THE VISUAL PIGMENTS 



retinenci and then to add 0- 1 N caustic soda solution. After allowing 

 the mixture to stand for 15-30 min its density spectrum was measured. 

 The solution was then acidified (with one drop of concentrated 

 hydrochloric acid in order to avoid gross changes in concentration) 

 and its density spectrum measured again. The results of a typical 

 experiment are shown in Fig. 4.3. Curve A shows the density spec- 

 trum of the compound formed by retinenej and methylamine 

 (CH3 — NHg) in alkaline solution. This compound has a maximum 

 at 360-365 m^. Curve B shows the density spectrum after acidifica- 

 tion. This has a maximum at 435 m/j,. 



A number of compounds containing amino groups were tried (see 

 table). When interaction between the amino-compound and retinene^ 



Wavelengths of maximum absorption of mixtures ofretinenci 

 and amino compounds in aqueous ethanol 



(from Ball, Collins. Dalvi and Morton, 1949) 



106 



