PARA RUBBER. 109 



of clarification, the liquid left behind usually containing only 

 those ingredients of the latex which have remained in solution. 

 The coagulation of the proteid material occurs as soon as the latex 

 becomes neutral or faintly acid, no matter what proportion of 

 suspended globules of caoutchouc or other constituents may be 

 present in the latex. 



Burgess states that the natural method of coagulation is only 

 possible where a washing machine is used, and suggests that where the 

 latter is in use the latex might be allowed to stand for 24 or 36 hours, 

 and the natural fermentation allowed to take place and produce 

 coagulation. It is difficult to understand this contention, if by a 

 washing machine is meant one similar to that recommended by the 

 same authority for the manufacture of crfpe rubber in the Straits — 

 indeed, if it were so it would constitute a serious disadvantage to the 

 method of coagulation by natural means. As a matter of fact, bis- 

 cuit and sheet rubber can be prepared by the natural and artificial 

 methods with equal ease, without the use of any machinery beyond 

 an ordinary mangle and a blocking apparatus. 



On estates where the daily quantity of latex is small, the use of 

 chemicals and machinery for rapidly coagulating it is not always 

 necessary; the latex is put in shallow pans (see Plate 20, Series A) , and 

 allowed to set. The biscuits, when ready, are rolled to squeeze the 

 water out and then placed on wire gauze, wooden, or coir shelves to 

 dry. A strong current of dry air might be obtained by drawing the 

 air by means of a fan through a chamber containing chemicals such as 

 freshly-burnt lime or calcium chloride, which would absorb the water. 

 It should not be difficult to arrange a building on a plan somewhat 

 similar to the tea-drying and cacao-curing rooms in common use all 

 over Ceylon. 



Effect of Heat and Chemicals on Coagulation. 



Some kinds of latex can be heated for a long time — almost 

 indefinitely — without coagulation being effected, whereas other kinds 

 coagulate rapidly on the application of heat. 



According to Parkin the diluted latex of Para rubber is unaffected 

 by boiling. If the undiluted latex is boiled, water is driven off, and 

 the thickened milk may then become charred. 



The addition of certain chemical reagents to the heated latex 

 brings about coagulation ; dilute mineral acids, acetic acid, and 

 tannic acid are particularly active. 



Smoking and Coagulation. 



The coagulation of the latex may be hastened by exposing it to 

 heat and the products of combustion of a fire. The latex canbe co- 

 agulated fractionally by such a process, and the finished product.when 

 properly manufactured, is less liable to putrefaction than the rubber 

 prepared by many other methods. The smoke from burning palm 

 nuts used in the Amazon district contains, among other substances, 



