72 BEHAVIOUR OF IR )N SALTS, IN T[iE PRESENCE OF 



As to just how reactions of compounds containing trivalent 

 iron are hindered or prevented by the presence of native or 

 derived proteins, three possibilities present themselves : either 

 the protein may decrease the dissociation of the iron compound 

 to such an extent that ionic reactions are no longer possible ; or 

 it may exert a so called "protective action" on the iron salt, 

 similar to that of gelatine on colloidal gold, which is due to 

 the gelatine forming a very thin coating over each of the gold 

 particles^ ; or, lastly, the protein may be intimately associated 

 with the iron salt. Intimate association of the jDrotein and the 

 iron salt may be brought about through the formation of a 

 chemical compound, or by adsorption, giving rise to what may 

 be looked upon as a physical compound. 



If the phenomenon were to be ascribed to either decrease 

 in dissociation or to protective action, we should expect proteins 

 to hinder reactions of salts containing bivalent iron as well as 

 those of salts containing trivalent iron. On the other hand the 

 specificity of the proteins employed, points to their intimate 

 association with trivalent iron. 



It is well known that many colloids have a tendency to adsorb 

 certain substances, which are in true solution, with the forma- 

 tion of so called adsorption compounds. Since such compounds 

 do not possess a constant composition they cannot be looked 

 upon as chemical. The formation of such oompoundsi depends 

 on several factors of which the following are the more import- 

 ant : the nature and structure of the colloid, the nature of the 

 solvent, the nature of the dissolved substance, the condition of 

 the molecule of the dissolved substance, and lastly, the tem- 

 r^erature. 



In the foregoing experiments the nature and structure of 

 the colloidal albumen and gelatine are not very dissimilar, 

 while those of the ferric and ferrous salts employed are greatly 

 so. In view of what has been said we should expect to find 



1. Mines, G. R. : Proc. Physiol. Soc, November 18th, 1911. 



