90 CHEMICAL STATICS 



"neutral" caseinate; by Courant the " dicaseinate " of the base. 

 Both terminologies are objectionable since they imply or suggest 

 hypothetical stoichiometrical relations. Neutrality of its solutions 

 to an arbitrarily chosen indicator is no evidence of the unity of a 

 substance. As we shall see in considering the electrochemistry of 

 these substances, both that containing 2.4 per cent CaO and that 

 containing 1.5 per cent CaO are mixtures of two or more individual 

 salts of casein. We shall, however, for the sake of brevity in allu- 

 sion, employ the nomenclature of Soldner, as being the less objec- 

 tionable of the two. 



At neutrality either to litmus or to phenolphthalein all observers 

 agree that casein binds the alkalies and alkaline earths in equiva- 

 lent-molecular proportions. Thus regular stoichiometrical rela- 

 tions between the protein and these metals are clearly indicated 

 although the above cited data are insufficient to define them. With 

 regard to ammonium caseinate, however, some confusion exists 

 since Bechamp (3) states that it contains 1.17 to 1.21 per cent of 

 ammonia (= 1.94 to 1.99 per cent of CaO), while Salkowski (47) 

 states that it contains only 0.35 per cent of ammonia. Salkowski 's 

 method of preparing this compound, however, was faulty since he 

 precipitated it from alcoholic solution by the addition of NaCl, a 

 procedure which involved the possibility of double decomposition 

 and the partial substitution of sodium for ammonia in the casein 

 compound.* 



The quantitative results for casein, which we have so far cited, 

 may be stated in other words thus: At neutrality to litmus one 

 gram of casein binds 50 X 10~ 5 equivalent gram molecules of a 

 base, and at neutrality to phenolphthalein 80 X 10~ 5 equivalent 

 gram molecules. f 



It was formerly stated by the author (36) that if a given con- 

 centration of alkali be " saturated" with casein, that is, if it be 

 shaken up with excess of casein until no more of the protein will 

 dissolve, and then filtered, the filtrate is always neutral to litmus 

 and contains the quantity of casein required to form the "neutral" 

 caseinate of the base. In later communications (41) (42), I have 

 shown, however, that this conclusion was erroneous, the source of 



* Regarding the actual occurrence of such types of interaction between 

 casein salts and inorganic salts, Cf. W. A. Osborne (35) and Van Slyke and 

 Bosworth (57). 



t That is, gram molecules divided by the valency of the combining ion. 



