apparently normal latex, as it is capable of +acting as a "leaven" to the bulk. + +Contributory factors in the store are: + + (1) Lack of cleanliness of utensils, particularly of coagulating + dishes or tanks. + + The trouble becomes acute sometimes where wooden tanks are employed. + Unless the tank and the partitions are thoroughly and regularly + cleansed, the wood may become coated with a bacterial slime, which is + capable of causing what may be termed "fermentation" of the latex + layers in contact. + + The tank should be thoroughly cleaned occasionally with a weak (5 per + cent.) solution of sodium bisulphite. The partitions should be + scrubbed and placed in the sun twice or three times a week. + + (2) Allowing latex to stand too long before treatment. This point + needs no further expansion. + + (3) The use of a latex of too high a rubber content. Such latices are + difficult to handle in order to secure uniform mixture with the + coagulant. + + (4) The use of too concentrated a solution of coagulant. In + conjunction with (3) there may be a rapid and irregular coagulation, + giving rise not only to decomposition in parts (and subsequent + formation of gas), but also to the formation of true "air-bubbles" by + inclusion of air during stirring. + + (5) The use of insufficient coagulant. Coagulation is slow and + incomplete. + + (6) Defective straining and skimming. Small flocculated particles of + rubber may pass, or be rubbed through, the strainer. If allowed to + remain, they act as local points of danger. + + (7) The proximity of the coagulating latex to some source of heat, or + exposure to sunlight. + + (8) Any delay of drying in the preliminary stages, either before or + after the rubber enters the smoke-house. + +BLISTERS.--This description aptly fits the case in which sheet-rubber in +the smoke-house exhibits large bubbles of gas which distend the surface of +the rubber. When subjected to pressure, small "balloons" are formed, which +burst with a perceptible report. It was formerly the belief that this +defect was occasioned solely by an abnormally high temperature. That such +is not the case can be shown by the experience of estates which have had +only the rubber of a particular day or short period affected under normal +factory conditions. + +At the same time it is not disputed that the heat of the smoke-house exerts +an influence (causing expansion and distension), but it is advanced that +the gases had begun to form before the rubber entered the house. + +The view held is that decomposition had supervened or was taking +place--probably from one or more of the causes enumerated in the preceding +paragraphs. The heat of the smoke-house only serves to exaggerate the +effect. It is acknowledged that the degree of decomposition must be +initially greater than in the ordinary incidence of "bubbles." + +Beyond this point we are not in a position to put forward any definite +supposition as to the apparently haphazard occurrence of the phenomenon. + +It is to be noted, fortunately, that the defect is comparatively rare, and +seldom appears on estates which employ an anti-coagulant in the field. +While we have examined persistent cases, one of which led to a temporary +discontinuance of the preparation of smoked sheet rubber, we have not yet +been able to arrive at any satisfactory idea of the exact conditions +governing the incidence of "blisters." Our investigations only lead us to +two observations: + + (_a_) That blisters have appeared on the rubber of some estates after + wintering, and during the period of new leaf-development. + + (_b_) That the defect has been noted on other estates during a period + when there were frequent but not heavy rains, and when there was a + comparatively low average temperature. + +In either case, as the factors are beyond human control, it would be +expected that without any change being made in estate procedure, the +trouble would vanish as mysteriously as it appeared. This is our +experience; but as showing the possible intensive effect of a high +temperature in the smoke-house, it may be remarked that very infrequently, +in a batch of sheets exhibiting ordinary bubbles, a few hanging directly +above the furnaces show signs of a slight blistering effect. + +"SPOT" DISEASE IN SHEET RUBBER.--That "spot" disease may appear in +air-dried sheets was evident at the beginning of the outbreak in the spring +of 1911. The first cases noticed took the form of pink and bluish "blushes" +spreading over the whole of the sheets. Later, fungoid spots began to +appear. These mainly took the form of red or black blotches, and were very +unsightly. As "spot" disease cannot develop in smoked rubber, the obvious +and simple course to adopt was to smoke-cure the sheets. When it is stated +that "spots" do not develop in smoke-cured rubber, it is understood that +the smoke-curing must be efficient and must commence as soon as the rubber +has been rolled, and the surface water has drained away. If the sheets are +allowed to air-dry for a few days, the disease may develop, and then +smoke-curing will not get rid of the coloured patches. The operation of +smoke-curing will not get rid of the coloured patches. The operation of +smoke-curing may tone down the colour, but the spots would still remain +evident. + +SUPPORT MARKS.--It frequently occurs that one sees across the middle of +smoked sheets a wide mark. This is where the wooden support in the +smoking-chamber has been. As a rule, even in the most careful cases a faint +mark may always be seen, but in many instances this mark is exaggerated to +such an extent as to point to lack of care on the part of the store +supervision. If bays of racks remain empty over-night, they may possibly +become covered with a light sprinkling of fine wood-ash and tarry deposit. +Wet rubber placed upon these racks will pick up and retain the impurities, +and more often than not they cannot be washed out. It is incumbent upon the +manager to see that empty racks are thoroughly cleansed before placing wet +rubber upon them. The better plan is to arrange that the bars can be +removed easily from sockets. There should be in stock sufficient "spares" +for, say, two days' rubber. When the dry rubber is removed, the bars should +likewise be taken away, to be cleansed and kept in the factory until again +required. This will ensure that fresh rubber always rests upon a clean +support. + +On some estates, in order to guard against a pronounced "bar-mark," sheets +are moved and turned daily. + +In other smoke-houses the upper surface of the bar is chiselled in concave +form, so as to admit of the passage of smoke below the surface resting on +the bar. + +STICKINESS.--This is not to be confounded with "tackiness," from which the +rubber does not recover. Stickiness is only temporary, and may be remedied. +As a general rule, it is due to packing sheets, which have not a good +raised "ribbing," and which may have been coated with light tarry deposits +(see Glaze). This surface film may be removed by washing the sheets, or +scrubbing them, with cold water. Usually a further two days' air-drying +will make the rubber fit for packing; and if the smoke-curing has been +efficient, there should be no need to anticipate trouble from mildew. Some +estates adopt this practice daily with success, as a form of insurance +against complaints of surface deposits. + +RIBBING, SURFACE PATTERN.--While we know that the passing of sheets of +rubber between rolls, causing a particular raised pattern to appear, has no +effect upon the actual quality of the rubber, there is a great deal of +practical advantage gained. + +The practice ensures an increase of superficial area which is an aid in +drying, improves the appearance of the rubber for selling purposes, and is +of distinct advantage in enabling the rubber when packed to travel in +better condition. Sheets do not become so closely packed; sampling and +general handling are easier on delivery. + +As long as the plane surfaces are sufficiently and regularly distorted, +there would seem to be no limits to the type of pattern or "mark" which may +be placed upon the rubber. But in actual practice the variety is small. The +most popular type of "ribbing" is that best described as a small diamond +effect, produced by a pair of rolls cut with closely placed narrow grooves +running spirally. The spirals travel in the same direction on both rolls, +producing close-cut ribbing running in opposite directions on the surfaces +of the sheet. On sheets of standard thickness, the result approaches a +diamond effect. + +A few other patterns are employed, notably that producing longitudinal +stripes of varying thickness. On the whole, the type of pattern would seem +to be immaterial, if the points already indicated are achieved. + +It is seldom one encounters a case nowadays in which the "marking" is +unsuitable, but a few estates may be using an old type of patterned roll on +which the full diamond grooving is cut. As this appears on both sides of +the sheet of rubber, and as the ribbing does not coincide, a blurred effect +is seen when the sheet is viewed against the light. + +THICK ENDS, "SHEET CLIPPINGS."--It rarely happens, even with good equipment +and average supervision, that the preparation of smoked sheet is +unaccompanied by slight defects. For instance, in spite of rules and +regulations regarding manipulation of the coagulum, it is not uncommon to +find that some sheets, after rolling, have slightly thickened ends. In the +ordinary course of events these might delay drying considerably. It is the +practice on some estates to cut off these thickened ends while the rubber +is still wet. The pieces are then machined into crepe form, but as no +sodium bisulphite may have been used, the resulting rubber cannot be +classed as No. 1 Standard Crepe. + +The other alternative is to trim the ends when the bulk of the rubber is +thoroughly smoke-dried. The moisture containing portions are then returned +to the smoke-house until dry, and are subsequently packed without further +treatment as "smoked-sheet clippings." It will be plain that, except in the +particularity of form, these clippings differ in no degree from the +original sheets; and, owing to extra smoke-curing, may arrive in even +better condition. One must be prepared, however, to find that a slightly +lower price is offered. Whether the price obtained would be comparable with +that commanded by the crepe made from wet sheet slipping would depend upon +general ruling market conditions, and the degree of care exercised in +guarding against the inclusion of any inferior pieces of rubber. In +ordinary factory practice, there could be no room for abuse under the +latter clause. + +OTHER INFREQUENT DEFECTS.--This chapter will be closed with a reference to +other small defects which, although infrequent, cannot be classed as minor +complaints. In point of fact, when they occur, they assume an importance, +in the eyes of the consumer, which is not, perhaps, sufficiently +appreciated by producers. + +DIRT.--Trouble from this source should be absent, but carelessness on the +part of packing coolies may be responsible for occasional complaints. How +the dirt is incident may remain a mystery, but it has been noted that +sheets have at times been thrown upon a cement floor. A certain amount of +loose dust may thus adhere to the rubber. + +ASH.--The source of this surface deposit scarcely needs indication. Where +open-hearth furnaces are employed, and the wire-mesh floor screens are not +perfectly sound, fine ash may find its way into the upper chamber. If this +trouble is persistent in spite of precautions, the sheets should be +surface-washed and air-dried before packing. + +BARK.--Complaints of the presence of particles of bark in sheet rubber used +to be fairly frequent, but are now less common. The trouble may be traced +to the use of defective straining sieves when the latex is being handled. + +SPLINTERS.--The use of packing-cases of unplaned soft timber is responsible +for complaints of this nature on delivery. Without here discussing the +larger question of the ideal packing case, it is sufficient to emphasise +that the interior surfaces of wooden chests should be planed. The cases are +often so damaged in transit, that splinters of wood may be found throughout +the contents. The device adopted on some estates may go far to prevent +this. The cases are first lined with loose sheets, and finally other sheets +are arranged to overlap at the top of the case. The bulk is thus enclosed +in a wrapping of sheets, and any splinters or other deleterious substances +are confined to the surface of the mass. + + + + +PART V + +GENERAL + + + + +CHAPTER XIX + +_CHOICE OF COAGULANT_ + + +Almost without exception, the agent employed in the coagulation of +plantation (_Hevea_) rubber is acetic acid, or in some cases formic acid. +Under ordinary trade conditions supplies are always obtainable at +reasonable prices, but during the recent War the question of possible +substitutes was brought greatly to the fore. Fortunately the subject of +coagulation and coagulants had been previously studied to such effect in +laboratory practice, that there would have been small difficulty in +prescribing agents other than acetic acid in cases of expediency. As far as +our knowledge extends, all the possible substances which have the power of +coagulating latex have been tested. They include mineral acids, organic +acids, compounds known chemically under the general term of "salts," +alcohols, sugars, etc. + +The heading of this chapter must be seen to "beg the question," inasmuch as +it leads to the assumption that a coagulant (in the popular sense) is +necessary to secure coagulation. In point of fact, methods are sometimes +employed which depend upon no artificial coagulant to produce the desired +effect. To these methods reference will be made later. + +In this section it is proposed to describe briefly the more important +agents which are used, or might be used, in effecting coagulation. In the +class of those which are not in common use some could be used as +expedients, while others are only of scientific interest. + +ACETIC ACID.--There is no need to enter into a discussion of the merits of +this agent. In practice it remains the cheapest and safest coagulant known +at present. + +FORMIC ACID.--This agent is equally as safe to use as acetic acid, and as +easy to handle. Bulk for bulk its coagulative power is higher than that of +acetic acid. Its pre-war shipping price, when taken in conjunction with its +coagulative power, was slightly below that of acetic acid, but local prices +put the balance in favour of the latter. If prevailing costs put it on +terms of parity with acetic acid, there would appear to be no reason why +formic acid should not have a widely-extended use on plantations. + +CITRIC ACID, TARTARIC ACID.--The acids of the extracted juices of most +tropical fruits consist, to a large degree, of citric or tartaric acids. +These can be used in place of acetic acid as satisfactory coagulants in +case of emergency; but the questions of availability of supplies and of +costs preclude their more general adoption. + +OXALIC ACID.--This is a satisfactory coagulant as far as observed effect is +concerned. It produces a rubber paler than ordinary coagulants (without the +use of sodium bisulphite), as it has the nature of an anti-oxidant. + +It would not be a safe agent in the hands of coolies, as it is classed as a +poison. + +SULPHURIC ACID.--During the War, in a period of shortage of acetic acid and +of high prices, this agent was used with success on some estates. + +It scarcely need be remarked that it is a dangerous substance to handle, +and that its employment must be accompanied by close European supervision. + +At prevailing prices during the War it was very much cheaper than acetic +acid, and even at the present reduced cost of the latter the advantage +still lies with sulphuric acid. + +It must be emphasised, however, that the abuse of this agent to any but the +slightest degree is harmful to the resultant rubber. Hence its use would be +sanctioned _only in the absence of the commoner, and much safer, +coagulants_. + +In view of the possible incidence of such an emergency, the following +notes are given. It is impressed that strict adherence to the rules must be +given. + +HANDLING SULPHURIC ACID.