RUBBER 657 



Acetic Acid. Probably on over 99 per cent, of estates 

 acetic acid is the coagulant employed in the preparation 

 of Para rubber; its use may be described as a logical 

 outcome of the Amazonian smoking process, since the 

 fumes from the dry distillation or slow combustion of 

 woody material are comparatively rich in this acid. 



The proportions used, however, on different estates, 

 especially in the preparation of crepe rubber, are very 

 variable, and are no doubt one cause of the variability in 

 the rubber obtained. 



The writer and other investigators have found that 

 the minimum quantity of pure acetic acid necessary to 

 coagulate an average latex containing about 30 per cent, 

 of dry rubber is 0*1 c.c. per 100 c.c. of latex, or I part 

 per 1,000 of latex; this quantity is recommended as the 

 most suitable to use for coagulation. In the case of a 

 latex containing about ij Ib. of dry rubber per gallon, a 

 5 per cent, solution of acetic acid in the proportion of 

 3 fluid oz. of the diluted acid per gallon of latex is 

 recommended for coagulation purposes,' both in the 

 preparation of crepe and sheet rubber, which is an excess 

 on the safe side. 



Large quantities have been found to produce a rubber 

 of inferior qualities, although a considerable excess may 

 be used compared with mineral acids, such as sulphuric 

 and hydrochloric acid, without producing such deleterious 

 effects. The abuse and not the proper use of acetic acid 

 is to be condemned. 



Mineral Acids. Of the mineral acids, sulphuric and 

 hydrochloric acids may be used, and are more powerful 

 coagulants than acetic acid. Excessive quantities of 

 mineral acids are very deleterious. Nitric acid is not to 

 be recommended on account of its oxidizing action. 

 Sulphurous acid in the form of liquid sulphur dioxide 

 compressed in cylinders may also be used, and, as would 

 be expected, produces a fine pale rubber due to the 

 inhibition or destruction of the oxidizing enzymes 

 normally present in Hevea latex. 



Sulphuric acid is used on one estate in the Federated 

 Malay States in the writer's knowledge for the 

 coagulation of latex, the rubber from which is subse- 



