---------------------------------------- ------------------------------ ,,transcriber',s ,,notes3 99 ,minor typographical and lay-out errors have been corrected4 99 ,inconsistencies in spelling 7e4g4 hyphenated vs4 non-hyphenated words7 have not been corrected4 99 ,italics are represented by underscores as in text4 99 ,the original book uses a ,v symbol to describe ,v-shaped cuts4 ,these ,v symbols are represented as ,v4 99 ,changes made to original text3 99 ,table of ,contents3 99 ,early collection of latex transport changed to ,early collection of latex--,transport4 99 ,roof brick built houses changed to ,roof--,brick built houses4 99 ,the order of the sections under ,chapters ,,xii and ,,xxii has been changed slightly to reflect the order of the sections in the text4 99 ,tephrosia candiad changed to ,tephrosia candida4 99 ,archiev changed to ,archief4 99 about #a_/b square changed to about #a_/b inch square4 99 asbesto-slate changed to asbestos-slate as elsewhere4 99 ,formaline changed to ,formalin as elsewhere4 99 ,footnotes moved to under the paragraph they belong to4 99 ,page #ada3 ,the lengths of crepe were weighed carefully at #h a4m4 and #d a4m4 should probably read ,the lengths of crepe were weighed carefully at #h a4m4 and #d p4m4 ---------------------------------------- ------------------------------ ,,the ,,preparation ,,of ,,plantation ,,rubber ,,the ,,preparation ,,of ,,plantation ,,rubber ,,by ,,sidney ,,morgan1 ,a4,r4,c4,s4 ,,visiting ,,agent ,,for ,,estates ,,in ,,the ,,east2 ,,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 ,p4 ,,stevens1 ,m4,a4 7,,oxon417 ,,ph4,d41 ,f4,i4,c4 ,,consulting ,,chemist ,,to ,,the ,,rubber ,,growers' ,,association ,,in ,,london ,,constable ,,co4 ,,ltd4 ,,london 3 ,,bombay 3 ,,sydney #aibb ,,printed ,,in ,,great ,,britain ,,by ,,billing ,,and ,,sons1 ,,ltd41 ,,guildford ,,and ,,esher ,,preface ,mr4 ,sidney ,morgan's work on ,plantation ,rubber in the ,east is so well known that he hardly needs introduction4 ,an earlier book1 published in #aiad1 by the ,rubber ,growers' ,association1 entitled ,the ,preparation of ,plantation ,rubber1 was well received and widely read4 ,this book dealt in a very practical manner with problems with which the industry had to contend4 ,a second edition was subsequently published4 ,both editions are now out of print4 ,the present opportunity was therefore taken to revise the original work1 with the result that it has been enlarged and practically rewritten4 ,the information given is brought up-to-date1 and covers the whole process of production1 commencing with the planting of the tree1 passing on to the collection1 coagulation1 and curing of the rubber1 and concluding with the packing for export4 ,in the course of his work for the ,association1 ,mr4 ,morgan carried out a great deal of industrial research in rubber production1 including lengthy experiments on tapping1 the use of different coagulants and different conditions of coagulation1 and also on varying modes of rolling1 drying1 and smoking rubber4 ,he also went very fully into the types of construction and details of the machinery and buildings employed on estates4 ,much of this valuable work has escaped notice1 owing to its having been published in reports with limited circulation4 ,also a great deal of information was supplied to planters in a quiet and unobtrusive fashion1 in interviews1 visits to estates1 and on other similar occasions4 ,the knowledge and experience thus accumulated has been embodied in the present volume4 ,the subject-matter should interest not only those actually engaged in rubber planting1 but those otherwise directly or indirectly connected with the industry1 such as importers1 brokers1 and particularly the rubber manufacturers in this country and in ,america4 ,my experience has been that manufacturers as a whole have but a vague idea as to the methods employed in the preparation of plantation rubber1 and this work provides them with the opportunity of obtaining an insight into the actual operations on the estates4 ,it is most desirable that a closer bond should unite the plantation and manufacturing rubber industries4 ,such a result is best promoted by a better understanding of the problems with which each is confronted4 ,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 manufacturers4 ,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 up1 planting1 trenching1 and weeding the plantations which have replaced the virgin jungle4 ,the authors are indebted for most of these photographs to ,mr4 ,h4 ,sutcliffe1 one of the mycologists of the ,rubber ,growers' ,association4 ,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 rubber4 ,these results are largely due to the work of ,sidney ,morgan and his colleagues1 on whom the planters have relied for technical guidance and advice4 ,as regards my own contribution this is confined to a general outline of the subject4 ,i have1 therefore1 omitted reference to a number of matters which would have been dealt with in detail had space permitted4 ,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 years4 ,it was not found practicable to give detailed references in all cases4 ,the reports on which the conclusions are based will1 however1 be found among the regular quarterly reports made by the writer for the ,association up to ,june1 #aiai4 ,subsequent reports have been published in the ,monthly ,bulletin of the ,rubber ,growers' ,association4 ,we are indebted to the ,association for permission to publish details from these reports1 and also for the use made of numerous earlier reports published both in ,london and in the ,east4 ,,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 #a ,,chapter ,,ii ,,field ,,maintenance ,clean weeding--,selective weeding--,loss of top-soil--,grass ridges--,lallang eradication--,mimosa gigantea 7,m4 invisa7--,green cover-plants--,connection between weeding1 soil conservation1 and soil improvement #ac ,,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 tree1 present and future--,trees per acre #ai ,,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 cuts1 etc4--,tapping experiments--,r4,g4,a4 experiment--,alternate-daily versus daily tapping #bh ,,chapter ,v ,,tapping ,,and ,,collecting ,tapping knives--,personal equation in use of knives--,choice of latex cups--,cleaning of cups--,water in cups--,premature 7spontaneous7 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-scrap1 oxidation of--,prevention of oxidation--,bark-shavings--,collection and storage of shavings-- ,treatment of shavings--,collection of earth-scrap #ch ,,chapter ,,vi ,,transport ,,of ,,latex ,,and ,,coagulum ,percentages of first latex and other grades--,early collection of latex--,transport1 nature of--,light railways-- ,motor-lorries--,bullock-carts--,care of transport vessels--,use of an anti-coagulant during transport--,transport by coolie-- ,coagulation centres 7stations7--,transport of coagulum #ei ,,part ,,ii ,,factory ,,operations ,,chapter ,,vii ,,preliminary ,,treatment ,,of ,,latex ,reception at store--,receptacles--,jars--,tanks--,nec essity 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 #fe ,,chapter ,,viii ,,coagulation ,choice of coagulant--,strength of acid solution--,making stock solution--,quantity for use--,quantities under modern requirements--,care in mixing--,method of mixing with latex--,use of sodium bisulphite as an anti-oxidant--,quantities for use-- ,formulae--,abuse of the chemical--,residual traces in the dry rubber--,use of sodium sulphite as an anti-coagulant1 quantities for use--,formulae--,use of ,formalin as anti-coagulant --,formulae for use #gd ,,chapter ,,ix ,,preparation ,,of ,,sheet ,,rubber ,pale 7air-dried7 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 #hi ,,chapter ,x ,,preparation ,,of ,,crepe ,,rubber ,first consideration1 fine pale crepe--,standardised dilution of latex--,coagulation and coagulant--,quantities of coagulant-- ,colour of rubber--,sodium bisulphite 7use of7--,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-scra p--,fibrous matter in low- grade rubbers--,scrap-washers--,compound crepes--,increased care with lower grades--,block rubber from crepe--,smoked crepe versus sheet clippings #aaj ,,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 #acb ,,chapter ,,xii ,,sorting1 ,,grading1 ,,and ,,packing ,reducing number of grades--,reduction carried too far--,r4,g4,a4 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 #aej ,,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 #aei ,,chapter ,,xiv ,,factories ,general construction--,plenty of light--,floors--,drainage of-- ,how many storeys--,verandahs--,tanks1 situation of--,designs and lay-out--,drains--,water supply #agb ,,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 #agh ,,chapter ,,xvi ,,other ,,buildings 7continued71 ,,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 #baa ,,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--,gr eenish 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 #bbc ,,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 #bdi ,,part ,v ,,general ,,chapter ,,xix ,,choice ,,of ,,coagulant ,acetic acid in general use--,is a coagulant necessary8--,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 #bgh ,,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--,a,erobic--,anaerobic-- ,organisms--,maude-,crosse patent--,method of operation-- ,accelerating action of sugars--,accelerating action of soluble calcium salts--,ilcken-,down process--,slab rubber #bij ,,part ,,vi ,,vulcanisation ,,chapter ,,xxi ,,introductory ,,dealing ,,with ,,treatment ,,and ,,vulcanisation ,wild rubber contrasted with plantation rubber--,milling and mixing--,preparation for vulcanising--,vulcanising #cja ,,chapter ,,xxii ,,testing ,,of ,,plantation ,,rubber ,tests on raw rubber--,breaking strain--,behaviour of rubber during milling1 etc4--,preparation for testing--,tests on vulcanised rubber--,choice of a formula--,physical tests #cji ,,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 #cac ,,index #cbg ,,list ,,of ,,illustrations ,,page ,,seeds1 ,,showing ,,variable ,,size1 ,,shape1 ,,and ,,marking #b ,,felling ,,light 7,,secondary7 ,,jungle #c ,,seedling1 ,,showing ,,root-,,system ,,with ,,seed ,,still ,,attached #d ,,new ,,clearing #e ,,typical ,,young ,,clearing1 ,,aged ,,about ,,three ,,years1 ,,planted ,,on ,,virgin ,,soil4 ,,original ,,jungle ,,timber ,,slowly ,,rotting #f ,,light ,,jungle #g ,,dense ,,jungle #h ,,clearing ,,ready ,,for ,,planting #i ,,new ,,clearing3 ,,slopes ,,holed ,,for ,,planting2 ,,flat ,,area ,,being ,,drained #aa ,,typical ,,young ,,clearing1 ,,with ,,timber #ae ,,typical ,,young ,,clearing1 ,,with ,,timber #ag ,,typical ,,young ,,planted ,,area #bj ,,another ,,example ,,of ,a ,,recently ,,planted ,,area #ba ,,widely ,,planted ,,young ,,area1 ,,just ,,ready ,,to ,,be ,,brought ,,into ,,tapping #bd ,,field ,,of ,,old ,,rubber ,,trees ,,in ,,which ,,thinning ,,had ,,been ,,delayed ,,too ,,long #be ,,two ,,cuts ,,on ,a ,,quarter ,,circumference1 ,,on ,,an ,,old ,,tree #ca ,,the ,,single ,,cut ,,on ,a ,,quarter ,,circumference1 ,,on ,,an ,,old ,,tree ,,and ,,on ,,renewed ,,bark #cc ,,single ,,cut ,,on ,,half ,,circumference 7,,half-,,spiral7 #ce ,a ,v-,,cut ,,on ,,half ,,the ,,circumference #cg ,,single ,,cut ,,on ,,two-,,fifths ,,of ,,circumference #da ,,effects ,,upon ,,renewed ,,bark ,,of ,,previous ,,tapping #dd ,,another ,,example ,,showing ,,the ,,effects ,,of ,,previous ,,tapping #de #a4 ,,showing ,,effect ,,of ,,wintering #dh #b4 ,,new ,,growth ,,of ,,young ,,leaf ,,on ,,same ,,tree #di ,,effects ,,of ,,disease--,,mouldy ,,rot #ej ,,effects ,,of ,,disease--,,mouldy ,,rot #ea ,,effects ,,of ,,disease--,,mouldy ,,rot #eb ,,effects ,,of ,,disease--,,mouldy ,,rot #ec ,,raised ,,verandah ,,for ,,reception ,,of ,,latex2 ,,likewise ,,equipped ,,with ,,facilities ,,for ,,calculating ,,individual ,,daily ,,yield ,,per ,,coolie ,,by ,,sampling ,,of ,,latex #ff ,,end-,,section ,,sketch ,,of ,,verandah1 ,,etc41 ,,showing ,a ,,good ,,method ,,for ,,receiving ,,latex ,,and ,,filling ,,tank #gj ,,raised ,,verandah ,,for ,,reception ,,and ,,handling ,,of ,,latex #ga ,,another ,,set ,,of ,,dilution ,,tanks ,,on ,,raised ,,verandah #gb ,,two ,,views ,,of ,,dilution ,,and ,,mixing ,,tanks #ha ,,unit ,,modern ,,coagulating ,,tank 7,,two ,,views7 #ia ,,another ,,battery ,,of ,,tanks1 ,,with ,,dilution ,,tanks1 ,,raised1 ,,on ,,the ,,right #ib ,,closer ,,view ,,of ,,foregoing #ic ,,another ,,battery ,,of ,,tanks1 ,,without ,,dilution ,,tanks ,,or ,,means ,,of ,,gravitating ,,latex #ie ,a ,,sheeting ,,tank ,,containing ,,coagulum ,,for ,,crepe ,,preparation #if ,a ,,battery ,,of ,,sheeting ,,tanks 7,,pataling ,,estate74 ,,dilution ,,tanks1 ,,raised1 ,,on ,,the ,,left #ig ,,the ,,old ,,method ,,of ,,dripping ,,freshly ,,rolled ,,sheets ,,within ,,the ,,factory #ajh ,,the ,,newer ,,method ,,of ,,hanging ,,in ,,the ,,open ,,air #aji ,,three ,,grades ,,of ,,crepe ,,rubber #aaa ,a ,,washing ,,shed #aab ,,drying ,,graph4 ,,pale ,,crepe 7,,thin7 #adj ,a ,,shipment ,,of ,,rubber1 ,,packed ,,and ,,ready ,,for ,,transport #aee ,,on ,,its ,,road ,,to ,,the ,,railway3 ,,bullock-,,cart ,,transport #aeg ,a ,,battery ,,of ,,machines #afe ,,third ,,mile ,,type2 ,,horizontal ,,drum #aij ,,third ,,mile ,,type ,,of ,,furnace1 ,,used ,,in ,,conjunction ,,with ,,third ,,mile ,,smoke-,,house #aij ,,side ,,sectional ,,elevation 7,,pataling ,,type ,,of ,,furnace7 #aic ,,pataling ,,type ,,of ,,furnace #aic ,,large ,,smoke-,,house ,,of ,,ordinary ,,construction1 ,,with ,,shielded ,,ventilators ,,permanently ,,open #aid ,,brick ,,and ,,cement ,,superstructure ,,of ,,furnace ,,inside ,,the ,,building1 ,,but ,,fed ,,from ,,outside #aie ,,general ,,view ,,of ,,shelters ,,covering ,,approaches ,,to ,,furnaces #aif ,,near ,,view ,,of ,,shelter #aig ,,third ,,mile ,,type ,,of ,,smoke-,,house #aii ,,general ,,view ,,of ,,double ,,devon ,,type ,,of ,,smoke-,,house #bja ,,general ,,view ,,of ,,double ,,devon ,,smoke-,,house ,,and ,,factory ,,buildings #bjb ,,view ,,of ,,platform ,,of ,,devon ,,smoke-,,house2 ,,doors ,,of ,,compartments ,,open1 ,,and ,,one ,,rack ,,partially ,,withdrawn #bjc ,,double ,,devon ,,smoke-,,house ,,of ,,brick1 ,,with ,,roof ,,of ,,chinese ,,tiles1 ,,showing ,,loading ,,platforms ,,with ,,racks ,,withdrawn ,,from ,,smoking ,,chambers #bjd ,,side-,,view ,,of ,,preceding ,,photograph1 ,,showing ,,external ,,arrangement ,,for ,,stoking ,,furnaces #bje ,,front ,,view ,,of ,,double ,,devon ,,type ,,of ,,smoke-,,house #bjf ,,side-,,view ,,of ,,double ,,devon ,,type ,,of ,,smoke-,,house #bjg ,,the ,,new ,,barker ,,type ,,of ,,smoke-,,house3 ,a ,,small ,,unit #baj ,,suggested ,,arrangement ,,of ,,building #bah ,,three ,,specimens ,,of ,,fine ,,pale ,,crepe ,,suffering ,,from ,,spot ,,disease #bcg ,,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 knowledge1 and to be wise after the event is a failing which is not confined to those interested in modern planting methods4 ,looking at the matter broadly1 however1 it must be acknowledged that the pioneers1 wrong though they may have been on some points1 did remarkably well1 considering that there existed no real knowledge on the subject and that the methods employed were perforce of an empirical nature4 ,although we know a little more concerning the scientific aspects of rubber planting1 the sum total of that knowledge does not justify any drastic criticism of the methods employed by our predecessors4 ,in fact1 although we may be of opinion that on general lines there is little now to be learned regarding the planting of ,hevea ,brasiliensis1 our present knowledge does not preclude the possibility that future investigations may bring against us charges similar to those sometimes levelled at the earlier planters4 ,the main theme of the present volume is that of the preparation of rubber for the market4 ,hence it is not proposed to deal in detail with the work attaching to the opening and development of rubber estates4 ,for this the reader is referred to the literature dealing specifically with rubber planting4 ,certain points in connection with planting may advantageously be treated in a general way according to modern knowledge1 and of these it is proposed to discuss a few in the following pages4 ,illustration3 ,,seeds1 ,,showing ,,variable ,,size1 ,,shape1 ,,and ,,marking4 ,,seeds4--,the view is now generally held that many areas were planted from seed which was not collected in a discriminate manner2 and that probably the comparatively low yields obtained on areas of some estates may be due to the employment of seed from a poor strain4 ,to be able to decide whether such explanation fits the case demands a full knowledge of all the possible factors governing the question of yields4 ,it may1 or may not1 be a fact that seed from a poor strain is wholly or partially accountable for low yields2 but whatever the degree in which the seed influences the result1 it is an axiom that to obtain the best results in all planting industries a most judicious selection of seed should be made4 ,in short1 seed obtained from good-yielding specimens by selective treatment will eventually produce progeny of good-yielding strain4 ,illustration3 ,,felling ,,light 7,,secondary7 ,,jungle4 ,the recognition of these principles as applied to the planting of ,h4 ,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 consistency4 ,it does not follow that the tree of most rapid growth and development is necessarily the best yielder2 such is often not the case4 ,in the matter of selection1 therefore1 one has to take other standards than that of size2 and the issue is narrowed chiefly to a consideration of the yields of latex given by individual trees4 ,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 yielded4 ,the dry rubber content of latices from the same trees is found to be so comparatively regular1 allowing for climatic changes1 that it is sufficient for the purposes of selection to measure the volumes of latex yielded by individual trees4 ,illustration3 ,,seedling1 ,,showing ,,root-,,system ,,with ,,seed ,,still ,,attached4 ,unfortunately the industry is so young that the question of seed selection yet awaits study4 ,the task presents certain practical difficulties1 and would be by no means so easy to control as in the case of seed selection from other plants4 ,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 work4 ,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 man4 ,unfortunately neither the man nor the facilities for such experimental work exist at the present moment in the ,federated ,malay ,states4 ,on the scientific side the industry is incommensurably staffed1 and most of the workers' time is occupied with routine work connected with estate practice4 ,illustration3 ,,new ,,clearing4 ,in the middle distance1 felled trees awaiting burning2 in the foreground1 a flat and wet area with main drainage outlined4 7,by courtesy of the manager of ,membakut ,estate1 ,british ,north ,borneo47 ,illustration3 ,,typical ,,young ,,clearing1 ,,aged ,,about ,,three ,,years1 ,,planted ,,on ,,virgin ,,soil4 ,,original ,,jungle ,,timber ,,slowly ,,rotting4 ,,selection4--,it is possible1 however1 that the question of strain improvement will be solved in another manner than that of successive breeding from the seeds of high-yielding trees4 ,such investigatory work is now occupying the attention of scientific organisations in the ,east1 and credit is due to the stations in ,java which have begun experimental work in this direction4 ,in brief1 the scheme may be outlined as follows4 ,trees known to be uniformly good yielders are kept under observation1 and the seeds gathered carefully4 ,these seeds are germinated in a special nursery1 and the best-grown seedlings are selected for further operations4 ,at a certain stage a bud is taken from a high-yielding parent tree and grafted upon the stem of the seedling4 ,when this has struck the original head of the seedling is removed4 ,this ensures that one has in the seedling both the stem and future branch system of the same strain as the parent high-yielding trees4 ,it is possible to go a step farther1 and by certain processes induce a new root system to grow above the existing roots1 which are then removed4 ,one is then able to guarantee that the roots1 stem1 and branches will be of the original high-yielding strain4 ,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 laterals4 ,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-root4 ,illustration3 ,,light ,,jungle4 ,on the whole1 this system of propagation receives the approval of investigators1 and removes the objections which may be advanced against the development of a scheme entirely founded upon successive breedings from selected seed4 ,the course of the investigations1 also1 are thereby shortened considerably4 ,care must be exercised in the work of obtaining and grafting the buds1 but it has now been proved that by exercising reasonable precautions which are not beyond the intelligence and ability of subordinates1 an extremely high percentage of success can be attained4 ,illustration3 ,,dense ,,jungle4 ,until such time as this process becomes practicable the inception of a planted area must follow the lines usually adopted4 ,,nurseries4--,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 seeds4 ,the seed is planted in specially prepared beds1 and the percentage of germination noted for future reference4 ,the plants should be tended carefully1 and close observation made for the detection of disease or pests4 ,it is not uncommon to find that owing to lack of care in the preparation of the seed-bed1 the young plants are attacked by disease4 ,illustration3 ,,clearing ,,ready ,,for ,,planting4 ,surface timber removed1 but stumps remaining4 ,,stumps4--,at a stage1 varying according to the requirements of the estate1 when the plants are from twelve to eighteen months old1 they are lifted from the earth4 ,the roots and head are cut off1 and the stump is ready for immediate planting in the field4 ,naturally any appreciable delay in planting1 or unfavourable weather conditions1 will militate against the chances of successful striking2 and it is not uncommon to find that a certain number of supplies will be necessary4 ,,seed ,,at ,,stake4--,a method sometimes adopted is to put out seed in the field1 in prepared holes which indicate the exact position of the future trees4 ,usually three seeds are placed in each hole1 and if two or three germinate1 the plant having the healthiest appearance is retained1 and the others removed4 ,the possible objections to this method of planting are obvious to those acquainted with field conditions1 but in actual practice planting seed at stake has often proved highly successful4 ,naturally the results obtained must depend upon the selection of good seeds1 the care exercised in the preparation of the holes1 weather conditions1 and the discrimination exercised in the selection of the plants to be retained--apart from such disabilities as the depredations of rats and other pests4 ,,basket ,,plants4--,yet another and perhaps the most popular method at present is the germination and growth of seedlings in baskets specially constructed for the purpose4 ,these plants are kept under observation until of the required age and growth4 ,they are then conveyed to the field1 and the baskets are planted in prepared holes4 ,the baskets1 being of vegetable material1 are liable to be attacked by various diseases while in the nursery or after planting4 ,it is considered advisable1 therefore1 to treat them by dipping into some disinfectant such as tar1 or a mixture of tar and one of the common proprietary disinfectants4 ,otherwise a disease may be conveyed from the basket to the seedling4 ,,preparation ,,for ,,planting4--,there can be no other opinion than that ideally all land required for planting should be perfectly clear of timber of every description4 ,after felling and burning1 under ordinary conditions a certain amount of clearing is effected1 but in actual practice this amounts to comparatively little4 ,big logs and stumps are left because the cost of clean clearing is judged to be prohibitive and non-economic4 ,surface timber is gradually cleared in the course of development1 and usually large stumps are the last to be tackled4 ,the objection to this procedure is really not strong1 but unfortunately an important point is generally overlooked4 ,granted that most of the dreaded diseases travel beneath the surface of the ground by means of buried timber1 it is plain that as far as stumps are concerned1 the chief source of danger lies in the existence of the roots4 ,if these were carefully exposed and removed1 the isolated stumps would then not be such potential infection points4 ,it follows from this argument that the importance of removing buried timber cannot be too strongly insisted upon4 ,it is not uncommon to find that some years after the opening of an estate1 and after surface timber has been removed1 a large number of trees are affected with ,fomes lignosus 7formerly known as ,fomes semitostus74 ,such cases are directly attributable to the existence of buried timber1 and no local treatment will be successful unless the whole of the area is dug over carefully1 and all pieces of timber removed4 ,illustration3 ,,new ,,clearing2 ,,slopes ,,holed ,,for ,,planting2 ,,flat ,,area ,,being ,,drained4 7,by courtesy of manager1 ,membakut ,estate1 ,british ,north ,borneo47 ,,silt ,,catchment ,,trenches4--,granted the ultimate necessity of clean clearing1 it becomes necessary to take some precautions to prevent loss of soil by wash in young areas planted on sloping land4 ,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 wash4 ,its removal necessitates the institution of some method of preventing wash4 ,the establishment of terraces on steep slopes tends to the achievement of the desired result1 but this method is not extended to more moderate slopes where loss by wash is still considerable4 ,it is the opinion of the writers and others that the general case calls for the institution of silt catchment trenches1 which1 as the name denotes1 fulfil the duty of catching any surface soil and of retaining rainwater4 ,these trenches are usually laid out on contour1 and do not exceed a length of #bj feet4 ,they are usually from #ah inches to #b feet wide and deep1 and are so arranged on the slope that they occupy overlapping positions4 ,the actual number of trenches required will depend upon the angle of slope2 the steeper the slope the greater the number required--i4e41 the shorter will be the length of slope between any two trenches4 ,given a clean area1 it is obvious that the momentum acquired by running water 7and hence the amount of soil removed7 on any one slope will depend upon the distance travelled4 ,it is advisable1 therefore1 to place a larger proportion of the trenches on the upper part of the slope than on the lower1 so as to guard against the breaking down of the trench system under an abnormal downpour of rain4 ,on land thus prepared the writer has seen areas successfully planted1 which1 under ordinary conditions1 were condemned as being too steep for planting4 ,it is true that these trenches necessitate continual upkeep until the soil becomes well shaded by trees1 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 executed4 ,whatever may be the weaknesses exposed as a result of providing an insufficient number of trenches of inadequate dimensions1 there can be no question that they are a necessity4 ,,chapter ,,ii ,,field ,,maintenance ,,clean ,,weeding4--,intimately connected with the growth and development of the rubber tree one has to consider the conditions under which it is allowed to mature4 ,the argument has been used that1 since the habitat of ,hevea ,brasiliensis is in the jungle1 we should be proceeding against nature by introducing conditions unlike those under which the wild rubber tree grows4 ,it is difficult to treat such an argument seriously1 as by quoting parallel instances in arboriculture it could be shown that growth1 development1 and yields are improved by cultivation of wild plants4 ,it needs small experience with rubber-tree plantations to be convinced of the necessity for dealing with other growths1 which would otherwise soon surround and overshadow young rubber trees4 ,apart from checking and preventing woody undergrowths it is considered advisable to keep the ground more or less free from light vegetable growths1 which are roughly grouped under the heading of weeds4 ,naturally1 if these weeds are allowed to flourish and seed1 their eventual eradication may be a matter of extreme difficulty and expense4 ,it is the aim1 therefore1 of properly conducted estates generally to institute such a system of work that the weeding-gangs cover the whole estate at regular intervals2 and1 as a general rule1 it may be accepted that the shorter the interval between successive visits by the gang to any particular area1 the easier it is to keep weeds in check1 and the cheaper the work will eventually be done4 ,this procedure defines roughly what is implied by the term clean weeding1 and it is the policy adopted by most estates4 ,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 tea1 coffee1 tobacco1 etc4 ,in latter years the wisdom of scrupulous clean weeding under all conditions has been questioned2 and there can be no doubt that under certain special conditions a continuation of the policy of clean weeding is calculated to produce1 in course of time1 more harm than benefit4 ,as an instance1 the case might be cited of steep slopes on poor land4 ,continual clean weeding on such areas will lead eventually to a great loss of the surface soil1 unless some precautions are adopted for catching and retaining the fine silt particles4 ,it is to be noted that such a type of soil and slope1 when the shade is appreciable1 often produces no weeds heavier in growth than a very light grass4 ,it is urged that the necessity for strict clean weeding on such soils does not exist1 and1 in fact1 that it would be an injurious policy4 ,such arguments appear to be well founded in experience1 and the writers are in thorough agreement that such special cases deserve special consideration4 ,rigid adherence to a policy of clean weeding1 without regard to special conditions1 would be most inadvisable4 ,nevertheless1 such exceptional cases do not detract from the wisdom of clean weeding in general4 ,every planter of experience realises how easily fields become infested with weeds if the regular work is suspended or delayed4 ,it is probably quite true that the harm due to the presence of some weeds on an occasion is negligible2 but apart from this debatable point1 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 weeded4 ,this is common experience1 and for that reason alone a general policy of clean weeding is thoroughly sound2 especially if combined with some system of silt-retention4 ,,grass ,,squares4--,on some estates the practice of clean weeding is undertaken in combination with a system of silt-retention1 which depends upon the development and maintenance of ridges4 ,these are built up from the debris of weeding in the form of hollow squares4 ,grass is allowed to sprout and grow in these ridges1 and when it attains a certain height it is trimmed down so as to keep it within bounds4 ,the soil within the hollow square is clean weeded2 and it is maintained that loss of soil by wash is avoided4 ,under certain conditions there is a great deal to be said in favour of the method1 but in the opinion of the writers it should be regarded only as a method of expediency4 ,it is not to be preferred to the more thorough practice of soil-retention by means of silt-trenches1 although the latter method may be slightly more expensive in the end4 ,illustration3 ,,typical ,,young ,,clearing1 ,,with ,,timber4 ,planted rubber-stump in foreground4 ,,lallang ,,eradication4--,the greatest bugbear of the planter in connection with weeding is the incidence of lallang4 ,many proposals have been put forward at various times for the complete eradication of this pest2 but at present1 under ordinary circumstances1 there would seem to be no better method than by heavy and deep digging1 followed by regular attention4 ,the method is acknowledged to be expensive1 but any half-hearted measure otherwise taken will eventually prove to be even more costly4 ,one has to differentiate1 of course1 between the incidence of lallang attributable to negligence on the estate itself1 and the occasional outbreaks near boundaries1 due to seeds having been wind-borne from patches of lallang outside the boundaries ,but1 in general1 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 intervals4 ,as already intimated1 the usual method of eradication of areas of lallang is by thorough digging1 and the exposure of the strong root system to the sun4 ,as a matter of interest it may be noted that recently some success has been obtained by another method#a on areas which one may have in view for planting at some future date4 #a ,eradication of ,lallang1 ,w4 ,p4 ,handover1 ,the ,planter1 ,vol4 ,i41 ,no4 #a1 ,august1 #aibj4 ,it consists in the employment of ,mimosa gigantea1 which eventually smothers the growth of lallang4 ,the seeds are sown broadcast1 in drills1 or in pockets1 amongst the lallang4 ,in the course of about three months it overtops the grass and proceeds to travel4 ,at this stage the whole mass is pressed down1 and the pressing is repeated at regular intervals4 ,under favourable conditions1 in about twelve months1 an impenetrable mat has been formed1 which gradually forms a good mulch4 ,when it is desired to remove the ,mimosa1 the mass 7pressed down7 is cut and rolled up like a carpet4 ,cleared in this manner1 the area then needs regular weeding1 in order to check the development of any stray lallang shoots4 ,in actual practice it was found that the cost of this method was approximately two-thirds that of the usual digging method4 ,,green ,,cover ,,plants4--,some years ago it was quite common to find green cover-plants employed on estates with the primary idea of minimising weeding costs4 ,with most of these it was found later that their value was not real1 and that they harboured diseases1 and pests4 ,moreover1 when they were removed1 it was often found that an abundant crop of lallang and weeds resulted4 ,there can be no question that certain plants can be employed with advantage1 not only in the control of weeds1 but also by reason of benefit to the soil in which they are established4 ,these plants are leguminous1 and their use is restricted almost entirely to young areas1 inasmuch as they will not continue to grow when shade becomes marked4 ,of those best known in modern practice might be mentioned ,tephrosia candida 7,boga bean71 ,centrosema ,plumerii1 and ,dolichos ,hoseii 7,sarawak bean74 ,illustration3 ,,typical ,,young ,,clearing1 ,,with ,,timber4 ,young rubber plants in foreground4 ,two of these are easily distinguishable1 both with small crowns of leaves4 ,it is wrong to imagine1 however1 that the establishment of such leguminous cover-plants obviates weeding4 ,so far is this from being the case1 that in practice it is found that the weeding rounds must be conducted at first with the same regularity as in ordinary working1 but that naturally there is much less work to be done4 ,as the plants develop1 they can be pruned or dug into the soil1 as the case may be4 ,the addition of the green material to the soil1 either by digging or by burying in open trenches1 is calculated to cause improvement in the condition of the soil4 ,there may thus be a close connection between weeding1 soil conservation1 and soil improvement4 ,,chapter ,,iii ,,thinning ,,of ,,areas ,on this subject there is unanimity regarding the necessity for the operation4 ,divergence of opinion exists only as to a matter of degree4 ,on the one hand there is the school of planters who would advocate the advisability of planting up to1 say1 #bjj trees per acre1 with subsequent thinning out by selection4 ,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 maintain1 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 arise4 ,unfortunately for the latter school1 a very important point is overlooked--viz41 that size and general development are not criteria of yielding capacity4 ,it might thus follow that a stand of ninety well-grown trees per acre might give very disappointing yields per acre4 ,in a few instances this has been noted with #cj by #cj feet planting1 but it is doubtful whether the factor influencing such results has been appreciated4 ,the apostles of close-planting have this in their favour3 that if the trees to be removed are selected on proper lines1 it is possible to have all remaining trees of comparatively high-yielding strain4 ,this is a very sound argument1 but its practicability is limited very largely by the question of early growth and development4 ,it would seem the sane course in any event not to plant more trees per acre than may grow normally1 and without branch or root interference up to the fifth year 7the normal first year of tapping74 ,before this stage has been reached1 stunted or deformed trees will have been noted and removed1 so that in the first year of tapping thinning proper can be commenced4 ,in the past this has been effected wholly by selection of trees according to their general appearance and situation2 but it is now safe to predict that future operations will be based upon sounder and more scientific lines4 ,trees will be selected for removal according to their individual yields1 a standard which we have been advocating for years without much practical success4 ,in ,java and ,sumatra much good work has been done in this direction1 and recently a commencement has been made in the ,f4,m4,s4 ,illustration3 ,,typical ,,young ,,planted ,,area4 ,heavy original jungle timber4 ,it is within the daily observation of all planters that certain trees regularly give greater yields than others1 and that such trees are not to be distinguished by size or general development4 ,moreover1 with slight variations1 it has been found that a good yielding tree is consistently a good yielder1 and the converse holds true4 ,if1 therefore1 measurements of individual yields are taken at intervals1 and the results recorded during the first year of tapping of an area1 an excellent guide is obtained for the first round of thinning4 ,it is found in actual practice that five1 or even three1 readings during the year are sufficient to give the indication required4 ,it is not essential that simultaneous readings should be taken over a large area2 in fact1 such a step is really impracticable at first4 ,the simplest method is to employ either-- 7a7 ,a small uniform vessel in which the latex is measured by means of a thin slip of bamboo upon which graduations are marked4 7b7 ,a glass measure graduated regularly4 ,illustration3 ,,another ,,example ,,of ,a ,,recently ,,planted ,,area4 ,in both cases it is immaterial what units are represented by the graduations--whether cubic centimetres1 quarter ounces1 half-ounces1 or ounces1 as long as the unit is not too large4 ,it is preferable to employ a fairly small unit1 so that in taking readings from young trees a wider range may be obtained between poor yields and good yields4 ,in the case of older trees a larger unit may be taken4 ,the first stage in the operations is to number all trees in the field to be tested1 and to prepare a rough register1 with three or five vacant columns opposite each tree number4 ,it is not advisable to commence the record of yields until the panel of bark has been under tapping for a month or two4 ,it is found that an intelligent coolie can be taught the method of measuring and rough recording4 ,the latter is accomplished by means of marks made upon the virgin bark of the tree above the tapped area4 ,the marks may be made with a tapping knife1 by means of paint1 or with a lead pencil4 ,the simplest form of record consists in putting one mark for each graduation of reading4 ,in practice it is found that1 commencing about an hour after the first tree has been tapped 7in the case of young trees7 and following the course taken by the tapper1 the measurer of yields is able to do about #b full tasks 7#fej to #gej trees7 per diem4 ,each day progress is made through the field4 ,obviously on such a small scale and utilising only one measuring coolie the comparison is restricted very much2 but in any case this is immaterial as1 owing to the personal equation of the tapper1 comparison strictly should be limited and internal--i4e41 it should really be confined to one task only at a time4 ,in this way the worst trees in any task are indicated4 ,the keeping of the records may be entrusted to a field clerk1 but is better placed in the hands of a ,european4 ,the register is taken into the field and the rough records found on the trees are noted in the columns against the tree number4 ,most planters are aware in a general way of the disparity between the yields of individual trees1 but they would probably be surprised if they undertook the institution of such records4 ,the following figures must not be taken as typical4 ,they represent the average results from several tasks in a young field from which all ill-grown and deformed trees had been removed4 ,it is immaterial what the units represent1 as they are purely arbitrary and were selected for the purpose of obtaining a fairly wide range4 ,any trees which failed to yield sufficient latex to reach the first mark were registered at zero4 ,the following percentages were obtained3 ,zero #c per cent4 ,above mark #a #f #b #af #c #db #d #ab #e #ad #f #f #g #j #h #a #i #j --- #ajj ,it may be remarked that1 judging by ordinary standards1 it was impossible to discriminate between good yielders and others1 and if thinning were to be done on the usual lines it is quite possible that some of the best yielding trees would be removed4 ,taking the mark ,no4 #e as the datum line1 it will be noted that #gi per cent4 of the trees come below and #ba per cent4 above4 ,in the latter proportion the majority lie close to the datum line4 ,it will be seen that there are outstanding yielders even amongst these young trees1 and that it would be possible to mark about #aj per cent4 of the stand per acre at once for removal in the first round of thinning4 ,in the case of old trees it is possible that one would encounter greater extremes of yields than those shown in the foregoing table1 especially if a certain amount of thinning had been done previously on empirical lines4 ,sufficient has been written to show that the only reasonable basis for selection of trees in thinning is that of yields2 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 lines4 ,,yields ,,per ,,tree4--,a great feature is made in estate reports of the figure showing the average yield per tree per annum4 ,assuming an area to be yielding at the average high rate of #edj lbs4 per acre per annum1 with an average stand of ninety trees per acre1 the yield per tree per annum averaged over all trees is #f lbs4 ,keeping in mind the test-figures on a previous page1 it will be obvious that some of these trees may have given very much more than #f lbs4 during the year1 and some less4 ,in view of present information it would not be surprising to find that a few might have been yielding upwards of #ae lbs4 per annum4 ,unfortunately this information is only to be obtained by individual tests1 and under normal estate conditions the facts escape notice4 ,cases are known in which out-standing individual trees have been known to yield at the rate of #be lbs4 and more per annum4 ,illustration3 ,,widely ,,planted ,,young ,,area1 ,,just ,,ready ,,to ,,be ,,brought ,,into ,,tapping4 ,illustration3 ,,field ,,of ,,old ,,rubber ,,trees ,,in ,,which ,,thinning ,,had ,,been ,,delayed ,,too ,,long4 ,note height and comparative lack of girth4 ,,future ,,yields ,,per ,,tree4--,it has been shown that by selective methods based on yields1 poor trees can be eliminated4 ,whether by a process of seed-selection or by means of propagation based on bud-grafting and marcotting1 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 #be lbs4 per annum over any given area4 ,yields of #a1jjj lbs4 per acre per annum should be obtained easily4 ,,trees ,,per ,,acre4--,this brings us to the question as to how many trees one should leave to the acre after thinning operations4 ,figures have been given by various authorities1 but it appears to the writer at the present time to be impossible to lay down a general rule4 ,so much depends upon conditions4 ,in certain cases where the soil is admittedly poor1 the average growth below normal1 and thinning has been postponed too long1 the writer has been forced to the conclusion that it would be most inadvisable1 and commercially unsound1 to reduce the stand of trees below #abj per acre4 ,in such instances the average yield per tree equalled only #c lbs4 per annum1 and although the trees were upwards of nine or ten years old the crowns were small and sparse4 ,it is doubtful whether such trees will ever exhibit any further development1 and to thin them further would probably lead only to a diminution in the crop per acre4 ,under normal conditions of growth an arbitrary figure of eighty trees per acre has been selected as a standard by many estates4 ,in these cases it would probably be correct to state that thinning was undertaken on almost purely empirical lines--i4e41 that trees were not selected by tests of individual yields4 ,as far as such a method retained the apparently most vigorous trees it was successful2 but in view of what has been written it might explain some of the disappointing results which have followed upon such a system of thinning4 ,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 tests4 ,if the large majority of the trees appear to be fairly uniform in yields the first thinning must be confined to comparatively few trees4 ,where there is1 on the other hand1 a good percentage of high-yielding trees the final stand per acre may be appreciably less4 ,unless and until such information is available1 one cannot give any definite opinion as to the requisite number of trees to be retained per acre4 ,similarly1 intelligence must be displayed in deciding which of several uniformly-yielding trees should be removed4 ,in the average sense of this consideration one must pay no attention to symmetry of spacing1 but when dealing with trees of fairly uniform yields one needs to study the characteristic development of the trees individually1 in order to retain those which would appear to be most favourably situated with regard to surrounding trees4 ,,chapter ,,iv ,,tapping ,,systems ,broadly there are only two methods employed in obtaining the latex from ,hevea ,brasiliensis4 ,the first is that employed in ,south ,america1 where incisions are made by means of a light axe4 ,the other is the system of excision1 or paring1 of the bark practised on plantations in the ,east4 ,in the early days of the plantation industry1 the ,south ,american method seems to have been employed1 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 method4 ,at a comparatively early stage1 however1 the method of excision was introduced4 ,curiously enough there appears to be no record of its inception or of the individual who was responsible for the substitution of this method4 ,we have been so accustomed to regard it as one of the ordinary facts of estate procedure1 that this point seems to have escaped notice and enquiry4 ,as a variant of these two main methods1 a slight vogue was for a short while obtained by the operation known as pricking4 ,this was generally combined with excision of bark1 and was then known as the paring and pricking method2 but the simple operation of pricking alone had its adherents1 and various forms of instruments were designed to achieve the object4 ,as a means for obtaining a flow of latex1 pricking may have been effective1 but the general difficulties attaching to the collection of the latex was such as to put the method out of favour4 ,in the employment of paring and pricking1 a thin shaving of bark was excised on one occasion4 ,at the next tapping no bark was excised1 but a pricking instrument was used along the previously cut surface4 ,it was not proved that any advantage was gained by this method1 which was more commonly employed in ,ceylon than elsewhere1 and it would be surprising to find it in use at the present day4 ,in the ordinary way the method of excision is practised in such a manner that the cut gradually descends to the base of the tree4 ,planters with original views1 and of an enquiring nature1 often query the common practice2 and it has been suggested that as the latex descends by the force of gravity1 one's paring should be done in an upward direction1 thus obtaining a greater pressure of latex--and hence a greater flow4 ,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 cut1 but apart from this the argument would appear to be founded upon what is now accepted to be a fallacy--viz41 that the latex per se is manufactured in the leaves and gravitates down the tree4 ,,former ,,systems ,,of ,,tapping4--,to hark back ten years in the plantation rubber industry is equivalent to delving into history1 since development has been so rapid4 ,it was then thought necessary to place upon the trees a number of simultaneous cuts which the modern planter would judge to be inconceivably excessive4 ,were it not for evidence in the shape of photographs extant1 it would be difficult to convince a young planter that such systems were employed4 ,it was not uncommon for trees to have from six to ten cuts1 sometimes all placed on one half of the tree in a herring-bone fashion1 and sometimes divided into two portions1 each of which tapped the opposite quarter panel of the tree's circumference4 ,such superimposed cuts were spaced from #a foot to #ah inches apart4 ,on other occasions1 a spiral cut was employed1 commencing at a height of1 say1 #e feet1 and gradually descending to the cup at the base of the tree4 ,later systems varied from several cuts on a half-circumference1 or on a quarter of the tree1 tapped either daily1 or on alternate days1 to cases in which one-third or one-fifth of the tree was employed4 ,also popular were the systems of the ,v and half-spiral cuts on half the circumference4 ,it did not take long to be recognised that with all these systems demanding a number of simultaneous parings from the same panel of bark1 the rate of excision was so heavy that the period available for the renewal of bark was insufficient for continuous tapping4 ,as a result most of the systems specified have fallen into desuetude1 and the tendency has since been to reduce the number of cuts1 or the periodicity of tapping1 so as to allow for increasing periods of bark renewal4 ,in the earlier days1 a period of four years was thought to be an extremely generous allowance1 whereas six years is now becoming recognised as a minimum necessity4 ,eight years is not regarded as extravagant1 while with older bark on some estates periods of ten and twelve years have to be allowed for full renewal4 ,even so no finality has been reached1 and no general rule can be laid down4 ,local conditions of planting and growth exercise great influence1 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 bark4 ,in the main the most popular systems of tapping are3 7a7 ,one cut on a quarter of the tree1 tapped daily4 7b7 ,one cut on a third of the tree1 tapped daily4 7c7 ,one cut on half the circumference1 tapped on alternate days4 7d7 ,a ,v cut on half the circumference1 tapped on alternate days4 ,variants and extremes are3 7#a7 ,one cut on a quarter1 tapped on alternate days4 7#b7 ,one cut on a half1 tapped daily4 ,superficially viewed the latter is four times as strenuous as the former1 and the relative position seems to be inexplicable4 ,it may be explained that as a rule the former system is practised on old trees with poorly renewed bark1 in order to allow for adequate bark renewal2 and the latter is employed in opening young trees just brought into tapping1 when the rate of bark renewal is at a maximum4 ,illustration3 ,,two ,,cuts ,,on ,a ,,quarter ,,circumference1 ,,on ,,an ,,old ,,tree4 ,a few estates in this country still continue to tap trees by means of two superimposed cuts on a quarter of the tree4 ,this was a very popular system some four or five years ago1 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 yield4 ,for instance1 if one compares the system of two cuts on a quarter tapped daily with a similar system employing only one cut1 one finds that the major quantity of latex is yielded by the lower cut1 and that the single-cut system which excises approximately half the amount of bark gives about #hj per cent4 of the yield obtained by the tapping of two superimposed cuts4 ,of experiments to test the relative values of different systems of tapping there have been many4 ,most of them suffered from the initial handicap that they dealt with systems which were then popular4 ,in order to obtain any valid result they had to be undertaken over a long period4 ,meantime there was a progressive movement in actual estate practice towards a greater conservatism in bark removal1 and hence the experiments as originally planned lost value4 ,moreover1 in ,malaya it was difficult for experimenters to obtain practical support in the form of areas of trees suitable for experiment4 ,as a result experiments were often confined to small blocks of trees1 and a small number of blocks1 from which any conclusions derived were subject to considerable errors of experiment4 ,often comparisons were made between only two blocks1 and no allowance was made for varying factors1 such as initial differences in yielding capacities of the trees1 soil conditions1 or the personal equation of the tappers4 ,as a general rule1 therefore1 the results were vitiated to a very appreciable extent4 ,all these factors were later taken into consideration in an experiment undertaken on behalf of the ,rubber ,growers' ,association4 ,in this instance unique facilities were provided by the ,london ,asiatic ,rubber ,company on their property at ,semenyih ,estate1 and it is only fitting that the company should receive the recognition which its enterprise deserves4 ,it would have been a great advantage to have included in that experiment other features which have since come into prominence1 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 frequencies4 ,such data were required as a check upon a ,ceylon tapping experiment which had attracted much attention4 ,in that experiment trees were tapped at intervals ranging from one day to seven days2 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 intervals4 ,illustration3 ,,the ,,single ,,cut ,,on ,a ,,quarter ,,circumference1 ,,on ,,an ,,old ,,tree ,,and ,,on ,,renewed ,,bark4 ,in the ,semenyih experiment the system chosen was that which had the greatest contemporary vogue--viz41 two superimposed cuts on a quarter of the tree4 ,the various blocks were tapped respectively every day1 every second day1 and every third day4 ,it was found that the conclusions drawn from the ,ceylon experiment were not confirmed4 ,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 system4 ,the actual average yields from these systems over the whole period were in the order of-- ,daily4 ,two ,days4 ,three ,days4 #ajj per cent4 #fj per cent4 #de per cent42 and throughout the course of the experiment neither of the other sections showed any appreciable improvement in position relative to the daily section4 ,in actual yields per tapping over the whole period the alternate-day and the third-day divisions showed advantages of #bj and #ce per cent4 respectively over the daily portion4 ,at the beginning of the second year of experiment another section of blocks was opened with a single cut on a quarter1 tapped daily4 ,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 daily4 ,it appeared that the daily single cut yielded over the period of experiment #hj per cent4 of that obtained by tapping two cuts daily2 and that in the comparison between two cuts tapped alternate-daily and a single cut tapped daily the latter had an advantage of about #dj per cent4 in yield4 ,this result has been used by advocates of daily tapping generally1 but it does not constitute a fair argument1 inasmuch as the single cut was tapped twice as often1 and its position was always relatively low on the hole of the tree4 ,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 small4 ,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 tree1 thus placing the cuts in the opposing sections on the same level4 ,with the knowledge that the yield obtained from cuts is always greater per tapping by using the alternate-daily system1 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 tree4 ,illustration3 ,,single ,,cut ,,on ,,half ,,circumference 7,,half ,,spiral74 ,note4--,in this particular instance the cut is changed to the opposite half of the tree every half-year4 ,unfortunately no opportunity has been afforded up to the present of definitely proving this point by prolonged experiment under strict conditions4 ,it is true that the view is held strongly in some quarters as a result of the experience of managers1 chiefly on their own estates1 that alternate-daily tapping generally gives better yields than daily tapping4 ,in a number of instances this view is probably correct1 and the writers are in agreement2 but it is necessary to clear away some misconceptions which confuse the issue4 ,in the main there are two schools1 one of which plumps for alternate-daily tapping1 while the other adheres strongly to daily excision4 ,great confusion exists1 inasmuch as in many instances the disciples of these schools are really discussing different matters4 ,in the case of managers who argue for alternate-daily tapping their experience is gained1 with very few exceptions1 from systems in which the excision covers half the circumference of the tree2 whereas in almost all cases daily tapping is confined to a single cut on a quarter of the girth4 ,bearing on such a comparison there are1 as far as the writers are aware1 no reliable published experimental results4 ,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 permissible1 as we know that conditions generally may vary to an enormous degree4 ,the controversy has raged1 however1 to such an extent that many who are not directly engaged in estate practice have obtained confused impressions4 ,for instance1 it appears to be the belief in some quarters that alternate-daily tapping1 when applied to a single cut on a quarter of the tree1 will yield more than an exactly similar cut tapped daily4 ,in support of such a statement there does not appear to be any confirmation under normal conditions2 although such a result might be obtained in the case of old trees which have been heavily over-tapped in the past1 and on which the rate of bark renewal has been appreciably retarded4 ,it might also be the case eventually when trees with the opposing frequencies have been tapped for a period extending into many years2 but it is the opinion of the writers that under normal conditions such a result would be extremely doubtful4 ,when we come1 however1 to a comparison of daily tapping on a single cut on a quarter with double the length of that cut on half the circumference1 at the same height1 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 issue4 ,as already stated1 facts and figures of reliable experiment are wanting2 but it is the opinion and experience of the writers that the alternate-daily system at least suffers no disadvantage on the point of yields1 and in other respects1 such as conservation of labour and costs1 is superior to the daily system4 ,illustration3 ,a ,v-,,cut ,,on ,,half ,,the ,,circumference4 ,,chapter ,v ,,tapping ,,and ,,collecting ,,tapping ,,knives4--,the choice of a tapping knife is a subject upon which there is much divergence of opinion4 ,this must be so because no known knife has such apparent outstanding superior features or claims as would enable one to settle the point4 ,moreover1 the personal factor is so large that1 as far as the knives in common use are concerned1 it appears to exert the greatest influence4 ,the possibility of obtaining the ideal knife1 which will go to sufficient depth into barks of varying thickness to yield the maximum quantity of latex without wounding1 is quite as remote at the present time as it was some years ago4 ,meanwhile the search for that ideal knife continues1 and occasionally one learns of the alleged merits of some new instrument which1 it is said1 fulfils all requirements4 ,it is only to be regretted1 both for the sake of the inventor and for the expectant buyers1 that the claims always fail in some one or more particulars4 ,in ,malaya probably the number of different types of tapping knives may amount to a half-dozen1 but those most commonly in use are3 7#a7 ,the gouge--straight or bent4 7#b7 ,the ordinary farrier's knife4 7#c7 ,modifications of the farrier's knife1 such as the ,jebong4 ,argument on the respective merits of knives is popular1 and discussion seems endless4 ,it is claimed for the bent gouge that it is superior to the straight instrument1 because1 the leverage being downwards on the handle1 the tendency is to lift the cutting edge upwards and out of the bark1 whereas with a straight gouge the tendency is to push the knife downwards into the bark4 ,it is claimed1 therefore1 that the average shavings taken off by the bent gouge should be thinner than those obtained by the use of the straight instrument4 ,for similar reasons it is asserted that the ,jebong and other modifications are superior to the original form of the farrier's knife4 ,these points are generally accepted without great argument1 but when comparisons are made between the gouge and the farrier's knife 7with its modifications7 the opinions of planters are so varied and conflicting as to be almost irreconcilable4 ,two opinions based on experience with both types of knives are often wholly contradictory4 ,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 knife4 ,should coolies have been accustomed to the use of a particular form of instrument they become quite expert1 and any proposed change creates in the minds of coolies a prejudice which is considerable in effect on the quality of the handicraft4 ,such prejudice may be overcome in course of time1 but in the interval not a little damage may have been done in the shape of tapping wounds4 ,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 accord4 ,such alteration is ignored by the superintendents as long as the quality of the tapper's work is maintained at a high standard4 ,naturally there is a limit to such leniency1 and this limit is soon reached in the case of knives having adjustable parts controlled by screws1 or nuts and bolts1 etc4 ,some knives of this description really merit a much wider use than is afforded them at present2 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 popular4 ,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 vendors4 ,if they possess the merits attributed to them they will soon find favour1 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 wounds4 ,on the whole1 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 use4 ,,the ,,choice ,,of ,,latex ,,cups4--,it has come to be recognised that the maximum possible cleanliness is essential in all details of estate work1 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 trees4 ,terne-plate cups ousted the coco-nut shell1 and they had the merit of being cheap4 ,the interior coating of tin did not last long if the cups were properly cleaned4 ,the iron being exposed1 with a minutely roughened surface1 each microscopic projection served as a point around which latex coagulated4 ,scrapping the film of interior rubber became more and more difficult1 and often the cups were burnt in order to get rid of the accumulation of rubber4 ,the last state of such cups was worse than the preceding one4 ,on some estates fairly successful attempts were made to keep these cups clean by making the coolies bring them into the store each day4 ,terne-plate cups are not now in common use4 ,aluminium cups have their advocates1 but much the same argument applies to the difficulty of keeping them clean as was used in the foregoing paragraph4 ,on many estates1 however1 they are used with success1 the usual method of treatment being to make the coolies bring them into the store and clean them there4 ,owing to the comparative lightness of the material such a scheme is more feasible than was the case with terne-plate cups4 ,the cups now most in general use are either of glass or white-ware1 and probably those of glass are the most extensively employed4 ,there are many details to be studied in the choice between these two types of cups--e4g41 percentage of breakage in transport and in the field1 price when breakage is taken into account1 etc42 but these apart the glass cups have one advantage--namely1 the ability of the superintendents to see whether the cups have been properly cleaned4 ,in the case of white-ware cups this means an inspection and handling of individual cups1 whereas in the case of glass the point is settled by visual examination at a comparative distance4 ,illustration3 ,,single ,,cut ,,on ,,two-,,fifths ,,of ,,circumference4 ,the opening cut covers two-fifths4 ,subsequent cuts occupy one-fifth of circumference4 ,glass cups are made in two patterns1 one having a flat bottom and the other a conical base4 ,the latter is convenient for use when wire supports are employed1 the cup fitting into a loop placed beneath the spout4 ,used on the ground its shape is an obvious disadvantage1 as1 unless a hole is scooped for its reception1 it has to be propped up with sticks or stones4 ,often a touch is sufficient to upset the balance1 and latex is lost4 ,the flat-bottomed cup1 on the other hand1 may be used with success equally on a wire support or on the ground4 ,it is sometimes said that owing to its shape the ease of cleaning1 as compared with the half-spherical cup1 is diminished1 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 high4 ,this latter objection is being rapidly removed as the practice of using these sticks is losing vogue for various reasons1 and wire cup-holders will be in general use as soon as the cost of material becomes normal4 ,there are on the market1 and in fairly wide use1 cups of ,chinese and ,japanese manufacture4 ,these generally consist of brown earthenware with an interior glass finish4 ,these are cheap in comparison with glass and white-ware cups1 but it is a pity that the glass does not extend over the whole of the cup4 ,the outer surface has a tendency to collect rubber and dirt4 ,on some few estates small china bowls or saucers are still used and are quite satisfactory1 except for the favour with which they are regarded by natives on the outskirts of the estates4 ,,cleaning ,,cups4--,the question of cup-cleaning would appear to be a very simple one2 but in practice it is quite a source of worry to managers1 especially where a mixed labour force is employed4 ,tamil coolies can be made to clean their cups in the day's task and at odd times4 ,chinese coolies1 more often than not1 either refuse to give the necessary attention or else demand extra pay for the work4 ,the method of cup-cleaning employed more popularly within recent years was that of daily washing4 ,the tapper carried two buckets1 one for receiving the latex and the other containing water4 ,pouring the latex in the bucket the coolie then added a little water to the cup and added these rinsings to the latex collected4 ,the cup was next washed hastily in the bucket of water and replaced4 ,by the time the coolie has emptied and washed some #bjj cups 7about half the task generally7 the water has the consistency of dilute latex1 and the wet cup when replaced becomes coated with a thin film of rubber4 ,if the latex is always collected in one direction it will be clear that1 while the cups at one end of the task are comparatively clean1 those at the other end have the chance of being correspondingly dirty4 ,controversy has raged respecting this question of cup-washing1 and many estates have abandoned it as a daily practice4 ,coolies have not to carry an extra bucket of water4 ,the contents of the cups are poured into the latex-bucket1 and the bulk of the latex film remaining is also removed by the aid of a finger4 ,the cup is then replaced1 a thin skin of rubber forming on the interior surface4 ,as a general rule this is easily removed on the next occasion1 except perhaps in dry weather4 ,it is the custom on most estates employing this practice to have all cups receive special attention at regular intervals4 ,there are certain economic factors entering into the difference of opinion regarding the two broad methods employed4 ,in some cases--e4g41 on old areas--it would be practically impossible to follow the older method of daily cup-washing1 as the tappers have to employ two buckets for the collection of the latex4 ,the employment of special coolies for cup-washing would be necessitated1 such as may be seen sometimes on estates working ,chinese squatter labour--where the man taps1 a child assists in collecting1 and another child1 or the mother1 washes the cups4 ,it may be pointed out that in such instances the helpers are not paid by the estate4 ,their services merely mean a saving in time which is spent in the squatter's garden1 and perhaps the permission to the tapper to work a larger number of trees than would be allotted ordinarily to a task4 ,again1 on some estates1 the tappers1 while not being required to carry a bucket of water for cup-washing1 are given an increased number of trees to tap4 ,furthermore1 on hilly areas under tapping1 it is often manifestly unfair to expect the tapper to be able to carry two buckets during collection1 when the slope is such1 as to make the manipulation of even one bucket a matter of difficulty4 ,it will be seen1 therefore1 that there is no clear issue for argument concerning the two methods1 and that the point must be decided on the economic factors peculiar to each estate or district4 ,illustration3 ,,effects ,,upon ,,renewed ,,bark ,,of ,,previous ,,tapping4 ,note uneven surface and callosities4 ,illustration3 ,,another ,,example ,,showing ,,the ,,effects ,,of ,,previous ,,tapping4 ,,water ,,in ,,cups4--,much discussion used to take place regarding the necessity or otherwise for placing a small quantity of water in the cups when tapping4 ,it was recognised that the permission to use water 7with the idea of preventing coagulation7 led to much abuse1 apart from the question as to the utility of the method4 ,dirty water was often used1 although clean water may have been placed in the buckets when coolies left the muster-ground4 ,the small quantity of water often exceeded the actual yield of pure latex by hundreds per cent41 with the result that on arrival at the factory the diluted latex was below the standard desirable for the preparation of a good sheet-rubber4 ,,premature ,,coagulation4--,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 water4 ,the use of water often obtained from estate drains clearly led to increased trouble4 ,the extent to which such premature coagulation takes place varies greatly under the influence of many factors--e4g43 7a7 ,cleanliness of cups and spouts 7the latter an important item often overlooked1 and involving the presence of certain organisms which effect coagulation74 7b7 ,climatic conditions4 7c7 ,rate and volume of flow of latex4 7d7 ,size of tappers' tasks 7involving the length of interval between tapping1 and the collection of latex74 7e7 ,distance to be traversed between the site of the task and the store4 7f7 ,care in collecting1 to exclude extraneous matter4 7g7 ,nature of transport2 agitation of the latex to be reduced to a minimum4 7h7 ,nature of the soil1 and situation of the estate4 ,the last mentioned factor is of great importance4 ,as a general rule it is noted that premature coagulation is less marked on estates situated on comparatively hilly land4 ,the greatest effect is remarked on estates situated on the flat lands of the coastal area where peaty soils are a feature4 ,on many such estates1 in spite of the observance of all ordinary precautions1 it is not possible to receive the latex at the factory without a large percentage of prematurely coagulated rubber being found in the transport vessels4 ,,anti-,,coagulants4--,for this reason on these 7and other7 estates1 the use of small quantities of anti-coagulants is common4 ,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 obtained4 ,among the better known agents which have such an effect upon latex1 formalin and sodium sulphite 7not bisulphite7 are the chief4 ,the latter is the more popular as it is slightly cheaper and much more stable4 ,as now used1 it is in the form of an easily soluble powder 7anhydrous sodium sulphite74 ,the ordinary crystalline form of sodium sulphite as used in photography is not recommended1 on account of its comparative lack of power and its poor keeping qualities4 ,it will be obvious that1 given two equal quantities of different latices1 different amounts of an anti-coagulant may be required to produce the same effect4 ,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 estate4 ,unless this point is appreciated trouble may ensue4 ,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 tapped4 ,thus it happened that the latex from one field was found to have insufficient anti-coagulant present1 while that from another field could only be coagulated by the addition of an excess of acid4 ,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 division4 ,it has been found sometimes that a moist glossiness in the smoked sheet could be attributed to the use of an excess of sodium sulphite4 ,traces of the salt remained in the rubber1 and as the substance is hygroscopic1 moisture was being absorbed from the air1 to cause a surface deposit which often returned even after the sheets were surface-washed and re-dried4 ,if sodium sulphite is to be used in the field1 the following formula1 which is in wide use1 may serve as a basis for trials4 ,formula for ,use of ,sodium ,sulphite in the ,field4 7a7 ,dissolve anhydrous sodium sulphite in water at the rate of #a pound to #c gallons4 7b7 ,of this solution each coolie is given about #c_/d pint4 ,this is usually sufficient for a task of #cej trees4 ,the solution is used by shaking a few drops into the cup or1 diluted with an equal volume of water1 it is run down the main channel when the latex flows4 ,illustration3 #a4 ,,showing ,,effect ,,of ,,wintering4 ,on some estates it is found either unnecessary or impracticable to use the solution in this manner4 ,instead the anti-coagulant is placed in the bottom of the bucket prior to the commencement of collection4 ,the solution is