PRECIPITATION OF PROTEINS BY INORGANIC SALTS 165 



inhibitor coming first and the strongest last. A (+) indicates that 

 the salt which results from the union of the cation and anion causes 

 coagulation of Egg-albumin; while a ( ) indicates , that it does not. 



Cations. 



Anions. Mg NH K Na Li 



Fluoride .... + . + -f- 



Sulphate . . + + + + + 



Phosphate 



Citrate . 



Tartrate 



Acetate . 



Chloride 



Nitrate . 



Chlorate 



Bromide 



Iodide .... 



Thiocyanate. ... 



When the protein is combined with acid, however, or is "electro- 

 positive," the order of effectiveness of the different salts in bringing 

 about coagulation is exactly the reverse of the order of effectiveness in 

 bringing about the coagulation of protein combined with alkali ("elec- 

 tronegative") protein. The series is reversed in every respect; the 

 anions now induce coagulation and the cations inhibit it. The anions 

 coagulate in the order: 



CNS > I > Br > NO 3 > Cl > CH 3 COO 



while the cations inhibit coagulation in the order: 



Li > Na > K > NH 4 > Mg 



We have seen that, in order that Precipitation of a protein by salts 

 may occur, the protein must be ionized, but for Coagulation this condi- 

 tion is not requisite. In determining the rate of precipitation the 

 valency of the precipitating ion is of prime importance; in determining 

 the rate of coagulation it is of comparatively subordinate importance. 

 For precipitation very low concentrations of the precipitating salt 

 suffice, intermediate concentrations frequently, and indeed usually 

 redissolve the precipitate, and for coagulation high concentrations of 

 the salt are required. This latter fact, and the fact that the presence 

 of coagulating-salts aids coagulation by alcohol and by heat, suggests, 

 as it did to Hofmeister, that coagulation is dependent upon Dehydration 

 of the protein. 



Starting from the observation of Jones and Ota, that certain salts 

 when dissolved in water, produce an abnormal depression of the. 

 freezing-point, H. C. Jones and his pupils have built up a very large 

 body of evidence for the existence of hydrates (or " solvates") of sub- 

 stances in solution. These investigators find that both ions and undis- 



