112 'chemical statics 



The nature of the cation was, however, found to be not wholly 

 without influence, since the temperature at which egg-globulin 

 coagulates is lowest in the presence of ammonium chloride, and 

 highest in the presence of magnesium chloride, the series being 

 as follows: NH4, K, Na, Li, Ba, Mg. The curves expressing the 

 relationship between the concentrations of the salts employed 

 and the temperature of coagulation are, however, not parallel, 

 and in some cases cut one another, so that at higher concentra- 

 tions (4 N) the series runs as follows: Na, NH4, Li, Ba, Mg. 



Pauli also investigated the effect of mixtures of two salts, and 

 found, as had already been indicated by the results of Schafer 

 (71), that the coagulating action of salts upon proteins is additive, 

 that is, each salt exerts its separate effect and the precipitating 

 (or dissolving) power of the mixture is the algebraic sum of the sepa- 

 rate effects exerted by its components except when the two salts 

 have a common ion and so diminish each other's degree of disso- 

 ciation. This result has since been more fully confirmed by 

 Pauli (53) and by Mellanby (47). 



The globulins, as a class, are insoluble in distilled water, but 

 are soluble in dilute saline solutions. Further addition of salt 

 results in coagulation of the globulin. Non-electrolytes can bring 

 about the coagulation but not the solution of the globulin. From 

 these facts Pauli concluded that the solution of globulin is due 

 to the formation of compounds of the globulin with salts, of the 



type: Na - globuHn - CI. 



the further addition of salts to this solution resulting in the 

 precipitation of this compound. 



3. The Influence of the Electrical Condition of the Proteins 

 upon their Precipitation and Coagulation by Electrolytes. — The 

 action of very small quantities of salts in bringing about the 

 precipitation of colloids from their solution was first studied by 

 Graham (20). He ascertained, for example, that a solution of 

 colloidal aluminium hydrate prepared by dialysing the chloride 

 is so sensitive to the presence of salts that the mere addition of 

 a few drops of undistilled water suffices to precipitate it. This 

 type of action of salts upon colloids was further investigated by 

 Schultz (73), Prost (66), and Linder and Picton (44). 



Defining the precipitating-power of a salt as the reciprocal 

 of the concentration in gram-molecules per litre necessary to 

 coagulate a given solution of the hydrosol of sulphide of arsenic, 

 Schultz found that the relative precipitating-powers of the uni- 



