560 CYCLES OF ORGANIC AND IXORGAXIC SUBSTANCES 



also go into solid solution in the calcite phase. The question is 

 controversial whether average sea water would be at equilibrium 

 with a mixture of calcite and dolomite, 



2CaC03 (s) + Mg++ ^ CaMg(C03)2 (s) + Ca++ 



whether it would tend to transform calcite to dolomite, or the 

 other way round. The experimental data are contradictory, the 

 equilibrium is probably pressure-dependent, and we shall avoid 

 the question by again setting aside the dolomite; this does not 

 change the remxainder of our argument. 



Thus, lea\'ing out the dolomite, we add 0.37 mole CaCOs to our 

 mixture. At equilibrium, a small part of the calcite will have 

 dissolved. In Table III are given equilibrium constants for infinite 

 dilution (zero activities), and for sea water, which is an artificial 

 sea water of 35 per cent salinity, close to our average sea water; 

 the latter figures are from Buch (quoted by Harvey, 1957) and 

 Kramer (1958, 1959).* 



Table III. Apijroxiniate Kciuilihriuni Constants 

 Reaction 



CaCOs (s) ^ Ca + + + CO,— 



CO3— + H + ^HCOs'^- 



HCO3- + H + ^H2C03 



H,C03^C0.-(g) + HoO 



CaC03 (s) + H + ;:± Ca + + + HCO3- 



loglHCOsi -2.60 -3.34 -3.75 -4.10 



The \'alues for log [HC()3 ] have been calculated from log 

 [Ca++] = —1.99, and pH = 8.1, both of which are determined by 

 the equilibria solution silicates, according to the argument above. 



* Neither set of figures is as accurate as one may ha\e wished. Kramer (1959) 

 changed his first value (1958) for log A's(CaC03) by —0.12; and equal correction 

 is made here on his first value (1958) for 5°C. The "infinite dilution" figures are 

 estimates on the basis of not too concordant literature data and positively are not 

 claimed to be criticalh- deduced "best" values. However, the figures in Table III 

 may indicate the influence of temperature and ionic medium, and the appro.ximate 

 [HCOs"] and Pcoo to be' expected at cquililirium. 



