THE PHYSICAL CHEMISTRY OF SEA WATER 559 



on single silicate minerals, as yet too little seems to be known 

 about their relative stabilities to answer the question as to what 

 the real equilibrium will be after the additions mentioned. One 

 may predict that the solids will contain quartz, and at least two 

 more phases. Because of the wide occurrence of micas like glau- 

 conite, and of phillipsite, one may guess that they would corre- 

 spond to a real equilibrium state. The solution, on the other hand, 

 will contain the chloride ions, CI", which cannot leave it, and, 

 moreover, a sufficient number of positive ions to correspond to 

 the negative charge of 0.55M Cl~. The result will be, loosely 

 speaking, an ion exchange equilibrium of the positive ions between 

 the solution and the silicate phases. 



As a schematic example of the type of equilibria involved, one 

 may take a reaction : 

 3Al2Si205(OH)4 (s) + 4SiOo (s) + 2K+ + 2Ca++ + 9UoO ^ 



2KCaAl3Si50i6(H20)6 (s) + 6H + 

 log J^ = 6 log [H+] - 2 log [K+] - 2 log [Ca++] 



In addition, there will be ion exchange equilibria between the 

 solution and each separate phase. The experimental fact that K+ 

 is bound more strongly than Na"*" to layer silicates is reflected in 

 the ratios (Na/K),„Hd - 10-«•^^ (Na/K),„,„,i„„ = lO^*^^ in sea 

 water. Similarly, Ca++ is bound more strongly than Mg++, so that 

 there will be a concentration of Na+ and Mg++ in the sea water. 



A very important point is that these equilibria are pH-dependent 

 (see the equation above). Indeed, here we seem to have the main 

 buffering factor in the ocean. May I suggest that, when the 

 equilibrium relationships solution/silicate minerals are better 

 understood, it will be found that the pH of the ocean, 8.1, is 

 practically determined by the ratios of the constituents we have 

 considered up till now, and that the addition of the following 

 constituents will change pH only by, say, 0.1 or 0.2 unit. The 

 greatest change will perhaps be that on addition of FeOOH. 



Carbonate 



Now let us add 0.46 mole CaCOa and 0.09 mole MgCOa. As a 

 first approach to equilibrium these form 0.09 mole dolomite, 

 MgCa(C03)2, and 0.37 mole calcite, CaCOs. Some MgC03 would 



