THE PHYSICAL CHEMISTRY OF VISUAL PURPLE 



and was then reflected back through the solution. This augmented 

 the bleaching effect and also tended to eliminate the concentration 

 gradient in the visual purple solution arising from a one-way trans- 

 mission. The progress of the bleaching was followed by periodic 

 measurements of the transmission at right angles, i.e. along the 



10 

 20 

 30 

 40 

 I 60 



e 



30 - 

 40 



50 



100 



100 



Time (minutes) 



200 



Fig. 3.10. Transmission/time curves at 1^° and 32°C for visual purple 

 solutions bleaching under constant intensity lights of various wave- 

 lengths, as indicated. Transmissions were measured with light of 

 500 m/i wavelength. The broken line shows the change in transmission 

 in darkness at 32°C. 

 {St. George, 1952) 



10 mm dimension. In the bleaching experiments at 2°C the solution 

 was warmed up to 30°C on each occasion before a transmission 

 reading was taken, to allow intermediates (transient orange) to be 

 converted to the final product. 



Examples of the transmission/time curves obtained are given in 

 Fig. 3.10. These show that the reaction is independent of tempera- 

 ture with a bleaching Hght of wavelength 530 mju but is much affected 

 by temperature with bleaching Ughts of 678 m/u or 712 m/<. In 



87 