--(_a_) Always use glass or glazed earthenware +vessels. + +(_b_) Pour slowly and avoid splashing. Drops finding their way to clothing +or other fibrous material will destroy it locally; and if thrown upon any +part of the body may cause painful burns. + +(_c_) When diluting this agent always remember to pour the acid into the +water (_i.e._, the lesser into the greater), and never _vice versa_. Pour +the acid carefully and slowly down the side of the vessel, and stir well. + +(_d_) Should strong acid be spilled, do not throw water upon it. A supply +of sand or dry earth should be kept close at hand. Throw this upon the +acid. + +STORING SULPHURIC ACID.--(_a_) Jars or cases should be handled as seldom, +and as carefully, as possible. If the acid is contained in a case, the top +should be plainly indicated. + +(_b_) Stocks should be stored in a detached building which should not be +damp. Jars or cases should not stand on a wooden floor if possible. + +(_c_) See (_d_) above. + +BUYING SULPHURIC ACID.--(_a_) Commercial acid of specific gravity 1·84 is +the best of its kind. It contains impurities which are non-injurious to +rubber preparation. + +(_b_) It is always advisable, if possible, to buy the acid in small jars +containing not more than 100 lbs. each. Smaller jars, with a content not +exceeding 50 lbs., would be preferable. + +(_c_) If the acid is bought in jars, it should be stipulated that the +stoppers be covered with a plaster head, and that the containing crate or +case should have prominent labels or marks indicating the top of the case. + +FORMULA FOR USE OF SULPHURIC ACID.--It will be understood that as this +formula has been calculated for working with latex, having a consistency of +1-1/2 lbs. dry rubber per gallon, it applies in a strict degree only to +such latex. In other cases, where the dilution of the latex is not known, +the formula will serve as a basis for experiment until the correct quantity +has been discovered. + +(Sulphuric acid of specific gravity 1·84.) + + NOTE.--The directions must be followed carefully, and glass measuring + vessels should be used if procurable. + + (_a_) Measure out 1 pint of strong acid, and pour it carefully and + slowly _down the inner surface_ of a jar containing 20 gallons of + water. Do not pour it directly into the water. + + The heavy acid will sink to the bottom of the jar, and a good mixture + must be obtained by stirring well. + + (_b_) Of this solution (which is approximately 1 per cent. by weight), + use 1 gallon to 20 gallons of latex. + +Readers are doubtless now well aware of the corrosive action of strong +sulphuric acid, and we scarcely need point out that even the dilute acid +should not be kept in contact with the usual iron vessels found in +factories. The mixing of solutions should be done in one of the glazed +earthenware jars commonly in use. + +The formula given above works out at approximately 1 part strong acid to +2,000 parts of latex (of dry rubber content 1-1/2 lbs. per gallon). The +formula for using acetic acid with the same latex works out at about 1: +1,200. It will be apparent, therefore, that relatively sulphuric acid is a +more powerful coagulant than acetic acid. In terms of dry rubber obtained +from latex of the consistency indicated above-- + + 1 lb. sulphuric acid will produce 300 lbs. dry rubber. 1 lb. acetic + acid will produce 180 lbs. dry rubber. + +With both acids selling at the same rate, sulphuric acid would be more +economical in use; when its cost is less than that of acetic acid, which is +the normal condition, the economic advantage in favour of sulphuric acid is +augmented still further. + +It may be found that the standard formula for sulphuric acid will not +always give a perfectly clear remaining serum, even though an attempt is +made daily to work to a uniform consistency for all latices. It is +inevitable that the manipulation of the latices should be slightly in error +on occasions, or that a small mistake might occur in preparing the solution +of acid. Hence a clear remaining serum after coagulation may be secured +less often than a slightly turbid serum. This is as it should be. The +minimum quantity of acid may be adjusted so closely as to give such +results. If a clear serum is obtained always, that should be an indication +of continual excess of coagulant. Naturally, if a milky serum is always +obtained, the reverse is the case. + +As a last word on the subject, it may again be emphasised that the use of +sulphuric acid is not advised, except in an emergency; and that the +greatest possible care must be exercised in the observance of the strict +formula for use. + +HYDROCHLORIC ACID, NITRIC ACID.--These mineral acids would prove more +expensive than sulphuric acid. In addition they are much more uncertain in +action. For example, the use of a certain excess of hydrochloric acid would +not hasten coagulation, but would prevent it. Above all their effect, in +excess, is deleterious to the rubber. + +HYDROFLUORIC ACID.--This has a strong corrosive action on porcelain or +glass. Hence it has to be contained in bottles of gutta-percha or lead. It +is mentioned here merely because some years ago it found a use as a +coagulant, chiefly in Ceylon. It was sold in the form of a 10 per cent. +solution under the name of "Purub," and was the subject of a patent. + +It is effective as a coagulant, and has also an anti-oxidant action, which +was its chief recommendation when cheap and harmless anti-oxidants were not +commonly known. It is comparatively expensive, and, as indicated above, +difficult to handle and store. In short, it has nothing to commend it, in +comparison with acetic or formic acids. + +ALUM.--This substance has been used for years by native rubber producers as +a coagulant. It fulfils the desired purpose, and its popularity was +maintained because of the ease with which it could be stored and handled. +Unfortunately, this facility often led to the use of an excess, and native +sheets were often criticised as being brittle. Investigations have shown +that alum, even in minimum proportions, has an appreciably harmful effect +upon the quality of the rubber prepared by its use as a coagulating agent. +Its employment by native rubber producers has now been largely superseded +by acetic acid in some form. + +PYROLIGNEOUS ACID.--This is otherwise known under the names of "crude +acetic acid" and "crude wood vinegar." Owing to the shortage of acetic acid +during the War, attention was directed towards the possibility of making an +effective coagulant locally by what is termed the "dry distillation of +wood"--_i.e._, the wood is not burned but heated in a retort. The enquiries +could be placed in two classes: + + 1. Those which aimed at making the pure, strong acid of commerce. + + 2. Those which sought information concerning a crude coagulant + (pyroligneous acid) on estates. + +Regarding the first class, we can do no better than reproduce our remarks +published in the April local report of the Rubber Growers' Association for +1916--with the reservation that, on account of a threatened shortage of +timber, a local scheme might not now be feasible: + + "Probably the most common enquiry encountered since the rise in the + price of acetic acid is concerned with the possibility of making + acetic acid in this country. It may be stated that the proposition is + a feasible one, even on a fairly large scale. We have the essentials + necessary for such a scheme in: + + "1. A good supply of suitable timbers, the most valuable of + which, possibly, is mangrove timber, locally known as 'bakau.' + Other suitable timbers are known, but as far as preliminary + experiments show mangrove timber gives the best yield. At present + this timber is in great demand as a fuel for steam plants, but + with the extension of the local coal industry the timber may + become cheaper. + + "2. There would appear to be less valuable timber which would be + suitable for heating the retorts. Or, local coal might be used. + + "3. Supplies of lime at reasonable rates are available, as the + limestone formation in the peninsula is quite considerable in + extent. + + "4. Supplies of sulphuric acid are available from Japan, + Australia, Burma, etc., even at the present time, although + naturally rates are higher than normal. Under ordinary + conditions, supplies from England and parts of Europe would be + much cheaper than at current rates. + + "For the benefit of many readers perhaps a brief and nontechnical + description of the preparation of acetic acid would not be amiss, + and would explain the necessity for the essentials indicated + above. In brief, the process is as follows: + + "(_a_) A suitable timber is heated in a closed retort. This is + termed 'dry distillation,' and results eventually in the + carbonisation of the wood--_i.e._, charcoal is obtained in the + retort. + + "(_b_) Tar, vapours and gases are distilled over during the + carbonisation of the wood. These liquors and gases pass through + condensers. The gases pass away, while the condensed liquors + separate out into (1) wood tar, (2) a watery liquor called + pyroligneous acid or crude wood vinegar. + + "(_c_) The pyroligneous acid is separated from the tar, and again + distilled to obtain the acetic acid present. + + "(_d_) This crude acid is steam-heated with milk of lime, which + fixes the acid, forming calcium acetate (or acetate of lime). + + "(_e_) Eventually the calcium acetate is taken out in the form of + a thick paste, which is spread to dry. When dry this 'grey + acetate' is the main source of all glacial acetic acid now made. + + "(_f_) The acetic acid is released from the 'acetate of lime' by + the action of sulphuric acid. It is then distilled several times, + and under various conditions, in order to increase its strength. + In the past copper tubes were used for this purpose, but owing to + the fact that traces of copper were found to be injurious to + rubber, some works instal tubes of glazed earthenware for the + distillation. + + "Such is the process in outline, and it will be seen that no proposal + to manufacture _glacial acetic acid_ on an estate could be considered + feasible, although it would not present any great difficulty on a + large scale and under skilled direction. Furthermore, the cost of the + plant would be far too great for any estate." + +Although it is clear that pure acetic acid is beyond the scope of an +estate, crude pyroligneous acid has been produced on a varying scale in +this country and in Ceylon. In the latter country some success was obtained +by the distillation of coconut shells with comparatively inexpensive plant. +In this country, wood-distillation was practised on a few estates, but +improved facilities for obtaining pure acetic led to a termination of the +experiments, although sufficient crude acid could then be made at a +reasonable cost. + +The pyroligneous acid obtained, is generally clear, after nitration, and of +a dark brown colour. It has a peculiar odour reminiscent of smoked +sheet-rubber, or of creosotic substances in general. + +Its acid content depends chiefly upon: + + (_a_) The kind of timber heated in the retort. + + (_b_) The efficiency of the apparatus. + + (_c_) Condition of the timber as to moisture. + + (_d_) The temperature employed, and rate of working. + + (_e_) The point at which distillation ceases (_i.e._, the duration of + interval between commencement of heating and cessation of collection). + +Samples received from estates for testing purposes were found to contain +equivalents varying from 2 per cent. to 10 per cent. of acetic acid. + +They were all suitable coagulants when used in quantity calculated from the +discovered acidity, but produced rubber darker than ordinary when +air-dried. This effect was not of much importance in the preparation of +smoked sheets, but to produce a pale crepe it was necessary to employ +sodium bisulphite as an anti-oxidant. + +This darkening in colour is to be ascribed to the presence of traces of +phenols,[24] which are stated to exert an effect upon the rubber during and +after vulcanisation.[25] This subject will be discussed in another section. + +[24] Whitby, _Journal Soc. Chem. Industry_, vol. xxxv., No. 9, 1916. + +[25] See also "Preparation and Vulcanisation of Plantation Rubber" (Eaton, +Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture, +April, 1918. + +With this provision the crude pyroligneous acid which can be produced on +estates, could be employed as a coagulant until such time as the price of +glacial acetic acid was so low as to make the production of the crude acid +non-profitable. This point would be determined from a knowledge of the cost +of production per gallon, and the percentage of acetic acid per unit. For +example, if the cost of production (including cost of timber for +distillation, cost of fuel for heating the retort, cost of labour, etc.) +was 60 cents per gallon of crude acid containing 9 per cent. of acetic +acid, that would be equivalent approximately to buying glacial acetic acid +at $30 per demijohn of 44 lbs. + +SMOKED WATER.--A weak solution of pyroligneous acid may also be obtained +by passing smoke through water. With this object in view, a machine was +designed by the Federated Engineering Company of Kuala Lumpur. In this the +principle of retorting was not employed. Smoke was produced by ordinary +combustion in a compartment of the apparatus, and was drawn through water +by the action of a high-speed fan worked by hand. A solution, equivalent in +effect to a 2 per cent. solution of acetic acid, could be obtained at a +comparatively cheaper cost than crude pyroligneous acid produced by dry +distillation as it was then being practised. This was chiefly because of +the wasteful methods of fuel combustion, in the latter process, in the +heating of the retort. + +CHINESE VINEGAR.--This agent was found to be a satisfactory coagulant, and, +_a priori_, there is no reason why it should not be suitable, as it is +essentially a dilute solution of acetic acid. + +The qualities sold were generally colourless, and were probably the result +of acetic fermentation of rice. + +Samples tested showed a varying content of acetic acid, ranging roughly +from 3 per cent. to 8 per cent.; but on this basis of valuation it was +found generally that the price bore no relation to the degree of +efficiency. + +It was advanced not only that the vinegar was an efficient substitute for +glacial acetic acid, but that it was also cheaper. This latter claim was +proved to have no foundation in fact, even at the high price of acetic acid +prevailing during the period of stress. It is not likely, therefore, that +vinegar can displace acetic acid, except as an expedient. + +SULPHUROUS ACID.