( 13 ) 



neither of them has hitherto afforded a definite explanation of the 

 various photographic phenomena. 



As the photo-chemical process of analysis upon the silver haloid 

 is only characterized by a continuous reduction process, it is quite 

 natural to assume this also in the cases of the solarized latent image 

 Still there are a few phenomena which seem to contradict this. 



Thus W. Abney l ) assumed the formation of an oxybromide, and 

 founded this assumption on the fact observed that potassium bichro- 

 mate and potassium permanganate, perhydrol and a few anorganic 

 acids promote solarization. The anti-solarizing action, also pointed 

 out by him, of reducing agents, like pyrogallol, ferrous sulphate, 

 ferrocyanide of potasium, nitrites, and sulphites, has only been judged 

 from the appearance or non-appearance of polarization, and may be 

 entirely reduced to retarded development. 



Lüppo - Cramer 2 ) considers the oxidation theory of solarization 

 absurd. He points to the solarization of the plate even if no oxygen 

 is admitted, and to the circumstance that all the agents that prevent 

 solarization, are halogen-absorbing substances. As a characteristic 

 example he mentions silver nitrate, the anti-solarizing action of which 

 is, according to him, to be ascribed to halogen-absorption, not to 

 oxidation, and considers this action analogous to that of nitrites, 

 sulphites and hydroquinone. 



This view is at variance with his criticism of the oxidation theory, 

 in which he also points to the continuous loss of halogen in the 

 case of continued exposure of the silver haloid, and to his obser- 

 vation that a bromide solution counteracts solarization, and may even 

 entirely neutralize the latent image 3 ). Consequently halogen-absorption 

 must promote solarization. The promotion of solarization mentioned 

 by W. Abney, and referred to above is not to be ascribed to oxida- 

 tion, but to halogen absorption. 



That oxidation of the substance of the latent image neutralizes 

 solarization, has been ascertained by J. M. Eder 4 ) with his chromic 

 acid reaction, and by K. Schaum and W. Braun 5 ) with their ammo- 

 nium persulphate reaction. That in this case we really have not the 



i) Proc. Roy. Soc. 1873; Vol. 27; p. 291 a. 451. 



2 ) Lüppo-Cramer. Phot. Probleme. 1907; S. 138. 



3) J. M. Eder, Jahrb. f. Phot. u. Repr. 1902; S. 481. 

 *) Phot. Korresp. 1902: S. 647. 



J. M. Eder, Jahrb. f. Phot. u. Repr. 1903; S. 23. 



J. M. Eder, u. E. Valenta, Beitrage zur Photochemie. 1904; II; S. 618. 

 J. M. Eder, Handb. d. Phot. 1903; Bd. Ill; S. 828. 

 B ) Phot. Mitt. 1902; S. 224. 



