156 CASEIN. 



When we consider the integral character of the medium 

 as a factor of sensitised strata in photography generally, and 

 especially in silver chloride printing-out papers, and the part 

 it plays in the presence of silver salts of organic acids, as 

 well as the extent to which it influences the print and the 

 character of the photographic picture, we cannot regard as 

 useless any endeavour to attain perfection by the use of 

 fresh substances as media. Just as it would be erroneous 

 to rest content with what has been already attained in this 

 subject, and to take up the standpoint that the known media 

 albumen, gelatine, collodion, vegetable albumen, algic jellies, 

 resin, starch, etc. fulfil all requirements, and afford sufficient 

 means for the manifestation of the individuality of the photo- 

 grapher in the production of artistic effects, so also is the 

 prospect certain that the means of artistic expression and 

 technical advantages in photography can be widened by the 

 adoption of new substances as media. 



Among the numerous colloidal amorphous substances 

 whose chemical and physical properties indicate the prob- 

 ability of their application as photographic media, a place in 

 nearly the front rank is occupied by casein, which has al- 

 ready formed the subject of investigation for this purpose 

 by various photographic chemists. Their experiments have 

 remained unsuccessful, owing to the difficulty of overcoming 

 the technical imperfections of casein strata for photographic 

 purposes to an extent that could make their advantages 

 apparent. 



So far as these experiments have been made public and 

 brought to the writer's knowledge, they were all undertaken 

 with the object, mutatis mutandis, of dissolving casein in 

 alkalies and employing this solution, together with the re- 

 quisite quantity of chlorides to ultimately form silver chloride, 

 to coat paper for sensitising with silver nitrate. These 

 attempts therefore were directly allied to the albumen pro- 



