SUNDRY APPLICATIONS OF CASEIN. 161 



papers, but will probably find application in numerous other 

 ways. 



By using iodides to precipitate the casein it should be pos- 

 sible to obtain, by sensitising in an acid bath, silver iodide 

 pellicles suitable for physical development ; whilst the use of 

 bromides would furnish silver bromide pellicles. 



Casein stirred up in water can be dissolved in any weak 

 acid by gentle heat, furnishing a hyaline, gelatinous solution. 

 This solution poured over a glass plate, celluloid film, paper 

 or the like, while warm, will set on cooling and dry with a 

 brilliant gloss. The dried film, which is still slightly soluble 

 in water, may be floated or immersed in a solution of any 

 metallic haloid, and thereby rendered insoluble, a sufficient 

 quantity of the haloid salt for the formation of the silver 

 haloid being incorporated in the casein stratum at the same 

 time. Chlorides, bromides and iodides, or mixtures of same 

 can be used in this way. The resulting stratum is as tough 

 as leather, whilst permeable to liquids, and it can be rendered 

 as flexible as desired by adding glycerine. It may be sensi- 

 tised by a neutral or faintly acid solution of silver nitrate, 

 inasmuch as this latter reacts on the metallic haloid in the 

 stratum, to form the corresponding silver haloid. According 

 as the casein has been fixed with chlorides or bromides, the 

 product will be either a faintly sensitive chloride printing-out 

 casein stratum or a highly sensitive bromide stratum suitable 

 for development. The method, which is specially adapted 

 for printing-out papers, is patented. These papers, which 

 may be advantageously prepared by the aid of baryta, exhibit 

 several valuable properties, which fill a long-felt want in 

 practice^ 



They print fairly quickly, in agreeable tones, and are 

 easily toned in a sulphocyanide bath, which gives warm, pure 

 tones, free from double toning. Neutral combined toning 



and fixing baths can also be used. Even in warm water 



11 



