190 



Biological Stains 

 Br Br 



NaO 



COOCH3 



C2iH905Br4Na; Mol. Wt. 683.943 

 {An acid dye; absorption maxima about 520y [JfSS.d]) 



There is no evidence that this dye has been furnished to biol- 

 ogists as a stain. The alcohol soluble eosin known in the biological 

 laboratory is apparently the following. 



Rio ETHYL EOSIN C. I. NO. 770 



Synonyms : Eosin, alcohol soluble. Eosin S. 



This is similar to methyl eosin, but is the ethyl ester: 



Br Br 



NaO 



O 



COOCHoCH, 



C22Hii05Br4Na; Mol. Wt. 697.969 

 {An acid dye; absorption maximum 524--527) 

 Solubility at 26° C: in water 0.03%; in alcohol 1.13% 

 A spectral curve of this dye is given in graph 3, Fig. 24. 



Ethyl eosin is apparently the alcohol soluble eosin ordinarily 

 sold by biological supply houses. For some time after the first 

 World War it was difficult to secure this dye in America, and one 

 stain company for a few years furnished the color acid of eosin Y 

 when alcohol soluble eosin was ordered. (The color acids of all 

 these dyes are alcohol soluble but almost insoluble in either hot or 

 cold water; methyl and ethyl eosin, on the other hand, are slightly 

 soluble in cold water but strongly soluble in hot water and alco- 

 hol.) This error has now been corrected, and true ethyl eosin 

 as obtainable from .American manuf acturer§, is on the Commission 



