10 



PHOTOCHEMISTRY OF VISUAL PURPLE. I 



mode of procedure assumes two things: one, that there is no period 

 of induction in the photochemical action; and the other, that there 

 is no after effect. If either of these is associated with the reaction, 

 a different type of result, — qualitative perhaps, certainly quantitative, 

 • — is to be expected depending on whether the exposure is continuous 

 or interrupted. 



In order to settle this point several series of experiments were 

 made in the following way. Seven or eight tubes of similar concen- 

 tration and depth were prepared. One or two were run through in 

 the ordinary way. The remaining tubes were exposed for a series of 



TABLE I. 



Experiment 85, Showing the Course of the Decomposition of Visual Purple by Light. 



increasing intervals; one for, say, 5 minutes, another for 8 minutes, 

 another for 12 minutes, and so forth. In this way each solution was 

 brought to a stage of decomposition by a continuous exposure as 

 opposed to a series of intermittent exposures. 



An example of such an experiment is given in Fig. 5. The black 

 rectangles represent a single tube exposed intermittently in the or- 

 dinary way. The white rectangles each represent a separate tube of 

 visual purple exposed continuously up to the point when its concen- 

 tration was determined. The curve is again that of a monomolecular 

 reaction, and it is apparent that it represents accurately the course 

 of both types of experiment. 