--The anti-oxidant effect of sodium bisulphite and sodium +sulphite is due to the liberation of the gas, sulphur dioxide. This gas +dissolves easily in water, forming an acid solution called sulphurous acid. + +This acid solution is an effective coagulant in fairly small quantity. Not +only so, but it produces, in addition, the anti-oxidant effect noted in the +employment of sodium bisulphite. It is thus possible to produce rubber +varying in shade of paleness by means of a single solution. + +In the event of sulphurous acid being used, it would be necessary to +import cylinders of sulphur dioxide from which the solution could be +prepared in factories each day. There would be no insurmountable difficulty +in this, as it is only necessary to pass the gas through a series of closed +vessels containing water. Enough solution could be prepared at one time for +three or four days, but preferably the solutions should be as fresh as +possible. Altogether there would seem to be possibilities in the use of +sulphurous acid for preparing pale crepe rubbers, providing the cost is +within comparable limits with the commoner coagulants at present in use, +and that no adverse effect on the rubber can be shown to result. If the +cost did not exceed the combined cost of acetic acid and sodium bisulphite, +the employment of sulphurous acid solution might be worthy of +consideration. There is one drawback to the use of sulphurous acid +solution, and that lies in the proximity of the limits of the quantities +necessary for coagulation and that which is in excess, and prevents +coagulation. Thus, with ordinary field latex having about 20 per cent. dry +rubber content, the minimum necessary for coagulation per 100 c.c. of latex +is about 8 c.c. of a 1 per cent. solution. The maximum quantity possible +for use is about 15 c.c. of a 1 per cent, solution, so that great care +would have to be exercised in avoiding an excess of coagulant, otherwise +coagulation would be effectually prevented. + +It is believed that the preparation of rubber by this method is the subject +of a patent secured by Messrs. Boake, Roberts, and Co., London. + +SUGARS.--Coagulation may be effected by the addition of small quantities of +sugars.[26] These are assumed to be effective by fermentative conversion +into lactic and acetic acids. The presence of lactic acid is supposed to +have a twofold effect: + +[26] "Preparation and Vulcanisation of Plantation Para Rubber" (Eaton, +Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture; +Gorter and Swart, Bulletin No. 6, West Java Expt. Station. + + (_a_) As a direct coagulant. + + (_b_) In its action upon certain organisms which, in the ordinary + course of events, would delay or prevent coagulation. Although work on + an experimental scale has been done, as far as we know no practical + application has been made of the employment of sugars as coagulating + agents. + +VARIOUS SALTS.--Of experimental interest only it may be recorded that +coagulation has been effected by means of various chemical "salts"--_e.g._, +calcium chloride, barium chloride, magnesium chloride, sodium chloride, +aluminium sulphate, magnesium sulphate, sodium sulphate, etc. None of these +has been found to have any practical application, except, perhaps, calcium +chloride, which is used in small quantity as an accelerating agent in a +special process of anaerobic coagulation, which will receive mention in the +following chapter. + +At one period during the War and the dearth of acetic acid, it was found +that there were available in England large supplies of the acid sulphate of +sodium (sodium hydrogen sulphate), which proved to be an effective +coagulant. Experimental work gave satisfactory results, but no practical +application resulted when supplies of acetic acid were again obtainable. + +VARIOUS PROPRIETARY COMPOUNDS.--We have seen many proprietary coagulants +advertised and pass into the limbo of forgotten things. They can generally +be divided into two classes. The first embraces those founded upon a +woefully incomplete knowledge of requirements. The second covers those +which meet requirements, but for which exaggerated claims are made and +excessive prices charged. + +As as instance of a substance which fell under both classifications might +be mentioned the case of "Coagulatex." Pretentious claims were made, and it +was emphasised that the liquid contained no _vegetable acids_. Acetic and +formic acids might be quoted as examples of vegetable acids, and as these +have been shown to be the most satisfactory coagulants now employed one +fails to imagine where lay the value of the guarantee given by the +advertisers of "Coagulatex." + +On analysis the liquid was found to consist mainly of sulphuric acid, +against the indiscriminate use of which warnings have been given. Thus it +was a dangerous substance for common use. + +Furthermore, comparing the value with its sulphuric acid content, it was +found that the price required for "Coagulatex" was roughly four times the +contemporary cost of commercial sulphuric acid in the Federated Malay +States. + +Those in charge of estates should realise, therefore, that no proprietary +coagulants should be adopted until a proper report of tests, and a +comparative valuation, has been obtained from one of the research +laboratories. + +CARBONIC ACID GAS, CARBON DIOXIDE.--Now of only scientific interest, it may +be noted that some years ago great claims were made for the use of carbon +dioxide gas as a coagulant. In actual practice we were unable to effect +coagulation by passing the dry gas into latex. It was suggested that the +original investigators were misled by failure to secure a dry and clean +gas. It would appear that probably the gas was prepared by the action of +hydrochloric acid upon marble or limestone. Unless intervening "washers" +and "driers" were used, the liberated gas, when passed into latex, would +carry with it traces of hydrochloric acid, which would effect coagulation. + +ALCOHOL.--In the cheap form of methylated spirit, alcohol has been employed +by us as a speedy coagulant for many years. Latex run slowly into alcohol +coagulates instantaneously. The method has been in common laboratory use. + +The employment of alcohol has also been made the part-subject of a patent +process of coagulation, to which reference will be made in the succeeding +chapter. + +VEGETABLE EXTRACTS.--At various times experimental work has been directed +towards the use of liquids of purely vegetable origin, such as the juices +of tropical fruits, and of a waste product of tropical industry--the +so-called "milk" (or water) of ripe coconuts. + +In the former class there is usually a natural acidity, but in coconut +water the acidity is chiefly the result of fermentation of the carbohydrate +(sugar) constituents. + +These substances were all found to effect a more or less satisfactory +coagulation, but it is unlikely that they would be suitable for practical +application on a large scale. + +As being more directly related to the subject of coagulation in general +than to coagulants in particular, a discussion of several special processes +will be relegated to the ensuing chapter. + + + + +CHAPTER XX + +_SPECIAL METHODS OF PREPARATION_ + + +Every year appears to bring forth some new ideas in the mode of rubber +preparation. Some of them are based in principle upon the oldest known +method--_i.e._, the native Brazilian process of making "Hard Para." Others +strike a new note, and in a few cases the claims put forward are +substantially confirmed by results. In other instances the claims are too +pretentious, and discredit may be brought upon schemes which, although +lacking in comparative success, are yet commendable for the ingenuity +manifested. + +To the present not one of these new methods has been able to compete to any +marked degree in general practice with the established methods of ordinary +preparation. A few continue to find local application, but most have either +been abandoned or are gradually falling into desuetude. + +We do not propose to discuss in fine detail all the various claims made on +behalf of these special processes, or to enter into controversies. The aim +is to present to the reader an outline embodying the main principles and +advantages claimed. + +DA COSTA PROCESS.--Briefly, this was a method by which coagulation was +effected with smoke. The smoke was generated by the combustion of wood in a +special compartment, and was forced into latex by means of a jet of steam. +It was really only applied to the preparation of coagulum intended for +crepe form. The exact degree of coagulation effected was uncertain, and the +final colour of the rubber precluded it from being classed as a modern No. +1 product. + +"BYRNE CURING" PROCESS.--This is a process for treating coagulum obtained +by ordinary methods. + +It was the subject of a patent obtained by Messrs. E. J. and F. A. Byrne, +and at one time had a considerable vogue on estates. The chief claim +advanced was that the rubber produced was in all respects equal to Fine +Hard Para, and could be shipped while still moist without detriment to the +physical qualities. + +The principle of the process was the treatment of coagulum, in either sheet +or thick crepe form, with vapours produced by the volatilisation of two +special fluids. This treatment was undertaken in comparatively small wooden +sheds, in which the coagulum was placed. The "smoke" was conducted into the +curing sheds from furnaces outside the building. The sheds were covered +externally with "felt" material to prevent leakage of the vapours, and a +very dense smoke was obtained. + +The furnaces were specially designed, and consisted essentially of a +"hot-plate" heated by a powerful kerosene blast-flame. On top of the +machine were two reservoirs controlled by taps. In these were placed the +special fluids which were released in definite proportion. The composition +of the fluids was not divulged, but it is assumed that the principal +ingredients were (_a_) wood tar products, (_b_) crude pyroligneous or +acetic acid. The mixture of these, dropping on the hot plate at the correct +temperature, spontaneously volatilised, to form dense whitish fumes, having +an intense and not disagreeable odour of wood combustion. A duct led from +the back of the machine into the curing-shed, where the vapours were +distributed through perforations in the pipe. + +The coagulum usually remained under treatment in the shed for three to four +hours, and then was removed for ordinary air-drying. When taken from the +curing-shed it had a pinkish colour, which later developed into a dark +brown by a natural process of oxidation. The exterior of the rubber, on +shipment, resembled the appearance of smoked sheets; while the interior, on +cutting, was seen to be still white. As packed for shipping, the rubber +contained from 10 to 15 per cent. of original moisture, for the usual sheet +form, and even more when "slab" rubber was prepared. + +Originally either crepe or sheet rubber was made, but later the preparation +of the crepe form was displaced largely by "slab" rubber. These "slabs" +were really very thick sheets, which had been subject to only slight +pressure. + +Still later the preparation of the "slab" form was displaced by "loaf" +rubber. This form was built up by winding together ordinary thin sheets +which had been subject to the "cure." Only slight tension was needed, +during the operation of winding, to cause close adhesion of the component +wet layers, and the final result was a "loaf" or roll dark in colour, and +apparently dry when examined superficially. On being cut, even after an +interval of months, the middle portion was still so moist as to be quite +white. + +In course of time it was discovered that all the claims made for the +process could not be substantiated, and for various reasons (which need not +be detailed) most of the estates which had adopted the scheme reverted to +ordinary methods of preparation. At the time of writing few, if any, +continue to work the process. It appears to be agreed, as the result of +investigations, that in no degree does the process yield advantage over +ordinary methods. + +FREEZING PROCESS.--A patent was secured a few years ago to cover a process +whereby coagulation was effected by refrigeration. + +Latex remained for several hours in the refrigerating chambers of an +ordinary ice-making plant. The resulting solid mass, on being thawed, +yielded a coagulum appearing in no way to differ from that obtained by +ordinary methods of coagulation. + +Provided the process exerted no influence for good or evil upon the quality +of the resulting dry rubber, the value of it would appear to depend upon +the relative cost of working, plus considerations of capital expenditure +and depreciation on the plant. At the present time it would be difficult to +imagine that the cost of preparation alone would compare favourably with +that sustained by ordinary coagulative methods. + +Furthermore, beyond the expensive refrigerating plant, the usual machinery +of a factory would still be required if the ordinary market demands are to +be met. + +Finally, it has not been found[27] that any advantage in the final physical +qualities of the rubber is obtained by the employment of this process. + +[27] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham, +and Day), Bulletin No. 27, F.M.S. Department of Agriculture. + +WICKHAM PROCESS.--This process, invented by Sir Henry Wickham, aimed at the +production of a rubber resembling Fine Hard Para. The principle employed +was that underlying the preparation of the best rubber in Brazil--viz., +coagulation of superimposed thin layers of latex by the action of smoke and +heat. + +In essential the machine employed consisted of a rotating drum into which +latex and smoke entered. The result was the formation of thin "skins" of +rubber which, coagulating _in situ_, formed a mass corresponding to "Fine +Hard." + +That the rubber was fully satisfactory as to quality is acknowledged, but +economically and in practical utility the process was unsuccessful, the +rate of output being so low. + +DERRY PROCESS.--The invention of Mr. R. Derry, late of the Singapore +Botanic Gardens, this in principle resembled the Wickham and other +processes. It aimed at a mechanical imitation of the native method of +producing Fine Hard Para. + +In place of the rotating drum, an endless belt was used. This travelled +over pulleys, more or less horizontally placed. The upper of these could be +raised to varying height above the level of the other, and likewise could +be so adjusted as to tighten the belt. + +The under layer of the belt impinged, in its travel, upon the surface of a +layer of latex contained in a shallow tray. The belt was operated by +hand-power, and the height of the latex trays was adjustable. + +The trays of latex were situated at the lower end of the machine which lay +outside the smoking-chamber. It will be understood that the vastly major +part of the total length of belt was always within the chamber. + +Smoke was generated by combustion of wood in an external structure, was +brought into the chamber by a wide duct, and was then distributed below +the belt by means of perforated pipes. + +The thin film of latex picked up by the belt was coagulated partly by the +action of smoke constituents by evaporation due to heat. Assuming (1) that +the belt was of adequate length, (2) that the rate of travel was not +excessive, (3) that the latex was not too dilute, (4) that the temperature +of the smoke was sufficiently high, (5) that the smoke was sufficiently +dense and not too damp--then the process should be a continuous one. + +It will be clear that success could only be obtained by a careful +adjustment of all these factors. The latex must, necessarily, be of a +fairly rich consistency (at least 2-1/2 lbs. dry rubber per gallon), but +unfortunately there is considerable difficulty in maintaining such latex in +a state of fluidity for the period demanded by this process, without loss +of latex. Naturally, the addition of an anti-coagulant would retard the +rate of output of the machine to a marked degree. + +The layer of rubber thus formed on the belt was stripped off, and hung for +further air-drying, as it still contained a fair percentage of moisture. + +As a really practicable method for treating plantation latex, the process +failed by reason of its low rate of output over a given interval. This +alone was sufficient to condemn it, apart from the facts (1) that it was +not shown to be a cheaper method than coagulation by acetic acid, (2) that +the resulting rubber was not proved to be of superior intrinsic value to +rubber prepared by ordinary methods. + +SPONTANEOUS COAGULATION.