THE PREPARATION OF PLASTIC MASSES FROM CASEIN. 



ising, were treated with 7| Ib. of soda (equal to about 40 per 

 cent, of the weight of casein present). After a short time 

 the colour changed, and on passing the liquid again through 

 the separator, a greasy, muddy sediment was eliminated. 

 The casein, precipitated from the resulting liquid by acids, 

 was colourless and transparent in thin sheets. 



In German patent 147,994 (19th February, 1901) a pro- 

 cess was described for imparting to dried casein the necessary 

 plasticity to enable it to be moulded, this result being attained 

 by moistening the casein with a little acid, e.g., acetic acid, 

 instead of water, before pressing. 



When freshly precipitated from milk, casein is plastic 

 and can be easily pressed in moulds. On account of the 

 large percentage of water in this fresh casein, however, the 

 articles prepared from it are difficult to dry without warping 

 and cracking ; and the casein itself is very liable to decompose. 

 On the other hand, the use of the stable, dry casein is at- 

 tended with the drawback that it loses its original plasticity 

 in course of conversion into the commercial form, and this 

 plasticity is not recoverable by moistening the dry product ; 

 consequently, exceedingly high pressure and warmth are re- 

 quired to form the same into a homogeneous mass. This 

 leads to the danger of the colour and hardness of the article 

 being affected by the heat. 



This plasticity, however, can be restored by treating the 

 casein with a trace of acid, preferably at the stage of moisten- 

 ing the mass before pressing. The degree of this acidity 

 varies, of course, with the different kinds of commercial 

 caseins, but can be easily found by trial. The acetic acid 

 used for souring milk in dairies will do for the purpose very 

 well. 



To prepare a hard casein mass, casein, either in solution 

 or in the dry, soluble state, is converted into the insoluble 



form by acids or salts, and treated with formaldehyde. It 



8 



