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The Supplement to the Tropical Agriculturist 



be clear. If it shows much turbidity , then it 

 means that a certain amount of caoutchouc is 

 being lost, and this is owing to the addition of 

 two little or too much acid— a point upon which 

 managers of estates should keep their eye. 



Formic Acid. 

 Formic acid has been suggested in more than 

 one quarter as a substitute for acetic acid. 

 I may say that I have never experimented 

 with this reagent, but it does not recom- 

 mend itself to me for two or three reasons. 

 It is more expensive and an unpleasant subs- 

 tance to handle. It is also a stronger acid, and 

 so presumably more care would have to be ex- 

 ercised in the amount requisite. Acetic acid has 

 this great advantage that the quantity necessary 

 can be considerably exceeded without ill effects, 

 whereas with a stronger acid a slight excess 

 means incomplete coagulation — and so waste. 

 Dark Rubber. 



The question of the dark colour often assumed 

 by plantation rubber has recently received the 

 attention of Mr Bamber, who has shown how it 

 may be avoided. If the clots resulting from acid 

 coagulation be dippped in hot water, the darken- 

 ing is permanently prevented. The heat destroys 

 the special ferment, oxydase as it is called, 

 which in the presence of oxygen brings about 

 this change of colour. Dr. Spence, of the Bio- 

 Chemical Department, Liverpool University, 

 has also been investigating this matter and has 

 come to similar conclusions. 



Hot Acid Treatment. 

 In my experiments on Hevea latex, in 1898-9, 

 I was never troubled by the rubber clots dark- 

 ening through this cause, but then most of the 

 rubber samples were prepared by hot and not 

 cold acid treatment. Unless there is some 

 serious objection to the hot treatment, it seems 

 preferable, for the coagulation is brought about 

 quicker and at the same time the oxydase is 

 destroyed ; further, any foreign particles, such 

 as fragments of bark, float to the top during 

 the heating and can readily be skimmed off. 

 Let me draw attention here also to the import- 

 ance of thoroughly washing the spongy clots of 

 rubber so as to remove all trace of acid. 



Proteid in Rubber. 

 The coagulation of Hevea latex is due, as is 

 now generally admitted, to the presence of a 

 small quantity of soluble albuminous (proteid) 

 matter which, on the addition of a slight amount 

 of acid, comes out of solution and draws itself 

 together into a clot, entangling in its meshes 

 the globules of caoutchouc. A spongy mass of 

 rubber is the result. The wet clot soon moulds 

 and purifies, owing to the proteid it contains. 

 The addition of creosote prevents this, as it is 

 detrimental to the growth of moulds and bac- 

 teria. Castilloa rubber prapared by creaming or 

 centrifugalisation will not mould as it is free 

 from proteid. 



The question arises, is the quality of rubber 

 altered by the presence of tnis small amount 

 of coagulated proteid ? To ascertain this, rub- 

 ber would have to be prepared free from pro- 

 teid and compared with a sample made in the 

 ordinary way. No rubber, as yet, has been 

 directly prepared in Ceylon, or the East 



generally, from Hevea latex from proteid. The 

 latex will not cream, neither will it undergo 

 centrifugalisation in a separator. Mr Biffen. 

 however, appears to have centrifugalised this 

 latex in tropical America, judging by the ac- 

 count in his paper on "Rubber Coagulation," 

 published in 1898. It was tried in Ceylon 

 without success. Perhaps it might be worth 

 while to attempt the separation in a machine 

 revolving more rapidly than 6,000 revolutions 

 per minute. If separation resulted, then rubber 

 free from proteid could be prepared and com- 

 pared with the coagulated kind and also with 

 native Para. Thus some light would pro- 

 bably be thrown on the effect of proteid on 

 the quality of rubber. At any rate, this 

 problem could now be studied in the case 

 of Castilloa rubber. The presence in caoutchouc 

 of a little proteid may have a beneficial effect 

 on its properties. 



It would also be interesting to know whether 

 the rubber of Castilloa would be equal in 

 quality to that of Hevea, if both were of an 

 equal degree of purity. Castilloa contains, as 

 a rule, more resin, and this, of course, lowers 

 its quality. But if the resin were removed, 

 would its caoutchouc then be equal in quality 

 to that of Hevea ? 



Centrifugalisation. 

 To return to the question of centrifugalisa- 

 tion, little appears to have been heard of this 

 process, since it was boomed ten years ago. 

 It certainly seemed a promising method for 

 Castilloa latex. It may, of course, be in use 

 in the plantations of this tree in Mexico 

 from which, judging by reports, a quan- 

 tity of commercial rubber may be coming 

 in the near future. Perhaps centrifugalisa- 

 tion is a wasteful method. A certain number of 

 the caoutchouc globules may remain in suspen- 

 sion, just as in milk separation all the fat 

 globules are not removed, if otherwise the fluid 

 remaining would be clear. 



Corrosive Sublimate. 

 An easy way of preparing rubber from Hevea 

 latex is by the addition of a small quantity of a 

 solution of corrosive sublimate (mercuric chlo- 

 ride). The rubber clot is not only formed but 

 " cured " at the sametime, as this reagent is one 

 of the strongest antiseptics known. 



Of course, an obvious and serious objection 

 to this treatment is the very poisonous character 

 of this salt. Still it might be interesting to 

 know the manufacturers' opinion of a large 

 sample of rubber so prepared. 



Concluding Remarks. 

 By way of concluding these considerations, it 

 seems abundantly evident that in spite of the 

 success already achieved by the rubber-planting 

 industry, the time has not yet arrived for mana- 

 gers of estates to settle down to any one stereo- 

 typed or rule-of-thumb method of rubber pre- 

 paration. This is still in the experimental stage. 



Directors of companies and those responsible 

 for estate supervision and control must be ever 

 on the alert to try and adopt, if necessary, new 

 methods, when brought to their notice by com- 

 petent persons. If they falj top early into one 



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