PARA-RUBBER CULTIVATION 597 



The following chain of reasoning was put forward by way of 

 explaining this acid coagulation. 1 " The latex is slightly 

 alkaline. The proteid is of such a nature as to be insoluble in 

 neutral solution, but soluble in alkaline or acid media, i.e. it is an 

 alkali-albumen. When the alkalinity is neutralised by the 

 necessary amount of acid, the proteid comes out of solution and 

 produces with the globules of caoutchouc the clots of rubber. 

 If excess of acid be added, then the proteid remains in solution, 

 being now in an acid medium. The acid required for coagulation 

 bears a definite ratio to the quantity of pure latex only, no 

 matter what its dilution may be, because the alkalinity is not 

 altered in amount by this dilution. Acetic, being a weaker acid 

 than the others, does not bring about the changes so rapidly." 



The coagulating power of several salts was tried on the 

 latex of Hevea. None of them were very satisfactory, excepting 

 mercuric chloride (corrosive sublimate). They either gave an 

 incomplete coagulation, or else a large quantity of the reagent 

 was required. A solution of mercuric chloride, however, rapidly 

 separates out the caoutchouc and very little is needed. This is 

 not surprising as the salt is one of the strongest precipitants for 

 proteins. Magnesium sulphate was, of the salts tried, the next 

 best coagulant. Mercuric chloride has not been experimented 

 with on a large scale. One serious objection to its use is its 

 very poisonous nature. It would, however, be interesting to 

 have a large sample of such rubber reported on by a manufac- 

 turer. It furnishes a very tough kind of caoutchouc, which 

 might possibly have a special use. Such a coagulant has one 

 advantage over acetic acid. It preserves the rubber, whereas 

 that made by means of the acid will mould and rot if kept damp, 

 unless an antiseptic be added. 



Victor Henri's 2 fairly recent researches on the coagulation 

 of latex deserve mention. He employed for his experiments 

 latex which had been submitted to dialysis, until no appreciable 

 quantity of saline matter remained in it. Such dialysed latex 

 behaves differently in regard to coagulation. Alcohol, for 

 example, which is a strong coagulant of ordinary latex, has no 

 effect on the dialysed variety, but after the addition of a salt 

 coagulation sets in, hence the presence or absence of salts has 

 much influence on the clotting of latex. 



1 Parkin, Annals of Botany, 1900, 14, 197. 



2 Henri, V., Compt. Rend. Soc Biol. 1906, 60, 700. 



