74 BEHAVIOUR OF IRON SALTS, IN THE PRESENCE OF 



the air for some time ; the white or pale blue precipitates thrown 

 down by hydrochloric acid from solutions of soluble Prussian 

 blue decolorized by albumen; and the fact that this latter 

 precipitate turns to a deeper blue on treatment with hydrogen 

 peroxide or on exposure to the air, constitute additional evidence 

 of the existence of a chemical complex. The return of the blue 

 colour to colourless solutions of soluble Prussian blue and gela- 

 tine, and to the substance precipitated by hydrochloric acid from 

 colourless solutions of soluble Prussian blue and abumen, indi- 

 cates that in the soluble Prussian blue protein complex the 

 trivalent iron of the soluble Prussian blue has undergone reduc- 

 tion and is present in the bivalent condition. 



The results obtained in this investigation indicate 'that 

 native and derived proteins prevent the ordinary reactions of 

 substances containing trivalent iron, owing to the formation of 

 associations between the protein and the iron salt. There is 

 reason to believe that this phenomenon is partly physical and 

 partly chemical: physical in that the colloid attracts the iron 

 salts and forms adsorption compounds ; and chemical in that the 

 proteid actually combines with the iron salt. These physical 

 and chemical complexes are readily broken down by hydrochloric 

 acid. Complexes of soluble Prussian blue with gelatine are also 

 decomposed in solution by hydrogen peroxide, but those with 

 albumen are not. One the other hand, these complexes seem 

 fairly stable towards heat, and in the case of those formed 

 with soluble Prussian blue a temperature of 100 does uot 

 effect decomposition. Through the formation of complexes of 

 proteins with soluble Prussian blue, the trivalent iron of the 

 latter is probably reduced to the bivalent condition. ~No 

 indication that complexes are formed by proteins and salts 

 containing bivalent iron has been obtained. Neither cane 

 sugar, glycerine, nor tartaric acid appear to form chemical or 

 adsorption compounds with either ferro- or ferri-salts. 



It is the intention of the writer to extend these experiments. 