made as in 7a7 above1 and roughly half an ordinary latex-cupful is placed in each bucket4 ,illustration3 #b4 ,,new ,,growth ,,of ,,young ,,leaf ,,on ,,same ,,tree4 ,,collecting ,,pails4--,all vessels intended for the transport of latex should have a smooth and curved interior1 so that cleansing may be easy4 ,preferably the interior and exterior surfaces should be glazed1 but it is often found that the enamel chips easily1 and that the handles are too frail in construction4 ,the shoulder-pieces1 to which the handles are joined1 are often too lightly attached to the bucket4 ,something stouter in the shape of enamelled ware is required1 without an appreciable increase in weight4 ,until such a utensil is available1 the heavily galvanised and brass-bound milk-pails used on some estates are as good as anything at present in vogue1 providing they are kept scrupulously clean4 ,illustration3 ,,effects ,,of ,,disease--,,mouldy ,,rot4 7a7 ,note on right hand the panel next in order for tapping2 a hopeless position4 ,illustration3 ,,effects ,,of ,,disease--,,mouldy ,,rot4 7b7 ,the present cut badly infected2 above there is no renewal of bark4 ,the collecting pails should be kept under cover1 when not in use1 either at the muster grounds or at the factory4 ,on some estates coolies are allowed to take them to their quarters1 where they are used for various purposes4 ,curious effects of this practice have sometimes been noticed4 ,as an example might be quoted an instance in which premature coagulation was found to take place to a surprising degree4 ,it was discovered eventually that the coolies 7,javanese in this case7 were in the habit of utilising the buckets for the preparation of their food4 ,a liquid extract of a popular fruit was often made4 ,this extract was very markedly acid in character1 and as the buckets were not afterwards thoroughly cleansed1 the latex of the following day suffered4 ,illustration3 ,,effects ,,of ,,disease--,,mouldy ,,rot4 7c7 ,as in 7b72 another tree4 ,preferably all buckets should have a lid of slightly funnel shape4 ,this is inverted during collection1 and thus prevents much dirt falling into the latex4 ,illustration3 ,,effects ,,of ,,disease--,,mouldy ,,rot4 7d7 ,at close quarters4 ,note wounds due1 apparently1 to bad tapping1 but really caused by the disease4 ,,payment ,,by ,,result4--,the arguments for and against the institution of this practice are many4 ,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 pound4 ,it is fully recognised1 both by advocates and opponents of payment by result1 that the personal equation of the tapper is a very important factor4 ,a good skilled tapper will always obtain a higher yield than an ordinary individual from the same task of trees1 and without any more injury to the trees4 ,it is argued1 therefore1 that such an operative should be given the benefit of his skill4 ,apart from this1 it is claimed that even the average tapper does not do his best work if he knows that he will get his daily wage1 no matter what his yield may be1 as long as he does not injure the trees by wounding4 ,it is claimed that this sense of security leads to shallow tapping which1 while it has an agreeable appearance1 does not produce the available amount of rubber4 ,on the other hand1 it is advanced in opposition that under a scheme of payment by result the tappers' only consideration is the matter of obtaining rubber1 and that considerable damage in the form of wounds is done by over-deep tapping4 ,that there is a great deal of truth in these statements is not to be doubted4 ,much1 of course1 depends upon the amount and quality of the supervision possible1 and upon the standard demanded4 ,it is a notable fact1 however1 that on estates which first introduced the system some years ago the quality of the tapping compares favourably with that of average estates1 and in a few instances within the experience of the writer the tapping is of a high standard4 ,possibly these are exceptional instances1 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 result4 ,it will be recognised by planters that apart from the personal factor in tapping1 the worker might be so unfortunate as to be placed in an area from which the yield is naturally low1 either by reason of its youth or from other natural causes4 ,obviously such individuals are entitled to special consideration in respect of the rate per pound paid for the rubber obtained4 ,again1 on very hilly land it may be not humanly possible for a worker to tap the usual number of trees4 ,hence to place him on a parity with other tappers1 as far as wage-earning capacity is concerned1 a higher rate than ordinary must be given4 ,it will be plain1 therefore1 that on any one estate it is generally impossible to set a standard rate per pound for payment by result2 the rate may vary1 for example1 from1 say1 #c cents per pound in old and high-yielding tasks to #ab cents or more per pound on young areas of the same estate4 ,naturally the actual rates paid will primarily depend upon the average yield per tree or yield per acre1 and the lower the average yield the higher the rates to be paid per pound4 ,thus1 on low-yielding properties where the natural conditions render a high yield impossible the rate per pound may reach a figure of #bb cents 7approximately #f;d474 ,the methods of arriving at the yield of rubber brought in by individual tappers vary1 but broadly they fall into two classes3 7a7 ,that in which the volume of latex is ascertained 7either by measuring or by weighing71 a sample is drawn1 and the final calculation made from the weight of the more or less dry sample4 7b7 ,that in which1 after noting the volume1 the calculation is based upon a reading of the dry rubber content of the latex1 obtained by means of an instrument such as the ,metrolac1 or any other instrument working on the same principle4 ,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 coolies1 as the observed results act as a great deterrent against various malpractices1 such as neglecting to tap trees1 adulteration of the latex1 etc4 ,,tree-,,scrap4--,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-scrap4 ,normally it is collected on all estates1 but the method of collection varies according to the class of labour employed4 ,on most estates1 where the labour is ,tamil or ,javanese1 it is supposed to be removed as fully as possible before the tapping cut is reopened4 ,the narrow strips are then placed in a bag or basket carried by the tapper4 ,chinese tappers usually decline to follow this practice of first peeling off the scrap1 and remove it by the operation of tapping1 with the result that the scrap when brought into the store has adhering to it various shavings of bark4 ,unless these can be thoroughly cleaned off the scrap cannot truly be classed as tree-scrap4 ,,oxidation ,,of ,,tree-,,scrap4--,it is often noted that some scrap is dark in colour1 and in this condition it is generally spoken of as oxidised scrap4 ,the oxidation is probably due to an enzyme1 and also to the presence of chemical substances of a phenolic nature4 ,in the course of laboratory experiments with normal latex1 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 processes1 and the rapidity with which the darkening was effected depended upon the quantity of the phenol added4 ,if this rapidly oxidising latex be mixed with normal latex1 it would seem that the whole bulk of the latex is affected by this tendency to rapid oxidation4 ,it is observed that this condition under which any tree may yield rapidly oxidising latex is not a permanent one4 ,,care ,,of ,,tree-,,scrap4--,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 way4 ,,to ,,prevent ,,oxidation4--,as a rule the scraps are picked over1 and heavily oxidised pieces are sorted out2 otherwise the crepe rubber prepared exhibits black streaks4 ,the scraps should not be allowed to remain in the sun 7which induces tackiness71 and if they have to be kept over night they may be placed in a weak solution 7#a per cent47 of sodium bisulphite to arrest oxidation4 ,it should be recognised that such a solution will not bleach already darkened scrap-rubber1 and the nature of its action is only anti-oxidant4 ,,bark ,,shavings4--,in the matter of collecting bark-shavings much depends upon the organisation and nature of the labour force4 ,probably1 on the majority of estates bark-shavings are collected systematically1 but on quite a number considerable laxity in this respect has been noted4 ,this may arise from lack of adequate supervision or from the peculiar systems of working which seem to pertain to ,chinese labour4 ,granted that the trees are well scrapped1 and that the percentage of rubber obtained from shavings under such circumstances would be extremely small 7say #b per cent4 by weight on the total output71 it does not need much calculation to see that annually the loss of rubber to the estate must be considerable4 ,it would also seem to follow that1 if the adult labour declines to pick up bark-shavings carefully1 it might pay to employ children for the purpose4 ,or1 as is done in some places1 the adult labour might find it advantageous to collect bark-shavings at low rates per pound4 ,it is a well-known fact that if bark-shavings be allowed to accumulate in a heap for any but a short period1 a fermentative and heating action is set up4 ,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 two4 ,should this be allowed to persist1 as would happen in the case of a breakdown of engine or machines1 it usually results in the final crepe rubber becoming tacky when approaching dryness4 ,to avoid this heating effect it is necessary to have spare jars or proper tanks in which the shavings may be soaked in water4 ,in this condition bark-shavings may be kept for many days4 ,for the same reason 7i4e41 the heating effect and consequent tackiness7 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 commended1 quite apart from the possibility of actual loss by theft1 which is thus rendered easy4 ,it will be clear that where the trees are scrapped efficiently before tapping1 the amount of rubber to be obtained from the treatment of pure dry shavings would be almost nil1 and would scarcely repay the cost of collection and working4 ,in actual practice1 however1 it is not possible to guarantee that the shavings are free from some scrap-rubber4 ,shavings brought in by ,tamils and ,javanese carry only a small amount of rubber1 whereas where ,chinese tappers are employed the yield of rubber may be as high as #ce to #dj per cent4 upon the total weight of the material treated4 ,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-particles4 ,,collection ,,of ,,earth-,,scrap4--,this1 the lowest grade of rubber1 is found at the base of the tree4 ,theoretically1 if proper precautions are observed1 the amount should be comparatively small1 but in actual practice it may be very appreciable4 ,the usual contributory causes are3 7a7 ,failure to replace cups beneath the spouts of trees which continue to drip latex after collection4 7b7 ,collection of latex at too early a stage4 7c7 ,failure on the part of the tapper to ensure the flow of latex1 by means of the spout1 into the cup4 7d7 ,flowing of latex over the edge of the cut before it reaches the vertical channel4 7e7 ,wash-cuts on wet days1 when the volume of rainwater down the tree is sufficient to wash the latex out of the cup4 ,the amount of earth-scrap collected on any estate will depend1 all other things being equal1 upon the labour expended in its collection4 ,certainly on well-organised estates1 having ample labour1 the amounts collected are huge in comparison with other estates4 ,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 up4 ,here1 again1 it is advised that the collected earth-scrap should not be allowed to remain in heaps upon the floor of the factory4 ,it should be placed in suitable tanks containing water1 and quite a considerable portion of the cleansing work is thus taken from the machines4 ,,chapter ,,vi ,,transport ,,of ,,latex ,,and ,,coagulum ,,percentage ,,of ,,first ,,latex ,,and ,,other ,,grades4--,one of the problems confronting any manager is the question of the percentage of first-grade rubber calculated upon the whole output4 ,inquiries are constantly being received for advice as to what the various percentages of each grade of rubber should be4 ,this is a question to which no definite list of figures can apply4 ,there are so many little factors influencing the result4 ,some estates are not particularly careful in collecting tree-scrap4 ,hence quite a quantity of tree-scrap finds its way into the crepe made from bark-shavings4 ,on the other hand1 bark-shavings are not collected systematically on some estates1 and the total output is thereby diminished4 ,in consequence the first-grade rubber shows a higher percentage than it would otherwise4 ,again1 if the earth-rubber is not regularly collected the percentages of the best grades are higher than they should be4 ,in comparing the percentages of each grade of rubber from any two estates1 therefore1 one should have all the information possible as to the various working details of the estates4 ,without wishing to lay down any definite proportions which can be applied to all estates it might be said that1 taking averages over a large number of estates1 the percentages to be aimed at are3 ,first-grade latex #ge per cent4 to #hj per cent4 ,other grades #bj #be ,for these figures one promises that all lower grades are collected and accounted for carefully and regularly4 ,the distribution of the lower grades will depend upon the field practices of the particular estate1 but the following list might be given for an estate keeping all lower grades distinctly separate3 ,first-grade latex #ge per cent4 ,cup-washings ,coagulated lump1 etc4 #aj ,tree-scrap #i ,bark-shavings #d ,earth rubber #b --- #ajj ,emphasis is again laid on the statement that these figures must not be accepted as a standard4 ,nevertheless1 they may prove of some service to managers in giving an idea of what the general line of percentages may be4 ,there are special circumstances1 such as distance of transport and the nature of the land1 which at present would render the attainment of more than #ge per cent4 first-grade rubber impossible on some estates4 ,still the fact remains that if the percentage is low through distance of transport1 etc41 some method will have to be discovered by means of which the difficulty maybe overcome4 ,on a few estates the percentage of first-grade rubber obtained sometimes reaches #he1 but these results are rather out of the ordinary4 ,an estate which collects all lower grades properly is doing well if the percentage of first-grade rubber is #ge or over4 ,,early ,,collection4--,as already noted in the preceding chapter1 one of the factors influencing premature coagulation is that of the interval elapsing between the commencement of tapping and the collection of latex4 ,it will be seen that this ordinarily would depend1 in turn1 upon such considerations as the size of the tappers' tasks1 the spacing of the trees1 and the natural conformation of the land over which the tappers have to perform their tasks4 ,in general it need only be remarked that every possible consideration should be given to this question1 and that any delay should be avoided4 ,,transport4--,wherever possible it is endeavoured to convey latex from field to factory by man-power4 ,tamil coolies1 as a rule1 place the bucket on the head2 ,chinese and ,javanese coolies like to use a balanced carrying-pole4 ,where distance renders these methods too costly in time and labour1 it is usual to have field centres where the latex is collected and dispatched to the factory generally 7a7 by means of vessels conveyed on light railways2 7b7 in large cans placed on motor-lorries2 7c7 in cylindrical galvanised drums supported on two wheels and drawn by bullocks4 ,there may be variants1 but these are the chief means of transport in bulk over a distance4 ,where possible1 the best system is that employing a trolley-line1 as great agitation of the latex is avoided1 and the time in transit is much reduced4 ,the usual method of transport by bullock power is slow1 and as estate roads 7and even ,government roads7 are often below the standard expected in this country1 the jolting undergone by the latex is1 to say the least1 not calculated to afford a high yield of first-grade rubber4 ,the late ,mr4 ,f4 ,w4 ,f4 ,day advocated the use of a circular perforated wooden grid1 to be floated on the latex1 in order to moderate the wave effect produced by jolting4 ,whatever the means of bulk-transport employed1 it should be the care of those in charge to see that vessels are not allowed to remain in the sun longer than is necessary4 ,even during the journey they should be shaded in the best possible manner4 ,these large transport vessels usually receive what is really only perfunctory attention in the matter of cleaning4 ,they should receive the same care as would be exercised in dealing with milk cans in other countries4 ,ordinary sluicing with water is not sufficient1 and if they cannot be sterilised by means of boiling water1 they should be treated1 after ordinary washing1 with a #e per cent4 solution of sodium bisulphite every day4 ,,anti-,,coagulant ,,for ,,transport4--,when anti-coagulants are not used in the cups or buckets1 it is advisable to use them in the bulk-transport vessels4 ,either formalin or sodium sulphite is of service1 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 centres4 ,for this reason sodium sulphite is now generally employed4 ,formula for ,use of ,sodium ,sulphite in ,transport4 7a7 ,dissolve #a pound of powder in #c gallons of water4 7b7 ,of this solution1 place half a gallon in the vessel for every #cj to #dj gallons of latex4 ,,transport ,,by ,,coolie4--,as already pointed out1 the extent to which man-power can be used in transport of latex is generally limited4 ,on small estates it is an easy matter for coolies to carry the latex to the factory1 but on larger estates many difficulties may arise1 which may also militate against the successful use of other means of transport4 ,it is not uncommon to find1 therefore1 that a policy of decentralisation has been adopted4 ,,coagulation ,,centres4--,divisions of the estate have their own small stations at which latex is received and coagulated4 ,in this way it is possible to receive latex without much delay1 and with benefit to the resultant rubber1 especially if prepared in sheet form4 ,much controversy has arisen regarding these decentralised establishments1 but the fact remains that on large estates1 which are efficiently controlled1 the scheme has been highly successful from all points of view4 ,on the other hand1 it is alleged that this method of working increases costs1 and often gives an unsatisfactory quality of rubber4 ,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 required1 and should be capable of seeing that no mistakes are made4 ,given uniform equipment in all stations1 and uniform rules for treatment of the latex1 there does not appear to be any valid reason why the product of one station should be inferior to that of the others4 ,neither is it so in the case of several estates which might be quoted4 ,in the matter of costs of working the writer has had to investigate several cases regarding which there was dissatisfaction4 ,in some instances it was found that the stations had not been placed advantageously with respect to a water-supply2 and instead of one or two coolies pumping for an hour or two1 a larger number had to be employed for hours in the carriage of water from the nearest available source4 ,this meant that1 as the coolies were on daily wage1 the force appeared to be much bigger than that usually required4 ,in other cases there were too many store coolies1 when often the place of some could have been taken for the necessary period by tappers arriving early from the nearer fields4 ,sometimes costs were increased by reason of the use of an excess of chemicals1 owing to the lack of uniform rules throughout the several stations4 ,in spite of all that has been written1 and the verbal instructions that have been given1 it was not uncommon to find unstable chemicals such as sodium bisulphite exposed to the moist air4 ,in this way not only was there waste of material1 but also the probability of inferior rubber being made4 ,,transport ,,of ,,coagulum4--,on the whole if it is a question between the transport of latex and the transport of coagulum1 the writer would always favour the latter1 for reasons which have possibly been made clear in the preceding paragraphs4 ,in effect1 it should be recognised that the less handling and transport the latex receives the better the general result4 ,if proper precautions are taken1 the transport of coagulum intended for the preparation of crepe should present no difficulty1 and should have no injurious effect upon the quality of the resultant rubber4 ,it is only too common1 nevertheless1 to note defects1 in the finished crepes1 which can only be attributed to a failure to observe reasonable care in the transport of the coagulum4 ,for example1 it has been observed that a mass of coagulum from a coagulation station has been conveyed on the floor of a bullock-cart1 or motor-lorry1 previously used in the carriage of other materials4 ,unless the boards have been most scrupulously cleansed1 the coagulum is found to be contaminated1 often to a marked degree4 ,again1 although the cart may be clean1 it may have to travel some distance on roads carrying a fair amount of motor traffic4 ,even should the cart have a canopy1 road-dust is often whirled through the open sides of the cart2 and in the districts where red laterite roads are common1 the stain of such dust often persists in the finished crepe4 ,it scarcely need be remarked that coagulum should be transported in closed wooden boxes or in galvanised iron drums fitted with lids2 and that preferably sufficient water should be present in these receptacles to allow the coagulum to float4 ,all such containers should receive the same scrupulous attention as the vessels employed in the transport of latex4 ,the successful transport of coagulum for sheet-making is fraught with much greater disabilities1 and it is usual to note on most estates that the resulting sheets from out-stations are always inferior1 in final result1 to those coagulated and prepared at the central factory4 ,if the flat pieces of coagulum are placed in piles of any height it is common to find1 on arrival at the factory1 that much adhesion has been caused4 ,there is great difficulty in separating the pieces1 and often the successful operation is impossible4 ,it is usual to hand-roll the coagulum before transport1 but it is often found that by the time the rubber reaches the factory it has become too hard for subsequent good results4 ,one of the strong arguments in favour of the establishment of divisional stations is to be found in the preceding paragraph4 ,sheet-making1 as it necessitates the employment of only light machines suitable for hand-power1 is a feasible proposition in a field station4 ,there is no reason for sheets made thus to be in any way inferior to those made at a central factory2 in fact1 they are often better1 as the latex has the chance of being treated when comparatively fresh4 ,if it is found necessary to transport sheet-coagulum1 every possible precaution should be taken against piling the pieces4 ,after hand-rolling some estates bring the rubber from the field-stations to the central factory in drums of water1 others in shallow boxes containing not more than half a dozen sheets in a pile4 ,a method proposed long ago1 but not in practice1 was to have a number of shallow trays subdivided so that each compartment held one sheet only4 ,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 box1 in which squeezing and adhesion of the pieces of coagulum would be avoided4 ,naturally any such device would increase appreciably the weight to be transported1 and on this ground would not find popular favour except where motor-power is used for road transport4 ,,part ,,ii ,,factory ,,operations ,,chapter ,,vii ,,preliminary ,,treatment ,,of ,,latex ,,reception ,,of ,,latex ,,at ,,the ,,store4--,bearing in mind the remarks in ,chapter ,,vi4 on the conditions under which latex is transported1 it follows that nothing but the very best and most suitable vessels should be used in the store4 ,a point to which adequate attention is not given in many factories might be mentioned here4 ,considering the importance attached to colour in the dry rubber by brokers and consumers1 and knowing how extremely trivial are the causes which may mar the colour1 it is rather surprising that better provision is not made for the reception and handling of latex in factories4 ,too often the receiving vessels are placed on the floor of the store close to the entrance4 ,coolies bringing in latex cannot avoid bringing with them quite a considerable amount of dirt4 ,presuming that a hose-pipe has been installed1 and that the floor is constantly being sluiced down with water1 no great harm will result4 ,but would it not be ever so much better if the dirt were kept out8 ,in how many factories is provision made for this8 ,such an arrangement is not difficult to make1 and is already in practice on a few estates4 ,a verandah is built outside the wall of the factory and all latex is received there4 ,in another place open chutes are provided which terminate in the straining sieves4 ,the coolie thus stands on the verandah where he removes coagulated lump and impurities from the latex1 which is then poured down the chute1 passing through the sieve into large coagulating jars or tanks4 ,too often it would appear1 from the writers' observation1 there is a lack of adequate supervision on the arrival of latex at the store4 ,much can be learned from an inspection of the coolies' buckets1 and the cause of small defects in the finished rubber can often be thus traced4 ,leaves1 stems1 bark-shavings1 and dirt appear in the buckets1 and it is a source of constant surprise to imagine how even unintelligent coolies can allow such things to happen4 ,these objects are removed before or during straining1 but still they ought not to be there in the first place1 and the fact that such a state of things exists is evidence of neglect on the part of the coolies or lack of supervision4 ,efforts are made in a large number of cases to cope with these troubles1 but on some estates things are allowed to proceed in the same slipshod way1 and too much responsibility is thrown on the straining process4 ,illustration3 ,,raised ,,verandah ,,for ,,reception ,,of ,,latex2 ,,likewise ,,equipped ,,with ,,facilities ,,for ,,calculating ,,individual ,,daily ,,yield ,,per ,,coolie ,,by ,,sampling ,,of ,,latex4 ,it is suggested that it should be the business of a ,european to supervise the reception of latex every day4 ,this is at present quite impossible on some estates1 but it does not alter the fact that this supervision should be provided1 and is extremely necessary4 ,it is surprising how the point is overlooked in many factories--not that they are in a dirty state1 but they fall short of being classed as clean factories for want of the little that makes the difference4 ,possibly those in charge do not believe that all this fuss need be made1 but the writers can assure them1 from a practical knowledge of a very large number of factories1 that cleanliness does pay4 ,it might not be credited to ,tamil coolies1 but yet it is probably true1 that the moral effect of working under the cleanest and best conditions has an influence upon the store coolies1 and that their work is better in consequence4 ,everything which will tend to simplify the cleansing of the factory should therefore be installed4 ,hose-pipes1 glazed tiles1 clean floors1 plenty of light and air are not fads or fancies1 but considerable factors in determining the final quality of the rubber4 ,there is considerable truth in the suggestion that the coagulating room and machine room should be as spick and span as a modern home dairy4 ,,straining ,,of ,,latex4--,this is a most necessary process1 and one which usually entails much trouble and time which one could wish avoided4 ,it will be admitted that the trouble could be reduced greatly if the regulation of field processes could be made more stringent4 ,in spite of knowledge that impurities must not be allowed to enter the cups1 coolies will ignore the rule that the cup must not be placed in position until the bark shaving has been cut4 ,the result is that pieces of bark fall into the cups1 and coolies are generally too careless or too hurried to remove them4 ,again1 when cups are placed on the ground1 it is easy to see that dirt may adhere to them4 ,in the collection of latex some of this dirt may fall into the bucket4 ,since the introduction of cup-holders on many estates the trouble from this source has decreased considerably1 but1 nevertheless1 it may be taken for granted that even under the best of conditions all latex requires straining4 ,the best type of strainer has yet to be evolved4 ,usually it consists in principle of a piece of fine brass mesh contained in some form of holder4 ,theoretically such a strainer should work well1 but in actual practice nearly all strainers are a source of continual worry4 ,undiluted latex1 as received at the factory1 is of a rich consistency1 containing very fine particles of dirt and often minute particles of prematurely coagulated rubber4 ,the latter soon clog a fine mesh strainer1 while the former may pass through4 ,when the flow through the strainer becomes slow1 the coolie in charge generally rubs the top surface of the sieve with a piece of coagulum1 thus forcing material through the mesh4 ,he then rubs the under-surface1 with the result that undesirable matter falls into the strained latex4 ,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 one1 which should be cleansed at once with water4 ,in practice the factory coolie will probably only carry out instructions when the eye of the superintendent is alert4 ,as a result of the rubbing and consequent strain1 the brass mesh usually breaks away from its support and the fracture may not be detected for some time1 during which irreparable damage may have been done to the resultant rubber4 ,in view of the presence of the fine particles of dirt1 to which allusion has been made1 fine sieving of the latex appears to be essential1 especially when sheet-rubber is to be prepared4 ,the fine sieves are generally of the type known as #fj mesh1 and they do not usually give thoroughly satisfactory results even when the gauze is supported and strengthened by means of cross-wires placed underneath4 ,the general fault with these strainers is that a sufficiently wide selvage is not allowed in the clamped edges of the gauze1 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 cleaning4 ,many estates use two strainers2 the first a more robust one containing #cj mesh gauze1 and the second the fine #fj mesh4 ,even this device does not bring about the desired immunity from trouble4 ,relief could be obtained if the latex were always in a more freely fluid form4 ,estates employing anti-coagulants in the field benefit in this respect4 ,other estates1 although finally using the finest of mesh1 experience far less trouble than most estates by reason of a difference in method of working4 ,this can be explained by an outline of the system adopted on a particular estate3 7a7 ,on arrival of the rich latex at the store1 all visible coagulated lumps and other extraneous matter are removed by the tapper4 7b7 ,each tapper's latex is diluted with a quantity of water4 7c7 ,the diluted latex passes through two sieves1 one above the other4 ,the top sieve is of stout perforated zinc sheet1 with #aj circular holes to the inch4 ,this removes all large particles4 ,the lower is of #cj mesh brass gauze1 and practically no rubbing is required4 ,the latex is now in glazed-tile tanks1 in which it is further diluted to the required standard by means of a recording instrument4 7d7 ,the latex flows by means of a chute into the coagulating tanks1 passing through a large #fj mesh sieve4 ,it is not guaranteed that this method will furnish a complete absence of very fine particles of dirt in sheet rubber1 as the human element enters so largely into the question2 but it can be stated that no complaints have been received on the point of specks of dirt since this system was inaugurated4 ,on the same estate fine sieving in the preparation of pale crepe has been abandoned as an unnecessary refinement4 ,the two coarse sieves mentioned above are employed only1 and it is to be acknowledged that the results justify the procedure4 ,,bulking ,,of ,,latex4--,not long ago advanced estates used to combine all latex before coagulation1 in order to obtain uniformity of product4 ,previously it had been the custom to deal only with comparatively small separate volumes of latex1 with obviously great disadvantage4 ,since the introduction of instruments such as the ,metrolac1 by means of which any volume and all volumes of latex may be reduced to a common standard of dry rubber content1 the necessity for bulking has passed4 ,it is not now necessary to keep latex standing1 perhaps for two hours1 awaiting the arrival of other latex from distant fields4 ,,standardisation ,,of ,,latex4--,in modern practice1 as already pointed out1 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 product4 ,for the reception and subsequent handling of the latex various schemes have been devised1 and they are usually planned in connection with coagulating tanks used in the preparation chiefly of sheet rubber4 ,illustration3 ,,end-,,section ,,sketch ,,of ,,verandah1 ,,etc41 ,,showing ,a ,,good ,,method ,,for ,,receiving ,,latex ,,and ,,filling ,,tank4 ,t1 ,sheet coagulation tank2 ,c1 cylinder for reception and dilution of latex2 ,,gg1 gutter2 ,,pp1 raised platform on verandah2 ,,ss1 steps leading to platform2 ,w1 dwarf wall2 ,,ee1 expanded metal partition2 ,,oo1 open4 ,in the successful working of a tank it is necessary1 in order to obtain the best results1 to standardise all latex4 ,this cannot be effected properly in the tank itself1 and hence it is the practice to dilute each lot of latex to standard before it is run into the tank4 ,in the ordinary way this would entail a great deal of labour in handling the diluted latex4 ,to obviate this1 the scheme outlined in the accompanying sketch has been suggested on several occasions and in various quarters4 ,such a scheme or modification of it has been put into successful practice on several estates4 ,although the drawing was made some considerable time ago when estates were not then prepared to go so far in this direction1 subsequent modifications show only minor differences which1 while leaving the original principle intact1 testify to a fertility of resource in adapting the idea to existing circumstances and buildings4 ,the drawing is in toto almost a replica of the original installation now in successful use on the ,kinrara ,estate of the ,ledbury ,rubber ,company4 ,on this company's ,ledbury ,estate likewise a similar system is employed1 except that the reception verandah is part of a natural formation and needed no such direct raising4 ,several other estates have now adopted the scheme1 which has been proved to be of practical value4 ,the writers make no claim to originality in the idea1 which might have occurred to many independently on the introduction of coagulating tanks4 ,illustration3 ,,raised ,,verandah ,,for ,,reception ,,and ,,handling ,,of ,,latex4 ,,verandah4--,in reproducing the drawing it is believed that the sketch will convey practically all the information required4 ,it may be explained that the coolies are allowed to enter only the outer part of the verandah4 ,the buckets are handed across the low wall into the care of factory coolies1 who strain the latex through gauze sieves into the latex cylinders4 ,,latex ,,reception ,,vessels4--,these cylinders may be similar to the tanks commonly used for transport of latex from distant fields to the factory4 ,an #hj-;gallon cylinder is easily mounted by its trunnions on a suitable iron framework which is superimposed on a skeleton truck4 ,illustration3 ,,another ,,set ,,of ,,dilution ,,tanks ,,on ,,raised ,,verandah4 ,the latex is diluted down to standard in the cylinders1 the truck is moved opposite the compartment to be filled1 and a light movable gutter is placed beneath the vent of the outlet pipe4 ,this pipe is fixed in the bottom of the cylinder1 and is provided with a large stop-cock which is operated by a spanner key4 ,the stop-cock should be of the simplest type1 capable of being taken apart and assembled in a minute or so4 ,the orifices should be large enough for a coolie to insert at least two or three fingers so as to facilitate cleaning1 and the pipe should have no right-angle bends4 ,on the inside of the cylinder a scale of gallons may be painted1 so that one may possess a knowledge of the quantities run into1 or required for the completion of1 any compartment4 ,a ,,screw ,,plug ,,unsatisfactory4--,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 experience4 ,in one instance the vent pipe as designed was fitted with a screw plug at the end4 ,unfortunately with this arrangement the flow could not be regulated1 and owing to the head of the latex it dashed violently down the gutter1 struck the bottom of the coagulating tank1 and thence was scattered over the factory4 ,,another ,,installation4--,in another type of installation1 in place of the vessels travelling upon a raised verandah platform1 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 gantry4 ,this method is practicable1 but may be regarded as less satisfactory in general working than the verandah method of treatment4 ,a ,,modern ,,installation4--,in the most recent scheme for dealing with the reception of latex1 its standardisation1 and conveyance to the coagulating tank1 the main principle of the first system outlined is retained2 but the receptacles are not mobile4 ,glazed-tile tanks are employed1 the capacity of each being approximately equivalent to that of each unit coagulating tank4 ,the accompanying illustrations show the general arrangement and some details of the system of reception tanks employed on the well-known ,pataling ,estate4 ,,chapter ,,viii ,,coagulation ,whether it is necessary to employ any coagulant1 or whether latex should be allowed to coagulate naturally1 will not be discussed at this stage4 ,neither will mention be made of any patent processes of coagulation which employ other than acid mediums4 ,these subjects will be treated in a subsequent section of the book4 ,,choice ,,of ,,coagulants4--,it is not proposed here to enter into a discussion as to the merits of the dozens of known coagulants4 ,suffice it to state that acetic acid1 although the oldest general coagulant1 still remains the best and safest at the present time4 ,there is a deal to be said in favour of the use of another organic acid1 formic acid4 ,it is equally as safe as acetic acid1 and quite efficacious2 the only drawback is that1 taking all things into consideration1 it is very slightly more expensive4 ,acetic acid1 therefore1 will always be implied in this chapter when the word acid is used4 ,,strength ,,of ,,acid ,,solution4--,in the old days it was the rule rather than the exception to find pure1 undiluted acid used in coagulation4 ,in many cases no harm resulted1 for the simple reason that1 owing to the large proportion of water in the latex1 the acid was thereby very much diluted4 ,the estates had to thank the over-dilution of the latex for the non-injury of the resulting rubber4 ,some estates make up a stock solution of #a part acid to #bj of water1 and use this with success because of the fair amount of added water present in the latex4 ,it must be understood that what is being referred to now is not the absolute quantity necessary for coagulation1 but the proportions--i4e41 the respective volumes of acid and water in the solution of acid made up every day4 ,that the strength of the acid solution1 as well as the quantity used1 has an effect upon coagulation can be easily demonstrated in the following way3 ,take separate and equal lots of the same latex1 and to each add the same quantity of pure acid1 but in each case diluted with varying quantities of water4 ,it will be found that coagulation is quickest where pure acid is employed1 and slowest where the acid is most dilute4 ,it will also be found that1 providing the quantity of acid employed was sufficient for coagulation1 the best and most uniform coagulation is obtained from the use of the most dilute acid1 within limits4 ,it will often be found that where pure acid has been employed coagulation is local--i4e41 we have lumpy coagulation1 and often a very milky remaining liquor4 ,this is due to the fact that1 as coagulation is immediate upon the spot which is first touched by the pure acid1 a deal of the acid is enclosed within the rubber at that spot1 and hence other portions of the latex are deprived of acid4 ,it is in such cases that most air-bubbles are enclosed4 ,as the dilution of the acid solution is increased the mixing is more thorough and uniform4 ,coagulation is slower1 and air-bubbles can escape to the surface4 ,,method ,,of ,,making ,,stock ,,solution4--,experiments have been repeatedly made in the laboratory with acid solutions of varying dilution1 from pure acid down to #a part of acid in #ejj parts of water4 ,while it has been found that a #a in #e solution can be used where the latex is very dilute 7say1 #a part of latex to #e parts of water71 and a #a in #bj solution may be used in fairly dilute latex 7for crepe-making71 it is undoubtedly a fact that for latex as generally standardised on estates a much more dilute solution of acid should be used--e4g41 #a in #ajj1 or even #a in #bjj1 of water4 ,it must be borne in mind that the quantity of acid necessary for coagulation is not changed1 but merely the dilution4 ,let us take a concrete case to illustrate the point3 ,on an estate at present the stock solution is made up by diluting #a pint of acid with #bj pints of water1 and #a gallon of this is necessary to coagulate #ej gallons of pure latex4 ,it is desired to use a stock solution of #a pint of acid to #ajj pints of water4 ,evidently1 therefore1 #e gallons of this stock solution contain only the same quantity of pure acid as #a gallon of the old solution contained1 and it will be necessary to add #e gallons for every #ej gallons of pure latex4 ,thus3 #a to #bj2 #a gallon necessary for #ej gallons pure latex4 #a to #ajj2 #e gallons necessary for #ej gallons pure latex4 ,it may be pointed out that the quantities worked out in the foregoing examples are not absolutely and mathematically correct1 but they are quite close enough for all practical purposes4 ,it may be advanced by someone that if a dilute solution of acid1 such as #a in #ajj1 is used the bulk of this stock solution 7#e gallons to #ej gallons of latex7 is very great1 and might be injurious to the quality of the resulting rubber4 ,a moment's consideration will show that1 after all1 the volume of acid solution is only one-tenth that of the volume of latex4 ,this can have no effect upon the quality of the rubber4 ,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 rubber4 ,it is to be remembered that1 except in cases where the proportion of added water to latex is absurdly large1 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 added4 ,it is acknowledged that1 where the water to be put into the cups can be guaranteed to be of good quality1 no great objection would be raised against placing the smallest possible quantity of such water in the cups4 ,but how many estates have such good water easily available to the coolies1 and how many estates can be sure that only that smallest possible quantity would be used8 ,it is a notorious fact that1 even on estates where the quantity of water used was supposed to be a minimum1 the proportion of water to latex in some cups often exceeded even three or four to one4 ,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 quality4 ,,quantity ,,of ,,acid4--,as a result of repeated experimental work it has been found that1 for pure average latex1 the quantity of acid necessary for complete coagulation1 reckoned in parts of pure acid to parts of latex1 is3 #a part pure acid2 #a1jjj parts average latex4 ,where the latex is rather richer than average 7above #cj per cent4 dry rubber7 probably a little more acid would be required1 and similarly if the dry rubber content is lower the quantity of acid must be less4 ,it used to be a common belief that the more dilute the latex the greater the quantity of acid necessary1 but this would only apply to cases of extreme dilution of latex4 ,as a matter of fact1 up to certain limits of added water1 the reverse is actually the case--i4e41 the more water in the latex the less acid must be added1 assuming that for pure latex the proportion of pure acid to latex is taken as #a part to #a1jjj parts4 ,this was found to be the case up to dilutions of three or four times the volume of latex4 ,to take concrete examples which will perhaps make the truth more clear3 ,assuming we commence by making up our stock solution of acid by adding #ajj parts of water to #a part of pure acid1 this gives us a mixture of #a to #ajj4 ,for #a gallon of pure latex it would be necessary to add one-tenth of its volume of the above mixture--i4e41 #af ozs4 ,suppose we take a gallon of pure latex and add a gallon of water1 we now have #b gallons of so-called latex4 ,but we still have only #a gallon of real latex present in the diluted latex1 and it is only necessary to add sufficient acid to coagulate this gallon--i4e41 #af ozs4 ,further1 if #a gallon of latex be diluted with #b1 #c1 or even #d gallons of water it is still only necessary to add #af ozs4 of the acid mixture4 ,at dilutions beyond this limit1 however1 it is necessary to add a little more acid to obtain complete coagulation4 ,in the process of preparing sheet rubber it is very necessary to see that the minimum quantity of acid is used1 otherwise visible defects are caused4 ,but in coagulating latex intended for preparing crepe1 where the rubber undergoes protracted washing on the machines1 the presence of a slight excess of acid in coagulation is not calculated to cause any deterioration in the quality of the rubber4 ,advantage must not be taken of this statement to argue that more than a slight excess may be used without injury to the rubber1 as it can be shown that the use of a large excess of acid results in an inferior rubber4 ,,quantities ,,necessary ,,for ,,modern ,,requirements4--,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 energy4 ,the general figure given in a preceding paragraph 7#a part pure acid to #a1jjj parts of latex7 may be accepted as the rough basis for working4 ,in modern practice1 however1 undiluted latex is usually diluted to a standard which may vary on different estates from #a-a_/d lbs4 to #a-a_/b lbs4 dry rubber per gallon4 ,latices of these strengths can be coagulated at a ratio of #a part pure acid to #a1bjj parts of standardised latex2 and this quantity need not be exceeded1 except in cases where an appreciable amount of some anti-coagulant is present in the latex4 ,the proportion may then be raised to #a in #a1jjj4 ,if considered advisable the acid may be used in a #a_/b per cent4 solution for sheet preparation2 but in any case it is advised for the sake of uniformity that a #a per cent4 solution should be employed in the preparation of both sheet rubber and crepe rubber4 ,in most modern factories1 measuring vessels of various capacities are to be found1 and it is always more satisfactory to have the solution made up in approximately correct strength at the rate of #a oz4 of pure acid to #e pints of water4 ,often1 however1 on some estates ,european supervision of this work is not possible1 and the preparation of the acid solution has to be left in the hands of a 7more or less7 skilled coolie4 ,it is thus necessary to find some less fine1 but still approximately correct1 method of procedure4 ,in the ,east the kerosene tin is in universal favour for the carriage of water1 and there is no reason why it should not be utilised as a standard measure for preparing the dilute acid solution1 providing it is not allowed to become rusty4 ,the capacity of the tin is #d gallons 7#fdj fluid ozs471 so that a one-hundredth part would be approximately #f-a_/b ozs4 ,it is suggested that this quantity should be measured out by means of a glass graduated vessel1 and then that an aluminium cup should be cut down so as to hold the exact quantity4 ,this would reduce the making of a solution1 sufficiently approximate to #a per cent4 strength for all practical purposes1 into a simple operation of mixing pure acid and water in the ratio of one cupful of acid to #a kerosene tin of water4 ,the actual quantity of solution required for the coagulation of any volume of standardised latex can be calculated easily from the ratio #a3a1bjj4 ,as the strength of solution is #a3ajj it will be seen that the quantity to be taken is always one-twelfth that of the volume of latex--e4g43 7a7 ,if the latex tank holds #ij gallons of standardised latex1 #g-a_/b gallons of dilute acid solution are required4 7b7 ,a tank containing #abj gallons of latex would need #aj gallons of the #a per cent4 acid solution4 ,it is assumed that all estates1 not only in the preparation of sheet rubber1 but also in the making of crepe rubber1 always employ the system of standardising latex in order to obtain uniformity4 ,they are ill-advised if they do not follow this practice2 but in case average undiluted latex is treated in coagulation1 the quantity of acetic acid to be used should be calculated from the ratio #a3a1jjj4 ,if the acid solution is to be employed in #a per cent4 strength1 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 used1 when the quantity must be increased as experience directs4 ,it will be recognised1 of course1 that undiluted latex may only be used in any case for the preparation of crepe rubber2 or in some exceptional case1 such as the special preparation of slab rubber4 ,,care ,,in ,,mixing4--,it is essential that the mixture of dilute acid and latex should be thoroughly intimate4 ,this can only be attained by careful manipulation1 especially in the case of sheet preparation4 ,where crepe rubber is to be made it may be permissible to employ a solution stronger than #a per cent41 but it is not advised4 ,the acid should be poured into the latex while stirring1 and the agitation should continue for such a period as to ensure thorough mixing in all parts4 ,it will be appreciated that in the preparation of sheet rubber this period may not be unduly prolonged1 otherwise the latex will have begun to coagulate before skimming and the placing of the partitions in their respective slots can be effected4 ,furthermore1 while in the preliminary treatment for crepe rubber1 the formation of enclosed bubbles and surface froth is immaterial4 ,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 minimum4 ,for crepe-making a perforated board1 with handle attached at right angles to the face of the board1 may be used2 but in shallow sheet-coagulating tanks1 broad paddles 7which may or may not be perforated7 give good results as long as there is a sufficient number used to cover the area of the tank in reasonable time4 ,obviously also1 where the area of any tank or compartment is of any appreciable size1 the dilute acid solution should be poured in from various points so as to obtain a good even distribution4 ,in some cases the acid is distributed from a sprinkling can1 but this is a refinement which experience shows to be unnecessary4 ,in actual practice1 working on a tank measuring #ab ft4 by #d ft41 no difficulty is found if coolies pour in acid solution from four points4 ,the degree of success depends entirely upon experience and efficient supervision4 ,this remark applies equally to the use of various devices1 such as rakes with broad teeth1 used as stirring implements4 ,there is room for display of ingenuity in this direction1 and it is found often that1 while they are used successfully on one estate1 they may be condemned on another4 ,illustration3 ,,two ,,views ,,of ,,dilution ,,and ,,mixing ,,tanks4 ,below1 on the right1 coagulating tanks4 ,at the far end strainers4 ,each dilution tank is of equal capacity to the corresponding coagulating tank4 ,,use ,,of ,,sodium ,,bisulphite4--,some few years ago a demand for pale crepe rubbers sprang up1 and this demand has been maintained4 ,the total quantity of pale rubber put on the market previously could only have amounted to very little1 and that little was obtained by luck and various tricks in manipulation4 ,it must be premised that if coagulation is allowed to take place1 either naturally or with the aid of acetic acid1 the resulting rubber will almost inevitably oxidise on the surface1 except in the cases of very dilute or young latices4 ,even supposing that this darkening of the surface does not take place in the wet stage1 it is often found that a rubber expected to dry to a pale colour does not fulfil expectations1 and a dull neutral shade results4 ,this darkening of crepe rubber may be attributed to a slow process of oxidation1 which continues until the rubber is dry4 ,from these remarks it will be seen that the process of oxidation is a natural one1 and that any pale rubber formerly shipped was the outcome of circumstances outside the control of the estate1 except in such cases where boiling of the coagulum1 etc41 was resorted to4 ,the fact that one rubber happened to be a shade darker than another was absolutely no criterion as to the value of the rubber1 but apparently the market thought1 and still thinks1 otherwise1 although the actual necessities of manufacturers for a pale crepe to be employed in special processes must be comparatively small4 ,the prevention of this natural oxidation was a problem which exercised the minds of all responsible for the preparation of pale rubbers1 and much time and thought were expended upon it4 ,various theories were propounded1 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 houses4 ,to this end windows were to be kept shut1 or else they were provided with ruby-coloured glass1 which incidentally kept out the air4 ,in spite of these precautions1 little success attended the expenditure of so much energy and thought4 ,it was absolutely necessary that some chemical agent should be discovered which would make the preparation of pale crepe possible for any estate4 ,this chemical would have to fulfil several requirements before it could become popular3 #a4 ,it must be a simple substance capable of being easily handled4 #b4 ,it must be very soluble1 so that solutions could easily be made up by inexpert workers4 #c4 ,it must be cheap4 #d4 ,it must be quite innocent of any harmful effect upon the quality of the rubber4 ,after months of investigation into the properties of other chemicals the writers decided that the only one which satisfactorily answered all requirements was sodium bisulphite4 ,the writers make no pretension to any claim of having discovered the properties of this substance1 which was a common chemical1 and widely known4 ,even its action on latex was suspected before they engaged upon the work4 ,these matters are only mentioned because the credit1 if any1 should be given to the laboratories of the ,rubber ,growers' ,association4 ,as soon as it began to be known on the market that sodium bisulphite was being used in the preparation of pale crepe1 a great outcry was made1 and estates were warned that no more rubber prepared in this way would be accepted4 ,it was said that the chemical would destroy the nerve of the rubber1#b and it was definitely stated that rubber prepared with this chemical was brittle4 ,it must be remembered that brokers had some legitimate excuse in raising objections to the introduction of new and strange chemicals for preparing rubber1 as they were quite without means of judging whether the rubber had suffered harm or not4 ,still1 on the other hand1 private tests had been made in conjunction with ,messrs4 ,beadle and ,stevens for fully eight months before the name of the chemical was mentioned in reports1 and they had decided from the results of vulcanisation tests that the chemical was quite innocuous4 ,then1 and only then1 did we consider it advisable to recommend the use of sodium bisulphite in general estate practice4 ,owing to the initial prejudice against rubber prepared with sodium bisulphite1 the results of our preliminary work were published by permission of the ,rubber ,growers' ,association4#c ,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 #aiaa4 ,at the present time it is probably accurate to state that it is now used by all estates preparing fine crepes4 ,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 producers4 ,while we are prepared to believe1 we can only plead that from our point of view the supply arises from the demand4 ,such are the conditions governing the sale of rubber that1 irrespective of the requirements of the ultimate user1 we have to market rubber which is valued almost completely upon its appearance at the time of sale4 #b ,williams1 ,international ,rubber and ,allied ,congress1 ,london1 #aiad4 #c ,the ,employment of ,sodium ,bisulphite in the ,preparation of ,plantation ,rubber1 ,beadle1 ,stevens1 and ,morgan1 ,india-rubber ,journal1 ,august #b1 #aiac4 ,as long as such conditions prevail estates must continue to adopt any device of proved harmlessness1 in order to obtain the best possible price for their product1 and not because we desire to continue a practice which some assure us to be unnecessary1 and which1 moreover1 adds somewhat to the cost of production4 ,,quantities ,,of ,,sodium ,,bisulphite4--,it must be premised that1 although sodium bisulphite is employed on some few estates in the preparation of sheet rubber1 we do not advise the practice4 ,it is unnecessary1 and may lead to some little trouble and delay in drying4 ,in any case1 sodium sulphite gives the results desired for sheet rubber 7see following74 ,it must be understood1 therefore1 that we are concerned here1 in the case of sodium bisulphite1 with its employment in the preparation of fine pale crepe only4 ,as the dry rubber contents of latices vary with the age of the trees1 the general health of the trees1 the seasons and general climatic conditions1 the relative strain imposed by depletion of reserves through tapping1 etc41 it will be clear that the effect produced by a definite quantity of sodium bisulphite in any given volume of latex will also vary--i4e41 the effect depends upon the potential amount of rubber present4 ,a dilute latex needs less sodium bisulphite than a richer latex to produce the same effect in colour4#d #d ,incidentally there are certain occasions1 as in the opening of areas of bark rested for long periods1 when the latex is of a rich yellow colour4 ,sodium bisulphite will not bleach this colour1 and it is well to remark again at this stage that the action of the chemical is only to avoid or arrest oxidation 7darkening74 ,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 estate1 the effect upon the dry rubbers will vary4 ,this explains why some estates obtain different shades of rubber in their fine pale crepes4 ,the remedy obviously is to reduce the variation in latices by diluting them all to a standard rubber content as is done in sheet preparation4 ,one is thus assured that the prescribed quantities of sodium bisulphite will meet requirements in every case1 and that waste will be avoided4 ,working with a standard of #a-a_/b lbs4 dry rubber per gallon the following formula should serve as a maximum3 ,formula for ,use of ,sodium ,bisulphite4 7a7 ,dissolve sodium bisulphite in water at the rate of #a lb4 to #aj gallons4 7b7 ,of this solution use #a gallon to every #aj gallons of latex4 ,,making ,a ,,solution4--,the making of a solution of the chemical would seem to be a simple matter1 but to judge by the ill-effects sometimes observed in the dry rubber the simplicity of the operation appears to have been overrated4 ,great care must be exercised in preparing the solution1 and the work should not be left to the few minutes preceding its actual requirement2 such has been found to be the case in several factories1 so that it is not surprising if the rubber is defective4 ,the powder should be added gradually to water with thorough stirring1 which should be continued for five minutes at least4 ,even then there may often be seen at the bottom undissolved particles1 sand1 and other impurity4 ,it is necessary1 therefore1 in such cases to decant the solution through a piece of cotton cloth before using4 ,no solid particles should be allowed to enter the latex4 ,,abuse ,,of ,,sodium ,,bisulphite4--,it is now generally recognised that the abuse of sodium bisulphite1 in the form of an excess1 leads mainly to delay in the period of drying and the production of an overpale rubber4#e ,it is probable that few estates1 if any1 now experience trouble due to this non-observance of the rules and quantities laid down for use4 #e ,the ,preparation of ,plantation ,rubber1 ,morgan1 #aiac1 p4 #gd4 ,,residual ,,traces ,,of ,,sodium ,,bisulphite4--,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 rolls4 ,these traces must have been very minute1 but they were sufficient to retard the progress of drying4 ,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 extraction4 ,these samples were tested for the presence of sulphates4 ,of the series tested that sample prepared with bisulphite in the proportion of #a part to #fjj parts latex showed only a trace of sulphate present2 while the one prepared #a3b1djj gave an equal quantity4 ,intermediate samples contained no trace of sulphate4 ,on the whole1 therefore1 the presence of sulphate in crepe rubber is adventitious1 and properly washed crepe prepared with moderate quantities of bisulphite may be taken as free from any residual quantities4 ,meanwhile there cannot possibly be any doubt of the advantages gained by the use of sodium bisulphite1 and it would not be very wide of the mark if the statement were made that1 in the event of this chemical being discarded1 most contracts for pale crepe could not be fulfilled4 ,,sodium ,,sulphite4--,it would not be amiss to insist upon the point that while the nature of sodium bisulphite1 as employed in the preparation of rubber1 is anti-oxidant1 sodium sulphite is employed chiefly for its anti-coagulant property4 ,it is not used1 therefore1 in the making of crepe rubber1 but is of service in the preparation of sheet rubber1 where the aim is to keep the latex in good fluid condition as long as is necessary1 and to retard coagulation slightly so that enclosed bubbles of gas or air may escape4 ,formulae have been given for its use in the field when required4 ,on some estates this practice is not found necessary1 but a quantity of solution is always placed in the bottom of the reception vessels prior to the straining of latex into them4 ,only a small quantity is used1 and as a working basis the following formula may be adopted3 ,sodium ,sulphite3 ,for ,use in the ,factory4 7a7 ,dissolve #b ozs4 of anhydrous sodium sulphite in a gallon of water4 7b7 ,the gallon of solution1 placed in the bottom of the reception jar or tank1 is sufficient for the treatment of #dj gallons of standardised latex 7#a-a_/b lbs4 dry rubber per gallon74 ,the warning previously given regarding the necessity for thoroughness in the preparation of solutions is here reiterated4 ,stirring should be thorough1 say for five minutes1 and if there is any sediment or undissolved matter the solution should be strained through cloth before using4 ,where uniform jars or tanks are in use1 the majority of which will contain uniform quantities of latex daily1 the practice of using the chemical can be made almost fool-proof even in the hands of coolies4 ,a calculation is made of the quantity of powder required for each vessel daily4 ,the necessary number of lots is weighed out each morning and each placed in an envelope4 ,the process is thus simplified by the fact that the contents of an envelope1 neither more nor less1 are required for each unit reception vessel4 ,even the weighing can be done by a coolie if he is given a counterpoise 7of lead1 for example7 equivalent to the required weight4 ,it will not be found necessary to do any vigorous stirring of the solution with the latex1 as the latter is strained into the solution and the continued addition of successive quantities is sufficient to give a good mixture4 ,,use ,,of ,,formalin4--,few estates now use formalin 7formaldehyde7 as an anti-coagulant4 ,it must be acknowledged that when not abused there are points in favour of its employment in preference to sodium sulphite1 but these are outbalanced by certain disadvantages4 ,the argument may be stated thus3 ,points for3 7#a7 ,if made up freshly it is an effective anti-coagulant4 7#b7 ,formalin being the solution of a gas in water1 there is no residual substance left in the rubber to delay drying4 7#c7 ,its use gives a bright clear rubber4 ,points against3 7#a7 ,its cost at all times is greater than that of sodium sulphite4 7#b7 ,if the jar is not sealed there is loss by evaporation1 thus increasing the cost4 7#c7 ,its effect upon the rubber is uncertain4 ,even in normal quantity it is said to cause brittleness or shortness4 ,certain few estates1 however1 have continued its use1 and no trouble is claimed to ensue4 ,the following formula is stated to give satisfactory results in the preparation of sheet rubber1 when applied as in the preceding paragraphs bearing on the employment of sodium sulphite3 ,formula for ,use of ,formalin 7,formaldehyde74 7a7 #a pint of formalin is diluted with #e gallons of water4 7b7 ,of this solution #a gallon is required for #ej gallons of standardised latex4 ,in noting this formula the writer gives no recommendation regarding its use4 ,whatever may be the actual facts regarding the effect of formalin upon the vulcanisation of rubber1 when used in minimum proportions1 there can be no question concerning its injurious effect if used in excess4 ,beyond this the factors of cost and loss militate against its wider employment4 ,,chapter ,,ix ,,preparation ,,of ,,sheet ,,rubber ,,pale ,,sheet4--,the first form in which plantation rubber was prepared was as biscuits or sheets4 ,this form remained in favour for some years4 ,the first biscuits or sheets were rather dark in colour owing to the natural oxidation which followed4 ,then it was discovered that by diluting the latex the degree of oxidation was diminished1 and later it was found that if the soft coagulum were placed in almost boiling water for a short time the resulting rubber was pale4 ,thus there arose gradually a demand for pale sheet4 ,with our present knowledge we are in a position to state that the pale biscuits were not in any way superior to the darker ones1 and they were in most cases actually inferior4 ,it was found also as time progressed that sheet rubber1 on air-drying1 became covered with external surface moulds1 and that1 more often than not1 the smell of the drying rubber was the reverse of pleasant4 ,even when dry the sheets had to be continually brushed free from moulds1 and by the time the rubber reached the market it was again usually mouldy4 ,such are1 even now1 the handicaps under which those who prepare pale sheets have to labour4 ,few1 however1 are the estates making pale sheets1 and they are confined almost entirely to native holdings4 ,to those accustomed only to the preparation of crepe rubber1 where coagulation can be effected in large batches1 the preparation of sheet rubber always seems to demand much more labour4 ,as a matter of fact1 although the preliminary operations certainly do demand more care and labour than in crepe-making1 there are compensating advantages in the machining stage4 ,for the preparation of sheet of the highest quality on any but the largest scale1 elaborate installations of machinery are quite superfluous1 as equal results can be obtained with pairs of rolls worked by hand4 ,,uniformity ,,of ,,product4--,there will be no need to enter again into a discussion of the preliminary operations of receiving and straining latex for sheet-making4 ,they have been fully dealt with in ,chapter ,,vii4 ,it used to be the general custom to mix the acid and latex in each individual dish1 and in some small or non-progressive factories that is still the procedure4 ,quite apart from the question of labour entailed1 the process is quite unnecessary4 ,even if comparatively small volumes of latex are handled1 standardisation by dilution should be the rule1 and the acid solution should be added to the bulk4 ,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 #dj gallons if the organisation is efficient4 ,on any but a small scale the labour entailed in the handling and cleaning of pans is excessive1 and shallow tanks are now employed on most estates4 ,the reception and standardisation of latex by dilution has already been discussed in ,chapter ,,vii4 ,the combination of this practice with the employment of shallow coagulating tanks has simplified working and reduced the cost of labour4 ,it is not intended to enter into any lengthy discussion relative to the merits of sheets made in pans as against those made in tanks4 ,it is granted that it is possible to make a pan sheet superior in appearance to the general average of tank sheets2 but from an economic standpoint the introduction of the use of tanks into all but the smallest factories is only a matter of time1 if the demand for this class of rubber persists4 ,,the ,,ideal ,,tank4--,even the most modern installations of sheet-coagulating tanks must be regarded as merely temporary devices1 as1 given facilities1 the room for improvement is so wide4 ,the first tanks made erred in being too large1 and as the result of experience the size of units has now been reduced to a maximum of #ab feet by #d feet by #a foot deep4 ,illustration3 ,,unit ,,modern ,,coagulating ,,tank 7,,two ,,views74 ,construction of brick and cement with lining of glazed tiles4 ,note slots incorporated in side tiles4 ,partition boards in piles in the background4 ,tanks are at present constructed either of hard timber or of brick and cement faced with glazed tiles2 both types have inherent drawbacks4 ,the wooden tanks are difficult to keep clean and in sweet condition4 ,the glazed tiles1 unless extremely well laid1 allow the acid serum 7from which the rubber is removed7 to percolate between the interstices4 ,thus pockets of liquid collect beneath the tiles1 and in process of the decomposition of certain constituents dissolved in the serum evil-smelling gases are set free4 ,illustration3 ,,another ,,battery ,,of ,,tanks1 ,,with ,,dilution ,,tanks1 ,,raised1 ,,on ,,the ,,right4 ,note drainage cocks1 chute1 and sieve in position4 ,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 tank4 ,if such adjuncts could be secured1 the disabilities indicated above would be perhaps wholly removed4 ,unless there is a demand from estates1 however1 it is idle to expect a supply to be forthcoming4 ,an even greater improvement would take the form of unit tanks cast in glazed white-ware with the necessary slots incorporated in the sides4 ,at present no known firm makes such tanks of sufficient size4 ,a unit could measure 7internally7 #f feet by #d feet by #a foot deep1 with slots #a-a_/b inches apart1 and #c_/h inch in width4 ,the tanks might be reinforced with iron bars1 so that they could either be used alone or embedded in the usual brick structure4 ,the junctions of the bed-plate and side-pieces could be finely rounded so as to facilitate cleaning1 and at one end a draining-hole could be made1 say1 #a inch in diameter4 ,illustration3 ,,closer ,,view ,,of ,,foregoing4 ,note partitions in position and coagulum being removed4 ,meantime both the hard-wood tanks and those of glazed tiles find their particular applications4 ,the former is generally employed in smaller factories1 or where future large increases of crop preclude the present installation of a fixed system4 ,the latter find use in large factories1 or where no new areas remain to come into bearing4 ,,modern ,,installation4--,as an example of a modern installation of coagulating tanks1 we can do no better than offer reproductions of the system now in use on ,pataling ,estate4 ,a warning must be given against employing all tanks of stone-ware or cement unless well glazed4 ,almost without exception1 irrespective of the material used in the construction of coagulating tanks1 wooden partitions are employed4 ,in the few exceptional cases the partitions are either of glass or of aluminium4 ,the former would appear to be the ideal substance1 were it not for initial cost and loss by breakage4 ,these disabilities may possibly be overcome in course of time4 ,,care ,,of ,,tanks4--,the use of aluminium would have been wider had it not been for lack of supplies and the question of cost during the ,war4 ,a novel method of employing aluminium partitions was introduced in the factory of ,tremelbye ,estate4 ,there were no slots in the sides of the glazed-tile tanks1 but the necessary slots were very ingeniously created by means of aluminium distance-pieces1 the two long edges of which were turned at right angles to the face of each piece to a depth of about #a_/d inch4 ,the ends of the thin aluminium partition moved in the slot thus formed between two adjacent distance-pieces4 ,the friction between the surfaces was sufficient to allow all the partitions1 when in position1 to be raised well above the floor of the tank1 so that a uniform level of latex was obtained4 ,slight hand-pressure only was then required to push the partitions down4 ,naturally the cleansing of glass or aluminium partitions presents no difficulty1 but in the case of wood failure to ensure thorough cleanliness leads to possible defects in the finished dry rubber4 ,provided the wood could be made waterproof1 no trouble would ensue1 and hence various measures have been tried with that object in view4 ,when new the boards have been surface-waxed or varnished1 and the treatment has been repeated on occasions4 ,but in course of time the surface film of waterproof material has disappeared1 partially or wholly1 and the trouble recurs4 ,when partitions become sodden with serum1 the surfaces are liable to be coated with a slime1 consisting largely of organic growths which have an effect upon the latex1 causing pitting on the surface of the coagulum and enclosed bubbles within4 ,illustration3 ,,another ,,battery ,,of ,,tanks1 ,,without ,,dilution ,,tanks ,,or ,,means ,,of ,,gravitating ,,latex4 ,it