662 



LATENT PERIOD OF MYA 



terials formed by this photochemical activity may be considered di- 

 rectly proportional to the length of exposure. Since the reciprocal 

 of the latent period represents the rate of the process which determines 

 it, the data of Figs. 3 and 4 show that the velocity of the latent period 

 process is a linear function of the concentration of freshly formed 

 precursor materials. 



This at once rules out the diffusion explanation. There is one 

 case in which the rate of diffusion is a linear function of the con- 





0.9 



I 



o o.os o./o o./s 

 J^xposare ■■ — - 6ecoods 



Fig. 3. The relation between the reciprocal of the latent period and the ex- 

 posure period. The points are derived from the averages of the reaction time 

 given in Fig. 1. 



centration. This is when the concentration of diffused material is 

 maintained at zero or nearly zero by continually removing the dif- 

 fused substance, or by allowing the diffusion to proceed into a com- 

 paratively large volume. This is obviously not the situation here, 

 because it is essential that the precursor substances accumulate in 

 sufficient quantity to initiate a response. An additional objection 

 to the diffusion idea is the temperature coefficient of the latent 

 period. The latent period shows a value oi \j. = 19,680 (Arrhenius, 



