1904] The Chemical Dynamics of Photographic Development. 455 



Table I. 



and confirming a, 5, d. 



Developer, 4'0 c.c. FeS0 4 , M/l. 

 40-0 K 2 C 2 4 , M/l. 



1-0 KBr, N/10. 

 to 50-0 with H 2 0. 



Table II. 



D 6 = 50 CMS. 



Do = 10 CMS. 



These facts are in agreement with Hurter and Driffield's statement that 

 development tends to a limit depending upon the exposure. They con- 

 sidered that their results were represented by the formula D = D^ (1 - a*)* 

 where D = density at time t, D^ = ultimate density, and a is a constant. 

 They stated that this was arrived at " on the idea that the number of 

 silver bromide particles affected by light is greatest in the front layer 

 of the film and decreases in geometrical progression as each successive 

 layer is reached," and " that the developer reduced the particles as it 

 penetrated the film." Apart from the inherent improbability of this 

 process taking place so regularly, it would, as was pointed out by 

 Luggin,f give results in contradiction to the law of constant-density 



* ' J. Soc. of Chem. Ind.,' May, 1890. 

 f ' Zeit. f. Phys. Chem.,' 23, p. 622. 



