Gums, Resins* 



tf 



[July, 1910. 



the coagulation of latex will be brought 

 into line with the facts now known res- 

 pecting the so-called "strength" in wheat 

 flour and the behaviour of proteins 

 generally in regard to precipitation, 



Two matters of great importance from 

 a practical point of view deserve to be 

 noticed in regard to coagulation. In the 

 first place the reagent employed has in 

 all probability a specific influence on the 

 quality of the rubber produced and 

 especially on its behaviour in vulcani- 

 sation. 



S condly, coagulation alone is not 

 snf.icient. It should be combined with 

 curing. Rubber prepared by acetic acid 

 Will mould and deteriorate if not kept 

 dry. Hence in the Ceylon experiments 

 creosote was used and recommended 

 as a preservative. This, however, does 

 not seem to be generally practised. 

 Much of the plantation rubber now 

 on the market is not cured, but being 

 produced in thin sheets it dries rapidly 

 and so reaches London, as a rule, in 

 good condition. 



There is no doubt, however, that 

 cured plantation rubber will in the 

 future gain the favour of the market. 

 It is significant now that what is known 

 as " smoked sheet " commands the 

 highest price. It remains to be seen 

 whether a convenient wet method of 

 coagulation can be introduced which 

 will produce a satisfactorily cured 

 rubber. If the coagulant and preser- 

 vative can be combined in one reagent, 

 so much the better. Formic acid, mer- 

 curic chloride and "Purub" have this 

 double property, if any of them may 

 prove satisfactory otherwise. If acetic 

 acid be adhered to, then some antiseptic 

 must be supplied in addition, 



This apparent necessity of curing the 

 rubber has focussed attention once more 

 on the Amazon smoking method. 

 Wickham for one strongly advocates 

 this practice, and has invented an ap- 

 paratus for the purpose. 



Some of the Eastern estates have met 

 the difficulty half way by first prepar- 

 ing the rubber in thin sheets by means 

 of acid coagulation and then submit- 

 ting these to the action of smoke from 

 burning wood. The rubber is thus sur- 

 face-cured only. It has just been point- 

 ed out that rubber so treated (smoked 

 sheets) fetches at present the top price 

 in the market. Previously pale crepe 

 was most in favour, largely on account 

 of its light colour. A cured rubber, 

 retaining its pale tint, would seem to 

 be the desideratum, and this would be 

 difficult to obtain by any smoking 

 method. Consequently it would seem 



likely that a wet system, both of coagu- 

 lating and curing, will ultimately be 

 adopted in Para rubber cultivation ; 

 especially as a watery or much diluted 

 latex can more easily be dealt with by 

 wet coagulation than by means of 

 smoke. 



Electrical Method of Separation. 



Cockerill, of the Ceylon Technical Col- 

 lege, has recently shown that rubber can 

 be separated from Hevea latex electri- 

 cally. The caoutchouc is deposited on the 

 anode. Few details are to hand yet. 

 In any case it is doubtful if such a 

 method would be practicable on estates, 

 Nevertheless it is of considerable scien- 

 tific interest. 



Composition op the Latex and Rubber. 



A moderate number of analyses have 

 been made of Hevea latex and rubber ; 

 several are by Mr. Kelway Bamber, 

 chemist to the Ceylon Government. 

 Below are given in round figures the 

 average percentage composition of the 

 latex drawn from the tree-trunk (after 

 wound-response has commenced) and 

 also that of the rubber prepared 

 therefrom. 



Hevea brasiliensis percentage 

 composition. 





Latex. 



Rubber. 



Water 



55 to 63 



0-5 



Caoutchouc... 



40 to 32 



94-0 



Resin 



21 



3-0 



Protein 



21 



2-5 



Ash 



0-4 



0-5 



Sugar, etc. ... 



0-4 





The percentage of water and caou- 

 tchouc will naturally vary inversely. 

 Para rubber is remarkable for the low 

 proportion of resin — a point much in 

 its favour. Other rubbers usually have 

 more. The comparatively large amount 

 of protein in the latex is noteworthy ; 

 a considerable part of it naturally be- 

 comes incorporated with the rubber 

 through coagulation. 



Lack op Strength in Rubber erom 

 Young Stems. 



The possibility of preparing commer- 

 cial rubber from the young stems and 

 leaves of caoutchouc-plants has often pre- 

 sented itself in the past ; but in respect 

 to Hevea and some other rubber trees as 

 well, there is one fatal objection to this 

 project. The latex from these parts of 

 the plant produces a " rubber " some- 

 what adhesive, with little elasticity and 

 strength. 



This is a peculiar point and has not 

 yet been clearly explained. The writer- 

 has suggested that perhaps the latex 



