AND CALCIUM CARBONATE, ETC., OF WATER SOLUTIONS. 247 



where fcgag is expressed in molar terms and P is the partial pressure of the 

 carbon dioxide above the solution (see p. 243). 

 Equation (28) may be transformed then into 



^^ = 2 X fcgas X ^>"^^"" X KcaCOs (30) 



JL "^ Ionization 



an equation which holds for saturated solutions of calcium carbonate and 

 bicarbonate in equihbrium with sohd calcium carbonate and gaseous car- 

 bon dioxide of any pressure P at a given temperature. The composition 

 of such saturated solutions has been determined by Schloesing, and since 

 from his data the values of Chcos and of P can be ascertained, and since 

 all the constants excepting the solubility product KcaCOs are now known, 

 the value of this constant can now be determined." 



The value of the first ionization constant of carbonic acid is 3.04 X lO"';** 

 the value of the second ionization constant is 7 X lO""." Geffcken's'* recent 

 very exact determinations of the absorption of carbon dioxide by water, 

 made with an improved apparatus, give somewhat higher values than found 

 by Bunsen years ago. At 16°, the temperature at which Schloesing's deter- 

 minations were made, by interpolation of the values found by Geffcken for 

 15° and 25°, the coefficient of absorption is found to be 0.9890 (reduced to 

 0°.760 mm.) instead of 0.9753. The change in solubility produced by the 

 presence of the small amount of salts present (in Schloesing's experiments 

 this is only 0.01 equivalent, as an average) is negligible. The coefficient 

 0.9890 corresponds to a constant feg^g equal to 0.04415 in molar terms. 



Substituting the values of our three known constants in equation (30) 

 we obtain : pg q 04 v 1 0-^ 



^^=2X0.04415X^y|-^XKcaco3 



= 383.4 xKcacOs 

 and „ 



^K 



___t^HC03__ (31) 



^^"°^"7.264xVP 



Schloesing's results give the total amount of calcium carbonate dissolved: 

 it is present almost exclusively as calcium bicarbonate. The degrees of 

 ionization, a, of the calcium bicarbonate in the various solutions may be 

 put equal to the degrees of ionization of calcium acetate in equivalent con- 

 centrations;* then, in any given solufon 



CHC03 = «X^Cca(HC03)2 (32) 



" Bodlaender, loc. cit. 



"Page 243. 



"Page 245. 



'^Loc. cit. 



«Bodlaender used calcium chloride and nitrate for this purpose. As salts of organic 

 acids usually are somewhat less ionized than salts of stronger inorganic acids, it seemed 

 better to ascertain the degree of ionization by comparison with calcium acetate. The con- 

 ductivities for calcium acetate are given in Kohlrausch and Holborn's Leitfahigkeiten on 

 page 161 and the degrees of ionization are calculated in the usual way. There is an average 

 difference of about 4 per cent between these coefficients of ionization and those used by 

 Bodlaender. 



