CASEIN AND OVOMUCOID 



205 



paper and joined by straight lines. The abscissa of the point of 

 intersection of the two broken curves thus drawn yields the number 

 of gram equivalents of KOH which are bound by the given per- 

 centage of casein in the production of an absolutely neutral 

 solution.* Dividing the number of gram equivalents of KOH 

 neutralized by the casein by the percentage concentration of the 

 casein we obtain the number of gram equivalents of KOH 

 neutralized by 1 gram of casein at absolute neutrality. The 

 following are the results computed from the data tabulated 

 above : 



The values of the combining capacities of the casein at neutrality 

 to litmus computed in this manner are seen to be appreciably 

 constant. The average value is 51 X 10~^ equivalents per gram 

 of casein, which is in excellent agreement with that obtained by 

 titration, namely, 50 X 10~^ equivalent gram molecules per gram. 

 Solutions of ovomucoid require the addition of a small quantity 

 of acid to obtain an absolutely neutral solution. f The amount 



* It was at first thought necessary to pa^s the curve y = ax^ + hx^ + ex + 

 d, through four of the points of the experimental curve v = /(6i) and to deter- 

 mine algebraically the point of intersection of this curve with the curve 

 y = 4107 — 0.060 logio x; this was, however, found to be an xmnecessary 

 refinement, as the results obtained did not differ appreciably from those 

 obtained by the simpler method described above. 



t In this connection attention may be called to the fact, which is revealed 

 in the above tables, that when 1 per cent ovomucoid is dissolved in 6.95 X 

 10-^ N acid, although the ovomucoid neutralizes a Uttle of this acid, yet this 

 solution is actually more acid than the solution which is obtained by dissolving 

 1 per cent ovomucoid in 0.0005 N HCl. A similar phenomenon was observed 

 by W. B. Hardy in solutions of serum globulin (22). It is possible that this 

 indicates a slight decomposition of the salt which was present in these solu- 

 tions by the protein, or, more probably that it is due to a small proportion of 

 the free protein ionizing according to the equation R.COOH = RCOO' + H+. 