is recommended1 therefore1 that wooden tanks1 after ordinary cleansing daily1 should be swabbed out with a #e per cent4 solution of sodium bisulphite4 ,wooden partitions should receive the same treatment1 and once a week at least 7or every day if possible7 they should be placed in the sun for an hour or two1 care being taken that both sides of a partition are exposed in turn4 ,before being placed in the latex1 all wooden partitions should be made wet on the surfaces4 ,some years ago the writers had made a partition of vulcanite1 which apparently would have proved of great service but for the initial cost4 ,the advent of the ,war put the matter out of the question1 but it is possible now that such a material would be worthy of extended trial4 ,except in the matter of cost1 it would appear to have advantages over any substance yet tried2 and if it were possible for estates to supply their own lower grade rubbers direct1 the cost might be reduced considerably4 ,illustration3 ,a ,,sheeting ,,tank ,,containing ,,coagulum ,,for ,,crepe ,,preparation4 ,behind wall in background are the tanks in which latex is standardized4 ,note vent1 to the left1 through which latex flows and wooden stopper on edge of tank4 ,,standard ,,latex4--,enough has been written 7see ,chapter ,,vii47 to familiarise the reader with the use of this term for the description of latex diluted daily to a level of dry rubber content4 ,whatever may be the practice elsewhere1 it is now fairly general on estates in ,malaya to reduce all latices to a uniform strength for the preparation of sheet rubber4 ,it is claimed that only in this manner can uniformity of product be achieved4 ,the selection of a standard has been the outcome of general experience4 ,it has been found that if too high a standard is taken difficulties arise1 such as 7#a7 unsatisfactory and uneven coagulation1 7#b7 too thick a coagulum for easy working in general1 7#c7 too extended a period of drying and smoke-curing1 and hence too dark a colour in the finished rubber4 ,illustration3 ,a ,,battery ,,of ,,sheeting ,,tanks 7,,pataling ,,estate74 ,,dilution ,,tanks1 ,,raised1 ,,on ,,the ,,left4 ,on the other hand1 too low a standard also brings trouble in its train4 ,the coagulum is too porous1 will not stand handling1 and the resultant sheet is too thin unless an abnormal thickness of coagulum is prepared4 ,furthermore1 over-dilution means an increase in the number of tanks required for any original volume of latex4 ,this involves an increase in floor area1 and perhaps in the size of the building4 ,the soft sheets1 when rolled1 may spread to such a width as to cause the edges to be squeezed under the cheek-blocks of the machines1 etc4 ,for all practical purposes1 whether sheets are prepared in pans or in tanks1 it has been found that the optimum results are obtained by the adoption of a standard approximating and not exceeding #a-a_/b lbs4 dry rubber per gallon4 ,primarily this standard has a direct connection and interdependence with the distance between the partitions 7or between the slots7 in coagulating tanks4 ,the distance found most practicable is #a-a_/b inches4 ,this thickness of coagulum1 when prepared from latex not exceeding a standard of #a-a_/b lbs4 dry rubber per gallon1 is found to yield a very satisfactory sheet in all respects4 ,it will be seen that we have two possible main factors of variation3 7a7 ,distance between partitions1 causing visible differences in thickness of coagulum4 7b7 ,dry rubber content of latex1 causing differences in the density 7e4g41 hardness or softness7 of the coagulum4 ,the effect of variation in 7a7 will be clear4 ,even when latex of a standard of #a-a_/b lbs4 per gallon is employed the resulting sheet may be either too thin or too thick4 ,similarly1 as already argued1 the use of too low or too high a standard of dilution 7when the factor of distance between partitions is not allowed to vary7 is capable of causing much difficulty4 ,while this is correct1 broadly1 it is found in the experience of some estates that their requirements are satisfied by a slightly lower standard than #a-a_/b lbs4 per gallon4 ,thus it is not uncommon to note the adoption of a standard equivalent to #a lb4 #d ozs4 or #a lb4 #f ozs4 dry rubber per gallon4 ,experience dictates1 however1 that for the recognised standard measurements of modern tanks the practical limits of satisfactory density of latex lie between #a-a_/d lbs4 and #a-a_/b lbs4 per gallon4 ,,standardising ,,instruments4--,for standardising latex by dilution all that is required is an instrument which will preserve a perpendicular position while floating in latex1 will be sufficiently sensitive to indicate fairly small differences in density of latex1 and has one mark on its aerial portion accurately indicating a density corresponding to the required standard4 ,on scientific grounds it can be demonstrated that such an instrument as employed in common practice would not be strictly accurate4#f ,it is not proposed1 in this section of the book1 to discuss such considerations4 #f ,de ,vries1 ,archief voor de ,rubbercultuur4 ,instruments of this nature are represented by the ,metrolac 7originating from the ,rubber ,growers' ,association7 and other similar recorders4 ,they generally consist of a submersible bulb with a projecting stem which is graduated4 ,the ,metrolac differs from others in that the bulb is of torpedo form 7thus reducing skin friction71 and the graduations on the stem indicate actual weight of dry rubber per gallon instead of the ordinary specific gravity figures4 ,theoretical considerations to the contrary1 it is found in actual practice in ,malaya and ,ceylon that1 although such instruments are naturally delicate and require careful manipulation1 they are of considerable practical value and satisfy a definite requirement4 ,until an instrument of greater accuracy and equal simplicity can be discovered all estates should regard the possession of a few ,metrolacs as essential4 ,the nature of their construction and the average conditions under which they are used 7and abused7 make it impossible to rely upon their accuracy indefinitely or for any long period4 ,it is always recommended1 therefore1 that there should be at least two instruments available1 one of which may be in daily use1 while the other is kept in safe custody and only employed1 say1 once a week for purposes of checking the accuracy or degree of inaccuracy of the other4 ,this can be done with reasonable approximity by placing both instruments in a tall vessel containing well-mixed and diluted latex4 ,instruments showing a marked degree of inaccuracy should not be preserved2 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 adjustment4#g #g ,this applies to the gilt brass instruments4 ,as the result of experiment the ,rubber ,growers' ,association are now introducing glass instruments4 ,these are necessarily more fragile1 but while unbroken can be relied on to give correct readings4 ,where field coagulating stations have been instituted on estates1 it is strictly necessary that instruments should be provided in all cases2 and it should be a rule that these are tested and corrected weekly by a standard instrument employed for that purpose only4 ,this need was well recognised by many estates when1 during the ,war and the consequent shortage of supply of ,metrolacs1 a demand arose which was met in some degree by crude instruments of local manufacture1 such as that commonly known as the ,castlefield bobber1 contrived and made by the enterprising manager of the estate of that name4 ,the demand for the more accurate instruments can now be met4 ,,methods ,,of ,,using ,,the ,,instruments4--,the ,metrolac was devised and introduced by the writers on behalf of the ,rubber ,growers' ,association1 and directions for its use were given4 ,tables were prepared by means of which simple calculations for the dilution of any given latex could be made4 ,these did not find an extended application1 inasmuch as in the majority of cases native workers only were in charge of the processes of rubber preparation4 ,in point of fact1 such calculations are not strictly necessary1 as the operation of standardising the latex can be done quite simply and skilfully by a trained native4 ,latex as it reaches the store in average weather from any particular division or field does not vary greatly in density4 ,the trained coolie or foreman1 basing his practice on experience1 adds to the latex a quantity of water1 and then makes a first test with the standardising instrument4 ,several additions of water 7with thorough stirring7 may have to be made before a test indicates that the correct density has been obtained1 but it is surprising how quickly a skilled worker will arrive at the desired standard4 ,extreme or absolute accuracy is not insisted upon or desired1 as avoidable delay is to be deprecated1 and the result in any case is sufficiently exact for practical purposes4 ,,skimming4--,during the gravitation of the latex from the reception vessels 7in which the standardising of the latex is effected7 to the coagulating tanks1 much surface froth is usually caused4 ,this is best removed by means of a thin board of a width slightly less than the breadth of the tank4 ,the skimmings are sometimes placed in pans and subsequently made into a second grade of sheet rubber1 or they receive treatment with a small proportion of sodium bisulphite and eventually appear as fine pale crepe4 ,the practice varies usually according to the form in which the general ,no4 #a grade is prepared4 ,on some estates a great deal of the frothing is avoided by placing in position at the receiving end of the tank a perforated partition4 ,this partition may be made of wood1 or of stout zinc 7or aluminium7 carrying ten circular holes to the inch4 ,through this the latex percolates1 while the froth is retained on a small area4 ,the froth is removed prior to the addition of the acid4 ,after stirring in the acid solution most estates again skim the surface of the latex2 but if the stirring has been performed properly there should be little froth4 ,this1 when it collapses1 in any case will appear only on the upper edge of the strip of coagulum1 and after rolling should not be visible4 ,it would appear1 therefore1 that the second skimming is not necessary4 ,,style ,,of ,,sheet4--,within the last few years the custom of making plain sheet--i4e41 sheet having a plain surface--has gradually given place to the preparation of ribbed sheet--i4e41 sheet having a pattern marked on the surface4 ,it would probably be correct to say that plain 7smooth7 sheet is now only prepared by natives or by some estates just come into bearing4 ,even in the latter case there is no reason why smooth sheet should be made1 as hand machines are sold which will do all the work required4 ,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 result4 ,one advantage claimed for ribbed sheet which may entirely justify the preference exhibited by consumers1 relates to the question of packing4 ,when rubber arrives at home it is frequently found to be in an almost solid block1 due to the pressure of the sheets superimposed in the case4 ,the smoother the surfaces of the rubber in contact the greater the adhesion and the denser will be the mass1 and consequently the greater the difficulty in separating individual pieces4 ,under such circumstances it is plain that the difficulty is diminished if the sheets have a raised pattern on them4 ,it is noted also that the liability to mildew-growth is greater the smoother the surfaces of the rubber4 ,on these grounds the marking of sheet rubber is to be commended4 ,these reasons apart1 it is really astonishing the difference made in the appearance of the sheets by impressing upon them a ribbed pattern1 and it is highly probable that the market value of the rubber is slightly increased4 ,it is not our duty to attempt to reason why this simple operation should increase the market value of sheet rubber2 it is sufficient to recognise that it is so1 and that money may be thrown away by neglecting to cater for the taste of the market4 ,of the patterns impressed upon sheet rubber there is a variety1 but the general style is that known as the spirally close-cut ribbing4 ,,standard ,,sheet4--,leaving for the present the question of pattern of mark1 one cannot do better by way of introduction than to reproduce the instructions#h given generally to estates4 #h ,handbook on ,preparation of ,rubber1 ,rubber ,growers' ,association1 ,may1 #aiag1 p4 #bh4 ,,rolling ,,and ,,marking ,,of ,,sheet ,,rubber4--,working with standard latex it is found that strips of coagulum #a-a_/b inches in thickness require little rolling to produce sheets of desirable thickness4 7#a7 ,the sheets or strips are first given a preliminary rolling with a heavy hand-roller made of hard wood4 ,the roller is passed once in one direction1 and once in the reverse direction4 7#b7 ,the coagulum is then passed through smooth machines twice1 once with the rolls fairly open1 and once with a narrower space4 ,it is not found advisable to close the smooth rolls so tightly that the rubber is made too hard4 7#c7 ,the sheets or strips are then passed once through a pair of marking rollers4 ,various types of patterns are used1 but the one which appears to give the most satisfactory results is that known as the close-cut spiral4 ,this produces the semblance of a small diamond pattern on the rubber4 ,the surface of the sheet is raised in well-defined ridges1 which appear to present the maximum drying surface exposed to the atmosphere of the smoke-house4 ,thus1 not only is the appearance of the sheet rendered attractive1 but also the period of drying is reduced4 ,starting with standard latex and following the procedure here described for rolling and marking1 sheets should be ready for packing in ten or eleven days4 ,if the period is longer1 it is possible that the design or structure of the smoke-house is at fault4 ,,when ,,to ,,work ,,the ,,coagulum4--,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 it4 ,for reasons of practical economy in factory working1 it is usual to allow sheet rubber to remain over night1 and the coagulum receives attention early next morning4 ,during the interval 7averaging about eighteen hours71 the coagulum consolidates1 leaving an almost clear serum if the correct quantity of acid has been added to the latex4 ,any but the very slightest trace of milkiness in the serum indicates an insufficiency of coagulant4 ,if the serum is always definitely clear1 there may be grounds for believing that an excess is being used4 ,if the quantity of coagulant has been calculated to an average nicety1 the serum should be just dubiously free from milkiness4 ,the firmness gained by the coagulum on standing in the serum overnight should enable it to be handled next morning without any marked stretching1 and in some estates the rubber is put direct through the first pair of smooth rolls without a preliminary consolidation by means of hand-rolling4 ,some estates prefer to handle the coagulum while rather softer1 as it is claimed3 7a7 ,that the coagulum is easier to work1 and sheets of improved appearance can be made4 7b7 ,that there is greater freedom from bubbles4 7c7 ,that the incidence of rust is lessened4 ,these claims are substantiated in practice2 but in the case of the third1 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 machined4 ,in such cases all latex must reach the store comparatively early in the day--e4g41 before noon4 ,three hours is allowed for coagulation1 and the working of the rubber is then commenced4 ,as a general rule this means that the operations of rolling and marking must be completed1 a short interval given for dripping1 weighing must be done1 and the rubber placed in the smoke-house before night falls 7as a rule about #f4cj p4m474 ,unless factories dealing with a large crop are well equipped with artificial light1 such a course is not open to them2 in any case it remains true that night work should be avoided if possible4 ,if1 however1 it can be arranged without increasing the cost of production1 there would appear to be no objection to the early working of the coagulum as described above4 ,,hand-,,rolling4--,as already indicated1 some few estates do not give the strips of coagulum any preliminary hand-rolling1 as the rubber is considered to be sufficiently firm to be handled into the first machine4 ,on most estates hand-rolling is found necessary1 owing to the tendency of the long strips to stretch unduly1 giving badly shaped sheets4 ,this hand-rolling should be done carefully1 and is best effected on a specially constructed table4 ,this consists essentially of an inch-thick hard-wood plank about #b inches wider1 and #d or #e feet longer1 than the strip of coagulum4 ,along the edges of the plank1 and at right angles to its upper flat surface1 may be fastened strips of wood about #a_/b inch square in section1 thus forming a shallow tray open at either end4 ,these strips serve two purposes3 7a7 ,as the wooden roller is wider than the plank1 they prevent the coagulum being rolled too thin and too firm4 7b7 ,they prevent the coagulum being squashed too wide1 and tend to keep the edges straight4 ,to avoid thick ends it is sometimes considered advisable to insert1 at either end of the rolling table1 shallow wedges about #f inches long1 of the same width as the table 7between the edge-strips71 and with the sharp end of the wedge pointing in the direction of the length of the table4 ,the ends of the coagulum are drawn up and finished on these inclined planes4 ,these points may appear to be extreme refinements1 but as long as rubber is valued on such grounds we must endeavour to meet the system imposed upon us4 ,,smooth-,,rolling4--,it is advised that1 after hand-rolling1 the coagulum should be passed through at least two machines having smooth-rolls4 ,on some estates three such machines are employed4 ,the purpose of this procedure is to reduce the thickness of the coagulum gradually4 ,the same could be effected1 of course1 on one machine2 but obviously the distance between the rolls would have to be readjusted at each operation and for each piece of coagulum4 ,apart from the time thus wasted1 there is the certainty1 in view of the rough adjustment of the machines1 that the chances of obtaining uniformly thick sheets would be slight4 ,the machines should be arranged as a battery1 with the marking rolls at one end1 so that the operations are consecutive4 ,it is erroneous to imagine that heavy machines 7such as those used in crepe preparation7 are required4 ,light machinery only is necessary for sheet-making2 but any available heavy smooth-roll machines in a crepeing battery may serve admirably for the purpose4 ,,marking4--,heavy machines are unnecessary for the purpose of putting a pattern on sheet rubber4 ,if the rubber has been properly prepared a light pair of rolls is capable of exerting sufficient pressure to cause a good upstanding pattern4 ,rolls are cut in various designs3 some with diamond grooves on both rolls2 some with grooves of varying width and depth encircling the circumference of the rolls1 thus creating a stripe effect on the rubber2 and some with diagonally-cut spiral grooves placed closely together4 ,the last has the greatest vogue at present1 while the first has almost gone out of favour4 ,an objection lodged against the second design is that the edges of the grooves sometimes cut through the rubber1 so that the dried sheet divides in strips4 ,it would appear in such instances that either the coagulum was too thin and soft1 or that the grooves had been cut too deeply and sharply4 ,in any case the choice of a design is an arbitrary matter1 and should depend upon the effect produced on the rate of drying and the general appearance4 ,the popular close-cut spiral roll is machined with varying measurements1 but the usual design has grooves #a_/h inch wide by #a_/h inch deep and #c_/af inch apart4 ,many estates have a particular brand cut in the middle of the rolls for purposes of identification4 ,if this is done it is advised that the main grooving of the rolls be carried into the branding strip2 otherwise grip will be lacking on this portion1 and a certain amount of cockling of the sheets will result4 ,sheets are often seen in which the potential effect of the grooving is reduced to a comparatively flat pattern in place of the desired ridges4 ,the fault is generally attributed to the shortcomings of the marking rolls4 ,while it is true that the grooving often deteriorates by friction-wear when the rolls are running free1 experience generally decides that the deficiency in the appearance of the rubber should be attributed to faulty previous preparation rather than to the marking rolls4 ,sets of rolls have been changed often without justification or an improved result4 ,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 grooves4 ,this has been found to be a common fault1 and the general effect is to delay drying in spite of the thinness of the rubber4 ,again1 the trouble may have been due to an incorrect standardisation of the latex1 generally in the direction of too heavy a density 7too rich a latex7 being employed4 ,the original thickness of the coagulum would be normal1 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 ordinary4 ,if this firmness is appreciable the resistance of the rubber to the squeezing action of the marking rolls will result in a flat pattern--i4e41 the grooves cannot be filled1 and the ridges are low4 ,it is advised that all rolls used in the preparation of sheet rubber should be at least #ah inches wide1 in order to avoid the appearance of thickened edges which delay drying4 ,working with the correct standard of dilution of latex1 and following the procedure indicated in the foregoing paragraphs1 the dry sheet should not exceed an average thickness 7over ridges and depressions7 of #a_/h inch4 ,,preparation ,,for ,,smoke-,,curing4--,it used to be the custom to allow sheet rubber to air-dry first for periods varying from one to several days4 ,naturally moulds were soon formed1 and when the sheets were quite smoke-cured a mass of the dead moulds could be seen1 if not over the whole sheet1 at least in the corners of each diamond mark4 ,it has been demonstrated in practice that there is no advantage in allowing sheets to air-dry partially before smoking4 ,in fact1 to obtain the greatest benefit from smoke-curing1 sheet rubber should be placed in the smoke-house as soon as possible4 ,the same effect of mould-growth may be noted if the wet sheets are placed in a smoke-house insufficiently heated4 ,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 rolling4 ,these will be enlarged upon in a subsequent section of the book1 and at present it will suffice to indicate the procedure which experience directs as likely to give the best results4 ,when the lengths of coagulum leave the marking machine they are usually laid in piles containing two dozen or more strips4 ,the piles are then cut into the required lengths1 the exact length generally being determined by the available perpendicular distance between the supports in the smoke-house4 ,it is necessary to remark that the piles of sheets should not be allowed to accumulate1 but should be dealt with in subsequent treatment progressively4 ,if for some reason this is not possible1 then all piles of sheets should be turned on edge so as to assist the draining away of the serum or mother-liquor1 which continues to ooze from the rubber for some time after the squeezing in the machines4 ,where hot water is available the freshly cut sheets should be passed into it as soon as possible1 and given a thoroughly good swilling4 ,the caution must be given that the hot water should be changed very frequently and1 if possible1 after every batch1 say1 of a hundred sheets4 ,the sheets should then be carried immediately to racks on which they are hung to drip4 ,generally these racks are situated under cover1 but there is no reason why they should not be placed in the open air without cover or shade4 ,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 cover4 ,while the sheets are fresh and loaded with internal moisture1 the effect of sun-heat upon the surface1 when exposed for1 say1 two hours1 is nil2 and the safety of the process can be guaranteed1 provided the stated limit is not exceeded to an appreciable extent4 ,illustration3 ,,the ,,old ,,method ,,of ,,dripping ,,freshly ,,rolled ,,sheets ,,within ,,the ,,factory4 ,after dripping for an hour or so1 the sheets should be placed in the smoke-house4 ,if it is a bright sunny day1 no extra precautions need be taken2 but on cool1 dull days it would be advisable to light the fires earlier than usual1 consistent with the work required to be done in the house--e4g41 in the removal of dry rubber4 ,there would appear to be no reason why the dry sheets should not be first removed1 so that on dull or wet days smoking can be commenced as soon as the wet rubber has been hung4 ,on a few estates where the smoke-houses are worked continuously1 except for a few hours in the morning1 a portion of the building is separated by a partition for the reception of the wet rubber4 ,the sheets are taken directly from the marking rolls and placed in the chamber1 beneath which a fire is started4 ,the sheets thus drip in a warm and smoke-laden atmosphere until next morning1 when they are weighed and removed to the smoke-house proper4 ,it is claimed that freedom from rust is thus obtained4 ,it will be clear that in the treatment of the rubber preparatory to smoking the whole process should be continuous1 and delay should be avoided if the best results are to be obtained4 ,illustration3 ,,the ,,newer ,,method ,,of ,,hanging ,,in ,,the ,,open ,,air4 ,,smoking ,,of ,,rubber4--,the assumption may have been noted above that the sheet is to be smoked4 ,as far as our knowledge extends1 none but small native estates now prepare sheet rubber of any other type1 with the exception of certain patent processes4 ,air-dried sheets are generally made on small-holdings1 and are bought in the market chiefly for the purpose of macerating and making into blanket crepe4 ,we have no intention1 therefore1 of discussing the possibilities or qualities of air-dried sheets1 as the output of sheet-rubber from our estates is always in smoked form4 ,the drying 7or1 properly1 smoking7 stage will be discussed in ,chapter ,,xi4 ,,chapter ,x ,,preparation ,,of ,,crepe ,,rubber ,,no4 #a1 ,,or ,,fine ,,pale ,,crepe4--,considering first the preparation of the highest grade1 fine pale crepe1 it must be stated that the difficulties attached to the process are generally not sufficiently appreciated4 ,in this pale rubber minor blemishes are so plainly apparent that their importance is highly exaggerated1 and what would worthily escape notice in smoked rubber assumes disproportionate prominence in pale crepes4 ,the very fact that such a delicate material as colourless coagulum has to be manipulated in coarse iron rollers1 with the attendant oil and grease worries1 should be sufficient to deter one from criticising too harshly the occasional lapses of an estate struggling to give of its best to the market4 ,at the same time there can be no doubt that if precautions are taken to attend to all likely sources of contamination1 defects in pale crepe may be avoided to a wonderful extent2 and on some estates the observance of elementary rules enables the preparation of the finest pale crepe to be made almost mechanically4 ,,standardisation ,,of ,,latex4--,the question of the standardisation of latex has been dealt with in a general way in ,chapter ,,vii41 and the reader is now familiar with the trend of the argument in its favour4 ,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 sheet4 ,unless the dry rubber content is invariable1 and the quantities of chemicals fixed1 the colour of the crepe may vary appreciably4 ,it may be pointed out that it is not essential to adopt the same standard of dilution as for sheet preparation4 ,given that latices from all fields or divisions are fairly uniform1 and of high rubber content1 the standard may be taken at a figure equivalent1 for example1 to #b lbs41 or #b-a_/b lbs41 or even #c lbs4 per gallon4 ,it is wise1 nevertheless1 to take a lower standard for several reasons4 ,for instance3 7a7 ,the average dry rubber content varies with climatic conditions1 position of the cut on the tree1 general health of the tree1 etc4 ,on a rainy day the dry rubber content may be lowered too greatly by adventitious circumstances4 7b7 ,recording instruments often fail to give even approximately correct readings in rich latex4 ,errors may thus be made easily4 7c7 ,a fairly soft coagulum means easier working on the machines1 less labour1 and proportionately cheaper costs4 ,illustration3 ,,three ,,grades ,,of ,,crepe ,,rubber4 ,left to right3 fine pale crepe2 second quality pale crepe2 compound crepe4 ,it is advised1 therefore1 that for general purposes the same standard as that found suitable for sheet rubber should be taken--viz41 #a-a_/b lbs4 dry rubber per gallon4 ,at all events the standard should not exceed #b lbs4 per gallon4 ,,coagulation ,,and ,,coagulant4--,coagulation may be undertaken without any special arrangement of tanks1 and is usually effected in the ordinary ,shanghai glazed earthenware jars containing about #de gallons4 ,given reasonable care1 and a fairly fool-proof system of calculation for the quantities of chemicals required1 no difficulty need be experienced4 ,illustration3 ,a ,,washing ,,shed4 ,sheets are soaked in hot water in tanks in the background1 and then scrubbed under a spray of cold water4 ,on a larger scale it is advised that proper reception tanks1 in which standardisation can be effected1 should be installed4 ,where both sheet rubber and fine crepe are being prepared1 the whole system of sheet-coagulating tanks may be employed with considerable advantage1 even to the insertion of the partitions4 ,if ordinary jars are used1 and the coagulum is left until the following morning1 the mass of rubber has to be cut up into pieces of a size suitable for the machines4 ,the knives or saws are sometimes rusty1 and the colour of the coagulum is affected4 ,the coolies often feed into the machines lumps which are too large1 with the result that portions are thrust under the cheek-blocks and become stained4 ,when a sheet-coagulating tank is used all labour of cutting the coagulum is obviated4 ,the long strips are handled and fed into the rolls easily4 ,it may be seen1 likewise1 that actual work is thus saved in machining4 ,,quantity ,,of ,,coagulant4--,for a general discussion on the coagulant and quantities employed1 the reader is referred to ,chapter ,,viii4 ,it is there recommended that for latex standardised to a level of #a-a_/b lbs4 per gallon1 the proportion of pure acetic acid should be in the ratio of #a3a1bjj4 ,directions are there given for the making of the solution1 and the calculation of the quantity required for any given volume of latex4 ,it is pointed out that for average undiluted latex the basis of calculation1 for quantities of acetic acid required1 should be taken on the ratio #a3a1jjj4 ,where latex exceeds a dry rubber content of #c lbs4 per gallon1 it may be necessary to increase the quantity of acid to #a3hjj4 ,if a standard of #b lbs4 per gallon is adopted1 the formula given for the #a-a_/b lbs4 standard will not give full satisfaction1 and the quantity of acid solution must be increased slightly in order to obtain complete coagulation4 ,assuming that the original solution is prepared in #a per cent4 strength1 the following difference would be noted3 7a7 ,one part pure acetic acid to #ajj parts water 7theoretically #ii parts74 7b7 #a-a_/b lbs4 per gallon4 #b lbs4 per gallon4 ,of the above solution use #a gallon ,of the above solution use #a to every #ab gallons of standardised gallon to every #aj or #aa latex4 gallons of standardised latex4 ,it is not possible to lay down an exact figure governing all cases1 as so much depends upon the treatment undergone by the latex before it reaches the store4 ,some estates continue to use solutions of greater strength1 generally #e per cent41 in crepe preparation4 ,while such solutions may be effectively stirred in when the latex is dilute1 it is advised that for intimate mixture the solution need not be stronger than #a per cent4 ,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 coagulum4 ,if the rubber is to remain until next morning1 the average formulae will be found suitable2 but if it is required to work the coagulum with an interval of less than three hours1 an excess of acid must be employed4 ,the excess need be comparatively small1 unless the interval is much reduced4 ,for instance1 it is the practice on some few estates to begin the machining of the coagulum about half an hour after coagulation commences2 in which case it is usual to add from a quarter to a half of the normal quantity in excess4 ,it need scarcely be pointed out that unless this procedure is strictly unavoidable it should be discouraged on account of the waste of coagulant involved4 ,incidentally1 the use of strong solutions of acid under such circumstances may lead to increased deterioration of the rolls4 ,,colour ,,of ,,fine ,,crepe4--,we are sometimes assured that manufacturers do not pay the attention to the question of colour which sale conditions would lead one to believe4 ,as far as we are concerned1 and as long as there is no direct traffic between producer and consumer1 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 markets4 ,this1 in spite of the knowledge that1 all other things being equal1 the arbitrary distinctions in colour afford no indication of the intrinsic value of the rubber4 ,under present circumstances it is plain that if paleness is demanded it has to be supplied4 ,probably without exception all estates employ sodium bisulphite as the agent for the prevention of that darkening 7oxidation7 which is natural in drying rubber4 ,,sodium ,,bisulphite4--,a formula for use of this chemical is given in ,chapter ,,viii41 and is applicable to latex standardised to #a-a_/b lbs4 dry rubber per gallon4 ,if a higher standard is chosen the quantity calculated as in 7b7 of that formula may be increased slightly1 and the exact requirements found by experience4 ,the caution must again be given that the employment of an excess of sodium bisulphite will lead to the production of an over-pale rubber1 and a prolongation of the drying period4 ,if thick crepes are made1 an excess of the chemical is sometimes made visible by a greyish powder deposited on the edges of the strips of dry rubber4 ,it must be emphasised that the formula in ,chapter ,,viii4 indicates the maximum quantities required for use with standard latex4 ,many estates will find it expedient to use less of the chemical2 and if it is found that the desired result is not obtained from normal proportions1 attention should be directed to the points discussed in the following paragraph4 ,,evaluation ,,and ,,deterioration ,,of ,,sodium ,,bisulphite ,,and ,,sodium ,,sulphite4--,sodium bisulphite and sodium sulphite are both bought for our purpose in the form of a fine crystalline powder1 and on analysis good specimens should contain over #ij per cent4 pure substance1 when packed in well-sealed vessels4 ,it has often happened that shippers or local sellers1 by inadvertence1 have supplied the one chemical in place of the other--to the detriment of the rubber and the discomfiture of managers of estates4 ,the error1 as a rule1 has not been detected for some time1 and then perhaps only as a result of complaints or enquiries reaching the laboratories4 ,to the layman1 and certainly to the native who usually has charge of these substances1 it is not a simple matter to distinguish between them without special knowledge4 ,there are certain elementary tests1 however1 which can be applied on all estates serving to make the distinction1 but affording no information regarding the actual quality of the chemicals4 ,they are given in a comparative form on page #aaf4 ,samples of doubtful specimens may be sent to the laboratories for analysis1 but the bulk of the chemical should not be used4 ,during the ,war some very poor shipments were received1 and much trouble was caused4 ,under normal conditions there can be no question that it is to the interests of chemical manufacturers to supply the best article2 and it is anticipated that in future there should be no difficulty in procuring shipments of a high degree of purity4 ,sodium ,bisulphite4 ,sodium ,sulphite4 #a4 ,if in good condition it #a4 ,it has no perceptible has a powerful odour of odour4 sulphur dioxide4#i #b4 ,in solution it should turn #b4 ,in solution it should turn a blue litmus-paper red4 a red litmus-paper blue4 #c4 ,it exhibits a marked tendency #c4 ,the tendency to cake to cake if the is less marked than in drum is allowed to the case of the bisulphite4 remain open4 #i ,high-grade sodium bisulphite has very little odour1 but by the time it reaches the estate1 and as a result of short exposure to the moist atmosphere of the tropics1 a little decomposition sets in and a strong odour of sulphur dioxide gas is noticeable4 ,it will be evident that1 as sodium bisulphite under normal conditions gives off a gas when exposed to the atmosphere1 it deteriorates in quality continuously4 ,it is the potential presence of this gas which makes the powder effective as an anti-oxidant and disinfectant4 ,it is within the experience of all accustomed to the handling of this chemical1 that in addition to the loss of gas1 the powder cakes into a hard mass on exposure4 ,if only the top layer is caked1 the remainder may be in fair condition2 but no caked portions should be used1 as they cannot be of good quality4 ,they may1 however1 be used for the treatment of scrap rubber1 to be discussed later4 ,,care ,,of ,,sodium ,,bisulphite4--,the ready tendency of sodium bisulphite to deteriorate on exposure should give sufficient indication regarding its treatment in storage4 ,it should be bought only in drums 7or other air-tight containers71 and should be stored in a dry place4 ,no drum should be opened until required1 and the common practice of keeping an open drum on the floor of the factory should be avoided4 ,drums are of two sizes1 generally containing #a_/d or #a_/b cwt4 respectively4 ,it will be obvious that1 although the prime cost may be cheaper with the larger quantity1 it would always be preferable to secure the smaller drums1 as the loss on exposure will be less4 ,most commonly the #ef lb4 drum is purchased4 ,it should not be difficult to calculate the period during which the contents will be consumed1 on the basis of a maximum of #a lb4 per #ajj gallons of latex4 ,a #ef lb4 drum1 assuming no loss or waste1 should be sufficient to treat at least #e1fjj gallons of latex 7say1 #h1ejj lbs4 of rubber7--if the bisulphite is of first-class quality1 and the use is applied only to the preparation of fine pale crepe4 ,where the quantity used per diem is small1 it is advised that precautions should be taken to preserve the quality of the chemical when a drum is opened4 ,it might be of advantage to place the contents of the drum in smaller sealed tins1 or to have made a special container 7with a closely fitting lid7 into which the powder can be placed as soon as the drum has been opened4 ,,mixing ,,solution ,,with ,,latex4--,emphasis has been laid1 in ,chapter ,,viii41 upon the necessity for care in the preparation of the solution4 ,equal regard must be given to the mixture of the solution with the latex4 ,on a few estates it used to be the practice to add the powder to the solution of acid1 with stirring4 ,obviously this led at least to a great loss of efficiency1 owing to the rapid escape of the gas which was evolved4 ,the solution of sodium bisulphite should be poured into the latex in as uniform a distribution as possible4 ,the mixture of solution and latex should be thoroughly stirred1 and if only natives are in charge a minimum period of five minutes should be prescribed before the addition of the coagulant4 ,a thorough stirring should again follow the advent of the acid4 ,if these elementary rules are not observed faithfully1 the deficiency will most probably be manifested in the dry rubber in the shape of streaks of varying shades of colour4 ,finally it may be insisted upon that deteriorated sodium bisulphite should not be used4 ,in order to obtain an effect double the quantity may be required1 and the residual salts left in the rubber on evaporation of the moisture will be responsible for prolonged drying1 surface deposits1 and possibly spot disease4 ,,former ,,methods ,,of ,,making ,,pale ,,rubber4--,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 devices1 among which the following might be quoted3 7a7 ,use of excessive quantities of strong acetic acid4 7b7 ,extreme dilution of latex in conjunction with excessive quantities of acid4 7c7 ,extreme dilution in conjunction with steaming and excess of acid4 7d7 ,extreme dilution of latex in conjunction with excess of acid and subsequent heating of the coagulum in hot water4 7e7 ,the use of excess of a mineral acid such as sulphuric acid4 7f7 ,the skimmings and very dilute latex1 coagulated with excess of acid4 ,,working ,,the ,,coagulum4--,description of the details of necessary machinery for crepe-making is relegated to ,section ,,iii4 of this book4 ,here we shall treat only of the matter in general4 ,in the preparation of crepe rubber heavy machinery is necessary1 and ample engine-power must be available4 ,the machines should comprise three types3 7a7 ,with rolls cut in such fashion1 and run at such different speeds1 as to have a macerating effect upon the coagulum4 ,such machines or rolls will be referred to as macerators4 7b7 ,intermediate rolls1 grooved in varying designs and geared differentially4 ,these reduce the thick rough crepe obtained from the macerators into a form suitable for passing to the rolls described in 7c74 ,they are sometimes called crepers1 but as this term may be applied equally to the macerating rolls1 they will be termed the intermediate rolls4 7c7 ,smooth rolls usually run at approximately even speeds and1 as their name denotes1 devoid of any grooving4 ,they are called smooth rolls or finishers4 ,without such equipment it is not possible to prepare the grade which is known as fine pale crepe4 ,in the common acceptation of this term crepe of ,no4 #a quality generally connotes fineness and paleness with a thin crepe which has a good1 smooth1 and fairly well-knit texture4 ,it is1 of course1 possible to make a thick pale crepe1 using only the macerators and intermediates1 but the finish will be that typical of the particular grooving of the intermediate rolls4 ,for the preparation of crepe ordinarily1 the possession of smooth rolls is a sine qua non4 ,for reasons which will be explained more fully in the chapter dealing with the defects of crepe rubber1 the practice of preparing thick crepes direct from the coagulum is now very uncommon4 ,thick crepes are generally made by reworking dry rubber1 either in the form of thin crepes or from air-dried sheets4 ,the market for the latter in ,malaya is confined almost entirely to ,singapore1 where factories buy native rubber and re-work it into thick crepe4 ,the bulk of the output of ,no4 #a crepe from estates is in the form of thin fine pale crepe4 ,the artificial standard set up by buyers and brokers necessitates this thin crepe being of even texture and fairly free from small holes 7looseness74 ,what difference the small holes are to make in the vulcanising properties of the rubber is beyond our knowledge2 but such being the standard1 it must be attained if the full price is to be obtained4 ,in order to secure the desired effect the coagulum must be passed consecutively through the three types of rolls1 and undergoes a varying degree of working in each4 ,given the necessary equipment of machines1 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 7or even less in exceptional cases74 ,there is no intention of suggesting that this is possible on all estates4 ,clearly the number of times the rubber passes through the rolls will depend upon the total efficiency of the machines4 ,this in turn involves such factors as 7a7 the size of the rolls1 7b7 the number of machines of each type1 7c7 the gearing of the pinions1 7d7 the speed of the drive1 etc4 ,again1 much depends upon the nature of the coagulum worked4 ,a fairly soft coagulum will offer less resistance1 and conversely a dense coagulum will require more machining4 ,it has been shown by the writers in previous publications that over-working of the coagulum has an effect on the vulcanisation of the rubber2 and this has been confirmed by others4#aj ,apart from this point1 it should be recognised that over-working1 beyond that necessary to produce a thin crepe of even texture1 is to be deprecated1 on the ground of economy1 in working4 #aj ,bulletin ,no4 #bg1 ,department of ,agriculture ,f4,m4,s41 ,april1 #aiah1 ,preparation and ,vulcanisation of ,plantation ,para ,rubber1 ,eaton1 ,grantham and ,day4 ,owing to the existing differences in equipment and speed of drive1 etc41 the regular practice of any one estate may be unsuitable for another4 ,it remains1 therefore1 a matter of study for each estate to discover the minimum number of times which rubber should pass through the machines1 consistent with the factors indicated above4 ,in any case it may be assumed that if any factory cannot prepare a good crepe by passing the rubber1 say1 twelve times through the rolls1 there is some deficiency in the machines1 or of speed2 the coagulum may be too hard1 or the rolls may be badly worn4 ,,lower ,,grades ,,of ,,crepe ,,rubber4--,even a few years ago it was plain that the lower grades of crepe 7i4e41 all grades lower than first latex rubber7 were not sufficiently appreciated in the market4 ,there was often a marked difference in price between a first-grade crepe and crepe made from naturally coagulated lump4 ,this arose chiefly from lack of knowledge4 ,it has since been recognised in some measure that no reason exists for such a wide difference in price1 and more recently the margin between even the first-grade rubber and the lowest grade of scrap rubber has been a gradually diminishing one4 ,providing sufficient care is exercised in the preparation of the lower grades1 one would expect to see but very small difference in prices between any two grades4 ,it is true that adequate attention has been given to the preparation of the scrap grades only in comparatively recent years1 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 grades4 ,,naturally ,,coagulated ,,lump ,,rubber4--,the grade of rubber made from the naturally coagulated lump which forms in buckets and carts is usually of a mixed colour1 due to the fact that the lumps oxidise very quickly4 ,when they are allowed to remain overnight before being machined1 it can be imagined that the colour of the dry crepe would be very dark1 or would contain very dark streaks4 ,such is ordinarily the case1 unless special precautions are taken4 ,providing that the coagulated lump is free from bark1 leaves1 and leaf-stems1 and certain other precautions taken1 the difference in price between coagulated-lump crepes and first-grade crepes should be very slight4 ,too often1 however1 not sufficient supervision is given to the coagulated-lump rubber1 and it is common to see it come into the factory containing leaves and bark4 ,these should be picked out before the latex is strained1 but obviously it would be better to ensure that they did not enter the buckets in the first place4 ,it would seem reasonable to suppose that if some means could be employed for preventing or checking the surface oxidation of naturally-coagulated lump rubber1 there would be a corresponding improvement in the colour of the dry crepe4 ,that such a method is practicable has been demonstrated on many estates4 ,the lump when lifted out of the latex is allowed to drain for a few minutes1 and is then 7without squeezing7 placed in a dilute solution of sodium bisulphite4 ,a #a per cent4 solution is sufficiently powerful4 ,it is not to be thought for a moment that by the use of sodium bisulphite any previous oxidation will be counteracted2 all that is claimed for the treatment is that any further surface oxidation will be checked1 and the rubber may be allowed to remain until the next day1 for working1 if it is so desired4 ,it will probably be found that quite a quantity of latex has been expressed from the lumps by contraction1 and acid may be added to obtain the rubber from this4 ,on other estates the lump rubber is worked on the machines as it is received1 and the resulting crepe is submerged in a weak solution of sodium bisulphite over-night4 ,it is then rinsed in water and hung to drip before weighing and placing in the drying house4 ,under certain conditions some of the lump rubber darkens rapidly during transport to the store1 and any such oxidised portions must be rejected if a uniform colour is to be expected in the crepe4 ,following the procedure indicated above1 some estates find it possible to prepare from naturally coagulated lump rubber a crepe which can be classed as ,no4 #a grade4 ,,skimmings ,,and ,,washings4--,the skimmings of tanks1 as already shown1 may be prepared sometimes as a second quality of smoked sheet2 but generally they are amalgamated with the rinsings of cups and buckets1 treated with sodium bisulphite and acid1 and made into crepe form4 ,the cup-washings1 as they arrive at the store1 represent a very dilute latex1 the rubber from which is generally of a greyish colour4 ,bucket-washings should yield a good type of pale rubber if they are obtained properly4 ,to obtain the maximum quantity of good rubber the buckets should first be rinsed4 ,a gang should be taken1 a small quantity 7say a quart7 of water poured into the first bucket1 and this dilute latex used progressively in all the buckets of that gang of tappers4 ,the result is a fair latex which can be added to the bulk of ,no4 #a latex1 provided it is free from dirt4 ,where sheet rubber is being prepared1 carefully strained cup-washings or bucket-washings may be utilised in the dilution of the latex to the required standard1 thus increasing slightly the percentage of first-grade rubber4 ,,tree-,,scrap4--,as tree-scrap is a naturally coagulated rubber1 it should be expected to show up well in quality4 ,this is usually the case2 but from what has been said of the effect of sun-heat it will be understood that if trees are not regularly scrapped1 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-baked4 ,in hot dry weather1 on widely planted areas tapped on alternate days1 it has been noticed that scrap remaining for two days often exhibits a resinous appearance1 and feels sticky to the touch4 ,if tree-scrap is to be made as a separate grade1 as used to be the general custom1 care should be taken to see that it is free from bark and dirt4 ,on some estates where scrap-rubber is paid for per pound collected1 it is usually the rule to insist that scrap shall be washed free from dirt and picked free of bark4 ,this course is to be commended1 but might probably prove impracticable to the majority of estates4 ,theoretically1 of course1 the operation of machining should rid the scrap of all traces of bark2 but in practice it does not do so4 ,some proportion of the tree-scrap is usually found to be heavily oxidised1 and naturally if a crepe of uniform colour is to be obtained these dark scraps must be rejected1 otherwise dark streaks will be formed4 ,coolies should be instructed to sort out the dark pieces before arriving at the store4 ,,bark-,,shavings4--,it has been intimated in a previous section that the method of obtaining and collecting bark-shavings varies with the type of labour employed4 ,where the scrap is removed from the edge of the bark on each occasion before tapping1 the amount of rubber to be extracted from the dry shavings is very small--so small1 in fact1 that when the price of rubber is low1 it is doubtful whether it pays to collect and work the material4 ,on the other hand1 where trees are not scrapped before tapping1 the bark-shavings and tree-scrap are collected together1 and the amount of rubber derived from the mixture may be #cj to #dj per cent4 upon the gross weight--depending chiefly upon the quality of the tapping 7i4e41 in this case1 the thickness of the paring74 ,another factor influencing this figure would be the effect of using an anti-coagulant on the cuts4 ,bark-shavings entail such wear upon the ordinary machines during working1 especially if fairly free from rubber1 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 equipment4 ,whenever possible1 bark-shavings should receive treatment on the day of collection4 ,it used to be quite common to see heaps of bark-shavings accumulating on the floor of a factory1 and generating excessive heat4 ,yet these heaps were allowed to stand about for a day or days4 ,is it any wonder then that tackiness was found to develop when the rubber was dry8 ,it is here definitely laid down that no heaps of bark-shavings should be accumulated even for half a day4 ,tanks should be provided in which the shavings should be submerged in water4 ,,earth-,,scrap4--,of all grades of crepe this is the one most liable to become tacky in transit4 ,this tackiness to a large extent cannot be avoided1 as old pieces of earth-scrap may be brought in amongst the bulk4 ,probably these old pieces have been exposed to the sun for days1 and have become quite resinous4 ,it would be practically impossible to go through all earth-scrap in order to find these odd pieces1 but unless this were done one could not guarantee that the earth-rubber would always be free from tackiness4 ,the difficulty does not appear1 however1 on estates where earth-rubber is collected systematically at very frequent intervals4 ,,fibrous ,,matter ,,in ,,low-,,grade ,,rubbers4--,it is sometimes found in this and other lower grade rubbers that pieces of cloth or cotton-waste are concealed4 ,coolies may have used them for cleaning cups1 or the store coolies may have been at fault4 ,earth-scraps especially should be examined1 before working1 for such extraneous matter4 ,,scrap-,,washers4--,these are heavy machines specially devised for the treatment of lower grade rubbers4 ,in these the raw rubber is well masticated and freed from impurities1 if the machine functions efficiently4 ,there are several types of these machines1 all of which are efficient4 ,that best known is the ,universal washer1 made by ,joseph ,baker1 ,sons1 and ,perkins1 ,ltd4 7formerly ,perkins ,engineering ,company74 ,coming into local favour during the ,war1 the ,u4,e4 scrap-washer1 made by the ,united ,engineering ,company 7,singapore71 gives very good service4 ,the ,c4,c4,c4 washer1 made by the ,colombo ,commercial ,company1 is suitable for the purposes of an average estate4 ,there are others1 less well known4 ,most of these machines are made in varying sizes to meet the requirements of small1 medium1 or large estates2 and if funds are available1 a scrap-washer should be regarded as an essential item in the machinery of any estate employing engine power4 ,the rate of output of scrap-washers will depend mainly upon the speed at which they are driven1 and when ordering the equipment it would be advisable to state the ordinary speed of the back-shaft1 length of drive1 etc4 ,it does not follow that the larger the rate of output1 the greater is the efficiency of the washer4 ,the point is not as to what quantity of rubber can be taken out per hour1 but what quantity is actually freed from impurities4 ,it is advisable for the superintendent to obtain a thorough knowledge of the general construction and principles of the particular scrap-washer employed4 ,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 depended4 ,it was often found that these parts1 which were intended to be removed and cleaned at intervals1 had become firmly fixed and could not be removed for inspection4 ,it must be recognised also that the machines are liable to considerable damage if extraneous substances are allowed to enter--for example1 tapping-knives1 stones1 pieces of iron1 spouts1 etc41 which are sometimes present in the loose scraps of rubber or shavings1 owing to the carelessness of coolies4 ,under the best regulated-system1 such accidents occasionally occur1 but a great deal of trouble could be avoided by having it understood that each charge must be sorted over before entering the washer4 ,again a deal of extra work1 and much wear and tear1 is caused by the abuse of the scrap-washer--e4g41 in the cleansing of earth-scrap4 ,as this reaches the factory it often contains a quantity of internal or adhering earth4 ,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 stirring4 ,in a similar manner dry bark-shavings1 which have been allowed to accumulate1 could be softened4 ,in the actual working of scrap-washers instructions are generally given by the makers4 ,these sometimes advise the introduction of warm water 7or of steam into the cold water supply7 for an interval during the working of each charge4 ,where possible1 such instructions should be followed1 as by this means the individual pieces of rubber are massed together1 in the final stage1 into a sausage form which is easy to transport and to manipulate in the ordinary crepeing battery4 ,,compound ,,crepes4--,the attitude of both buyers and sellers with regard to the types of lower grade rubbers appears to be changing4 ,in the past1 from any one estate there might be obtained as many as six grades of crepe below ,no4 ,i4 ,these comprised3 7#a7 ,a pale rubber 7often streaked7 obtained from coagulation of cup washings and bucket rinsings4 7#b7 ,a pale rubber 7often streaked7 obtained by coagulation of the skimmings from the surface of the ,no4 #a latex4 7#c7 ,a streaked and dull rubber prepared from naturally-coagulated clots found in cups1 buckets1 and latex carts4 7#d7 ,a streaked rubber prepared from scrap which had coagulated upon the face of the cut bark4 7#e7 ,a brownish and streaked rubber made by maceration of bark-shavings to which pieces of tree-scrap adhered4 7#f7 ,a dark rubber1 often tacky1 prepared from scrap found in or on the ground near the base of the trees4 ,as it is often a matter of weeks between any two regular collections1 it is easy to understand why the dry rubber was more liable to be tacky than any other grade of crepe4 ,it will have been evident to all who have acquaintance with these grades1 as shipped from many different estates1 that the diversity in the various shipments must have been rather bewildering4 ,there appeared to be a regrettable lack of uniformity1 even in the appearance of1 say1 a bark scrap rubber from any two estates4 ,when1 in addition to these variations1 the further complication of condition of cleanliness is introduced1 one may realise the difficulty attaching to the evaluation of these rubbers as they appeared upon the market4 ,although the foregoing paragraph is written in the past tense1 it should be pointed out that within certain limits the trouble continues to exist with respect to the output of a great number of estates4 ,in the case of many1 it has been realised that the manufacturer does not want to buy a large number of parcels1 all differing in some respect4 ,it is probably correct to state that what a manufacturer requires is a big parcel uniform in appearance and treatment1 even though the colour may not be so light as that of many smaller lots4 ,this statement is modified with the proviso that the rubber1 no matter what its colour or appearance may be1 must be free from dirt1 grit1 and bark4 ,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 daily4 ,naturally the shade of colour of this compound crepe will depend largely upon the types of rubber employed1 but as a rule it is somewhat darker than the highest of the types employed in the mixture4 ,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 processes4 ,neither would it appear that the seller suffers any monetary loss4 ,in point of fact it will be found probably that the reverse is the case4 ,for instance1 supposing it were decided to mix for a compound crepe-- 7a7 ,naturally coagulated lump rubber4 7b7 ,tree-scrap4 7c7 ,bark-shavings scrap4 ,the product would be darker in colour than 7a7 and slightly better than 7b74 ,let it be granted that there might be a monetary loss on 7a71 it is probable that there would be a slight gain in comparison with the usual prices obtained for 7b7 and 7c74 ,now1 as a general rule1 the actual percentage of crop made into 7b7 is appreciably less than that made into 7c7 and still less than 7b7 and 7c7 together4 ,apparently1 therefore1 there would be a margin of profit on the whole by making a compound crepe4 ,it may be pointed out1 on the other hand1 that there might be expended on the manufacture of this crepe more time and labour1 but as against this the labour of sorting and grading would be simplified4 ,unfortunately this process is not open to estates which do not possess a scrap-washer4 ,it is essential that the rubber should be free from grit1 sand1 and bark particles4 ,in the absence of a scrap-washer for the cleansing of the bark-shavings1 it would be futile to attempt to make a compound crepe containing that type of rubber1 as one would run the risk of spoiling the whole4 ,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 means4 ,until that time the preparation of compound crepes must be the privilege only of well-equipped estates1 unless other estates can send their lower grade rubbers for treatment in a scrap-washer to their more fortunate neighbours4 ,in previous publications a diminution in the number of grades of crepe rubber has been advocated1 and it is gratifying to find that in many cases the amending grades suggested have been improved upon4 ,many estates now make only three grades of crepe--viz43 7a7 ,no4 #a4 ,from latex coagulated in the store4 7b7 ,no4 #b4 ,compound4 7c7 ,no4 #c4 ,earth-rubber4 ,it will be seen that the compound crepe includes all types between fine pale crepe and earth-rubber4 ,naturally one could not safely recommend the inclusion of earth-rubber in any compound crepe1 as the risk of possible tackiness in the whole would be serious4 ,in the case of the bark-shavings rubber to be incorporated1 it is first cleaned alone in the scrap-washer4 ,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 crop4 ,besides the estates having only three grades1 there are others which make four--viz43 7a7 ,no4 #a4 ,from latex coagulated in the store4 7b7 ,no4 #b4 ,compound1 from cup washings1 etc41 skimmings1 and naturally coagulated lump4 7c7 ,no4 #c4 ,compound1 from tree-scrap and bark-shavings rubber4 7d7 ,no4 #d4 ,earth-scrap4 ,other variations are possible1 but their number is limited1 and they all conduce to simplification of working1 and a supply to the market of rubber having greater uniformity4 ,,need ,,for ,,increased ,,care ,,with ,,lower ,,grade ,,rubber4--,in the ordinary procedure of estate-working there appears to be an undesirable variety in the style of lower grade crepes4 ,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 made4 ,this is a great mistake4 ,with the exception of the lowest grade 7earth-rubber71 it would not be unfair to state that the quality of the rubbers on testing should be very little inferior to the ,no4 #a product4 ,often1 as in the case of naturally coagulated rubbers1 they are superior in some respects to ordinary fine pale crepe4 ,doubtless manufacturers are aware of these facts1 but what course is open to them if they find the rubber spoiled for their purpose by the presence of particles of sand1 grit1 or bark8 ,the possible injury caused by these ingredients cannot be insisted upon too strongly1 and it must be evident that great care should be exercised in the preparation of the lower grades of crepe4 ,as to the particular form of the lower grade crepe rubber1 one may apply the remarks made under the section dealing with the best grades4 ,it is common to find thin crepes1 medium crepes1 and blanket crepes4 ,more often than otherwise1 the medium and thicker crepes are prepared direct in those forms4 ,it follows that they are liable to attacks of spot disease1 which1 however1 is not easily visible in the lowest grades1 owing to the dark colour of the rubber4 ,furthermore1 it is not possible to cleanse the rubber so thoroughly if thick crepes are made4 ,,block ,,rubber4--,few estates now prepare block rubber1 which is essentially crepe rubber pressed into blocks4 ,in the ordinary process the fresh coagulum is lightly rolled into thin crepe1 which is then vacuum-dried4 ,there are slight variations in the subsequent procedure4 ,sometimes the rubber as it comes from the vacuum drier is merely allowed to remain on racks overnight before blocking4 ,in other instances1 the sticky rubber from the vacuum drier is passed once or twice through wet1 smooth rolls and hung to dry for some days4 ,the dry crepe is then folded into the pressing box or cut to suit the size of the box4 ,pressure is applied for some time1 and finally the rubber is taken out in one homogeneous mass4 ,naturally the appearance of the block depends upon the quality of the parent crepe4 ,some block rubber is made up thick2 other is made in slabs about #c inches or #d inches in thickness4 ,with the latter1 it should be possible1 when held up to the light1 to see the shape of a hand held between it and the source of light4 ,it is possible that an erroneous idea of the strength of block rubber has been formed4 ,it should only be necessary to point out that essentially block rubber is merely pressed crepe rubber4 ,it is inconceivable that the mere action of pressing layers of crepe together would increase the physical quality of the rubber4 ,the advantages which block rubber possesses are the compactness of the output1 its ease of packing1 and a saving in freight2 but there is the disadvantage1 from the consumer's point of view1 that extra labour is involved in the preparatory work of cutting up the blocks4 ,,smoked ,,crepe ,,and ,,sheet ,,clippings4--,there appears to be no certain demand for any grade of smoked crepe1 and probably all which is put into the market is really comprised of 7#a7 clippings obtained from the ends of sheets1 7#b7 sheets which have been malformed in machining1 or 7#c7 sheets showing the presence of many bubbles4 ,as to the first class it might be explained that through defective rolling1 thick ends or edges may be caused4 ,these show signs of contained moisture when the bulk of the sheet is perfectly dry1 and as undue delay would otherwise result these moist strips are trimmed and either returned to the smoke-house1 or machined to form crepe4 ,similarly a torn or otherwise badly formed sheet1 when brought from the smoke-house1 may be made into crepe1 rather than it should prejudice the selling price of the bulk under ruling conditions4 ,in the same manner1 although bubbles have no influence upon the quality of the rubber on vulcanisation1 sheets thus affected are generally made into crepe4 ,it cannot possibly be argued that rubber of this description would be in any way inferior to the best smoked sheet for manufacturing purposes1 but owing to the prevailing system of evaluation for market purposes1 it is necessary to resort to the expedients indicated above4 ,on some estates the rubber specified in the three classes mentioned is not made into crepe1 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 demand4 ,in point of fact1 the buyers are really obtaining a first-class article 7except in superficial appearance7 at a reduced price4 ,,chapter ,,xi ,,drying ,,of ,,rubber ,,air-,,drying ,,of ,,crepe4--,it is still the prevailing custom to air-dry crepe rubbers4 ,a few estates1 it is true1 have artificial driers installed1 and in some necessary cases others will be erected4 ,but in the majority of cases where money has been expended in building air-drying sheds1 as long as it is only possible to ship rubber regularly air-drying is likely to remain in favour4 ,the great drawback to air-drying is that one is so dependent upon the weather conditions4 ,in favourable weather the rubber dries well1 but in a long period of wet weather rubber may accumulate at an alarming rate1 and the accommodation is sometimes severely taxed4 ,of course1 the rate of drying under the best conditions is mainly dependent on the thickness of the crepe1 and every endeavour should be made to maintain a thin style of preparation4 ,if this precaution is not taken1 the rubber is liable to recurrent attacks of spot disease1 and one's troubles are very much augmented4 ,this is a disability to which rubber treated in artificial driers is not liable4 ,still1 air-dried rubber can be made equal1 if not superior1 in appearance to pale rubbers prepared by other processes4 ,for the lowest grades of crepe air-drying is always likely to remain the only method1 as it would be extremely unsafe to submit them to heat4 ,it is noted in ordinary practice that the rate of drying on different estates1 for the same type of rubber1 may vary widely4 ,naturally the construction of the house has a great effect1 and this subject will receive attention in a subsequent chapter4 ,similarly the position of the drying-shed exerts an important influence1 and the erection of the building in low-lying surroundings is always calculated to prolong the drying period appreciably4 ,incidentally this means that the building must be larger than a normal rate of drying would otherwise demand4 ,the combination of a poor type of drying-house1 a low-lying situation1 and a prolonged wet season1 might render it advisable to abandon the air-drying of high grade crepes in favour of artificial drying4 ,,artificial ,,driers ,,for ,,crepe4--,it is more common to find artificial driers in use in ,ceylon than in ,malaya1 possibly because these driers have been in use in ,ceylon for other products4 ,some time ago the question of installing artificial driers received the serious attention of a number of estates in this country1 chiefly on account of the incidence of fungoid and bacterial diseases in crepe rubber4 ,the simple treatment for the prevention of these diseases is to get the rubber dry in the shortest possible space of time4 ,in most cases it is found sufficient to roll crepe thin for air-drying in order to prevent the appearance of coloured spots4 ,it is found1 however1 that some drying-houses are so badly planned and constructed1 that quick drying under even the best of conditions is a practical impossibility4 ,cases have been known in which the disease may disappear almost entirely during a period of freedom from rain1 only to recur as soon as wet weather sets in again4 ,there can be no doubt that1 on the whole1 the number of cases of spot disease is on the decline2 but equally it is certain that a very few estates will always be liable to outbreaks as long as drying is attempted in existing houses4 ,for these reasons it is a poor policy to temporise1 and the only sound policy in extreme cases would be to give up ordinary air-drying in favour of some method of artificial drying4 ,as regards the majority of estates preparing pale crepe for various reasons1 it is not expected that any will instal artificial driers4 ,money has been expended in elaborate buildings which certainly do the work for which they were designed4 ,as long1 therefore1 as the accommodation is sufficient1 and regular shipments are the rule1 it is expected that ordinary air-drying will still remain the general practice4 ,of the better-known artificial driers1 there are only three which merit serious consideration in these pages4 ,they are the vacuum driers1 the ,colombo ,commercial ,company's hot-air drier1 and the ,michie-,golledge process4 ,,vacuum ,,driers4--,the vacuum drier is so well known that only a brief description need be given4 ,it consists of a chamber heated by steam pipes and capable of having the contained air and moisture withdrawn by a pump4 ,this description sounds very simple1 and in practice the operation of vacuum drying is really a simple one1 and can well be entrusted to an intelligent coolie under efficient supervision4 ,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 placed4 ,still1 in spite of the apparent simplicity of the process1 there would appear to be a number of little details which1 if overlooked1 prove to be factors influencing the result to a considerable degree4 ,thus it is not uncommon to find complaints that the rubber is not dry when packed4 ,the writers have seen rubber taken from a vacuum drier still containing a visible quantity of moisture4 ,one would have imagined that continuous working of the drier would give the experience necessary to obtain dry rubber1 but1 apparently1 such is not the case in a number of instances4 ,elaborate instructions are given by the makers1 but often they are more honoured in the breach than in the observance4 ,really1 there are only two points to bear in mind3 7#a7 ,that the rubber must be fairly thin4 7#b7 ,that the temperature be not allowed to rise too high4 ,some makers advise #adj deg4 ,f4 as a maximum1 but no harm results from a temperature of #aej deg4 to #afj deg4 as long as the interval is not prolonged4#aa #aa ,these figures refer to temperatures recorded by thermometers placed in the folds of the rubber4 ,these two points presume that the vacuum drier is true to its name1 and that one can obtain a maximum steady pressure4 ,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 #bh inches within fifteen minutes of starting the pump2 and with the pump stopped1 there should not be a greater fall in pressure than #a inch within ten minutes after stopping the pump4 ,one of the most frequent sources of error is the control of steam pressure which is responsible for the temperature of the drier4 ,it is quite unnecessary and unwise to maintain any steam pressure once the drying is well under way4 ,all that is necessary is to heat the chamber well1 with a steam pressure of #e lbs41 before inserting the rubber4 ,as soon as the maximum vacuum pressure has been obtained1 steam should be shut off from the heating pipes1 and it will be found that the temperature is well maintained throughout the operation with a rise of ten to twenty degrees at the end4 ,if the drier is working at a vacuum pressure of #bh inches1 and if the crepe has been prepared thin enough1 the rubber should be quite dry within two hours4 ,should the operation have to be extended to two and a half hours at #bh inches vacuum pressure1 it is a sign that the crepe is too thick4 ,on such occasions it is often noticed that these thicker crepes are not thoroughly dry1 having moist spots enclosed in them4 ,on re-rolling1 these moist patches become easily visible1 and are a source of great annoyance1 