SUNDKY APPLICATIONS OF CASEIN. 157 



cess, under the erroneous idea that casein being an albu- 

 minoid substance would behave similarly to egg albumen. 



The writer has repeated and checked a number of these 

 experiments, and found it impossible to obtain papers of any 

 practical utility by the method in question. Pure casein 

 was dissolved in alkalies, with the aid of warmth, both caustic 

 alkalies (potash, soda and ammonia) and carbonates (sodium 

 carbonate and bicarbonate) being used, the casein being 

 stirred up with water and brought into solution by adding 

 the dissolved alkalies. In some cases the resulting solutions 

 were treated with common salt or ammonium chloride and 

 filtered, so that uniform glossy layers could be obtained on 

 papers, either plain or surfaced with baryta. Flexibility was 

 readily obtainable by the addition of glycerine to the casein 

 solution. The dried papers were then sensitised in the usual 

 way, both in neutral silver baths and in those containing 

 citric acid. Nevertheless, although the conditions were 

 varied in numerous ways, and the papers resembled albumen 

 papers in many respects, the film softened, either occasion- 

 ally in the toning bath or invariably in fixing or washing, 

 and in some cases came off altogether, though this could 

 be prevented by using an alum bath before fixing. Some- 

 what better results were obtained by using casein solutions 

 hardened with formaldehyde, inasmuch as the papers then 

 could be toned, fixed and washed. The papers had the same 

 general character as albumen paper, without any advantages 

 over the latter. When sensitised, even in an acid bath, their 

 keeping properties were very poor, which, indeed, is not sur- 

 prising in view of the presence of the formaldehyde reducing 

 agent. Further attempts in the same direction were aban- 

 doned as hopeless; and those made with a view to using 

 casein in the preparation of emulsions proved equally un- 

 successful, silver caseate being invariably thrown down in 

 large flakes, impossible to divide sufficiently fine by mechan- 



