SELIG HECHT 287 



In order to control the temperature of the exposed solution the 

 capillary tube containing it is kept in a water bath. This is a cylin- 

 drical glass vessel, 12 cm. in diameter, and of 900 cc. capacity. The 

 temperature of the bath is maintained constant by the addition of 

 water at a higher or a lower temperature from a nearby reservoir. 

 In this way the temperature is easily kept within 1°C. Such a bath 

 is accurate enough for our purposes, as will presently be evident. 



The exposure tube of visual purple is immersed, attached to the 

 rotating apparatus, and kept in the dark for 5 minutes for its contents 

 to reach the temperature of the bath. This is more than enough 

 when we recall that a thermometer having a larger diameter than 

 the capillary tube comes into thermal equilibrium in much less time. 

 After 5 minutes the shutter is opened, and the light allowed to act 

 on the solution, which is rotated in the usual manner. After the 

 proper exposure, the light is shut off, and the concentration of the 

 exposed solution determined. As in the previously reported work, 

 readings are made to the nearest 5 per cent. The tube is then returned 

 to the bath, allowed 5 minutes in the dark to come to the temperature 

 of the bath, and again exposed for an interval. The concentration 

 is again determined, and the process repeated until the solution is 

 fully bleached. 



The source of illumination is a 250 watt, concentrated-filament, 

 stereopticon Mazda lamp run on the ordinary lighting circuit. The 

 intensity used throughout these experiments on temperature effects 

 is 50 meter candles. At this intensity bleaching is complete in half 

 an hour. 



III. 



A number of preliminary experiments showed definitely that the 

 effect of temperature on the velocity of the bleaching process is very 

 small indeed. In this I can confirm the roughly quantitative, early 

 work of Kiihne (1879). For example, in a series of three experiments 

 performed, one at 7°G., another at 23°C., and a third at 36°C., the 

 velocity constants for the bleaching process were 0.038, 0.041, and 

 0.039 respectively. This gives a value for the temperature coeffi- 

 cient as Qio = 1-00. The same value for ^lo was found for a set of 

 experiments in which the velocity of decomposition was determined 



