8l2 



THE POPULAR SCIENCE MONTHLY 



juice, and carefully drying the clot after it has been subjected to pres- 

 sure. For experimental purposes, alcohol may be employed as a co- 

 agulating agent ; while, on an industrial scale, alum has been tried 

 with apparently an excellent result. The milk is strained to remove 

 solid impurities, after which a small proportion of alum solution is 

 added. The clot which separates is next drained or pressed, after 

 which it is dried. Caoutchouc dissolves more or less perfectly, accord- 

 ing to its condition in various liquids, among which may be mentioned 



Fig. 4. Cube of Para Caoutchouc unswelled. 





Fig. 5. Similar Cube swelled by the Prolonged Action or Benzole. 



the various fixed and hydrocarbon oils, chloroform, ether, and carbon 

 disulphide. Unless, however, the caoutchouc has been masticated or 

 otherwise degenerated, it is doubtful whether a true solution is ob- 

 tained. When a clear limpid solution is required, one of the best solv- 

 ents is that proposed by Payen, namely, carbon disulphide, mixed with 

 five per cent, of absolute alcohol. If one part of masticated caout- 

 chouc is dissolved in thirty parts of the above solvent, a solution is 

 obtained which can be filtered through paper, and may be employed 

 in covering the most delicate molds with successive layers of caout- 

 chouc. 



Caoutchouc may be utterly ruined by the use of impure solvents, 

 and those experimenting with India-rubber solutions should, in cases 

 where it is desirable to regenerate the caoutchouc by allowing the 

 solvent to evaporate, take the utmost care not to employ any solvents 

 which contain fatty or greasy matter. 



Weak or diluted acids have little or no action on caoutchouc in the 



