SELIG HECHT' 



289 



It may therefore be concluded that the temperature coefficient 

 for 10°C. for the bleaching of visual purple by light is practically 1.00. 

 This corroborates our idea that the bleaching reaction is a simple 

 photochemical transformation, consisting most probably of a single 



reaction. 



2. There is an additional point to be made with regard to the 

 magnitude of the temperature coefficient. In any photochemical 



JOO 



^ 



C 



eo 



6o 



■40 



zo 



/O 



20 



Ey.posure 



JO 



rp/nc/fes 



^o 



50 



Fig. 1. Temperature and the velocity of photochemical decomposition of 

 visual purple. The curve is a mono molecular isotherm; the rectangles are the 

 experimental results of one set of experiments. 



reaction there is always the possibility that the reaction proper takes 

 place with a practically instantaneous velocity at the walls of the 

 vessel, and that the kinetics of the reaction really represent the diffu- 

 sion velocity of the photosensitive substance to the place of reaction. 

 The temperature coefficient of diffusion velocities, though lower 

 than those of ordinary chemical reactions, is usually higher than 1.00, 



