(18 ) 



by optical sensitizers, but in this case the silver iodide-bromide plate 

 behaves more like a silver iodide plate. 



At the 79 th German Physical and Medical Congress held in Dresden 

 in 1907 W. Scheffer 1 ) communicated a solarization theory founded 

 upon his microscopic investigations 2 ), which explains solarization in 

 quite a simple way. 



When the exposed silver bromide gelatine plate is being developed 

 certain grains ("Ausgangskörner") send out germs, upon which the 

 reduced substance is deposited, because other grains ("JNahrkörner", 

 formerly called "Lösungskörner") are dissolved in the developer and 

 cause the growth of the germs. In an overexposed emulsion too 

 many germ-producing grains "explode", and an insufficient number 

 of "feeding" grains remain, so that no image of sufficient density 

 can be formed. Consequently this theory is founded upon the transition 

 of "feeding" grains into germ-producing ones by exposure, or rather 

 of silver haloid into silver subhaloid. 



This theory cannot be reconciled to the fact found by J. Sterry 3 ), 

 J. M. Eder 4 ) and Lüppo-Cramer 6 ), that solarization can also appear 

 with primary fixation, for in this case the feeding substance is sup- 

 plied from without. The same holds good with regard to daguer- 

 reotypy. 



B. Homolka's solarization theory 6 ): "In the decrease of the amount 

 of silver bromide I recognize the primary cause of solarization", is 

 irreconcilable to the above, not to mention the circumstance that 

 these two theories cannot explain the second reversion of solarization, 

 and cannot account for the fact that even with the strongest over- 

 exposures an excess of silver haloid, i.e. of feeding substance, can be 

 proved to be still present in the emulsion. 



From the solarization with primary fixation it therefore appears, 

 that the silver haloid germ loses this germinating property on further 

 exposure, i. e. through the continued photochemical decomposition it 

 has passed into another subhaloid containing less halogen, which 

 possesses no germinative property. 0. Wiener 7 ) proved the possibility 

 of the existence of more subhaloids. Let us call the first the «-silver 

 subhaloid and tile second the ^-silver subhaloid. 



i) Phot. Korresp. 1907 ; S. 487. 



2) Phot. Rundschau. 1907 ; S. 65 u. 142. 



Phot. Korresp. 1907. S. 233 u. 384. 

 3). J. M. Eder. Jahrb. f. Phot. u. Repr. 1899; S. 289. 



4) J. M. Eder. Handb. d. Phot. 1906; Rd. I; T. 2; S. 312. 



5 ) Lüppo-Cramer. Phot. Probleme, 1907; S. 150. 



6) Phot. Korresp, 1907; S. 168. 



7) J. M. Eder. Jahrb. f. Phot. u. Repr. 1896; S. 55. 



