110 PARA RUBBER, 



small quantities of acetic acid, acetone, and creosote. The acetic 

 acid is probably the agent responsible for effecting the coagulation ; 

 the other substances, particularly the creosote, are absorbed, the lat- 

 ter acting as an antiseptic in preventing the rapid decomposition of 

 the albuminoids present. In Brazil the latex is poured into a shallow 

 basin 60 cm. to 1 metre in diameter and 20 to 30 cm. deep, and 

 pieces of bark, dirt, &c, removed. A fire is then made of wood and 

 resinous substances, and is kept going either with green branches cf 

 Mimusops elata, All., or with palm nuts from Attalea excelsa, 

 Mart., and Maximiliana regia, Mart; these palms are usually 

 grown in the Botanic Gardens of in various parts of the Tropics, 

 the latter species being more commonly known as the " Cocurito " 

 pa m. A chatty, open at both ends, is placed on the fire and 

 the smoke allowed to issue from the upper aperture. 



A paddle-like implement is then dipped into or covered with the 

 latex, and held over the smoke until the latter is coagulated. It 

 is stated by Bonnechaux* that 8 litres of latex are completely 

 coagulated in about 1 J hour by these means. The decomposition 

 of the albuminous substances in the rubber may be prevented by 

 the addition of suitable antiseptic reagents to the latex, when the 

 rubber is prepared in other ways, though quickness in drying or 

 complete extraction of the moisture from coagulated rubber is 

 often sufficient to bring about the same result. Dickson's 

 apparatus is devised to meet many of these requirements. 



Coagulation by Chemical Reagents. 



In coagulation by such means the object is to use reagents which, 

 while effectively and rapidly precipitating the albuminous material, 

 will not have a detrimental effect on the rubber produced. 



Many compounds, such as picric acid, would rapidly coagulate the 

 proteids, but the effect on the resulting rubber would be bad. 

 Weber and Parkin have shown that many acids may be used in the 

 coagulating process, but it is unnecessary to do more than mention 

 those which have, from practical experience, been proved more or 

 less acceptable to producers in the Tropics and manufacturers in 

 Europe. 



Acetic acid. — This is cheap, always procurable, is not dangerous 

 to handle, and is as effective as formic acid. It is not as powerful 

 as tannic acid, though it is effective in bringing about the coagulation 

 of the latex while cold. The commercial article varies in strength, 

 and the quality should be noted by the purchaser. 



Formic acid. — This, though similar to acetic acid in its effect, is 

 more expensive, weight for weight. The advantages of using this 

 reagent are (1) that less is required than acetic acid, and (2) it has 

 antiseptic properties. Whether acetic or formic acid is used, it 

 should be applied in definite proportions, and no more need be used 

 than is required to just precipitate the albumen in the latex. The 

 same may be said of hydrofluoric acid. 



* Jumelle, I. c. 



