sorption curve are characteristic of the individual dye, while the 

 magnitude of extinction coefficients (the height of the curve) varies 

 directly with the amount of dye present. The absorption curves 

 of dyes which are very closely related in structure are sometimes so 

 similar as to be practically identical. In such instances the indi- 

 vidual dyes may be recognized by means of quantitative deter- 

 minations of the degree in which their absorption is modified under 

 the influence of suitable variations in conditions. 



i.5r 



420 



4(0 



500 



Fig. 5. Absorption curves of: 



1. Thionin 



2. Methylene blue. 



3. Apparent mixture of these two dyes, incorrectly marketed (altho in good faith) 

 as a dye intermediate between them in chemical composition. 



The absorption curves of typical yellow, orange, red, violet, and 

 blue dyes are recorded in Figure 3. It will be noted that their maxi- 

 mum absorption in each case falls within the range of the comple- 

 mentary color (cf. Fig. 1). The great majority of dyes of these 



30 



