134 PARA RUBBER. 



each 500 c.c. of latex 20 to 25 c.c. of a 5 per cent, formic acid 

 solution were added." And in summing up the results of his 

 experiments : " (a) Much less formic acid than acetic acid is 

 required ; formic acid, having more than double the value of 

 acetic as a coagulant, is more economical from a practical stand- 

 point. (/>) Formic acid is of marked value as an antiseptic agent, 

 preserving the raw moist samples of rubber prepared by means 

 of it from putrefaction and decomposition. It would appear, 

 indeed, that in this condition formic acid combines the properties 

 of acetic acid and creosote, and could be employed, therefore, with 

 advantage where coagulation by means of acetic and creosote is 

 indicated (moist block rubber). " 



DISCOLORATION OF RUBBER AND OXIDISING ENZYMES. 



Lack of uniformity as regards the colour of plantation rubber 

 is often the cause of inferior prices being realised, and rubber 

 brokers state that this is one of its primary defects. 



Kelway Bamber is of opinion that discoloration is due to 

 the action of an oxidising enzyme on the soluble organic matter 

 in the latex. He states that the enzyme may be destroyed, and 

 the colour of the rubber uniformly maintained by heating the 

 latex or the rubber after coagulation. 



By the first method the latex should be raised to a tempera- 

 ture of 167 Fahr. by the incorporation of steam. 



For the destruction of the enzyme in the rubber, immediately 

 after it leaves the rolling machine, it should be immersed in hot 

 water, i.e., temperature about 170 to 180 Fahr., for several 

 minutes. The heated rubber should then be re-rolled and again 

 immersed in hot water for a short time. 



In Vol.iii.No.4 of the Bio-Chemical Journal, Spence contributes 

 a valuable article on the presence and function of oxydases (i.e., 

 oxidising enzymes) in latex, wherein he states that the darkening 

 in colour of raw rubber is due to an oxydase which is associated 

 with the protein or the so-called insoluble constituent of the 

 rubber. 



" TACKINESS." 



The sticky or "tacky" condition so commonly associated 

 with the lower grades of rubber and which has frequently been 



