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By W. Ostwald 1 ), K. Schaum and W. Braun 2 ) it was supposed 

 that the reduction of the silver bromide with chemical development 

 was in the first instance brought about by a minimum amount of 

 silver bromide dissolving as positive silver- and negative haloid-ion, 

 after which the reduced substance was precipitated upon the germs. 

 Lüppo-Cramer 8 ) succeeded in showing that a number of developing 

 processes which were formerly looked upon as being purely chemical 

 in their nature, not only in reality proceed physically, but that 

 every chemical development is also partly of a physical character. 

 W. Scheffer 4 ) was the first to show by a microscopical investigation 

 that the entire chemical development is physical in its nature, i.e. 

 it is brought about by molecular attraction between the photo- 

 chemically reduced silver haloid, the germ, and the reduced feeding- 

 substance. This, consequently, accounts for the altered structure of 

 the exposed silver bromide gelatine plate before and after development 6 ). 



Still the development of the photographic plate by the so-called 

 chemical method really shows a difference from the physical method. 

 Lüppo-Cramer 8 ) succeeded in demonstrating that the substance of the 

 image in the case of a negative developed by the so-called chemical 

 method, still contained bromine by the side of ordinary silver, which 

 bromine he supposed to be a constant solution of silver in silver 

 bromide. From this he infers that during the development, beside 

 the silver another intermediate product must originate. It is only 

 natural to assume, on the analogy of the reduction process of the 

 silver haloid to silver through subhaloid, that also in the case of 

 so-called chemical development the reduction takes place in the same 

 way. Thus it appears that between chemical and physical develop- 

 ment there is only this difference that the former keeps the subhaloid 

 in solution with more difficulty than the latter, owing to which 

 perfect reduction cannot take place. This at the same time accounts 



i) W. Ostwald. Lehrb. d. allgem. Chemie. 1893; Bd. 2; S. 1078 



2) J. M. Eder. Jahrb. f. Fhot. u. Repr. 1902; S. 476. 

 Phot. Mitt. 1902; S. 229. 



8 ) Lüppo-Cramer. Phot. Probleme 1907. S. 159. 



*) Phot. Rundschau 1907; S. 142. 

 Phot. Korresp. 1907; S. 384. 



6). S. E. Sheppard and C. E. K. Mees. (Zeitsch. f. wiss. Phot. 1905; Bd. Ill; 

 S. 355) consider V- Bellach's observation that the size of the grain of the 

 developed image decreases during the drying of the emulsion, to be in accordance 

 with G. Quincke's foam-structure theory of the silver haloid grains which, according 

 to him, contain gelatine. The non-coalescence of the exposed with the developed 

 grain shows the incorrectness of this view. 



6) Pbot. Korresp. 1905 S 319 



