68T 



bv operating widi the latex later, the quantity of acid that has to 

 he added in order to reach a certain stage, is found to be a little 

 smaller. 



We will still give a few examples, how much the percentages 

 of acid found uiay varv when latex from different origin is used, 

 viz. for hydrochloric acid and for the limits of the first range of 

 coagulation with mixtures with 5 and 2°/, latex. 



[f we calculate the differences in own acidity of the diluted latices, 

 we see that the differences in acidity for the limits differ fairly 

 strongly from tiiem, lliough a general lelation can be clearly noticed. 

 In fact a strictly quantitative correspondence could not be expected 

 as the lalices differed not only in acidity but also in percentage of 

 rubber and in secundary substances. 



^ 9. InvesticiatimiK of others. 



As mentioned in the introduction, we find in literature a good 

 many investigations, pointing to the existence of irregular series 

 with Hevea latex. 



J. Parkin, one of the first investigators who was engaged with 

 acid-coagulation of Hevea latex '), used for his experiments ten 

 times diluted latex and stated therewith the transition liquid — coagu- 

 lated — liquid. Parkin, whose experiments weie limited to small addi- 

 tions of acid, did not notice the second range of coagulation. As 

 an explanation PARKtN assumed, thai the protein, present in latex, 

 is insoluble in a neutral liquid, bul dissolves in alkali or acids. 

 Parkin was of opinion that Hevea latex is alkaline: therefore 

 addition of acid would first cause neutralization, with precipitation 

 of the protein and, as a result, of the rubber as well, whilst, at a 

 higher acidity the protein would dissolve again. Parkin further stated 

 that with acetic acid the range of coagulation is wider than with 

 other acids, and thought this a decided advantage for practice, 

 because by addition of too much acid the coagulation would not 

 fail so sooi). 



Because in the practice of plantations one never causes the per- 

 centage ot rubber of the latex to sink below J5 oi- 12 '/« ('• e. in 

 our terminology, one never uses mixtures with less than 50 to 40 '/o 

 latex), where with acetic acid no irregular series occur, there was 

 for a long time no further interest for these phenomena. W. Crossleï ') 

 again gave a few figures for upper — and lower limit of the 



I) Circulars Royal Botanic Gardens Peradeniya Vol. I il899), 149. 

 ') India Rubber Journal 41 (1911), 1206. 



46 

 Proceeding* Royal Acad. Amsterdam. Vol. XXVI. 



