1904.] The Chemical Dynamics of Photographic Development. 461 



a fairly constant maximum period was reached. This initial induction 

 was already noticeable in N/500 bromide, and increased as the con 

 centration of the bromide increased. Further, it was modified by the 



value of D^, i.e., of (AgBr), being shorter for higher values of this. 

 Values of K were obtained from " maximum " period. 



Results. 



Developer, N/25 Ferrous oxalate. 

 N/1000 KBr. 



I. a. K = 0-0280 (0-0230-031). Increase due to fog, 

 b. K = 0-0280 (0-0300-026). 



II. KBr = N/100. HI. KBr = N/50. 



a. K = 0-0145 (0-01420-017). a. K = 0-0123 (0-01100-0147)1 



b. K = 0-0142 (0-01690-0137). b. K = 0-0113 (O'OIO 0-0130). ' 



And with N/12'5 Ferrous oxalate 



Series I. KBr = N/50. 



a. K = 0-0181 (0-01660-0203). b. K = 0-0182 (0-0195 0-0176). 

 Tabulating results we get 



Developer lsT/12'5 Ferrous oxalate. 



Concentration of Br. Telocity constant. 



0-002 N 0-0404 



0-020 N 0-0181 



And for the lower concentration N/25 Ferrous oxalate. 

 Concentration of KBr. Z. K x log Br. 



0-001 N 0-0280 0-0280 



0-002 N 0-0203 0-0265 



0-010 N 0-0143 0-0285 



0-020 N 0-0118 0-0274 



C = 0-0276 



It will be seen that the results obtained with bromide are fairly 



represented by the simple empirical formula K x logio Br = constant, 

 i.e., as the bromide is increased in geometrical progression, the velocity 

 diminishes in arithmetical. 



We may discuss here the theoretical grounds from which the 

 behaviour of bromide might be deduced. 



It has been suggested that the action of bromide is due to the 

 reversal of development, silver bromide being re-formed and develop- 



