244 EQUILIBRIUM BETWEEN CARBON DIOXIDE OF ATMOSPHERE 



dioxide in salt solutions and for the changes in the ionization of salts in 

 mixtures. While the recalculation did not change the order of the results, 

 it removed the uncertainty as to the effect of these corrections. 



From the two equations for the ionization of carbonic acid, III and IV, 

 we get by dividing III by IV: 



C HCO3 K Ionization 



CO3 X ChsCOs K"ionization 



= K (22) 



The constant K can be readily calculated from any of McCoy's results, 

 and then tt/ . q nd v i n-^ 



Kn -'^ Ionization o-y)^ A -i-^ CyW 



Ionization ^ tt" \^'^) 



In 0.0999 normal solution of sodium bicarbonate according to table 2,* 

 under a partial pressure of 0.00161 atmosphere (P), McCoy found 68.2 per 

 cent bicarbonate and 31.8 per cent carbonate. The degrees of ionization 

 of these salts can be put equal to those of sodium acetate and sodium 

 sulphate, respectively, similar salts ionizing very much alike, and the deter- 

 minations of the ionization of the acetate and sulphate from their conduc- 

 tivities being far more reliable than the estimations from the conductivities 

 of bicarbonate and carbonate solutions which really represent complex 

 mixtures. A consideration of the curves for the conductivities for sodium 

 carbonate and sulphate shows them in fact to be practically parallel for 

 more concentrated solutions in which the hydrolysis of the carbonate is 

 small, but for more dilute hydrolyzed solutions the curve for the carbonate 

 bends and cuts the sulphate curve, which is an indication of hydrolysis. 

 Hence it was deemed safer to determine the degree of ionization from the 

 sulphate and acetate curves. Then in the experiment ^ mentioned we have 



CHCO3 =0.0999 X0.682 X 0.783 =0.05335 

 Ccoa =0.0999X0.5X0.318X0.687 =0.01091 



The solubility of carbon dioxide in salt solutions is smaller than in 

 water. A correction was made for this by putting the solubility equal to 

 that of 0.1 normal potassium chloride solution. From the results of Geff- 

 cken,^ whose work is the best on the subject, the decrease in the coefficient 

 of absorption is practically proportionate to the concentration of the salt, 

 the coefficients for pure water, for 0.5 molar and 1.0 molar solutions of 

 potassium chloride forming practically a rectilinear curve, the concentra- 

 tions and the coefficients being used as coordinates. By interpolation on 

 the curve, the coefficient of absorption for 0.1 molar potassium chloride 

 at 25°, the temperature at which McCoy worked, is 0.742, reduced to 



* hoc. cit. 



'The degree of ionization of 0.1 molar sodium acetate, Kohlrauech und Holborn, 

 Leitfahigkeiten, pp. 159 and 200, is calculated as 0.783. 



The degree of ionization of 0.1 equivalent sodium sulphate, ibid., is 0.687. In a mix- 

 ture of the two, the degrees of ionization would be very slightly modified, but a calculation 

 of the change made on the basis of the principle of isohydric solutions showed the correc- 

 tion to be negligible. 



^ Lnc. cit. 



