92 CHEMICAL STATICS 



solved in 100 cc. of 0.048 N Ca(0H)2 solution and then 40 cc. of 

 N/IO HCl were cautiously delivered into the solution by means of 

 a pipette of which the opening was held below the surface of the 

 fluid, the fluid being rapidly and continuously stirred meanwhile 

 through the agency of a small motor. The total volume was then 

 made up to 200 cc. and the mixture filtered through soft filter- 

 paper. By measurement of the refractive index of this filtrate it 

 was found that the 0.0008 equivalent of Ca(0H)2 unneutralized 

 by HCl had, under these conditions, only held in solution 0.2 

 gram of casein; although, as we have seen, in the absence of 

 CaCl2, 0.0008 equivalent of Ca(0H)2 will readily dissolve one 

 gram of casein, rendering the solution neutral to phenolphthalein. 

 In a subsequent chapter (X) it will be shown that a definite 

 relationship subsists between the initial alkalinity of a solution 

 and the depression of its electrical conductivity which is brought 

 about by the addition to it of a definite proportion of casein. This 

 relationship is of such a character that by exterpolation from the 

 measurements made upon solutions of potassium caseinate con- 

 taining from 25 X 10"^ to 300 X 10"^ equivalents of base per 

 gram of casein, it would appear that the depression of con- 

 ductivity caused by casein is zero when the proportion of base is 

 sufficient and only just suflacient to hold the casein in solution (42), 

 namely, 11.4 X 10"^ equivalents per gram. Similar exterpola- 

 tion from measurements of the depression of the conductivity of 

 Ca(0H)2 solutions consequent upon the addition of casein leads to 

 the conclusion that the depression of conductivity would vanish 

 at an initial alkalinity corresponding to a proportion of 11.9 X 10""' 

 equivalents of Ca(0H)2 per gram of casein, a value so close to 

 that obtained for the combining-capacity of casein for the alkalies 

 at "saturation" with casein that I have previously inferred that 

 bases dissolve casein in equivalent-molecular proportions (46). 

 Van Slyke and Bosworth have, however, measured the combining- 

 capacity of casein for alkaline earth bases at "saturation" of the 

 base with casein by the more direct method of first dissolving the 

 casein in an excess of the base and then neutralizing the excess with 

 hydrochloric acid and dialysing the mixture until free from soluble 

 chlorides (57). In this way they have found that a compound of 

 casein with calcium hydrate which contains 11.25 X 10~^ equiva- 

 lents of base per gram exists but is not soluble in water, the 

 lowest proportion of base yielding a soluble compound being 



