LATER INVESTIGATIONS 121 



are formed, insoluble, that is, on dilution of the system with 

 water. The alkaline earths, moreover, afford a strong contrast 

 to the alkalies, in that the precipitating-power of the cation is 

 increased by the anions, in the series which is characteristic for 

 electropositive protein (54). In other words, when egg-white is 

 acted upon by salts of the alkaline earths the protein behaves, so 

 far as the action of anions upon it is concerned, as though it were 

 in acid solution. Pauli believes that the alkaline earth reacts 

 with OH groups of the protein to form the comparatively slightly 

 dissociated hydrates of the alkaline earths, the acid which is set 

 free inducing the acid reaction of the medium. In other words, 

 Pauli's view is that protein aids the action of water in bringing 

 about hydrolytic dissociation. Other colloids would appear to 

 act similarly, since Whitney and Ober (80) found that on the 

 addition of neutral halogen salts of the alkaline earths to col- 

 loidal arsenic sulphide the reaction of the solution becomes acid. 

 The influence of added salts of the alkalies and magnesium 

 upon the precipitation of proteins by heavy metals varies with 

 the concentration of salt employed (55). At low concentrations 

 (0.005 m.) the salts inhibit precipitation in the order: 



SO4 < Cl< C2H3O2 < NO3 < Br < I< SON, 



while in high concentrations (4 m.) they encourage precipitation 

 in the order: 



SO4 > CI > C2H3O2 > NO3 > Br > I > SCN. 



This is simply a particular instance of the rule, to which the 

 attention of the reader was drawn in the earlier part of this 

 chapter, that the salts may act as precipitants and as coagulants 

 at low and at high concentrations respectively, acting as solvents 

 at intermediate concentrations. The heavy metal salts afford no 

 exception to this rule. At low concentrations they precipitate, at 

 higher concentrations they dissolve, and at still higher concentra- 

 tions they coagulate the proteins of egg-white (55). Copper sul- 

 phate acting upon egg-albumin would appear to afford an excep- 

 tion since it does not coagulate even in saturated solution. That 

 the exception is apparent and not real is, however, shown by the 

 observation of Galeotti (17) that in sufficiently supersaturated 

 solution copper albuminate is coagulated by copper sulphate, 

 addition of merely saturated copper sulphate solution redissolves 



