NaSO., 



ch/ 



SO,Xa 



(An acid dye; absorption maximum of water blue 2B 



about 5Jf.6.5.) 



It is a widely used histological stain, having valuable counter- 

 staining properties. It is also of use as an indicator, due to the dis- 

 appearance of the color upon complete neutralization, as in the 

 case of acid fuchsin. As an indicator, however, it has the disad- 

 vantage that the blue color is but slowly restored upon addition of 

 acid. 



Its chief histologica uses are : by Stroebe and Huber as a cyto- 

 plasm stain preceding safranin; by Galli for axis cylinders; fre- 

 quently by botanists as a contrast for safranin in vascular plant 

 tissue, or for magdala red in algae; and very widely by pathologists 

 in the Mallory connective tissue stain, in which it is combined with 

 orange G and acid fuchsin; by Unna in contrast to orcein for stain- 

 ing epithelial sections, and in studying the process of chromolj^sis. 



(c) Hydroxy Phenyl Methanes (Rosolic Acids) 



The rosolic acid dyes, as stated above, are tri-phenyl methane 

 derivatives in which the amino groups of the rosanilins are re- 

 placed with hydroxyl groups, thus giving them acidic instead of 

 basic character. The compounds of this group are not very im- 

 portant as dyes and are scarcely used as stains. The greatest 

 interest of the biologist in them is due to their use as indicators, 

 since in acid solution the quinoid ring disappears and the compound 

 becomes colorless, while alkali changes it back to the colored form. 

 Thus: 



H /—\ OH 



HO 



OH 



+2XaOH = 



leuco-rosolic acid 



+ sodium = 

 hydroxide 



_C 



+2H.0 



disodium rosolate 



7S 



