THE PREPARATION OF RUBBER 73 



Para rubber in Ceylon ; and mercuric chloride for coagu- 

 lating Funtumia latex. 



Alkaline liquids, such as a solution of soap or wood 

 ashes, are sometimes employed for coagulating certain 

 latices. In some parts of Central America the natives 

 employ a solution of soap for preparing Castilloa rubber. 



Alcohol and acetone readily and completely coagulate 

 latex, but their use for the purpose is restricted to the 

 laboratory. 



The special applications of these general methods of 

 coagulation to the latex of particular plants will be dealt 

 with in succeeding chapters. 



Mechanical Methods of Preparing Rubber. — In many 

 parts of Africa the natives prepare rubber by beating 

 the bark of the underground stems (rhizomes) of certain 

 species of Landolphia and Clitandra, or of the stems and 

 roots of rubber vines. The stems or roots are first allowed 

 to dry thoroughly, in order that the latex may be com- 

 pletely coagulated. The bark is then stripped ofE and 

 submitted to a beating process, whereby a portion of 

 the bark is eliminated and the threads of rubber become 

 aggregated into a mass. The crude product thus obtained 

 is well washed to remove the loose fragments of bark, 

 and after being softened by immersion in hot water it is 

 again beaten, the treatment being repeated until the 

 rubber is sufficiently free from vegetable matter (see 

 p. 195). Rubber prepared in this way is generally 

 classed as " root rubber." 



Machines have been constructed on a similar principle 

 for the extraction of rubber from bark by mechanical 

 means, and also for the preparation of rubber from the 

 Guayule plant. 



Extraction of Rubber by Solvents. — This method is 

 principally employed at the present time for the extrac- 

 tion of rubber from the Guayule plant, in which the latex 

 occurs in isolated cells and can therefore not be obtained 

 by tapping. The dried plants are crushed and then 

 treated with a suitable solvent which removes the rubber. 

 The greater part of the solvent is afterwards recovered 

 by distillation and the rubber obtained is purified. 



Forms in which Rubber is Prepared. — Freshly coagulated 

 rubber is a white, opaque, porous mass which holds a 

 considerable quantity of the serum of the latex in its 



