SELIG HECHT 9 



in which a is the original 100 per cent concentration, and a-x the per 

 cent of material still unbleached. It is apparent that the experi- 

 mental results follow the curves pretty well. 



To show this in the usual way Table I is given presenting the 

 results of a fourth experiment. It will be observed that the values of 

 the velocity constant k are fairly constant. This uniformity is par- 

 ticularly striking if two things are kept in mind: first, that the meas- 

 urements are single determinations only, not averages; and, second, 



20 40 60 eo /oo 



d'xposure — - /^/nutes 



/20 



Fig. 4. Results of Experiment 56. Intensity, 12 meter candles; ^=0.011. 



that they are read usually to the nearest 5 per cent concentration. 

 For further comparison there are inserted the values calculated from 

 the formula assuming the average value of ^ (= 0.030). The simi- 

 larity between the observed and calculated values is obvious. 



2. Each of the experiments so far considered represents the changes 

 in a single tube of visual purple. The solution is exposed for an inter- 

 val, its concentration determined, then exposed for a second interval, 

 and the process repeated until no further change occurs. Such a 



