254 WELI^S: ARAGONITE PROM SEA- WATER 



second ionization constant, is given by Seyler and Lloyd ^ as 

 4.91 X io~^^ The value for [H + ] is 6.61 X io~^ for the water 

 under scrutiny, which yields equations (10) and (11) given above. 



It may be noted in passing that the free CO2, or H2CO3, must 

 have a very small concentration in this water as [HCO3-], 

 according to equation (10), must equal 53 [H2CO3], thus requiring 

 a verj' large proportion of the total CO2. 



The solution of equations (7) to (11) gives [H2CO3] = 

 4.49 X 10-', [CO3— ] = 1.96 X IO-^ [HCO3-] = 2.64 X lo-l 



From the preceding data [Ca+^][C03 — ] = 3.59 X lO"^ X 

 1.96 X lO"^ = 7.23 X io~^° for the Copenhagen water. 



The analytical data for unaltered surface sea- water studied at 

 Tortugas are: Pu+ = 8.20, titration carbonate alkalinity = 

 0.00223, total CO2 = 0.090 gram per liter. Calculations similar 

 to those indicated above give the results shown below with the 

 values first obtained for the Copenhagen water. 



[H + ] [HCOj-] [COi — ] [Ca++l|C03--] 



Copenhagen water 6.61 X io~^ 2.64 X lo"'' 1.96 X lo"" 7.2 X io~'" 



Tortugas water 6.03 X io~^ 6.85 X io~^ 5 33 X lo"^ 19. i X io~i» 



It may be noted that there is little difference in [H+] in the 

 two waters, the principal differences being in the figiu-es for 

 [HCO3-] and [CO3— ]. This illustrates the buffer action of the 

 carbonates in sea-water. 



With reference to the low "solubility-product" value for the 

 Copenhagen water, the Tortugas water appears to be fully satu- 

 rated with calcium carbonate. A similar conclusion was reached 

 by J. F. McClendon from experiments in which sea- water was 

 agitated with calcite and aragonite, and the changes in pu+ and 

 titration alkalinity observ^ed.^ The Copenhagen water, however, 

 shows a relatively large loss in total CO2. It is hoped that further 

 data for sea-water collected under definite conditions will be 

 available shortly. It is also hoped that in a future paper attention 

 can be given to the possibility of improving the expressions for 

 the mass-law equilibria used in the present paper. 



* Journ. Chem. Soc. London iii: 158. 1917-1918. 

 ^ Carnegie Institution Publication 252: 255. 



