6 



Scientific Proceedings (ioi). 



effect on hydrogen ion concentration, i.e., it increases hydrogen 

 ion concentration to 0.5 to 1 molar beyond which it decreases it. 

 Magnesium chloride, however, gave a similar effect on freezing 

 point depression, although not so pronounced as magnesium sul- 

 phate. We could not find anything in the hydrate theory as 

 developed at present to account for the peculiar bend in the 

 magnesium chloride hydrogen ion curve. 



We do not believe that the figures for hydrogen ion concen- 

 trations in the presence of salts given in this paper, are the true 

 values. They should be termed apparent concentrations of 

 hydrogen ion as determined by the method in general use at this 

 date. 



For the determination of the hydrogen ion concentrations, a 

 Wolff 15,000 bridge with a galvanometer to determine the null 

 point was used. As hydrogen electrode, a No. 16 Browne and 

 Sharp gauge platinum wire (platinized) fused in a glass tube in- 

 serted in the Clark 1 cell was used. The calomel element con- 

 tained 3.5 molar potassium chloride solution saturated with 

 calomel and was the same design as that described by Fales and 

 Vosburgh. 2 The E.M.F. was determined by means of a Weston 

 cell that had been checked by the Bureau of Standards. The 

 hydrogen contained in a tank under pressure, was carefully washed 

 through saturated mercuric chloride solution, alkaline permanga- 

 nate, alkaline pyrogallol and a tower of cotton fibers. The 

 measurements were made at room temperatures which varied 

 between 22 0 and 26 0 C, the proper corrections being made. No 

 correction for barometric pressure was made since it is so small. 

 (See Harned, loc. cit.) No attempt was made to calculate and 

 correct for the solution contact potential because we know of no 

 satisfactory method of doing so, especially where solutions con- 

 taining divalent ions are concerned. It is emphasized however, 

 that the differences in effects reported in this paper cannot be 

 attributed to solution contact potential. This point was demon- 

 strated by Harned, and Fales and Vosburgh proved there is no 

 contact potential at 25 0 C, between a saturated solution of po- 



1 Clark, J. Biol. Chem., 23, 475 (191 5). 



■ Fales and Vosburgh, J. Am. Chem. Soc, 40, 129 (1918). 



