242 EQUILIBRIUM BETWEEN CARBON DIOXIDE OF ATMOSPHERE 



been confirmed by the work of Bodlaender on calcium and barium bicar- 

 bonate and of McCoy on sodium bicarbonate. 



Equation 14 represents the equilibrium condition between carbonate ions, 

 hydrogen ions, and bicarbonate ions, or the secondary ionization of carbonic 

 acid expressed in ^^q^, ^ g. +CO3" (15) 



and the constant of the equation may be called the second ionization con- 

 stant of this acid. 



The primary ionization of carbonic acid, which must supply the major 

 portion of hydrogen ions, is expressed in 



HjCOg^H+HCO/ (16) 



and we have then: 



Ch X ChCOs _ T^f (■\'7\ 



pr~ ■'^ loaizatioQ K'- ' / 



'^H2C03 



^'ionization ^^Y) t^en, be called the first ionization constant of carbonic 

 acid. 



The concentration of carbonic acid in solution is, according to Henry's 

 law, at a given temperature, proportionate to the concentration or partial 

 pressure of the gaseous carbon dioxide in the atmosphere with which the 

 solution is in equilibrium, viz: 



CH,C03=fcgasXCcO. (18) 



This completes the equations involved in the complex condition of 

 equilibrium we are considering. Summarizing our conclusions, we have 

 the following four mathematical equations expressing the conditions of 

 equilibrium in saturated solutions of calcium carbonate and bicarbonate in 

 contact with the atmosphere, all the constants of which must be simul- 

 taneously fulfilled for the condition of equilibrium: 



I^ Cca X CcOs = Ksolub. Prod. 



11^ CH2CO3 = ^gas X CcOj 



III' Ch X ChCOs = ^'ionization X Ch.COs 



IV* Ch X CcOs = K"ionization X ChcOs 



The solubihty of calcium carbonate, either as carbonate or as bicarbon- 

 ate, reaches a limit when the solubility product of equation I is reached, 

 and the value CcOg. the concentration of the carbonate ions, in this equa- 

 tion is in turn a function of equation IV; two values of this equation are 

 functions of equation III, in which in turn the concentration of the dis- 

 solved carbonic acid ChoCOs is dependent on the atmospheric carbon dioxide 

 as expressed in equation II. 



The constants of equations II, III, and IV are known, and the constant 

 of equation I, which we wish to determine, can be obtained from the other 

 constants with the aid of Schloesing's experimental work on the solubility 

 of calcium carbonate. 



' The solubility product of a saturated solution. 



* The solubility of carbon dioxide under varying partial pressures. 



* The primary ionization of carbonic acid. 



* The secondary ionization of carbonic acid. 



