Studies on T H E Formation and Ionization of T H E Compounds of Casein W I T H Alkali. Iv. the Transport Numbers of the Compounds of Casein with the Alkali Earth Elements.*? by David M. Greenberg And

In a previous communication (1) it was shown that data obtained from transference experiments with alkali solutions of casein could be best interpreted on the assumption that the carriers of the current are alkali metal cations and casein anions. In the present studies on the transport numbers of solutions of casein with the alkali earth elements, the data appear to indicate that part of the metallic element is bound by casein in such a way as to produce a complex ion, which, in migrating, carries with it the metallic element in a direction opposite to the path of the cation. The idea of complex ions is not wholly new. Northrop and Kunitz (2) have suggested the formation of complex ions between certain cations and gelatin to account for the deviations which they obtained from the calculated values for the distribution of the ions according to the Donnan membrane equilibrium theory. These authors, however, were unable to show any stoichiometric relations governing the formation of the complex ions. The theory proposed by Robertson (3) postulates that only complex ions of protein with the metallic element exist in solution. These are formed by the union of the acid or alkali with the C O H N groups of the protein molecule. The experimental results of the present investigation afford considerable evidence in favor of the view that definite stoichiometric relationships govern the formation of complex ions of casein