(23) 



From H. Luggin's modified proposition it appears clearly, how the 

 chemical sensitizers promote the photochemical decomposition process 

 of the silver haloids by halogen absorption. They consequently pre- 

 vent regression. 



Lüppo-Cramkr l ) describes the following experiment, which confirms 

 this. Precipitated silver chloride shows neither with silver nitrate, 

 nor with ammonia, both chloride absorbents, any increased sensi- 

 tiveness to light when photochemically decomposed ; in an emulsion 

 where the rapid escape of the liberated halogen is prevented, the 

 action of the chemical sensitizer is therefore observed. From this 

 it follows that the chemical sensitizer does not react upon the silver 

 haloid itself at all. 



Even from the considerable deviations from the reciprocity rule 

 in a silver bromide gelatine plate with very low light intensities it 

 follows that gelatine is not a chemical sensitizer, which has also 

 been proved in another way, experimentally, by Iatpo-Cramer. 2 ) 



While the chemical sensitizers act very favourably in the printing- 

 out process, they have no, or even a detrimental influence in the 

 case of silver haloid emulsions intended for development, as has 

 been pointed out by Lüppo-Cramer 3 ). If it is borne in mind that 

 the a silver subhaloid germ itself is a substance very sensitive to 

 light, which with loss of halogen, passes into the 3 zilver subhaloid 

 without germinative property, it is clear that a too active chemical 

 sensitizer does not promote reducibleness. 



A number of chemical sensitizers, however, are oxidizers at the 

 same time. From what has been said above it has appeared that 

 oxidation transforms the f? silver subhaloid into a silver subhaloid 

 (neutralization of solarization), which may be thus represented : 

 f> silver subhaloid -J- oxygen — silver oxide (Ag,0 ?) -f « silver 

 subhaloid. 



This reaction seems to proceed very slowly in the case of sub- 

 bromides. 



Owing to this complications may arise, so that the chemical sen- 

 sitizer, while on one hand promoting the photochemical reduction, 

 on the other hand again partly oxidizes the silver subhaloid that 

 has been, formed. Here the action of the chemical sensitizer is 

 favourable for the process of development, as in the case of the 



i) Phot. Korresp. 1901; S. 224. 



Lüppo-Cramer. Wissensch. Arbeiten 1902; S. 87. 



J. M. Eder. Jahrb. f. Phot. u. Repr. 1906; S. 648. 

 *) Lüppo-Cramer. Phot. Probkme. 1907; S. 33. 

 3) Phot. Korresp. 1903; S. 25. 



