THE HOMOGENEITY OF VISUAL PIGMENT SOLUTIONS 



pletion by a single exposure to white light (see Fig. 6.6) are shown in 

 Fig. 6.7 by the full-Une curve. 



The small difference between the direct measurements of the total 

 changes (fuU-hne curve in Fig. 6.7) and the sum of the separate 

 changes (dotted curve in Fig. 6.7) are due to thermal decomposition 



500 550 



Wavelength in m^ 



Fig. 6.7. Composite nature of the bleak total difference spectrum. 

 Full-line curve, density changes in a bleak extract when completely 

 bleached by white light. Curve 1 (•), density changes in another 

 sample of the same extract when exposed to orange-red light ; curve 2 (O), 

 additional changes on further exposure to the orange-red light; curve 

 3 (+), additional and final changes on further exposure to white light. 

 Dotted-line curve, algebraic sum of curves 1-3. pH 8-15, r= 20°C. 

 {Dartnall, 1955) 



of the photosensitive pigments between sampling times (1 day). 

 Apart from this, the summed changes of density agree with the direct 

 changes resulting from a single exposure to white Hght. This shows 

 that the total end result was not dependent on the mode of bleaching. 

 The experiments also show that the bleak solutions could be 

 bleached in dissimilar stages. Thus (Fig. 6.7) the density losses were 



173 



