' 

 122 COLLOID CHEMISTRY OF THE PROTEINS 



acids dissolve less of the protein, a measure of the strength 

 being given by the value of i/w, where n is the number of gram 

 equivalents of the acid necessary for the solution of unit weight 

 of globulin. Strong and moderately strong dibasic acids have 

 one-half, some of the tribasic acids one-third, of the capacity for 

 solution of the globulin shown by monobasic acids. These 

 results can be expressed alternatively by the statements that in 

 formation of soluble globulin salts, the globulin and acid react 

 in molecular proportions, or that the neutral globulin salts of 

 polybasic acids are soluble in water, but not the basic salts. 



Hardy determined in a similar way the extent to which 

 globulin is dissolved by bases, with the following results, 

 expressed as before : 



Table 68. 



The solubility of the globulin in the diacid baryta is thus half 

 as great as in the alkali hydroxide solutions. It is therefore 

 true in this case also that the reaction which produces soluble 

 salts with alkalis proceeds in molecular proportions. The 

 neutral salt with baryta, but not the acid salt, is water-soluble. 

 This result is very remarkable, and Hardy found that it also 

 obtained for acid and alkali albumin prepared from egg 

 albumin and dialysed free from salts. 



The behaviour of globulin with very weak acids is simply 

 explained on the basis of the considerable hydrolysis of the salt 

 formed. This is shown by the precipitate of globulin, which 

 only clears when an excess of the acid (for example, for acetic 

 acid five times as much) is present. It then gives a complete 

 solution as do the stronger acids. A comparison of the 

 behaviour of globulin towards acetic acid with that towards 

 ammonia is instructive, for the strength of the acid and base 

 are much the same, the affinity constant being 1-8 x io~ 5 . 

 Whereas acetic acid only dissolves a fifth as much as a strong 

 monobasic acid, ammonia dissolves the same quantity as 