--All readers will be aware of the phenomenon of +the curdling or souring of milk. The behaviour of _Hevea_ latex, under +certain conditions, may be taken to be analogous. Difficulty is experienced +in maintaining fluidity--a difficulty which appears to vary in great degree +according to locality, nature of soil, age of trees, the relative demand +made upon the trees by the system of tapping employed, etc. + +It is sometimes found, before the latex reaches the store, that it may +exhibit one of various stages of premature (spontaneous) coagulation: + + (_a_) To all appearances it may be quite fluid, but a close + examination shows it to consist mainly of a serum containing very + minute particles of rubber in suspension (microscopic coagulation). + + (_b_) In a later stage these particles coalesce to form larger + "flocks" (macroscopic coagulation). + + (_c_) The whole, or practically the whole, of the latex may have + coagulated, forming one mass of rubber with a milky residual serum. + +Passing from this aspect of the question, it may be noted as peculiar facts +that: + + (1) A shallow layer of latex is less likely to coagulate spontaneously + (_i.e._, without the addition of a coagulant) than a deeper volume. + + (2) The shallow layer, and also the surface of the deeper volume + (where exposed to air), on standing will be found to develop a + superficial film of finely coagulated particles, yellowish in colour, + and having an offensive odour due to decomposition of protein matter. + + (3) While this partial coagulation is confined only to the surface of + a shallow layer of latex, it will be found that below the surface film + of the deeper volume a much more definite coagulation has taken place. + The coagulation will be practically complete, and the coagulum, apart + from a spongy appearance, is normal in character. This coagulum is + free from the offensive odour noted above. + + (4) On testing the surface film of both the shallow layer and the + deeper volume, it will be found to be _alkaline_ in character; whilst + the lower liquid surrounding the main portion of the coagulum in the + deeper volume of latex is of an _acid_ nature. + +These observed facts are sufficient to indicate that there are apparently +_two distinct types of spontaneous coagulation_, and that the latter takes +place particularly where the latex is more or less out of contact with the +atmosphere. We may, therefore, differentiate thus: + + (_a_) _In contact with air (aerobic)_: incomplete spontaneous + coagulation, accompanied by yellowish slime, offensive in odour and + alkaline in character. + + (_b_) _Out of contact with air (Anaerobic)_: Practically or wholly + complete. There is no offensive odour under normal conditions and the + serum is acid in character. + +It is concluded[28] that there are present in latex, on collection in the +field, two types of organisms. Those which work in contact with air +(aerobic) show a tendency to _prevent_ coagulation and to form an alkaline +yellow slime on the surface of the latex. The others, which work in the +absence of air (anaerobic), may, under favourable conditions, cause +complete coagulation unaccompanied by any decomposition or offensive odour +within a normal period. If air is rigidly excluded, the coagulum obtained +is quite satisfactory for all purposes. + +[28] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham, +and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918; "De la +Coagulation naturelle du Latex d'Hevea Brasiliensis" (Denier and Vernet), +_Comptes Rendus l'Académie des Sciences_, No. 3, July, 1917. + +This type of coagulation, without the employment of a chemical coagulant, +and under anaerobic conditions, was the subject of a patent granted in 1914 +to Messrs. Maude, Crosse and others. The process has been in use on Cicely +Estate (Perak) for some years. With subsequent slight modifications the +apparatus consisted in essential of a tank with a loose cover. The flanges +of the cover were sufficiently long to dip into a water-seal surrounding +the tank. Thus the cover may rise and fall without an inrush of air. + +Coagulation, in fact, can be effected thus in any kind of air-tight +receptacle; and experimentally the reader can obtain a satisfactory result +by filling completely with latex the bottle which has a loose stopper. + +Under the patent held the coagulum may be prepared either for crepe-making, +or for sheets by a modification of the tank. + +The crepe when dry does not have the bright appearance of the ordinary +"Fine Pale" standard prepared with the aid of the anti-oxidant sodium +bisulphite. + +Unfortunately the addition of this substance to the latex in normal +proportions is not possible under anaerobic conditions, as it is found to +prevent coagulation, probably owing to its sterilising effect upon the +anaerobic organisms. + +To prevent the oxidation of the rubber in actual practice, the freshly +prepared crepe is soaked in a solution of sodium bisulphite before hanging +to dry. The resulting colour of the rubber is quite good. + +It was shown by Eaton and Grantham that anaerobic coagulation is slightly +uncertain in action. Owing probably to variations in the composition of the +latices, or to the extent of infection by organisms, coagulation may one +day be complete and on other days less satisfactory. + +They found further that, by the addition of small quantities of sugars, +coagulation under both aerobic and anaerobic conditions was improved. The +conclusion formed was that the addition of sugars created a medium +favourable to the development of anaerobic organisms and unfavourable to +those which cause decomposition of the natural nitrogenous constituents of +latex. + +This work was confirmed by Gorter and Swart,[29] who attributed the action +to the conversion of sugar to lactic, acetic, and succinic acids by +fermentation. + +[29] Gorter and Swart, Bulletin No. 6, West Java Station. + +Denier and Vernet, whose work has already been mentioned, studied the +presence of the organisms in latex, and succeeded in isolating one which, +under anaerobic conditions, effects coagulation within twenty-four hours. +Sometimes to produce complete coagulation it was found necessary to employ +small quantities of sugars--_e.g._, 1 gramme per litre of latex (1:1,000). + +It is to be noted also that the addition of small quantities of soluble +calcium (lime) salts to latex has much the same effect as the employment of +sugars. Recent investigations[30] showed that the addition of 0·5 to 1 +gramme of calcium chloride per litre of latex caused complete coagulation +in closed vessels within twenty-four hours, a result agreeing with the +findings of Barrowcliff. + +[30] "Archief voor de Rubbercultuur," Nederlands Indies, 1920, 4, 273. + +On page 308 of the same publication, experiments on the effect of sugars +are described, in connection with _aerobic_ coagulation. Observations from +a further set of experiments tended to indicate a direct connection between +the effects of tapping and spontaneous coagulation. It is suggested that +heavy tapping causes a diminution in the latex of those substances which +act in some way as accelerating agents in coagulation--_e.g._, sugars. The +smaller the proportion of these substances, the slower and less complete is +natural (spontaneous) coagulation. + +ILCKEN-DOWN PROCESS.--This process is the subject of patents granted in +1915 to Messrs. Ilcken and Down. It has been in fair prominence, and has +been tried experimentally on several estates and in public demonstration. + +It is a coagulating process, and, in the original specification, employed +as agents a mixture of alcohol (in the form of methylated spirit) and +benzene (petrol), or alcohol with petrol and coal-tar naphtha. The mixture +was injected in the form of a fine spray into the latex, contained in a +tank specially fitted with paddles. + +Later modifications covered the addition of a small quantity of glycerine; +or, failing supplies of that substance, coconut oil. + +Many advantages are claimed for the process, but most of them cannot be +substantiated. The two chief claims are: + + 1. The production of a uniform standard of rubber. + + 2. The obtainment from a unit volume of latex of a greater weight of + rubber than can be obtained from an equal volume of the same latex by + ordinary coagulation with acetic acid. It is to be inferred that the + agents employed have the power of adding to the coagulum some of the + substances which usually remain in solution in the clear serum. + +Regarding the first of these claims, it has been shown[31] that the rubber +is not uniform in its behaviour on vulcanisation, and that its variability +is similar to that of rubber prepared by other processes. + +[31] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham, +and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918. + +The second claim has been the subject of much controversy. Experiments made +on estates under the supervision of, or in the absence of, the patentees +have given conflicting results. When varying factors have been eliminated, +the general conclusion was that no increase in weight of rubber was +obtained. + +Private laboratory investigations led to a similar verdict, and Eaton[32] +records a confirmatory finding. More recently the claims made for the +process were investigated in Java[33] under varying conditions. Three +series of experiments were made: + +[32] _Ibid._ + +[33] "Archief voor de Rubbercultuur" (De Vries and Spoon), Central Rubber +Station, Java, May, 1921. + + (1) During the rainy monsoon and at a height of 1,800 feet. + + (2) During the dry monsoon on a low-country estate. + + (3) In the experimental gardens at Buitenzorg during bright sunny + weather and the most favourable conditions. + +The agents used were (_a_) a mixture of alcohol and fusel oil, (_b_) +alcohol and petrol (benzene). + +In these experiments no advantage in weight of rubber was obtained by the +Ilcken-Down process, and it would thus appear that the principal claim +fails to be substantiated. + +The general composition of the rubber was approximately the same as +ordinary crepe obtained from undiluted latex. The rubber on vulcanisation +was found to be normal in behaviour, and was similar to the controls. + +The coagulum ordinarily is affected by oxidation, and does not produce a +fine pale crepe. To remedy this defect the freshly prepared crepe is soaked +in a solution of sodium bisulphite and sulphuric acid. + +It may be noted that in the recent experiments coagulation was effected in +vacuum in a specially designed wooden tank. From a study of the previous +section on "Spontaneous Coagulation," the reader will perceive that results +equal to those obtained by the Ilcken-Down process can be obtained +_without_ the necessity of using such agents as alcohol, petrol, or fusel +oil. + +SLAB RUBBER.--This type of preparation has been the subject of much +discussion of recent years. There is nothing really special in the mode of +preparation, and in its original form "slab" rubber is only a thick sheet +which may be obtained by coagulation with acetic acid or other agents. + +The coagulum, when removed from the serum, is subjected to comparatively +slight pressure, and the "slab" thus made is either placed to air-dry at +once, or may be subject to treatment in other liquids before drying. + +The rubber is not allowed to remain until wholly dry, but is shipped while +still containing an appreciable percentage of enclosed moisture. + +It is claimed[34] that the production of "slab" rubber by standardised +methods eliminates to a great degree the variability which at present +characterises plantation rubber, and that a fast-curing medium is obtained. +These claims will be discussed in later chapters dealing with the +vulcanisation of rubber, and demand no notice in this section. + +[34] "Preparation and Vulcanisation of Plantation Rubber" (Eaton, Grantham, +and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918. + +From the producers' point of view, it may be noted that the preparation of +slab rubber is a simple process, but not altogether as pleasant probably as +might be desired, when undertaken in crude form. + +The appearance of the partially dry slabs is unattractive, but that does +not signify if the quality of the vulcanised product satisfies +requirements. + +For the average producer, the difficulty lies in having to meet the demands +of the general market. Even, therefore, if one assumes that the intrinsic +qualities of slab rubber are all that the claims advance, it would be +necessary for the producer to be assured of definite and regular sales. + +At present it would probably be fair to state that practically all the +"slab" rubber being prepared is produced by those who are also consumers. +They are thus in the enviable position of being able to satisfy their +requirements as to the mode of preparation. Until such time, therefore, as +there exists a regular demand for "slab" rubber in the general market, the +vast majority of estates must proceed on ordinary lines of preparation. + + + + +PART VI + +VULCANISATION + +(BY DR. H. P. STEVENS) + + + + +CHAPTER XXI + +_INTRODUCTORY DEALING WITH TREATMENT AND VULCANISATION_ + + +In the foregoing chapters the methods of treating latex, coagulating, +rolling and curing, or drying, have been described in great detail. These +details will give the reader some idea of the precautions taken, and +procedure necessary to produce rubber which will be acceptable to the +market. The expressions "inferior rubber," "defective crepe," "poor quality +sheets," etc., are frequently met with, but these expressions must not be +taken to indicate any defect in the rubber for manufacturing purposes, but +merely that the rubber is defective for selling purposes--that is to say, +being unsightly, it will not fetch the full market price. + +Raw rubber, as produced on the plantations, is almost invariably subjected +to the process of vulcanisation in the production of manufactured rubber +articles as we know them. Previous to the advent of plantation rubber, the +raw material was purchased by the manufacturer in a moist and impure +condition; frequently the rubber was adulterated with sand, dirt, and even +small stones. Consequently it was the invariable practice of the rubber +manufacturer to wash the raw rubber and convert it into crepe, which was +then hung and air-dried before use. The effect on the rubber, if of high +grade, was more severe than the washing and crepeing process on the +plantation, because the rubber was not a soft coagulum but generally dried +on the surface and semi-hard. The power required was considerable, and the +resulting crepe was consequently softer and more susceptible to heat than +plantation first latex crepe. Much of the "wild" rubber was soft and tacky +and inferior to "earth-scrap." + +Vulcanising in its simplest aspect consists in mixing the rubber with +sulphur and heating the product under regulated conditions. The effect of +heat on the inferior grades of "wild" rubber is very marked. A soft, +sticky, and resinous material is transformed into a relatively tough and +elastic product. The effect of vulcanising on the better grades is less +marked, but immediately apparent. On the other hand, the effect of +vulcanising is least apparent on first latex plantation grades, because in +these we have a raw rubber prepared in a manner best suited to retain its +natural characteristics. + +The need of vulcanising in the process of manufacturing rubber goods became +an axiom in pre-plantation days, and it is only quite recently that +attempts have been made to utilise raw rubber directly, without +vulcanisation, particularly for shoe soles. For this purpose a thick dense +crepe has been found satisfactory. Smoked sheet rubber is not generally +suitable, apparently owing to its microphysical structure. It is possible +that the process of rolling in the making of dense crepe compacts the +rubber particles, yielding a harder and more resilient product. The rolling +must not be carried too far, or the "working" of the rubber will +approximate to a preliminary mastication, and the product will be weakened. + +The utilisation of crepe rubber directly has not yet been sufficiently +tested to enable a definite conclusion to be reached as to its future +scope, but it is obvious that for use in a raw state some modification in +preparation may be advantageous. The present method--_e.g._, coagulation +with acetic acid--does not yield the hardest and toughest rubber. + +Hardness and toughness are actual drawbacks in the utilisation of rubber +which is required for vulcanising. When the output of plantation rubber +began to increase and to displace the inferior wild sorts, manufacturers +complained of the increased power consumption of their machines. The power +was required mainly to "break down" or "mill" the rubber preliminary to the +mixing with sulphur and other ingredients. It is obvious that a material +such as raw rubber cannot be mixed with powders such as sulphur with a +pestle and mortar, or in any simple form of mixing machine. This difficulty +was overcome by the earlier experimenters by immersing the rubber in a bath +of molten sulphur. The latter was gradually absorbed and "dissolved" in the +rubber, and the heat of the bath caused the dissolved sulphur to combine +with the rubber to produce vulcanised rubber. The limitations of such a +process are apparent. Thus the vulcanised rubber retains the form in which +it was originally shaped. Moreover, other ingredients, such as mineral +matters, cannot be dissolved or absorbed by the rubber in this manner. The +method eventually adopted consisted in "breaking down," "milling," or +"masticating" the rubber by passing it continuously between differentially +geared steam-heated rollers. By this means a high-grade rubber is converted +into a soft, plastic mass, which will "take up" sulphur, mineral matter, +and other ingredients as desired. The mixing operation may be carried +through on the same roller machine as was used for breaking down the +rubber, or separate machines of other designs may be adopted. Details of +the process will be found in books dealing with rubber manufacturing.