and Magazine of the Ceylon Agricultural Society. 



593 



ubmit for testing purposeB samples of planta- 

 tion rubber, prepared, of course, in the same 

 way, from trees of various ages. Personally, 

 I should be rather surprised to find any marked 

 difference in the quality of the rubber drawn 

 from 10 year old trees as compared with that 

 from 20 year old ones, all other conditions 

 being equal. It is, of course, true that 

 the latex from the shoots and leaves of 

 Hevea does not afford good caoutchouc, but this 

 comes from the laticiferous vessels formed in 

 primary growth. In the secondary growth 

 whereby the stem increases in thickness, the 

 new laticiferous vessels which are continually 

 being formed, contain probably from the begin- 

 ning good caoutchouc. On this assumption, 

 then, as soon as the few primary laticiferous 

 vessels dry up and become obliterated by 

 the expansion of the stem, the latex will give 

 rubber of full quality, and continue to do so. 

 Wound Response. 



It has been suggested to me that the in- 

 feriority of plantation rubber may be due to the 

 over rapid formation of latex through excessive 

 response to wounding. That is to say, the glob- 

 ules arise so fast that they have not time to 

 mature into proper caoutchouc. This possibility 

 does not appeal to me. Though the physi- 

 ology, or shall I say pathology, of wound res- 

 ponse is still imperfectly understood, yet the 

 phenomenon can hardiy be due to a rapid for- 

 mation of new laticiferous vessels near the 

 place of injury, for it is noticeable often after 

 the lapse of 24 hours, a time too short one 

 would imagine, even in the tropics, for a large 

 addition of new tubes. It is more likely occa- 

 sioned by an abundant infiltration of water into 

 the neighbouring intact tubes, as well as perhaps 

 into those which have been served, but have 

 stopped bleeding through being plugged with 

 hardened latex. On re-opening the wound, the 

 greater turgidity of the vessels and kheir more 

 liquid conteuts results in a much more copious 

 flow of latex. It is a recognised fact, I believe, 

 chat the latex from rewounding is thinner, con- 

 taining a lower percentage of caoutchouc, than 

 that issuing from first cuts, but the weight of 

 rubber obtained is greater, owing to the much 

 increased flow. Exact experiments, however, do 

 not seem to have been conducted to show the 

 relation of rubber-weight to latex volume from 

 a continuous series of tappings. A too frequent 

 tapping may result in a very watery latex, which 

 is not economical to collect. Handy means have 

 been devised for rapidly estimating the percen- 

 tage of rubber in a sample of latex. With these 

 planters could be guided. If the caoutchouc fell 

 to, say, below lOpercent, then thetappingshould 

 be discontinued, or the interval between suc- 

 cessive tappings extended. 



But to return to the main point. Though it 

 seems improbable that the quality of the caout- 

 chouc should be affected detrimentally by 

 climate, immaturity of the tree or excessive 

 tapping, yet these possibilities should not be 

 disregarded, but be made the subject of deci- 

 sive experiment. 



Mode op Preparation. 



Probably the defect in plantation rubber is 

 largely due to the mode of preparation. It 

 seems doubtful if the method of pulling and 

 stretching the rubber clots into the crepe form, 



75 



or of pressing them into thin sheets or biscuits 

 is a good one. A maximum amount of surface is 

 thus exposed for oxidation, and further, perhaps, 

 the vigorous manipulation itself hasan injurious 

 effect on the elastic property of the rubber. 

 Consequently the block form adopted by some 

 planters seems preferable. But to produce dry 

 blocks which will not mould or purify, the 

 rubber must first be obtained in thin sheets in 

 order to be thoroughly dried, and these after- 

 wards pressed into blocks. The supposed evils 

 arising from thin rubber are thus only partly 

 obviated. 



Cured Block Rubber. 



Hence recourse must be had to the complete 

 process devised at' the Royal Botanic Gardens, 

 Ceylon, nearly ten years ago, viz., coagulation 

 by means of acetic acid with the addition of a 

 preservative such as creosote. Block rubber can 

 thus be made which need not be dry and yet 

 will not mould. A sample of rubber thus pre- 

 pared was shown on the Ceylon Government 

 stall at the recent exhibition and manufacturers 

 were said to have pronounced it to be the 

 kind of raw material they desired. 



Rubber probably preserves its good qualities 

 better in the presence of a certain amount of 

 moisture. 



These considerations, then, point to the plan- 

 tation rubber of the future being compressed 

 direct from the clots into blocks of uniform size, 

 and of a thickness bordering on an inch, which 

 will allow the buyers to soe at a glance that 

 they are free from impurities, and also permit the 

 superfluous water to evaporate fairly readily. 



Block rubber thus prepared should be sub- 

 mitted in quantity to the manufacturers to be 

 vulcanised and tested, so as to see how it com- 

 pares with the best native Para. Inall tests of the 

 commercial value of raw rubber, the final appeal 

 must always be to the manufacturer; thechemist 

 alone is not sufficient. Let us hope there are 

 English firms enterprising enough to carry out 

 these tests and so assist the planters, especially 

 seeing that this new tropical cultivation is almost 

 wholly due to British endeavour. 



Smoking Process. 

 The defect in plantation rubber as hitherto 

 supplied has aroused in certain minds the idea 

 that a smoking process based on the native 

 method in use in the Amazon valley should be 

 adopted. Though probably rubber as good as the 

 best native Para might be produced by it, yet I 

 think it would have distinct disadvantages from 

 a planter's point of view. A considerable waste 

 would be likely to ensue in the manipulation. 

 Even if that drawback was removed, the rubber 

 obtained would be dark in colour owing to the 

 smoke, whereas the manufacturers are greatly 

 attracted by the lightly tinted plantation 

 rubber now on the market. This kind 

 allows articles to be made which are almost 

 transparent, a distinct advantage in certain 

 cases. Its quality is also more easily judged. 

 Pale rubber seems, at the moment, destined to 

 supersede the dark kind. 



Acetic Acid Process. 

 One advantage of the acetic acid process is 

 that, if the reagent is carefully used, every par- 

 ticle of caoutchouc can be extracted from the 

 latex. The liquid which is left behind should 