inasmuch as they take quite a long time to dry out4 ,as mentioned before1 the crepe for vacuum drying should be thin4 ,there is no necessity to give it a superfine finish1 and the presence of small holes is quite permissible1 as they disappear on subsequent re-rolling4 ,the thin crepe may be folded loosely to the length 7or breadth7 of the tray several times1 but in no other way can the drier be expected to perform its work satisfactorily4 ,a case was noted in which thin crepe was excellently prepared1 and four or five layers were rolled together for vacuum drying4 ,naturally this mode of procedure does not give the drier a fair chance1 and it would be ridiculous to judge vacuum drying on the results4 ,after two and a half hours at a temperature of #ade deg4 ,f4 the rubber appeared to be only about three parts dry1 and the subsequent air-drying extended well into a fortnight4 ,it is the common practice to screw up the door of the chamber as tightly as possible4 ,as a rule it is found in course of time that the obtainable maximum vacuum pressure decreases4 ,this may be attributed solely to the forcible screwing up of the door4 ,around the inside edges of the door are strips of rubber compound1 the function of which is to form a tight joint4 ,should the door be screwed up too tightly1 these strips become deformed in course of time1 and slight leaks occur4 ,it should be pointed out that it is only necessary to screw up the door at the beginning of the operation4 ,when the vacuum has been obtained1 the screw pressure may be released1 as the atmospheric pressure outside the chamber is more than ample to keep the door in a close fitting position4 ,this will be obvious from the fact that the difference in pressure between the inside and the outside of the door amounts to1 say1 #bh inches atmospheric pressure--i4e41 nearly #ad lbs4 per square foot4 ,by slackening the screw handles1 therefore1 as soon as the indicator shows the maximum working vacuum pressure1 the life of the door joints may be prolonged1 and the drier will remain efficient for a longer time4 ,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 correctly4 ,in the same way a thermometer suspended behind the observation window cannot indicate the temperature of the rubber1 as in both of these positions the thermometer must be influenced by radiation from the walls of the chamber4 ,the only position in which the correct temperature could be indicated is between the folds of crepe4 ,this can be arranged easily so as to enable one to read the temperature from the observation window4 ,,colombo ,,commercial ,,company',s ,,drier4--,the drier of the ,colombo ,commercial ,company consists in principle of a number of small chambers or units in which crepe rubber is placed1 and through which hot air is passed4 ,as in the case of vacuum drying1 a great deal depends upon the preliminary treatment of the rubber4 ,if the crepe is not rolled thin enough drying will be unduly prolonged1 with a possibility that the rubber will become tacky4 ,the temperature usually obtained is about #aej deg4 ,f41 and if the rubber is thin the production of an installation of two chambers should be at the rate of #a lb4 of dry rubber per minute4 ,the usual period of drying is under two hours4 ,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 trays4 ,the thin crepe is folded several times1 as in the case of vacuum-drying4 ,figures obtained from the actual working of a drier in ,ceylon are given below3 ---------------------------------------- -------------------------------- ,,chamber #a4--,,temperature #afj deg4-#ahj deg4,f4 ---------------------------------------- ---------,,chamber #b4--,,temperature ,,no4 ,,of ,,drying ,,weight ,,of ,,weight ,,of #aej deg4-#afe deg4,f4 ,tray4 ,period4 ,wet ,rubber4 ,dry ,rubber4 ---------------------------------------- ----------------------------- ,hrs4 ,mins4 ,lbs4 ,lbs4 #a #a #bb #g-a_/b #f ,worked similarly #b #a #db #g-a_/b #f to ,no4 #a4 ,yielded #c #a #eg #g-a_/b #f in #b hrs4 #bc mins4 #d #a #eg #g-a_/b #f #gj-c_/d lbs4 dry rubber1 #e #a #eg #g #e-c_/d from #hg-a_/b lbs4 wet #f #a #eg #g-a_/b #f rubber4 #g #b #j #g-a_/b #f #h #b #j #g-a_/b #f #i #b #aa #f-a_/b #e #aj #b #aa #g-a_/b #f #aa #b #aa #g-a_/b #f #ab #b #ah #g-a_/b #f ---------------------------------------- ----------------------------- #hh-a_/b #gj-c_/d ---------------------------------------- ----------------------------- ,it will be seen1 therefore1 that the drier had an output in #b hrs4 #bc mins4 of #ada-a_/b lbs41 which is at the rate of #a lb4 per minute approximately4 ,as the rubber leaves the driers it resembles vacuum-dried rubber in being surface-sticky4 ,this stickiness is only temporary1 and is got rid of by passing the crepe through wet rolls4 ,opinions differ as to when this rolling should be given4 ,on some estates the rubber is only allowed to cool a little before passing through the rolls2 on others it is given a day or so before rolling4 ,the methods of rolling also differ4 ,in some factories the rubber has been cut to lengths before drying1 and these lengths are merely rolled together by simple pressure4 ,other estates prefer to re-macerate the crepe while still fairly warm and soft4 ,it is probable that little harm1 if any1 results from this re-maceration while the rubber is soft1 as it is more easily worked in this condition4 ,the thick rubber is then generally hung for a few days to air-dry before packing4 ,as most of the moisture taken up by the dry rubber is surface moisture1 three or four days is usually found ample for air-drying4 ,,michie-,,golledge ,,system4--,the ,michie-,golledge system comprises a process of preparation and drying4 ,the latex is diluted with two1 three1 or four volumes of water and coagulated with acid in a vessel which is rotated with a churning motion4 ,in this cylinder there are curved and fixed blades4 ,the revolving cylinder and its ribs force the latex against the curved blades so as to cause an eddy in the middle of the machine4 ,here the rubber coagulates and accumulates1 the remaining liquor whirling round outside the blades4 ,it can be imagined that with such dilute latex1 the coagulum is very soft and spongy4 ,this soft mass is passed through a machine which cuts it into worms about #c_/af inch in section4 ,these are placed upon wire trays and dried by means of hot air4 ,the worms when dry are re-macerated and built up into medium and thick crepes4 ,the colour of the rubber prepared by this process is usually very good4 ,when treated in a ,colombo drier the worms usually require about two hours to dry1 so that crepe rubber may be packed at latest on the fourth or fifth day1 as in the case of vacuum-dried rubber4 ,,rate ,,of ,,air-,,drying ,,of ,,crepe ,,rubber4--,in spite of the facts that some estates have been making thin pale crepes for years1 and that so much has been written concerning the preparation of this grade of rubber1 one occasionally meets with a case in which an estate seems to be unable to prepare thin pale crepe1 or if it does the period of drying is much longer than obtains on most estates4 ,again1 when cases of infection by spot disease in fairly thin crepes are submitted1 it is usually found that the particular crepes are of that type which1 though fairly thin1 show whitish spots of moisture when the bulk of the rubber is nearly dry4 ,this type of crepe is to be noted for the excessive period of drying in comparison with other crepes of equal thinness4 ,it has been advanced elsewhere#ab that a factor of the most considerable importance in the rate of drying of crepe rubber is the type of drying-house and its situation4 ,this accounts very largely for observed differences in the rate of drying of thin crepes on different estates4 ,yet even where two drying-houses may be of the same type1 and the situations may be comparable1 one still observes that one thin crepe dries more quickly than another4 ,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 house1 although the methods of coagulation and preparation exhibit no apparent diversity4 ,in all these conflicting cases allowance is made for the weather conditions1 and the observed differences seem to be inexplicable4 ,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 crepe1 apart from the question of thinness2 and it seemed possible that this factor would account for the discrepancies noted above1 either partially or wholly4 #ab ,preparation of ,plantation ,rubber1 ,morgan1 #aiac1 chapters xii4 and xiii4 ,with a view to determining to what degree the drying of crepe rubber was hastened by the extent to which the rubber was rolled1 experiments were made4 ,it was hoped1 also1 that some idea would be gained of the particular stage in crepe rolling which had the greatest effect upon the rate of drying4 ,in preparing crepe in the estate in the ordinary way the coagulum is passed through three sets of rollers1 and the stages may be described as3 7#a7 ,rough rolling4 7#b7 ,medium rolling4 7#c7 ,smooth rolling4 ,in the first the coagulum is broken down by passing through the machines until a thick rough crepe is formed4 ,this passes to the intermediate rollers1 where it is worked down to a medium crepe4 ,the rubber finally goes to the smooth running at approximately even speeds4 ,passing through these a number of times it emerges as a thin uniform crepe1 free from lumpiness and free from holes1 which should dry in from ten to twelve days4 ,in the experiment the rubber was passed through the machines with varying frequency1 the number of times in each machine being progressively increased1 while the working on the other machines remained constant4 ,it was determined that the rate of drying was affected only by the extent to which the crepe was worked in the smooth rolls4 ,the less often the rubber passed through these rolls1 the slower the rate of drying4 ,beyond a limit in the other direction1 increased rolling did not reduce the period of drying4 ,it follows1 therefore1 that crepes which have a good thin finish should dry in a minimum period4 ,illustration3 ,,drying ,,graph4 ,,pale ,,crepe 7,,thin74 ,,when ,,does ,,air-,,drying ,,take ,,place8--,experiments#ac were conducted with a view to discovering1 if possible1 the rate at which crepe rubber dries1 and the extent of drying during the night under weather conditions such as prevail ordinarily in ,malaya4 ,it is to be remembered that1 during the day1 most drying-houses are fairly open and that the temperature ranges from about #hh deg4 ,f4 in the lower rooms to over #ajj deg4 in the upper rooms 7near the roof7 when the sun shines4 ,at night1 however1 there is usually a decided drop in the temperature1 and unless it is a very clear night the air is generally saturated with moisture4 ,in addition the drying-house is closed as thoroughly as possible1 and we should expect the atmosphere of the house to be laden with moisture from the wet and drying rubber4 ,it would be a just inference1 therefore1 that the rate of drying during the night would be much less than the rate of drying during the day1 and the results of experiments confirm this very fully4 ,one was hardly prepared1 however1 to find that1 under certain circumstances and at a certain stage1 the amount of drying is nil2 not only so1 but it was found under certain conditions that the amount of drying which took place was negative--i4e41 the rubber weighed slightly more when taken out in the morning than it had weighed the previous afternoon4 #ac ,rubber ,growers' ,association1 ,malaya ,local ,report1 ,no4 #b1 #aiad4 ,,crepe ,,may ,,increase ,,in ,,weight4--,as an instance of the kind of result obtained a graph is here given of the rate of drying of a batch of pale crepe4 ,this was hung to dry in the top room of a drying-house in which rubber ordinarily dries quickly4 ,the rubber was hung in a good position1 with the bulk of output1 near a window which was open for some time during the day4 ,in order to restrict the day interval of drying to the actual period in which the sun was likely to be in evidence1 the day was taken to begin at #h a4m4 and end at #d p4m41 the night interval covering the remaining sixteen hours4 ,thus the night interval was twice as long as the period of day drying4 ,the lengths of crepe were weighed carefully at #h a4m4 and #d a4m41 and the average of the several weights was plotted in a graph4 ,the weights are placed vertically and the duration of drying horizontally4 ,it will be seen that the rubber was quite dry and fit for packing on the sixth day1 as far as could be judged in the usual way by casual inspection4 ,peculiarly enough at this time it weighed slightly more than had been registered on the fourth and fifth days1 but the difference did not amount to more than about #j4d per cent4 ,in examining the graph it should be borne in mind that the steeper the slope of the curve downwards the quicker the rate of drying1 and that when the curve takes an upward direction there is an addition of moisture instead of abstraction4 ,it will be noted that when drying takes place the slopes more nearly approximating the vertical represent the extent of day drying1 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 moisture4 ,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 of4 ,thus1 from the graph1 it may be calculated that about #hj per cent4 of the total moisture content was lost in the first two days1 and over #ic per cent4 in two and a half days4 ,yet three days had to elapse before the remaining #g per cent4 of total moisture was lost--i4e41 before the rubber was judged to be ready for packing4 ,it will be seen that after this stage had been reached the rubber alternately lost and gained in weight1 with a tendency to increase4 ,this increase was attributed to the presence of surface moisture after hanging overnight1 when the rains had become frequent4 ,some light is thus shed upon a subject which has puzzled both shippers and receivers of crepe rubber4 ,,differences ,,in ,,weight4--,it will be obvious that if rubber is allowed to hang after becoming dry1 and is taken down1 packed1 and weighed in the early morning1 it will weigh more than when it reaches a drier climate4 ,the loss in weight under such circumstances might amount to even #a per cent4 ,it may seem to some an unnecessary refinement to introduce1 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 correct4 ,it is extremely singular to note how quickly the curve changes its slope after the major portion of the moisture has evaporated1 and it will be very plain that in the last stages any decrease in weight during the day would appear to be counterbalanced1 or more than counterbalanced1 by the addition of moisture during the night4 ,it may be pointed out1 however1 that this increase in weight during the later stages of drying of pale crepe is mainly1 if not altogether1 due to surface moisture4 ,the chief point of interest is the fact that in the case of thin pale crepe1 quite #hj per cent4 of the total moisture content is lost during the first two or three days1 and that1 owing to the negative influence of the night atmosphere1 the final drying is delayed4 ,it will be understood that the foregoing results applied to thin pale crepe4 ,thin lower-grade crepes appeared to dry at more uniform rates1 but the differences between the rates of drying at night and during the day were similarly notable4 ,,aids ,,to ,,normal ,,air-,,drying4--,these experiments were undertaken in a drying-house1 favourably situated for rapid drying1 in which the average period of drying for thin crepes is nine days4 ,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 trees4 ,in extreme cases of this nature the use of large fans and heating pipes has been advocated4 ,it is believed that in some cases these installations have given satisfaction1 but that in others the degree of improvement obtained has not been in economic proportion to the outlay incurred4 ,,smoke-,,curing ,,of ,,sheet ,,rubber4--,it will have been evident that one of the disadvantages of air-drying sheet is the incidence of moulds4 ,now it is found that moulds should not develop in smoke-curing2 and if they do1 then the smoke-curing has been insufficient or inefficient4 ,the difference in the drying period also is a strong argument in favour of smoke-curing1 so that all-round it is seen that there are many valuable advantages to be gained by smoke-curing sheet in comparison with air-drying1 and no disadvantages4 ,the manipulation of the rubber1 after it leaves the marking rolls and preparatory to smoke-curing1 has been discussed in ,chapter ,,ix4 ,it is sufficient only to allow adequate time for furnace water to drip from the sheets before transferring them to the smoke-house4 ,as it is the general rule to roll sheet rubber in the morning1 this arrangement fits in very well4 ,the furnaces of the smoke-house are usually extinguished as soon as the sun is well risen1 and the rest of the day is occupied in sorting dry sheets1 etc4 ,towards noon the day's wet sheets should have been admitted1 and smoking may be commenced as soon as the sun is well in the west--say1 at half-past four o'clock or earlier4 ,it used to be the custom on a few estates to smoke during the daytime and to discontinue smoking at night4 ,as the night-air in ,malaya is usually heavily laden with moisture1 it will be plain that such a policy was a topsy-turvy one4 ,it is vastly more reasonable to smoke-cure at night2 usually the heat of the sun during the day is quite sufficient in itself to promote the drying of rubber2 but there is no reason why smoking should not be carried on in the daytime in wet weather1 should it be found expedient to do so4 ,,recording ,,instruments4--,during the night the care of the smoke-houses is usually in the hands of natives1 except for occasional surprise visits from a ,european superintendent4 ,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-house4 ,ordinary thermometers are quite unsuitable1 and even thermometers registering maximum and minimum temperatures are of little avail1 inasmuch as they record only the degree of heat attained at a particular moment1 and do not indicate any period during which a particular temperature was maintained4 ,it is evident that something more informative is required4 ,there are many types of suitable recording instruments or pyrometers1 some of which can be electrically connected1 so as to cause the ringing of a bell1 placed in the superintendent's office or house1 on the attainment of a certain temperature4 ,the type best known in estate practice is that named the ,thermograph1 in which a pen traces a curve or graph on a plotted piece of paper carried by a rotating cylinder which is actuated by clockwork4 ,such instruments can be purchased through most of the local firms dealing in estate supplies4 ,from experience it can be asserted that1 given intelligent attention1 these instruments yield very satisfactory results4 ,the apparatus should not be placed always in one position in the smoke-house1 but should be moved frequently so as to obtain information regarding the distribution of heat4 ,,temperature ,,of ,,smoke-,,curing4--,in the question of temperature of drying1 it is well to be as strict as possible2 not that any great harm will result from a rise of #aj deg4 above that recommended1 but because the higher the temperature recorded the larger the fires must have been1 and consequently the more real danger there was of the store becoming ignited4 ,it has been shown#ad that the temperature giving the maximum benefit of drying and quality was found experimentally to be rather above the temperature usually prescribed for smoke-houses1 but in the experimental work there was no danger from fire4 #ad ,preparation of ,plantation ,rubber1 ,morgan1 #aiac1 chapter x4 ,the figure given in previous publications as a maximum working temperature for smoke-houses was #aaj deg4 ,f41 but certainly the temperature may be as high as #acj deg4 if it is considered safe to allow fires to be so arranged4 ,one or two estates are known to work at temperatures of #acj deg4 ,f4 and over1 in spite of the recommendations of the writers4 ,if those estates care to risk it they may do so1 with increased rapidity of drying2 but no responsibility can be taken for whatever may happen in smoke-houses where the temperature is allowed to remain1 as in one case1 at #afj deg4 ,f4 ,naturally the range of temperature is strictly limited by the properties of the substance to be treated1 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 commodity1 apart from the consideration of the possible destruction of the building4 ,,period ,,of ,,drying4--,considerable differences are noted in the periods of drying on various estates2 but1 as there is more than one factor influencing the results1 it is not easy at first to find why these differences should exist4 ,really there are three factors3 7#a7 ,relative thickness of rubber4 7#b7 ,extent and quality of rolling4 7#c7 ,temperature of drying4 ,it is presumed that the smoke-houses are identical in type and efficiency1 and that smoking is in force for the same length of time each day4 ,there need be no discussion of these points2 the effect of each is so obvious4 ,the thinner the sheet1 the quicker the rate of drying2 the better the sheet has been rolled1 the shorter the period of drying2 the higher the temperature1 the more rapid the drying4 ,it has been shown in ,chapter ,,ix4 that the condition of the sheet after rolling depends primarily upon the standard of dilution of the latex and the original thickness of the coagulum4 ,if these factors are correctly controlled1 the rolling should give a sheet which is fairly soft and porous--i4e41 it should not have been subjected to such pressure as to make it both thin and hard4 ,an average sheet of rubber which has been well rolled should be smoke-dried at a temperature of #abj deg4 ,f4 in about ten days4 ,if sheets take appreciably longer to dry1 then the three foregoing factors must be examined4 ,on the other hand1 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 days4 ,it frequently happens in such cases1 however1 that the smoking is insufficient1 and by the time the rubber reaches home it has begun to show signs of surface moulds4 ,it is evident1 therefore1 from this discussion that3 7#a7 ,if smoked sheet develops surface moulds within a short period after smoking1 the duration of curing has been insufficient1 or the quality of the smoking is at fault4 7#b7 ,the actual time taken to smoke-dry rubber may be insufficient to smoke-cure it4 7#c7 ,the rate of drying of smoked sheet depends upon-- 7a7 ,the relative thickness of the rubber4 7b7 ,the preliminary treatment of rolling4 7c7 ,the temperature of the smoke-house1 and 7d7 ,the type of smoke-house used4 ,this point will be treated in a subsequent chapter4 ,,fuels ,,for ,,smoking4--,the general idea formerly held was that the beneficial effects of smoking were to be attributed to the constituents of the smoke1 and chiefly the creosotic substances4 ,this is not now the opinion of the writers1 who attribute the effect largely to the temperature of drying and constituents of the smoke other than creosotic substances4 ,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 odour1 but it is becoming increasingly known that the employment of substances rich in creosote is not required or desirable4 ,estates used to be put to considerable expense in the purchase of bakau 7a mangrove timber rich in creosote and creating much heat71 under the idea that it was the best material and almost indispensable4 ,most estates now restrict themselves to the consumption of timber obtained from their own areas4 ,thinning-out programmes are largely responsible for the supply1 but the local authorities are much concerned regarding future supplies2 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 future4 ,this seems to be desirable1 as it is difficult to imagine that the place of timber can be taken by any other material in the smoke-curing of rubber4 ,unless some such precautions are taken it is not difficult to predict that1 in course of time1 some estates will be able to continue the preparation of smoked sheets only at considerable expense in obtaining suitable fuel from a distance4 ,it is not true that any kind of timber is suitable as a fuel to be used in a smoke-house4 ,all timbers are suitable1 either alone or in mixture with others1 provided that the wood is not too green4 ,naturally an absolutely dead and crumbling wood will smoulder1 but does not develop sufficient smoke4 ,a green timber will give an acrid and moist smoke1 but demands the consumption of a certain amount of dry timber in addition if it is to be used4 ,rubber-tree prunings and sawn rubber trees obtained by thinning-out may be used in mixture with dead wood1 provided the logs are stacked to dry in the sun for some weeks before use4 ,if the timber is too green1 steam is formed as well as smoke1 and the sheets of rubber may have a moist surface glaze4 ,,sun-,,drying ,,sheet ,,rubber4--,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 holdings4 ,from what one has learned of the extraordinary care which must be exercised in all the processes of rubber preparation1 one fails to understand how such rubber reaches the market without becoming tacky4 ,that some of it does become slightly tacky is certain1 but on the whole native rubber1 though crudely prepared1 is usually sound4 ,the native idea of giving sheet rubber a preliminary drying in the sun is to hasten the total period of drying4 ,that the period is curtailed would seem to be the case1 but it is open to doubt1 as the effect of sun-drying1 if unduly prolonged1 is to create a thin surface film of dry rubber which retards the drying of the rubber below the surface4 ,working with wet crepe rubber1 the writer found that1 to all external appearances1 there was no effect upon the rubber when it was allowed to sun-dry for four or five hours4 ,with periods of from six to ten hours the crepe becomes slightly sticky1 chiefly on that portion across the support4 ,when removed to the air-drying house this tackiness developed further1 and the rubber1 on the line of support1 became so weak that it stretched and broke4 ,reasoning by analogy1 it would appear that no apparent harm would result to sheet rubber from sun-drying for periods up to four or five hours4 ,from experience 7see ,chapter ,,ix471 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-curing4 ,,artificial ,,driers ,,for ,,sheet ,,rubber4--,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 way4 ,the practice was found to be impossible1 as the length of time required and the temperature were responsible for the destruction of the form of the rubber2 it became tacky and semi-liquid4 ,,the ,,chula ,,drier4--,although several suggestions of devices for artificially drying sheet have been made1 only one is known to be in use at the present time4 ,in the original form this was used for drying other tropical products4 ,it consists of a large iron chamber1 in which are several compartments divided by means of baffle-plates4 ,at one end there is a small furnace and1 by means of a fan1 smoke and hot air are drawn through the compartments4 ,owing to the temperature attained 7#adj deg4 to #afj deg4 ,f47 sheet rubber cannot be completely dried in the chambers1 and is1 as a rule1 only treated in this manner for one or two days4 ,drying is then completed in an ordinary air-drying house4 ,it is claimed that drying is expedited1 and that the rubber can be packed in ten days4 ,in the more recent modification1 the smoke and hot air which leave the ,chula drier pass through a large room in which may be hung either sheet or crepe rubber4 ,it would seem that all sources of danger have not been eliminated from the process1 as on one estate a wooden room containing rubber was ignited by a spark which passed through the drier4 ,yet another form exists in which the furnace is outside the main building1 and in the ordinary course of working only heats a series of open pipes through which air is drawn by a powerful fan4 ,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 rubber4 ,the hot air or smoke is distributed in the lower room by means of main and branch pipes1 and passes through an open floor to the room above4 ,with such an arrangement it is possible1 therefore1 to prepare either air-dried or smoke-cured rubber4 ,if the method could be successfully applied to the drying of crepe it would be of great assistance on some estates4 ,there would seem to be a difficulty in working it for the drying of sheer rubber and crepe together1 as the temperature suitable for the one is excessive for the other4 ,given an efficient control over the temperature of the hot air1 the house should be successful in the drying of crepe1 provided the rubber is not hung in folds of too great length4 ,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-house1 but it is not clear that such a system would have any advantage over a modern smoke-house1 in types of which rubber can be fully cured in periods ranging from five to ten days4 ,,chapter ,,xii ,,sorting1 ,,grading1 ,,and ,,packing ,the question of standardising the output of our plantations is one which has occupied attention for some years1 with a not inconsiderable degree of success4 ,meanwhile opinion is growing in favour of proceeding along the line of reducing the number of plantation grades to a minimum4 ,at present some confusion exists4 ,some estates make up tree-scrap and bark-shavings together2 one estate puts tree-scrap1 earth-scrap1 and bark-shavings into one uniform crepe2 other estates have three or more separate scrap grades--e4g41 lump-rubber and washings1 tree-scrap1 earth-scrap1 and bark-shavings scrap4 ,there is a movement on foot at present to try to restrict plantation rubber to three grades3 ,,crepes--#a4 ,first ,quality ,latex4--,i4e41 crepe made from the true coagulum obtained from the regulated coagulation of strained latex4 ,this is a pale rubber1 and may be prepared satisfactorily if the directions given in preceding chapters are followed4 ,naturally there must be1 in all factories1 some defective rubber of this grade4 ,for various reasons the crepe may be of inferior colour1 or is slightly contaminated with dirt or traces of oil and grease1 etc4 ,this defective rubber should be placed aside most rigorously and plainly marked as off-quality4 ,if a proper scheme of standardisation of latex and chemicals is followed1 there should not be any such variety in shades of colour1 such as was common in ,no4 #a crepe in the past4 ,comparatively few estates in ,malaya now prepare thick 7or blanket7 crepes in the ,no4 #a grade1 but in such cases the same rules must be applied as govern the sorting of thin fine pale crepes4 #b4 ,compound ,crepe1 ,no4 #a4--;,in this it is proposed to include cup-coagulated lumps1 coagulated lumps from transport vessels1 skimmings1 bucket rinsings1 cup-washings1 and tree-scrap4 ,it has been shown in ,chapter ,x4 that strict care is necessary to eliminate all oxidised 7dark7 scraps4 ,these are relegated to a lower grade4 ,the possession of a scrap-washer is necessary if the best results are to be obtained4 ,on some estates the ingredients of this compound crepe1 while fresh1 are placed in a common jar or tank to which a quantity of sodium bisulphite 7#a per cent4 solution7 and acid are added4 ,the resulting conglomerate mass is cut up for working4 #c4 ,compound ,crepe1 ,no4 #b4--,this grade would include the remaining lower grades--viz41 bark-shavings1 scrap1 and earth-rubber scrap4 ,,reduction ,,carried ,,too ,,far4--,however desirable it may be to diminish the number of grades1 it must be pointed out that diminution and simplification are not necessarily synonymous terms in this matter4 ,it is well known that on estates where the earth-rubber is only brought in at lengthy intervals1 say of a week1 the resulting crepe is sometimes very tacky4 ,this is only natural1 and is due to the prolonged exposure to the sun's rays4 ,with the improved machinery now at our disposal1 and with the increasing attention which will be given to the lower grades in the future1 it is possible to prepare from average bark-shavings crepe free from bark1 and of quite a good colour4 ,where trees are not scrapped before tapping1 there would seem to be no objection to amalgamating the rubber obtained from the bark-shavings with the ,no4 #a ,compound crepe2 and it would be a distinct danger and possible loss if this good rubber were to be mixed with earth rubber4 ,the liability of the latter to become tacky is well recognised2 and if possible it should be maintained as a separate grade1 in which it would be permissible to mix only rubber obtained from actually dry shavings from scrapped trees1 or heavily-oxidised scraps which have been rejected from other grades4 ,,sheets4--,broadly there are no fine distinctions to be made at present in the grading of smoked-sheet rubber2 it is either ,no4 #a1 or if any so-called defect is visible the sheets must be rejected and plainly marked as off-quality4 ,clippings 7trimmings7 may either be made into crepe or shipped under their own description4 ,,rubber ,,growers' ,,association',s ,,recommendations4--,taking the foregoing arguments into full consideration1 it would seem that1 strictly speaking1 the number of grades cannot be reduced to less than four at present without producing some amount of confusion4 ,in its handbook1#ae the ,rubber ,growers' ,association remarks3 #ae ,preparation of ,plantation ,rubber1 #aiag4 ,the fewer grades the better1 and regularity of each grade is most important4 ,the grading should be as follows3 7,no4 #a7 ,fine crepe 7or ,no4 #a sheet71 made from the free or liquid latex4 7,no4 #b7 ,clean light brown crepe1 made from lumps and skimmings4 7,no4 #c7 ,scrap crepe1 made from tree-scrap4 7,no4 #d7 ,dark crepe1 made from bark-shavings1 earth rubber1 and the lower quality of scrap4 ,tacky rubber should be packed separately4 ,compound ,scrap ,crepe4--,estates using scrap-washers should make a compound crepe of grades ,nos4 #b and #c1 which will make one compound free from bark and specks4 ,all rubber intended for ,no4 #d should be most thoroughly washed4 ,concerning these recommendations the remarks in preceding paragraphs should be studied4 ,,care ,,in ,,sorting4--,whether dealing with smoked-sheet1 pale crepe1 or lower grades1 the strictest care is necessary in sorting and grading4 ,this work must of necessity be relegated to coolies1 and they should be trained men4 ,instructions must be definite1 and doubtful specimens of rubber should always be placed aside for the decision of the ,european superintendent4 ,any pieces showing unmistakable signs of what are regarded as defects should be stringently rejected4 ,in the case of pale crepe1 when the defect is confined only to a small area it is permissible to cut out the affected portion4 ,similarly there can be no objection1 in the case of smoked sheets1 to an occasional sheet being treated in this manner4 ,on the majority of estates these rules are observed carefully1 but some estates yet have to learn that defective pieces of rubber may not be concealed in a bulk of otherwise good quality4 ,samplers have often an uncanny knack of hitting upon the defective specimens1 and it is entirely the fault of the estate's sorters if these pieces are submitted as being representative of the mass4 ,,choice ,,of ,,cases4--,consumers complain justly of the presence of chips1 splinters1 and wood-dust4 ,it will be evident1 therefore1 that whatever the type of case employed the interior surfaces should be smooth1 there should be no cracks or gaps in the timber1 and the cases should be cleaned out before using4 ,there remains great room for improvement in the means and method of packing1 and in spite of suggested alternatives we are at present restricted to the use of wooden cases4 ,from comparisons of actual quality and fulfilment of the requirements indicated above1 there can be no question that cases made of three-ply wood1 such as the ,venesta1 are in every respect superior to the ordinary wooden cases of ,momi type4 ,the consideration of cost and available supplies1 of course1 enters largely into the question1 and three-ply cases are not at present so largely employed as they deserve to be4 ,a new type of case was recently exhibited in ,singapore4 ,it emanates from the ,u4,s4,a4 and is made of a fibrous material1 resembling in appearance a very stout cardboard4 ,the complete case when assembled consists really of two boxes1 one of which is inverted and slides down over the other4 ,packing is completed by means of stout wire1 which is strained by a simple ratchet arrangement4 ,it is claimed that from #bbe to #bej lbs4 of rubber can be contained4 ,other claims made amount to the statement that the case is practically indestructible under normal conditions of handling and shipping4 ,a demonstration given certainly appeared to substantiate the statement fully4 ,rubber packed in cases of various and average type was allowed to fall from a height of about twenty feet4 ,in all instances the wooden cases of every type were either smashed or badly burst1 whereas the fibre cases were merely dented4 ,these cases are obtained in flat sections1 which1 in assembling1 are folded and clamped by means of copper rivets in a special but simple machine4 ,it was pointed out that objection might be lodged against the use of copper for this purpose4 ,more recently there is announced a new packing case which is stated to be made from low-grade rubbers1 but information is rather vague4 ,,bags4--,there are in local use stout canvas bags which have the advantage of being used many times1 as long as they are waterproof and kept in good dry condition4 ,their employment for the conveyance of smoked-sheets would appear to be permitted1 but crepe rubbers sent in them are often reported upon as being massed at the edges1 and hence difficult to sample4 ,,bales4--,attempts to bale rubber for the market have been frequent1 but no success seems to have attended the efforts4 ,in some quarters the failure has been ascribed to prejudice on the part of buyers1 but it is the opinion of the writers that the objections to baling are1 or could be1 well-founded4 ,massed rubber often cannot be inspected properly1 and hence is always open to suspicion that internally there may be unsuitable portions4 ,there have been several schemes put forward for winding crepe rubber on spindles so as to form a cylindrical package complete in itself4 ,we have seen the process1 and certainly the method had much which appeared commendable4 ,apart from other objections which might be raised1 there is always the one prominent objection mentioned in the preceding paragraph4 ,while baling of rubber is thus not likely to suit the general market1 there is no reason why1 as in one or two instances1 it should not be practised by agreement between producer and consumer4 ,it is believed that slab rubber is shipped in bales from ,sumatra to the ,u4,s4,a4 ,quite recently a proposal has been put forward to revert to a simple form of baling for ordinary plantation rubber4 ,under this scheme wooden cases are discarded1 the packing material being composed of scrap-grade crepe rubber which1 it is claimed1 could be put to use by the manufacturer4 ,an obvious drawback would be evident if these bales happened to be exposed to direct sunlight or a continuous high temperature4 ,the tackiness which might supervene would make the handling of such bales unpleasant1 even if it did not affect the internal rubber4 ,,folding ,,for ,,packing4--,in the packing of smoked sheets it would appear to be advisable to avoid1 if possible1 the folding of any pieces1 as the objection is made that such rubber is difficult to sample on arrival1 especially in cold weather4 ,sheets should be prepared or cut to such length that they occupy the full superficial area of the box1 either singly or side by side4 ,illustration3 ,a ,,shipment ,,of ,,rubber1 ,,packed ,,and ,,ready ,,for ,,transport4 ,the same remark applies to the packing of crepe rubbers1 except that here we deal with units of folded rubber4 ,crepes are generally folded by hand1 and coolies usually work to a certain dimension by means of a standard stick4 ,the work is slow1 but often gives employment1 at a cheap rate of pay1 to women and weak coolies4 ,several machines have been invented to replace this labour4 ,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 case4 ,it is called the ,senang folder1 and is made by the ,general ,engineering ,company 7,radcliffe7 ,ltd41 ,radcliffe1 near ,manchester4 ,,care ,,in ,,assembling4--,whatever the type of case employed1 great care must be given to the assembling of parts and the final fastening4 ,it is not uncommon to find in the operation of putting on the strapping that nails have been driven into the rubber4 ,extra bands of strapping are sometimes advised1 and where these bands pass over the sides 7not edges7 of the case only specially short nails should be used4 ,all wood should be planed1 and in cases other than three-ply should be of stout wood1 not less than #e_/h inch in thickness4 ,all timber used should be of uniform type and thickness4 ,,methods ,,of ,,packing4--,the usual method of packing crepe is to fold the lengths to some measure of the dimensions of the case4 ,this is done in a haphazard fashion on some estates1 with the result that either space is lost or the packing is badly arranged4 ,some ingenuity can be displayed in the packing of sheet rubber in order to avoid folding the sheets1 which1 besides increasing the difficulty of sampling1 leads to loss of space4 ,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 packing4 ,a few estates employ tanks of such calculated dimensions as will yield uniform sheets which pack flat and fill the superficial area of the case4 ,in view of the contamination which sometimes characterises the employment of wooden cases it is sometimes advised that the interior should be lined with sheets1 or pieces of crepe1 the ends of which are later folded over the top of the mass4 ,in this manner it is stated that contamination is confined only to the exterior of the contents of the case4 ,,weight ,,of ,,contents4--,the dimensions of average cases are #ai inches by #ai inches by #bd inches1 giving a capacity of #e cubic feet4 ,in these it is possible to pack #aej lbs4 of crepe rubber and #bjj lbs4 of sheet rubber 7about #e per cent4 more in cases of three-ply wood74 ,it may be noted that boxes arrive in better condition when fully packed4 ,the foregoing figures are not adhered to strictly4 ,for example1 some estates find it expedient to ship rubber in actual ton lots1 and for this purpose pack only #adj lbs4 of crepe per case1 giving sixteen cases to the ton4 ,other estates1 using presses1 pack more per case than the quantities noted above4 ,at present there does not appear to be any definite regularity in practice4 ,illustration3 ,,on ,,its ,,road ,,to ,,the ,,railway3 ,,bullock-,,cart ,,transport4 ,in all instances it should be the invariable rule that the rubber should be weighed before packing1 and that all cases should contain uniform nett quantities of any particular type of rubber4 ,invoicing1 etc41 will thus be greatly facilitated4 ,if these practices are followed1 and the rubber always weighed on the same scales 7assuming it to be perfectly dry when packed7 complaints of short-weight should be infrequent4 ,,short ,,weights4--,in some cases the occurrence of short weights on arrival at ports would appear to be inexplicable4 ,it often happens that the constituent parts of wooden cases have been in stock for a considerable period4 ,if for no other reason than that indicated below1 all cases1 either before or after assembling1 should be thoroughly dried in the sun4 ,short weight could be accounted for to some degree by a lack of observance of this elementary rule1 as it is most probable that there would be a perceptible difference in weight of the wooden case in a drier atmosphere4 7a7 ,if rubber is weighed in the box1 and the average tare of the case deducted from the gross weight 7in order to obtain the nett weight71 any loss in the weight of the timber would appear as a deficiency of rubber at the distant port4 7b7 ,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 warehouse4 ,if the rubber is weighed in the box1 any observed deficiency would be attributed to a loss of weight in the rubber4 ,,part ,,iii ,,machinery ,,and ,,buildings ,,chapter ,,xiii ,,machines ,the number of manufacturers of machines for preparing rubber would seem to be on the increase1 and there can be little doubt that this competition will result in a continued improvement in the design of machines4 ,it cannot be denied that there has been room for such improvement1 and it is believed that manufacturers will display judgment in putting only their best quality into the work4 ,while design and finish are very excellent in their way1 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 quality4 ,generally1 the complaint seemed to be that the rolls were too soft1 and that the grinding effect was far too great4 ,the damage to pale rubber in such cases is considerable1 as it is impossible to keep the rolls free from fine dark powder4 ,the effect is generally noticed more in the smooth rolls with which a finish is put upon the crepe4 ,cases have occurred frequently in which rolls have been returned1 because of the injury caused to pale rubber1 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 involved4 ,it is a moot point1 however1 in many instances how far the quality of the rolls is actually responsible for the damage done to the rubber4 ,in the experience of the writers it is certain that complaints regarding the rolls were unjustifiable1 and that the injury had been caused by carelessness in the feeding of the machine4 ,especially in the case of smooth finishing rolls1 it is clear that if the rolls are allowed to run idle for more than the briefest possible interval grinding must take place4 ,the complaints apply not only to the rolls themselves1 but also to the brass linings for shaft-bearings4 ,cases are known in which a brass liner was so worn within a few weeks as to be quite useless4 ,if the matter ended there it would not be so bad2 but there is always the possibility of particles of brass finding their way into trays1 and so into the rubber4 ,the damage which ensues to the rubber is quite irreparable4 ,this particular defect arising from the presence of brass will be dealt with in a later chapter4 ,but here again it is necessary to point out that such wear on brass liners may be caused by the standards 7ends7 of the rolls being eccentric2 and the case may be analogous to the placing of new wine in old bottles4 ,en passant it may be remarked that in any case brass liners are not strictly necessary4 ,white-metal alloys are in use on rubber machines1 and cast-iron bearings have been employed satisfactorily for years4 ,it would be well for managers to remember1 therefore1 that when machines have to be ordered1 nothing but the best is good enough1 and that the difference between good machinery and passable machinery is probably immensely greater in effect than any saving in expenditure would warrant4 ,,adequacy ,,of ,,machines4--,in general1 the factories which prepare sheet rubber are usually equipped with adequate machinery4 ,this arises from the fact that machines are necessary for preparing all grades below the first1 even if they are not necessary for the making of sheet4 ,thus all the necessary macerators and finishing machines are installed1 but the major part of the output is in sheet form4 ,for the preparation of sheet1 no heavy machinery is required2 all that is necessary are light machines for rolling the sheets and expressing as much moisture as possible4 ,to obtain a pattern on the sheet1 another light machine may be used4 ,it may be imagined1 then1 that the work of rolling sheet rubber by power machines is small1 and that a large quantity of rubber can be worked off in a comparatively short time4 ,it follows1 therefore1 that the preparation of the lower crepe grades can be proceeded with at once1 and that the whole work of the factory is expedited4 ,the case of factories which have to prepare all first-grade rubber in crepe form is quite different1 especially when thin rubber has to be made4 ,the care which has to be exercised in preparing pale crepe rubber is very great in comparison with what is demanded by sheet rubber4 ,the rubber has to go first through the uneven-speed macerators1 from there to the intermediate rollers1 thence to the finishing rollers4 ,considerable ingenuity has to be displayed in the arrangement of the machines1 so that one section will not work faster or slower than another4 ,more often than not1 the attempt to arrive at such a desirable arrangement fails1 owing to an insufficiency of machines4 ,such a statement will probably read strangely to the uninitiated2 but an example will make it plain4 ,a factory may have a battery of six machines1 one only of which is a finishing machine 7smooth rolls74 ,with five macerators and intermediate machines working continuously1 it will be more than the work of one finishing pair of rolls to keep pace1 especially as so much more care has to be exercised in finishing than in rough crepe-making4 ,the obvious course to adopt is to substitute a pair of smooth rolls1 with suitable gear ratio1 for a pair of macerators or intermediates4 ,if1 however1 the macerators and intermediates are already fully occupied the whole of the time1 any such change would be of small benefit4 ,what is really needed in this case is more machinery4 ,it might be pertinently asked what constitutes an adequate equipment of machines for crepe-making4 ,the writers cannot give a number1 but have no hesitation in stating that if a factory cannot complete its whole day's work before dark1 it is inadequately equipped4 ,no work should be done after dark1 if possible1 as it cannot receive the supervision which crepe-making demands4 ,to make comparison between the number of machines in any two factories and their respective outputs is not sound argument1 as the out-turn of two similar machines will depend upon the speed at which the rolls travel--i4e41 the gearing between the machines and the engines4 ,thus1 while one machine will out-turn #dj lbs4 of crepe per hour1 another may only have an output of #cj lbs41 although the machines may be identical in pattern4 ,to make calculations based on a rate per hour for any known make of machine1 and to apply those calculations to the existing machinery in any factory1 in an attempt to judge whether there is a sufficient number of machines1 would be a mistake1 unless one were also supplied with the relative speeds at which the rolls work4 ,finally1 on the question of adequacy of machines1 it must be pointed out that an insufficient number of machines must result in a poor product1 since all rolls have to be used for all grades4 ,even with the greatest possible care it happens that pale crepe is sometimes spoiled because it is contaminated with foreign matter1 resulting from the working of lower grades on the same machines4 ,this is one of the great arguments in another direction for the installation of a scrap-washer4 ,in conclusion1 the writers can only give their opinion that one must not decide the question of adequacy by the number of existing machines1 but by the time taken each day in working off the rubber1 providing one can be satisfied that the best arrangement of the existing machines has been made4 ,,ideal ,,arrangement4--,as to what this best arrangement may be1 guidance can be obtained from the results of experience here given4 ,it must be premised that the output of any factory preparing fine pale crepe is limited by the output of the smooth finishing rolls4 ,broadly1 it will be recognised that if there is any excess of capacity in a battery it should be found in the smooth-roll machines4 ,this sufficiency1 or excess of capacity1 may sometimes be attained by an alteration in the gearing of the drive of the rolls from the back-shaft1 or by an addition to the number of machines4 ,in the former case1 there are practicable limits of speed1 beyond which the second alternative measure must be adopted4 ,,speed4--,the usual speed at which the back-shaft travels ranges from #fj to #gj revolutions per minute4 ,taking first the macerating machines1 the intermediate gearing between the shaft and the rolls should give a driving speed of about #bj revolutions per minute on the faster-travelling roll4 ,this is equivalent1 with a #ae-;inch diameter roll1 to a peripheral speed of about #fj to #fe feet per minute4 ,the intermediate and smooth rolls can be arranged to travel more quickly1 but the maximum comfortable speed for proper feeding and control appears to be about #be revolutions per minute on even-speed rolls4 ,in view of the fact that the rubber at each successive machine becomes longer and thinner1 it will be seen that a smooth-roll machine could not cope with the output of a macerator in the same period of time4 ,if1 therefore1 the macerator is fully occupied for the greater part of the time1 an additional smooth-roll machine must be installed1 even though the existing one has been speeded up to practicable limits4 ,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 7i4e41 differentially geared71 as opposed to the smooth rolls on which the cog-wheels are usually of the same size 7i4e41 even speed74 ,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 above2 in the smooth rolls a squeezing action only is effected4 ,to give an idea of the ratio of the speeds of the rolls in each machine in a typical working battery1 the following particulars may be noted3 ,,gear ,,ratios4-- ,machine4 ,differential ,ratio4 #a4 ,macerator #cb-ag #b4 ,intermediate 7coarse grooved7 #cb-ag #c4 7fine grooved7 #cj-ai #d4 ,smooth 7uneven speed7 #cj-ai #e4 7finishing7 #be-bd #f4 7 7 #be-bd ,it will be seen that the so-called even-speed smooth rolls run at approximately the same rate4 ,it is advised that in all cases the gear wheels should be cut helically4 ,those who have experience of the noise of some batteries after they are slightly worn will appreciate such a remark4 ,,grooving ,,of ,,rolls4--,concerning the choice of grooving1 there is divergence of opinion1 some managers preferring one type1 which others reject in favour of another type4 ,provided any particular type can be shown to be as effective as required1 no necessity for laying down hard-and-fast rules seems to exist4 ,the following particulars serve to describe a battery well known to the writers1 and accustomed to produce the finest quality of thin pale crepe and lower grades3 ---------------------------------------- ------------------------- ,no4 of ,times ,machine4 ,grooving4 ,rubber passes through4 ---------------------------------------- ------------------------- #a4 ,macerator ,deep horizontal grooves2 square-cut1 #e_/af inch x #e_/af inch x #e_/h inch spaces #c #b4 ,intermediate ,horizontal grooves2 #c_/af inch x #c_/af inch x #c_/h inch spaces #b #c4 ,fine spiral grooves2 #a_/h inch x #a_/h inch x #a_/d inch spaces #b #d4 ,geared smooth ,nil #a #e4 ,even smooth #a #f4 #a ---------------------------------------- ------------------------- ,total #aj times ---------------------------------------- ------------------------- ,the actual rate of output of this installation is the capacity of the last smooth machine4 ,this is about #ahj lbs4 per hour1 while the output of the macerator is approximately double this amount4 ,thus the macerator only works for about half the time4 ,this applies also to the two intermediate machines4 ,after a study of the preliminary remarks1 it would not be difficult to suggest methods for improving the condition of affairs4 ,it would appear that1 in order to obtain a uniform rate of working in such a battery1 the relative peripheral speeds of the several machines should be--7#a71 7#b71 and 7#c7 #ajj2 7#d7 #aej2 7#e7 and 7#f7 #bjj4 ,the remarks on the practical limits of speed should be borne in mind4 ,in this case the smooth rolls travelled at #bc revolutions per minute4 ,as already stated1 it is not intended to lay down definitely that1 e4g41 horizontal grooving alone should be cut on macerating rolls4 ,some estates employ with satisfaction a deep square-cut spiral #a_/d inch by #a_/d inch by #a_/d inch or #a_/b inch spacing2 others use a large diamond pattern4 ,similarly various types of grooving are cut in the intermediate rolls4 ,illustration3 ,a ,,battery ,,of ,,machines4 ,on the left1 light marking rolls for sheet rubber2 on the right1 heavy machines for crepe preparation4 ,in the middle background1 scrap-washing machines outside the main building4 ,it has been remarked in the chapter dealing with crepe preparation that much depends upon the condition of the coagulum4 ,there is no necessity1 or desirability1 for having a standard higher than #b lbs4 dry rubber per gallon1 and it has been argued that it would be better to select a standard of #a-a_/b lbs4 ,the tougher the coagulum1 the more the power required1 and the slower the rate of output of the leading machines4 ,in ordering machines for crepe-making1 only large rolls should be considered--e4g41 rolls having a diameter of #ab inches to #ah inches and from #ae inches to #ah inches face4 ,,rolls ,,running ,,hot ,,or ,,free4--,if the rolls are found to become hot1 work on that machine should be stopped1 and an examination made1 otherwise there is the possibility of the crepe becoming sticky and tacky when dry4 ,although comparatively cold water may be flowing upon the rubber and the rolls1 little alleviation may be noticed1 inasmuch as the source of heat lies generally at the bearing ends of the rolls4 ,this may be tested by placing the hand on the top of the standard of the machine4 ,the development of the heat may be due to lack of lubrication1 worn bearings1 or sometimes faulty setting-up of the machines4 ,allusion has been made to the necessity for avoiding the running free of rolls--i4e41 in the absence of rubber4 ,the grinding of the rolls1 when working close together1 produces a fine powder1 which causes a more or less pronounced deposit on pale crepe4 ,when the rolls have been in action for some time and become slightly worn1 this deposit may be confined only to the edges of the rubber4 ,,sheeting ,,machines4--,the foregoing paragraphs have dealt entirely with machines for crepe preparation4 ,concerning machines for use in sheet-making1 the ground has been mainly covered in ,chapter ,,ix4 ,where both crepe and sheet are made1 it is permissible and advantageous to use the heavy smooth rolls for the rolling of the sheets1 and it is only necessary to instal one or two light machines for placing a pattern on the rubber4 ,where a heavy battery does not exist1 light machines with smooth rolls may be employed satisfactorily4 ,even engine-power is not necessary for the preparation of excellent sheets1 but the output is limited where hand-power only is employed4 ,estates are known on which upwards of #a1jjj lbs of sheet rubber are made daily with hand-power machinery in one station4 ,beyond this figure1 it is deemed advisable to instal a small engine1 say of #g-i horse-power4 ,this is ample to drive a battery of three smooth-roll machines and two markers1 and yet have sufficient reserve to actuate a small pump for the water supply4 ,,lubrication ,,of ,,machines4--,it must always appear to those inexperienced in engineering matters that existing methods for lubricating rubber machinery are distinctly crude1 when one considers the delicacy of the material to be prepared4 ,many existing machines are still lubricated with oil1 which has to be administered in generous quantities4 ,generally1 such machines have been so designed that the excess of oil may find an easy passage into the tray which receives the rubber4 ,if not1 it drops just outside the tray to the floor1 and is washed away in great gouts4 ,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 rubber4 ,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 devised4 ,it is probable1 however1 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 lubricators4 ,coolies should not be allowed to handle them1 and the responsibility should be placed upon a foreman or the engine-driver4 ,,trays4--,the most unsuitable and damage-causing part of the vast majority of machines1 without doubt1 is the tray4 ,on nearly all machines the tray is wider than the effective portion of the rolls1 so that any excess of lubricant may drop into it4 ,on others1 not only is the tray wider than the rolls1 but its edge either is in contact with the shaft of a roll or just a small distance away4 ,the edge of the tray is thus favourably situated for acting as a wipe1 and the lubricant is transferred to the inside of the tray4 ,considering that the effective portion of rolls is about two-thirds of their length1 it must be unnecessary to have trays wider than the length of the rolls4 ,for the preparation of fine crepe trays are quite superfluous1 and their place can be taken by a narrow piece of board if required4 ,if the bed of the machines has been covered with glazed tiles1 even a piece of board is not necessary4 ,where trays have been removed from the fine-crepe rolls on a number of estates1 a marked decrease in the number of spoiled pieces of rubber has resulted4 ,it must be recorded that the foregoing paragraph appeared in our #aiac publication4 ,after a lapse of over seven years1 the remarks remain as true as when originally written4 ,one of us is continually meeting with cases in which the defects are plainly attributable to the cause indicated above1 and the fault often lies with the management of estates4 ,on most machines the trays are not fixtures1 and could be removed if desired4 ,,arrangement ,,of ,,machines4--,in considering the future arrangement of machines1 the first care should be to see that machines and windows are to be found together4#af ,of all the factory operations1 rolling of rubber should be given the maximum light4 ,at the same time it would not be advisable always to choose a southern aspect1 unless outside shades were supplied4 ,the best position for setting up machines1 therefore1 is along a wall having a number of windows4 ,this is extremely convenient also from the view of power transmission1 and gives the maximum free floor space to the factory4 ,in setting up machines1 foresight must be displayed1 otherwise one may find1 when future extensions are made1 that the extra machines may obstruct an entry or exit4 #af ,windows imply the existence of walls4 ,such is the conventional design of factories4 ,it may be pointed out that walls are not necessary4 ,the roof may be supported on pillars between which expanded metal of large size may be placed4 ,this fulfils all requirements and gives the maximum of light and air4 ,many new factories have been erected to such a design4 ,for the actual erection of machines1 no labour should be accepted without ,european supervision4 ,at present there are machines which are practically useless owing to faulty workmanship1 and on many machines bearings run hot for no apparent or explicable reason4 ,whether the fault lies with the turning of the rolls or the setting of the machine cannot be decided2 but at any rate too much care cannot be expended on the supervision of setting up machines4 ,there is no reason why everything in a factory should not be made as easy to clean as possible4 ,for this desirable condition all machines should have the beds faced with tiles4 ,a word of caution should be given against using marble slabs under the machines1 as they would be eroded in time by the slight amount of acid washed out of the rubber4 ,there would be no such objection against the use of white glazed tiles1 if they are well set4 ,,access ,,to ,,back ,,of ,,machine4--,in a few factories it has been noticed that the drainage of water from the machines runs to the front of them4 ,this means that the coolies are put to unnecessary inconvenience and discomfort1 and they often suffer from sore feet4 ,all water should drain to the back of the machines4 ,the necessity for seeing that these drains are kept clear might then induce those in charge to examine the back of the machines4 ,it is often the case that1 while the front of the rolls and tray are kept clean1 little attempt is made to cleanse those parts which are not visible or accessible from the front4 ,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 machines4 ,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 machines4 ,there should have been no occasion for such surprise1 for the back of the machines is quite as accessible to them as to the visitor4 ,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 makes1 such as ,shaw's1 ,bridge's1 ,robinson's1 ,bertram's1 ,walker's1 ,carter's1 ,iddon's1 etc4 ,this list does not include local manufacturers such as the ,united ,engineers4 ,it must not be imagined that their machines are not recommended4 ,as a matter of fact1 their machines compare well with those made at ,home4 ,it would be well to judge in the final decision upon-- #a4 ,cost4 #b4 ,the experience of those already using the machines4 #c4 ,simplicity of parts4 #d4 ,lubrication system4 #e4 ,mode of adjusting rolls4 #f4 ,fitting of trays4 ,,engines4--,it is not intended here to discuss particular makes of engines1 or even to attempt to lay down definite statements with regard to the type of engine4 ,without a full knowledge of local circumstances1 it is not possible to recommend whether the engine shall be oil-driven1 gas-driven1 or steam-driven4 ,assuming a copious supply of very cheap timber1 there could be no objection to the employment of a steam-engine2 but for most estates such a choice is out of the question4 ,again1 in deciding between oil and gas1 local economic factors must be considered4 ,suction-gas plants are now made1 in which a wonderful variety of refuse can be consumed in the production of gas1 whereas ordinarily estates are restricted to the use of either charcoal or anthracite coal4 ,both oil and gas driven engines are eminently suitable for the purpose of a rubber factory1 and the results obtained on different estates with either are often discussed in favour of one or the other4 ,the selection ultimately narrows itself down to one of cost of running1 in which availability of supplies becomes an essential feature4 ,,power4--,no matter what type is selected1 there should be made an ample allowance for margin of power4 ,the general experience of estates has been that when the first portion of the estate comes into bearing1 there is a desire to avoid great outlay1 which should really have been secured in the original capital4 ,the result has been that as later the estate expands1 the original power unit is found to be inadequate1 and a larger engine has to be purchased4 ,in a short while the original engine is found to be unsuitable even as a stand-by1 inasmuch as it is incapable of doing more than a portion of the work required4 ,this means eventually that another large engine is required4 ,had sufficient margin of power been allowed originally1 only two engines would have been bought1 as against the three indicated above4 ,without going into finer details1 it is usual to allow a rate of #aj horse-power per heavy machine used for crepe preparation4 ,in actual practice1 when a battery is working under full load1 the power demanded is about #f horse-power per machine4 ,thus a #ej horse-power engine running six machines and a scrap-washer is really running with only a small margin of power1 and if large pieces of hard coagulum are placed in the washer or the macerator there may be a sudden stoppage4 ,assuming an average estate commences with only three machines for crepe-making1 on an expanding programme1 allowance of power should be made for six machines and a scrap-washer1 if the purchase of larger power units is to be avoided later4 ,,chapter ,,xiv ,,factories ,,general ,,construction4--,on the question of general construction there is little to be said1 except that buildings are now being properly designed in more permanent form than were some of the earlier buildings4 ,on the whole there is little fault to be found with factories in general1 except in so far as the output has outgrown the accommodation4 ,most factories are now erected in iron1 but there are a few which are built of bricks4 ,it should be premised that a factory in which rubber is to be prepared should be as light and airy as possible4 ,in this respect quite a number of the older factories are lacking1 and they seem to have been designed to exclude as much air and light as possible4 ,under these circumstances1 the building is always dark1 there is always an air of dampness1 dirt may accumulate1 and there is usually a bad smell4 ,rubber prepared under these conditions is always liable to be below the high standard which should be attained1 and the general tone of the factory is depressing4 ,,plenty ,,of ,,light4--,the old idea that light must be excluded is now known to be erroneous2 so that in designing a factory1 provision should be made for ample light and air4 ,it should not be forgotten that in tropical climates1 iron buildings may become uncomfortably hot1 as most of our older factories are4 ,usually it will be found that the ventilation is imperfect4 ,there is a lack of window space1 and the roof is imperfectly ventilated4 ,the ridge of the roof should be opened up by means of a jack-roof1 so that the warm air rising naturally may escape at the highest point of the building4 ,these are defects which should be remedied in old buildings4 ,as a rule no rubber remains in the factory at night-time1 except in the form of coagulum1 the loss of any of which would be noted with ease4 ,the conventional idea of enclosing the factory with walls of galvanised sheeting1 wood1 or brick1 is not strictly necessary4 ,in modern buildings these walls are replaced by large-mesh expanded metal1 thus making the machine-room perfectly light and plentifully ventilated4 ,under such conditions1 dirt cannot accumulate unseen1 and the general tone of the work is raised4 ,,the ,,floor4--,the floor should be of thick concrete1 and have a good surface layer of cement4 ,preparations are now advertised for which claims are made that their employment renders the surface of such floors waterproof and dustproof4 ,if these claims can be substantiated when the use is applied to the floors of rubber factories1 the employment of a preparation of this nature should result in a considerable saving of expense and trouble4 ,preferably the floor should not be flat1 but should slope slightly from the longitudinal middle of the building to the sides on either hand4 ,if the floor is level it usually results in accumulation of water1 the cement breaks in patches1 and the factory always appears to be dirty4 ,,position ,,of ,,machines4--,all machines should be arranged adjacent to and parallel with one of the long sides of the building1 and should be raised about #f inches above the floor1 so that water may escape easily4 ,tanks for the reception of latex1 scrap rubber1 etc41 should be placed along the opposite wall to the machines1 and the intermediate length of the building should be entirely free from fixtures4 ,it was not uncommon in older factories to find the engine situated in the middle of the floor1 so that what with the space occupied by the engine1 and the space rendered unavailable by the belt-drive1 the real accommodation of the factory was sadly diminished4 ,in no modern factory should the engines be brought into the main room4 ,they should always be accommodated in a special compartment1 situated outside the wall1 along the inside of which machines are placed4 ,in this way considerable floor space is left available1 and the machines may be worked by direct drive4 ,not only so2 but if a suction-gas plant is worked1 there can then be no excuse for particles of coal or charcoal dust being found in the factory4 ,,position ,,of ,,engines4--,it scarcely need be pointed out that if the engines are placed outside the wall which is opposite the machines1 a long belt-drive would be necessitated1 and that the presence of the belt would prevent the use of end doors4 ,it is presumed in these arguments that two engines are to be installed4 ,one can hardly imagine a modern factory in full working being equipped with only one engine1 which might possibly have an excess of power necessary to drive all the machines4 ,in the case of breakdown1 which sometimes happens in the best supervised factories1 it would be small consolation to know that this excess of power was present theoretically4 ,,how ,,many ,,storeys4--,there can be no doubt that1 taking all things into consideration1 the best type of factory is that consisting only of one floor4 ,the factory should be quite separate from all other buildings1 and if attempts are made to conserve ground space by putting a drying-room over the factory1 much trouble will ensue1 especially if pale crepes are to be made4 ,in the first place1 the factory is made very much darker1 and hence more difficult to keep clean2 secondly1 the ventilation of the factory is seriously interfered with2 and thirdly1 it is manifestly prejudicing the drying of rubber to place it directly over a room which is always more or less awash with water4 ,at night such a building would reek with a moisture-laden atmosphere1 and little drying could be expected to take place in that interval4 ,from actual experience it has been shown that rubber hung to dry in such a room1 situated over a damp factory1 is very liable to attacks of spot diseases1 since the presence of perpetual moisture is favourable to the development of these diseases4 ,if a double-storey building has to be worked1 it will be readily seen that no first-grade rubber should be allowed to dry in it4 ,the accommodation over the factory may be restricted to the purpose of receiving lower grade rubber which is not so liable to spot diseases1 and possibly does not take so long to dry as first-grade rubbers of equal thickness4 ,it is evident1 therefore1 that the erection of double-storey factories is false economy1 as separate drying-houses have to be built eventually4 ,this conclusion does not apply with the same force to factories worked in conjunction with smoke-houses for preparing sheet rubber1 but1 nevertheless1 such a factory should not have another floor above the work-room4 ,,verandahs4--,one of the worst features in many factories is the necessity for coolies to bring latex into the factory4 ,as already mentioned1 the floors of factories are usually running with water 7or should be71 and it can be imagined that the passage to and fro of scores of coolies must bring in a great quantity of dirt4 ,not only so2 the very presence of the coolies is a hindrance