596 SCIENCE PROGRESS 



of Hevea latex. Since these Ceylon experiments, a few other 

 coagulants have been recommended, and these are appended 

 below the horizontal line : 



Grams per 

 100 c.c. latex. 



Sulphuric acid o"i 



Hydrochloric acid o'i 



Nitric acid o'3 



Acetic „ o"95 



Oxalic „ o'2 



Tartaric,, 0*25 



Citric „ o'5 



Mercuric chloride o"8 



Formic acid 1 0*45 



Hydrofluoric acid 2 — 



Acid potassium tartrate 3 o'i6 



In the first place with respect to the acids, an excess has 

 to be avoided, otherwise the coagulation ceases to be complete 

 and rubber globules are left in the mother liquid. The range 

 for complete coagulation is very small with all the acids tested, 

 except acetic. With sulphuric, for example, the amount can 

 hardly be doubled without interfering with the coagulation ; 

 whereas with acetic it can be increased some four times before 

 the residual liquid shows turbidity. In fact one quarter or 

 nine times the necessary amount of acetic acid may be added 

 with very little waste of rubber — a very considerable range 

 within the limits of which it is easy to keep in practice. For 

 this reason acetic has much the advantage over the others, even 

 though a greater weight is required than in the case of any of 

 the other acids. 



In the second place the quantity of acid needed depends only 

 upon the amount of pure latex, and is independent of its 

 dilution. A definite weight of acid is required to coagulate 

 completely 100 c.c. of latex, no matter whether this be diluted 

 to five or ten times its volume with water. The latex of Hevea 

 can thus be diluted to any extent, and yet its particles of caout- 

 chouc remain capable of being drawn together into a clot by the 

 addition of the requisite quantity of acid. This was even done 

 for latex diluted two thousand times. 



1 Spence, D., India- Rubber Journal, 1908, vol. xxxv. p. 425. 



3 A weak solution of this acid has been introduced as a coagulating and curing 

 agent under the fancy name of " Purub." Little information is yet to hand as to 

 its use on estates. 



3 Bird, J. A., Official Account, Ceylon Rubber Exhibition, 1906, p. 145. 



