AND CALCIUM CARBONATE, ETC., OF WATER SOLUTIONS. 243 



The solubility factor of carbon dioxide in water, fcg^g of equation II, has 

 been determined by Bunsen^ for different temperatures. The solubility is 

 usually given in liters (a) of gas, reduced to 0° and 760 mm., absorbed by 

 1 liter of water; then to reduce this to terms of gram molecular concentra- 

 tions as required for the application of the mass-action law, we make 



%a3 = 22 4 ^^^^ 



since a gram molecule of a gas occupies 22.4 liters under normal conditions. 

 For instance, at 16°, 0.9753 liter is absorbed or 0.9753/22.4 = 0.04354 mole, 

 if the carbon-dioxide gas has the pressure of 1 atmosphere. For any other 

 pressure P of the gas, expressed in atmospheres, the molar concentration 

 of dissolved carbonic acid is, then, according to II 



CH,COa=fcgasXP (20) 



In salt solutions the solubility is considerably less than in pure water, 

 as determined by Setchenow^ and more recently by Geffcken,^ and, when 

 salts are present, corrections made on the basis of these determinations 

 will be used. 



The first ionization constant of carbonic acid (equation III) has been 

 determined by Walker and Cornack* from the conductivity of aqueous 

 solutions of the acid. The secondary ionization is so small (see below) 

 that it scarcely contributes to the conductivity of carbonic acid and con- 

 sequently it can be neglected in the determination. The value found for 

 the first ionization constant is: 



K'lonization =3.04X10-^ (21) 



The second ionization constant of carbonic acid (equation IV) was cal- 

 culated by Bodlaender ^ from Shields's * experiments on the hydrolysis of 

 sodium carbonate, but, owing to an error in Shields's calculations, found by 

 McCoy,^ the value given by Bodlaender (1.295 X 10~") can not be accepted. 

 It was recalculated by McCoy from Shields's results and found to be 12.0 X 

 10~" or ten times as large as Bodlaender's value. McCoy then determined 

 the constant by a study of the condition of equilibrium between sodium 

 bicarbonate, carbonate, and carbonic acid, and from the values for deci- 

 normal solutions of bicarbonate he obtained 6.0X10~", which was only 

 half as large as the constant calculated from Shields's data; 0.3 normal and 

 normal bicarbonate solutions gave still other values. 



A recalculation of this constant, which is important for our work, was 

 made from McCoy's data, and corrections which were indicated by the 

 latter, but not carried out, were made for changes in the solubility of carbon 



1 Liebig's Annalen, 93, 20 (1855); Dammer, Handbuch der Anorganischen Chemie 

 II, 372. See also Geffcken, Zeitschrift fur Physikalische Chemie, 49, 257 (1904). 

 ^ Dammer, Handbuch der Anorganischen Chemie, ii, 1, 367. 

 ^ hoc. clt. 



* Journal of the Chemical Society, London, 77, 8 (1900). 



* Loc. cit. 



'Zeitschrift fur Physikalische Chemie, 12, 174 (1893). 

 ^ Loc. cit. 



16 



