Gelatin in the Photographic Process 



351 



8), very long and thin silver filaments occur and at 

 the same time pronounced surface structures appear 

 on the crystal. 



The results show that it is possible by the carbon 

 replica method to render tine structures of undevel- 

 oped and developed silver halide crystals visible 

 which were previously inaccessible to investigation. 



I should like to thank Prof. Friescr for the detailed 

 discussions he held with mc upon the suhjcct in question. 

 The electron micrographs were made by Dr. Kirchcr in 

 the inorganic analytical laboratory of the Farbcnfabriken 

 Bayer, Leverkusen, and I should also like to express 

 m\ thanks to him. 



In addition, i am indebted to Miss ina Lehnert and 

 Mr. Hans-Jorg Metz for valuable assistance during the 

 experiments. 



Prof, von Borries always devoted his special attention 

 to these problems and generously assisted us in dealing 

 with them. 



References 



1. Bradley, D. E., Brit. J. Appl. Pliys. 5, No. 2, 62 (1954). 



2. Evans, T. and Mik mfll, J. W., Report ol" Bristol C"on- 



lercnce 1954 (409). ndects in Crystalline Solids. 



3. pRrESiR, H. and Kiiin, E., Mitt. Agfa 1, I. Springer 



Verlag, Berlin, 1955. 



4. HiixiEs, J. M. and Mit( iiii i , J. \V., Pliil. Mai;. (7), 44, 



223, 357 (1953). 



5. Klein, E., Mitt. Agfa 1, 10. Springer Verlag, Berlin, 1955. 

 — Phot. Korr. 91, \19, 199 (1955). 



6. Biinsentagung 1956 Freiburg. Z. Elektrocheni. 60, 

 998 (1956). 



7. KoNiG, H. and Helwiu, G.,Z. Physik 129, 491 (1951). 



8. KoMCi, H. and Knoch, M., Phys. Vi'iluimli. 2. 14 (1955). 



Gelatin in the Photographic Process 



G. Vandermeerssche, C. Maertens and G. Lion 



Centre de Microscopie Electroniqiie, Medical, Industriel et Agricole, Briissels-Uccle 



As early as 1935 Russian scientists have tried to 

 find a practical classification for photographic gela- 

 tins (5). This classification was based only on the 

 value of gamma and on the sensitivity of emulsions 

 prepared with the diflferent gelatins but American 

 workers proved this classification to be impractical 

 (12). 



It is the aim of the present paper to show the 

 marked differences which exist when emulsions are 

 made under completely identical conditions except 

 for the fact that different gelatins are used. 



The raw material which had been used to make 

 the six different types of gelatin can be classihed in 

 two main groups, ossein and skin. The duration 

 of liming for the skin gelatin has been similar for 

 two of the specimens but there was a difference in 

 treatment, one skin-gelatin being prepared with 

 nitric acid, the other with hydrochloric acid. 



Fig. 1. Gelatin 1: ossein from hard bone, 1st extraction. Fig. 4. Gclaiin 4: ossein from sinews. 



Fig. 2. Gelatin 2: ossein from hard bone, 3rd extraction. Fig. 5. Gelatin 5: skin, nitric acid treatment. 



Fig. 3. Gelatin 3: ossein from soft bone. Fig. 6. Gelatin 6: skin. Indrochloric acid treatment. 



The emulsions were exposed to light (one minvitc) and then developed. 



The ossein gelatins were different with respect to 

 their extraction-temperatures and also with respect 

 to the fact that one sample came from hard bones, 

 another one from soft bones and a third one from 

 sinews. 



The emulsions were prepared in the classical way as 

 indicated in the literature on photographic emulsion 

 techniques (3, 13). As developers we have used the for- 

 mulas given in the Gevaert handbook. A first series of 

 emulsions has been exposed to light, developed and then 

 washed in order to remove most of the gelatin present 

 on the specimen grid. A second series has been treated 

 in the same way but the gelatin has been remo\ed before 

 exposure to light. Use has also been made of the specimen 

 preparation technique described by Hamm and Comer 

 (7), which consists in utilizing the thin tilm of the sii\cr- 

 gelatin complex which exists as a tightly fitting en\elopc 

 around the photographic grains. In that case the gold 

 development has been applied. 