to the efficient working of the factory1 and considerable floor-space and time are wasted4 ,this feature in factory working is all the more annoying because the necessity for it could so easily be obviated4 ,all that is necessary is the erection of a wide1 open verandah outside the wall of the factory4 ,here all latex could be received and strained1 scrap-rubbers could be received and passed through an opening into tanks placed in convenient position4 ,water could be laid on in this verandah so that coolies might wash their buckets1 and the whole verandah might be enclosed only with expanded metal so as to avoid interference with the lighting of the factory4 ,in this way it would be quite unnecessary for any field coolie to enter the factory proper1 and this would facilitate cleanliness4 ,such an arrangement has been discussed by the writers many times during the last few years1 but the number of estates which have made such provision is still in the minority1 and the same slipshod and dirt-making procession of coolies continues to walk through the factories1 and the same piles of bark-shavings and scrap-rubber continue to accumulate and ferment in a few instances4 ,an indication of types of verandahs is given in ,chapters ,,vii4 and ,,ix4 ,these are not intended to be representative of a universal design1 but may be suggestive in the planning of others according to local conditions4 ,,situation ,,of ,,tanks4--,it will be noted that these verandahs are raised from the ground-level to a height of about #c feet in order that latex may be gravitated1 with a slight fall1 into the coagulating tanks which are within the factory4 ,there exists a real necessity for this practice1 inasmuch as otherwise to obtain gravitation of latex 7which is quicker and cheaper than handling7 the coagulating tanks would have to be either placed on the floor or sunk beneath the level4 ,the risk of contamination of latex or coagulum under such circumstances would be appreciable4 ,apart from this1 it is advisable to have the coagulating tanks raised to a height of between #b and #c feet1 to secure the advantage of ease of working in the processes of coagulation and the handling of coagulum--a not inconsiderable factor4 ,in some modern designs it is proposed to place the coagulating tanks in a separate building4 ,this would seem to be an unnecessary refinement in a new building1 if observance is given to the suggestions made in previous paragraphs4 ,,designs ,,and ,,lay-,,out4--,in a previous publication#ag comment was made upon grievous errors in designs prepared by those inexperienced in the requirements of the tropics4 ,there is little ground now for complaint1 and local engineering firms are fully capable of advising upon1 and constructing1 suitable buildings4 #ag ,preparation of ,plantation ,rubber1 ,morgan1 #aiac4 ,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 crop4 ,if it should be decided at first merely to cater for contemporary requirements1 the fullest consideration should be given in discussing design of building and lay-out of machinery to the practicability of later extension4 ,the site should be large enough for the eventual group of buildings1 the building should be easily capable of extension with the least cost1 and the same forethought should govern the lay-out of the machinery4 ,,drains4--,lastly1 there is the question of drains4 ,generally speaking1 all factories are well provided with drains1 and the only difficulty is that of getting an adequate fall for efficient drainage4 ,but there is a certain amount of laxity exhibited in the matter of providing sieves in drains4 ,to anyone acquainted with factory working1 it must be apparent that quite a lot of small pieces of rubber are washed into the drains4 ,this rubber should be collected at intervals during the day2 but in many instances that collected is only a fraction of what escapes4 ,wherever possible the drainings of a factory should be carried as far as is practicable from the buildings by means of cement drains4 ,too often these are short1 and lead into earthen drains4 ,even if no pieces of rubber are present1 the serum from the coagulum is subject to decomposition1 the effluvium from which is objectionable4 ,,water ,,supply4--,it is essential that a good supply of water should be available4 ,this should be distributed by pipes all round the building1 so that a hose may be used in every part for the thorough cleansing of the factory at intervals during the hours of working4 ,summing up1 it might be said that a good factory1 therefore1 should have the following features3 #a4 ,plenty of windows1 or walls of expanded metal4 #b4 ,a jack-roof in the ridge1 and hence a good system of ventilation4 #c4 ,engines in compartments outside the walls of the factory4 #d4 ,machines close to and parallel with the wall outside of which the engines are placed4 #e4 ,latex tanks and other fixtures along the wall opposite the machines4 #f4 ,a long middle free space1 at either end of which a large double door should be placed in the end walls4 #g4 ,a good concrete and cement floor sloping slightly from the middle towards each long wall4 #h4 ,an abundant water supply1 and several lengths of hose4 #i4 ,the building should be of only one floor1 and have ample head room4 #aj4 ,there should be an outside1 open verandah upon which latex may be received1 etc42 preferably outside the wall which is opposite to the machines4 #aa4 ,the system of drainage should be thorough1 and the drains should be adequately screened1 so that all particles of rubber may be collected4 ,,chapter ,,xv ,,other ,,buildings ,,drying-,,houses ,,for ,,crepe4--,it has already been shown in the previous chapter that one type of drying-houses--viz41 that over a factory--stands condemned1 except for the drying of low-grade rubbers4 ,generally speaking1 a great advance has been made in the design of crepe drying-houses during recent years1 and it has been possible even to improve older ones so as to bring them into line with the more modern buildings4 ,houses for drying crepe rubber may be of one floor1 two floors1 or even three floors4 ,doubtless those built with three floors were designed with a view to economising the available site for factory buildings1 and as long as the ventilation is good there can be no very great objection to them4 ,it might be pointed out1 however1 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 building4 ,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 floor1 as the temperature of the top floor must be many degrees higher than that of the other two rooms4 ,it would be expected1 therefore1 that the rate of drying in the middle storey would be slower than that in either of the other two4 ,in houses of two floors this objection would not have to be met1 and drying-houses of this type are successful and common4 ,,how ,,many ,,storeys8--,again nothing could be urged against a building of two or three storeys in which the ground floor was occupied as a packing-room1 except that1 by negligence in not allowing wet crepe a preliminary dripping period1 water might fall upon the packed rubber below4 ,as a matter of experience1 such a house is1 taking all into consideration1 the cheapest and most suitable type for any estate with an increase in output4 ,even at the outset there should be a separate room in which sorting and packing is undertaken4 ,this is conveniently the lower room of a drying-house4 ,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 pattern1 so that the air may circulate right through the building4 ,this is usually and very successfully attained by laying down wide slats of wood1 with spaces of an inch or more between them4 ,it is not advisable to have spaces wider than #a-a_/b inches1 otherwise there is a certain amount of danger to the limbs of individuals who have to work or supervise in the building4 ,in any case1 it is very convenient to have pathways of planks running the whole length of the floor1 so that the supervision is made more convenient4 ,if this is done1 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 room4 ,at present1 in some drying-houses1 this means of suspension is used1 but no planks are laid down1 and it becomes necessary to walk over the drying rubber4 ,this is a detail1 but it is one which does not make for the improvement of rubber1 and the expenditure of a small sum would be sufficient to rectify the matter4 ,from every point of view1 it would be desirable to have the floor of the packing-shed 7or the packing-room in a combined house7 raised from the ground1 to a height of1 say1 #c feet2 or the height of a bullock-cart or motor-lorry4 ,not only is ventilation improved1 but there would be a great saving in labour4 ,packed cases could be wheeled directly on a level with the cart or lorry4 ,a great many estates favour drying-houses of one storey4 ,these are eminently suitable1 provided that the site is suitable1 and that the relative dimensions of the house are favourable to efficient ventilation4 ,it is a common mistake to find buildings of which the breadth is out of proportion to the height4 ,obviously1 if the height is not considerably in excess of the breadth1 ventilation will be defective4 ,for a single-storey drying-house1 the maximum height should bear the ratio to the breadth of #c3b1 and in a house of this type specially long pieces of crepe can be utilised4 ,naturally1 in a house of two storeys1 this factor is not likely to be neglected1 and if the lower room is used for packing purposes the rate of drying should be rapid4 ,again1 when a single-storey building is contemplated1 it is well to make strict examination of local conditions4 ,if the site is low-lying and surrounded by trees it will be clear that tall buildings are required1 and that a house of more than one floor is to be preferred4 ,considerations of this nature would have prevented the erection of some dry-sheds which do not give a satisfactory rate of drying4 ,,ventilation4--,no matter how many floors there may be in a drying-house1 the greatest attention should be given to the question of ventilation4 ,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 building4 ,it is not often that such a rule is infringed in the ventilation of rubber drying-houses1 but several of the older buildings erred in this respect4 ,in a good modern house there is a space 7about #b feet in height7 all round the base of the walls merely closed with expanded metal2 this admits cool air4 ,an exit for warm air is provided in the ridge of the roof by either ventilation chimneys or by a jack-roof4 ,the latter is preferable1 as it provides for a more free and uniform escape4 ,in some drying-houses1 besides the ridge openings1 the space along the eaves is left open4 ,this would seem to be undesirable1 as it provides for the entrance of outer air1 which might combat the ascending warm air and so interfere with the natural upward currents4 ,provided that a jack-roof or other suitable openings have been installed1 there is1 therefore1 no necessity for the existence of open spaces at the eaves1 and they probably do more harm than good4 ,in the tropics1 on days of sunshine1 there must always be an upward current of air in well-designed houses4 ,temperatures of #aje deg4 ,f4 are easily recorded in the ridge space of a building1 while the temperature in the lower part of the house may be at least #ae deg4 ,f4 lower4 ,on the floor of an upper room a temperature of #ij deg4 ,f4 is commonly noted1 and in buildings with three storeys the usual day temperature of the top room is about or over #ajj deg4 ,f4 ,even1 therefore1 when there is no trace of a breeze1 there must be a displacement of air in an upward direction1 though it may not be detected without tests being applied4 ,it is often asked whether a temperature of #ajj deg4 ,f41 such as is obtained in the upper room1 is calculated to injure the quality of the rubber4 ,there need be no fear on this ground2 the experience of many estates goes to show not only that no harm results1 but also that the drying of the rubber is expedited4 ,there would seem to be no reason why crepe rubber should not be dried at a temperature of #ajj deg4 ,f4 ,it must be understood1 however1 that higher temperatures for crepe rubber are not recommended1 as it has been proved that the rubber is affected4 ,the fact becomes obvious with continued treatment at temperatures much above #ajj deg4 ,f41 for the rubber stretches and breaks across the support4 ,,windows4--,concerning the subject of window space in a drying-house1 there has been much discussion at various times4 ,years ago it was common to find windows widely open with the sunshine streaming in4 ,naturally1 tackiness developed in some of the rubber1 and care was then taken to keep the windows closed4 ,thus the rooms were darkened and air excluded4 ,there followed a period in which windows were fitted with ruby-coloured glass to keep out the actinic rays of the sun1 which were responsible for tackiness1 and excess of light1 which was supposed to be responsible for the rapid oxidation of rubber4 ,unless special precautions were observed in the processes of coagulation and preparation1 it was not proved that the exclusion of light prevented or lessened the natural oxidation of crepe rubber4 ,since the introduction of sodium bisulphite for the prevention of oxidation1 there has been no cause to worry as to the possible effect of light1 as no perceptible darkening of the rubber takes place4 ,it follows1 therefore1 that no trouble need be taken to exclude light1 although the necessity for excluding direct sunshine still exists4 ,windows may be left open as long as the sun does not reach them4 ,this can usually be arranged in a drying-house by manipulating the windows at intervals during the day1 so that those in the shady side of a building are always open1 while those on the sunny side are always closed4 ,if it is thought that this manipulation cannot be entrusted with success to the store coolies1 the case may be met by having all windows constructed on the louvre pattern1 so that1 although the windows are closed all day1 air and light are not excluded4 ,should it be desired to retain the existing type of windows1 which open outwards1 and to keep them open all day1 a simple arrangement of ruby-coloured cloth on an outstanding wooden frame may be placed within the walls of the building1 or the shutters of the windows may be hinged at the top to open outwards4 ,unless there is a pronounced breeze1 or it is required to examine the rubber closely1 there is no necessity to have windows open1 except in the case of a house in which the bottom floor is used as a packing-room4 ,the windows of this chamber may remain open during the day1 to advantage in sorting and packing1 and also to the proper ventilation of the building4 ,thus the direct rays of the sun are rendered harmless1 while air and light are allowed to enter4 ,,hot-,,air ,,drying-,,houses4--,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 fan4 ,provided that the temperature of the hot air could be so regulated as not to exceed #ajj deg4 ,f41 there would be merit in the system4 ,such matter of regulation could be solved by having a duct in the main air passage1 through which cool air could be admitted in such proportion as to modify the temperature of the hot air4 ,as the process is worked at present1 the temperature attained is often well above #ajj deg4 ,f41 and there is a danger of thin crepe placed in this house over-night being found upon the floor in the morning4 ,unless the crepe is prepared thick and cut into fairly short lengths1 it will not bear its own weight at higher temperatures2 and if it is made thick1 drying is impracticably prolonged4 ,it is probable that1 with a temperature of #ajj deg4 ,f41 and a steady current of air1 average thin crepe would dry in such a drying-house within six or seven days4 ,this would be an improvement upon the usual rate of drying in most factories1 although several ordinary drying-houses are known in which thin crepe will dry naturally in that period4 ,,smoke-,,houses4--,no discussion of theoretical considerations regarding the process of smoke-curing will be attempted here4 ,we are concerned only with the necessity for supplying a demand for smoke-cured sheet rubber4 ,broadly1 the process is akin to the smoke-curing of herrings1 and the objects are much the same--viz41 7#a7 drying1 7#b7 preservation--except that while herrings are only dried partially1 rubber should be dried perfectly4 ,on a small scale a primitive smoke-house could be built easily and cheaply1 and such a building might be fully as efficacious as the most elaborate and expensive installation4 ,in the early days of estates it was not uncommon to see temporary smoke-houses constructed of wood1 and roofed with attaps 7palm leaves74 ,some of the best rubber in the market has come from wooden buildings1 but naturally the risk of destruction by fire is considerable4 ,for imperative reasons it may be sometimes found necessary to smoke rubber when the only available building is a single-storey one4 ,as a temporary measure1 the building may be converted into a smoke-house by placing the fires in pits sunk deeply into the ground1 and effectively screened above by iron baffle plates4 ,but it is not advisable that smoking be continued in such a single-storey building1 as the best effects are not obtained1 and the risk of fire is far too great4 ,,usual ,,types4--,at first sight it would appear that the best type of smoke-house would be one consisting of a tall building1 covering a comparatively small superficial area1 and having a number of superimposed chambers in which the rubber could be hung to dry4 ,in practice there are several solid objections which limit the height and the number of floors4 ,chief among these is the question of temperature4 ,if smoke-curing is to be effective1 a certain temperature must be attained and maintained4 ,to obtain such results in a house of excessive height would be difficult1 if not impossible1 under normal conditions4 ,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 range1 etc4 ,until recent years smoke-houses could be classed as belonging to one of two types3 7#a7 ,those having external furnaces4 7#b7 ,those having internal furnaces4 ,the number of the former existing at the present time must be very small1 as it has been shown that the arrangement of the furnace outside the house is unsatisfactory in comparison with the other type of house4 ,in discussing the question of smoke-houses1 therefore1 it will be understood that the standard type accepted is that having an internal furnace4 ,in its original form it was known as a ,kent drier1 and consisted of a tall two-storey wooden building4 ,the walls of the lower chamber had the form of an inverted and truncated pyramid4 ,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 above4 ,this is the principle upon which many smoke-houses in ,malaya are designed4 ,on a very large scale it is not claimed that the sloping sides of the lower chamber lead to economy in the number of fires1 but merely divert the smoke in an upward direction4 ,it is acknowledged that vertical lower walls are quite effective1 and it is an easier matter to fit in doors4 ,it may be noted that the usual type of smoke-house now in general use consists of a building of two storeys1 in the lower of which are situated the furnaces1 while rubber is hung on racks in the upper room4 ,sometimes there may be a third storey1 also used as a drying 7curing7 chamber4 ,as a rule the drying-room is one long unit1 as also is the furnace chamber2 but in some cases they are subdivided by vertical partitions into smaller chambers1 for ease of working and better control4 ,this applies with some force in the case of very long houses standing in an open space4 ,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 building4 ,with these exceptions1 the ordinary type of smoke-house functions very efficiently1 and is capable of drying average sheet 7from standardised latex7 in a period ranging from seven to eleven days4 ,should the building not be capable of such performance1 in spite of the strict observance of all rules laid down for the processes of preparation1 then there is some defect in ventilation or in the distribution of heat4 ,,general ,,ventilation4--,the ordinary rules of ventilation in drying-houses apply equally to a smoke-house4 ,there should be a slow current of air and smoke from the lowest point to the highest point in the building4 ,in spite of all that has been written on this subject1 it is by no means uncommon to encounter the idea that a smoke-house should be perfectly closed in order to get good results4 ,as to what must become of the 7say7 #be per cent4 of moisture which the rubber contains there is no knowledge4 ,in dozens of cases1 when complaints regarding slowness of drying have been investigated1 it has been necessary to point out the need for providing a rational system of ventilation4 ,naturally only a slow current of air and smoke is required4 ,the creation of an appreciable draught would have the effect of increasing the fuel consumption of the furnaces1 raising dust from the ash1 and of causing a temperature higher than that which is known to be desirable4 ,it will be clear1 therefore1 that if there are to be any openings at the base of the walls they should be small in area1 and should have some device by means of which the current of air can be efficiently regulated4 ,in the usual case the construction of the building is not calculated to render it air-tight1 and the necessity for providing special air inlets does not arise4 ,,windows4--,windows are not strictly necessary1 and are only intended to be of service during the time in which coolies are at work within the building4 ,the operations of examining rubber1 turning sheets1 removing dry rubber1 cleaning racks and floors1 and putting wet rubber into position1 usually occupy some hours daily4 ,during this interval the windows should be widely opened if the weather is favourable1 and should remain so until the fires have been lighted4 ,it should not be forgotten that during the heat of the day quite an appreciable degree of drying is possible4 ,advantage can be taken of this2 but there is no necessity to extend the interval unduly1 and it is of greater advantage to proceed with smoke-curing when the work in the drying-chambers has ceased4 ,,racks ,,of ,,supports4--,still referring to the usual type of smoke-house1 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 building4 ,narrower passages run between the bays of the racks to facilitate ease in handling and inspection4 ,the wooden supports may be placed about #c inches apart horizontally1 and #ae or #ah inches apart vertically4 ,a full bay of racks should contain nine or more lines of support in each of the planes which are #ae or #ah inches apart vertically4 ,the number of these planes is governed only by the height of the room1 measured from the floor to eaves4 ,the supports should be of smooth timber1 and need not exceed #a-a_/b inches square in section4 ,it is usual and advisable to smooth off the rectangular edges of the supports or bars1 to avoid the incidence of splinters of wood adhering to the rubber4 ,the bars should not be fixtures1 but may either be accommodated in slots1 or may rest between two nails1 so that it is possible to give them a rotary motion by turning the projecting ends4 ,this practice is followed in smoke-houses1 the idea being to move the drying sheets slightly each day1 with a view to the prevention of a pronounced mark across the sheets4 ,care should be taken to see that the vacant racks are thoroughly cleaned before fresh rubber is placed upon them1 otherwise a distinct dirty mark is caused across the middle of the sheet4 ,this mark usually cannot be removed1 even by scrubbing with water4 ,where this mark occurs regularly in all sheets1 attention should be turned to the openings beneath the bays of racks1 if open fire furnaces are employed4 ,it will generally be found that gauze of too wide mesh has been fitted4 ,this should be removed or covered with a finer gauze4 ,a more effective way of dealing with the trouble1 provided other precautions have been taken1 is to have plenty of spare wooden bars4 ,it should be a rule stringently enforced that1 as soon as racks are emptied1 the bars should be removed to the factory to be cleansed thoroughly4 ,a spare set should enter the smoke-house with each batch of fresh rubber4 ,the actual number of spare sets required could be limited to a two days' supply1 and the extra cost would be recouped easily4 ,,floor ,,of ,,drying-,,chamber4--,the floor of the chamber is usually of planks1 except that the space under each bay of racks should be filled with expanded metal4 ,with the use of wood fires there is always a large amount of light ash formed1 which may find its way into the upper chamber4 ,to counteract this1 screens of fine mesh gauze are laid over the expanded metal4 ,this gauze may be fitted into a movable wooden frame1 so that when it becomes necessary to clean it the whole may be removed4 ,the difficulty is that with furnaces of the open-fire type the rise of dust is so great that the gauze screens soon become clogged1 especially as the slight tarry matter in the smoke condenses on the gauze1 causing the dust to adhere4 ,with the better types of furnaces1 the employment of gauze screens is not necessary1 as there should be very little rise of dust4 ,it is sufficient to use only expanded metal1 to prevent any displaced pieces of rubber falling into the furnace chamber4 ,,furnaces ,,generally4--,the crudest and dirtiest method of fuel consumption in the preparation of smoked-sheet rubber is that of making a fire on the ground4 ,this is still a common practice1 and should be condemned as being both wasteful and harmful4 ,under prevailing conditions coolies will1 in spite of instructions1 heap up a pile of logs in order to save themselves the trouble of stoking the fire in small quantity and at regular intervals4 ,a small supply of water is kept at hand with which to quench the fire somewhat if it threatens to cause trouble4 ,naturally a large quantity of fine ash is thus thrown up1 and the rubber above receives the deposit4 ,if the coolie does not happen to be sufficiently awake1 of course a house burns occasionally4 ,from this primitive type of furnace1 others have been evolved4 ,these usually take the form of more or less shallow trucks1 the majority of which are similar in principle to the fire on the ground1 except that the container can be withdrawn from the house for the purpose of removing the ash4 ,sometimes they are even more objectionable than the ground fire1 inasmuch as1 being raised above the ground level1 an under-draught through fire-bars is caused1 and consumption of fuel is so much the more rapid4 ,,pits4--,it is clear that large fires are not desirable1 and that combustion should be slow1 provided that the necessary temperature can be maintained4 ,the lines along which the development of furnaces needed to extend are therefore plain4 ,the simplest device adopted was the digging of pits in the ground4 ,sometimes these pits received the addition of an iron truncated cone which was movable4 ,naturally the combustion was slow1 but sufficient heat was obtained if the pits were large enough or in sufficient number4 ,an objection was that the ash had to be cleared in situ1 and in the process the earthen pits gradually increased in size4 ,in all cases it was necessary to suspend an iron baffle-plate above the furnaces to distribute smoke and arrest any sparks4 ,,pot ,,furnaces4--,the next development was the employment of pot-furnaces4 ,these consist of iron drums1 sometimes merely resting on the ground1 and sometimes mounted on trucks for easy withdrawal4 ,these drums radiate sufficient heat if present in sufficient numbers1 and the fuel consumption is low4 ,they are usually manipulated by starting a fire in the bottom and packing in logs cut to the necessary length4 ,some have no lids1 while others are fitted with perforated caps4 ,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 draught4 ,in a few cases this perforation has been exaggerated to the form of a hinged door4 ,unless this can be closed with ease1 and is closed according to instructions1 part of the object of this type of furnace is defeated2 fuel consumption is rapid1 and the temperature is too high4 ,in the original form pot-furnaces have been found to be effective on many estates1 and are still employed with satisfaction4 ,,iron ,,stoves4--,working on exactly the same principle1 on some estates one finds small iron stoves in use4 ,sometimes broad pipes are attached for the better distribution of the smoke2 if this is the case it should be noted that the pipes should have a slight downward slope1 and that the bend at the end should be turned downwards4 ,in this way condensed moisture and creosotic matter falls to the ground1 and does not lodge in the pipe4 ,the life of the conduit is thus prolonged4 ,usually such stoves are in use where the head-room of a smoking chamber is insufficient for other types1 or where the nature of the site does not permit of sunken furnaces being installed4 ,they are of value likewise on occasions where the fuel supply is limited to a rich timber such as mangrove-logs 7bakau71 when it is necessary to ensure a low combustion with low cost of fuel4 ,,horizontal ,,drum-,,furnaces4--,to overcome difficulties inherent to drums or pot-furnaces1 the next development was that in which the drum was made to assume a horizontal position1 and adapted ingeniously to a simple system of working from the outside of the building4 ,reference to the drawings given will explain how this is effected4 ,in the first illustration 7,no4 #b7 it will be noted that the drum is supported upon brick pillars1 with one end projecting through the wall of the building4 ,at the other end a short chimney is mounted1 having within it a damper which is adjustable from the outside4 ,over this chimney is suspended a simple baffle-plate1 made from a ,chinese iron cooking-pan4 ,the outer end of the drum is furnished with a hinged and latched door1 in which a small air-regulator is accommodated4 ,in the second set of drawings 7,no4 #a7 the drum is increased in size and fitted in a special manner for incorporation with a distinct type of building4 ,such a scheme was first put into effect by ,mr4 ,r4 ,c4 ,sherar1 the manager of ,third ,mile ,estate1 ,seremban1 ,f4,m4,s41 and for ease of reference the house and furnace will hereafter be mentioned when necessary as the ,third ,mile type4 ,illustration3 ,,third ,,mile ,,type2 ,,horizontal ,,drum4 ,this type of furnace is suitable for adapting to existing buildings with perpendicular lower walls4 ,illustration3 ,,third ,,mile ,,type ,,of ,,furnace1 ,,used ,,in ,,conjunction ,,with ,,third ,,mile ,,smoke-,,house4 ,it will be seen that the furnace has at the farther end a door for the removal of ash4 ,as this1 if badly fitting1 may result in too great a draught1 it is well to insist upon good workmanship4 ,other adjustable air-inlets are provided1 and the drum is enclosed in a brick chamber4 ,,rate ,,of ,,combustion4--,however successful this furnace may have proved in the hands of trained coolies1 one must feel that with such a number of air-inlets 7whether accidental or designed7 there would always be present the possibility of obtaining too rapid a combustion4 ,in the original forms of drums or pot-furnaces of various kinds1 a very slow rate of combustion was attained4 ,naturally a relatively larger proportion of carbon remained unconsumed1 and there was a small proportion of ash4 ,in these respects the furnaces resembled charcoal-burners4 ,in point of fact1 some estates used this principle for the dual purpose of smoke-curing the rubber1 and at the same time obtaining a supply of charcoal to provide fuel for their suction-gas engines4 ,this is a consideration in times when managers are desirous of discovering any devices which tend towards reduction of costs4 ,it will be clear that1 under ordinary circumstances1 the condition of what remains after the combustion of the fuel gives an indication of the rate at which the wood has burned1 and this test should apply to all furnaces4 ,that in which there is the most ash and the least charcoal is the one least to be desired4 ,in direct connection with this consideration1 one must recognise that a fire which is sunk below the level of the ground exposes the least surface from which heat may radiate2 and hence1 in order to obtain the maximum benefit of heat from a slow-combustion furnace1 it should be above ground-level1 or should have a superstructure from which the heat may be dissipated4 ,simple drum furnaces1 with slow combustion1 have the further advantages that a charge of fuel will need no attention for possibly eight to ten hours1 and practically no ash is found to be ejected4 ,these advantages have great practical importance4 ,the first minimises any disabilities arising from neglect on the part of coolies1 and the second makes for increased cleanliness in the drying-chamber4 ,while these advantages would appeal to most estates1 there would appear to be a further advantage to small estates which have only temporary timber smoke-houses4 ,with a slow rate of combustion in a furnace of this type1 danger from fire is diminished considerably4 ,bearing in mind the slow rate of combustion1 and hence the comparatively low temperature obtained1 it will be plain that drum furnaces should be employed in larger number than ordinary open-hearth fires2 and the drums can be so placed as to ensure the best possible uniform distribution of heat and smoke4 ,large furnaces are sometimes seen1 with flues of brickwork4 ,in view of the foregoing remarks1 it will be obvious that these tend to large fires and a rapid combustion1 and hence must be classed as undesirable4 ,,brick ,,stoves4--,developing from drum furnaces1 another type comes into existence4 ,in principle it consists of an enclosed brick furnace1 with feeding door1 and a low conical dome surmounted by an adjustable cap or spark-arrester4 ,the rate of combustion can be influenced by a suitable movement of the cap1 which is operated by a screw4 ,this type of furnace has been installed on several estates by the engineering department of ,messrs4 ,harrisons and ,crosfield1 and is understood to give satisfaction4 ,,pataling ,,type4--,with the exception of the ,third ,mile type already mentioned1 all the furnaces described are open to a strong objection1 in that the coolies have to enter a room1 usually filled with hot smoke1 in order to attend to the fires4 ,the mere opening of the door of the building is sufficient to fan most fires into a blaze and to raise sparks4 ,apart from these points1 it is natural for coolies to avoid entering too often1 with the result that they generally stoke with the maximum load of timber4 ,even should they not sleep the danger is clearly great4 ,illustration3 ,,side ,,sectional ,,elevation 7,,pataling ,,type ,,of ,,furnace74 ,illustration3 ,,pataling ,,type ,,of ,,furnace4 ,to obviate these drawbacks1 furnaces which are fed from the outside of the building were designed4 ,there have been various forms1 but as they were first installed on ,pataling ,estate1 in the present form1 they may be known under the description of the ,pataling type of furnace4 ,they are eminently satisfactory1 and have a low rate of fuel consumption4 ,they are very safe1 and in fact1 if worked with average intelligence in supervision1 can be regarded as being fool-proof4 ,there is practically no ejection of fine ash1 and no fine-mesh screens need be employed4 ,they can be adapted to any building having either vertical or sloping walls of galvanised iron4 ,illustration3 ,,large ,,smoke-,,house ,,of ,,ordinary ,,construction1 ,,with ,,shielded ,,ventilators ,,permanently ,,open4 ,in foreground1 movable folding racks on which sheets drip in the open air4 ,this smoke-house is equipped with brick furnaces fed from the outside 7,pataling ,estate74 ,in essential the furnace consists of a shallow pit below ground-level1 lined with brick1 and having a square brick superstructure rising #d feet above the floor of the building4 ,on top of the brick walls rests a sheet of boiler-plate perforated with small holes4 ,the hearth being below ground-level1 and with the extra #d feet of height above the floor1 it follows that if ash is disturbed it is confined4 ,from the drawings it may be seen that the pit is prolonged to the side wall of the building1 with steps leading up to the ground-level4 ,the top and sides of the opening are made with galvanised sheeting1 forming a kind of short tunnel in which the coolie may stand upright4 ,the outer face of the brick furnace forms the inner end of the tunnel1 and accommodates the door of the furnace4 ,the bottom of the pit is filled up with clay and stones almost to the level of the bottom of the door4 ,this ensures a very shallow hearth1 and guards against an unduly large fire4 ,obviously it is not desirable or necessary to make the hearth of fire-bars1 as was done in one instance1 with the provision of a door below for removing the ash4 ,this would lead only to a strong draught being created1 with a high rate of fuel consumption4 ,illustration3 ,,brick ,,and ,,cement ,,superstructure ,,of ,,furnace ,,inside ,,the ,,building1 ,,but ,,fed ,,from ,,outside4 ,on the top of the superstructure rests a sheet of perforated boiler-plate4 ,the actual fire-pit is below ground-level1 and to the left may be seen parts of the sides and top of the downward approach1 from the outside1 to the door of the fire-pit4 ,the openings can be screened by a narrow sloping lean-to1 which serves to keep out rain1 and provides shelter for the stock of fuel and the coolie4 ,the iron furnace-door should be well made1 with an easily worked latch2 but it is not necessary that it should be perfectly fitting4 ,any slight aperture will serve to provide the necessary air-inlet1 but in any case it should not be more than slight4 ,,consumption ,,of ,,fuel4--,regarding this furnace1 it may be said in conclusion that it is more satisfactory in general working than any other furnaces yet encountered4 ,obtaining information from over sixty estates1 on the question of fuel consumption compared with output of rubber1 it was found that1 as far as ordinary smoke-houses were concerned1 the ,pataling type of furnace showed the lowest unit consumption of fuel4 ,illustration3 ,,general ,,view ,,of ,,shelters ,,covering ,,approaches ,,to ,,furnaces4 ,this was at the rate of slightly less than #a lb of fuel per #a lb of thoroughly cured sheet rubber4 ,the figure on some estates mounted as high as #d-a_/b lbs4 of fuel per lb4 of rubber4 ,naturally this factor may have been affected by failure to utilise the drying space to its fullest capacity1 but in the main the high rate of consumption could be attributed solely to the deficiencies of the furnaces4 ,,floor ,,of ,,furnace-,,room4--,as a rule no attempt is made to improve the natural earthen floor4 ,whether open-hearth fires1 truck furnaces1 or drums are employed1 it is usual to find a floor with an inch or two of dust upon it4 ,where all endeavours are directed in other directions towards cleanliness1 it appears strange that this should be overlooked4 ,in contrast1 houses employing the ,pataling type of furnace 7or others7 have concrete and cement floors1 which can be kept quite clean4 ,cleanliness should be as zealously attempted in the smoke-house as in other departments4 ,illustration3 ,,near ,,view ,,of ,,shelter4 ,steps lead downwards where the wall of the smoke-house has been removed4 ,,roof4--,in any type of smoke-house1 the roof should fit tightly at the eaves1 and the only vent should be in or near the roof-ridge4 ,in an ordinary smoke-house1 the opening should take the form either of a low jack-roof or of squat chimneys protected against rain4 ,if a jack-roof is chosen1 it may be so low as to need no scheme of adjustment1 or otherwise adjustable swing shutters must be provided4 ,the chimneys may be made with such low fitting between the cap and the body that no interior swinging flaps are required4 ,during the operation of smoke-curing the smoke vents must remain open to a degree which is arrived at by experience4 ,failure to provide a comparatively free egress for smoke and moisture will bring trouble in its train4 ,after a house has been in use for some time1 it will be noted that the timber becomes covered with a shiny tarry coating deposited by the smoke4 ,if the rubber remained in the house for an equal period1 it would take on the same appearance4 ,during the interval between the entry and the exit of the rubber some amount of deposit does take place1 and it is this mixture of creosotic substances which plays a part in fitting the rubber to withstand growths of mildew which would otherwise form4 ,if proper smoke-vents are not provided1 the moisture evaporating from the sheets is unable to escape quickly enough1 with the result that a great deal condenses at night-time upon the inner surface of the comparatively cool roof1 and falls back upon the rubber in unsightly black drips1 which leave a distinct mark on the sheet4 ,even if vents are open1 this may happen during seasons of rain4 ,the temperature of the moist smoke in the roof-ridge may be as high as #acj deg4 to #adj deg4 ,f41 while the outer atmosphere may have been cooled by rain to #gj deg4 ,f4 ,such a difference on the two surfaces of the roof must lead to condensation within the house1 with consequent dripping4 ,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 rubber2 but often for want of renewal the last state was worse than the first4 ,modern houses have often an inner lining1 a few inches below the roof4 ,this is made of soft wood which receives any product of condensation and absorbs it4 ,,other ,,types ,,of ,,smoke-,,house4--,so far we have confined the arguments to smoke-houses of the usual type4 ,there are others which vary in either design and method of working1 or in the material of the structure4 ,mention may be made of the most prominent of these4 ,,brick ,,houses4--,some houses are constructed of brick1 and may have one or two storeys above the furnace chamber4 ,the floors are sometimes made of ferro-concrete1 and the furnaces may also be of this material4 ,these brick houses give satisfaction1 but there would seem to be some difficulty in obtaining and maintaining the desired temperature1 although it is not quite plain why this should be so4 ,the principle of these buildings is the same as that of the ordinary iron house1 and the suggestions made in previous paragraphs apply with equal force4 ,,third ,,mile ,,type4--,reference has been made to the ,third ,mile type of furnace4 ,this is an integral part of a smoke-house1 which for clearness of distinction may be known as the ,third ,mile type of smoke-house1 the original of which was erected on the ,third ,mile ,estate1 ,seremban1 ,f4,m4,s4 ,illustration3 ,,third ,,mile ,,type ,,of ,,smoke-,,house4 ,in essence the design consists of a building1 having two storeys for rubber-drying1 and a shallow inverted pyramidal base1 ending on the ground in ,third ,mile furnace1 already described and illustrated4 ,it will be seen that the principles of ventilation employed are those indicated for an ordinary house--viz41 air-inlet near the ground 7with little draught71 and smoke-vent at the roof-ridge4 ,the windows shown in the drawing are only for purposes of inspection of the rubber during the day1 and form no part of the scheme of ventilation during the hours of smoking4 ,it is claimed that the efficiency of the house is high4 ,certainly the work of attending to the furnaces is simplified1 and there should be small ground for excuse if negligence is displayed4 ,,jackson ,,house4--,this was brought into notice under the description of the ,jackson ,cabinet1 and it was claimed that average sheets could be dried in a few days4 ,it consisted of a small house of one storey1 having several tiers of racks4 ,smoke and heat were generated in a small stove placed outside the wall4 ,a smoke vent was provided in the roof4 ,these cabinets had a certain vogue as part of a small unit installation1 with a fair degree of success4 ,it is not clear1 however1 that such speed in drying is required4 7,this point will receive further attention in a subsequent chapter47 ,,devon ,,type4--,in its full original design this type owes its origin to ,mr4 ,h4 ,e4 ,nixon1 ,general ,manager of the ,devon ,estates1 ,malacca1 where it forms part of unit divisional installations worked under a scheme of decentralisation4 ,the original units consisted of a building erected with an iron framework covered with sheets of asbestos-slate1 and a roof of galvanised iron4 ,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 chambers1 and on which the racks are loaded and unloaded4 ,by this device it is possible to remove the contents of any compartment bodily without interfering with the continuity of curing in the other compartments4 ,that is to say1 smoking in such a house can proceed day and night if necessary1 and yet the rubber in any part of the house can be examined1 can be removed1 or can be replaced without cessation of smoking4 ,it will be seen from the illustrations that the house is more or less of the same general design as the ,third ,mile type1 with the addition of external platforms4 ,it has two storeys for the reception of rubber2 and a basal furnace-room with sloping sides converging downwards into a pit containing a large drum-furnace4 ,this is mounted on a low truck1 and travels on a short length of railway4 ,illustration3 ,,general ,,view ,,of ,,double ,,devon ,,type ,,of ,,smoke-,,house4 ,the platforms are common to both units4 ,building of brick with iron roof 7,batu ,caves ,estate74 ,each of the curing-rooms is divided into four compartments 7making eight compartments in all74 ,these are closed by swing doors1 each of which is the full width of a compartment1 and has a slight overlapping edge4 ,through these doors light railways run into the house and out upon the platforms4 ,on the rails bays of racks run1 and when fully loaded they are easily moved4 ,the racks were designed with a frame of stout hard wood1 but light angle-iron could be utilised4 ,illustration3 ,,general ,,view ,,of ,,double ,,devon ,,smoke-,,house ,,and ,,factory ,,buildings4 ,timber in foreground cut to length for stoking4 ,note water-tower and engine cooling-tanks adjacent to factory4 ,the chimney style of smoke-vent has an internal butterfly flap1 which is controlled by means of a wire from the outside4 ,in the ordinary course of smoke-curing1 it is advised that this flap should be permanently open so as to reduce the possibility of internal condensation of moisture and creosotic matter4 ,the exact degree to which it should be open must be found by experience4 ,illustration3 ,,view ,,of ,,platform ,,of ,,devon ,,smoke-,,house2 ,,doors ,,of ,,compartments ,,open1 ,,and ,,one ,,rack ,,partially ,,withdrawn4 ,note below each rack opening through which smoke rises1 covered with wire netting4 ,although reference has been made several times to compartments1 it should be understood that the chambers are not subdivided internally by means of partitions4 ,there exists only the external effect of compartments in the form of the eight swinging doors which allow for the withdrawal of1 or insertion of1 any one unit of racks at any time without interference with the bulk of the rubber4 ,illustration3 ,,double ,,devon ,,smoke-,,house ,,of ,,brick1 ,,with ,,roof ,,of ,,chinese ,,tiles1 ,,showing ,,loading ,,platforms ,,with ,,racks ,,withdrawn ,,from ,,smoking ,,chambers4 ,federated ,engineering ,co41 ,ltd41 ,kuala ,lumpur4 ,illustration3 ,,side ,,view ,,of ,,preceding ,,photograph1 ,,showing ,,external ,,arrangement ,,for ,,stoking ,,furnaces4 ,federated ,engineering ,co41 ,ltd41 ,kuala ,lumpur4 ,,detailed ,,description4--,as enquiries are often received it is permissible to reproduce the following detailed description of the original house4 ,this appeared in the ,fourth ,local ,report 7,malaya7 #aiaf1 issued to subscribers by the ,rubber ,growers' ,association4 ,the house has a steel frame-work1 #bb feet long1 #af feet wide1 and #bb feet high4 ,of the length1 #ad feet is occupied by the platforms1 and #h feet by the chambers4 ,these measurements can be varied4 ,the whole of the width 7#af feet7 is occupied by compartments of which one series is placed above the other4 ,illustration3 ,,front ,,view ,,of ,,double ,,devon ,,type ,,of ,,smoke-,,house4 ,glenmarie ,estate3 ,batu ,tiga ,co4 ,platforms4--,the loading verandahs or platforms are of ordinary 'seriah' timber4 ,compartments and ,furnace ,chamber4--,these are enclosed with ,bell's ',poilite' sheets1 each of which measures #h feet by #d feet by #c_/af inch4 ,the sheets are affixed to the steel stanchions1 doors1 etc41 by galvanised bolts 7#a inch by #a_/d inch7 which pass through iron flats measuring #h feet by #b inches by #c_/h inch 7about74 ,these iron flats hold the sheets at the edges4 ,the dimensions of the compartments are #h feet by #h feet by #d feet4 ,racks4--,these are eight in number1 and measure just under #h feet by #h feet by #d feet4 ,the capacity of each is roughly about #dej lbs41 of dry sheet rubber4 ,the racks are mounted on #f-;inch iron wheels1 running on rails of stock size1 ',t' iron 7#a-c_/d inches by #a-c_/d inches by #a_/d inch74 ,the sheets are hung on split bamboos4 ,to prevent these projecting over the edge of the rack and catching in the doors when the rack is moved in or out1 a thin strip of wood1 about #a_/b inch high1 is nailed along the sides of the rack4 ,illustration3 ,,side ,,view ,,of ,,double ,,devon ,,type ,,of ,,smoke-,,house4 ,building constructed of galvanised iron4 ,shows door to furnace chamber1 and ventilator4 ,furnace4--,this is of the type that aims at slow combustion4 ,it consists of a cast-iron cylinder1 #c feet in diameter and #d feet high1 carried on a truck made of a sheet of boiler-plate1 and mounted on small wheels1 so that the whole can be moved easily out of1 and into1 the furnace chamber for easy cleaning and stoking4 ,the furnace chamber is a pit lined with concrete1 just wide enough to take the trolley1 and about #ab feet long4 ,the top of the furnace1 which is almost flush with the ground-level1 consists of a sheet of zinc or galvanised iron with numerous holes about #c inches in diameter4 ,over these holes are strips of mosquito gauze1 as flame and dust arresters 7see note below74 ,there are no holes in the sides or bottom of the cylinder4 ,over the furnace is hung a baffle-plate1 measuring #d feet by #d feet4 ,above this1 on the first floor-level1 the bottom of the compartments is covered with wire netting1 to prevent any rubber dropping accidentally into the furnace chamber4 ,the furnace chamber is fitted with an iron-frame door1 swinging on perpendicular hinges4 ,method of ,stoking4--,the timber used is a mixture of jungle wood and rubber-tree wood1 cut to lengths of about #a-a_/b feet4 ,in the ordinary way the furnace is charged at #f p4m41 and at six-hour intervals a little more fuel is added1 but a new charge is not necessary4 ,during the daytime1 when the heat of the sun is sufficient to raise the temperature appreciably1 a smaller fire is maintained4 ,temperature4--,there is no difficulty in maintaining a temperature of #abj deg4 ,f4 ,by continuous smoking1 average sheets prepared from standardised latex can be fully cured in five days4 ,this represents #aaj hours of smoke-curing1 which is at least equal to ten days' intermittent smoking in an ordinary house4 ,capacity4--,there are eight racks1 each accommodating #dej lbs4 of standardised sheet rubber4 ,the loading capacity of the house1 therefore1 is #c1fjj lbs4 ,as each charge is cured in five days1 the monthly output may be #ba1jjj lbs4 ,the cubic capacity is #b1jdh cubic feet4 ,as there are no gangways1 etc41 this is fully utilised4 ,this gives a rate of monthly output capacity to over #aj-a_/d lbs4 dry rubber per cubic foot of drying space2 an excellent figure much in advance of values obtained in the great majority of ordinary smoke-houses4#ah #ah ,since the above was written1 it has been found possible to eliminate the gauze4 ,a mild steel top has been made1 perforated with #b-;inch holes4 ,practically no dust is ejected from the furnace1 and there are no flames4 ,owing to shortage of supplies during the ,war1 similar buildings have been erected with frames of well-seasoned hard wood1 which was protected by strips of asbestos-slate or galvanised iron4 ,the latter material was also substituted in the covering walls4 ,later1 houses were erected of brick1 with other minor modifications4 ,as a natural development1 the latest buildings consist of two of the original houses face to face1 under a common roof1 and served by common platforms4 ,as originally designed1 the house was intended to meet the needs of a small estate1 or a division of an estate1 having a maximum output of about #bj1jjj lbs4 of sheet rubber per month4 ,the possibility of an extension of this idea has been shown to be great4 ,the furnace has been described as situated in a pit4 ,situated on a bank or on sloping ground1 it was easy to arrange for withdrawal of the furnace4 ,in some cases this has not been possible1 and various modifications have been effected4 ,the most satisfactory yet encountered is that in which a shallow brick pit is surmounted by an iron cone1 about #d feet in height4 ,this is fitted with a cap having small perforations4 ,the fire burns in the pit1 and the heat is radiated by the cone4 ,it would have been more effective to have allowed greater height in the furnace chamber1 and to have employed the travelling drum-furnace as in the original design4 ,in order to avoid interference in draught by a space between the bottom of the doors of the compartments and the platform 7due to the presence of rails71 the floor of the platform is laid level with the top of the rails2 or to the bottom of the doors is attached a swinging flap1 notched for accommodating the rails when in position4 99 99 99 99 99 ,there are in use houses of other designs1 which all more or less vary only in some modifications from the types described4 ,hence they do not call for special comment4 ,recently a rather distinct departure has been noted in a structure designated the ,barker smoke-house4 ,,barker ,,patent4--,in essential this consists of a long narrow structure erected with an appreciable slope from one end to the other4 ,at the lower end is a small furnace enclosed in a brick compartment4 ,the smoke from this furnace travels up the slope to the other end1 at which the rubber enters4 ,the sheets are hung on bars which are attached to a unit framework4 ,this frame slides1 by its own weight1 upon timber side supports4 ,a sufficient number of these units occupies the full effective length of the structure4 ,the removal of stops at the lower end enables the foremost frame to be removed1 and the succeeding frames slide into a new position4 ,thus the freshly prepared sheets1 entering at the higher end1 gradually and automatically move towards the furnace as the frames of dry rubber are removed from the lower end4 ,illustration3 ,,the ,,new ,,barker ,,type ,,of ,,smoke-,,house3 ,a ,,small ,,unit4 ,the racks slide automatically from top to bottom on withdrawal of the lower frames through door at front4 ,the furnace is contained in the brick compartment at the lower 7front7 end4 ,thus far only small units have been seen4 ,it is claimed that1 properly prepared1 sheet rubber can be smoke-cured in about five or six days1 and it is stated that installations have been in successful working for sufficiently long periods to prove their efficacy4 ,the device is better known in ,java and ,sumatra than in ,malaya4 ,the capacity of a unit building is stated to be #g1jjj lbs4 per month1 calculating on a six days' cycle of working4 ,in a more recent design provision is made at the lower end for a water tank1 into which all rubber can be discharged in case of fire4 ,,chapter ,,xvi ,,other ,,buildings 7continued7 ,,and ,,situation ,,of ,,buildings ,,sorting-,,room ,,and ,,packing-,,room4--,it is in these departments that most factory installations are lacking4 ,more often than one cares to acknowledge1 sorting and packing are done under conditions which place a premium upon poor work4 ,as a consequence1 consignments of rubber are often marred by the inclusion of defective specimens4 ,the result is that shipments may be rejected when tendered against contracts1 or that allowances in price have to be made4 ,in many instances it would not be fair to lay the blame upon the manager or an assistant1 as it is obviously impossible for an individual to inspect every piece of rubber4 ,neither would it be strictly fair in some cases to ascribe the fault to pure carelessness on the part of the coolies4 ,often the only provision made for this important work is the lower room of a drying-shed1 which may also contain hanging rubber4 ,under these circumstances1 space is cramped1 and the light often poor4 ,small defects may pass unnoticed1 and the general surroundings do not conduce to keen work4 ,where1 for economic reasons1 the sorting and packing operations are conducted in the drying-shed1 there should be ample space free from hanging rubber1 and it should not be possible for wet rubber placed in the upper room to drip upon the dry rubber below or upon packed cases4 ,there should be plenty of light1 and for this reason windows should be ample4 ,usually the window-frames are fitted with wooden shutters1 which are preferably hung on horizontal hinges from the top of the frame4 ,by this device it is not necessary to close all windows during a shower of rain1 and rubber may be stacked near a window with reasonable chance that direct sunlight will not be allowed to fall upon it4 ,in dealing with smoked sheet1 it is advised that the rubber to be examined should be placed upon tables facing the windows1 so that each piece may be scrutinised in a strong light4 ,crepe rubber also is best examined in a strong light1 but preferably with one's back towards the source of light or at an angle to it4 ,for this work coolies usually are most efficient when sitting on the floor4 ,it will be clear from the foregoing remarks that the best conditions would be secured in a separate building especially constructed4 ,a single room would be all that is required2 at one end sorting could be undertaken1 while packing could be done at the other end4 ,no hanging rubber should be allowed in the room4 ,the floor should be of hard timber1 and raised from the ground1 to the height approximately of a bullock-cart or motor-lorry1 as the case may be4 ,the boxes of rubber could thus be transported by small hand-trucks on a level with the transport vehicle1 reducing labour to the minimum4 ,the ventilation of the building should be good1 especially if cases of rubber are to be stored therein2 and the entire structure should be weather-proof4 ,,store-,,rooms ,,for ,,rubber ,,and ,,storage4--,the question of storage of rubber in factory buildings has always possessed importance1 but has demanded increased consideration recently4 ,from experience in this country1 it is clear that cement floors for store-rooms or packing-sheds are the least suitable4 ,they are often visibly damp1 especially in the early morning4 ,to allow rubber1 packed or unpacked1 to remain upon a cement floor in the tropics1 is to court trouble from moulds1 external or internal4 ,if the employment of a cement floor is unavoidable1 the rubber and boxes should be raised on wooden supports1 giving a clearance of at least #c or #d inches1 and there should be clear ventilation space between tiers of boxes4 ,experience indicates that the best type of floor is that already advised for sorting and packing rooms--i4e41 a good hard timber floor raised at least #c feet above ground-level4 ,apart from the advantage in labour specified in the previous paragraphs1 this provision of ample ventilation space below the floor is a great consideration in the preservation of the timber4 ,raised store-rooms become essential in low-lying districts which are at all subject to flooding1 yet the writer has seen many boxes of rubber damaged by flood-water entering a packing-room situated on the level4 ,the question has often been raised recently as to the length of the period during which rubber may be safely stored in this country4 ,the answer can be only supplied by experience1 of which up to the present we have none possible of being classed as reliable4 ,whatever storage may have been done in the past has been influenced greatly by the unsuitability of the storage accommodation1 and the fact that often the rubber was not prepared with a view to prolonged storage4 ,while the market demand was strong1 rubber was being shipped and passed into circulation1 at a rate which did not demand investigation of the subject of local storage4 ,in the year #aiah conditions were such as to bring the matter into prominence1 and we were able to tender advice on the lines given in this chapter4 ,the necessity passed1 but has again arisen4 ,our experience goes to prove that if rubber is properly prepared and thoroughly dried before packing1 it will remain in good condition for a period of a year or more in this country4 ,how much beyond a year it may be kept remains to be determined4 ,the assumption of proper preparation leaves great room for reservations4 ,in the case of crepe rubbers1 there is no great difficulty1 provided that the recognised methods and formulae are employed1 and that the rubber is packed only when perfectly dry4 ,under those conditions1 the higher grades of crepe remain apparently unaffected on storing4 ,any appreciable deterioration may be attributed to defective preparation or external causes1 such as accidental damage by water4 ,the prolonged storage of lower grade rubbers is attended by more risk1 especially in the case of the lowest grade 7earth-scrap7 from estates which neglect the practice of regular and frequent collection of the raw product4 ,the same reservation applies to crepes made from tree-scrap which is not collected daily4 ,in these types of crepe rubber tackiness may be initially present only in small degree1 but the final damage may be immensely greater by close contact of the folded rubber during prolonged storage4 ,when we come to discuss the possibility of storage of smoked sheets1 the difficulties become immensely greater4 ,we have yet no reliable experience as to the keeping properties of this grade when properly prepared1 fully cured1 correctly packed1 and stored under the best of local conditions4 ,it is understood1 of course1 that in the qualification by the term local conditions1 we assume it to be more difficult to store rubber generally in ,malaya than in a temperate climate4 ,the average temperature and humidity of the atmosphere are here much more favourable to the development of mould growths than would be the case1 say1 in ,great ,britain4 ,in discussing this question1 as far as it refers to the preservation by storing of smoked sheet rubber1 it is not fair to draw conclusions as to the likely behaviour of packed rubber from data based upon observation of loose specimens4 ,we have samples of smoked sheets prepared in #aiaj1 and these1 superficially1 appear to have remained unchanged4 ,no mould is present and1 as far as intermittent observation enables us to judge1 moulds have never been incident4 ,whether such rubber would have been preserved in this condition had it formed part of a packed case1 is a point upon which we have no experience2 neither can we give any opinion4 ,it seems true1 however1 that loose specimens keep better than bulk samples of the same preparation4 ,it cannot be argued that the present good condition of these old specimens may be due to correct preparation4 ,in those days methods and formulae were rather haphazard1 especially in view of the fact that the daily variability of dry rubber content of latices was not then recognised4 ,one would rather submit the factor of adequate smoke-curing as the chief influence in the superficial preservation of smoked sheets4 ,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 drying4 ,as a result1 very dark rubber was produced1 which was thoroughly impregnated with the products of wood combustion4 ,there would seem to be little doubt that this procedure was responsible for the prolonged freedom from mould growths4 ,market standards have varied to some degree since1 with a tendency to prefer a paler product than that in vogue1 say1 six or seven years ago4 ,moreover1 standardised methods of preparation have been introduced1 with the result that sheets of a desirably high standard can be produced in from ten to fourteen days1 when smoke-curing is conducted only during night hours4 ,some estates are equipped with smoke-houses which1 by continuity of working day and night1 provide smoke-dried rubber in from five to six days2 but the actual hours of smoke-curing are approximately equal to those of the ordinary type of house4 ,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 sheets1 and also for some complaints of under-curing1 where the term specifically refers to a failure to dry and cure the rubber thoroughly4 ,boxes of smoked sheets1 which had been stored for varying periods up to five months1 were recently inspected1 and1 in the majority of instances1 surface moulds were found to be plentiful4 ,in all cases it was observed that the trouble was intensified where boxes of rubber were stored in contact with cement floors4 ,this under-curing is not a question solely of the duration of smoke-drying1 although probably the modern practice of curtailing the period has exerted a great influence4 ,to make this clear1 it may be stated that1 given two batches of uniformly prepared wet sheets1 it would be possible to smoke-cure them for equal periods in different houses1 so as to produce one batch very much paler in colour than the other1 although the total hours of actual smoke-curing would be identical4 ,in order to produce such effects1 all that is necessary is to employ different timbers for fuel or different types of furnaces4 ,in the one case there would be produced heat and very little smoke1 while in the other the necessary heat would be obtained plus plenty of smoke4 ,the best results naturally are obtained by the employment of the happy medium1 and if smoked sheets have to be stored1 the ordinary period of smoke-curing should be prolonged to an interval consistent with the capacity of the smoke-house4 ,all precautions taken in preparation and curing can be nullified1 as already indicated1 by unsuitable storage conditions4 ,,tool-,,sheds ,,and ,,store-,,rooms4--,in some factories it is the rule to see lime1 cement1 spare rolls1 sieves1 and a general heterogeneous assortment occupying part of the rubber-drying rooms4 ,the inconvenience is often great2 and it certainly seems that these stores and tools are of sufficient value to be accommodated in suitable buildings4 ,,situation ,,of ,,factory ,,buildings4--,there can be no doubt that a great deal of the spot disease trouble1 and the general slowness of drying1 can be attributed in many factories to the unsuitability of the site chosen4 ,probably the idea which actuated those responsible for the choice of site generally was proximity to a water supply4 ,this would account for the fact that a number of factories are situated in valleys or near swamps4 ,more often than not1 also1 the actual clear space is very limited1 and rubber trees grow close up to the walls of the buildings4 ,under such circumstances1 it is difficult to see how these buildings can be anything but dark and damp1 and it is not difficult to understand the slow rate of drying4 ,in a few cases the sites chosen proved to be so unsuitable that the estates were confronted with a very serious problem1 the solution to which was1 either the erection of another complete set of buildings in a more suitable spot or the installation of artificial driers4 ,it must be laid down as an axiom that the first essential in a suitable site is that water may be brought to it easily1 but1 as already indicated1 this does not mean that the buildings need be placed in actual proximity to the water-supply4 ,the mistakes made by pioneers in this work are not likely to be repeated1 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 elevation1 whence the supply is gravitated to bungalows1 coolie lines1 and the factory4 ,the importance of securing a plentiful supply of good water for factory purposes cannot be exaggerated1 and it is a point which is only thoroughly appreciated on estates where smoke-sheet rubber has to be prepared4 ,the second essential1 but of equal importance1 is that there shall be an ample open space on which the sun may shine all day4 ,there must be no trees too near the buildings1 and there should be no adjacent swamps4 ,preferably1 the site should be on a raised position1 so that it will be impossible for surrounding trees to cut off sunshine1 even when they are fully grown4 ,from such an arrangement it will follow that the factory will be light and airy1 and the drying-houses will receive the maximum of benefit to drying from direct sunshine on the roof and walls4 ,there can be little doubt that these considerations play a most important part in determining the rate of drying of the rubber1 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 result4 ,presuming that the thin crepes made in two factories are equal in thickness1 it is not uncommon to find that in a drying-house1 situated in a wide open space1 the period of drying may be as low as six or seven days2 while in another drying-house1 situated near a swamp and surrounded by trees1 the period may be as high as eighteen days to twenty-one days4 ,the figures quoted are not fictitious1 but are facts actually noted in the course of the writers' experience4 ,a great deal also depends upon the exact position of buildings4 ,thus1 to obtain the maximum of light in a factory1 it will be obviously beneficial to erect it with the long sides running east and west1 so that the windows face the north and south1 and the large end doors face the east and west respectively4 ,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 enter2 but a moment's consideration shows that the south side would give the best results4 ,by the time the sun has come round to the south1 it is usually high in the heavens1 and the direct sunshine does not fall very far into the room4 ,even should it play upon the machines for an hour or two during the day1 no harm could result to the rubber which was being worked1 as no piece would remain there a sufficiently long time to be injured in the slightest degree4 ,placed in this position1 the maximum benefit of light would be obtained1 whereas if the length of the building ran east and west1 the machines would have only either the morning or afternoon light4 ,illustration3 ,,suggested ,,arrangement ,,of ,,building4 ,while it is advisable to erect a factory running east and west1 the drying-houses should run north and south4 ,in this position the maximum wall area will be exposed to the sun during the day1 and it will be possible to manipulate the windows of the drying-rooms so that those along one side are open1 and it will never be necessary to close all the windows at any time of the day4 ,thus the windows facing east will be closed1 and those facing west will be open until after midday2 then vice versa4 ,with such an arrangement a more uniform temperature may be obtained than by any other arrangement of the buildings4 ,if the building ran east and west1 the windows on the north side could remain open all day1 while those facing south would have to remain closed practically all day4 ,the south side of the house would be heated by the sun1 while the north side would remain cool1 and the rates of drying would be correspondingly unequal4 ,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 south4 ,similarly1 to obtain the best drying effect during the daytime in a smoke-house the building should run north and south4 ,by this means the temperature will be maintained to the maximum possible by sun heat1 and the rate of drying will correspond4 ,references to ,sketch ,plan4 ,drying-house ,no4 #b should be of two storeys1 and unless a separate sorting and packing room is to be built1 ,no4 #a should also have two floors 7see previous notes on packing-rooms74 ,in the factory-- ,v shows the position of the verandah1 which may be quite open and only divided from the inner room by ,s1 a wall composed of very strong expanded metal1 which allows light and air to enter the factory4 ,t1,t are the glazed tile tanks for the reception of latex1 scrap rubbers1 and bark-shavings4 ,m shows the position of the machines on the south side of the factory1 with the direction of extensions1 and ,e1,e the compartments in which the engines are bedded4 ,in these positions it is possible to obtain direct drive to the machines4 ,d1,d are large double swing or sliding doors 7the latter for preference always74 ,these1 while suiting transport of rubber1 provide also for a free draught of air4 ,if possible the scrap-washing machine should be placed outside the wall of the factory1 and tanks for the reception of scrap rubbers may then be situated in convenient proximity4 ,economy of labour is obtained by grouping all factory buildings as closely as possible1 but it should be borne in mind that smoke-houses should be regarded as a possible source of danger from fire4 ,this point has a practical bearing upon rates of insurance1 and it is essential that the smoke-house should be situated at a minimum of #ej feet from any other building or group of buildings4 ,in this connection1 also1 it may be noted1 as being of further practical interest1 that1 in the insurance of smoke-houses1 preferential rates are given to those having a good type of slow-combustion furnace4 ,,choosing ,a ,,factory ,,site4--,sufficient has been written to make it clear that the choice of a site for factory buildings is a matter demanding weighty consideration4 ,much1 of course1 depends upon the planted area1 and the rate at which it comes into bearing4 ,under certain circumstances which will be obvious1 it is permissible to instal first a group of buildings of a temporary nature only1 the future site and permanent buildings to be chosen later when the main portion of the estate comes into bearing4 ,often1 however1 one finds that1 from lack of forethought1 the estate has been committed to considerable expense in the establishment of equipment1 which later is proved to be unfavourably situated with regard to the majority of the area in ultimate bearing4 ,in such case1 transport of latex is