CONSEQUENCES OF THE POLYPEPTID STRUCTURE 27 



although insoluble in water, will displace carbonic acid from its 

 combination with calcium hydrate (W. A. Osborne, Cf. Chap. V). 

 Solutions of caseinates of the bases may be obtained which are 

 pronouncedly acid in reaction (Robertson, Cf. Chap. V). Since 

 in all these cases the molecular concentration of the protein 

 is very low, and the compounds which are formed are quite 

 highly electrolytically dissociated (Cf. above), were the forma- 

 tion of these compounds due to the replacement of OH' groups of 

 — NH3OH groups by acid radicals or of H+ groups in — COOH 

 groups by bases, then the "strength," i.e., the degree of disso- 

 ciation of edestin as a base must be equal to or greater than 

 that of NaOH, while that of casein as an acid must be much 

 greater than that of H2CO3 and comparable with the degree of 

 dissociation of NaOH at very high dilutions (since Na caseinate 

 may be prepared which is acid in reaction). Such conclusions, 

 applied to bodies which are amphoteric, are, of course, absurd. 

 Were the formation of potassium caseinate due to the formation 

 of a salt such as 



RCOO' + K+ 



an acid solution of this compound could no more exist than an 

 acid solution of potassium aluminate. As in similar cases which 

 occur in the domain of inorganic chemistry, we can interpret 

 these phenomena only by assuming that the basic radical in the 

 casein compounds, and the acid radical in the edestin compound 

 are bound up in a non-dissociable form. Since the casein com- 

 pounds, at least, when in solution in water, are notable conduc- 

 tors of electricity, they must dissociate at some other point in 

 the molecule than that of the union between the base and the 

 protein. 



(iii) Each equivalent * of a monobasic acid or monacid base 

 neutralized by serum globulin or casein yields two equivalents of 

 the protein compound (Cf. Chap. X). This obviously corre- 

 sponds with the mode of dissociation depicted above, while, if 

 terminal — NH2 or —COOH groups accomplished the union, 

 each equivalent of neutralized acid or base would produce only 

 one equivalent of salt. 



(iv) On successive additions of 1, 2, 3, etc., equivalents of 



* That is, gram-molecule divided by the valency of the combining radical, 

 in this instance unity. 



