730 JOHN JOHNSTON AND E. D. WILLIAMSON 



of a certain group of properties of sea-water, properties which, more- 

 over, are of high importance in connection with certain biological 

 problems. The mode of treatment is similar to that employed by 

 Stieglitz, 1 who, at the instance of Chamberlin, carried out series of 

 calculations to ascertain the proportion of CaC0 3 which one might 

 expect to find in gypsum that had been deposited from solutions 

 saturated with respect to both CaS0 4 and CaC0 3 at different partial 

 pressures of C0 2 in the atmosphere in contact with the solution. 

 The principles, therefore, are not new, though the point of view 

 differs somewhat; and we now have the advantage of more extensive 

 data than were available in 1907. 



The data bearing on the solubility of pure calcite have been col- 

 lated and discussed at length in two recent papers, 2 to which the 

 reader desirous of fuller information on the chemical side is referred. 

 As it would lead too far to discuss here all details of the solubihty- 

 product constant and of its mode of calculation, we shall give only 

 the established conclusions which are pertinent to the present dis- 

 cussion, premising that a symbol inclosed within brackets represents 

 the concentration (expressed in moles per liter) of that particular 

 ionic or molecular species. 



1 . In a solution at a fixed temperature saturated with pure calcite, 

 the solubihty-product — i.e. [Ca ++ ] [CO 7], the product of the respec- 

 tive concentrations of calcium-ion and carbonate-ion — is a constant, 

 independent of the proportion of free C0 2 in the solution and of the 

 presence of other salts. This characteristic solubility-product con- 

 stant is to be carefully distinguished from the solubility which, as 

 ordinarily measured, is the concentration of total calcium in a solu- 

 tion in equilibrium with solid calcite; and this calcium is associated 

 with bicarbonate and hydroxide (and with any other anion present, 

 e.g., chloride or sulphate) as well as with carbonate — indeed, under 

 ordinary atmospheric conditions but a small fraction of the total 



1 J. Stieglitz, "The Relations of Equilibrium between the Carbon Dioxide of the 

 Atmosphere and the Calcium Sulphate, Calcium Carbonate, and Calcium Bicarbonate 

 in Water Solutions in Contact with It," in "The Tidal and Other Problems," by 

 T. C. Chamberlin et al., Carnegie Inst. Publ. No. 107 (1909). 



2 J. Johnston, Jour. Am. Chem. Soc, XXXVII (1915), 2001, hereinafter desig- 

 nated for convenience as op. cit.; Johnston and Williamson, ibid., XXXVIII 

 (1916), 975. 