[35] +It will suffice here to explain that when rubber is kneaded between two hot +rollers moving at different speeds the rubber forms a continuous band +around the slower moving roller, and if the distance between the rollers be +adjusted the excess of rubber held back by the nip of the rollers will form +a "bank" or moving wedge-shaped mass on the top of the nip. This closes the +space between the rollers, so that sulphur and powder placed on the rubber +pass round towards the nip, and are there driven into the rubber. In this +manner it is easy to mix, say, 10 per cent. of sulphur into the rubber +without a single particle falling through. In technical mixes where large +quantities of powders require to be mixed there is always some caking, and +part of the powder falls between the rollers into a tray underneath. This +is swept up with a broom and put back on to the rollers, the process being +repeated until the whole of the ingredients have been incorporated. + +[35] For instance, "India-Rubber and its Manufacture," by H. L. Terry. + +From this description it follows that, preliminary to mixing, it is +necessary to thoroughly masticate or "plasticise" the raw rubber. Much of +the "wild" rubber was of so inferior a quality that it very readily broke +down, and but little mastication was necessary. It was soft and resinous, +and readily took up the powders which were to be mixed with it. The better +grades of wild rubber, such as Fine Para, were more difficult to break +down, but not so difficult as most plantation rubber, because they had +already received a preliminary "working" in the process of washing and +crepeing, and we have already explained that such treatment takes more +power than the crepeing of the soft moist coagulum on the plantations. The +amount of "working" or "plasticising" produced in the rubber is connected +with the power expended; the greater the expenditure of power, _caeteris +paribus_, the greater the working effect on the rubber. Although the +manufacturers possessed a relatively soft rubber in the form of washed Fine +Para, it was customary in most cases to employ this rubber in conjunction +with washed lower grades to produce a soft plastic material for further +treatment. Now, however, the manufacturer has little else but plantation to +deal with, and most of it more difficult to break down than washed Para +crepe. This is the reason why a hard, tough rubber is no longer a +desideratum with manufacturers, although originally taken as an indication +of good quality. For the majority of purposes they want something which +will break down easily. Hence if a rubber could be produced answering to +these requirements, without loss of vulcanising quality, it would be +preferred. + +Having incorporated sulphur and other ingredients, the plastic mass is +sheeted and run between layers of calico to prevent the superimposed sheets +from adhering. From this "calendered sheet" the article, whatever it may +be, is built up. The calender rollers are heated so as to keep the rubber +compound plastic. There is a limit to the thickness of the sheet which can +be produced. It is a difficult operation to perform satisfactorily so as +to yield a smooth surface and a sheet free from enclosed air. When cool the +rubber hardens and is readily handled. The object to be manufactured is +then built up from the calendered sheet. Thus in the manufacture of a motor +tyre the tread is built up on the casing or carcase by laying the sheets on +the canvas and rolling these with a hand or power operated roller, so that +they adhere firmly, the first layer to the canvas of the casing and +subsequent layers to one another. This rough description will suffice to +illustrate how important it is that the rubber when mixed should be plastic +enough to give a smooth sheet, and to allow the sheet to be manipulated in +building up the article in process of manufacture. The testing of rubber in +regard to its plasticity and power to absorb finely divided mineral matter +will be discussed in a later chapter. We may, however, point out here, that +the mineral matter is not generally added as an adulterant, but because of +certain specific properties it confers on the product. + +To proceed with our outline of vulcanisation, we have now arrived at the +stage at which the goods are built up and ready for vulcanising. For this +purpose they are generally enclosed in some manner, either in metal moulds +bolted together, or tightly wrapped in cloth, as, _e.g._, in the +manufacture of inner tubes, hose, etc. In the latter case, you can detect +the cloth mark on the finished product. Sometimes the rubber is +spewed--that is, driven out of a barrel by means of an endless screw +revolving in it. In this way rubber tubing, perambulator tyres, and such +articles, may be made. More recently even tyre treads and the shaped rubber +for band tyres (heavy solid tyres) have been extruded in this manner, for +the process is much cheaper than building up a tyre from calendered sheet, +and then cutting the mass to shape by hand. But for spewing the rubber mass +must be very soft and plastic; this condition is not obtainable unless the +raw rubber originally used can be made thoroughly plastic without damage. +Nor can it be effected with a rubber mass containing much finely divided +mineral matter, as this hardens the mixture. + +For other purposes the rubber is swollen in a solvent, such as coal-tar +naphtha, and subsequently masticated; the soft dough is then shaped or +spread on cloth, and vulcanised after allowing the solvent to evaporate. +Here, again, the properties of the raw rubber are of immense importance. +Thus, the more plastic the dough, the less solvent required, and the less +there is to drive off before vulcanising. The plasticity of the dough will +depend on the plasticity of the raw rubber, and so forth. It is evident +that the physical properties of the raw rubber are of great importance. +They directly affect the manufacturing operations up to the vulcanising +stage, and indirectly affect the results obtained on vulcanising. + +The actual vulcanising consists of heating the mass of mixed rubber for +a definite time and at a definite temperature, each "heat" being chosen +to suit the particular mixture. These data are arrived at +empirically--that is, by trying a number of "heats" and choosing that +which appears the most suitable. The suitability will depend on the +nature of the article, the service to which it is to be put, and the +time it is intended to last. All vulcanised rubber goods, whatever the +process, have a limited life or period during which they can be relied +on to give useful service. After a time, vulcanised rubber tends to +harden, cracks appear on the surface when the article is bent or +stretched, and eventually the rubber becomes rotten and "perished." This +tendency varies with the quality of the original raw rubber and the +conditions of vulcanising. Before plantation rubber was available, the +manufacturers were dependent on inferior wild grades for a great part of +their output, and, consequently, the goods made from these inferior +rubbers never showed very good mechanical properties and soon +deteriorated. The severest critics of plantation rubber have admitted +the advantages to the manufacturers of the replacement of the lower wild +grades by plantation rubber.[36] But even the best grades give a +vulcanised product which rapidly deteriorates if the vulcanisation is +carried too far. This results from too long heating, or too high a +temperature, and the product is termed "overvulcanised" or +"overcured."[37] The appearance of the product is deceptive, as the +physical properties are remarkably good if the overvulcanising is not +more than 50 to 100 per cent. in excess of the normal cure. Only in the +case of very much overvulcanised rubber do we obtain a product which is +brittle from the beginning. + +[36] See Williams, "The Rubber Industry," 1914, p. 284. It must also be +remembered that the inferior wild grades were derived from latices often +containing a large proportion of "resinous" matter, and which could not +yield a really high grade of vulcanised rubber whatever the care and skill +employed in preparation. + +[37] The terms "curing" and "vulcanising" are generally employed as if +synonymous. Twiss has suggested that the former be applied in regard to a +change in physical properties, and the latter to the chemical change +whereby sulphur is combined with the rubber. The term "curing" is also +applied to the process of preparation of raw rubber. This must be kept in +mind so as to avoid confusion. + +The degree of vulcanising will vary with the type of article to be +produced, and where a long life is desired, the tendency will be to +"undervulcanise"; but if the best mechanical properties are desired, the +tendency will be towards "overvulcanising," or, more correctly, "fully" +vulcanising. These considerations are aptly illustrated by reference to +pneumatic tyres. The inner tube need not possess high tensile strength, +provided that it is easily distensible, for the reason that, during use, it +is protected by the casing of the tyre proper, which confines and supports +it against the air-pressure applied. Inner tubes are therefore cured to +give a long life without developing the maximal physical properties. On the +other hand, the casing and tread of the tyre are required to withstand +severe mechanical conditions--particularly the constant flexing of the +cover, and the abrasion of the road surface. Tyres are not stored for any +long period, and, when put into service, have a limited period of useful +life. Consequently it is needful to develop maximal mechanical properties, +and vulcanisation is therefore carried further than in the manufacture of +inner tubes. + +The rate of cure is controlled by a number of factors in addition to the +period and temperature of vulcanisation, in particular by the proportion +and nature of the other ingredients, especially sulphur and accelerators, +and also by the rubber itself. The main complaint as regards plantation +rubber is that it varies excessively in this respect. This matter will not +be discussed here, but is only introduced in order to explain the +importance of a constant rate of vulcanising to the manufacturer. +Plantation rubber should, therefore, be prepared so as to be as uniform as +possible in this respect, and the earlier part of this book gives full +details of the precautions advised, and in many cases adopted on the +plantations. Unfortunately, it is impossible to secure uniformity of +methods among all producers, even when they are Europeans, to say nothing +of the native producers, who account for perhaps one-third of the output. +Hence the importance of branding the rubber whenever possible, so that the +manufacturer may identify the rubber he purchases. If found satisfactory, +he can then secure further supplies from the same estate. + + + + +CHAPTER XXII + +_TESTING OF PLANTATION RUBBER_ + + +This subject may be subdivided into (_a_) Tests on the raw rubber; (_b_) +tests on the vulcanised rubber. + +The tests on the raw rubber may be carried out (1) on the sample of sheet +and crepe as received. For this purpose the rubber is cut into a strip, +which is clamped between grips and gradually stretched to breaking-point. +The ring testing machine can be adapted for this purpose by replacing the +rollers with clamps. As the thickness of the samples to be tested will +vary, it is advisable to cut the strips of such a width that the +cross-sectional area of all test pieces is the same--say, 40 sq. mm. The +method is applicable to both sheet and crepe rubber. (2) Tests may be made +as to the behaviour of the rubber during milling or mastication. Small +batches are milled under uniform conditions, preferably in an enclosed +masticator such as Baker and Perkins supply. The power taken (as measured +by the current taken to drive the motor actuating the machine) and the time +are recorded. A further test may be applied to the milled or masticated +rubber, to ascertain the amount and the time taken to incorporate a finely +divided mineral matter, such as carbon black, zinc oxide, or one of the +refined clays.[38] The results are not very exact, and the difference in +plasticity and dryness noted are usually less than found when working with +full-sized machines in the factory. (3) The rubber, either raw or +masticated, may be "dissolved" in a "solvent," such as benzene, and the +viscosity of the "solution" measured. Generally speaking, the less viscous +the solution, the more plastic the rubber. + +[38] Bulletin Rubber Growers' Association, January, 1921, p. 43; August, +1921, p. 340. + +The testing of vulcanised rubber has been treated in such detail in the +recent works of Whitby[39] and De Vries[40] that a few special points only +will be dealt with here. The preparation of samples for testing involves +first the sheeting of the mixture of rubber, sulphur, and other +ingredients, if any. The sheets may be 1 to 2 mm. thick. They are soft and +adherent, and must be kept between layers of calico to prevent adhesion. A +sheet of rubber is then built up by laying three or four sheets evenly upon +one another, and pressing together to form a sheet 5 mm. thick. The thick +sheet is then roughly cut to shape and vulcanised in a mould by heating in +steam under pressure. From the vulcanised sheet so obtained the rings for +testing are cut (45 mm. internal diameter. 