( 14 ) 



phenomenon of retarded development I could observe through the 

 formation of a dull surface image. Further Lüppo-Cramer l ) proved 

 that the silver subhaloid of Poitevin's photochromies undergoes 

 regression to silver haloid by oxidation. J. JM. Eder 2 ) described the 

 same thing in his investigations of the latent image with the nitric 

 acid reaction. 



Quite a different view of the progressive photochemical analysis 

 of silver haloids, was given by H. Luggin 3 ). He stated that in the 

 case of more intensive exposure, also a proportionately greater 

 amount of formed silver haloid, under the influence of the increasing 

 halogen pressure takes from the silver haloid the power of afrording 

 germ-points for the deposit of metal, and that consequently halogen- 

 absorbents (chemical sensitizers) would be the best means of keeping 

 the halogen pressure as low as possible, and so of preventing solari- 

 zation. Consequently he considers solarization as a phenomenon con- 

 sisting in the prevention of germ-formation. His statement: "The 

 beginning of solarization may often be obviated by selecting smaller 

 stops and increasing the exposure accordingly," is confirmed in the 

 case of silver iodide gelatine 4 ). 



Still this proposition that halogen absorption prevents solarization 

 is at variance with what goes before. I have therefore investigated 

 this matter more closely. 



Silver haloid is decomposed by the action of light, but a polished 

 silver bar exposed in the light to halogen vapours, at once combines 

 with it to form halogen silver. Consequently in the presence of an 

 excess of halogen the silver haloid is not decomposed. 



A highly sensitive silver bromide gelatine plate, which was partly 

 coated with collodion, was exposed to direct daylight. It was observed 

 that the photo-chemical decomposition under the collodion remained 

 considerably behind that of the free surface, and had not even 

 increased appreciably after an exposure of several weeks. The violet 

 brown discolouration appeared only at the free surface, and could be 

 removed by the plate being rubbed carefully. A plate, exposed at the same 

 time on the glass side, also showed retardation as to the photo- 

 chemical decomposition process, and against the glass the silver 

 bromide seemingly remained unaltered. Consequently the fact that 

 halogen prevents diffusion counteracts decomposition. In the case of 



!) Phot. Korresp. 1907; S. 439. 

 s ) See note 4, p. 



3) J. M. Eder, Jahrb. f. Phot. u. Repr. 1898; S. 162. 



4) J. M. Eder, Handb. d. Phot. 1906. Bd. I; T. 2; S. 309. 

 Lüppo-Cramer, Phot. Probleme. 1907; S. 152. 