fraught with difficulties and may be expensive4 ,in the instance of an estate which will gradually come into bearing1 it is not easy to decide whether a temporary installation shall first be provided1 or whether1 in anticipation of future demands1 a complete equipment shall be erected4 ,so much depends upon the financial aspect of the question1 and upon the rate at which areas will come into bearing4 ,as far as is possible1 the best policy would be that of a compromise under which the site would suit later requirements1 and the factory would be so planned as to be capable of future easy extensions both of buildings and machinery4 ,it is not possible to lay down any definite data as regards requirements based on acreage1 or to make comparisons between any two estates of similar acreage4 ,the important factors determining such requirements are3 7a7 ,area4 7b7 ,shape of the estate4 7c7 ,topography of the estate4 7d7 ,available supplies of water4 ,naturally the ideal site for factory buildings would lie in a central position1 given other favourable conditions4 ,,centralisation ,,or ,,decentralisation4--,it is the experience of a number of estates that1 all other conditions being favourable1 there is a limit beyond which the centralisation of factory work leads to an unwieldy position4 ,we are not here concerned with the few extremely large estates running into tens of thousands of acres4 ,in those cases the total area would be divided into economic sections4 ,the argument there would resolve itself into a discussion on the size of an economic section4 ,this1 in turn1 would be dependent upon the type of main product1 involving the question of transport of latex or coagulum1 and the possible provision of batteries of heavy machinery4 ,the differentiation between the transport of latex and coagulum1 respectively1 is a most important one1 and has a powerful influence in determination of the maximum of centralisation possible4 ,whereas properly prepared coagulum may be safely transported by bullock-cart1 light-railway1 or motor vehicle for many miles1 latex1 on the other hand1 demands very careful treatment4 ,anti-coagulants may be employed to preserve fluidity1 but only within certain limits4 ,even under these conditions1 other factors 7chiefly climatic7 exert an influence which renders the transport of latex for any distance a matter of anxiety4 ,it will be plain1 therefore1 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 made4 ,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-centralised4 ,apart from the difficulties inherent to the transport of latex in a state of good preservation1 there is the added difficulty of dealing quickly with large volumes of latex brought from various quarters4 ,none of these should be allowed to remain standing if the best results are to be secured2 but obviously there must at times be some congestion4 ,even on a small scale it is often found that the latest batches of latex are unfit for the preparation of good sheet rubber1 and the trouble may be easily exaggerated when working on a large scale4 ,the centralisation of work on crepe preparation1 therefore1 is limited only to a comparatively slight degree by distance of transport1 and in the main only by the size of the necessary equipment of machinery and drying accommodation4 ,the successful preparation of sheet rubber is1 on the contrary1 governed chiefly by the factor of transport4 ,with this consideration in view1 several large estates1 preparing sheet rubber as the chief grade1 have found it necessary to decentralise the factory work1 with very satisfactory results4 ,outlying sections are given uniform and complete equipments of necessary buildings on a small scale1 and hand-driven light machines4 ,uniform coagulating tanks are installed1 and the methods and quantities of chemicals employed are carefully standardised4 ,experience has shown that often the best sheet rubber coming to the market has been prepared on small estates2 and the same applies to the product of these decentralised stations on large estates4 ,there is no a priori reason why the product from one station should differ in the smallest particular from that of another1 apart from minor fluctuations which are due to variable weather conditions affecting the latex4 ,if the contrary is found to be the case1 it indicates failure on the part of the person responsible to follow the regular rules and methods4 ,in the natural scheme of development of a large estate1 it would be necessary1 of course1 to have a comparatively small centrally situated factory1 equipped with power and heavy machinery for working scrap rubbers in the preparation of crepe grades below ,no4 #a in quality4 ,as the yield per acre increases1 or the area in bearing expands1 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 ,no4 #a crepe rubber1 in order to be able to comply with prevailing market demands under which preferential rates fluctuate between pale crepe and smoked sheet4 ,,part ,,iv ,,the ,,finished ,,rubber ,,chapter ,,xvii ,,defects ,,in ,,crepe ,,rubbers ,,general ,,style ,,of ,,finish4--,broadly1 there is no single and definite style of finish1 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 finish4 ,very little thick or blanket crepe is now made on estates in ,malaya1 so that beyond the mention of that type little need be written4 ,a fair amount of blanket crepe is sold in the ,singapore market1 but it should generally be regarded as re-made rubber--i4e41 it may have been prepared from thin crepes1 or from native pale sheets1 in local rubber-washing factories4 ,in appearance these crepes have a rough finish1 and vary in colour according to the crude material employed4 ,the general preference of the market at present is for a thin1 smooth-finished crepe1 with a close-knitted surface--i4e41 free from what is described as laciness4 ,what effect this looseness of finish can possibly have upon the quality of the rubber is not understood1 but the standard type set up by the market must be comparatively free from small holes4 ,under existing conditions governing the sale and purchase of rubber1 various standards are set up4 ,these really have no bearing upon the intrinsic qualities of the rubber1 and are concerned almost entirely with superficial attributes4 ,they are necessary in the absence of any proper scheme of evaluation for the establishment of certain standards of comparison1 which imply that the rubber is apparently clean1 free from certain recognised defects1 and has been carefully prepared--as far as can be determined by a superficial examination4 ,thus the question of finish has attained disproportionate importance1 but must be respected when preparing rubber for sale4 ,under ordinary conditions1 thin crepe rubber1 as it leaves the finishing machines1 has what may be termed deckled edges4 ,on many estates1 in order to comply with market conditions1 the edges of the wet crepe are trimmed1 and the trimmings re-made into lengths of crepe4 ,this is done under the impression that the market price is influenced by the evenness of the edges of crepe rubbers4 ,again1 it sometimes happens that1 owing to wear of the rolls1 the finished dry crepe may show a faint but distinct pattern of mark--a diamond or a horizontal bar4 ,since these are not accepted under the standard comparisons1 rubber exhibiting these characteristics does not obtain the top market price4 ,in other words1 these innocent and innocuous marks are regarded as defects and penalised accordingly4 ,enough has been written to show how very important becomes the question of finish4 ,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 rubber4 ,methods of preparation and formulae for the employment of chemicals are so well laid down that1 up to the stage of machining1 no difficulty need be encountered4 ,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--i4e41 macerators1 intermediate crepers1 and smooth finishing-rolls4 ,this subject has received full discussion in ,chapter ,,xiii41 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 condition4 ,if1 on the other hand1 the factory has ample machinery for requirements1 and a good finish cannot be obtained on the thin crepe1 then it is time the rolls were attended to and changed1 or that the ratios of the driving pinions were altered4 ,,dirty ,,edges4--,it seems to be almost impossible to keep old machines clean1 and it is equally difficult to keep the edges of crepe free from oil and dirt4 ,usually these dark edges are to be found on crepe which is rather wide1 and it will be noticed that where wide crepe is made1 unless special precautions are taken1 the edges of the rubber often pass under the edges of the hopper and so pick up dirt and oil4 ,on most machines it is a great mistake to attempt the preparation of wide crepe2 nothing but narrow crepe must be made4 ,to obtain this it is necessary to decrease the width of the hopper placed above the rolls4 ,this can easily be effected by blocks of heavy hard wood1 cut to shape and fastened in position4 ,sometimes the dark edges of crepe are due to another cause4 ,rolls may be gradually worn in the middle1 so that to obtain a good finish it becomes increasingly necessary to tighten up the screws which regulate the distance between the rolls4 ,it thus happens that just at1 and beyond1 the edges of the rubber the rolls grind upon each other1 and fine particles of iron and graphite are transferred to the rubber4 ,in such a case it is evident that either the rolls must be turned or that a new pair of rolls must be substituted4 ,,iron-,,stains4--,one of the causes of iron-stain on rubber has been mentioned in the preceding paragraph4 ,this particular kind of iron-stain must not be confounded with rust-stain1 and gives a dark dirty colour4 ,it results from the grinding together of the rolls1 and is usually noticed in the finishing of fine pale crepe4 ,for this operation it is necessary to screw up the rolls tightly1 and it will be plain that1 whenever the rolls are vacant of rubber1 there is a tendency for them to grind upon each other1 thus setting free fine particles of iron and graphite4 ,in order to avoid this1 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 rubber1 which may be kept for the purpose4 ,in some factories this trouble apparently does not exist1 while in others the amount of wear on the rolls is surprisingly great1 and the damage done to the rubber is excessive4 ,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 material4 ,some rolls seem to be excessively soft1 and from these contamination by iron-stain is great4 ,for this reason rolls are sometimes rejected1 and there would appear to be an objection to any but chilled steel rolls for the final stage of finishing crepe rubbers4 ,,rust-,,stains4--,rust-stains1 on the other hand1 throw the responsibility entirely upon the labour and supervision of the factory4 ,rust is formed upon the rolls when they are at rest1 and any one passing pale rubber between the rolls before they have been thoroughly cleaned is guilty of culpable negligence4 ,even when apparently clean1 a piece of lower grade rubber should be passed through the rolls several times so as to remove any slight trace of rust remaining4 ,rust-stains have also been caused in a few cases by the large knives which are used to cut up lumps of coagulum1 or by allowing freshly coagulated rubber to come into contact with iron vessels in the factory4 ,a similar appearance has been traced in a few instances to contamination of the coagulum in transit by the dust of the reddish rock 7laterite7 employed in localities for road-making4 ,,oil-,,marks4--,the origin of oil-marks in crepe has already been described in ,chapter ,,xiii4 ,the whole question resolves itself into one of cleanliness1 moderation in lubrication1 and supervision4 ,the machines should be inspected every day1 and once a week rolls may be swabbed down with a #aj per cent4 solution of caustic soda applied by means of a piece of cloth fastened round the end of a stick4 ,immediately after this operation water should be turned on and the rolls set in motion1 so that all traces of caustic soda are thoroughly removed4 ,if possible1 lubrication by oil should be substituted by grease lubrication through screw caps4 ,particular attention should be paid to the back of the machines4 ,none but the individual in charge of engines should be allowed to lubricate the machines1 and he should be held responsible for any excess of lubricant4 ,as a rule oil-marks are restricted to the edges or the proximity of the edges of crepe1 but sometimes the streak is to be found in the middle of the length4 ,in such a case it is almost certain that the oil or grease has been picked up by the rubber in the tray4 ,it sometimes happens1 if the liners of the bearings are eccentrically worn1 that a few drops of dirty oil or a particle of grease are squirted out to some distance4 ,these usually find a resting-place in the tray1 and the contamination may then appear in any part of the rubber4 ,it will be clear1 therefore1 that all trays beneath machines should be examined as the probable source of danger from contamination by oil and dirt4 ,if the trays are as wide as or wider than the effective portion of the rolls1 they should be discarded4 ,in their place 7except sometimes in the case of the macerating machine7 all that is necessary is a movable piece of board1 in width not less than from #d to #f inches shorter than the width of the rolls4 ,any oil or grease ejected from the bearings will thus be allowed to fall clear of the board2 and defects due to oil streaks1 etc41 will be very much diminished1 if not entirely obviated4 ,this point in connection with the damage possible by the existence of wide trays is commended to the notice of manufacturers of machines for plantations1 as it is common to find that trays are made which contravene the rule prescribed by experience4 ,in fact1 trays on some machines have been so designed as to act as traps for all dirty matter exuding from the bearings4 ,not only so2 they are sometimes made of such a shape and height that oil or grease lodging upon the edges act as a wipe to the rolls1 thus increasing the possibility of contamination4 ,until this defect was investigated1 it was common to note continued contamination of pale crepes in spite of all precautions taken in cleaning the rolls at frequent intervals4 ,the trouble due to this cause is intensified when the same machines are employed for the preparation of scrap-rubber crepes and ,no4 #a crepe4 ,small pieces of scrap find their way towards the bearings and lodge on the edges of the trays4 ,unless a thorough inspection is made before proceeding with the working of the ,no4 #a 7pale7 grade1 contamination may be continuous4 ,,dirt4--,streaks due to the presence of dirt 7as apart from oil or grease contamination1 or that due to pieces of oxidised scrap7 are unusual1 and when they do appear their origin seems to be somewhat of a mystery4 ,it could scarcely be advanced that the dirt was picked up on the machines1 as it is difficult to imagine where such dirt could come from4 ,in one or two instances there has been fairly clear evidence that the dirt was contained in the coagulum1 and the only explanation fitting the case is that it fell into the latex after straining and during the course of coagulation4 ,on cutting open lumps of coagulum brought in from the field division1 it has sometimes been noticed that dirt is included1 and the foregoing explanation is the only reasonable one4 ,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 coagulated4 ,,holes4--,on some estates it would seem impossible1 with the existing machines1 to make really good crepe4 ,the complaint is that1 if thin crepe is attempted1 it is invariably found to be full of holes2 and as1 apparently1 the presence or absence of small holes in crepe rubber is a factor which influences buyers1 this defect must be avoided at all costs4 ,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 explain4 ,as a matter of fact1 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 washing4 ,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 valuation4 ,this is usually achieved by making a very thin crepe and rolling together two lengths when wet4 ,the resulting crepe may be slightly thicker than ordinary1 and the method employed may be usually detected by the appearance of the edges unless these are trimmed4 ,,greenish ,,and ,,tacky ,,streaks4--,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 perceptible4 ,experience indicates that these streaks are much more dangerous than they appear superficially1 inasmuch as they contain traces of brass from the liners of the bearings4 ,the presence of the copper in brass is responsible for a gradual disintegration of the rubber1 commonly recognised as tackiness4 ,in fact1 copper may be said to be a poison to rubber1 and every effort should be made to avoid possible sources of contamination4 ,the effect may be proved easily and perceptibly by fastening together several pieces of crepe rubber by means of a brass paper-fastener4 ,in course of time a salt of copper1 green in colour1 will be formed1 and it will be found that the portions of rubber in contact with the fastener have perished and become tacky4 ,this contamination of crepe rubber may take place in two ways3 7#a7 ,by the ejection of actual particles of brass from the bearings of machines1 due to eccentric grinding of the standards of the rolls upon the brass bushes4 ,these particles are carried by exuded oil or grease into trays1 and thence to the rubber4 7#b7 ,by the action of an acid lubricant upon the brass1 with the formation of a metallic soap which has a decided green colour1 unless obscured by the dark colour of the oil or grease4 ,it is transferred to the crepe rubber in the manner indicated above4 ,the inevitable effect1 apart from the superficial defect1 is incipient tackiness4 ,the extent to which this may develop will depend upon the amount of the copper compound present1 but it should be remembered that an exceedingly small trace is capable of causing a disproportionately large amount of damage4 ,this effect is further magnified if the tacky piece of rubber is packed in close contact with previously unaffected rubber4 ,when the defect is discovered1 the affected portions should be cut out1 and the cuttings should be burned4 ,to mix them with the lowest scrap grades1 as may be done thoughtlessly1 is only inviting further trouble4 ,besides the source of danger already indicated1 it may be found1 but far less frequently1 that contamination may arise from the presence in the rubber of small pieces of the brass mesh which is generally used for straining latex4 ,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 alone4 ,this does not agree with our experience4 ,an experiment was made to test the point using fresh oil and grease drawn from drums in stock1 specimens of the same lubricants to which traces of a copper salt were added1 and samples of lubricants taken from the bearings of several machines4 ,the treated pieces of rubber were placed in contact with untreated pieces of crepe which served as blanks4 ,notes were made at intervals extending over a period of two years4 ,the conclusions arrived at were3 7#a7 ,although there was surface discoloration1 no tackiness had been caused by fresh 7unadulterated7 lubricant2 neither were the blanks affected4 7#b7 ,in the majority of specimens upon which had been smeared a small streak of lubricant taken from the bearings of machines1 tackiness had supervened1 and had developed likewise in the contact blanks4 7#c7 ,in all cases where a trace of copper salt had been used to adulterate the fresh lubricant1 tackiness was to be noted in the course of a short period 7a week upwards7 after the rubber was dry4 ,development was slow1 but progressive1 over the full period of experiment1 and the blanks in contact were affected4 ,the degree of affection was determined by the proportion of copper salt employed4 ,in the worst cases the affected strip of rubber had deteriorated and disintegrated to such a degree as to cause a distinct longitudinal gap1 the edges of which appeared to consist of a moist gummy substance of a deep syrup colour4 ,the adjacent blanks in some cases exhibited a similar appearance in lesser degree1 or were merely affected by a characteristic brownish stain4 ,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 necessary4 ,experience shows that it is not necessary4 ,machines in use for years have been running with plain bearings of iron or other metallic substances4 ,satisfaction is obtained without the use of brass4 ,,cotton ,,and ,,other ,,fibre4--,one of the most frequent complaints made against low grade crepes is the presence of fibre--generally classed in a wholesale fashion as cotton-waste4 ,it is true that some years ago most of the complaints were genuine in referring the cause to cotton-waste4 ,the defect arose chiefly owing to the careless use of this material in the factory4 ,lumps of waste when discarded were often thrown to the ground1 and became mixed with the heaps of scrap rubber and bark-shavings awaiting attention4 ,the fault was one of sheer negligence1 and nothing can be advanced in extenuation4 ,even when the soiled waste was thrown into the external drains1 it often returned to the factory mixed up with the scraps of rubber recovered by means of the drain-screens4 ,as far as the complaint concerns itself with cotton-waste only1 the remedy is plain1 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 mechanics4 ,in the vast majority of cases1 however1 the defect arises from circumstances beyond the direct control of the factory1 and under conditions which make it difficult to check the evil4 ,although against instructions1 and for the purpose of fulfilling other orders1 some coolies persist in using pieces of cloth for cleaning cups4 ,in course of time1 unless the practice is detected1 this cloth becomes coated with rubber4 ,careless coolies throw it away1 when it may be collected by the individuals who gather earth-scrap2 or it may be brought into the factory in the tappers' scrap-bag4 ,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-washer4 ,it is an easy matter to condemn the sorting as being careless1 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 workers4 ,it will be clear that contamination by fibrous matter should be limited practically to the lowest grades of rubber4 ,the appearance of cotton-waste in high-grade crepes must be most unusual1 and the writers have not yet seen a case in a drying-house4 ,that it does occur1 however1 seems to be evident from brokers' reports4 ,it is extremely difficult to imagine how the waste enters the rubber4 ,one possible explanation is that a coolie may have been cleaning the rolls surreptitiously with waste1 which may have passed later into the rolls together with rubber4 ,another explanation was offered in one factory by the observed fact that coolies engaged in cutting up coagulum1 ready for passing into the machines1 kept a wad of waste for the purpose of keeping the knife-blade clean4 ,this may have found its way into the rolls4 ,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 matter4 ,,bark ,,and ,,grit4--,with ordinary machines and the usual process of working1 it would seem impossible to wash and macerate some of the scrap rubbers sufficiently to free them entirely from bark4 ,this applies specially to the grade of rubber prepared from bark-shavings4 ,specimens have been handled in which it was practically impossible to detect bark1 but in such instances the amount of working necessary would be such as to interfere seriously with the regular working of the factory4 ,even with the employment of special scrap-washing machines1 complaints of the presence of bark in dry crepe have been received1 but it is certain that this mode of operation reduces the quantity of bark to a minimum4 ,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 limited1 it must be recognised that the working of lower grades of rubber is usually insufficient1 and that where possible it is the duty of estates to pay more attention to these lower grades4 ,a considerable improvement in this direction has been noticed of recent years4 ,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 grounds1 and that they are not frivolous objections put forward for the purpose of depressing the price of the article4 ,the sooner such an idea is jettisoned the better4 ,there would appear to be a good future demand for the lower grades1 and it is only natural that consumers will be willing to pay the best price only for an article which is clean4 ,the same arguments apply to the complaints regarding the presence of sand and grit4 ,the quantity of the latter found in low-grade crepes from some estates is surprisingly high4 ,its presence can often be shown by the simple device of spreading a piece of crepe over the upturned and hollowed palm of one hand1 while striking the rubber with the other hand4 ,the incidence of bark in higher grades of crepe may be due to inadvertence or to gross negligence4 ,in the former class one might put those occasions on which pieces of bark are embedded in lumps of naturally coagulated rubber4 ,a piece of bark-shaving may fall unnoticed into latex and be partially responsible for the coagulation which takes place4 ,this piece of coagulated lump may be massed with others1 and hence1 unless each small piece is cut up1 the bark is not perceived4 ,or again1 by some unknown means1 a piece of shaving may drop into a jar of latex1 and so become embedded in the coagulum4 ,sometimes this becomes evident on cutting up the rubber1 but it is quite as likely to pass unseen4 ,on the whole1 the presence of bark in first-grade rubber is most unusual1 and should be seen before the rubber is packed4 ,in the class due to negligence may be included cases in which careless coolies place the cup upon the ground before tapping4 ,pieces of shavings fall into the cup1 and coolies are too lazy to pick them out4 ,more often than not coagulation in the cup is caused4 ,as it is impossible for the ,european staff to supervise each individual tree tapped1 some cases must continue to pass unheeded4 ,sometimes bark-shavings are brought in with the latex1 and if a broken sieve is being used1 these1 with other impurities1 pass into the jar1 and are embedded in the coagulated rubber4 ,this must be classified as negligence1 for no manager would willingly allow the use of a broken sieve4 ,again1 naturally coagulated lump rubber on arrival at the factory sometimes contains evident pieces of bark1 leaves1 and stems of leaves4 ,for lack of supervision the average coolie would not think of picking out these obvious impurities1 and would pass the whole mass into the machines4 ,,oxidation ,,streaks4--,since the introduction of sodium bisulphite defects due to streaks1 caused by portions of the coagulum becoming oxidised1 have practically ceased to exist4 ,in the usual course1 and without the use of an antiseptic agent1 the freshly coagulated rubber has a surface darkened by oxidation4 ,unless this dark surface were carefully cut off1 there would result a crepe containing dark streaks caused by the mixture of the oxidised surface portion with the bulk of the paler coagulum4 ,the presence of oxidation streaks in ,no4 #a crepes1 now being made1 would imply either that no anti-oxidant substance was in use1 or that the quantity necessary to prevent this surface oxidation is exceedingly small4 ,although the price obtained would appear to be influenced by the presence of oxidation streaks1 no evidence can be obtained that the actual quality of the rubber suffers to the same degree as does the appearance--i4e41 there is no evidence to show that a pale rubber1 in which surface oxidation has been inhibited1 is intrinsically superior to one in which slight natural oxidation has been incident4 ,,yellow ,,latex ,,streaks4--,this appearance of yellow-latex streaks in not common1 and may be accounted for by incomplete mixture of two different latices4 ,it is a fact of common observation that1 when a new portion of bark is being tapped for the first time1 there is a distinct yellow tinge in the latex excluded4 ,as tapping progresses1 this colour vanishes2 usually it may persist for a period varying from two weeks to more than a month4 ,should this latex be poured into ordinary latex without thorough mixing1 it is sometimes found that1 when the crepe rubber is dry1 there are distinct yellow streaks4 ,it should be remembered that1 as the rubber content of the latex from first tappings is high1 this latex is lighter than latex which is more dilute1 so that the mixed latices must be well stirred with a broad paddle to obtain intimate mixture4 ,it would be much better to keep yellow latex apart1 and coagulate it separately1 if at all possible4 ,in such case the resultant crepe may be of a distinct canary yellow in tint4 ,in scrap-crepes of the higher grade this distinct yellow colour is often visible in streaks which indicate the presence of tree-scrap1 etc41 obtained from recently opened tapping areas4 ,,bisulphite ,,streaks4--,these1 again1 arise from defective mixing4 ,in the dry rubber it is seen that there are streaks of colourless rubber in a general mass1 which may be of varying shades of yellow2 or1 a length of exceedingly pale rubber is apparently streaked in patches with a darker shade of colour4 ,a solution of sodium bisulphite is heavier than latex1 and there would be a tendency1 therefore1 for the chemical to sink in the large mixing jar4 ,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 share4 ,especially would this effect be seen where coagulation takes place quickly1 and experience bears out the truth of the suggestion4 ,another factor which has some bearing on the point is the strength of solution in which sodium bisulphite is used4 ,in the ordinary course of working1 the acid coagulant is added immediately after sodium bisulphite has been stirred in4 ,should a strong solution of the bisulphite be used1 and if coagulation takes place quickly1 it is easy to see that the possibilities of obtaining a uniform and intimate mixture are small4 ,probably in no factory is the sodium bisulphite now added to latex in powder form1 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 rubber4 ,the undissolved particles sink to the bottom of the coagulating jar or tank1 and there slowly dissolve1 forming local strong solutions4 ,the effect upon the rubber in the vicinity of these strong solutions is much more marked than in the bulk of the coagulum1 and hence lighter streaks or patches appear in the dry rubber4 ,in spite of apparently complete mixture by good stirring1 it will be seen that it is possible1 therefore1 to have failed in this direction if any undissolved powder remains in the solution of sodium bisulphite4 ,,spot ,,disease4--,few managers of estates preparing pale crepe rubbers are unacquainted with this defect4 ,it is manifested by the appearance of small coloured spots varying in density 7i4e41 number to a unit area7 and differing in hue4 ,the most common colours are black and orange1 but spots of brick-red1 yellow1 violet and ruby and green tints have been noted1 the last named very seldom4 ,sometimes in place of definite spots1 or colonies1 the colour is spread over practically the whole surface of the rubber as a flush4 ,these coloured spots1 or flushes1 indicate infection by minute fungi1 which are present in the latex prior to coagulation4 ,the infection of the latex takes place in the field by means of spores1 which are only visible with a microscope4 ,it is not feasible to discuss any method of preventing this infection of latex by air-borne spores1 as the eventual preventive measures are so simple4 ,but it may be believed that under ordinary weather conditions most latices are infected before reaching the factory4 ,it is likewise true that even fine pale crepes shipped in perfect condition may contain possibilities of trouble in the form of dormant spores1 the development of which may commence and continue if favourable conditions arise4 ,the subject of ',spot' ,diseases has been treated fully in previous publications1#ai and it is not proposed here to enter into any lengthy discussion4 #ai ,preparation of ,plantation ,rubber1 ,sidney ,morgan1 #aiac4 ,spotting of ,plantation ,rubber1 ,keith ,bancroft1 #aiac2 ,bulletin ,no4 #af1 ,f4,m4,s4 ,department of ,agriculture4 ,spotting of ,prepared ,plantation ,rubber1 ,a4 ,sharpies1 #aiad2 ,bulletin ,no4 #ai1 ,f4,m4,s4 ,department of ,agriculture4 ,if any reader is desirous of producing the defect experimentally1 all that is necessary is to prepare a piece of crepe rubber of rather more than ordinary thickness1 roll it up while wet1 and place aside for some days4 ,this experiment reproduces the conditions favourable for the development of the spores1 and spots of various colours may result4 ,it will be clear that the chief factor influencing the result is the continued presence of plenty of moisture4 ,this condition may be created inadvertently in the course of factory practice1 if piles of crepe rubber are allowed to remain for any appreciable period before hanging to dry4 ,for this reason batches of wet crepe should always be placed on edge1 to allow free drainage of surface moisture1 if the rubber cannot be taken at once to the drying-sheds4 ,illustration3 ,,three ,,specimens ,,of ,,fine ,,pale ,,crepe ,,suffering ,,from ,,spot ,,disease4 ,the condition also is provided if the thickness of the crepe is excessive4 ,in some factories1 having no smooth-roll finishing machines1 the crepes may have a distinct raised pattern upon them4 ,it is usual to note that if spot disease appears in such crepes1 it is incident to much greater degree in the thicker portions of the rubber--i4e41 upon the raised pattern4 ,the direct connection between the rate of drying and the appearance of coloured spots or flushes is thus established1 and it only remains to adopt precautionary measures which will lead to an avoidance of delay 7#a7 between machining and hanging1 7#b7 in drying4 ,it is indicated1 therefore1 that1 if spot disease is to be avoided1 the prime consideration is the preparation of a thin crepe which will dry quickly under average conditions4 ,it may sometimes happen that even very thin crepes will sometimes be found affected on some estates4 ,in such instances1 it will be found that the design or situation of the drying-house is at fault1 and that specially favourable conditions for the development of the fungi have been created by excessively wet weather4 ,should the trouble persist in spite of the preparation of the thinnest crepe1 it would be advisable either to abandon this form of ,no4 #a product or to consider the installation of artificial aids to drying4 ,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 disease4 ,there appears to be an idea held in some quarters that sodium bisulphite may be so employed as a fungicide4 ,this does not agree with our experience1 which is confirmed by ,sharpies 7,bulletin ,no4 #ai1 ,f4,m4,s4 ,department of ,agriculture74 ,in #aiac experiments with chinosol were undertaken at the ,pataling ,laboratory of the ,rubber ,growers' ,association1 and an account of the method of treatment was given in a printed report issued to subscribers4 ,dr4 ,p4 ,arens1#bj of the ,malang ,experimental ,station 7,java71 has also recommended the use of chinosol4 ,the substance is expensive1 but is effective in very small quantity4 ,on the whole1 given average conditions in factory practice1 such aids should not be necessary1 and where keen supervision is not available may lead to other difficulties4 #bj ,guide to the ,preparation of ,rubber1 ,arens1 #aiah2 ,communications from the ,experimental ,station 7,malang1 ,java74 ,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 fungi4 ,the condition necessary to such an occurrence is supplied by the presence of moisture4 ,thus1 to state instances which are by no means uncommon1 if a box of rubber is allowed to remain exposed to rain1 or is damaged by flood-water1 or by sea-water during transit1 or 7sometimes7 if the rubber is packed in a damp case1 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 period4 ,no means are known by which these coloured spots1 due to the growth of chromogenic organisms1 can be removed from the rubber4 ,naturally1 although they may be present in the darker lower grades of crepe1 they are not so easily visible as in pale crepe4 ,it follows1 therefore1 that every possible precautionary measure must be taken when pale crepe has to be prepared4 ,we are often asked whether it is possible for an infected piece of rubber to affect sound rubber hanging in the same building2 and whether1 in case of spot disease appearing1 it is necessary to disinfect the drying-house4 ,in a general sense1 the answer to both queries is in the negative4 ,it has not been proved possible to transmit the disease from one piece of crepe to another1 except by the closest possible contact and in the presence of an abundance of moisture4 ,a dry crepe1 even when in close contact with an infected dry specimen1 has not been found to be affected4 ,unless1 therefore1 pieces of rubber are pressed together1 under favourable conditions as to moisture1 there has been observed no transfer of disease4 ,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 building4 ,furthermore1 after the removal of diseased rubber from the drying-shed1 freshly prepared rubber may be hung on the same supports without becoming affected1 and without any intermediate treatment of the wooden bars1 providing the crepe is thin and weather conditions are good4 ,in our experience1 no case has been observed in which the disease has been communicated to freshly prepared rubber by reason of the previous presence of affected rubber4 ,in our opinion1 therefore1 any scheme for disinfecting the interior of a drying-house1 as a preventive measure against the spread of spot disease1 is unnecessary4 ,all other things being equal1 it is plain that much will depend1 as to the incidence of coloured spots1 upon the design and situation of the drying-house4 ,sufficient has been written in previous chapters to indicate the importance of these points as affecting the rate of drying1 upon which hinges the possibility of the appearance of spot disease4 ,in conclusion1 the chief points in any discussion of this subject may be summarised thus3 #a4 ,no coagulum should be left without working for longer than the ordinary period4 ,otherwise1 the prevailing conditions are very favourable for the development of the disease4 #b4 ,thin crepe only should be made4 ,the quicker the rate of drying the less possibility is there of the coloured spots appearing4 #c4 ,crepe should never be allowed to remain folded overnight1 and batches of folded wet crepe should be placed on edge to drain off surface moisture4 ,the rubber should be hung to dry as soon as possible4 #d4 ,several species of fungi causing coloured spots have been recognised1 and it has been proved conclusively that it is possible to infect latex and also fresh coagulum4 #e4 ,as far as our present knowledge goes1 it appears that infection takes place chiefly1 if not entirely1 by means of the latex in the field-vessels4 ,it may take place during transport also1 or even during coagulation4 #f4 ,while it is certain that infection can be caused by contact1 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 least1 under ordinary drying conditions4 #g4 ,there is reason to believe that no further infection takes place once the rubber is well into the drying stage1 and that dry rubber is not infected even by contact4 ,from this one might infer that1 as long as rubber remains dry1 infection cannot take place during the voyage to the port of consignment4 #h4 ,coloured spots do not appear until the rubber is about half dry1 because that period is necessary for the development of the fungus to that stage in its life-history when it excretes colouring matter4 ,the fungus in its earlier and colourless stage may have been present from the time the latex entered the cup4 #i4 ,the natural habitat of the fungi would appear to be decaying vegetable matter in the field4 #aj4 ,finally1 if it is found impossible to be rid of fungoid-spot disease after having exercised all care and observed all known precautions1 nothing remains but to supersede the ordinary drying process by some system of quick drying1 such as the vacuum-drying process or a hot-air draught system1 in which the rubber dries so quickly that any possibility of appearance of spots is entirely removed4 ,,surface ,,moulds ,,or ,,mildews ,,on ,,crepe ,,rubber4--,defects of this nature are most uncommon in the higher grades of crepe rubber1 but cases of affection in the lower grades are not rare4 ,it will be evident from all previous discussions that the incidence of these moulds must be due to an extremely slow rate of drying4 ,the necessary conditions would be supplied by one or more of the following causes3 7a7 ,making the crepe too thick4 7b7 ,hanging the crepe in a badly ventilated or badly situated building4 7c7 ,occasionally by abnormally wet weather4 7d7 ,allowing piles of crepe to remain too long before hanging4 7e7 ,using excessive quantities of deteriorated sodium bisulphite4 ,in short1 any factor contributing towards a retarded rate of drying may be responsible for the appearance of surface mildews4 ,the last mentioned cause is of not infrequent occurrence4 ,knowing the chemical to be of poor quality1 relatively more is used to produce the desired anti-oxidant effect4 ,unless the rubber is particularly well washed on the rolls1 there remains within it a residue of sodium bisulphate1 an oxidation product of the bisulphite4 ,this is hygroscopic to some degree--i4e41 it takes up moisture from the atmosphere4 ,hence drying is delayed1 and even should mildews not develop the chemical may sometimes be seen on the surface of the rubber as a whitish bloom4 ,the enumeration of the possible causes of mildews on crepe rubber is sufficient to indicate the necessary precautions to be taken1 and the discussion will not be extended further4 ,,tackiness ,,in ,,rubber4--,tackiness is a term used to denote a deterioration of rubber which renders it sticky1 and1 beyond this1 implies that some physical and chemical change in the nature of the substance has taken place4 ,in fact1 it is no longer rubber1 but an oxidation product containing much resinous matter4 ,it does not behave as rubber1 and hence its value is much depreciated4 ,with modern ideas of erection of factories to guard against the introduction of direct sunlight1 it was hoped that this defect had practically ceased to exist4 ,in one grade of rubber it would be expected that tackiness would continue to appear4 ,earth-rubber1 often exposed to direct sunlight for a week1 would naturally become tacky1 and this tackiness cannot be avoided unless the earth-scrap is to be collected more frequently4 ,but in many cases even the higher grades of rubber show signs of tackiness4 ,experiments have been carried out at various times and in various places to determine the cause of tackiness4 ,for some time the theory of bacterial origin was in favour1 but none of the experimental results was convincing4 ,bacteria may be present in tacky rubber2 but1 on the other hand1 many cases of bacteria in rubber have been observed in which there was no tackiness4 ,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 rubber4 ,in opposition to the results which were stated to have been obtained1 there was no spread of tackiness4 ,other investigators have obtained similar results4 ,one writer proposed to explain tackiness as caused by excess of moisture4 ,this perfectly simple explanation unfortunately displays only a profound ignorance of the subject1 and does not take into account the fact that tackiness is incident in rubber after dryness has been reached4 ,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 holdings1 with no resulting harm as long as plenty of moisture is present in the rubber4 ,,tackiness ,,the ,,result ,,of ,a ,,slow ,,process ,,of ,,change4--,as stated above1 tackiness does not appear until the rubber is dry1 and even then it is to be noted that it is possible for tackiness to appear in rubber arriving in ,london1 which showed no indications of tackiness when packed for shipment4 ,,tackiness ,,caused ,,by ,,traces ,,of ,,copper ,,salts4--,spence1 as the result of investigations1 has pointed out that none of the various theories put forward to account for tackiness--viz41 the action of bacteria1 premature putrefaction1 oxidation1 excess of moisture1 the action of enzymes1 etc4--have any basis in scientific proof1 and believes that the cause of tackiness cannot be directly attributed to bacteria4 ,it has been stated that the only known way of causing rubber to become tacky is to expose it to sunlight or heat4 ,while agreeing that in the ordinary way this statement is correct as far as one rules out the employment of chemical substances1 it must be pointed out that tackiness of the worst degree may be caused by the presence of traces of copper or copper salts4 ,this point has already been touched upon in a preceding paragraph dealing with the defect of green streaks in pale crepe rubber4 ,in the course of laboratory experiments tackiness has often been induced by the use of traces of copper salts4 ,the rate at which tackiness is induced appears to be dependent upon the amount of copper salt used1 but once it begins1 the rubber molecule is very rapidly broken down1 and resins are formed4 ,as the formation of resins is accompanied by the inclusion of oxygen in the chemical constitution1 it would be expected that dry rubber becoming tacky should increase in weight4 ,this is found to be the case1 and to give an idea of how this weight increases with the progress of tackiness1 the results below may be studied4 ,it will be seen that the maximum quantity of copper sulphate used amounted to #j4jbe per cent1 7approx47 upon the weight of latex taken4 ,now it is highly probable that only a fraction of this quantity was retained in the rubber on coagulation1 the remainder being in solution in the serum4 ,furthermore1 as the rubber was well washed and worked down to thin crepe1 the total quantity of copper salt remaining in the dry crepe must have been exceedingly small4 ,yet the effect is most marked and should impress upon all managers the necessity for guarding against any possible contamination caused by brass or copper4 ---------------------------------------- ------------------------------- ,sample4 ,weight of ,rubber4 ------ ---------------------------------------- ,after ,further ,further ,percent- ,amount of ,copper ,salt4 ,when ,interval,interval,intervalage in ,in- ,dry4 of ,four of ,sevenof ,threecrease in ,weeks4 ,weeks4 ,weeks4 ,weight4 ---------------------------------------- --------------------------- ,grms4 ,grms4 ,grms4 ,grms4 #a #j4jb grms4 copper sulphate per #ajj c4c4 #dcj #dda #dhb #dhh #ac4e latex #b ,ditto #dbh #dci #dha #dhf #ac4ee #c #j4ja grms4 copper sulphate1 per #ajj c4c4 latex #ifb #ihg #ajce #ajcf #g4g #j4ja grms4 copper acetate1 per #ajj c4c4 latex #d #j4jbe grms4 copper sulphate1 per #ajj c4c4 #ejb #eac #eeh #efj #aa4e latex ---------------------------------------- --------------------------- ,in view of the effect thus produced by the addition of traces to latex of a copper salt1 and the observed effect on rubber of contact with copper salts1 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 moulds6 ,with the exception of this chemical action we know of no other means by which tackiness is produced1 beyond those of direct sunshine and heat4 ,cases governed by these two causes are common on estates4 ,they are confined chiefly to the lowest grades of scrap rubber1 when the component raw materials have been exposed to the sun for a period before being brought to the factory4 ,it is now comparatively rare to find cases of tackiness in the higher grades of crepe1 and when they occur1 one may look for evidence of gross carelessness in the admission of direct sunshine4 ,usually this means the failure of some individual to regulate window shutters according to the position of the sun in the sky4 ,more rarely does it happen that tackiness may have been induced by placing thin crepe rubber too near the iron roof of the drying-shed4 ,regarding the question as to whether tackiness may be communicated by direct contact1 opinion appears to be divided4 ,it has been stated that sound rubber left in contact with tacky specimens was found to be unaffected after two years4 ,on the other hand1 it is claimed that tackiness has been induced in a sound rubber by infecting it with small pieces which were tacky4 ,in a preliminary article on the effect of copper and copper salts upon pieces of dried and sound crepe#ba it was noted1 after one year1 that tackiness had been communicated from the treated portion to the blank in contact4 ,there is sufficient evidence to warrant the injunction that tacky rubber should be excluded from contact with sound rubber4 ,if shipped it should be packed separately4 #ba ,report ,i41 #aiaf 7,sidney ,morgan71 ,rubber ,growers' ,association 7,malaya74 ,compounds have been put upon the market which assumedly claim to be cures for tackiness4 ,these are merely palliatives1 consisting of starch1 talc1 or chalk powders1 which counteract stickiness4 ,,no ,,cure ,,for ,,tackiness4--,at the present stage of our knowledge1 there appears to be no cure for tackiness4 ,neither do we see the necessity for a cure when the phenomenon may be avoided by taking simple precautions1 which may be briefly summarised thus3 7#a7 ,any permanent openings through which it is possible for direct sunlight to enter1 whether large or small1 should either be totally closed or provided with some substance which cuts off the direct effect of the sunlight--e4g41 ruby glass or ruby glazed cloth4 7#b7 ,rubber should under no circumstances be placed near any source of heat4 7#c7 ,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 it1 even should coolies neglect to obey rules4 7#d7 ,instruments or vessels of copper or brass should not be used where acids are employed4 ,,lack ,,of ,,uniformity ,,in ,,colour4--,the complaint is far less real than it was a few years ago4 ,the introduction by the ,rubber ,growers' ,association of the ,metrolac led to uniform dilution of latices varying in rubber content4 ,previously the only known method of obtaining uniformity in colour and appearance was that by which latices from all fields were mixed together in bulk4 ,even so the uniformity applied only to the one bulking operation1 and any other day's results might show considerable variation from the first standard4 ,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 day4 ,the introduction of sodium bisulphite as an anti-oxidant exerted a great influence upon the colour of pale crepes generally2 but considerable variation would still have been notable but for the adoption of the scheme for uniform dilution1 in addition to the use of small quantities of anti-oxidant4 ,on most estates it is now possible1 with slight exceptions due to abnormal conditions1 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 day4 ,where this is not the case it must be suspected that there has been some carelessness in manipulating the latex or the chemicals4 ,attention has been drawn to the fact that there may be exceptional cases1 when the determining factors lie beyond the control of factory processes--e4g41 heavy rains causing over-dilution of latex1 the yielding of yellow latex from newly opened areas1 etc4 ,but on the whole there is now no reason why the general average product from any estate should not be uniform in colour and appearance4 ,furthermore1 it should be possible for large groups of estates1 by the adoption of uniform methods1 to produce similar rubber from all the plantations4 ,moreover1 apart from some differences caused by factors which still need determination1 the total product in a general sense should not only be uniform in appearance but uniform in physical and chemical properties4 ,,block ,,rubber4--,this mode of preparation is employed only in comparatively few instances4 ,the block is prepared from crepe rubber1 which has been dried either in a hot-air drier or in a vacuum chamber4 ,there is another type of block which is made by placing layers of dry crepe under considerable pressure4 ,this is not the true type of block1 and the layers are quite distinct--i4e41 they do not amalgamate4 ,usually this pressed rubber consists of lower grades of crepe1 and it should not be popular1 inasmuch as it leaves too wide an opportunity for the inclusion of dirt1 bark particles1 and other impurities1 which cannot be seen generally on account of the protective colour of the rubber4 ,in the true type of block1 the layers are in a plastic condition1 due to heat1 when they leave the drying-chamber2 and being immediately submitted to great pressure the result is a homogeneous mass in which the layers disappear by amalgamation4 ,only the best grade of crepe is employed1 and given the absence of defects in the layers there should be no complaint regarding the final block4 ,prepared in slabs which are three or four inches in thickness1 the product is easily handled1 and should be sufficiently translucent to make it possible to distinguish the shape of the hand when held between the block and the light4 ,this is not possible when blocks are made of greater thickness4 ,the only complaints which it should be possible to lodge against block rubbers are3 7a7 ,the inclusion of dirt and other matter4 7b7 ,the use of layers of crepe which have some defect4 7c7 ,the inclusion of air-bubbles4 ,the remedy for 7a7 and 7b7 lies in the hands of the factory superintendent4 ,the last ground of complaint is dependent upon the style of preparation of the original layers of crepe4 ,when layers of crepe are placed one upon the other1 and submitted to great pressure1 it is natural to suppose that air would be contained in spaces1 and would be unable to escape4 ,to guard against this1 it would seem necessary to prepare the crepe thin and with a fairly good surface finish4 ,it must be obvious to all acquainted with the processes involved in the preparation of block rubber1 that no possibility exists for the presence of air-bells actually enclosed in thin crepe4 ,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 air1 a small proportion of which is bound to be retained owing to the nature of the surface of crepe rubber4 ,that this has always been true of the preparation of block rubber cannot be denied4 ,it is possible1 of course1 for one type of block to show the presence of air-bells more than another type1 the proportion of air enclosed in blocking depending upon the nature of the crepe of which the block is composed4 ,a block built up of layers of smooth1 fine crepe would be expected to contain less air-bells than a block composed of layers of a rough crepe4 ,block rubber has been seen which was free from air-bells1 but this was the thin variety of block prepared for show purposes with far greater care1 probably1 than would be expended in commercial preparations4 ,,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 stages4 ,,milky ,,residue ,,or ,,serum4--,if the serum is not clear after the ordinary period allowed for coagulation1 it indicates one of the following possible causes3 7a7 ,failure to obtain complete mixture by thorough stirring4 7b7 ,insufficiency of acid solution4 ,this may be real or indirectly due to the presence of an excess of anti-coagulant such as formalin or sodium sulphite4 7c7 ,in cases where other coagulants than acetic or formic acids have been employed the failure may be due to an excess of1 or an unsuitable1 coagulant--e4g41 hydrochloric acid4 ,,coloured ,,surface ,,blotches ,,and ,,unpleasant ,,odour4--,sometimes the surface of the coagulum exhibits yellowish or bluish streaks and patches4 ,it will be found generally that the yellowish colour is possessed by a slimy substance1 of offensive odour1 which may be scraped from the surface4 ,either insufficient acid has been used1 or the mixing of latex and coagulant has been at fault4 ,,dark ,,discoloration ,,of ,,the ,,rubber4--,this may be stated to be a natural process when fresh rubber is exposed to the atmosphere4 ,it is usually described as oxidation1 and it will be noted to be absent1 or to occur to less degree1 on those portions of the rubber which are protected from the atmosphere by being below the surface of the remaining liquid4 ,this surface change may be prevented 7see ,chapters ,,viii4 and ,,ix47 by the use of small quantities of sodium sulphite 7for preference7 or bisulphite4 ,,soft ,,coagulum1 ,,spongy ,,under-,,surface1 ,,tearing ,,of ,,coagulum4--,if the whole mass of coagulum is too soft1 while coagulation appears to be complete1 over-dilution of the latex has occurred4 ,this may apply also to the case in which the under-surface only is spongy and soft4 ,if coagulating-tanks are employed1 the upper edge may be comparatively hard1 while the lower is soft and weak4 ,often the spongy portion may adhere to the partitions4 ,this prevents the natural rise of the coagulum1 due to retraction1 as the mass sets4 ,the pull between the free upper portion and the adhering lower edge causes splitting and tearing of the coagulum1 with marked porosity 7spongy appearance74 ,the two factors to receive attention are the standard of dilution and the condition of the surfaces of the partitions4 ,if these have minute cracks into which latex can penetrate1 and in which coagulation takes place1 the boards should be discarded4 ,given the conditions indicated above1 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 complete4 ,the surface water finds its way downwards between strips of coagulum and the partitions1 thus increasing the upward tension between the free and adhering portions4 ,the main idea governing the practice of flooding the tanks is to prevent oxidation 7darkening7 of the upper edges4 ,if a small quantity of sodium sulphite is employed as an anti-oxidant and to retard coagulation1 it is not necessary to flood tanks4 ,,pitting ,,of ,,surfaces4--,in pan coagulation this pitted appearance is usually limited to the under-surface1 while coagulum prepared in tanks may exhibit the defect on both faces4 ,the existence of these numerous pits1 or small depressions1 points to the presence of bubbles of gas which have been unable to escape freely4 ,as the formation and retention of gas-bubbles is not a normal occurrence in coagulation1 we are led to infer that some special conditions must have arisen4 ,these may be supplied by one or more of the following contributory causes3 7a7 ,the latex had begun to sour before arrival at the factory or while waiting to be treated4 ,this premature coagulation is usually checked or diminished by the employment of anti-coagulants 7see ,chapters ,,viii4 and ,,ix474 ,it is generally accompanied by the appearance of enclosed gas-bubbles in the dry rubber4 7b7 ,there may have been a slight insufficiency of coagulant1 or the admixture was not thorough1 thus allowing a slow putrefactive change to take place in the incompletely coagulated areas4 7c7 ,the wooden partitions may not have been effectively cleansed4 ,the existence of a thin slime1 of bacterial origin1 is sometimes noted4 ,this is accountable for putrefactive effects in the surfaces of the coagulum1 or in the serum1 giving rise to the formation of gases4 ,if these cannot escape freely1 by reason of adhesion between the coagulum and the partitions1 pitting occurs4 ,,thickened ,,ends ,,or ,,edges1 ,,after ,,rolling4--,as a rule these defects may be ascribed to the employment of too rich a latex1 or faulty manipulation4 ,even if the standard of dilution should be correct it sometimes happens that1 in the preliminary rolling of a long strip of rubber1 coolies begin in the middle1 rolling with a forward pressure and tension towards the ends of the strip4 ,this is generally not so much the fault of the coolie as being due to the lack of proper facilities for preliminary rolling4 ,the table should be about #c feet in height1 so that ease of working is obtained merely by natural pressure due to the position in which the worker stands4 ,the use of a heavy wooden roller would contribute towards this result1 inasmuch as it obviates the use of force1 and the pressure is almost entirely in a vertical direction4 ,,mis-,,shapen ,,sheets4--,it is sometimes noted that sheets may be wider and thicker at the ends than in the middle4 ,manipulation alone1 as indicated above1 is not solely responsible4 ,the primary cause is to be traced to over-dilution of latex1 giving a very soft coagulum which responds too readily to tension and pressure4 ,faulty treatment in rolling exaggerates the tendency for the strip of sheet to become narrow and thin in the middle1 wider and thicker at the ends4 ,,thickened ,,patches1 ,,torn ,,sheets1 ,,dog-,,ears1 ,,creases4--,these elementary defects are all due to careless working4 ,while occasional errors cannot be avoided1 there is no real excuse for the continuance of trouble to any degree1 under average supervision4 ,thickened patches are often caused in conjunction with torn sheets1 and the trouble may be ascribed to faulty practice in allowing too heavy a pile of wet strips to accumulate before machining4 ,or a comparatively small pile may have been transported some distance4 ,it is difficult to separate the strip1 and occasionally the separation is only effected at the expense of two sheets1 one of which is torn and the other has a portion of the first strip adhering to it4 ,dog-ears due to the folding over of corners of the sheets1 and creases due to the rumpling of the coagulum1 are generally the result of haste and lack of average care4 ,machine coolies1 more often than not1 will not be at any pains to straighten out folds before passing the coagulum through the rolls4 ,,greasiness ,,before ,,smoking4--,under ordinary methods of working this should never be encountered4 ,it may be taken to show that the machined rubber has been allowed to remain1 either hanging or in piles1 far too long before entering the smoke-house4 ,the appearance is most marked if the rubber has remained in a cool and moist atmosphere--e4g41 if it has been hanging over-night in a closed and badly-ventilated factory4 ,in a marked degree this is to be observed in the preparation of air-dried sheets1 unless they are exposed1 when freshly prepared1 to the action of the sun for a period4 ,this period1 in the case of rubber prepared on native small-holdings1 generally extends over several days--until the sheets are more than half dry4 ,in the preparation of smoked sheet1 the greasy appearance and the cause outlined contribute to a defect which is eventually described as stretching rusty4 ,,surface ,,blemishes4--,the coagulum1 during coagulation and subsequently1 can be contaminated in various ways4 ,in most cases a little intelligence or increased care would prevent the occurrence of these defects4 ,when the coagulum remains over-night1 in the absence of a cover1 it is not uncommon to note the presence of dirt 7from the roof above1 or blown in from the outside71 the droppings of mice and rats1 flies and small insects4 ,in theory these should be seen and removed by the factory hands4 ,in practice1 except while under immediate supervision1 the extraneous matter is often rolled into the soft coagulum4 ,a fairly common cause of this surface contamination is the exhaust from the power-unit2 generally the worst offender is a steam-engine4 ,grit and smuts continually find their way into the factory1 alighting on the tables1 in the latex1 in the water1 and on the freshly prepared rubber4 ,they are rolled into the soft rubber and lead to marked depreciation in the selling value4 ,the radical remedy seems obvious1 but is often beset with many difficulties not unconnected with financial considerations4 ,other superficial blemishes1 such as those due to the presence of rust marks1 oil or grease patches1 etc41 are self-explanatory1 if a little thought is brought to bear upon them2 and it is not proposed here to discuss such defects more fully4 99 99 99 99 99 ,having now dealt with certain defects which are visible in wet rubber1 we come to the discussion of others which are only perceptible either during or after the drying period4 ,as far as is known no plantations of any size now prepare sheets other than in the form of smoke-dried rubber1 with the exception of a few which make a special form of thick and partially air-dried product known as slab rubber4 ,it is not proposed1 therefore1 to treat in any detail with air-dried sheet rubber4 ,certain obvious defects are common to both air-dried and smoke-cured sheets1 and these will be first discussed4 ,,unevenness ,,of ,,appearance4--,this lack of uniformity may refer either to size or colour1 or to both4 ,apart from any other contributory causes1 this variation is due1 in pan sheet1 to a neglect to standardise the dilution of all latices1 or to lack of uniformity in the quantity of standardised latex placed in each receptacle4 ,where tanks are employed all sheets from the same tank should be of the same size before rolling1 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 machines4 ,unless all latices are standardised by means of an instrument1 it is of course probable that the content of one tank may be found to differ from that of another4 ,in a general sense1 whether air-dried or smoke-cured sheets are considered1 a thin strip will dry more quickly than a thick one1 and should be paler in colour when viewed by transmitted light--i4e41 when the rubber is held between the eye and the source of light4 ,it is necessary1 therefore1 to guard against the possibility of variations in thickness caused by faulty manipulation4 ,the distance between the squeezing rolls 7smooth7 and between the marking rolls 7patterned7 should be adjusted and should remain set until the conclusion of work4 ,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 adjustments4 ,this is1 however1 inevitable if there is only one smooth-roll machine1 as it is always desirable to reduce the thickness of the coagulum by at least two stages through even-speed smooth rolls4 ,in some factories there are three light power-driven smooth-roll machines1 the gaps between pairs of rolls being set so as to obtain a gradual thinning effect upon the fresh coagulum1 which is then passed once between patterned rolls4 ,with such equipment it is found possible1 in some cases1 to omit the preliminary hand-rolling1 and the strips of coagulum from the tank are passed direct through rolls set with a wide gap4 ,this work demands much care1 as it is necessary to avoid any distortion of the coagulum which may be caused by its own weight and length4 ,,variation ,,due ,,to ,,oxidation4--,the subject of oxidation has been mentioned in the opening paragraphs of this chapter4 ,it will have been learned that oxidation is a natural process1 and that it may be prevented by the employment of anti-oxidants such as the sulphite or bisulphite of soda4 ,in earlier days it was sometimes prevented by steeping the thin rubber in very hot water4 ,in the absence of an anti-oxidant the degree of oxidation may vary daily and in different batches of latex on any one day1 so that there is always the possibility of a lack of uniformity due to oxidation effects4 ,this would be more evident in air-dried sheets than in smoke-cured rubber1 as in the latter case the darkening of the surface would be masked by the colour induced by the smoke-drying process4 ,to obviate this variation anti-oxidants are used on most estates1 but the accidental or misinformed abuse of these chemicals may lead to further lack of uniformity4 ,hence it is necessary to follow carefully the formulae prescribed by experience4 ,,colour ,,of ,,smoked ,,sheets4--,it may be of interest to note that the effect known as oxidation is attributed to the presence of micro-organisms called enzymes 7ferments7 in the latex4 ,it can also be produced artificially in various ways--e4g41 by the use of the crude product of wood-distillation 7pyroligneous acid7 as a coagulant1 or by the addition to the latex of small quantities of a phenol such as carbolic acid4 ,it is thus possible to prepare in sheet form a rubber which has the appearance of having been smoke-cured1 although it may never have been in a smoke-house4 ,it will be clear1 therefore1 that apart from other causes1 the colour of the cured sheets may be influenced by oxidation of the fresh coagulation1 and by the constituents of the smoke4 ,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 colour4 ,there is thus no real connection between colour and period of cure1 although in a general sense the longer the interval the darker the colour4 ,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-cured4 ,the influence of the effect of the hypsical condition of the wet rubber upon the final colour must be thoroughly grasped4 ,one may take two sheets of apparently the same thickness1 and smoke-cure them in juxtaposition within the same house1 only to find that one dries much more rapidly than the other4 ,as a consequence1 the first1 when fully cured1 will be of a medium golden brown colour2 while the other1 owing to protracted smoking1 will be dark4 ,evidently there must be some distinct difference between the two in physical condition prior to the smoking4 ,here the factor involved is the rubber-content of the latex4 ,given two pieces of coagulum of identical thickness1 but prepared from latices of different dry rubber content1 it will be obvious that to reduce them to similar thickness1 more pressure will be necessary in one case--i4e41 that piece of coagulum will be much more dense 7more consolidated7--while the other will be comparatively soft and porous4 ,into the latter warm smoke can penetrate much more easily1 and the internal moisture can escape more rapidly4 ,the full cure may be made1 say1 within twelve days1 while the tougher sheet may demand up to twenty days4 ,to attain uniformity in colour1 therefore1 the following points must be studied and controlled as far as is possible3 7a7 ,uniform dilution of all latices4 7b7 ,uniform dimensions of coagulating receptacles4 7c7 ,uniform volumes of standardised latex4 7d7 ,uniform quality and quantities of chemicals4 7e7 ,uniform methods of manipulating the coagulum4 7f7 ,uniform conditions of fuel and accommodation during smoke-curing4 ,,surface ,,gloss4--,in the choice of fuel there is room for control if one has good timber available4 ,this point opens up a discussion on the vexed question of over-smoking1 as the term is sometimes applied to a pronounced dry glossy appearance of the surface of sheets4 ,three main factors are involved3 7#a7 ,the nature of the fuel4 7#b7 ,the ratio between furnace capacity and the capacity of the smoke-house4 7#c7 ,the rate of combustion4 ,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 rubber4 ,such fuel1 therefore1 should at most only be employed as the smaller portion in a mixture with dead timber4 ,it is impossible to lay down any general rules for the guidance of estates1 as the timber available varies so widely in nature4 ,experience must be the only guide1 and it should not be difficult to obviate the defect4 ,even so1 there must be minor differences between the results obtained on estates1 so that it is not possible to make strict estimations of the smoke-curing period by an examination of the surface appearance of rubber1 even under the best of conditions4 ,some estates find that the rubber has a distinct gloss in ten days1 while others may smoke-cure for twice that period without difficulty4 ,evidently1 therefore1 the question of available fuel is of prime importance4 ,it may be remarked that very satisfactory results are always obtained from the use of fairly dry timber obtained from thinned rubber trees1 mixed with the dead timber of old logs and stumps found on the estates4 ,obviously if a smoke-house has a superabundance of furnaces1 producing more heat and smoke than is required1 glazing will result4 ,the point is tested by the average temperature maintained and the average rate of drying4 ,the result of a high temperature would be the possibility of volatile tarry matter being driven in excess to the upper chamber4 ,that this effect is eventually produced even at optimal temperatures is evident from an examination of the wood-work within the upper room4 ,it is clear1 also1 that the rate of combustion exerts an influence4 ,in a general sense a rapid consumption of fuel would augment the quantity of tarry matter passing into the upper chamber over any given period1 and the possibility of glazing would be increased4 ,on the other hand1 it is possible that a surface glaze might be formed if the temperature were uniformly too low1 especially if the rubber were rather thick4 ,the rate of drying would be so slow1 that if a timber rich in tarry matter were employed1 the rubber might be exceedingly glossy4 ,in order to guard against the appearance of a heavy glaze1 then1 the following points must be observed3 #a4 ,the fuel must be carefully selected by experience4 #b4 ,the sheets must not be thick4 ,no sheets should be thicker than #a_/h inch measured in average section across the ribs4 #c4 ,the temperature must not be too high4 ,an average working temperature of #abj deg4 to #abe deg4 ,f4 should be ample4 #d4 ,if the sheets are fairly thick1 a low average temperature should be avoided4 ,no lower average than #aaj deg4 ,f4 should be allowed4 ,,dull1 ,,black ,,surface4--,this is the opposite of the previous case1 and generally is accompanied by a fairly heavy darkening of the surface due to oxidation effects4 ,the fuel used is too dead1 and needs the addition of some substance containing a fair amount of creosotic matter4 ,the appearance of the rubber does not justify the assumption that it has been over-smoked4 ,as a matter of fact1 this type of rubber often becomes affected by mildew fairly rapidly1 thus showing that the smoking has been inefficient4 ,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 period4 ,the general custom is to soak such sheets in cold water1 and then to scrub the surfaces1 sometimes using soap1 in order to cleanse the rubber and free it from the glaze4 ,this operation may be done too well1 in which case the rubber will have a dull appearance1 and may be rather more liable to develop surface mildew after a time4 ,,moist ,,glaze1 ,,greasiness ,,of ,,surface4--,this describes the condition of sheet rubber when taken from the smoke-house4 ,sometimes the greasiness does not develop until the rubber has been out of the smoke-house for a day or two4 ,as far as experience shows at present it may be due to two causes3 