CH, 



\ 



N 



CH, 



.S. 



Tri-methyl thionin 

 (Azure B, Kehrmann) 



Asymmetric di-methyl-thionin 

 (Azure A, Kehrmann) 



CH, 



H 



\ 



I 



/ 



N 



X^ 



Symmetrical di-methyl thionin 

 (not an azure dye) 



Bernthsen (1906) and MacNeal (1906) simultaneously and in- 

 dependently described the easy method of preparing azure by 

 oxidizing methylene blue by chromate in acid solution and Mac- 

 Xeal (1925) has perfected this method so that it is now possible to 

 obtain large yields of Azure A and a fair yield of Azure B. 



Azure I (Giemsa) is a trade name applied to a secret prepara- 

 tion which appears to be a somewhat variable mixture of Azure A 

 and Azure B. Azure II (Giemsa) is an intentional mixture of 

 Azure I (Giemsa) with an equal quantity of methylene blue. 



The azures are important constituents of all the polychrome 

 methylene blue stains and are present in undetermined and variable 

 amounts when these solutions are empirically prepared. For the 

 preparation of the tetrachrome blood stain of MacXeal (see p. 90), 

 a definite quantity of Azure A (Asymmetric di-methyl-thionin) is 

 required. 



METHYLENE VIOLET (Bcrnthscn) 



Methvlene violet is formed whenever methvlene blue is heated 



with a fixed alkali or alkali carbonate. It is a feeble base with the 



formula 



CH3 



N 



CH, 



.0 



"N= 



Its preparation from methylene blue is more difficult than that of 

 Azure A. A fair yield (30 to 40 per cent) may be obtained by 

 oxidizing methylene blue in dilute ammoniacal solution with 

 potassium chromate and then driving off the ammonia by boiling 

 with the addition of sodium carbonate. It may also be prepared 

 from Azure A by boiling this with dilute alkali carbonate. Methy- 

 lene violet precipitates out as needle crystals, insoluble in water. It 



49 



