( 26 ) 



grain plate, i. e. one with a small grain surface, in other words, 

 with a small quantity of ,? silver subhaloid, which has been exposed 

 till solarization has set in, is treated, the reaction in the gelatine will 

 be complete sooner than with a greater quantity of j? silver subhaloid 

 in the same gelatine plate, as is the case with fine grain emulsions. 

 The reducibleness will consequently show an increase (not to be 

 confounded with acceleration), so that in proportion to the strength 

 of the thiosulphate solution employed, and the duration of the action, 

 the solarization will be removed, either to a smaller or to a greater 

 extent, or totally. 



This phenomenon was observed experimentally by Kogelman x ), 

 Vidal 2 ) and E. Exglisch 3 ), while Lüppo Cramer 4 ) could not demon- 

 strate solarization at all with primarily fixed, highly sensitive, coarse- 

 grain plates, which fix more slowly than fine-grain ones. 



Sulphocyanides act analogously in reducing solarization. 



In the case of Sabatier's polarization the strong decrease (dis- 

 appearance ?) of development of the image after it has appeared is 

 not to be ascribed to the decrease of the number of germs, as they 

 have already fulfilled their function 5 ). So the decrease of develop- 

 ment can only be a reduction of the speed of development, which is 

 to be accounted for by a strong decrease in the supply of feeding 

 substance. From the theory given above of the so-called chemical 

 method of development it has appeared that the silver subhaloid 

 proves to be less soluble in the developer than the silver haloid. 

 Therefore the more soluble silver haloid can, after reduction, be 

 precipitated upon the germ, which still remains unchanged in its 

 place. Consequently if the secondary exposure is of an intense nature, 

 the feeding substance will be enveloped by subhaloid, by which 

 development is retarded. This will take place in the developer all 

 the more readily, because it is an absorbent of halogen. 



In conclusion reference may be made to a possible explanation of 

 the variations in the optical sensitizing of the photographic plate 

 which is characterized by a considerable decrease in reducibleness 

 being noticeable in the places where the power of absorption is spec- 



i) J. M. Eder. Jahrb. f. Phot. u. Repr. 1895; S. 419. 



2) Bull. Soc. franc. Phot. 1898; p. 583. 



3 ) J. M. Eder. Jahrb. f. Phot. u. Repr. 1901 ; S. 608. 



. . . . . 1902: S. 79. 

 . . . . . 1904; S. 423. 



4 ) Lüppo-Cramer. Phot. Probleme. 1907; S. 150. 



5 ) So far there is not a single reason for assuming that this reduced substance 

 consists exclusively of « silver subhaloid gerirs, which pass into /3 silver subhaloid 

 by the secondary exposure, by which further development would be checked. 



