162 COMPOUNDS OF THE PROTEINS 



a positive charge from the hydrogen ions of hydrochloric acid, we must 

 next inquire what becomes of the chlorine ion of the acid? It cannot 

 exist in a free state with unneutralized charges, and no way exists 

 for it to neutralize its charge except by attachment to an oppositely 

 charged albumin molecule. But this attachment of both ions of the 

 hydrochloric acid to the albumin differs in no distinguishable way 

 whatever from chemical combination. 



That the hydrogen ions of acids are actually bound by the protein 

 may readily be shown by employing the hydrogen electrode or even 

 by the aid of indicators. The anions of acids must therefore be like- 

 wise attached to the protein particles. Now let us suppose that the 

 charge communicated to the protein particle by the hydrogen ion of the 

 acid is neutralized by the anion of a precipitating salt, what will happen 

 to the cation of the precipitating salt? Its charge must be neutralized, 

 and this can only be accomplished by its union with the protein com- 

 plex or else by its union with the acid radical which is also attached to 

 the protein. In the first alternative, the train of events would be 

 represented by the equation: 



2 Protein HC1 + Na 2 SO 4 = (Protein HCl) 2 Na 2 SO4 



and in the second alternative by the equation: 



2 Protein HCl + Na 2 SO 4 = Protein 2 H 2 SO 4 + 2NaCi 



In other words, from whatever point of view we may regard the 

 precipitation of proteins by inorganic salts, as soon as we examine 

 closely the details of the process, it becomes indistinguishable, by any 

 criterion which we at present possess, from a chemical reaction, and it 

 seems to be quite unnecessary to invent a special hypothesis to account 

 for this particular type of chemical reaction, the need of which is not 

 experienced in interpreting any other of the immense variety of chemi- 

 cal reactions yielding precipitates with which we are familiar. 



It remains, however, to account for the peculiar relationship of 

 precipitating power to the valency of the precipitating ion which led 

 to the elaboration of Whetham's hypothesis. Now this hypothesis, 

 when carefully examined, is seen to consist in nothing more than a 

 restatement, in terms of the probabilities of molecular collisions, of the 

 Guldberg and Waage Mass-law which applies to all chemical reactions. 

 According to this law, the velocity with which any given chemical 

 reaction proceeds, varies directly as the active masses of each of the 

 reacting molecules. In the case under consideration, presuming that a 

 given number (e. g. one) of molecules of protein react with one molecule 

 of a salt of a monovalent metal to form a compound, then twice as many 

 molecules of the protein may be supposed to react with a molecule of a 

 salt of a divalent metal, and three times as many with a salt of a triva- 

 lent metal. Assuming that the active mass of the colloid (the molecu- 

 lar concentration multiplied by the degree of electrolytic dissociation) 