7a7 ,the use of an excess of sodium bisulphite or sodium sulphite4 ,the use of sodium bisulphite is not recommended generally for sheet-making4 ,it may cause the rubber to be too pale in colour1 and the abuse of it may delay the drying unduly4 ,in the latter case1 a trace of the salt may remain within the rubber or upon the surface4 ,if so1 as the substance remaining is fairly hygroscopic1 it will take up moisture from the atmosphere and may cause the surface of the sheets to have a moist and shiny appearance4 ,the moist surface deposit comes away upon the hand when the sheets are touched1 and is difficult to remove entirely4 ,on some estates a very small quantity of the bisulphite is employed1 as it is found to be of service in the prevention of bubbles1 but in unskilled hands the method is open to abuse1 and is1 therefore1 not recommended for general use4 ,a large number of estates now use sodium sulphite in very small quantities as an anti-coagulant and a preservative for latex in the field4 ,the abuse of this very useful substance carries its own penalty4 ,the substance is hygroscopic2 and if an excess is present the drying period will be protracted1 and the sheets will have a very moist surface film4 ,it may be found sometimes that only some of the sheets are affected4 ,this indicates that1 whereas uniform quantities of a solution of sodium sulphite have been served out in all fields1 the proportion may have been excessive in the case of fields giving a latex of comparatively low rubber content4 ,what suits the latex from old trees may be excessive probably for the latex of younger trees4 ,this is not an infallible rule1 as in the case of older fields in which immature bark is being tapped1 it is to be noted that the dry rubber content of latex may be less than that of latex obtained from younger trees4 ,this type of moist glaze is not easy to remove4 ,ordinary surface washing had but a temporary effect1 and the trouble recurs4 ,the only way of dealing with the difficulty is to soak the sheets for days in running water 7or in successive changes of water7 and to re-smoke until dry4 7b7 ,the second type of moist glaze is not so difficult to deal with1 and may be removed as a rule by washing the sheets when the rubber is otherwise apparently dry4 ,it appears to be mainly a matter of unsuitable fuel for smoking and of failure to provide adequate ventilation4 ,a large number of estates have been thinning-out or are doing so systematically4 ,the logs thus obtained are often used as fuel in the very green stage4 ,the smoke thus generated must be moist1 and if the building is entirely closed1 this moisture must be deposited eventually upon the rubber and racks4 ,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 smoke2 but if the logs from rubber-trees are to be used1 they should be stacked in the sun for some time4 ,even then1 preferably1 they should not be used alone4 ,a judicious admixture of dead and rotting jungle-timber appears to give very satisfactory results4 ,,virgin ,,spots ,,and ,,patches4--,if the description really indicates the defect it simply means that portions of the sheets are not dry4 ,when cut they exhibit the typical whitish1 opaque appearance described as virgin4 ,it is doubtful whether any rubber put upon the market as ,no4 #a product nowadays can have this complaint levelled at it4 ,in the extreme case it points to gross negligence on the part of the packer4 ,sometimes what are taken to be small spots of virgin are really patches of tiny air or gas bubbles4 ,the point can be easily determined by cutting through the patch and examining the cut edges4 ,,surface ,,moulds ,,or ,,mildew4--,during the last two years1 complaints regarding the incidence of mouldy rubber 7i4e41 relating chiefly to the presence of mildews on the surface7 have become increasingly common4 ,to judge by the comments of producers1 who as a rule never again see their rubber after it leaves the estate1 one would infer that the defect is imaginary1 and that the complaints are made solely with a view to repudiation of contracts or the general cheapening of an article of commerce4 ,they can often point out1 with a certain amount of truth1 that there has been no change in the methods of preparation or curing1 and that previously there were no complaints4 ,it is forgotten1 however1 that in former years the smaller output of rubber was taken into consumption more rapidly than of recent years4 ,that is to say1 the interval between smoke-curing and the employment of the rubber in the manufacture of goods did not demand such a long period of storage4 ,hence the effects of smoke-curing are now more likely to vanish4 ,going still further back in the history of plantation rubber1 we can point to the time when smoked sheets were allowed1 or had1 to remain in the curing-sheds for very extended periods4 ,loose specimens of rubber prepared during that decade still exhibit no signs of mildew growth4 ,in later years a demand arose for sheets paler in colour than the old type1 and in order to meet that demand1 a change had to be made in methods4 ,this led to a system of working whereby it was possible to smoke-dry sheets thoroughly in from twelve to fourteen days4 ,this interval was further reduced on many estates1 until some were producing rubber which appeared to satisfy all requirements after only five or six days' curing4 ,this does not refer to the case of estates having smoke-houses of continuous-working type1 but to those on which smoking was confined practically to the hours of night4 ,under former conditions of rate of production and consumption1 this short period of smoke-curing would possibly have been ample2 but even this is very doubtful1 as often the rubber would not stand the relatively short journey from the estate to ,singapore without mildew-growth being incipient4 ,we have often received specimens of rubber sent from estates for criticism1 and have noted that within a comparatively brief period mildew was to be seen4 ,the whole matter resolves itself into a question of thorough efficiency of smoking4 ,this is not dependent on duration of smoking alone1 but involves other factors1 such as the kind of fuel employed1 the rate of combustion of fuel1 the average temperature sustained1 the ventilation of the smoke-house1 and the situation of the building4 ,other occasional contributory factors are contemporary adverse climatic conditions and the possible abuse of an anti-coagulant such as sodium sulphite4 ,it has been shown that after a time1 given suitable conditions involving the presence of moisture1 moulds may appear on sheets which were apparently fully smoke-cured1 and that under the same conditions other and older samples were unaffected4 ,it is argued that the latter sheets had evidently been smoked more efficiently than the others4 ,hence it is fair to assume that1 except under very special conditions1 which do not apply to the ordinary procedure in the shipping1 storage1 and sale of rubber1 moulds will not develop upon sheets which have been properly smoked4 ,the term properly smoked signifies efficient smoking for all practical purposes under ordinary procedure1 and implies or includes all the advantageous factors which have been discussed or alluded to in preceding paragraphs4 ,without discussing in wearisome detail conditions which may give rise to the incidence of mildew on properly smoked rubber1 it may be pointed out that the following are favourable to the growth of moulds3 7a7 ,storing sheets in a damp place before packing4 7b7 ,packing sheets in wooden cases which are not thoroughly dry4 7c7 ,piling up cases of rubber in a badly ventilated store-room4 7d7 ,placing the cases on a cement floor4 7e7 ,wetting of cases by sea-water or by rain during transport1 etc4 ,,black ,,streaks1 ,,spots ,,or ,,patches4--,the origin of these is not difficult to trace4 ,they are caused by drippings from the roof1 and contain condensation products from smoke plus moisture4 ,the ventilation of the roof-ridge should receive attention1 and if the trouble persists it will be necessary to place some absorbent screen below the sloping roof4 ,sackcloth is sometimes used1 but leads to a worse state of affairs unless changed frequently4 ,in most modern smoke-houses having an iron roof there is an inner lining of soft timber4 ,there scarcely seems a necessity to discuss the case in which an iron roof has become perforated by the action of smoke4 ,the remedy is too obvious to describe4 ,,whitish ,,or ,,grey ,,streaks4--,this is a very uncommon defect1 and is generally to be traced to a building in which fairly new galvanised sheets have been employed4 ,the zinc surface becomes oxidised1 and the whitish powder which is formed flakes1 or is carried away by drops of moisture condensing on the surface of the iron sheets4 ,,rust4--,sometimes if a sheet is stretched forcibly and allowed to retract quickly1 the hitherto clear surface will be seen to be marred by a rusty deposit4 ,the rubber is then described as stretching rusty1 and its value is depreciated4 ,this defect has caused more trouble during recent years than any other4 ,it is not proposed here to argue the question as to whether the presence of this film1 which appears when some rubbers are stretched1 is detrimental to the physical qualities of the product on vulcanisation4 ,with the mere statement of opinion that it could do no apparent harm1 we may pass to the aspect of the case as it affects the buyer and consumer4 ,if one were to judge by the attention drawn to the appearance of smoke sheet-rubber after it has been stretched and allowed to retract1 one would imagine the defect to be of comparatively sudden and recent incidence4 ,this is not so4 ,the peculiarity must have existed for years1 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 cups4 ,as the substances which cause the defect to be visible are partially soluble in water1 it would follow that when working with the very dilute latices which were characteristic of the earlier years of the plantation industry1 the remaining liquid in the pan after coagulation would contain an appreciable quantity of soluble substances which would otherwise have been retained in the coagulum4 ,conversely1 the richer the latex1 the greater the percentage of protein matter retained in the coagulum4 ,in the case of very rich latex1 it must be within the knowledge of every manager that the quantity of remaining liquid in the pans would be almost nil4 ,we may assume that the greater part of these soluble proteins would be enclosed in the structure of the rubber1 but as the fresh coagulum must retain a quantity of liquid amounting to from #fj to #gj per cent4 by weight 7we are now referring to rich latices71 it follows that some of the soluble protein matter must be removed when the coagulum is placed under pressure4 ,even after the pressure is released more of the contained liquid will exude from the surface of the rubber2 and from experience it is easy to imagine that this exudation1 becoming progressively feebler1 will continue until the rubber begins to dry4 ,then1 with the evaporation of the surface moisture1 the protein matter1 either in original form or as a degradation product1 remains on the surface of the rubber as a thin1 solid film or crust4 ,as drying continues1 the interior moisture escaping through the pores of the rubber evaporates1 leaving behind the substances hitherto held in solution4 ,should1 however1 the sheet be thick and_/or the temperature of drying low1 the rubber may dry first on the outside1 forming a thin skin of dry rubber1 which delays further drying indefinitely4 ,it will be seen1 therefore1 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 matter4 ,moreover1 these sheets will be slow in drying1 and in all probability will have a surface gloss and a dark colour4 ,hence it is not difficult to understand that some brokers regarded the presence of the so-called rust as an indication of over-smoking4 ,to show that this is not so1 and further that the presence of rust has nothing whatever to do with smoke-curing1 it may be stated that the presence of this protein film may be seen on unsmoked sheets which have been prepared from rich latex1 from too deep a layer of more dilute latex1 or from some thick sheets which have been rolled only very lightly4 ,in fact1 the presence of the protein film was noted on unsmoked sheet in #aiaj1 when it was seen to resemble a thin yellowish glaze which could be scraped off with a pen-knife4 ,later1 sufficient of this substance was removed from some very thick air-dried sheets1 or thin slabs1 to fill a small test-tube4 ,when the sheets were bent or twisted1 the apparent surface of the rubber 7i4e41 the protein glaze7 cracked in all directions4 ,in the case of sheets prepared from less rich latex1 the surface film naturally is extremely thin1 and no cracking is observed4 ,if the fresh sheets are placed in a smoke-house1 the drying film will take up colour from the constituents of the smoke1 and it will be invisible4 ,somewhat analogous to the instance of a transparent glass giving a visible and opaque powder when crushed1 so the transparent film on stretching breaks up into a visible powder which is lighter in colour than the rubber on which it is superimposed4 ,it will be noted that since the introduction of standard methods of preparation1 involving uniform dilution of latex1 say1 to a content of #a-a_/d or #a-a_/b lbs4 dry rubber per gallon1 complaints as to rust have decreased considerably4 ,it is to be further noted as a peculiar fact that while two estates may be apparently working on identical lines1 both as regards manipulation of latex and subsequent treatment of the coagulum1 the rubber of the one may always be free from rust1 while that of the other is often1 if not always1 condemned for the alleged defect4 ,obviously1 in such a case1 there must be an initial difference between the two latices as regards the percentage of proteins present2 or there must be some small unrecognised difference at some stage of working4 ,it will now be clear that rust is caused by a film of matter which is formed on the surface of the pressed coagulum1 being there deposited by the exudations from within the rubber and through the pores4 ,it is1 therefore1 necessary to avoid any conditions which will favour the formation of this deposit--e4g41 allowing sheets to remain too long in a moist atmosphere before placing in the smoke-house4 ,at present there would seem to be only two methods which are successful in the prevention of a rusty appearance in the dry rubber4 ,singularly enough1 the two methods appear to be directly opposed in principle4 ,they are3 ,a4 ,,the ,,hot-,,water ,,treatment4--,this method has been in constant use on estates which have old trees giving rich latices4 ,these latices are always diluted to a uniform standard daily4 ,some estates which formerly suffered from the defect now experience no difficulty1 and in other instances1 where no complaint has yet been received1 the treatment has been followed consistently4 7#a7 ,after the sheets have been through the marking rolls1 it is the general custom to allow them to drip for about three hours4 ,this interval is really excessive for the mere draining away of the surface water1 but as a rule it is just sufficient to allow a portion of the liquid retained in the rubber to exude4 ,it has been shown that this liquid may contain some protein matter in solution4 ,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 touch4 ,if the sheets are allowed to hang overnight1 the presence of the exuded matter may be detected also by its odour4 7#b7 ,obviously1 any method which will remove this surface film should be of great benefit4 ,it is found that the best results are obtained by allowing sheets to drip for about two hours1 and then placing them in hot water for five or ten minutes4 ,the water should be hot as the hand can conveniently bear1 and it need hardly be pointed out that the same water should not be used for the whole day's output4 ,for preference there should be three or four vessels1 each capable of holding a fair proportion of the total number of sheets1 and frequent changes of hot water4 7#c7 ,after remaining in the hot water for the period mentioned1 the sheets are removed singly1 each one being surface washed or swilled as it is taken out4 7#d7 ,it is important to see that the sheets are now well washed or scrubbed under running cold water1 or in frequent changes of water4 ,the reason for this procedure is plain4 ,if the sheets are merely hung again to drip after removing from the hot water1 some moisture is bound to remain on the surface of the sheet4 ,as this surface moisture contains some protein matter in solution1 it is evident that1 as the water evaporates1 the solid protein is again deposited on the surface of the rubber4 ,this would explain why some estates were unsuccessful with the hot-water treatment4 ,it is not essential that the running water should be cold2 it may be conveniently lukewarm if drawn from the cooling tanks of the engines4 ,but it is essential for the best results that there should be running water1 so that the substance in solution is carried away4 ,if the sheets are merely washed in a large vessel1 which has been filled with clean water1 it must be obvious that1 by the time some scores of sheets have been washed1 the protein matter in solution on the surface of the sheets has been transferred to the washing water1 so that the later sheets of the batch are liable to show the defect again on drying4 ,b4 ,the second method is much more simple1 and entails no extra labour such as is demanded by the first method4 ,a successful issue1 however1 is rather more uncertain1 and the method appears to give the best results with sheet-rubber prepared on young estates or from more dilute latex4 ,in this method1 the sheets after rolling are allowed to drip for a very short interval1 so that the surface water is mainly removed4 ,the sheets are then placed in the smoke-house1 and smoking is commenced at once4 ,in some cases where the defect had appeared continuously for a long period1 it was found to vanish entirely as soon as the method was adopted2 but when tried on some of the older estates1 the results were very doubtful1 and a return was made to the hot-water treatment4 ,the explanation of the action which takes place is rather obscure1 but two theories may be advanced4 7a7 ,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 matter4 ,in such case1 the rubber is still in a highly porous condition1 and it might be advanced that the heat of the smoke may help to maintain that condition4 ,thus the contained liquid might evaporate so quickly as to leave behind the dissolved substances in the minute cellular structure of the rubber4 ,in other words1 instead of the internal moisture exuding slowly to the surface in liquid form1 it may leave the rubber1 even in the first stages1 in an evaporated condition1 just as it does in the subsequent stages of drying4 ,thus no dissolved protein matter would be brought to the surface of the sheet and be deposited there4 7b7 ,the other theory also demands the first assumption propounded in the preceding theory1 but subsequently perhaps is less feasible as it assumes a chemical action of which we have no definite knowledge4 ,the idea is that as the rubber is in a porous condition1 and is placed quickly in an atmosphere of smoke1 the heat may maintain that condition to such a degree1 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 liquid4 ,the contained liquid would be water which has in solution possibly a very slight trace of the coagulant employed1 of sugars1 of protein matter1 and of inorganic salts4 ,of these the substances which would evaporate would be probably the water and the coagulant in most cases4 ,if a salt had been used as a coagulant1 the dissolved trace would be deposited within the rubber in this case1 whereas if a rich latex had been employed or a thicker sheet made from more dilute latex1 some of the salt would be brought to the surface and there deposited together with the protein matter4 ,this has actually been experienced in practice1 and it has been possible to remove minute crystals from the edges of the rubber so prepared4 ,it will be evident that in order for either theory to contain an element of probability1 the rubber must be soft 7porous7 when placed in the smoke-house1 and must also be fairly thin4 ,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 thin4 ,when thicker sheets are made1 either from rich latex or from a deeper layer of comparatively dilute latex1 the method is not uniformly successful4 ,,other ,,views ,,on ,,rust ,,causation4--,later experimental work on rust formation by ,hellendoorn#bb leads to the observation that rustiness is caused1 not actually by the deposition of original serum-substances1 but by the decomposition thereof1 under the action of aerobic micro-organisms4 #bb ,the ,cause of ,rustiness in ,sheet-,rubber1 ,h4 ,j4 ,hellendoorn1 ,archief voor de ,rubbercultuur1 ,october1 #aiai 7,communication from the ,central ,rubber ,station1 ,buitenzorg1 ,java74 ,without going into a full discussion of the subject1 the following points noted in the experimental work may be quoted3 #a4 ,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 atmosphere4 #b4 ,sheets placed immediately in a temperature of1 say1 #aaj deg4 to #acj deg4 ,f4 never showed rust2 but if air-dried at ordinary room temperature1 rust might appear4 #c4 ,rust can be prevented by soaking freshly prepared sheets in dilute solutions of disinfectants--e4g41 formalin1 sodium bisulphite1 or chinosol4 ,if subsequently the sheets are hung for any length of time in a moist atmosphere1 the protective effect of the disinfectant gradually vanishes and rustiness may be produced4 ,the same disinfecting effect may be obtained by the use of steam or hot water4 ,it was found that there was less liability to the formation of rust when sheets were immersed in water at a temperature of #ie deg4 to #abj deg4 ,f41 whilst steeping at #adj deg4 ,f4 gave complete freedom4 #d4 ,it was shown that the micro-organisms which cause decomposition of the serum-products flourish only in the presence of air--i4e41 they are aerobic in character4 ,it is not uncommon to find1 therefore1 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-room4 #e4 ,the optimal temperature for development of the particular organisms appeared to be about #ajj deg4 ,f41 in a moist atmosphere4 #f4 ,soaking the sheets in water 7except the short immersion in hot water1 which we recommend71 even for a period extending over a week1 does not hinder the formation of rust4 #g4 ,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 persist4 ,the simplest means of prevention is to soak the sheets first for a short period in water1 and then to hang them to drip for a few hours in a well-ventilated place1 outside the factory and under cover4#bc #bc ,we advise and practise hanging sheets in the open1 without shade or cover4 ,it will be gathered that1 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 film1 the general conclusions are identical with those given by us in preceding paragraphs and previously advised in the ,malayan reports of the ,rubber ,growers' ,association4 ,,bubbles4--,the presence of bubbles in sheet-rubber has for years been the bane of some managers' existence1 and the bone of contention between sellers and buyers4 ,taking the argument down to bed-rock1 producers urge that the presence of bubbles has no influence upon the ultimate quality of the rubber on vulcanisation4 ,they assert that the alleged defect is merely a peg upon which to hang an unreal grievance1 serving the purpose of the buyer under the existing conditions of sale4 ,all this may be true1 but as long as the present system continues1 it must be recognised that kicking against the pricks is a futile recreation4 ,the sympathy of the writers is certainly on the side of the producers1 inasmuch as they realise how extremely difficult1 and even impossible at times1 it is for the most careful individual to prepare sheet-rubber free from this blemish4 ,much has been written1 and many have been the discussions1 on this vexed subject2 and it is recognised that sometimes1 in spite of all precautions1 there may suddenly be an incidence of bubbles in rubber which is ordinarily free from them4 ,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 combat1 and often beyond human control4 ,the contributory causes are many and varied4 ,it should be premised that1 although the defect is described as air-bubbles1 it is seldom that the appellation is strictly correct4 ,rarely do the bubbles contain air4 ,in the vast majority of cases they contain gases in minute quantity4 ,these gases may be considered to arise1 broadly1 from some decomposition of substances 7other than rubber71 contained either in the coagulum or in the serum4 ,in a general way1 if this decomposition is evidenced by an unpleasant odour1 it is described under the term of putrefaction4 ,we are not concerned here with the question as to how far such decomposition may be ascribed to a purely chemical action1 or to the indirect result of the presence of certain bacteria or other micro-organisms4 ,suffice it to state that1 at least as far as field operations influence the result1 the decomposition is generally to be attributed to the work of micro-organisms4 ,conditions favourable to the incidence and development of these are to be found when absolute cleanliness in all details is not aimed at4 ,with this preamble we may proceed to classify possible causes of the formation of bubbles into two groups3 7a7 ,those originating in field operations4 7b7 ,others which may arise after the arrival of the latex at the factory4 ,,in ,,the ,,field4--,decomposition may be caused by3 7#a7 ,spouts1 buckets1 and cups being dirty4 ,regular cleaning is necessary4 ,if the buckets are allowed to be taken to the lines by tappers1 trouble may ensue4 ,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 buckets1 which had been used by coolies for preparing their food4 7#b7 ,delay in commencing work4 ,this means similar delay in collecting the latex which is exposed to greater heat than under ordinary circumstances4 7#c7 ,exposure to the sun's rays4 ,the heating of the latex may provide improved conditions favourable to the development and action of micro-organisms4 7#d7 ,allowing latex to stand too long before collection4 ,this usually is the result of giving tappers too great a task4 7#e7 ,the addition of water to the latex1 either purposely or accidentally1 in the form of rain4 ,the water may be slightly acid in character1 or it may carry micro-organisms from the bark into the latex4 7#f7 ,tapping trees at too great a height4 ,the latex generally has an abnormal distance to travel before reaching the cup4 7#g7 ,sometimes the latex from old trees1 or from trees after wintering 7just prior to full renewal of leaf71 contains more than the usual proportion of substances 7e4g41 sugars71 which are capable of effecting flocculation or coagulation4 7#h7 ,too great a distance for transport4 ,the trouble arising from this cause is likely to be much increased if the journey has to be made over bad roads4 ,in such case the physical action augments the effect likely to be produced by long standing4 ,the foregoing do not include all possible causes1 but serve to indicate the directions from which trouble may be mainly anticipated4 ,it will be plain that any latex which exhibits symptoms of premature coagulation 7or minute flocculation7 should be regarded as a potential source of bubbles in sheet-rubber4 ,it will be equally obvious that the employment in the field of any harmless substance of an anti-coagulant nature is to be encouraged4 ,this point is discussed in detail in ,chapter ,v4 ,,in ,,the ,,factory4--,as a general rule it may be understood that the mischief has been done before the latex is handled at the factory4 ,sometimes it is perceptible from the peculiar appearance of the latex1 and in such case the batch should not be used for the preparation of sheet-rubber4 ,often it is found that only the last to arrive at the store is visibly affected4 ,this should not be mixed with other apparently normal latex1 as it is capable of acting as a leaven to the bulk4 ,contributory factors in the store are3 7#a7 ,lack of cleanliness of utensils1 particularly of coagulating dishes or tanks4 ,the trouble becomes acute sometimes where wooden tanks are employed4 ,unless the tank and the partitions are thoroughly and regularly cleansed1 the wood may become coated with a bacterial slime1 which is capable of causing what may be termed fermentation of the latex layers in contact4 ,the tank should be thoroughly cleaned occasionally with a weak 7#e per cent47 solution of sodium bisulphite4 ,the partitions should be scrubbed and placed in the sun twice or three times a week4 7#b7 ,allowing latex to stand too long before treatment4 ,this point needs no further expansion4 7#c7 ,the use of a latex of too high a rubber content4 ,such latices are difficult to handle in order to secure uniform mixture with the coagulant4 7#d7 ,the use of too concentrated a solution of coagulant4 ,in conjunction with 7#c7 there may be a rapid and irregular coagulation1 giving rise not only to decomposition in parts 7and subsequent formation of gas71 but also to the formation of true air-bubbles by inclusion of air during stirring4 7#e7 ,the use of insufficient coagulant4 ,coagulation is slow and incomplete4 7#f7 ,defective straining and skimming4 ,small flocculated particles of rubber may pass1 or be rubbed through1 the strainer4 ,if allowed to remain1 they act as local points of danger4 7#g7 ,the proximity of the coagulating latex to some source of heat1 or exposure to sunlight4 7#h7 ,any delay of drying in the preliminary stages1 either before or after the rubber enters the smoke-house4 ,,blisters4--,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 rubber4 ,when subjected to pressure1 small balloons are formed1 which burst with a perceptible report4 ,it was formerly the belief that this defect was occasioned solely by an abnormally high temperature4 ,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 conditions4 ,at the same time it is not disputed that the heat of the smoke-house exerts an influence 7causing expansion and distension71 but it is advanced that the gases had begun to form before the rubber entered the house4 ,the view held is that decomposition had supervened or was taking place--probably from one or more of the causes enumerated in the preceding paragraphs4 ,the heat of the smoke-house only serves to exaggerate the effect4 ,it is acknowledged that the degree of decomposition must be initially greater than in the ordinary incidence of bubbles4 ,beyond this point we are not in a position to put forward any definite supposition as to the apparently haphazard occurrence of the phenomenon4 ,it is to be noted1 fortunately1 that the defect is comparatively rare1 and seldom appears on estates which employ an anti-coagulant in the field4 ,while we have examined persistent cases1 one of which led to a temporary discontinuance of the preparation of smoked sheet rubber1 we have not yet been able to arrive at any satisfactory idea of the exact conditions governing the incidence of blisters4 ,our investigations only lead us to two observations3 7a7 ,that blisters have appeared on the rubber of some estates after wintering1 and during the period of new leaf-development4 7b7 ,that the defect has been noted on other estates during a period when there were frequent but not heavy rains1 and when there was a comparatively low average temperature4 ,in either case1 as the factors are beyond human control1 it would be expected that without any change being made in estate procedure1 the trouble would vanish as mysteriously as it appeared4 ,this is our experience2 but as showing the possible intensive effect of a high temperature in the smoke-house1 it may be remarked that very infrequently1 in a batch of sheets exhibiting ordinary bubbles1 a few hanging directly above the furnaces show signs of a slight blistering effect4 ,,spot ,,disease ,,in ,,sheet ,,rubber4--,that spot disease may appear in air-dried sheets was evident at the beginning of the outbreak in the spring of #aiaa4 ,the first cases noticed took the form of pink and bluish blushes spreading over the whole of the sheets4 ,later1 fungoid spots began to appear4 ,these mainly took the form of red or black blotches1 and were very unsightly4 ,as spot disease cannot develop in smoked rubber1 the obvious and simple course to adopt was to smoke-cure the sheets4 ,when it is stated that spots do not develop in smoke-cured rubber1 it is understood that the smoke-curing must be efficient and must commence as soon as the rubber has been rolled1 and the surface water has drained away4 ,if the sheets are allowed to air-dry for a few days1 the disease may develop1 and then smoke-curing will not get rid of the coloured patches4 ,the operation of smoke-curing will not get rid of the coloured patches4 ,the operation of smoke-curing may tone down the colour1 but the spots would still remain evident4 ,,support ,,marks4--,it frequently occurs that one sees across the middle of smoked sheets a wide mark4 ,this is where the wooden support in the smoking-chamber has been4 ,as a rule1 even in the most careful cases a faint mark may always be seen1 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 supervision4 ,if bays of racks remain empty over-night1 they may possibly become covered with a light sprinkling of fine wood-ash and tarry deposit4 ,wet rubber placed upon these racks will pick up and retain the impurities1 and more often than not they cannot be washed out4 ,it is incumbent upon the manager to see that empty racks are thoroughly cleansed before placing wet rubber upon them4 ,the better plan is to arrange that the bars can be removed easily from sockets4 ,there should be in stock sufficient spares for1 say1 two days' rubber4 ,when the dry rubber is removed1 the bars should likewise be taken away1 to be cleansed and kept in the factory until again required4 ,this will ensure that fresh rubber always rests upon a clean support4 ,on some estates1 in order to guard against a pronounced bar-mark1 sheets are moved and turned daily4 ,in other smoke-houses the upper surface of the bar is chiselled in concave form1 so as to admit of the passage of smoke below the surface resting on the bar4 ,,stickiness4--,this is not to be confounded with tackiness1 from which the rubber does not recover4 ,stickiness is only temporary1 and may be remedied4 ,as a general rule1 it is due to packing sheets1 which have not a good raised ribbing1 and which may have been coated with light tarry deposits 7see ,glaze74 ,this surface film may be removed by washing the sheets1 or scrubbing them1 with cold water4 ,usually a further two days' air-drying will make the rubber fit for packing2 and if the smoke-curing has been efficient1 there should be no need to anticipate trouble from mildew4 ,some estates adopt this practice daily with success1 as a form of insurance against complaints of surface deposits4 ,,ribbing1 ,,surface ,,pattern4--,while we know that the passing of sheets of rubber between rolls1 causing a particular raised pattern to appear1 has no effect upon the actual quality of the rubber1 there is a great deal of practical advantage gained4 ,the practice ensures an increase of superficial area which is an aid in drying1 improves the appearance of the rubber for selling purposes1 and is of distinct advantage in enabling the rubber when packed to travel in better condition4 ,sheets do not become so closely packed2 sampling and general handling are easier on delivery4 ,as long as the plane surfaces are sufficiently and regularly distorted1 there would seem to be no limits to the type of pattern or mark which may be placed upon the rubber4 ,but in actual practice the variety is small4 ,the most popular type of ribbing is that best described as a small diamond effect1 produced by a pair of rolls cut with closely placed narrow grooves running spirally4 ,the spirals travel in the same direction on both rolls1 producing close-cut ribbing running in opposite directions on the surfaces of the sheet4 ,on sheets of standard thickness1 the result approaches a diamond effect4 ,a few other patterns are employed1 notably that producing longitudinal stripes of varying thickness4 ,on the whole1 the type of pattern would seem to be immaterial1 if the points already indicated are achieved4 ,it is seldom one encounters a case nowadays in which the marking is unsuitable1 but a few estates may be using an old type of patterned roll on which the full diamond grooving is cut4 ,as this appears on both sides of the sheet of rubber1 and as the ribbing does not coincide1 a blurred effect is seen when the sheet is viewed against the light4 ,,thick ,,ends1 ,,sheet ,,clippings4--,it rarely happens1 even with good equipment and average supervision1 that the preparation of smoked sheet is unaccompanied by slight defects4 ,for instance1 in spite of rules and regulations regarding manipulation of the coagulum1 it is not uncommon to find that some sheets1 after rolling1 have slightly thickened ends4 ,in the ordinary course of events these might delay drying considerably4 ,it is the practice on some estates to cut off these thickened ends while the rubber is still wet4 ,the pieces are then machined into crepe form1 but as no sodium bisulphite may have been used1 the resulting rubber cannot be classed as ,no4 #a ,standard ,crepe4 ,the other alternative is to trim the ends when the bulk of the rubber is thoroughly smoke-dried4 ,the moisture containing portions are then returned to the smoke-house until dry1 and are subsequently packed without further treatment as smoked-sheet clippings4 ,it will be plain that1 except in the particularity of form1 these clippings differ in no degree from the original sheets2 and1 owing to extra smoke-curing1 may arrive in even better condition4 ,one must be prepared1 however1 to find that a slightly lower price is offered4 ,whether the price obtained would be comparable with that commanded by the crepe made from wet sheet slipping would depend upon general ruling market conditions1 and the degree of care exercised in guarding against the inclusion of any inferior pieces of rubber4 ,in ordinary factory practice1 there could be no room for abuse under the latter clause4 ,,other ,,infrequent ,,defects4--,this chapter will be closed with a reference to other small defects which1 although infrequent1 cannot be classed as minor complaints4 ,in point of fact1 when they occur1 they assume an importance1 in the eyes of the consumer1 which is not1 perhaps1 sufficiently appreciated by producers4 ,,dirt4--,trouble from this source should be absent1 but carelessness on the part of packing coolies may be responsible for occasional complaints4 ,how the dirt is incident may remain a mystery1 but it has been noted that sheets have at times been thrown upon a cement floor4 ,a certain amount of loose dust may thus adhere to the rubber4 ,,ash4--,the source of this surface deposit scarcely needs indication4 ,where open-hearth furnaces are employed1 and the wire-mesh floor screens are not perfectly sound1 fine ash may find its way into the upper chamber4 ,if this trouble is persistent in spite of precautions1 the sheets should be surface-washed and air-dried before packing4 ,,bark4--,complaints of the presence of particles of bark in sheet rubber used to be fairly frequent1 but are now less common4 ,the trouble may be traced to the use of defective straining sieves when the latex is being handled4 ,,splinters4--,the use of packing-cases of unplaned soft timber is responsible for complaints of this nature on delivery4 ,without here discussing the larger question of the ideal packing case1 it is sufficient to emphasise that the interior surfaces of wooden chests should be planed4 ,the cases are often so damaged in transit1 that splinters of wood may be found throughout the contents4 ,the device adopted on some estates may go far to prevent this4 ,the cases are first lined with loose sheets1 and finally other sheets are arranged to overlap at the top of the case4 ,the bulk is thus enclosed in a wrapping of sheets1 and any splinters or other deleterious substances are confined to the surface of the mass4 ,,part ,v ,,general ,,chapter ,,xix ,,choice ,,of ,,coagulant ,almost without exception1 the agent employed in the coagulation of plantation 7,hevea7 rubber is acetic acid1 or in some cases formic acid4 ,under ordinary trade conditions supplies are always obtainable at reasonable prices1 but during the recent ,war the question of possible substitutes was brought greatly to the fore4 ,fortunately the subject of coagulation and coagulants had been previously studied to such effect in laboratory practice1 that there would have been small difficulty in prescribing agents other than acetic acid in cases of expediency4 ,as far as our knowledge extends1 all the possible substances which have the power of coagulating latex have been tested4 ,they include mineral acids1 organic acids1 compounds known chemically under the general term of salts1 alcohols1 sugars1 etc4 ,the heading of this chapter must be seen to beg the question1 inasmuch as it leads to the assumption that a coagulant 7in the popular sense7 is necessary to secure coagulation4 ,in point of fact1 methods are sometimes employed which depend upon no artificial coagulant to produce the desired effect4 ,to these methods reference will be made later4 ,in this section it is proposed to describe briefly the more important agents which are used1 or might be used1 in effecting coagulation4 ,in the class of those which are not in common use some could be used as expedients1 while others are only of scientific interest4 ,,acetic ,,acid4--,there is no need to enter into a discussion of the merits of this agent4 ,in practice it remains the cheapest and safest coagulant known at present4 ,,formic ,,acid4--,this agent is equally as safe to use as acetic acid1 and as easy to handle4 ,bulk for bulk its coagulative power is higher than that of acetic acid4 ,its pre-war shipping price1 when taken in conjunction with its coagulative power1 was slightly below that of acetic acid1 but local prices put the balance in favour of the latter4 ,if prevailing costs put it on terms of parity with acetic acid1 there would appear to be no reason why formic acid should not have a widely-extended use on plantations4 ,,citric ,,acid1 ,,tartaric ,,acid4--,the acids of the extracted juices of most tropical fruits consist1 to a large degree1 of citric or tartaric acids4 ,these can be used in place of acetic acid as satisfactory coagulants in case of emergency2 but the questions of availability of supplies and of costs preclude their more general adoption4 ,,oxalic ,,acid4--,this is a satisfactory coagulant as far as observed effect is concerned4 ,it produces a rubber paler than ordinary coagulants 7without the use of sodium bisulphite71 as it has the nature of an anti-oxidant4 ,it would not be a safe agent in the hands of coolies1 as it is classed as a poison4 ,,sulphuric ,,acid4--,during the ,war1 in a period of shortage of acetic acid and of high prices1 this agent was used with success on some estates4 ,it scarcely need be remarked that it is a dangerous substance to handle1 and that its employment must be accompanied by close ,european supervision4 ,at prevailing prices during the ,war it was very much cheaper than acetic acid1 and even at the present reduced cost of the latter the advantage still lies with sulphuric acid4 ,it must be emphasised1 however1 that the abuse of this agent to any but the slightest degree is harmful to the resultant rubber4 ,hence its use would be sanctioned only in the absence of the commoner1 and much safer1 coagulants4 ,in view of the possible incidence of such an emergency1 the following notes are given4 ,it is impressed that strict adherence to the rules must be given4 ,,handling ,,sulphuric ,,acid4--7a7 ,always use glass or glazed earthenware vessels4 7b7 ,pour slowly and avoid splashing4 ,drops finding their way to clothing or other fibrous material will destroy it locally2 and if thrown upon any part of the body may cause painful burns4 7c7 ,when diluting this agent always remember to pour the acid into the water 7i4e41 the lesser into the greater71 and never vice versa4 ,pour the acid carefully and slowly down the side of the vessel1 and stir well4 7d7 ,should strong acid be spilled1 do not throw water upon it4 ,a supply of sand or dry earth should be kept close at hand4 ,throw this upon the acid4 ,,storing ,,sulphuric ,,acid4--7a7 ,jars or cases should be handled as seldom1 and as carefully1 as possible4 ,if the acid is contained in a case1 the top should be plainly indicated4 7b7 ,stocks should be stored in a detached building which should not be damp4 ,jars or cases should not stand on a wooden floor if possible4 7c7 ,see 7d7 above4 ,,buying ,,sulphuric ,,acid4--7a7 ,commercial acid of specific gravity #a4hd is the best of its kind4 ,it contains impurities which are non-injurious to rubber preparation4 7b7 ,it is always advisable1 if possible1 to buy the acid in small jars containing not more than #ajj lbs4 each4 ,smaller jars1 with a content not exceeding #ej lbs41 would be preferable4 7c7 ,if the acid is bought in jars1 it should be stipulated that the stoppers be covered with a plaster head1 and that the containing crate or case should have prominent labels or marks indicating the top of the case4 ,,formula ,,for ,,use ,,of ,,sulphuric ,,acid4--,it will be understood that as this formula has been calculated for working with latex1 having a consistency of #a-a_/b lbs4 dry rubber per gallon1 it applies in a strict degree only to such latex4 ,in other cases1 where the dilution of the latex is not known1 the formula will serve as a basis for experiment until the correct quantity has been discovered4 7,sulphuric acid of specific gravity #a4hd47 ,,note4--,the directions must be followed carefully1 and glass measuring vessels should be used if procurable4 7a7 ,measure out #a pint of strong acid1 and pour it carefully and slowly down the inner surface of a jar containing #bj gallons of water4 ,do not pour it directly into the water4 ,the heavy acid will sink to the bottom of the jar1 and a good mixture must be obtained by stirring well4 7b7 ,of this solution 7which is approximately #a per cent4 by weight71 use #a gallon to #bj gallons of latex4 ,readers are doubtless now well aware of the corrosive action of strong sulphuric acid1 and we scarcely need point out that even the dilute acid should not be kept in contact with the usual iron vessels found in factories4 ,the mixing of solutions should be done in one of the glazed earthenware jars commonly in use4 ,the formula given above works out at approximately #a part strong acid to #b1jjj parts of latex 7of dry rubber content #a-a_/b lbs4 per gallon74 ,the formula for using acetic acid with the same latex works out at about #a3 #a1bjj4 ,it will be apparent1 therefore1 that relatively sulphuric acid is a more powerful coagulant than acetic acid4 ,in terms of dry rubber obtained from latex of the consistency indicated above-- #a lb4 sulphuric acid will produce #cjj lbs4 dry rubber4 #a lb4 acetic acid will produce #ahj lbs4 dry rubber4 ,with both acids selling at the same rate1 sulphuric acid would be more economical in use2 when its cost is less than that of acetic acid1 which is the normal condition1 the economic advantage in favour of sulphuric acid is augmented still further4 ,it may be found that the standard formula for sulphuric acid will not always give a perfectly clear remaining serum1 even though an attempt is made daily to work to a uniform consistency for all latices4 ,it is inevitable that the manipulation of the latices should be slightly in error on occasions1 or that a small mistake might occur in preparing the solution of acid4 ,hence a clear remaining serum after coagulation may be secured less often than a slightly turbid serum4 ,this is as it should be4 ,the minimum quantity of acid may be adjusted so closely as to give such results4 ,if a clear serum is obtained always1 that should be an indication of continual excess of coagulant4 ,naturally1 if a milky serum is always obtained1 the reverse is the case4 ,as a last word on the subject1 it may again be emphasised that the use of sulphuric acid is not advised1 except in an emergency2 and that the greatest possible care must be exercised in the observance of the strict formula for use4 ,,hydrochloric ,,acid1 ,,nitric ,,acid4--,these mineral acids would prove more expensive than sulphuric acid4 ,in addition they are much more uncertain in action4 ,for example1 the use of a certain excess of hydrochloric acid would not hasten coagulation1 but would prevent it4 ,above all their effect1 in excess1 is deleterious to the rubber4 ,,hydrofluoric ,,acid4--,this has a strong corrosive action on porcelain or glass4 ,hence it has to be contained in bottles of gutta-percha or lead4 ,it is mentioned here merely because some years ago it found a use as a coagulant1 chiefly in ,ceylon4 ,it was sold in the form of a #aj per cent4 solution under the name of ,purub1 and was the subject of a patent4 ,it is effective as a coagulant1 and has also an anti-oxidant action1 which was its chief recommendation when cheap and harmless anti-oxidants were not commonly known4 ,it is comparatively expensive1 and1 as indicated above1 difficult to handle and store4 ,in short1 it has nothing to commend it1 in comparison with acetic or formic acids4 ,,alum4--,this substance has been used for years by native rubber producers as a coagulant4 ,it fulfils the desired purpose1 and its popularity was maintained because of the ease with which it could be stored and handled4 ,unfortunately1 this facility often led to the use of an excess1 and native sheets were often criticised as being brittle4 ,investigations have shown that alum1 even in minimum proportions1 has an appreciably harmful effect upon the quality of the rubber prepared by its use as a coagulating agent4 ,its employment by native rubber producers has now been largely superseded by acetic acid in some form4 ,,pyroligneous ,,acid4--,this is otherwise known under the names of crude acetic acid and crude wood vinegar4 ,owing to the shortage of acetic acid during the ,war1 attention was directed towards the possibility of making an effective coagulant locally by what is termed the dry distillation of wood--i4e41 the wood is not burned but heated in a retort4 ,the enquiries could be placed in two classes3 #a4 ,those which aimed at making the pure1 strong acid of commerce4 #b4 ,those which sought information concerning a crude coagulant 7pyroligneous acid7 on estates4 ,regarding the first class1 we can do no better than reproduce our remarks published in the ,april local report of the ,rubber ,growers' ,association for #aiaf--with the reservation that1 on account of a threatened shortage of timber1 a local scheme might not now be feasible3 ,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 country4 ,it may be stated that the proposition is a feasible one1 even on a fairly large scale4 ,we have the essentials necessary for such a scheme in3 #a4 ,a good supply of suitable timbers1 the most valuable of which1 possibly1 is mangrove timber1 locally known as 'bakau4' ,other suitable timbers are known1 but as far as preliminary experiments show mangrove timber gives the best yield4 ,at present this timber is in great demand as a fuel for steam plants1 but with the extension of the local coal industry the timber may become cheaper4 #b4 ,there would appear to be less valuable timber which would be suitable for heating the retorts4 ,or1 local coal might be used4 #c4 ,supplies of lime at reasonable rates are available1 as the limestone formation in the peninsula is quite considerable in extent4 #d4 ,supplies of sulphuric acid are available from ,japan1 ,australia1 ,burma1 etc41 even at the present time1 although naturally rates are higher than normal4 ,under ordinary conditions1 supplies from ,england and parts of ,europe would be much cheaper than at current rates4 ,for the benefit of many readers perhaps a brief and nontechnical description of the preparation of acetic acid would not be amiss1 and would explain the necessity for the essentials indicated above4 ,in brief1 the process is as follows3 7a7 ,a suitable timber is heated in a closed retort4 ,this is termed 'dry distillation1' and results eventually in the carbonisation of the wood--i4e41 charcoal is obtained in the retort4 7b7 ,tar1 vapours and gases are distilled over during the carbonisation of the wood4 ,these liquors and gases pass through condensers4 ,the gases pass away1 while the condensed liquors separate out into 7#a7 wood tar1 7#b7 a watery liquor called pyroligneous acid or crude wood vinegar4 7c7 ,the pyroligneous acid is separated from the tar1 and again distilled to obtain the acetic acid present4 7d7 ,this crude acid is steam-heated with milk of lime1 which fixes the acid1 forming calcium acetate 7or acetate of lime74 7e7 ,eventually the calcium acetate is taken out in the form of a thick paste1 which is spread to dry4 ,when dry this 'grey acetate' is the main source of all glacial acetic acid now made4 7f7 ,the acetic acid is released from the 'acetate of lime' by the action of sulphuric acid4 ,it is then distilled several times1 and under various conditions1 in order to increase its strength4 ,in the past copper tubes were used for this purpose1 but owing to the fact that traces of copper were found to be injurious to rubber1 some works instal tubes of glazed earthenware for the distillation4 ,such is the process in outline1 and it will be seen that no proposal to manufacture glacial acetic acid on an estate could be considered feasible1 although it would not present any great difficulty on a large scale and under skilled direction4 ,furthermore1 the cost of the plant would be far too great for any estate4 ,although it is clear that pure acetic acid is beyond the scope of an estate1 crude pyroligneous acid has been produced on a varying scale in this country and in ,ceylon4 ,in the latter country some success was obtained by the distillation of coconut shells with comparatively inexpensive plant4 ,in this country1 wood-distillation was practised on a few estates1 but improved facilities for obtaining pure acetic led to a termination of the experiments1 although sufficient crude acid could then be made at a reasonable cost4 ,the pyroligneous acid obtained1 is generally clear1 after nitration1 and of a dark brown colour4 ,it has a peculiar odour reminiscent of smoked sheet-rubber1 or of creosotic substances in general4 ,its acid content depends chiefly upon3 7a7 ,the kind of timber heated in the retort4 7b7 ,the efficiency of the apparatus4 7c7 ,condition of the timber as to moisture4 7d7 ,the temperature employed1 and rate of working4 7e7 ,the point at which distillation ceases 7i4e41 the duration of interval between commencement of heating and cessation of collection74 ,samples received from estates for testing purposes were found to contain equivalents varying from #b per cent4 to #aj per cent4 of acetic acid4 ,they were all suitable coagulants when used in quantity calculated from the discovered acidity1 but produced rubber darker than ordinary when air-dried4 ,this effect was not of much importance in the preparation of smoked sheets1 but to produce a pale crepe it was necessary to employ sodium bisulphite as an anti-oxidant4 ,this darkening in colour is to be ascribed to the presence of traces of phenols1#bd which are stated to exert an effect upon the rubber during and after vulcanisation4#be ,this subject will be discussed in another section4 #bd ,whitby1 ,journal ,soc4 ,chem4 ,industry1 vol4 xxxv41 ,no4 #i1 #aiaf4 #be ,see also ,preparation and ,vulcanisation of ,plantation ,rubber 7,eaton1 ,grantham1 and ,day71 ,bulletin ,no4 #bg1 ,f4,m4,s4 ,department of ,agriculture1 ,april1 #aiah4 ,with this provision the crude pyroligneous acid which can be produced on estates1 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-profitable4 ,this point would be determined from a knowledge of the cost of production per gallon1 and the percentage of acetic acid per unit4 ,for example1 if the cost of production 7including cost of timber for distillation1 cost of fuel for heating the retort1 cost of labour1 etc47 was #fj cents per gallon of crude acid containing #i per cent4 of acetic acid1 that would be equivalent approximately to buying glacial acetic acid at #cj per demijohn of #dd lbs4 ,,smoked ,,water4--,a weak solution of pyroligneous acid may also be obtained by passing smoke through water4 ,with this object in view1 a machine was designed by the ,federated ,engineering ,company of ,kuala ,lumpur4 ,in this the principle of retorting was not employed4 ,smoke was produced by ordinary combustion in a compartment of the apparatus1 and was drawn through water by the action of a high-speed fan worked by hand4 ,a solution1 equivalent in effect to a #b per cent4 solution of acetic acid1 could be obtained at a comparatively cheaper cost than crude pyroligneous acid produced by dry distillation as it was then being practised4 ,this was chiefly because of the wasteful methods of fuel combustion1 in the latter process1 in the heating of the retort4 ,,chinese ,,vinegar4--,this agent was found to be a satisfactory coagulant1 and1 a priori1 there is no reason why it should not be suitable1 as it is essentially a dilute solution of acetic acid4 ,the qualities sold were generally colourless1 and were probably the result of acetic fermentation of rice4 ,samples tested showed a varying content of acetic acid1 ranging roughly from #c per cent4 to #h per cent42 but on this basis of valuation it was found generally that the price bore no relation to the degree of efficiency4 ,it was advanced not only that the vinegar was an efficient substitute for glacial acetic acid1 but that it was also cheaper4 ,this latter claim was proved to have no foundation in fact1 even at the high price of acetic acid prevailing during the period of stress4 ,it is not likely1 therefore1 that vinegar can displace acetic acid1 except as an expedient4 ,,sulphurous ,,acid4--,the anti-oxidant effect of sodium bisulphite and sodium sulphite is due to the liberation of the gas1 sulphur dioxide4 ,this gas dissolves easily in water1 forming an acid solution called sulphurous acid4 ,this acid solution is an effective coagulant in fairly small quantity4 ,not only so1 but it produces1 in addition1 the anti-oxidant effect noted in the employment of sodium bisulphite4 ,it is thus possible to produce rubber varying in shade of paleness by means of a single solution4 ,in the event of sulphurous acid being used1 it would be necessary to import cylinders of sulphur dioxide from which the solution could be prepared in factories each day4 ,there would be no insurmountable difficulty in this1 as it is only necessary to pass the gas through a series of closed vessels containing water4 ,enough solution could be prepared at one time for three or four days1 but preferably the solutions should be as fresh as possible4 ,altogether there would seem to be possibilities in the use of sulphurous acid for preparing pale crepe rubbers1 providing the cost is within comparable limits with the commoner coagulants at present in use1 and that no adverse effect on the rubber can be shown to result4 ,if the cost did not exceed the combined cost of acetic acid and sodium bisulphite1 the employment of sulphurous acid solution might be worthy of consideration4 ,there is one drawback to the use of sulphurous acid solution1 and that lies in the proximity of the limits of the quantities necessary for coagulation and that which is in excess1 and prevents coagulation4 ,thus1 with ordinary field latex having about #bj per cent4 dry rubber content1 the minimum necessary for coagulation per #ajj c4c4 of latex is about #h c4c4 of a #a per cent4 solution4 ,the maximum quantity possible for use is about #ae c4c4 of a #a per cent1 solution1 so that great care would have to be exercised in avoiding an excess of coagulant1 otherwise coagulation would be effectually prevented4 ,it is believed that the preparation of rubber by this method is the subject of a patent secured by ,messrs4 ,boake1 ,roberts1 and ,co41 ,london4 ,,sugars4--,coagulation may be effected by the addition of small quantities of sugars4#bf ,these are assumed to be effective by fermentative conversion into lactic and acetic acids4 ,the presence of lactic acid is supposed to have a twofold effect3 #bf ,preparation and ,vulcanisation of ,plantation ,para ,rubber 7,eaton1 ,grantham1 and ,day71 ,bulletin ,no4 #bg1 ,f4,m4,s4 ,department of ,agriculture2 ,gorter and ,swart1 ,bulletin ,no4 #f1 ,west ,java ,expt4 ,station4 7a7 ,as a direct coagulant4 7b7 ,in its action upon certain organisms which1 in the ordinary course of events1 would delay or prevent coagulation4 ,although work on an experimental scale has been done1 as far as we know no practical application has been made of the employment of sugars as coagulating agents4 ,,various ,,salts4--,of experimental interest only it may be recorded that coagulation has been effected by means of various chemical salts--e4g41 calcium chloride1 barium chloride1 magnesium chloride1 sodium chloride1 aluminium sulphate1 magnesium sulphate1 sodium sulphate1 etc4 ,none of these has been found to have any practical application1 except1 perhaps1 calcium chloride1 which is used in small quantity as an accelerating agent in a special process of anaerobic coagulation1 which will receive mention in the following chapter4 ,at one period during the ,war and the dearth of acetic acid1 it was found that there were available in ,england large supplies of the acid sulphate of sodium 7sodium hydrogen sulphate71 which proved to be an effective coagulant4 ,experimental work gave satisfactory results1 but no practical application resulted when supplies of acetic acid were again obtainable4 ,,various ,,proprietary ,,compounds4--,we have seen many proprietary coagulants advertised and pass into the limbo of forgotten things4 ,they can generally be divided into two classes4 ,the first embraces those founded upon a woefully incomplete knowledge of requirements4 ,the second covers those which meet requirements1 but for which exaggerated claims are made and excessive prices charged4 ,as as instance of a substance which fell under both classifications might be mentioned the case of ,coagulatex4 ,pretentious claims were made1 and it was emphasised that the liquid contained no vegetable acids4 ,acetic and formic acids might be quoted as examples of vegetable acids1 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 ,coagulatex4 ,on analysis the liquid was found to consist mainly of sulphuric acid1 against the indiscriminate use of which warnings have been given4 ,thus it was a dangerous substance for common use4 ,furthermore1 comparing the value with its sulphuric acid content1 it was found that the price required for ,coagulatex was roughly four times the contemporary cost of commercial sulphuric acid in the ,federated ,malay ,states4 ,those in charge of estates should realise1 therefore1 that no proprietary coagulants should be adopted until a proper report of tests1 and a comparative valuation1 has been obtained from one of the research laboratories4 ,,carbonic ,,acid ,,gas1 ,,carbon ,,dioxide4--,now of only scientific interest1 it may be noted that some years ago great claims were made for the use of carbon dioxide gas as a coagulant4 ,in actual practice we were unable to effect coagulation by passing the dry gas into latex4 ,it was suggested that the original investigators were misled by failure to secure a dry and clean gas4 ,it would appear that probably the gas was prepared by the action of hydrochloric acid upon marble or limestone4 ,unless intervening washers and driers were used1 the liberated gas1 when passed into latex1 would carry with it traces of hydrochloric acid1 which would effect coagulation4 ,,alcohol4--,in the cheap form of methylated spirit1 alcohol has been employed by us as a speedy coagulant for many years4 ,latex run slowly into alcohol coagulates instantaneously4 ,the method has been in common laboratory use4 ,the employment of alcohol has also been made the part-subject of a patent process of coagulation1 to which reference will be made in the succeeding chapter4 ,,vegetable ,,extracts4--,at various times experimental work has been directed towards the use of liquids of purely vegetable origin1 such as the juices of tropical fruits1 and of a waste product of tropical industry--the so-called milk 7or water7 of ripe coconuts4 ,in the former class there is usually a natural acidity1 but in coconut water the acidity is chiefly the result of fermentation of the carbohydrate 7sugar7 constituents4 ,these substances were all found to effect a more or less satisfactory coagulation1 but it is unlikely that they would be suitable for practical application on a large scale4 ,as being more directly related to the subject of coagulation in general than to coagulants in particular1 a discussion of several special processes will be relegated to the ensuing chapter4 ,,chapter ,,xx ,,special ,,methods ,,of ,,preparation ,every year appears to bring forth some new ideas in the mode of rubber preparation4 ,some of them are based in principle upon the oldest known method--i4e41 the native ,brazilian process of making ,hard ,para4 ,others strike a new note1 and in a few cases the claims put forward are substantially confirmed by results4 ,in other instances the claims are too pretentious1 and discredit may be brought upon schemes which1 although lacking in comparative success1 are yet commendable for the ingenuity manifested4 ,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 preparation4 ,a few continue to find local application1 but most have either been abandoned or are gradually falling into desuetude4 ,we do not propose to discuss in fine detail all the various claims made on behalf of these special processes1 or to enter into controversies4 ,the aim is to present to the reader an outline embodying the main principles and advantages claimed4 ,,da ,,costa ,,process4--,briefly1 this was a method by which coagulation was effected with smoke4 ,the smoke was generated by the combustion of wood in a special compartment1 and was forced into latex by means of a jet of steam4 ,it was really only applied to the preparation of coagulum intended for crepe form4 ,the exact degree of coagulation effected was uncertain1 and the final colour of the rubber precluded it from being classed as a modern ,no4 #a product4 ,,byrne ,,curing ,,process4--,this is a process for treating coagulum obtained by ordinary methods4 ,it was the subject of a patent obtained by ,messrs4 ,e4 ,j4 and ,f4 ,a4 ,byrne1 and at one time had a considerable vogue on estates4 ,the chief claim advanced was that the rubber produced was in all respects equal to ,fine ,hard ,para1 and could be shipped while still moist without detriment to the physical qualities4 ,the principle of the process was the treatment of coagulum1 in either sheet or thick crepe form1 with vapours produced by the volatilisation of two special fluids4 ,this treatment was undertaken in comparatively small wooden sheds1 in which the coagulum was placed4 ,the smoke was conducted into the curing sheds from furnaces outside the building4 ,the sheds were covered externally with felt material to prevent leakage of the vapours1 and a very dense smoke was obtained4 ,the furnaces were specially designed1 and consisted essentially of a hot-plate heated by a powerful kerosene blast-flame4 ,on top of the machine were two reservoirs controlled by taps4 ,in these were placed the special fluids which were released in definite proportion4 ,the composition of the fluids was not divulged1 but it is assumed that the principal ingredients were 7a7 wood tar products1 7b7 crude pyroligneous or acetic acid4 ,the mixture of these1 dropping on the hot plate at the correct temperature1 spontaneously volatilised1 to form dense whitish fumes1 having an intense and not disagreeable odour of wood combustion4 ,a duct led from the back of the machine into the curing-shed1 where the vapours were distributed through perforations in the pipe4 ,the coagulum usually remained under treatment in the shed for three to four hours1 and then was removed for ordinary air-drying4 ,when taken from the curing-shed it had a pinkish colour1 which later developed into a dark brown by a natural process of oxidation4 ,the exterior of the rubber1 on shipment1 resembled the appearance of smoked sheets2 while the interior1 on cutting1 was seen to be still white4 ,as packed for shipping1 the rubber contained from #aj to #ae per cent4 of original moisture1 for the usual sheet form1 and even more when slab rubber was prepared4 ,originally either crepe or sheet rubber was made1 but later the preparation of the crepe form was displaced largely by slab rubber4 ,these slabs were really very thick sheets1 which had been subject to only slight pressure4 ,still later the preparation of the slab form was displaced by loaf rubber4 ,this form was built up by winding together ordinary thin sheets which had been subject to the cure4 ,only slight tension was needed1 during the operation of winding1 to cause close adhesion of the component wet layers1 and the final result was a loaf or roll dark in colour1 and apparently dry when examined superficially4 ,on being cut1 even after an interval of months1 the middle portion was still so moist as to be quite white4 ,in course of time it was discovered that all the claims made for the process could not be substantiated1 and for various reasons 7which need not be detailed7 most of the estates which had adopted the scheme reverted to ordinary methods of preparation4 ,at the time of writing few1 if any1 continue to work the process4 ,it appears to be agreed1 as the result of investigations1 that in no degree does the process yield advantage over ordinary methods4 ,,freezing ,,process4--,a patent was secured a few years ago to cover a process whereby coagulation was effected by refrigeration4 ,latex remained for several hours in the refrigerating chambers of an ordinary ice-making plant4 ,the resulting solid mass1 on being thawed1 yielded a coagulum appearing in no way to differ from that obtained by ordinary methods of coagulation4 ,provided the process exerted no influence for good or evil upon the quality of the resulting dry rubber1 the value of it would appear to depend upon the relative cost of working1 plus considerations of capital expenditure and depreciation on the plant4 ,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 methods4 ,furthermore1 beyond the expensive refrigerating plant1 the usual machinery of a factory would still be required if the ordinary market demands are to be met4 ,finally1 it has not been found#bg that any advantage in the final physical qualities of the rubber is obtained by the employment of this process4 #bg ,preparation and ,vulcanisation of ,plantation ,rubber 7,eaton1 ,grantham1 and ,day71 ,bulletin ,no4 #bg1 ,f4,m4,s4 ,department of ,agriculture4 ,,wickham ,,process4--,this process1 invented by ,sir ,henry ,wickham1 aimed at the production of a rubber resembling ,fine ,hard ,para4 ,the principle employed was that underlying the preparation of the best rubber in ,brazil--viz41 coagulation of superimposed thin layers of latex by the action of smoke and heat4 ,in essential the machine employed consisted of a rotating drum into which latex and smoke entered4 ,the result was the formation of thin skins of rubber which1 coagulating in situ1 formed a mass corresponding to ,fine ,hard4 ,that the rubber was fully satisfactory as to quality is acknowledged1 but economically and in practical utility the process was unsuccessful1 the rate of output being so low4 ,,derry ,,process4--,the invention of ,mr4 ,r4 ,derry1 late of the ,singapore ,botanic ,gardens1 this in principle resembled the ,wickham and other processes4 ,it aimed at a mechanical imitation of the native method of producing ,fine ,hard ,para4 ,in place of the rotating drum1 an endless belt was used4 ,this travelled over pulleys1 more or less horizontally placed4 ,the upper of these could be raised to varying height above the level of the other1 and likewise could be so adjusted as to tighten the belt4 ,the under layer of the belt impinged1 in its travel1 upon the surface of a layer of latex contained in a shallow tray4 ,the belt was operated by hand-power1 and the height of the latex trays was adjustable4 ,the trays of latex were situated at the lower end of the machine which lay outside the smoking-chamber4 ,it will be understood that the vastly major part of the total length of belt was always within the chamber4 ,smoke was generated by combustion of wood in an external structure1 was brought into the chamber by a wide duct1 and was then distributed below the belt by means of perforated pipes4 ,the thin film of latex picked up by the belt was coagulated partly by the action of smoke constituents by evaporation due to heat4 ,assuming 7#a7 that the belt was of adequate length1 7#b7 that the rate of travel was not excessive1 7#c7 that the latex was not too dilute1 7#d7 that the temperature of the smoke was sufficiently high1 7#e7 that the smoke was sufficiently dense and not too damp--then the process should be a continuous one4 ,it will be clear that success could only be obtained by a careful adjustment of all these factors4 ,the latex must1 necessarily1 be of a fairly rich consistency 7at least #b-a_/b lbs4 dry rubber per gallon71 but unfortunately there is considerable difficulty in maintaining such latex in a state of fluidity for the period demanded by this process1 without loss of latex4 ,naturally1 the addition of an anti-coagulant would retard the rate of output of the machine to a marked degree4 ,the layer of rubber thus formed on the belt was stripped off1 and hung for further air-drying1 as it still contained a fair percentage of moisture4 ,as a really practicable method for treating plantation latex1 the process failed by reason of its low rate of output over a given interval4 ,this alone was sufficient to condemn it1 apart from the facts 7#a7 that it was not shown to be a cheaper method than coagulation by acetic acid1 7#b7 that the resulting rubber was not proved to be of superior intrinsic value to rubber prepared by ordinary methods4 ,,spontaneous ,,coagulation4--,all readers will be aware of the phenomenon of the curdling or souring of milk4 ,the behaviour of ,hevea latex1 under certain