Nitro and Azo Dyes 97 



like it thus recognized being C. 1. No. 353 (chlorazol fast pink 

 4BL) which differs from it primarily in that it is not methylated, 

 has two hydroxyl groups attached to the naphthalene rings, and 

 two sulfonic groups attached to the benzene rings. It has been 

 called for in certain vital staining procedures, having been intro- 

 duced for that purpose by Evans and Scott in 1921. 



u65 NIAGARA BLUE 4B C. I. NO. 510 



Synonyms : Pontamine sky blue 5BX. Direct sky blue. 



Benzo sky blue. 



H.N OH OH NH, 



\ I N = N_/~\^/~\_N = N 



./ \/\ OCH3 OCH3 



NaS03 S03Na NaSOi SOjNa 



C34H24N60i6S4Na4; Mol. Wt. 992.808 

 {An acid dye; absorption maxima about 6SJ!t,.2 and 589.5) 



Occasional references have been made to this dye in connection 

 with histology for some time, although it has never come into 

 general use. Recently Varrelman (1938) has employed it for 

 demonstrating the vascular system of plants, taking advantage of 

 its rise through stems which are stood in a solution of the dye. In 

 the vital staining of skin or of tumors a pontamine sky blue has 

 been recommended, which may be this dye or may be C. I. No. 518 

 which has been sold under the name of pontamine sky blue 

 6BX (Syn. Niagara sky blue 6B or direct sky blue). 



d68 MARSHALL RED 



d70 HICKSON purple 



These are two new dyes of unknown composition, but stated to 

 belong to the disazo group. They are discussed by Cannon (1941) 

 as having been manufactured in the course of his study of chlorazol 

 black E and of dyes of other colors found to be associated with that 

 dye. He claims that they are valuable nuclear stains in general 

 histology. 



d75 chlorazol black E C. I. NO. 581 



Synonyms: Pontamine black E, EX, or EXX. Erie black GXOO, 



B, BF. Direct black MS, RL, E, GX, EE, 2V, F or A. Direct 



deep black EW extra, E, EA, EAD extra. Renol black G. 



