COMPOSITION AND PROPERTIES OF CASEIN. 35 



which throw down the casein in an insoluble form from 

 solutions of any kind. Though this may be done better by 

 heating solutions or mixtures of casein along with lime or 

 milk of lime, still heat is not applicable in all cases. Such 

 precipitation can be effected at the ordinary temperature by 

 treating the casein solution or mixture with metallic salts, 

 especially those of copper (cupric sulphate), or with certain 

 organic substances, e.g., alkaline solutions of shellac, the addi- 

 tion of which immediately separates the water, contained in 

 the mass. A patent for the production of insoluble casein 

 was taken out in America by Dunham, according to whom 

 15 parts of borax and 85 of commercial casein are dissolved 

 in 400 parts of water, the solution being then treated with 

 15 parts of hexamethylene tetramine, and afterwards evap- 

 orated, the dried product being exposed to warmth and 

 moisture. In this form casein is a suitable substitute for 

 albumen. 



A far more important matter to the casein industry is 

 the German patent 99,509, or rather the additional patent 

 thereto, according to which casein, albumoses and the liquid 

 conversion products of glue and gelatine are rendered in- 

 soluble by formaldehyde. The insoluble products thus ob- 

 tained can and do find technical application in the form of 

 layers or coatings, as detailed below. 



For certain purposes in chromo-lithography it is necessary 

 to provide paper with a perfectly smooth, absorbent and yet 

 resistant surface. This object is now accomplished by coating 

 the paper with size or casein hardened with formaldehyde, a 

 simple operation which has become of great importance in 

 the paper industry as well as in chromo-lithography. 



Similar fine, insoluble layers of casein can also be prepared 

 without a paper backing, and are then specially adapted for 

 supporting sensitised emulsions in photography (photographic 

 films). In this case they supersede the celluloid hitherto 



