Miscellaneous Dyes 233 



salts of mineral acids are very unstable; they can often be stabil- 

 ized, however, by converting into zinc chloride double salts, and 

 those which are commercially available are ordinarily in this form. 

 In the formulae given below the unstable salt is listed in each case, 

 for the sake of simplicity. The diazonuim salts contain only one 

 — N = N+ group, the tetrazonium salts two. These salts are color- 

 less, but as the azo group (— N = N-), is a chromophore, their 

 transformation to colored compounds is easily effected. Their use 

 as histochemical reagents depends on the production of such 

 colored derivatives. 



Among the papers introducing diazonium salts into histochemis- 

 try is that of Manheimer and Seligman (1948) who proposed a 

 method of demonstrating alkaline phosphatase in normal and 

 neoplastic tissues. This was shortly followed by an adaption of 

 the method to acid phosphatase (Seligman, 1949). The reagent 

 used in this work was: 



a-NAPHTHOL DIAZONIUM CHLORIDE 



NCI 



Their histochemical applications are far from standardized, nor 

 is it certain yet which of them will be eventually preferred for the 

 purposes for which they are now employed in a rather experimental 

 way. All that seems advisable to do here is to list, with the for- 

 mula of the unstabilized salt, those that are known to be at 

 present commercially available. 



DIAZO SALT OF P-CHLORO-O-NITROANILINE 



NO2 



/ 

 Cl_/— \_N =: N— CI 



Trade name: Red 3GS salt (Nat. Aniline) 



DIAZO SALT OF 5-NITRO-2-AMINO NITROBENZENE 



NO2 



/ 



CH3_/~\_N = NCI 

 \_/ 



Trade name: Bordeaux GPS salt (Nat. Aniline) 



DIAZO SALT OF 5-NITRO-2-AMINO METHOXYBENZENE 



OCH3 



/ 

 02N_/~\_N=NC1 



