Spedrophotometric Analysis 



61 



In Fig. 6 is given the absorption curve of a dye mixture, together 

 with the curves of the component dyes. The mixture is reported 

 to have been marketed in good faith as asymmetrical dimethyl 

 thionin, a dye which is intermediate in constitution and in color 

 between thionin and methylene blue (see under azure A, on p. 109). 

 The absorption curve plainly indicates the presence of two dyes, 



C 



0) 



o 



o 



c 

 o 



■*- 

 u 



c 



•*- 



K 



UJ 



1. 



2. 

 3. 



440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 



Wave Lengths in Millinnicrons 



Fig. 6. Absorption curves of: 



Thionin. 



Methylene blue. 



Apparent mixture of these two dyes, incorrectly labelled (although in good 



faith) a dye intermediate between them in chemical composition. 



and suggests their probable identity. (It would be advisable to 

 effect the separation of small amounts of both dyes, if their positive 

 identification is desired.) The color of the mixture is very 

 similar to that of dimethyl thionin. The absorption curve of that 

 dye, however, is a simple and well-defined curve resembling those 