5 mm. face, and 4 mm. thick). +Rings obtained in this manner will not vary in diameter or thickness +(reckoned as sections of a tube), as these are controlled by the size of +the punch, but will vary a little in the face, as this is controlled by the +thickness of the sheet, which depends on the completeness with which the +mould is closed. More recently smaller moulds have been adopted, one mould +for each ring, and an annular space for moisture to develop a pressure +during vulcanising and prevent porosity. The moulds are vulcanised in an +oil bath, or oven of some description, in which a constant temperature is +maintained. I have adopted for some years a third method. The principle is +that used in the factory for making annular-shaped rubber articles, such as +washers, rings, elastic bands, etc. An aluminium mandrel, 45 mm. external +diameter, is taken, and the thin rubber sheet is wrapped round this, so as +to build up a tube about 4 mm. thick, the surplus rubber is cut off, and +the edge bevelled with a wet knife. The manipulation will vary somewhat +with the type of compound to be treated; thus, in some cases, it is +sufficient to well roll the tube with a hand roller to secure adhesion. In +other cases it is better to wipe the sheet of compound with a rubber +solvent previous to rolling. In the latter case time must be given for the +solvent to evaporate before vulcanising. The tube is next tightly wrapped +in wet cloth, and is then ready for the vulcaniser. Or the tube may be +enclosed in moulds which form an outer circular shell and take the place of +the cloth, but for most purposes, and in particular for the rubber-sulphur +mixing usually employed, it is sufficient to use cloth to obtain even and +regular tubes. The tube, after vulcanising, is slipped on to a wooden +mandrel and cut into rings on a lathe. Of these rings the internal diameter +is constant, for this is formed on the mandrel, also the face, which can be +cut accurately in the lathe, but the external diameter, and consequently +the thickness, may vary a little. + +[39] "Plantation Rubber and the Testing of Rubber." + +[40] "Estate Rubber." + +It appears, therefore, that all methods result in rings of approximately +the correct size, and it is usual to check, and, if necessary, make an +allowance for variation in dimensions. It is not possible to do this, even +approximately, with soft rubbers, as the rubber gives under the pressure of +the micrometer. No doubt a photographic method would give more accurate +results, but would take too long. I have found that a very close +approximation is obtainable by weighing the rings as the specific gravity +of the standard rubber mix is known. It is not necessary to weigh each +ring, but the whole five or ten taken for testing may be weighed together. + +The next point that arises is the choice of a formula for the test mix. +Practically all the work to date has been carried out on mixtures of rubber +with 7 to 10 per cent. of sulphur. For some purposes--_e.g._, detecting +variation in rate of cure--this mixing is satisfactory, but for other +purposes it is not. Nor is the behaviour of a rubber-sulphur mixing a sure +guide to the behaviour of one containing other ingredients, such as +litharge. Thus, two samples vulcanised satisfactorily when mixed with +sulphur only, but one of them gave unsatisfactory results in the presence +of litharge. It has long been recognised that mineral ingredients may +modify the product when vulcanised, but the modification is not necessarily +uniform. Consequently, tests should also be made, when practicable, with +vulcanised rubber containing other ingredients in addition to sulphur. + +As regards physical tests on the vulcanised products, these usually involve +determination of breaking load and elongation at rupture (usually recorded +as final length--that is, including the original length reckoned either as +unity or as 100 units). Simultaneously a load-stretch curve is recorded on +an autographic attachment. The type of curve varies with (1) state of cure, +or degree to which the rubber is vulcanised; (2) proportion of sulphur +and/or other ingredients; (3) specific nature of the rubber used. The last +factor is almost negligible compared with the two former--at any rate for +average quality rubber. As (2) is kept constant for any batch of tests, or +even for every test, it follows that the load-stretch curve is mainly +dependent on the state of cure, and the degree of vulcanising may be +measured by comparing either the elongation produced at a given load or the +load produced at a given elongation. Either set of figures is readily +determined by measuring up the load-stretch diagram. + +The peculiar type of the curves has long been a subject of comment and +speculation. Special properties have been attributed to the "slope" or +inclination of the upper and approximately straight portion of the curve. +According to the writer's investigations, the "slope" is largely dependent +on the degree of vulcanisation, so that it is difficult to "place" as an +index of the specific nature of a rubber.[41] Moreover, it has recently +been shown that the peculiar type of curve given by vulcanised rubber is +the result of plotting the load against the sectional area of the +unstretched test piece, whereas this area decreases progressively as the +test piece stretches. If this decrease be allowed for, the curve obtained +is an equilateral hyperbola.[42] Preliminary experiments with rubber +compounded with large proportions of finely divided mineral matter, such as +carbon black, show that the load-stretch curves obtained autographically +are likewise reducible to equilateral hyperbolæ. + +[41] Bulletin R.G.A., October, 1921, p. 397. + +[42] _Hatschek Journal Soc. Chem. Ind._ 1921; _Trans._, p. 251. + + + + +CHAPTER XXIII + +_THE PROPERTIES OF RUBBER_ + + +This section, like the last, is divisible into two subsections. The first +deals with raw rubber, the second with vulcanised rubber. + +We have already explained that, until recently, rubber was not used in the +unvulcanised condition, but that the excellent physical properties of +plantation rubber have made this possible. It is interesting to compare the +physical properties of raw rubber with that vulcanised with sulphur. A +compact sample of crepe as received from the East will give breaking strain +of over 30 kilos per sq. cm. and over 300 per cent. elongation. When mixed +with sulphur and vulcanised, a breaking strain of 150 kilos and elongation +of 1,000 per cent. are not unusual. It is possible that crepe rubber would +give higher figures if it could be prepared in the form of a compact ring, +as used for tests on vulcanised rubber. In any case, the figures for +vulcanised rubber are much in excess of those for raw crepe rubber. It must +also be remembered that a breaking strain of 150 kilos is not permanent +with vulcanised rubber, for reasons which will be explained later.[43] To +obtain a reasonably permanent vulcanised product, the vulcanisation would +not be carried further than to give a figure of 100 kilos. On the other +hand, raw rubber is remarkable on account of its great permanency, although +subject to some physical changes at ordinary atmospheric temperatures. +Tensile tests, although valuable, do not tell us all about the physical +properties of a sample of rubber. Abrasion tests, or tests designed to +measure resistance to wear and tear, would be more valuable, but, +unfortunately, these properties do not lend themselves to simple tests. +There are grounds for believing that raw rubber is superior in some +respects to fully vulcanised rubber, if prepared without the addition of +finely divided mineral substances which exert a toughening effect. + +[43] _Journal Soc. Chem. Ind._, 1916, p. 872. + +Sheet rubber gives results in some ways inferior to compact crepe rubber +when subjected to physical tests. Tensile strength seldom exceeds 15 kilos, +but the elongation is usually higher--up to 600 or 700 per cent. That is to +say, it stretches more, but breaks more easily. If, however, we take into +consideration the diminution in sectional area of the test piece during +stretching, it will be seen that crepe and sheet rubber have compensating +properties. + +As this matter of sectional area reduction during stretching is important, +both for raw and vulcanised rubber, it may be briefly referred to here. +When rubber is stretched, the volume does not appreciably alter--at any +rate, as regards uncompounded rubber. Hence the reduction of sectional area +on stretching bears a simple relationship to the amount of stretching. If +we double the length of the test piece, we halve the sectional area; if we +treble the length, we reduce it to one-third, and so forth. Hence, if we +multiply the breaking strain by the final length (_i.e._, length at break, +taking the original length = 1), we obtain a figure, the "tensile product," +which embodies both breaking strain and stretching capacity. In effect it +gives us the breaking strain calculated on the sectional area at the +_moment of rupture_ of the test piece. Adopting this formula, we obtain for +crepe-- + + _Tensile _Final Length--i.e., _Tensile + Strength._ Elongation + 1._ Product._ + 30 × 4 = 120 + +and for smoked sheet + + 15 × 8 = 120 + +The difference in properties between crepe and sheet may probably be +attributed to the heavier rolling of the crepe; which compacts the rubber. +But if the crepe is rolled too much, the tensile strength falls, and there +is no increased elongation to compensate. For the same reason, crepe which +has been rerolled in this country is inferior to crepe as received direct +from the plantation. At the most it is permissible to unite two or three +layers of thin crepe to a thicker one by a single passage through even +speed rollers, if the physical properties of the original rubber are to be +conserved.[44] + +[44] Bulletin R.G.A., February, 1922, p. 64. + +Attempts to prepare crepe for use in a raw state, by rerolling uneven or +irregular surfaced crepe in this country, only result in a rubber with +inferior physical properties. Nor can sheet be rerolled to give crepe of +good physical properties. The power required to break down the sheet and +the heat developed, even on cold rollers, are an indication of physical +properties destroyed. For subsequent vulcanisation this is not a matter of +importance, because the vulcanising process restores to the rubber the +properties which are lost in the process of rolling and milling or +mastication. + +Raw rubber has been used to some extent for proofing purposes, as for the +manufacture of material for hoods of motor-cars. In this case no attempt is +made to preserve the physical properties. The rubber is masticated, mixed, +taken up with solvent and spread on the cloth exactly as if it were to be +vulcanised. + +VULCANISED RUBBER.--We have already explained that the properties of +vulcanised rubber are dependent, to some extent, on the specific nature of +the raw rubber, or what De Vries terms the "inner qualities." That is to +say, differences appear on vulcanising which are not apparent from the +tests made on the raw rubber. Indeed, no investigation or analysis of the +raw rubber can enable one to foresee exactly how the rubber will behave on +vulcanisation. This illustrates the deficiency in our knowledge of +vulcanisation. When dealing with soft, resinous, or decomposed rubbers, it +is safe to anticipate a weak vulcanised product; but when we come to deal +with a number of samples of "standard" crepe or sheet--_i.e._, sheet or +crepe passing a certain standard of appearance--it is found that +differences in vulcanising properties cannot be foreseen. This matter is, +however, not so great a drawback as might be imagined, for reasonably well +prepared consignments of standard crepe or sheet differ but little from +one another, and the difference is mainly in the ease with which they break +down, or the rate or speed with which they vulcanise, and not with the +properties of the vulcanised product. Many of the plantation scrap grades +are equal to or nearly equal to "standard"; but some of these, as also the +rubber produced by native holders, show appreciable variation, and are the +source of most of the complaints which emanate from manufacturers. We shall +consider in turn the different grades and the effect of the usual surface +defects, such as mould, spots, etc. + +CREPE RUBBER.--Oil marks and tackiness are the most serious defects from +the manufacturing standpoint. In the first part of this book we have shown +that damage caused by the so-called oil marks is not due to the oil, but to +traces of copper from the bearings of the machines. There are several +metallic compounds which cause deterioration of rubber both raw and +vulcanised, but copper is the most deadly, and rubber showing signs of +deterioration is rightly rejected by the manufacturers. + +The only other defect of crepe rubber which has any bearing on its use in +manufacture is mould. Crepe rubber very seldom shows the ordinary surface +moulds not uncommon in sheet-rubber. There are, however, microscopic +growths which cause the development of coloured spots referred to in detail +in the earlier part of this book. The rubber hydrocarbon itself does not +appear to be affected by the moulds, but some of the serum constituents are +altered, with the result that the rubber vulcanises more slowly than it +otherwise would do. For this reason, crepe rubber with coloured spots may +give rise to trouble in the factory. + +SHEET RUBBER.--The commonest defect is mould.[45] This is usually of a +light surface type, easily brushed off, and numbers of vulcanising tests +failed to trace any reduction in rate of vulcanising or other defect due to +this. In spite, however, of the harmlessness of light surface moulds, they +are looked upon with suspicion by the manufacturer. Occasionally samples of +smoked sheet are offered contaminated with a "heavy" type of mould. The +sheet feels damp and "heavy" or flabby, and contains an excess of moisture; +sometimes a moist exudation is noticeable on the surface, and "virgin" +patches are present. Such sheet vulcanises more slowly than F.A.Q. samples, +but does not necessarily show other defects after washing and drying. + +[45] Bulletin R.G.A., February, 1921, p. 97; April, 1921, p. 190; June, +1921, p. 243; November, 1921, p. 472. + +"Stretching rusty," as already explained, is due to a dry film on the +surface of the sheet, and according to a recent investigation, this film +consists, not of serum substances, but of a microscopic mould growth, which +presumably grows on the serum substances. A sample of sheet which stretches +rusty gives the rubber a "dry" appearance, and for a long time +manufacturers mistook the surface film for resin. On the assumption that +such rubber was "resinous" they rejected it, and to this day it is regarded +as a defect, although it has no influence on the vulcanising properties of +the rubber. + +It is hardly necessary to point out that defective appearance, such as is +due to thickened edges, faint markings, bubbles, and so forth, have no +effect on the vulcanising properties of the rubber. They only point to some +irregularity or carelessness in preparation. The only justification for +distinguishing between rubber of good and bad appearance is that the former +bears the impress of careful preparation, and is therefore more likely to +be uniform in rate of vulcanising. + +Similar considerations apply to the colour of smoked sheet, which may vary +from a pale yellow-brown, through various shades of red-brown to dark +brown. There are various factors affecting the colour, but the buyer can +see but one--viz., the "degree" of smoking--and the rubber, from his point +of view, may be undersmoked or oversmoked. No doubt the degree of smoking +affects the vulcanising properties, but to a less extent than was at one +time imagined. In a recent paper[46] it has been shown that the average +breaking strain and rate of cure of a number of samples of smoked sheets +were practically the same for light as for dark sheets. + +[46] Bulletin R.G.A., December, 1921, p. 521. + +VARIATION IN PHYSICAL PROPERTIES.