AND CALCIUM CARBONATE, ETC., OF WATER SOLUTIONS. 245 



0°.760 mm. and fc,as=^ =0.03313* 



Then 



Ch.,co3 =0.03313X0.00161 =5.33X10-^ 



Inserting the values determined for the functions in equation (22) we have 



= 4.895 =K 



C='hco3 0.05335^ 



CH^cOaXCcoa 0.01991x5.33x10-* 

 The second ionization constant of carbonic acid is, then, according to 

 equation (23) ^^^^ 3.04X10"^ 



4895 



K^^H.C03= T^^:^ =6.21 X10-" 



A similar calculation for experiment 6, which McCoy considered as 

 presenting the most favorable conditions for accuracy and in which the 

 partial pressure of carbon dioxide was 0.00404 atmosphere, gave 6.205 X 10"". 



For experiment 1, table 3,t 0.3 normal bicarbonate was used, 57.9 per 

 cent remaining as bicarbonate, 42.1 per cent being converted into carbon- 

 ate when equilibrium was established under a partial pressure of carbon 

 dioxide of 0.00319 atmosphere. We have % as before 



Cncoa =0.3 X0.579 X0.70 =0.1216 

 Cco3 =0.3X0.5X0.421X0.584 =0.0369 



By interpolation of Geffcken's results, the coefficient of absorption of car- 

 bon dioxide by 0.3 normal potassium chloride at 25° is 0.720 and /jgas is 

 0.03214.§ Hence 



Ch,c03 =0.03214X0.00319 = 1.02X10-* 

 and 



C==HC03 0.1216^ 



=3,910=K 



Ch,co3 X Ccoa 1 -02 X 10-* X 0.0369 

 According to equation (23) we have, then, 



K'''lonization =7.8 X 10" 



We will use the mean of the two constants or 7 X 10~" for the calcula- 

 tions made in this investigation. 



THE DETERMINATION OF THE SOLUBILITY CONSTANT FOR 



CALCIUM CARBONATE. 



With the aid of the constant for the secondary ionization of carbonic 

 acid, of the constant for its primary ionization as determined by Walker 

 and Cornack, and the experiments of Schloesing on the solubility of calcium 

 carbonate under the influence of varying partial pressures of carbon dioxide, 



* McCoy used 0.0338 without correction for the changed solubility. 

 t Page 456, loc. cit. 



X The degree of ionization of 0.3 normal sodium acetate, loc. cit., is 0.70; of 0.3 equiva- 

 lent sodium sulphate, loc. cit., it is 0.584. 

 ? 0.0338 for pure water. 



'M 



