( 17) 



for the fact that the image developed with certain developers loses 

 density in the fixing bath; this loss of density is analogous to what 

 is observed in the case of P. 0. P. papers with silver chloride. 



This further explains another apparent contradiction. While with 

 silver chloride a lower and with silver bromide a higher degree of 

 sensitiveness to light is observed, in other words, while quantitatively 

 the same photochemic decomposition of silver bromide takes place 

 with less absorption of light energy than in the case of silver chloride 

 the exact opposite is seen to take place with the increase in density 

 during development, which has been pointed out by H. and R. E. 

 Liesegang l ), König s ) and Lüppo-Cramer 3 ). Considering that silver 

 chloride possesses a higher solubility, resp. has the power of bringing 

 a greater number of ions into solution than silver bromide, it is 

 easy to understand that quantitatively reduction can take place in a 

 larger measure per unit of time, notwithstanding silver chloride 

 is a more constant compound than silver bromide. 



With silver iodide the same thing is observed still better. The 

 reducibleness, resp. solubility is still less in this case, which has often 

 occasioned the unjustified conclusion, that silver iodide is less sensitive 

 to light than silver bromide, while the exact opposite is observed in 

 the case of daguerreotypy and the wet collodion process, since here 

 the feeding substance for development is introduced from without. 

 Accordingly Lüppo-Cramer could use with silver iodide developers 

 like amidol potassium carbonate, triamidophenol, diamidoresorcin, 

 and triamidoresorcin, which show a far too great rapidity of reaction 

 for silver bromide plates. 



The higher sensitiveness of silver iodide-bromide plates as compared 

 with silver bromide plates, owing to which more detail can be obtained 

 in the darkest parts of the image, may therefore be ascribed to the 

 more rapid formation of germs in the case of silver iodide, while the 

 silver bromide serves as feeding substance for the developer. This further 

 appears from the optical sensitizing of silver iodide-bromide plates. 



While silver bromide can easily be made colour sensitive, this is 

 not the case with silver iodide, which has been pointed out by 

 J. M. Eder 4 ), Lüppo-Cramer 6 ), and others. Still both may be dyed 



!) Phot. Mitt. 1901; S. 362. 

 Phot. Wochenbl. 1901; S. 405. 

 J. M. Eder. Jahrb. f. Phot. u. Repr. 1902; S. 572. 



2) Phot. Korresp. 1903; S. 14. 



3 ) J. M. Eder. Jahrb. f. Phot. u. Repr. 1903; S. 401. 



l ) J. M. Eder. Handb. d. Phot. 1906; Bd. I; T. 2; S. 269. 

 5 ) J. M. Eder. Jahrb. f. Phot. u. Repr. 1903; S. 46. 



...-.-, 1904; S. 390. 

 Zeitschr. f. wiss. Phot. 1903; Bd. I; S. 17. 



2 



Proceedings Royal Acad. Amsterdam. Vol. XI. 