--A very large number of tests on +vulcanised specimens of plantation rubber have been carried out. The +rubber was almost invariably mixed with 7 to 10 per cent. of sulphur, and +no other ingredient, and vulcanised to give the maximal breaking load. +Unfortunately, this determination is subject to a very appreciable +experimental error, so that a large number of determinations are necessary +to give a reliable figure. It is quite impracticable to make a large number +of determinations in routine testing, on account of the labour involved. It +is usual to make five, or possibly ten, determinations, although some +investigators have been content with two. It is generally conceded that any +exceptionally low figures should be ignored, as probably caused by some +flaw or irregularity in the test piece. On the other hand, a study of +actual determinations shows an occasional excessively high figure, and it +is questioned whether this also should be left out of account. Others +ignore all except the highest figure, and take this to represent the true +breaking strain. As a consequence, the figures published by different +workers show considerable variation. De Vries has analysed a large number +of the figures obtained in systematic examination of estate samples, and +has constructed curves to illustrate the results.[47] It is open to +question how far the variations shown are attributable to experimental +error. The figures show, however, that the variation in breaking strain is +relatively small, and not very different for crepe and sheet rubber. In our +opinion, undue importance should not be attached to very high or +exceptionally high figures for breaking strain, which are occasionally met +with. Provided the figure does not fall much below the average, the sample +may be regarded as satisfactory. It is very seldom that any sample of first +latex estate rubber does not show satisfactory figures. + +[47] "Estate Rubber," p. 466. + +THE RATE OF CURE OR RATE OF VULCANISATION is subject to more exact +measurement, whether this be based on the physical or the chemical +properties of the rubber. If the testing machine be provided, as is usual, +with an autographic attachment, the position of the curves traced on the +recording paper gives a measurement of the rate of cure. These load-stretch +curves, to which reference has already been made, take up a definite +position in accordance with the physical properties; it is only the length +of the curve, or the point where it terminates (which gives the breaking +strain and elongation at break), which is largely fortuitous. + +As a measure of rate of cure we may take the actual measurements made on +the record.[48] It is convenient to measure the elongation produced by a +load of 130 kilos per sq. cm., as all fully vulcanised rings of soft rubber +should give higher breaking load figures. For less cured or weaker samples +a lower figure may be taken, such as 60 kilos. We have found that when +fully vulcanised to give the maximal breaking strain, the elongation at a +load of 130 kilos is in the neighbourhood of 850 per cent. (final length +950 per cent.). This applies to ordinary samples of estate rubber under the +conditions of testing indicated above. If, however, the proportion of +sulphur be considerably reduced, or mineral ingredients in a fine state of +division be added to the mixing, or accelerators, whether organic or +inorganic, be employed, the above relationship no longer holds. Nor does it +hold with regard to plantation rubber prepared in an exceptional manner, +as, for instance, matured coagulum or "slab." + +[48] Bulletin R.G.A., June, 1921, p. 246. + +There is a second method of determining the rate of cure--namely, by +analysing a vulcanisate produced under standard conditions, and determining +the amount of sulphur which has entered into chemical combination with the +rubber. For this purpose the weighed sample is cut thin or creped thin, and +exhaustively extracted with acetone to remove any "free" sulphur--that is, +sulphur not in combination with the rubber. The sulphur remaining is then +determined and calculated as a percentage of the raw rubber contained in +the sample taken. This gives the so-called coefficient of vulcanisation. + +If we compare the coefficient with the time of cure at a constant +temperature for an ordinary sample of plantation rubber, they are found to +be approximately proportional, so long as the sulphur is in sufficient +excess. The amount of combined sulphur is, therefore, an index of the time +vulcanisation has been in progress (under standard conditions of +temperature, etc.), and, therefore, the coefficient is a measure of the +rate of cure. + +The change in position of the load-stretch curve is not directly +proportional to the time of heating, and it therefore follows that it is +also not directly proportional to the coefficient. For ordinary samples of +crepe and sheet the relationship is, however, not very far removed from +proportionality. This applies particularly to sheet rubber. The +relationship is readily seen on plotting one against the other and tracing +the curves. For sheet we get an almost straight line; for crepe there is +some curvature.[49] For ordinary estate samples of sheet and crepe rubber +the maximal breaking strain is obtained when the coefficient reaches +approximately five units, so that this corresponds to the elongation of 850 +per cent. at a load of 130 kilos. + +[49] Bulletin R.G.A., June, 1921, p. 246, October, 1921, p. 398. + +Either physical or chemical methods may, therefore, be used for determining +the rate of cure of ordinary sheet or crepe rubber, but great care must be +taken when interpreting the results obtained with rubber prepared in an +unusual manner. The rate of cure may be expressed in terms of the time +taken to vulcanise the rubber at a constant temperature (in our case 138° +C.), so as to give an elongation of 850 per cent. at a load of 130 kilos, +or to give a coefficient of five units. The higher the figure so obtained, +the slower curing the rubber. To express the results more directly as rate +of cure, we have adopted the plan of taking an average crepe rubber, +calling the rate of cure 100 units, and expressing the rate of cure of +other samples in these terms. Thus, a sample which gave a coefficient of +four only, in the time taken by the standard to give a coefficient of five, +would have a rate of cure four-fifths of the standard, that is, 80; or if a +sample takes only two hours to give an elongation of 850 per cent., whereas +the standard takes three hours, the rate of cure of the sample will be 3/2 +of standard or 150.[50] + +[50] _Journal Soc. Chem. Ind._, 1918, p. 280. + +As stated, the coefficient is approximately directly proportional to the +time of cure; it is also independent of the proportion of sulphur, if in +fair excess, and in the presence of inert ingredients. It is also +independent of the amount of mastication given to the original raw rubber, +however great. On the other hand, the position of the load-stretch curve is +variously modified by these factors--in some respects, therefore, the +coefficient is a more reliable index. However, the coefficient is +influenced by accelerators, so that here also great care must be exercised +when interpreting results. For the purpose of detecting variations in rate +of cure, it is best to choose a mixing which is particularly sensitive. In +the first place, there must be an ample excess of sulphur; and in the +second place, no ingredient should be added which will complicate the +load-stretch curves, and no accelerators should be present which may +possibly tend to obscure the vulcanising properties of the rubber itself. +It has been found, therefore, that the best mixing to use consists of +rubber with an excess of sulphur--say, in the proportion 9:1 without other +ingredients. The rate of cure of a specimen of plantation rubber is +attributed to the presence of certain natural vulcanising catalysts, +because it is found that carefully purified raw rubber (that is, with the +resinous and nitrogenous constituents removed) vulcanises very slowly or +hardly at all, but that on replacing the extracted matter the rate of +vulcanising is restored. The natural catalysts contained in the extracted +matter are influenced to a varying degree by some of the common ingredients +of manufactured rubber articles. This applies particularly to litharge +(oxide of lead), to which reference has already been made. Thus, acetone +extraction of raw rubber to remove resinous matter has but little effect on +the vulcanising properties of a mixture of rubber and sulphur. But if +litharge be a constituent, it is found that acetone-extracted rubber will +hardly vulcanise at all. From this, it follows that a rubber giving a low +acetone extract may be found to vulcanise exceptionally slowly in a mixing +containing litharge, whereas it shows no such defect when compounded with +sulphur only.[51] Litharge is used to a very large extent, as it has a +balancing effect in a rubber compound--that is to say, it allows of +appreciable variation in vulcanising conditions, without corresponding +alteration in the state of cure.[52] + +[51] _Journal Soc. Chem. Ind._, 1916, p. 874. + +[52] _Ibid._, 1915, p. 524. + +INFLUENCE OF VARIOUS FACTORS IN RAW RUBBER PREPARATION ON THE "RATE OF +CURE," OR "RATE OF VULCANISATION."--As the capacity of a rubber for +vulcanisation depends on the presence of small quantities of accessory +substances in the serum which act as catalysts, the rate of vulcanisation +(or curing) will depend on the nature and quantity of such substances +present in the rubber. A very small quantity of these substances has a +considerable influence on rate of vulcanising, and as the substances are +difficult to isolate and identify, our knowledge of their formation and +chemical nature is not as definite as is desirable. Substances have been +isolated having the characteristics of "simpler bases." Bodies of this +class are formed by putrefaction of organic matter, and can be separated in +much larger quantity from coagulated latex, which has been allowed to +putrefy before working up than from such which has been worked up without +giving time for an appreciable amount of putrefaction to take place. +Further, rubber from putrefied coagulum vulcanised much faster than that +ordinarily prepared, so that we are justified in connecting the +putrefaction bases with the rate of vulcanisation. Moreover, it has been +shown that any treatment of the latex or coagulum which inhibits the +development of putrefactive organisms also prevents the rubber vulcanising +as fast as would otherwise have been the case.[53] Also, the crude bases +isolated from fast vulcanising rubber have the power of increasing the rate +of vulcanisation when added to ordinary slow vulcanising rubber.[54] + +[53] Eaton and Co-workers: See Bulletin No. 27, F.M.S. Department of +Agriculture. + +[54] _Journal Soc. Chem. Ind._, 1917, p. 365. + +On the other hand, there are one or two facts which are difficult although +not impossible to fit in with theory. Thus, although the putrefaction bases +are very easily soluble in water and acetone, they cannot be removed by +washing on the creping rollers, or by acetone extraction. This may be due +to the power of colloidal substances to retain other crystalloidal +substances, such as the bases, which, in consequence, cannot be washed out. +A parallel case is the retention of small quantities of water soluble +substances in the soil. Also, the theory does not explain why rubber +obtained by evaporation of latex at relatively high temperatures is fast +vulcanising, although the possibility of putrefaction is excluded. + +As regards practical results, it follows that the rate of vulcanisation (or +cure) of a sample of rubber will depend on the time allowed to elapse +between the collection of the latex and treatment till the rubber is dry, +as also on atmospheric conditions. Thus, slow drying will result in an +increased rate of cure, for it gives an opportunity for putrefactive +organisms to play a part. The results will, however, be influenced by the +extent to which the rubber was washed previous to hanging, and so forth. +Smoking is an antiseptic process and will, therefore, tend to inhibit the +action of micro-organisms and produce a slower vulcanising rubber. On the +other hand, sheet contains more serum than crepe, so that there is more +food material for growth of micro-organisms. The net result is to give a +rubber (sheet) which usually vulcanises a little faster than crepe. + +Among other factors controlling the rate of cure, special mention should be +made of the nature and amount of coagulants. Weak "organic" acids, such as +acetic, lactic, tartaric, etc., used in the minimal proportions (1 to 1,200 +of standardised latex in the case of acetic acid), give the fastest +vulcanising rubber; "strong" mineral acids, such as sulphuric acid, even +when used in the minimal proportions (1 to 2,000), yield slower vulcanising +rubber. Acid salts, such as alum, are intermediate in effect. Increased +proportions of coagulant cause a reduction in rate of vulcanising with all +coagulants, and the effect is least noticeable in crepe rubber, +intermediate in sheet rubber, and most pronounced in "slab" rubber +(discussed below).[55] + +[55] Bulletin R.G.A., July, 1919, p. 39; September, 1920, p. 343; November, +1920, p. 433; October, 1921, p. 393; March, 1922, p. 134. + +OTHER TYPES OF PLANTATION RUBBER.--We have up to now confined our attention +to ordinary thin air-dried crepe and smoked sheet, as almost all plantation +rubber is now marketed in one or other of these two forms. There are, +however, other types, to which reference has been made. Of these, the most +important is the thick blanket crepe, made chiefly in Ceylon by rolling +together thin crepe, which has been artificially dried (Colombo drier or +vacuum drier). The heat of the driers causes a surface stickiness, which is +got rid of by rolling several thin layers together to give one thick one. +This rubber vulcanises at about the same rate as ordinary thin crepe, for +the relatively high temperature of drying does not appear to influence the +rate of cure. The rubber is generally softer than air-dried crepe, and is +easily "let down" in naphtha; it is, therefore, suitable for some solution +work. Generally speaking, the properties of blanket crepe do not differ +materially from ordinary thin crepe. Another type of rubber seldom met with +is matured slab or crepe, prepared from it. This type of rubber is being +made in small quantities on one or two estates, who supply direct to the +manufacturer. The method of preparation has already been described. It is +unsuitable for sale in the open market, as it contains a variable amount of +moisture, has the various surface defects such as slime, mould, and "rust," +and there is the additional disadvantage that it is not easy to judge of +its cleanliness or freedom from coarse impurities by inspection. If the +slab rubber be creped and air-dried on the spot, the product is of +satisfactory appearance, except that it is of low colour and may be +streaked. As the crepe so produced vulcanises almost as fast as the +original slab, the crepe embodies all the advantages of a fast curing +rubber with few of the disadvantages of the slab itself. We have made +experiments from time to time, and found that by a judicious use of sodium +bisulphite it is possible to produce a fast vulcanising crepe rubber +sufficiently even and light in colour to satisfy the Standards Committee. + +A fast curing raw rubber is not necessarily a desirable type for all +manufacturing purposes. In the vulcanising of large masses of rubber, a +slower rather than a faster vulcanising rubber may be desirable, so as to +give ample time for the heat to penetrate and spread evenly throughout the +mass. But for many purposes a fast curing rubber enables a larger output to +be obtained, so that artificial organic accelerators are coming more and +more into use. The addition of such accelerators might be obviated, if a +suitable fast curing rubber were available, but it is essential that such +rubber should be uniform. It is just in this respect that slab rubber or +crepe made therefrom is found to be deficient.