conditions1 may be taken to be analogous4 ,difficulty is experienced in maintaining fluidity--a difficulty which appears to vary in great degree according to locality1 nature of soil1 age of trees1 the relative demand made upon the trees by the system of tapping employed1 etc4 ,it is sometimes found1 before the latex reaches the store1 that it may exhibit one of various stages of premature 7spontaneous7 coagulation3 7a7 ,to all appearances it may be quite fluid1 but a close examination shows it to consist mainly of a serum containing very minute particles of rubber in suspension 7microscopic coagulation74 7b7 ,in a later stage these particles coalesce to form larger flocks 7macroscopic coagulation74 7c7 ,the whole1 or practically the whole1 of the latex may have coagulated1 forming one mass of rubber with a milky residual serum4 ,passing from this aspect of the question1 it may be noted as peculiar facts that3 7#a7 ,a shallow layer of latex is less likely to coagulate spontaneously 7i4e41 without the addition of a coagulant7 than a deeper volume4 7#b7 ,the shallow layer1 and also the surface of the deeper volume 7where exposed to air71 on standing will be found to develop a superficial film of finely coagulated particles1 yellowish in colour1 and having an offensive odour due to decomposition of protein matter4 7#c7 ,while this partial coagulation is confined only to the surface of a shallow layer of latex1 it will be found that below the surface film of the deeper volume a much more definite coagulation has taken place4 ,the coagulation will be practically complete1 and the coagulum1 apart from a spongy appearance1 is normal in character4 ,this coagulum is free from the offensive odour noted above4 7#d7 ,on testing the surface film of both the shallow layer and the deeper volume1 it will be found to be alkaline in character2 whilst the lower liquid surrounding the main portion of the coagulum in the deeper volume of latex is of an acid nature4 ,these observed facts are sufficient to indicate that there are apparently two distinct types of spontaneous coagulation1 and that the latter takes place particularly where the latex is more or less out of contact with the atmosphere4 ,we may1 therefore1 differentiate thus3 7a7 ,in contact with air 7aerobic73 incomplete spontaneous coagulation1 accompanied by yellowish slime1 offensive in odour and alkaline in character4 7b7 ,out of contact with air 7,anaerobic73 ,practically or wholly complete4 ,there is no offensive odour under normal conditions and the serum is acid in character4 ,it is concluded#bh that there are present in latex1 on collection in the field1 two types of organisms4 ,those which work in contact with air 7aerobic7 show a tendency to prevent coagulation and to form an alkaline yellow slime on the surface of the latex4 ,the others1 which work in the absence of air 7anaerobic71 may1 under favourable conditions1 cause complete coagulation unaccompanied by any decomposition or offensive odour within a normal period4 ,if air is rigidly excluded1 the coagulum obtained is quite satisfactory for all purposes4 #bh ,preparation and ,vulcanisation of ,plantation ,rubber 7,eaton1 ,grantham1 and ,day71 ,bulletin ,no4 #bg1 ,f4,m4,s4 ,department of ,agriculture1 #aiah2 ,de la ,coagulation naturelle du ,latex d',hevea ,brasiliensis 7,denier and ,vernet71 ,comptes ,rendus l',academie des ,sciences1 ,no4 #c1 ,july1 #aiag4 ,this type of coagulation1 without the employment of a chemical coagulant1 and under anaerobic conditions1 was the subject of a patent granted in #aiad to ,messrs4 ,maude1 ,crosse and others4 ,the process has been in use on ,cicely ,estate 7,perak7 for some years4 ,with subsequent slight modifications the apparatus consisted in essential of a tank with a loose cover4 ,the flanges of the cover were sufficiently long to dip into a water-seal surrounding the tank4 ,thus the cover may rise and fall without an inrush of air4 ,coagulation1 in fact1 can be effected thus in any kind of air-tight receptacle2 and experimentally the reader can obtain a satisfactory result by filling completely with latex the bottle which has a loose stopper4 ,under the patent held the coagulum may be prepared either for crepe-making1 or for sheets by a modification of the tank4 ,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 bisulphite4 ,unfortunately the addition of this substance to the latex in normal proportions is not possible under anaerobic conditions1 as it is found to prevent coagulation1 probably owing to its sterilising effect upon the anaerobic organisms4 ,to prevent the oxidation of the rubber in actual practice1 the freshly prepared crepe is soaked in a solution of sodium bisulphite before hanging to dry4 ,the resulting colour of the rubber is quite good4 ,it was shown by ,eaton and ,grantham that anaerobic coagulation is slightly uncertain in action4 ,owing probably to variations in the composition of the latices1 or to the extent of infection by organisms1 coagulation may one day be complete and on other days less satisfactory4 ,they found further that1 by the addition of small quantities of sugars1 coagulation under both aerobic and anaerobic conditions was improved4 ,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 latex4 ,this work was confirmed by ,gorter and ,swart1#bi who attributed the action to the conversion of sugar to lactic1 acetic1 and succinic acids by fermentation4 #bi ,gorter and ,swart1 ,bulletin ,no4 #f1 ,west ,java ,station4 ,denier and ,vernet1 whose work has already been mentioned1 studied the presence of the organisms in latex1 and succeeded in isolating one which1 under anaerobic conditions1 effects coagulation within twenty-four hours4 ,sometimes to produce complete coagulation it was found necessary to employ small quantities of sugars--e4g41 #a gramme per litre of latex 7#a3a1jjj74 ,it is to be noted also that the addition of small quantities of soluble calcium 7lime7 salts to latex has much the same effect as the employment of sugars4 ,recent investigations#cj showed that the addition of #j4e to #a gramme of calcium chloride per litre of latex caused complete coagulation in closed vessels within twenty-four hours1 a result agreeing with the findings of ,barrowcliff4 #cj ,archief voor de ,rubbercultuur1 ,nederlands ,indies1 #aibj1 #d1 #bgc4 ,on page #cjh of the same publication1 experiments on the effect of sugars are described1 in connection with aerobic coagulation4 ,observations from a further set of experiments tended to indicate a direct connection between the effects of tapping and spontaneous coagulation4 ,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--e4g41 sugars4 ,the smaller the proportion of these substances1 the slower and less complete is natural 7spontaneous7 coagulation4 ,,ilcken-,,down ,,process4--,this process is the subject of patents granted in #aiae to ,messrs4 ,ilcken and ,down4 ,it has been in fair prominence1 and has been tried experimentally on several estates and in public demonstration4 ,it is a coagulating process1 and1 in the original specification1 employed as agents a mixture of alcohol 7in the form of methylated spirit7 and benzene 7petrol71 or alcohol with petrol and coal-tar naphtha4 ,the mixture was injected in the form of a fine spray into the latex1 contained in a tank specially fitted with paddles4 ,later modifications covered the addition of a small quantity of glycerine2 or1 failing supplies of that substance1 coconut oil4 ,many advantages are claimed for the process1 but most of them cannot be substantiated4 ,the two chief claims are3 #a4 ,the production of a uniform standard of rubber4 #b4 ,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 acid4 ,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 serum4 ,regarding the first of these claims1 it has been shown#ca that the rubber is not uniform in its behaviour on vulcanisation1 and that its variability is similar to that of rubber prepared by other processes4 #ca ,preparation and ,vulcanisation of ,plantation ,rubber 7,eaton1 ,grantham1 and ,day71 ,bulletin ,no4 #bg1 ,f4,m4,s4 ,department of ,agriculture1 #aiah4 ,the second claim has been the subject of much controversy4 ,experiments made on estates under the supervision of1 or in the absence of1 the patentees have given conflicting results4 ,when varying factors have been eliminated1 the general conclusion was that no increase in weight of rubber was obtained4 ,private laboratory investigations led to a similar verdict1 and ,eaton#cb records a confirmatory finding4 ,more recently the claims made for the process were investigated in ,java#cc under varying conditions4 ,three series of experiments were made3 #cb ,ibid4 #cc ,archief voor de ,rubbercultuur 7,de ,vries and ,spoon71 ,central ,rubber ,station1 ,java1 ,may1 #aiba4 7#a7 ,during the rainy monsoon and at a height of #a1hjj feet4 7#b7 ,during the dry monsoon on a low-country estate4 7#c7 ,in the experimental gardens at ,buitenzorg during bright sunny weather and the most favourable conditions4 ,the agents used were 7a7 a mixture of alcohol and fusel oil1 7b7 alcohol and petrol 7benzene74 ,in these experiments no advantage in weight of rubber was obtained by the ,ilcken-,down process1 and it would thus appear that the principal claim fails to be substantiated4 ,the general composition of the rubber was approximately the same as ordinary crepe obtained from undiluted latex4 ,the rubber on vulcanisation was found to be normal in behaviour1 and was similar to the controls4 ,the coagulum ordinarily is affected by oxidation1 and does not produce a fine pale crepe4 ,to remedy this defect the freshly prepared crepe is soaked in a solution of sodium bisulphite and sulphuric acid4 ,it may be noted that in the recent experiments coagulation was effected in vacuum in a specially designed wooden tank4 ,from a study of the previous section on ,spontaneous ,coagulation1 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 alcohol1 petrol1 or fusel oil4 ,,slab ,,rubber4--,this type of preparation has been the subject of much discussion of recent years4 ,there is nothing really special in the mode of preparation1 and in its original form slab rubber is only a thick sheet which may be obtained by coagulation with acetic acid or other agents4 ,the coagulum1 when removed from the serum1 is subjected to comparatively slight pressure1 and the slab thus made is either placed to air-dry at once1 or may be subject to treatment in other liquids before drying4 ,the rubber is not allowed to remain until wholly dry1 but is shipped while still containing an appreciable percentage of enclosed moisture4 ,it is claimed#cd that the production of slab rubber by standardised methods eliminates to a great degree the variability which at present characterises plantation rubber1 and that a fast-curing medium is obtained4 ,these claims will be discussed in later chapters dealing with the vulcanisation of rubber1 and demand no notice in this section4 #cd ,preparation and ,vulcanisation of ,plantation ,rubber 7,eaton1 ,grantham1 and ,day71 ,bulletin ,no4 #bg1 ,f4,m4,s4 ,department of ,agriculture1 #aiah4 ,from the producers' point of view1 it may be noted that the preparation of slab rubber is a simple process1 but not altogether as pleasant probably as might be desired1 when undertaken in crude form4 ,the appearance of the partially dry slabs is unattractive1 but that does not signify if the quality of the vulcanised product satisfies requirements4 ,for the average producer1 the difficulty lies in having to meet the demands of the general market4 ,even1 therefore1 if one assumes that the intrinsic qualities of slab rubber are all that the claims advance1 it would be necessary for the producer to be assured of definite and regular sales4 ,at present it would probably be fair to state that practically all the slab rubber being prepared is produced by those who are also consumers4 ,they are thus in the enviable position of being able to satisfy their requirements as to the mode of preparation4 ,until such time1 therefore1 as there exists a regular demand for slab rubber in the general market1 the vast majority of estates must proceed on ordinary lines of preparation4 ,,part ,,vi ,,vulcanisation 7,,by ,,dr4 ,h4 ,p4 ,,stevens7 ,,chapter ,,xxi ,,introductory ,,dealing ,,with ,,treatment ,,and ,,vulcanisation ,in the foregoing chapters the methods of treating latex1 coagulating1 rolling and curing1 or drying1 have been described in great detail4 ,these details will give the reader some idea of the precautions taken1 and procedure necessary to produce rubber which will be acceptable to the market4 ,the expressions inferior rubber1 defective crepe1 poor quality sheets1 etc41 are frequently met with1 but these expressions must not be taken to indicate any defect in the rubber for manufacturing purposes1 but merely that the rubber is defective for selling purposes--that is to say1 being unsightly1 it will not fetch the full market price4 ,raw rubber1 as produced on the plantations1 is almost invariably subjected to the process of vulcanisation in the production of manufactured rubber articles as we know them4 ,previous to the advent of plantation rubber1 the raw material was purchased by the manufacturer in a moist and impure condition2 frequently the rubber was adulterated with sand1 dirt1 and even small stones4 ,consequently it was the invariable practice of the rubber manufacturer to wash the raw rubber and convert it into crepe1 which was then hung and air-dried before use4 ,the effect on the rubber1 if of high grade1 was more severe than the washing and crepeing process on the plantation1 because the rubber was not a soft coagulum but generally dried on the surface and semi-hard4 ,the power required was considerable1 and the resulting crepe was consequently softer and more susceptible to heat than plantation first latex crepe4 ,much of the wild rubber was soft and tacky and inferior to earth-scrap4 ,vulcanising in its simplest aspect consists in mixing the rubber with sulphur and heating the product under regulated conditions4 ,the effect of heat on the inferior grades of wild rubber is very marked4 ,a soft1 sticky1 and resinous material is transformed into a relatively tough and elastic product4 ,the effect of vulcanising on the better grades is less marked1 but immediately apparent4 ,on the other hand1 the effect of vulcanising is least apparent on first latex plantation grades1 because in these we have a raw rubber prepared in a manner best suited to retain its natural characteristics4 ,the need of vulcanising in the process of manufacturing rubber goods became an axiom in pre-plantation days1 and it is only quite recently that attempts have been made to utilise raw rubber directly1 without vulcanisation1 particularly for shoe soles4 ,for this purpose a thick dense crepe has been found satisfactory4 ,smoked sheet rubber is not generally suitable1 apparently owing to its microphysical structure4 ,it is possible that the process of rolling in the making of dense crepe compacts the rubber particles1 yielding a harder and more resilient product4 ,the rolling must not be carried too far1 or the working of the rubber will approximate to a preliminary mastication1 and the product will be weakened4 ,the utilisation of crepe rubber directly has not yet been sufficiently tested to enable a definite conclusion to be reached as to its future scope1 but it is obvious that for use in a raw state some modification in preparation may be advantageous4 ,the present method--e4g41 coagulation with acetic acid--does not yield the hardest and toughest rubber4 ,hardness and toughness are actual drawbacks in the utilisation of rubber which is required for vulcanising4 ,when the output of plantation rubber began to increase and to displace the inferior wild sorts1 manufacturers complained of the increased power consumption of their machines4 ,the power was required mainly to break down or mill the rubber preliminary to the mixing with sulphur and other ingredients4 ,it is obvious that a material such as raw rubber cannot be mixed with powders such as sulphur with a pestle and mortar1 or in any simple form of mixing machine4 ,this difficulty was overcome by the earlier experimenters by immersing the rubber in a bath of molten sulphur4 ,the latter was gradually absorbed and dissolved in the rubber1 and the heat of the bath caused the dissolved sulphur to combine with the rubber to produce vulcanised rubber4 ,the limitations of such a process are apparent4 ,thus the vulcanised rubber retains the form in which it was originally shaped4 ,moreover1 other ingredients1 such as mineral matters1 cannot be dissolved or absorbed by the rubber in this manner4 ,the method eventually adopted consisted in breaking down1 milling1 or masticating the rubber by passing it continuously between differentially geared steam-heated rollers4 ,by this means a high-grade rubber is converted into a soft1 plastic mass1 which will take up sulphur1 mineral matter1 and other ingredients as desired4 ,the mixing operation may be carried through on the same roller machine as was used for breaking down the rubber1 or separate machines of other designs may be adopted4 ,details of the process will be found in books dealing with rubber manufacturing4#ce ,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 roller1 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 nip4 ,this closes the space between the rollers1 so that sulphur and powder placed on the rubber pass round towards the nip1 and are there driven into the rubber4 ,in this manner it is easy to mix1 say1 #aj per cent4 of sulphur into the rubber without a single particle falling through4 ,in technical mixes where large quantities of powders require to be mixed there is always some caking1 and part of the powder falls between the rollers into a tray underneath4 ,this is swept up with a broom and put back on to the rollers1 the process being repeated until the whole of the ingredients have been incorporated4 #ce ,for instance1 ,india-,rubber and its ,manufacture1 by ,h4 ,l4 ,terry4 ,from this description it follows that1 preliminary to mixing1 it is necessary to thoroughly masticate or plasticise the raw rubber4 ,much of the wild rubber was of so inferior a quality that it very readily broke down1 and but little mastication was necessary4 ,it was soft and resinous1 and readily took up the powders which were to be mixed with it4 ,the better grades of wild rubber1 such as ,fine ,para1 were more difficult to break down1 but not so difficult as most plantation rubber1 because they had already received a preliminary working in the process of washing and crepeing1 and we have already explained that such treatment takes more power than the crepeing of the soft moist coagulum on the plantations4 ,the amount of working or plasticising produced in the rubber is connected with the power expended2 the greater the expenditure of power1 caeteris paribus1 the greater the working effect on the rubber4 ,although the manufacturers possessed a relatively soft rubber in the form of washed ,fine ,para1 it was customary in most cases to employ this rubber in conjunction with washed lower grades to produce a soft plastic material for further treatment4 ,now1 however1 the manufacturer has little else but plantation to deal with1 and most of it more difficult to break down than washed ,para crepe4 ,this is the reason why a hard1 tough rubber is no longer a desideratum with manufacturers1 although originally taken as an indication of good quality4 ,for the majority of purposes they want something which will break down easily4 ,hence if a rubber could be produced answering to these requirements1 without loss of vulcanising quality1 it would be preferred4 ,having incorporated sulphur and other ingredients1 the plastic mass is sheeted and run between layers of calico to prevent the superimposed sheets from adhering4 ,from this calendered sheet the article1 whatever it may be1 is built up4 ,the calender rollers are heated so as to keep the rubber compound plastic4 ,there is a limit to the thickness of the sheet which can be produced4 ,it is a difficult operation to perform satisfactorily so as to yield a smooth surface and a sheet free from enclosed air4 ,when cool the rubber hardens and is readily handled4 ,the object to be manufactured is then built up from the calendered sheet4 ,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 roller1 so that they adhere firmly1 the first layer to the canvas of the casing and subsequent layers to one another4 ,this rough description will suffice to illustrate how important it is that the rubber when mixed should be plastic enough to give a smooth sheet1 and to allow the sheet to be manipulated in building up the article in process of manufacture4 ,the testing of rubber in regard to its plasticity and power to absorb finely divided mineral matter will be discussed in a later chapter4 ,we may1 however1 point out here1 that the mineral matter is not generally added as an adulterant1 but because of certain specific properties it confers on the product4 ,to proceed with our outline of vulcanisation1 we have now arrived at the stage at which the goods are built up and ready for vulcanising4 ,for this purpose they are generally enclosed in some manner1 either in metal moulds bolted together1 or tightly wrapped in cloth1 as1 e4g41 in the manufacture of inner tubes1 hose1 etc4 ,in the latter case1 you can detect the cloth mark on the finished product4 ,sometimes the rubber is spewed--that is1 driven out of a barrel by means of an endless screw revolving in it4 ,in this way rubber tubing1 perambulator tyres1 and such articles1 may be made4 ,more recently even tyre treads and the shaped rubber for band tyres 7heavy solid tyres7 have been extruded in this manner1 for the process is much cheaper than building up a tyre from calendered sheet1 and then cutting the mass to shape by hand4 ,but for spewing the rubber mass must be very soft and plastic2 this condition is not obtainable unless the raw rubber originally used can be made thoroughly plastic without damage4 ,nor can it be effected with a rubber mass containing much finely divided mineral matter1 as this hardens the mixture4 ,for other purposes the rubber is swollen in a solvent1 such as coal-tar naphtha1 and subsequently masticated2 the soft dough is then shaped or spread on cloth1 and vulcanised after allowing the solvent to evaporate4 ,here1 again1 the properties of the raw rubber are of immense importance4 ,thus1 the more plastic the dough1 the less solvent required1 and the less there is to drive off before vulcanising4 ,the plasticity of the dough will depend on the plasticity of the raw rubber1 and so forth4 ,it is evident that the physical properties of the raw rubber are of great importance4 ,they directly affect the manufacturing operations up to the vulcanising stage1 and indirectly affect the results obtained on vulcanising4 ,the actual vulcanising consists of heating the mass of mixed rubber for a definite time and at a definite temperature1 each heat being chosen to suit the particular mixture4 ,these data are arrived at empirically--that is1 by trying a number of heats and choosing that which appears the most suitable4 ,the suitability will depend on the nature of the article1 the service to which it is to be put1 and the time it is intended to last4 ,all vulcanised rubber goods1 whatever the process1 have a limited life or period during which they can be relied on to give useful service4 ,after a time1 vulcanised rubber tends to harden1 cracks appear on the surface when the article is bent or stretched1 and eventually the rubber becomes rotten and perished4 ,this tendency varies with the quality of the original raw rubber and the conditions of vulcanising4 ,before plantation rubber was available1 the manufacturers were dependent on inferior wild grades for a great part of their output1 and1 consequently1 the goods made from these inferior rubbers never showed very good mechanical properties and soon deteriorated4 ,the severest critics of plantation rubber have admitted the advantages to the manufacturers of the replacement of the lower wild grades by plantation rubber4#cf ,but even the best grades give a vulcanised product which rapidly deteriorates if the vulcanisation is carried too far4 ,this results from too long heating1 or too high a temperature1 and the product is termed overvulcanised or overcured4#cg ,the appearance of the product is deceptive1 as the physical properties are remarkably good if the overvulcanising is not more than #ej to #ajj per cent4 in excess of the normal cure4 ,only in the case of very much overvulcanised rubber do we obtain a product which is brittle from the beginning4 #cf ,see ,williams1 ,the ,rubber ,industry1 #aiad1 p4 #bhd4 ,it must also be remembered that the inferior wild grades were derived from latices often containing a large proportion of resinous matter1 and which could not yield a really high grade of vulcanised rubber whatever the care and skill employed in preparation4 #cg ,the terms curing and vulcanising are generally employed as if synonymous4 ,twiss has suggested that the former be applied in regard to a change in physical properties1 and the latter to the chemical change whereby sulphur is combined with the rubber4 ,the term curing is also applied to the process of preparation of raw rubber4 ,this must be kept in mind so as to avoid confusion4 ,the degree of vulcanising will vary with the type of article to be produced1 and where a long life is desired1 the tendency will be to undervulcanise2 but if the best mechanical properties are desired1 the tendency will be towards overvulcanising1 or1 more correctly1 fully vulcanising4 ,these considerations are aptly illustrated by reference to pneumatic tyres4 ,the inner tube need not possess high tensile strength1 provided that it is easily distensible1 for the reason that1 during use1 it is protected by the casing of the tyre proper1 which confines and supports it against the air-pressure applied4 ,inner tubes are therefore cured to give a long life without developing the maximal physical properties4 ,on the other hand1 the casing and tread of the tyre are required to withstand severe mechanical conditions--particularly the constant flexing of the cover1 and the abrasion of the road surface4 ,tyres are not stored for any long period1 and1 when put into service1 have a limited period of useful life4 ,consequently it is needful to develop maximal mechanical properties1 and vulcanisation is therefore carried further than in the manufacture of inner tubes4 ,the rate of cure is controlled by a number of factors in addition to the period and temperature of vulcanisation1 in particular by the proportion and nature of the other ingredients1 especially sulphur and accelerators1 and also by the rubber itself4 ,the main complaint as regards plantation rubber is that it varies excessively in this respect4 ,this matter will not be discussed here1 but is only introduced in order to explain the importance of a constant rate of vulcanising to the manufacturer4 ,plantation rubber should1 therefore1 be prepared so as to be as uniform as possible in this respect1 and the earlier part of this book gives full details of the precautions advised1 and in many cases adopted on the plantations4 ,unfortunately1 it is impossible to secure uniformity of methods among all producers1 even when they are ,europeans1 to say nothing of the native producers1 who account for perhaps one-third of the output4 ,hence the importance of branding the rubber whenever possible1 so that the manufacturer may identify the rubber he purchases4 ,if found satisfactory1 he can then secure further supplies from the same estate4 ,,chapter ,,xxii ,,testing ,,of ,,plantation ,,rubber ,this subject may be subdivided into 7a7 ,tests on the raw rubber2 7b7 tests on the vulcanised rubber4 ,the tests on the raw rubber may be carried out 7#a7 on the sample of sheet and crepe as received4 ,for this purpose the rubber is cut into a strip1 which is clamped between grips and gradually stretched to breaking-point4 ,the ring testing machine can be adapted for this purpose by replacing the rollers with clamps4 ,as the thickness of the samples to be tested will vary1 it is advisable to cut the strips of such a width that the cross-sectional area of all test pieces is the same--say1 #dj sq4 mm4 ,the method is applicable to both sheet and crepe rubber4 7#b7 ,tests may be made as to the behaviour of the rubber during milling or mastication4 ,small batches are milled under uniform conditions1 preferably in an enclosed masticator such as ,baker and ,perkins supply4 ,the power taken 7as measured by the current taken to drive the motor actuating the machine7 and the time are recorded4 ,a further test may be applied to the milled or masticated rubber1 to ascertain the amount and the time taken to incorporate a finely divided mineral matter1 such as carbon black1 zinc oxide1 or one of the refined clays4#ch ,the results are not very exact1 and the difference in plasticity and dryness noted are usually less than found when working with full-sized machines in the factory4 7#c7 ,the rubber1 either raw or masticated1 may be dissolved in a solvent1 such as benzene1 and the viscosity of the solution measured4 ,generally speaking1 the less viscous the solution1 the more plastic the rubber4 #ch ,bulletin ,rubber ,growers' ,association1 ,january1 #aiba1 p4 #dc2 ,august1 #aiba1 p4 #cdj4 ,the testing of vulcanised rubber has been treated in such detail in the recent works of ,whitby#ci and ,de ,vries#dj that a few special points only will be dealt with here4 ,the preparation of samples for testing involves first the sheeting of the mixture of rubber1 sulphur1 and other ingredients1 if any4 ,the sheets may be #a to #b mm4 thick4 ,they are soft and adherent1 and must be kept between layers of calico to prevent adhesion4 ,a sheet of rubber is then built up by laying three or four sheets evenly upon one another1 and pressing together to form a sheet #e mm4 thick4 ,the thick sheet is then roughly cut to shape and vulcanised in a mould by heating in steam under pressure4 ,from the vulcanised sheet so obtained the rings for testing are cut 7#de mm4 internal diameter4 #e mm4 face1 and #d mm4 thick74 ,rings obtained in this manner will not vary in diameter or thickness 7reckoned as sections of a tube71 as these are controlled by the size of the punch1 but will vary a little in the face1 as this is controlled by the thickness of the sheet1 which depends on the completeness with which the mould is closed4 ,more recently smaller moulds have been adopted1 one mould for each ring1 and an annular space for moisture to develop a pressure during vulcanising and prevent porosity4 ,the moulds are vulcanised in an oil bath1 or oven of some description1 in which a constant temperature is maintained4 ,i have adopted for some years a third method4 ,the principle is that used in the factory for making annular-shaped rubber articles1 such as washers1 rings1 elastic bands1 etc4 ,an aluminium mandrel1 #de mm4 external diameter1 is taken1 and the thin rubber sheet is wrapped round this1 so as to build up a tube about #d mm4 thick1 the surplus rubber is cut off1 and the edge bevelled with a wet knife4 ,the manipulation will vary somewhat with the type of compound to be treated2 thus1 in some cases1 it is sufficient to well roll the tube with a hand roller to secure adhesion4 ,in other cases it is better to wipe the sheet of compound with a rubber solvent previous to rolling4 ,in the latter case time must be given for the solvent to evaporate before vulcanising4 ,the tube is next tightly wrapped in wet cloth1 and is then ready for the vulcaniser4 ,or the tube may be enclosed in moulds which form an outer circular shell and take the place of the cloth1 but for most purposes1 and in particular for the rubber-sulphur mixing usually employed1 it is sufficient to use cloth to obtain even and regular tubes4 ,the tube1 after vulcanising1 is slipped on to a wooden mandrel and cut into rings on a lathe4 ,of these rings the internal diameter is constant1 for this is formed on the mandrel1 also the face1 which can be cut accurately in the lathe1 but the external diameter1 and consequently the thickness1 may vary a little4 #ci ,plantation ,rubber and the ,testing of ,rubber4 #dj ,estate ,rubber4 ,it appears1 therefore1 that all methods result in rings of approximately the correct size1 and it is usual to check1 and1 if necessary1 make an allowance for variation in dimensions4 ,it is not possible to do this1 even approximately1 with soft rubbers1 as the rubber gives under the pressure of the micrometer4 ,no doubt a photographic method would give more accurate results1 but would take too long4 ,i have found that a very close approximation is obtainable by weighing the rings as the specific gravity of the standard rubber mix is known4 ,it is not necessary to weigh each ring1 but the whole five or ten taken for testing may be weighed together4 ,the next point that arises is the choice of a formula for the test mix4 ,practically all the work to date has been carried out on mixtures of rubber with #g to #aj per cent4 of sulphur4 ,for some purposes--e4g41 detecting variation in rate of cure--this mixing is satisfactory1 but for other purposes it is not4 ,nor is the behaviour of a rubber-sulphur mixing a sure guide to the behaviour of one containing other ingredients1 such as litharge4 ,thus1 two samples vulcanised satisfactorily when mixed with sulphur only1 but one of them gave unsatisfactory results in the presence of litharge4 ,it has long been recognised that mineral ingredients may modify the product when vulcanised1 but the modification is not necessarily uniform4 ,consequently1 tests should also be made1 when practicable1 with vulcanised rubber containing other ingredients in addition to sulphur4 ,as regards physical tests on the vulcanised products1 these usually involve determination of breaking load and elongation at rupture 7usually recorded as final length--that is1 including the original length reckoned either as unity or as #ajj units74 ,simultaneously a load-stretch curve is recorded on an autographic attachment4 ,the type of curve varies with 7#a7 state of cure1 or degree to which the rubber is vulcanised2 7#b7 proportion of sulphur and_/or other ingredients2 7#c7 specific nature of the rubber used4 ,the last factor is almost negligible compared with the two former--at any rate for average quality rubber4 ,as 7#b7 is kept constant for any batch of tests1 or even for every test1 it follows that the load-stretch curve is mainly dependent on the state of cure1 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 elongation4 ,either set of figures is readily determined by measuring up the load-stretch diagram4 ,the peculiar type of the curves has long been a subject of comment and speculation4 ,special properties have been attributed to the slope or inclination of the upper and approximately straight portion of the curve4 ,according to the writer's investigations1 the slope is largely dependent on the degree of vulcanisation1 so that it is difficult to place as an index of the specific nature of a rubber4#da ,moreover1 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 piece1 whereas this area decreases progressively as the test piece stretches4 ,if this decrease be allowed for1 the curve obtained is an equilateral hyperbola4#db ,preliminary experiments with rubber compounded with large proportions of finely divided mineral matter1 such as carbon black1 show that the load-stretch curves obtained autographically are likewise reducible to equilateral hyperbolae4 #da ,bulletin ,r4,g4,a41 ,october1 #aiba1 p4 #cig4 #db ,hatschek ,journal ,soc4 ,chem4 ,ind4 #aiba2 ,trans41 p4 #bea4 ,,chapter ,,xxiii ,,the ,,properties ,,of ,,rubber ,this section1 like the last1 is divisible into two subsections4 ,the first deals with raw rubber1 the second with vulcanised rubber4 ,we have already explained that1 until recently1 rubber was not used in the unvulcanised condition1 but that the excellent physical properties of plantation rubber have made this possible4 ,it is interesting to compare the physical properties of raw rubber with that vulcanised with sulphur4 ,a compact sample of crepe as received from the ,east will give breaking strain of over #cj kilos per sq4 cm4 and over #cjj per cent4 elongation4 ,when mixed with sulphur and vulcanised1 a breaking strain of #aej kilos and elongation of #a1jjj per cent4 are not unusual4 ,it is possible that crepe rubber would give higher figures if it could be prepared in the form of a compact ring1 as used for tests on vulcanised rubber4 ,in any case1 the figures for vulcanised rubber are much in excess of those for raw crepe rubber4 ,it must also be remembered that a breaking strain of #aej kilos is not permanent with vulcanised rubber1 for reasons which will be explained later4#dc ,to obtain a reasonably permanent vulcanised product1 the vulcanisation would not be carried further than to give a figure of #ajj kilos4 ,on the other hand1 raw rubber is remarkable on account of its great permanency1 although subject to some physical changes at ordinary atmospheric temperatures4 ,tensile tests1 although valuable1 do not tell us all about the physical properties of a sample of rubber4 ,abrasion tests1 or tests designed to measure resistance to wear and tear1 would be more valuable1 but1 unfortunately1 these properties do not lend themselves to simple tests4 ,there are grounds for believing that raw rubber is superior in some respects to fully vulcanised rubber1 if prepared without the addition of finely divided mineral substances which exert a toughening effect4 #dc ,journal ,soc4 ,chem4 ,ind41 #aiaf1 p4 #hgb4 ,sheet rubber gives results in some ways inferior to compact crepe rubber when subjected to physical tests4 ,tensile strength seldom exceeds #ae kilos1 but the elongation is usually higher--up to #fjj or #gjj per cent4 ,that is to say1 it stretches more1 but breaks more easily4 ,if1 however1 we take into consideration the diminution in sectional area of the test piece during stretching1 it will be seen that crepe and sheet rubber have compensating properties4 ,as this matter of sectional area reduction during stretching is important1 both for raw and vulcanised rubber1 it may be briefly referred to here4 ,when rubber is stretched1 the volume does not appreciably alter--at any rate1 as regards uncompounded rubber4 ,hence the reduction of sectional area on stretching bears a simple relationship to the amount of stretching4 ,if we double the length of the test piece1 we halve the sectional area2 if we treble the length1 we reduce it to one-third1 and so forth4 ,hence1 if we multiply the breaking strain by the final length 7i4e41 length at break1 taking the original length #a71 we obtain a figure1 the tensile product1 which embodies both breaking strain and stretching capacity4 ,in effect it gives us the breaking strain calculated on the sectional area at the moment of rupture of the test piece4 ,adopting this formula1 we obtain for crepe-- ,tensile ,final ,length--i4e41 ,tensile ,strength4 ,elongation #a4 ,product4 #cj x #d #abj and for smoked sheet #ae x #h #abj ,the difference in properties between crepe and sheet may probably be attributed to the heavier rolling of the crepe2 which compacts the rubber4 ,but if the crepe is rolled too much1 the tensile strength falls1 and there is no increased elongation to compensate4 ,for the same reason1 crepe which has been rerolled in this country is inferior to crepe as received direct from the plantation4 ,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 rollers1 if the physical properties of the original rubber are to be conserved4#dd #dd ,bulletin ,r4,g4,a41 ,february1 #aibb1 p4 #fd4 ,attempts to prepare crepe for use in a raw state1 by rerolling uneven or irregular surfaced crepe in this country1 only result in a rubber with inferior physical properties4 ,nor can sheet be rerolled to give crepe of good physical properties4 ,the power required to break down the sheet and the heat developed1 even on cold rollers1 are an indication of physical properties destroyed4 ,for subsequent vulcanisation this is not a matter of importance1 because the vulcanising process restores to the rubber the properties which are lost in the process of rolling and milling or mastication4 ,raw rubber has been used to some extent for proofing purposes1 as for the manufacture of material for hoods of motor-cars4 ,in this case no attempt is made to preserve the physical properties4 ,the rubber is masticated1 mixed1 taken up with solvent and spread on the cloth exactly as if it were to be vulcanised4 ,,vulcanised ,,rubber4--,we have already explained that the properties of vulcanised rubber are dependent1 to some extent1 on the specific nature of the raw rubber1 or what ,de ,vries terms the inner qualities4 ,that is to say1 differences appear on vulcanising which are not apparent from the tests made on the raw rubber4 ,indeed1 no investigation or analysis of the raw rubber can enable one to foresee exactly how the rubber will behave on vulcanisation4 ,this illustrates the deficiency in our knowledge of vulcanisation4 ,when dealing with soft1 resinous1 or decomposed rubbers1 it is safe to anticipate a weak vulcanised product2 but when we come to deal with a number of samples of standard crepe or sheet--i4e41 sheet or crepe passing a certain standard of appearance--it is found that differences in vulcanising properties cannot be foreseen4 ,this matter is1 however1 not so great a drawback as might be imagined1 for reasonably well prepared consignments of standard crepe or sheet differ but little from one another1 and the difference is mainly in the ease with which they break down1 or the rate or speed with which they vulcanise1 and not with the properties of the vulcanised product4 ,many of the plantation scrap grades are equal to or nearly equal to standard2 but some of these1 as also the rubber produced by native holders1 show appreciable variation1 and are the source of most of the complaints which emanate from manufacturers4 ,we shall consider in turn the different grades and the effect of the usual surface defects1 such as mould1 spots1 etc4 ,,crepe ,,rubber4--,oil marks and tackiness are the most serious defects from the manufacturing standpoint4 ,in the first part of this book we have shown that damage caused by the so-called oil marks is not due to the oil1 but to traces of copper from the bearings of the machines4 ,there are several metallic compounds which cause deterioration of rubber both raw and vulcanised1 but copper is the most deadly1 and rubber showing signs of deterioration is rightly rejected by the manufacturers4 ,the only other defect of crepe rubber which has any bearing on its use in manufacture is mould4 ,crepe rubber very seldom shows the ordinary surface moulds not uncommon in sheet-rubber4 ,there are1 however1 microscopic growths which cause the development of coloured spots referred to in detail in the earlier part of this book4 ,the rubber hydrocarbon itself does not appear to be affected by the moulds1 but some of the serum constituents are altered1 with the result that the rubber vulcanises more slowly than it otherwise would do4 ,for this reason1 crepe rubber with coloured spots may give rise to trouble in the factory4 ,,sheet ,,rubber4--,the commonest defect is mould4#de ,this is usually of a light surface type1 easily brushed off1 and numbers of vulcanising tests failed to trace any reduction in rate of vulcanising or other defect due to this4 ,in spite1 however1 of the harmlessness of light surface moulds1 they are looked upon with suspicion by the manufacturer4 ,occasionally samples of smoked sheet are offered contaminated with a heavy type of mould4 ,the sheet feels damp and heavy or flabby1 and contains an excess of moisture2 sometimes a moist exudation is noticeable on the surface1 and virgin patches are present4 ,such sheet vulcanises more slowly than ,f4,a4,q4 samples1 but does not necessarily show other defects after washing and drying4 #de ,bulletin ,r4,g4,a41 ,february1 #aiba1 p4 #ig2 ,april1 #aiba1 p4 #aij2 ,june1 #aiba1 p4 #bdc2 ,november1 #aiba1 p4 #dgb4 ,stretching rusty1 as already explained1 is due to a dry film on the surface of the sheet1 and according to a recent investigation1 this film consists1 not of serum substances1 but of a microscopic mould growth1 which presumably grows on the serum substances4 ,a sample of sheet which stretches rusty gives the rubber a dry appearance1 and for a long time manufacturers mistook the surface film for resin4 ,on the assumption that such rubber was resinous they rejected it1 and to this day it is regarded as a defect1 although it has no influence on the vulcanising properties of the rubber4 ,it is hardly necessary to point out that defective appearance1 such as is due to thickened edges1 faint markings1 bubbles1 and so forth1 have no effect on the vulcanising properties of the rubber4 ,they only point to some irregularity or carelessness in preparation4 ,the only justification for distinguishing between rubber of good and bad appearance is that the former bears the impress of careful preparation1 and is therefore more likely to be uniform in rate of vulcanising4 ,similar considerations apply to the colour of smoked sheet1 which may vary from a pale yellow-brown1 through various shades of red-brown to dark brown4 ,there are various factors affecting the colour1 but the buyer can see but one--viz41 the degree of smoking--and the rubber1 from his point of view1 may be undersmoked or oversmoked4 ,no doubt the degree of smoking affects the vulcanising properties1 but to a less extent than was at one time imagined4 ,in a recent paper#df 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 sheets4 #df ,bulletin ,r4,g4,a41 ,december1 #aiba1 p4 #eba4 ,,variation ,,in ,,physical ,,properties4--,a very large number of tests on vulcanised specimens of plantation rubber have been carried out4 ,the rubber was almost invariably mixed with #g to #aj per cent4 of sulphur1 and no other ingredient1 and vulcanised to give the maximal breaking load4 ,unfortunately1 this determination is subject to a very appreciable experimental error1 so that a large number of determinations are necessary to give a reliable figure4 ,it is quite impracticable to make a large number of determinations in routine testing1 on account of the labour involved4 ,it is usual to make five1 or possibly ten1 determinations1 although some investigators have been content with two4 ,it is generally conceded that any exceptionally low figures should be ignored1 as probably caused by some flaw or irregularity in the test piece4 ,on the other hand1 a study of actual determinations shows an occasional excessively high figure1 and it is questioned whether this also should be left out of account4 ,others ignore all except the highest figure1 and take this to represent the true breaking strain4 ,as a consequence1 the figures published by different workers show considerable variation4 ,de ,vries has analysed a large number of the figures obtained in systematic examination of estate samples1 and has constructed curves to illustrate the results4#dg ,it is open to question how far the variations shown are attributable to experimental error4 ,the figures show1 however1 that the variation in breaking strain is relatively small1 and not very different for crepe and sheet rubber4 ,in our opinion1 undue importance should not be attached to very high or exceptionally high figures for breaking strain1 which are occasionally met with4 ,provided the figure does not fall much below the average1 the sample may be regarded as satisfactory4 ,it is very seldom that any sample of first latex estate rubber does not show satisfactory figures4 #dg ,estate ,rubber1 p4 #dff4 ,,the ,,rate ,,of ,,cure ,,or ,,rate ,,of ,,vulcanisation is subject to more exact measurement1 whether this be based on the physical or the chemical properties of the rubber4 ,if the testing machine be provided1 as is usual1 with an autographic attachment1 the position of the curves traced on the recording paper gives a measurement of the rate of cure4 ,these load-stretch curves1 to which reference has already been made1 take up a definite position in accordance with the physical properties2 it is only the length of the curve1 or the point where it terminates 7which gives the breaking strain and elongation at break71 which is largely fortuitous4 ,as a measure of rate of cure we may take the actual measurements made on the record4#dh ,it is convenient to measure the elongation produced by a load of #acj kilos per sq4 cm41 as all fully vulcanised rings of soft rubber should give higher breaking load figures4 ,for less cured or weaker samples a lower figure may be taken1 such as #fj kilos4 ,we have found that when fully vulcanised to give the maximal breaking strain1 the elongation at a load of #acj kilos is in the neighbourhood of #hej per cent4 7final length #iej per cent474 ,this applies to ordinary samples of estate rubber under the conditions of testing indicated above4 ,if1 however1 the proportion of sulphur be considerably reduced1 or mineral ingredients in a fine state of division be added to the mixing1 or accelerators1 whether organic or inorganic1 be employed1 the above relationship no longer holds4 ,nor does it hold with regard to plantation rubber prepared in an exceptional manner1 as1 for instance1 matured coagulum or slab4 #dh ,bulletin ,r4,g4,a41 ,june1 #aiba1 p4 #bdf4 ,there is a second method of determining the rate of cure--namely1 by analysing a vulcanisate produced under standard conditions1 and determining the amount of sulphur which has entered into chemical combination with the rubber4 ,for this purpose the weighed sample is cut thin or creped thin1 and exhaustively extracted with acetone to remove any free sulphur--that is1 sulphur not in combination with the rubber4 ,the sulphur remaining is then determined and calculated as a percentage of the raw rubber contained in the sample taken4 ,this gives the so-called coefficient of vulcanisation4 ,if we compare the coefficient with the time of cure at a constant temperature for an ordinary sample of plantation rubber1 they are found to be approximately proportional1 so long as the sulphur is in sufficient excess4 ,the amount of combined sulphur is1 therefore1 an index of the time vulcanisation has been in progress 7under standard conditions of temperature1 etc471 and1 therefore1 the coefficient is a measure of the rate of cure4 ,the change in position of the load-stretch curve is not directly proportional to the time of heating1 and it therefore follows that it is also not directly proportional to the coefficient4 ,for ordinary samples of crepe and sheet the relationship is1 however1 not very far removed from proportionality4 ,this applies particularly to sheet rubber4 ,the relationship is readily seen on plotting one against the other and tracing the curves4 ,for sheet we get an almost straight line2 for crepe there is some curvature4#di ,for ordinary estate samples of sheet and crepe rubber the maximal breaking strain is obtained when the coefficient reaches approximately five units1 so that this corresponds to the elongation of #hej per cent4 at a load of #acj kilos4 #di ,bulletin ,r4,g4,a41 ,june1 #aiba1 p4 #bdf1 ,october1 #aiba1 p4 #cih4 ,either physical or chemical methods may1 therefore1 be used for determining the rate of cure of ordinary sheet or crepe rubber1 but great care must be taken when interpreting the results obtained with rubber prepared in an unusual manner4 ,the rate of cure may be expressed in terms of the time taken to vulcanise the rubber at a constant temperature 7in our case #ach deg4 ,c471 so as to give an elongation of #hej per cent4 at a load of #acj kilos1 or to give a coefficient of five units4 ,the higher the figure so obtained1 the slower curing the rubber4 ,to express the results more directly as rate of cure1 we have adopted the plan of taking an average crepe rubber1 calling the rate of cure #ajj units1 and expressing the rate of cure of other samples in these terms4 ,thus1 a sample which gave a coefficient of four only1 in the time taken by the standard to give a coefficient of five1 would have a rate of cure four-fifths of the standard1 that is1 #hj2 or if a sample takes only two hours to give an elongation of #hej per cent41 whereas the standard takes three hours1 the rate of cure of the sample will be #c_/b of standard or #aej4ej #ej ,journal ,soc4 ,chem4 ,ind41 #aiah1 p4 #bhj4 ,as stated1 the coefficient is approximately directly proportional to the time of cure2 it is also independent of the proportion of sulphur1 if in fair excess1 and in the presence of inert ingredients4 ,it is also independent of the amount of mastication given to the original raw rubber1 however great4 ,on the other hand1 the position of the load-stretch curve is variously modified by these factors--in some respects1 therefore1 the coefficient is a more reliable index4 ,however1 the coefficient is influenced by accelerators1 so that here also great care must be exercised when interpreting results4 ,for the purpose of detecting variations in rate of cure1 it is best to choose a mixing which is particularly sensitive4 ,in the first place1 there must be an ample excess of sulphur2 and in the second place1 no ingredient should be added which will complicate the load-stretch curves1 and no accelerators should be present which may possibly tend to obscure the vulcanising properties of the rubber itself4 ,it has been found1 therefore1 that the best mixing to use consists of rubber with an excess of sulphur--say1 in the proportion #i3a without other ingredients4 ,the rate of cure of a specimen of plantation rubber is attributed to the presence of certain natural vulcanising catalysts1 because it is found that carefully purified raw rubber 7that is1 with the resinous and nitrogenous constituents removed7 vulcanises very slowly or hardly at all1 but that on replacing the extracted matter the rate of vulcanising is restored4 ,the natural catalysts contained in the extracted matter are influenced to a varying degree by some of the common ingredients of manufactured rubber articles4 ,this applies particularly to litharge 7oxide of lead71 to which reference has already been made4 ,thus1 acetone extraction of raw rubber to remove resinous matter has but little effect on the vulcanising properties of a mixture of rubber and sulphur4 ,but if litharge be a constituent1 it is found that acetone-extracted rubber will hardly vulcanise at all4 ,from this1 it follows that a rubber giving a low acetone extract may be found to vulcanise exceptionally slowly in a mixing containing litharge1 whereas it shows no such defect when compounded with sulphur only4#ea ,litharge is used to a very large extent1 as it has a balancing effect in a rubber compound--that is to say1 it allows of appreciable variation in vulcanising conditions1 without corresponding alteration in the state of cure4#eb #ea ,journal ,soc4 ,chem4 ,ind41 #aiaf1 p4 #hgd4 #eb ,ibid41 #aiae1 p4 #ebd4 ,,influence ,,of ,,various ,,factors ,,in ,,raw ,,rubber ,,preparation ,,on ,,the ,,rate ,,of ,,cure1 ,,or ,,rate ,,of ,,vulcanisation4--,as the capacity of a rubber for vulcanisation depends on the presence of small quantities of accessory substances in the serum which act as catalysts1 the rate of vulcanisation 7or curing7 will depend on the nature and quantity of such substances present in the rubber4 ,a very small quantity of these substances has a considerable influence on rate of vulcanising1 and as the substances are difficult to isolate and identify1 our knowledge of their formation and chemical nature is not as definite as is desirable4 ,substances have been isolated having the characteristics of simpler bases4 ,bodies of this class are formed by putrefaction of organic matter1 and can be separated in much larger quantity from coagulated latex1 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 place4 ,further1 rubber from putrefied coagulum vulcanised much faster than that ordinarily prepared1 so that we are justified in connecting the putrefaction bases with the rate of vulcanisation4 ,moreover1 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 case4#ec ,also1 the crude bases isolated from fast vulcanising rubber have the power of increasing the rate of vulcanisation when added to ordinary slow vulcanising rubber4#ed #ec ,eaton and ,co-workers3 ,see ,bulletin ,no4 #bg1 ,f4,m4,s4 ,department of ,agriculture4 #ed ,journal ,soc4 ,chem4 ,ind41 #aiag1 p4 #cfe4 ,on the other hand1 there are one or two facts which are difficult although not impossible to fit in with theory4 ,thus1 although the putrefaction bases are very easily soluble in water and acetone1 they cannot be removed by washing on the creping rollers1 or by acetone extraction4 ,this may be due to the power of colloidal substances to retain other crystalloidal substances1 such as the bases1 which1 in consequence1 cannot be washed out4 ,a parallel case is the retention of small quantities of water soluble substances in the soil4 ,also1 the theory does not explain why rubber obtained by evaporation of latex at relatively high temperatures is fast vulcanising1 although the possibility of putrefaction is excluded4 ,as regards practical results1 it follows that the rate of vulcanisation 7or cure7 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 dry1 as also on atmospheric conditions4 ,thus1 slow drying will result in an increased rate of cure1 for it gives an opportunity for putrefactive organisms to play a part4 ,the results will1 however1 be influenced by the extent to which the rubber was washed previous to hanging1 and so forth4 ,smoking is an antiseptic process and will1 therefore1 tend to inhibit the action of micro-organisms and produce a slower vulcanising rubber4 ,on the other hand1 sheet contains more serum than crepe1 so that there is more food material for growth of micro-organisms4 ,the net result is to give a rubber 7sheet7 which usually vulcanises a little faster than crepe4 ,among other factors controlling the rate of cure1 special mention should be made of the nature and amount of coagulants4 ,weak organic acids1 such as acetic1 lactic1 tartaric1 etc41 used in the minimal proportions 7#a to #a1bjj of standardised latex in the case of acetic acid71 give the fastest vulcanising rubber2 strong mineral acids1 such as sulphuric acid1 even when used in the minimal proportions 7#a to #b1jjj71 yield slower vulcanising rubber4 ,acid salts1 such as alum1 are intermediate in effect4 ,increased proportions of coagulant cause a reduction in rate of vulcanising with all coagulants1 and the effect is least noticeable in crepe rubber1 intermediate in sheet rubber1 and most pronounced in slab rubber 7discussed below74#ee #ee ,bulletin ,r4,g4,a41 ,july1 #aiai1 p4 #ci2 ,september1 #aibj1 p4 #cdc2 ,november1 #aibj1 p4 #dcc2 ,october1 #aiba1 p4 #cic2 ,march1 #aibb1 p4 #acd4 ,,other ,,types ,,of ,,plantation ,,rubber4--,we have up to now confined our attention to ordinary thin air-dried crepe and smoked sheet1 as almost all plantation rubber is now marketed in one or other of these two forms4 ,there are1 however1 other types1 to which reference has been made4 ,of these1 the most important is the thick blanket crepe1 made chiefly in ,ceylon by rolling together thin crepe1 which has been artificially dried 7,colombo drier or vacuum drier74 ,the heat of the driers causes a surface stickiness1 which is got rid of by rolling several thin layers together to give one thick one4 ,this rubber vulcanises at about the same rate as ordinary thin crepe1 for the relatively high temperature of drying does not appear to influence the rate of cure4 ,the rubber is generally softer than air-dried crepe1 and is easily let down in naphtha2 it is1 therefore1 suitable for some solution work4 ,generally speaking1 the properties of blanket crepe do not differ materially from ordinary thin crepe4 ,another type of rubber seldom met with is matured slab or crepe1 prepared from it4 ,this type of rubber is being made in small quantities on one or two estates1 who supply direct to the manufacturer4 ,the method of preparation has already been described4 ,it is unsuitable for sale in the open market1 as it contains a variable amount of moisture1 has the various surface defects such as slime1 mould1 and rust1 and there is the additional disadvantage that it is not easy to judge of its cleanliness or freedom from coarse impurities by inspection4 ,if the slab rubber be creped and air-dried on the spot1 the product is of satisfactory appearance1 except that it is of low colour and may be streaked4 ,as the crepe so produced vulcanises almost as fast as the original slab1 the crepe embodies all the advantages of a fast curing rubber with few of the disadvantages of the slab itself4 ,we have made experiments from time to time1 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 ,committee4 ,a fast curing raw rubber is not necessarily a desirable type for all manufacturing purposes4 ,in the vulcanising of large masses of rubber1 a slower rather than a faster vulcanising rubber may be desirable1 so as to give ample time for the heat to penetrate and spread evenly throughout the mass4 ,but for many purposes a fast curing rubber enables a larger output to be obtained1 so that artificial organic accelerators are coming more and more into use4 ,the addition of such accelerators might be obviated1 if a suitable fast curing rubber were available1 but it is essential that such rubber should be uniform4 ,it is just in this respect that slab rubber or crepe made therefrom is found to be deficient4#ef ,the rate of cure depends on the functions of wild bacteria1 which are naturally sensitive to changes of conditions1 such as temperature1 etc4 ,the coagulated rubber depends on chance circumstances for infection1 and1 as a natural result1 the activity of the bacteria and the nature and amounts of active vulcanising agent produced will vary and be difficult to control4 ,consequently1 the rate of cure of slab rubber shows considerably greater variation than ordinary crepe or sheet4#eg ,this1 in our opinion1 is the main difficulty of utilising slab1 or crepe prepared from it4 ,experience in other industries1 using micro-organisms1 has shown that the only method of control has been to replace the wild growths by cultures of some particular strain1 as1 for instance1 in yeasts for brewing4 ,to control the rate of cure of slab1 it might be possible to use a special culture for the purpose4 #ef ,bulletin ,r4,g4,a41 ,january1 #aibj1 p4 #f2 ,january1 #aiba1 p4 #dg4 #eg ,ibid41 ,january1 #aibj1 p4 #fh4 ,other less usual methods of preparation1 referred to in the earlier part of this book1 do not call for particular mention1 as the properties of the rubber do not differ much from ordinary sheet or crepe4 ,it is mainly a matter of variation in rate of cure4 ,this short account of the vulcanising properties of plantation rubber would not be complete without a reference to ,fine ,hard ,para1 the premier rubber of the ,amazon4 ,this rubber has come to be regarded as the standard high-grade product with which plantation rubber may be compared1 and many manufacturers are still of the opinion that it is unsurpassed by any plantation product4 ,yet1 when subjected to the ordinary vulcanising tests1 we find that samples of ,fine ,hard ,para give figures very similar to average plantation rubber2 indeed1 it is not difficult to find specimens of plantation rubber which give appreciably higher figures on testing4 ,it is claimed1 however1 that ,fine ,para is more uniform than plantation rubber1 and can be relied on always to give the same results4 ,yet tests on a series of ,fine ,hard ,para specimens gave variations in rate of cure similar to those found for plantation4 ,some figures were published1 which tended to show that the variation was smaller for ,fine ,para1 but it turned out that each of the samples taken for examination consisted actually of a number of slices cut from different balls1 so that greater uniformity was not unexpected4#eh ,the superiority of ,fine ,para is1 therefore1 somewhat of a mystery4 ,it is probable that some manufacturers prefer to use it because they feel safer with it1 and know actually how it will behave from long experience4 ,in one respect ,fine ,para is possibly superior to most plantation rubber--that is1 for the preparation of raw rubber solution for sticking the seams of waterproof garments1 and for similar purposes4 ,the method of preparation may well influence the strength of the raw rubber when used for this purpose4 ,plantation rubber has been prepared in the same manner as ,brazilian ,para1 in particular on an estate in ,java4 ,the product resembles ,brazilian ,para in appearance4 ,vulcanising tests gave satisfactory figures1 but1 as already stated1 this would not serve to show that the rubber was equal to ,brazilian ,para from the manufacturer's standpoint4 #eh ,bulletin ,r4,g4,a41 ,september1 #aibj1 p4 #cdg4 ,,index ,acetic acid1 #gd1 #bgi ,acid1 acetic1 #gd1 #bgi --1 carbonic1 gas1 #bhi --1 formic1 #bgi --1 hydrochloric1 #bhb --1 hydrofluoric1 #bhb --1 mixing1 with latex1 #gi --1 nitric1 #bhb --1 oxalic1 #bgi --1 pyroligneous1 #bhb --1 quantity of1 #gf --1 sulphuric1 #bgi1 #bhf ,acids for coagulation1 effect of1 on rate of cure1 #cbc --1 quantities necessary for modern requirements1 #gh ,air-drying1 aids to normal1 #adc --1 of crepe1 rate of1 #ach --1 progress of1 #adj ,alcohol1 coagulation with1 #bhi ,alum1 coagulation with1 #bhb ,anti-coagulant for transport1 #fa ,anti-coagulants1 #df ,artificial driers1 #acc1 #adh ,ash on sheet1 #bgf ,assembling cases for shipment1 #aef ,bags for packing1 #aed ,bakau1 #adg ,bales for packing1 #aed ,bark in crepe1 #bcb -- -- shavings1 #ef1 #abc -- -- sheet1 #bgf ,bases in vulcanised rubber1 #cbb ,basket plants1 #aj ,blanket crepe1 properties of1 #cbd ,blemishes of surface1 #beb ,blister in sheet1 #bgb ,block rubber1 #abi1 #bdf ,breaking down of rubber1 #cjd -- load of test piece1 #caa ,bubbles in sheet1 #bfi ,buildings1 #aei ,bulking latex1 #fi ,byrne curing process1 #bgj ,calendered sheet1 #cjd ,carbon dioxide1 #bhi ,carbonic acid gas1 #bhi ,cases1 choice of1 for packing1 #aec ,catalysts1 natural1 in rubber1 #cab --1 vulcanising1 #cab ,centralisation of factories1 #bba ,chinese vinegar1 #bhf ,chinosol1 #bch ,chula drier1 #adh ,clippings1 sheet1 #bge ,coagulant1 #aaa --1 choice of1 #gd1 #bgh --1 quantity of1 #aac ,coagulation1 #gd1 #aaa -- centres1 #fb --1 premature1 #df --1 spontaneous1 #bid -- with alcohol1 #bhi -- -- sugars1 #bhg -- -- various salts1 #bhh ,coagulum1 soft1 #bdi --1 spongy undersurface of1 #bdi --1 tearing of1 #bdi --1 transport of1 #ei1 #fc --1 working of1 #ajc ,coefficient of vulcanisation1 #cai ,collecting latex1 #ch -- pails1 #dh ,collection1 advantages of early1 #fj ,combustion1 rate of1 in smoke house1 #aia ,compound crepes1 #abf -- -- ,no4 #a1 #aea -- -- ,no4 #b1 #aea ,contents of cases1 weight of1 #aef ,copper salts1 cause of tackiness1 #bdc ,cotton fibre in crepe1 #bcj ,creosotic substances1 #adf ,crepe1 air-drying of1 #acb --1 bark in1 #bcb --1 bearing of defects in1 on manufacture1 #caf --1 bisulphite streaks in1 #bce --1 colour of fine1 #aad --1 dirt in1 #bbg --1 dirty edges of1 #bbe --1 drying houses for1 #agh --1 fibre in1 #bcj --1 general style of finish1 #bbc --1 grades of1 #aej --1 greenish1 tacky streaks in1 #bbh --1 iron stains on1 #bbe ,crepe1 ,no4 #a fine pale1 #aaj --1 oil marks on1 #bbf --1 oxidation streaks in1 #bcd --1 rate of air-drying of1 #ach --1 rust stains on1 #bbf --1 smoked1 #acj --1 surface moulds on1 #bda --1 weight increased in drying house1 #ada --1 yellow latex streaks in1 #bcd -- rubber1 defects in1 #bbc -- --1 lower grades of1 #abj -- --1 preparation of1 #aaj -- --1 tensile strength of1 #cac ,cups1 cleaning1 #dj --1 water in1 #dd ,cure1 rate of1 #cah ,curing1 #cjg ,da ,costa process1 #bij ,decentralisation of factories1 #bba ,defects of sheet1 infrequent1 #bgf ,derry process1 #bic ,designs and layout of tanks1 #agf ,dirt in sheet1 #bgf ,discoloration of rubber1 dark1 #bdi ,drains for tanks1 #agf ,drier1 ,colombo ,commercial ,company's1 #acf ,driers1 artificial--for crepe rubber1 #acc -- --1 for sheet rubber1 #adh --1 ,chula1 #adh --1 vacuum1 #acd ,drum furnaces1 horizontal1 #ahi ,drying chamber1 floor of1 #ahg -- --1 arrangements of1 #ahf -- houses for crepe1 #agh -- --1 hot air1 #ahb -- --1 ventilation of1 #ahe -- --1 windows of1 #ahe -- of rubber1 #acb --1 period of1 #ade --1 rate of1 effect on rate of cure1 #cbc ,earth scrap1 #abd -- --1 collection of1 #eh ,edges1 thickened1 after rolling1 #bea ,elongation of test piece1 #caa ,ends1 thickened1 after rolling1 #bea ,engines1 #agj --1 position of1 #agd ,factories1 #agb --1 centralisation of1 #bba --1 decentralisation of1 #bba --1 number of floors1 #agd1 #agh --1 ventilation of1 #ahj --1 windows of1 #aha ,factory buildings1 situation of1 #baf --1 choosing site for1 #bbj --1 ideal arrangement of1 #afb -- operation1 #fe ,fibre cotton1 in crepe1 #bcj ,field maintenance1 #ac ,fine hard ,para properties of1 #cbe ,first latex and other grades1 percentage of1 #ei ,floor of drying chamber1 #ahg -- factories1 #agc -- furnace room1 #aif ,formalin1 #hg ,formic acid1 #gd1 #bgi ,formula for test mix1 #caa ,freezing 7coagulation7 process1 #bic ,fuel1 consumption of1 #aif ,fuels for smoking1 #adf ,furnace room1 floor of1 #aif -- --1 ,petaling type of1 #aib ,furnaces1 horizontal drum1 #ahi --1 pot1 #ahh ,germination1 #f ,grades1 number of1 #aea ,grading1 #aej ,grafting1 #h ,grass squares1 #ad ,greasiness before smoking1 #beb -- of surface1 #beh ,grit in crepe1 #bcb ,hand rolling sheets1 #ajd ,hevea ,brasiliensis1 #a ,hot air drying houses1 #ahb ,hydrochloric acid1 #bhb ,hydrofluoric acid1 #bhb ,ilcken-,down process1 #bih ,instruments1 method of using1 #ajj --1 recording1 #add --1 standardising1 #ih ,lallang1 eradication of1 #ae ,latex1 bulking1 #fi -- cups1 choice of1 #dj --1 decomposition of1 in the field1 #bgj --1 first and other grades1 percentage of1 #ei --1 first quality1 #aej --1 mixing acid with1 #gi --1 mixing sodium bisulphite solution with1 #aag --1 preliminary treatment of1 #fe --1 reception of1 at the store1 #fe --1 standard1 #if --1 standardisation of1 #fi1 #aaj --1 straining1 #fg --1 transport of1 #ei ,light1 importance of1 in factories1 #agb ,litharge1 #cab ,load stretch curve1 #cab1 #cai1 #cbj1 #cba ,low grade rubbers1 fibrous matter in1 #abd ,lower grade rubber1 care in manufacture1 #abi ,lubrication of machines1 #aff ,lump rubber1 naturally coagulated1 #abj ,machinery1 #aei ,machines1 access to1 #afi --1 adequacy of1 #afj --1 arrangement of1 #afh --1 lubrication of1 #aff --1 position of1 #agc --1 sheeting1 #aff --1 speed of1 #afb ,mangrove1 #adg ,marking sheets1 #aje ,metrolac1 #ih1 #ajj ,michie-,golledge system1 #ach ,mildew on surface1 #bfj ,milky residue on serum1 #bdi ,mixing acid with latex1 #gi ,moist glaze of surface1 #beh ,mould on surface1 #bfj ,moulds1 surface1 on crepe1 #bda ,natural catalysts1 #cab ,nitric acid1 #bhb ,nurseries1 #i ,overcured1 #cjg ,overvulcanised1 #cjf ,oxalic acid1 #bgi ,oxidation1 prevention of1 #ef --1 variation due to1 #bed ,packing1 #aej --1 bags for1 #aed --1 bales for1 #aed --1 cases1 choice of1 #aec --1 folding for1 #aee --1 methods of1 #aef --1 rooms1 #baa ,pale crepe1 ,no4 #a fine1 #aaj --1 rubber1 former methods of making1 #aah --1 sheet1 #hi ,patches1 #bei1 #bfj --1 virgin1 #bei ,payment by result1 #ec ,perished rubber1 #cjf ,physical properties of rubber1 variation of1 #cag ,pits for smoke houses1 #ahh ,pitting of surface1 #bej ,plantation rubber1 testing of1 #cji ,planting1 #a ,plasticising of rubber1 #cjd ,plasticity of plantation rubber1 #cji ,pot furnaces1 #ahh ,power units1 #agj ,premature coagulation1 #df ,preparation1 special methods of1 #bij ,pyroligneous acid1 #bhb ,racks1 #ahf ,rate of cure1 #cjg ,raw rubber1 physical properties of1 #cac -- --1 tests on1 #cji -- --1 uses of1 #cae ,recommendations1 ,rubber ,growers' ,association1 #aeb ,recording instruments1 #add ,ribbing of sheet1 #bgd ,rolling1 #bea ,rolls1 grooving of1 #afd -- running hot1 #afe -- -- free1 #afe ,roof of smoke house1 #aig ,rubber1 drying of1 #acb ,rubber ,growers' ,association1 ,recommendations1 #aeb ,rubber1 properties of1 #cac --1 smoking1 #aji ,rust1 cause of1 #bfg -- on sheet1 #bfb --1 treatment to prevent1 #bfe ,scrap washers1 #eg1 #abd ,screw plug1 unsatisfactory1 #gc ,seed at stake1 #aj ,seeds1 #b ,selection1 #e ,senang folder1 #aef ,serum1 milky residue on1 #bdi ,sheet1 ash on1 #bgf --1 bark in1 #bgf --1 bearing of defects on1 in manufacture1 #caf --1 blisters in1 #bgb --1 bubbles in1 #bfi --1 clippings1 #acj1 #bge --1 creases in1 #bea --1 dirt in1 #bgf --1 dog ears1 #bea --1 grades of1 #aea --1 infrequent defects of1 #bgf --1 pale1 #hi --1 ribbing of1 #bgd -- rubber1 artificial driers for1 #adh -- --1 defects in1 #bdi -- --1 preparation of1 #hi ,sheet rubber1 rolling and marking of1 #ajb -- --1 tensile strength of1 #cac --1 rust on1 #bfb --1 splinters in1 #bgf --1 stickiness in1 #bgd --1 style of1 #aja --1 support marks on1 #bgc --1 surface pattern of1 #bgd --1 thick ends of1 #bge ,sheeting machines1 #aff ,sheets1 mis-shapen1 #bea --1 thickened patches in1 #bea --1 torn1 #bea --1 unevenness of appearance1 #bec ,short weights1 #aeg ,skimming1 #ajj ,skimmings1 #abb ,slab rubber1 #bii -- --1 properties of1 #cbd ,slope1 #cab ,smoke curing of sheet rubber1 #adc -- --1 temperature of1 #add --1 houses1 #ahc -- --1 ,barker patent1 #bji -- --1 ,devon type1 #bjj -- --1 iron stoves for1 #ahi -- --1 ,jackson type1 #bjj -- -- of brick1 #aih -- -- rate of combustion in1 #aib -- --1 roof of1 #aig -- --1 ,third ,mile type1 #aii -- --1 types of1 #aih ,smoked crepe1 #acj -- sheets1 colour of1 #bee -- water for coagulation1 #bhf ,smoking1 effect on rate of cure1 #cbc --1 greasiness before1 #beb -- rubber1 #aji ,smooth rolling of sheets1 #ajd ,sodium bisulphite1 #hj1 #aad -- --1 abuse of1 #he -- --1 care of1 #aaf -- --1 deterioration of1 #aae -- --1 evaluation of1 #aae -- --1 making a solution of1 #he -- --1 quantity of1 #hd -- --1 residual traces of1 #hf -- -- solution1 mixing1 with latex1 #aag -- sulphite1 #hf -- --1 deterioration of1 #aae -- --1 evaluation of1 #aae ,sorting1 #aej1 #aeb -- rooms1 #baa ,spewing1 #cje ,splinters in sheet1 #bgf ,spontaneous coagulation1 #bid ,spot disease1 #bce -- -- in sheet rubber1 #bgc ,spots1 #bei1 #bfb --1 virgin1 #bei ,standard latex1 #if -- sheet1 #ajb ,standardising instruments1 #ih ,stickiness in sheet1 #bgd ,stock solution1 method of making1 #ge ,storage of rubber1 #bab1 #baf ,stoves1 iron1 for smoke houses1 #ahi ,straining latex1 #fg ,streaks1 #bfb ,stumps1 #i ,sugars1 coagulation with1 #bhg 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