WELI.S: ARAGONITE FROM SEA-WATe;r 253 



value 0.000359. If the assumptions made are approximately 

 correct this figure shows that the ionization of the calcium com- 

 pounds in sea-water is enormously repressed by the excess of 

 chlorine ions. 



In the same way, for the equilibrium 



NaHC03 :^ [Na+] + [HCO3-] (5) 



the following equation was found to hold over a moderate range 

 around the concentration 0.002 molal. The ionization is taken 

 as equal to that of sodium chloride at the same concentrations. 



[Na+] [HCO3-] ■■ ^ , .,. 



r-rr- = 0.746 (6) 



[NaHCOg]'"' 



This yields, when [Na+] = 0.237, [HCO3-] = 3.15 [Na- 

 HCOs]'^^ A consideration of the relations required by this 

 equation shows that the ionization of the bicarbonates in sea- 

 water must be largely repressed in spite of their low concentra- 

 tion. For simplicity the un-ionized carbonate and bicarbonate 

 in the solution under study will be considered to be present as 

 the sodium compounds, a logical view on account of the great 

 excess of [Na+]. 



The ionic concentrations [HCOa"] and [CO3 ] may now be 

 evaluated from the analytical data for the water under considera- 

 tion. Let a, b, c, d, and e represent the molal concentrations of 

 HaCOaCthe free CO2), CO3— , HCO3-, NasCOa, and NaHCOg, 

 respectively. The following equations are available : 



44(a -^b-\-c-\-d-{-e) = 0.057 (?) 



2h -\- c -{- 2d -\- e = 0.0017 (8) 



c = 3.15 e'-'' (9) 



c = 53a (10) 



b = 0.00743c (11) 



The last two equations are derived from the equations 



[HCO3-] = ^il!^?^2d (12) 



[H + ] 



IH + J 

 in which ki, the first ionization constant of carbonic acid, has the 

 value 3.50 X io~^ at 25°, according to Kendall,^ and ko, the 



* Joum. Amer. Chem. Soc. 38: i486. 1916. 



