THE VISUAL PIGMENTS 



unit yields a bleached fraction having a P1/P2 ratio 6-4 times that of 

 the original solution. At time 5, the enrichment factor is 99-5/40, 

 only 2^; at time J it is 40/5 = 8. The maximum possible value of the 

 enrichment ratio in the bleached fraction is obviously equal to the 

 ratio of the photosensitivities of the tv^o pigments, i.e. 10 in the present 



Percent P, bleached 



Fig. 6.5. Relation between the percentage amounts bleached of two 



pigments in a binary mixture. Curves are shown for various ratios of 



the photosensitivity of Pj to that of P^. 



case. This maximum is only achieved in a vanishingly-small amount 

 of bleaching. For this reason, the characterization of the more 

 photosensitive pigment is generally difficult. Thus, if, for example, 

 the original solution contained 1 part of P-^ and 10 parts of P2, the 

 best difference spectrum for P-^ which could be obtained, given a 

 photosensitivity ratio of 10: 1, would consist of equal contributions 

 from Pi and Pg- 



In Fig. 6.5 (constructed from the curves of Fig. 6.4), the relation 

 between the percentage amounts bleached of two pigments, P^ and 



168 



