6 PHOTOCHEMISTRY OF VISUAL PURPLE. I 



ments reported in this paper this was roughly ten revolutions per 

 minute. By this means an even exposure is obtained for this thin 

 column of solution. This obviates the necessity for stirring the solu- 



J 



^^^G/c755 Rod 



Glass Sleeve 



Buret Clamp 



^ DO sure Tube 



V/ sua I Purple 5o/uf/or> 



Fig. 1. Full size diagram of apparatus used for the exposure of visual purple 

 solutions to light. The exposure tube being attached to the glass rod, it is pos- 

 sible to rotate the tube on its own axis by rotating the glass rod. 



tion, and removes all errors associated with unequal illumination, dif- 

 fusion, etc. (cf. Sheppard, 1914, p. 239). In this respect the small 

 quantities of material and the thin test-tubes are of distinct advantage. 

 After the proper length of exposure the light is turned off, the tube 



