402 



bases was determined. For example, phenosaffranine (diamido-phenyl- 

 phenazonium chloride) was synthesised and found to exert a similar influence 

 upon trypsin, precipitating it wholly from solution under favourable conditions 

 of hydrogen ion concentration. 



Dimethyl-diamino-phenyl-phenazonium chloride, synthesised by the mild 

 oxidation of dimethyl-p-phenylene diamine and aniline ; amido-dianilido- 



N 



NH 



NH 



phenyl-phenazonium chloride prepared from amidoazobenzene and aniline 

 hydrochloride, also precipitated the trypsin from its aqueous solution. 



Simpler azine bases, the eurodines, also cause this precipitation. Thus 

 dimethyl-diamido-phenazine hydrochloride (1), and dimethyl-amido-toluazine 

 hydrochloride (2), were similarly active. All the water-soluble bases 

 which contained the heterocyclic azine nucleus were able to remove the trypsin 



N ^ /X A /v 



CH, 



Wn 



NH,'HCl 



NHiHCl 



(1) (2) 



from solution. The reduced to leuko compound produced by reduction of the 

 azonium base is incapable of this activity. In this compound the latent valencies 

 of the nitrogen atoms of the heterocyclic azine ring have become saturated with 

 hydrogen. Thus : — 



N 



H,N 



^Cl 



REDUCTION 



Dye chloride (red). 



Leuko base (colourless). 



This addition of hydrogen destroys its basic properties. The reduction is 

 accompanied by a colour change from red to colourless. The substance on re- 

 oxidation regains its red colour, and at the same time its precipitating power. 



