170 ELECTROCHEMISTRY 



Rohmann and Hirschstein (30) have shown that solutions of 

 silver caseinate contain no silver ions, since they fail to yield a 

 precipitate on adding sodium chloride. 



The most obvious conclusions to be drawn from these results 

 are (a) that the protein-base or protein-acid compounds are not 

 subject to dissociation at all; or else (b) that they dissociate the 

 positive and negative ions of the inorganic constituent in equiva- 

 lent proportions, i.e., undergo hydrolytic dissociation. 



That these assumptions are incorrect, however, is shown by 

 a large number of experiments which demonstrate that the pro- 

 tein compounds with inorganic bases and acids are true electro- 

 lytes, independently of any hydrolytic dissociation which they 

 may undergo in solution. For example, Sjoqvist (35) has shown 

 that if egg-albumin be dissolved in dilute hydrochloric acid, as 

 the concentration of albumin is increased, keeping that of the 

 HCl-solution constant, the molecular conductivity (calculated for 

 0.025 N HCl) diminishes until it reaches a constant minimum 

 value, which is attained when about four grams are dissolved 

 in 100 cc. of 0.025 iV HCl. Now the above quoted results of 

 Bugarszky and Liebermann show that in this solution at least 97 

 per cent of the hydrochloric acid is bound by the egg-albumin. 

 The observed ''molecular" conductivity (67 X 10""^) is at least 7 

 times greater than could be accounted for by the maximum 

 possible residuum of unneutralized hydrochloric acid and must 

 therefore be due to the protein-acid compound. 



Solutions of the caseinates of the alkalies and alkaline earths 

 can be obtained which are neutral or even acid to litmus (Cf. 

 Chap. V), these solutions therefore contain no free base; never- 

 theless they are excellent conductors of electricity (34) (23) (27) 

 (28) since a 2 per cent solution of potassium caseinate which is 

 neutral to litmus possesses a conductivity of 92.7 X 10~' recip- 

 rocal ohms per equivalent of base neutralized at 30° C. That 

 this conductivity is not attributable to associated impurities, 

 inorganic or otherwise, is shown by the following facts: 



(i) It bears a definite relation to the amount of base neutralized 

 by the protein (27) . 



(ii) The conduction of electricity is accompanied by migration 

 of the casein to the anode, and the amount of casein transported 

 to the anode is directly proportional to the quantity of electricity 

 which is transported through the solution (29). 