[56] The rate of cure depends +on the functions of wild bacteria, which are naturally sensitive to changes +of conditions, such as temperature, etc. The coagulated rubber depends on +chance circumstances for infection, and, as a natural result, the activity +of the bacteria and the nature and amounts of active vulcanising agent +produced will vary and be difficult to control. Consequently, the rate of +cure of slab rubber shows considerably greater variation than ordinary +crepe or sheet.[57] This, in our opinion, is the main difficulty of +utilising "slab," or crepe prepared from it. Experience in other +industries, using micro-organisms, has shown that the only method of +control has been to replace the wild growths by cultures of some particular +strain, as, for instance, in yeasts for brewing. To control the rate of +cure of slab, it might be possible to use a special culture for the +purpose. + +[56] Bulletin R.G.A., January, 1920, p. 6; January, 1921, p. 47. + +[57] _Ibid._, January, 1920, p. 68. + +Other less usual methods of preparation, referred to in the earlier part of +this book, do not call for particular mention, as the properties of the +rubber do not differ much from ordinary sheet or crepe. It is mainly a +matter of variation in rate of cure. + +This short account of the vulcanising properties of plantation rubber would +not be complete without a reference to Fine Hard Para, the premier rubber +of the Amazon. This rubber has come to be regarded as the standard +high-grade product with which plantation rubber may be compared, and many +manufacturers are still of the opinion that it is unsurpassed by any +plantation product. Yet, when subjected to the ordinary vulcanising tests, +we find that samples of Fine Hard Para give figures very similar to average +plantation rubber; indeed, it is not difficult to find specimens of +plantation rubber which give appreciably higher figures on testing. It is +claimed, however, that Fine Para is more uniform than plantation rubber, +and can be relied on always to give the same results. Yet tests on a series +of Fine Hard Para specimens gave variations in rate of cure similar to +those found for plantation. Some figures were published, which tended to +show that the variation was smaller for Fine Para, but it turned out that +each of the samples taken for examination consisted actually of a number of +slices cut from different balls, so that greater uniformity was not +unexpected.[58] The superiority of Fine Para is, therefore, somewhat of a +mystery. It is probable that some manufacturers prefer to use it because +they feel safer with it, and know actually how it will behave from long +experience. In one respect Fine Para is possibly superior to most +plantation rubber--that is, for the preparation of raw rubber solution for +sticking the seams of waterproof garments, and for similar purposes. The +method of preparation may well influence the strength of the raw rubber +when used for this purpose. Plantation rubber has been prepared in the same +manner as Brazilian Para, in particular on an estate in Java. The product +resembles Brazilian Para in appearance. Vulcanising tests gave satisfactory +figures, but, as already stated, this would not serve to show that the +rubber was equal to Brazilian Para from the manufacturer's standpoint. + +[58] Bulletin R.G.A., September, 1920, p. 347. + + + + +INDEX + + + Acetic acid, 74, 279 + + Acid, acetic, 74, 279 + --, carbonic, gas, 289 + --, formic, 279 + --, hydrochloric, 282 + --, hydrofluoric, 282 + --, mixing, with latex, 79 + --, nitric, 282 + --, oxalic, 279 + --, pyroligneous, 282 + --, quantity of, 76 + --, sulphuric, 279, 286 + + Acids for coagulation, effect of, on rate of cure, 323 + --, quantities necessary for modern requirements, 78 + + Air-drying, aids to normal, 143 + --, of crepe, rate of, 138 + --, progress of, 140 + + Alcohol, coagulation with, 289 + + Alum, coagulation with, 282 + + Anti-coagulant for transport, 61 + + Anti-coagulants, 46 + + Artificial driers, 133, 148 + + Ash on sheet, 276 + + Assembling cases for shipment, 156 + + + Bags for packing, 154 + + Bakau, 147 + + Bales for packing, 154 + + Bark in crepe, 232 + -- -- shavings, 56, 123 + -- -- sheet, 276 + + Bases in vulcanised rubber, 322 + + Basket plants, 10 + + Blanket crepe, properties of, 324 + + Blemishes of surface, 252 + + Blister in sheet, 272 + + Block rubber, 129, 246 + + Breaking down of rubber, 304 + -- load of test piece, 311 + + Bubbles in sheet, 269 + + Buildings, 159 + + Bulking latex, 69 + + Byrne curing process, 270 + + + Calendered sheet, 304 + + Carbon dioxide, 289 + + Carbonic acid gas, 289 + + Cases, choice of, for packing, 153 + + Catalysts, natural, in rubber, 312 + --, vulcanising, 312 + + Centralisation of factories, 221 + + Chinese vinegar, 286 + + Chinosol, 238 + + "Chula" drier, 148 + + Clippings, sheet, 275 + + Coagulant, 111 + --, choice of, 74, 278 + --, quantity of, 113 + + Coagulation, 74, 111 + -- centres, 62 + --, premature, 46 + --, spontaneous, 294 + -- with alcohol, 289 + -- -- sugars, 287 + -- -- various salts, 288 + + Coagulum, soft, 249 + --, spongy undersurface of, 249 + --, tearing of, 249 + --, transport of, 59, 63 + --, working of, 103 + + Coefficient of vulcanisation, 319 + + Collecting latex, 38 + -- pails, 48 + + Collection, advantages of early, 60 + + Combustion, rate of, in smoke house, 191 + + Compound crepes, 126 + -- -- No. 1, 151 + -- -- No. 2, 151 + + Contents of cases, weight of, 156 + + Copper salts, cause of tackiness, 243 + + Cotton fibre in crepe, 230 + + Creosotic substances, 146 + + Crepe, air-drying of, 132 + --, bark in, 232 + --, bearing of defects in, on manufacture, 316 + --, bisulphite streaks in, 235 + --, colour of fine, 114 + --, dirt in, 227 + --, dirty edges of, 225 + --, drying houses for, 178 + --, fibre in, 230 + --, general style of finish, 223 + --, grades of, 150 + --, greenish, tacky streaks in, 228 + --, iron stains on, 225 + + Crepe, No. 1 fine pale, 110 + --, oil marks on, 226 + --, oxidation streaks in, 234 + --, rate of air-drying of, 138 + --, rust stains on, 226 + --, smoked, 130 + --, surface moulds on, 241 + --, weight increased in drying house, 141 + --, yellow latex streaks in, 234 + -- rubber, defects in, 223 + -- --, lower grades of, 120 + -- --, preparation of, 110 + -- --, tensile strength of, 313 + + Cups, cleaning, 40 + --, water in, 44 + + Cure, rate of, 318 + + Curing, 307 + + + Da Costa process, 290 + + Decentralisation of factories, 221 + + Defects of sheet, infrequent, 276 + + Derry process, 293 + + Designs and "layout" of tanks, 176 + + Dirt in sheet, 276 + + Discoloration of rubber, dark, 249 + + Drains for tanks, 176 + + Drier, Colombo Commercial Company's, 136 + + Driers, artificial--for crepe rubber, 133 + -- --, for sheet rubber, 148 + --, "Chula," 148 + --, vacuum, 134 + + Drum furnaces, horizontal, 189 + + Drying chamber, floor of, 187 + -- --, arrangements of, 186 + -- houses for crepe, 178 + -- --, hot air, 182 + -- --, ventilation of, 185 + -- --, windows of, 185 + -- of rubber, 132 + --, period of, 145 + --, rate of, effect on rate of cure, 323 + + + Earth scrap, 124 + -- --, collection of, 58 + + Edges, thickened, after rolling, 251 + + Elongation of test piece, 311 + + Ends, thickened, after rolling, 251 + + Engines, 170 + --, position of, 174 + + + Factories, 172 + --, centralisation of, 221 + --, decentralisation of, 221 + --, number of floors, 174, 178 + --, ventilation of, 180 + --, windows of, 181 + + Factory buildings, situation of, 216 + --, choosing site for, 220 + --, ideal arrangement of, 162 + -- operation, 65 + + Fibre cotton, in crepe, 230 + + Field maintenance, 13 + + Fine hard Para properties of, 325 + + First latex and other grades, percentage of, 59 + + Floor of drying chamber, 187 + -- factories, 173 + -- furnace room, 196 + + Formalin, 87 + + Formic acid, 74, 279 + + Formula for test mix, 311 + + Freezing (coagulation) process, 293 + + Fuel, consumption of, 196 + + Fuels for smoking, 146 + + Furnace room, floor of, 196 + -- --, Petaling type of, 192 + + Furnaces, horizontal drum, 189 + --, "pot," 188 + + + Germination, 6 + + Grades, number of, 151 + + Grading, 150 + + Grafting, 8 + + Grass squares, 14 + + Greasiness before smoking, 252 + -- of surface, 258 + + Grit in crepe, 232 + + + Hand rolling sheets, 104 + + Hevea Brasiliensis, 1 + + Hot air drying houses, 182 + + Hydrochloric acid, 282 + + Hydrofluoric acid, 282 + + + Ilcken-Down process, 298 + + Instruments, method of using, 100 + --, recording, 144 + --, standardising, 98 + + + Lallang, eradication of, 15 + + Latex, bulking, 69 + -- cups, choice of, 40 + --, decomposition of, in the field, 270 + --, first and other grades, percentage of, 59 + --, first quality, 150 + --, mixing acid with, 79 + --, mixing sodium bisulphite solution with, 117 + --, preliminary treatment of, 65 + --, reception of, at the store, 65 + --, standard, 96 + --, standardisation of, 69, 110 + --, straining, 67 + --, transport of, 59 + + Light, importance of, in factories, 172 + + Litharge, 312 + + Load stretch curve, 312, 319, 320, 321 + + Low grade rubbers, fibrous matter in, 124 + + Lower grade rubber, care in manufacture, 129 + + Lubrication of machines, 166 + + Lump rubber, naturally coagulated, 120 + + + Machinery, 159 + + Machines, access to, 169 + --, adequacy of, 160 + --, arrangement of, 168 + --, lubrication of, 166 + --, position of, 173 + --, sheeting, 166 + --, speed of, 162 + + Mangrove, 147 + + Marking sheets, 105 + + Metrolac, 98, 100 + + Michie-Golledge system, 138 + + Mildew on surface, 260 + + Milky residue on serum, 249 + + Mixing acid with latex, 79 + + Moist glaze of surface, 258 + + Mould on surface, 260 + + Moulds, surface, on crepe, 241 + + + Natural catalysts, 312 + + Nitric acid, 282 + + Nurseries, 9 + + + Overcured, 307 + + Overvulcanised, 306 + + Oxalic acid, 279 + + Oxidation, prevention of, 56 + --, variation due to, 254 + + + Packing, 150 + --, bags for, 154 + --, bales for, 154 + --, cases, choice of, 153 + --, folding for, 155 + --, methods of, 156 + --, rooms, 211 + + Pale crepe, No. 1 fine, 110 + --, rubber, former methods of making, 118 + --, sheet, 89 + + Patches, 259, 260 + --, virgin, 259 + + Payment by result, 53 + + Perished rubber, 306 + + Physical properties of rubber, variation of, 317 + + Pits for smoke houses, 188 + + Pitting of surface, 250 + + Plantation rubber, testing of, 309 + + Planting, 1 + + Plasticising of rubber, 304 + + Plasticity of plantation rubber, 309 + + "Pot" furnaces, 188 + + Power units, 170 + + Premature coagulation, 46 + + Preparation, special methods of, 290 + + Pyroligneous acid, 282 + + + Racks, 186 + + Rate of cure, 307 + + Raw rubber, physical properties of, 313 + -- --, tests on, 309 + -- --, uses of, 315 + + Recommendations, Rubber Growers' Association, 152 + + Recording instruments, 144 + + Ribbing of sheet, 274 + + Rolling, 251 + + Rolls, grooving of, 164 + -- running hot, 165 + -- -- "free," 165 + + Roof of smoke house, 197 + + Rubber, drying of, 132 + + Rubber Growers' Association, Recommendations, 152 + + Rubber, properties of, 313 + --, smoking, 109 + + Rust, cause of, 267 + -- on sheet, 262 + --, treatment to prevent, 265 + + + Scrap washers, 57, 124 + + Screw plug, unsatisfactory, 73 + + Seed at stake, 10 + + Seeds, 2 + + Selection, 5 + + Senang folder, 156 + + Serum, milky residue on, 249 + + Sheet, ash on, 276 + --, bark in, 276 + --, bearing of defects on, in manufacture, 316 + --, blisters in, 272 + --, bubbles in, 269 + --, clippings, 130, 275 + --, creases in, 251 + --, dirt in, 276 + --, "dog ears," 251 + --, grades of, 151 + --, infrequent defects of, 276 + --, pale, 89 + --, ribbing of, 274 + -- rubber, artificial driers for, 148 + -- --, defects in, 249 + -- --, preparation of, 89 + + Sheet rubber, rolling and marking of, 102 + -- --, tensile strength of, 313 + --, rust on, 262 + --, splinters in, 276 + --, stickiness in, 274 + --, style of, 101 + --, support marks on, 273 + --, surface pattern of, 274 + --, thick ends of, 275 + + Sheeting machines, 166 + + Sheets, mis-shapen, 251 + --, thickened patches in, 251 + --, torn, 251 + --, unevenness of appearance, 253 + + Short weights, 157 + + Skimming, 100 + + Skimmings, 122 + + Slab rubber, 299 + -- --, properties of, 324 + + Slope, 312 + + Smoke curing of sheet rubber, 143 + -- --, temperature of, 144 + --, houses, 183 + -- --, Barker patent, 209 + -- --, Devon type, 200 + -- --, iron stoves for, 189 + -- --, Jackson type, 200 + -- -- of brick, 198 + -- -- rate of combustion in, 192 + -- --, roof of, 197 + -- --, "Third Mile" type, 199 + -- --, types of, 198 + + Smoked crepe, 130 + -- sheets, colour of, 255 + -- water for coagulation, 286 + + Smoking, effect on rate of cure, 323 + --, greasiness before, 252 + -- rubber, 109 + + Smooth rolling of sheets, 104 + + Sodium bisulphite, 80, 114 + -- --, abuse of, 85 + -- --, care of, 116 + -- --, deterioration of, 115 + -- --, evaluation of, 115 + -- --, making a solution of, 85 + -- --, quantity of, 84 + -- --, residual traces of, 86 + -- -- solution, mixing, with latex, 117 + -- sulphite, 86 + -- --, deterioration of, 115 + -- --, evaluation of, 115 + + Sorting, 150, 152 + -- rooms, 211 + + Spewing, 305 + + Splinters in sheet, 276 + + Spontaneous coagulation, 294 + + Spot disease, 235 + -- -- in sheet rubber, 273 + + Spots, 259, 262 + --, virgin, 259 + + Standard latex, 96 + -- sheet, 102 + + Standardising instruments, 98 + + Stickiness in sheet, 274 + + Stock solution, method of making, 75 + + Storage of rubber, 212, 216 + + Stoves, iron, for smoke houses, 189 + + Straining latex, 67 + + Streaks, 262 + + Stumps, 9 + + Sugars, coagulation with, 287 + + Sulphuric acid, 280, 286 + -- --, buying, 280 + -- --, formula for use of, 280 + -- --, storing, 280 + + Sun-drying sheet rubber, 147 + + Support marks on sheet, 273 + + Surface blotches, coloured, 249 + --, dull or black, 258 + -- pattern of sheet, 274 + + + Tackiness, cause of, 243 + --, copper salts cause of, 243 + -- in rubber, 242 + + Tanks, 90 + --, care of, 94 + --, designs and "layout," 176 + --, drains for, 176 + --, installation of, 93 + --, situation of, 175 + --, water-supply for, 177 + + Tapping, 38 + --, former systems of, 29 + -- knives, 38 + -- systems, 38 + + Tartaric acid, 279 + + Tensile product, 314 + + Test mix, formula for, 311 + -- pieces, making of, 310 + + Testing of plantation rubber, 307 + + Thick ends of sheet, 275 + + Thinning, 19 + + Timber for smoking, 147 + + Tool sheds, 216 + + Transport, 60 + -- by coolie, 62 + -- of coagulum, 59, 63 + -- of latex, 59 + + Trays, 167 + + Treatment of rubber in the factory, 301 + -- to prevent rust, 265 + + Tree scrap, 55, 122 + -- --, care of, 56 + -- --, oxidation of, 56 + + Trees per acre, 26 + + Trenches, silt catchment, 11 + + + Uniformity, 90 + -- in colour, lack of, 246 + + + Vacuum driers, 134 + + Variation due to oxidation, 254 + + Vegetable extracts, 289 + + Ventilation of drying houses, 185 + -- factories, 180 + + Verandas, 175 + + Virgin spots, 258 + + Viscosity of rubber solution, 309 + + Vulcanisation, 301 + --, rate of, 318 + + Vulcanised rubber, 318 + -- --, tests on, 309 + + Vulcanising, 307 + -- catalysts, 312 + --, "heat," 306 + + + Washers, scrap, 57, 124 + + Washings, 122 + + Water-supply for tanks, 177 + + Weeding, clean, 13 + + Weights, "short," 157 + + Wickham process, 293 + + Windows of drying houses, 185 + -- factories, 181 + + Working of rubber, 304 + + + Yields, 23, 25 + + + + + +End of the Project Gutenberg EBook of The Preparation of Plantation Rubber, by +Sidney Morgan + +*** END OF THIS PROJECT GUTENBERG EBOOK RUBBER *** + +***** This file should be named 35510-8.txt or 35510-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/5/5/1/35510/ + +Produced by Chris Curnow, Harry Lamé, Robin Curnow and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no 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