THE PHYSICAL CHEMISTRY OF SEA WATER 551 



of less than 3 mM is not too impressive compared with the total 

 concentration of ions in the solution, which is more than 200 times 

 greater. 



If we consider the origin of the ocean, we might say that the 

 ocean is the result of a gigantic acid-base titration : acids that have 

 leaked out from the interior of the earth, HCl, H2SO4, CO2, are 

 titrated with bases that have been set free by the weathering of 

 primary rock. In this acid-base titration, volcanoes against 

 weathering, it would seem that we are about 0.5 per cent from the 

 equivalence point. This, by the way, is better than most students 

 of chemistry do in their first titrations. 



It seems that either the pH of the ocean is somewhat precarious, 

 or there must be some other factor that determines the pH by 

 buffering. In the following, one possible factor will be pointed out. 



Mixing a Model Ocean 



It may be well to try to consider all the various substances that 

 have been of importance in the formation of sea water. 



Goldschmidt (1933, 1937a) started from estimates of the average 

 composition of igneous rocks, of sediments, and of sea water, and 

 from estimates of the quantities of sediments and sea water. He 

 came to the conclusion that for each kilogram of ocean water, 

 some 600 g of primary igneous rock must have been decomposed. 



Table II is based on Goldschmidt's estimates for the major 

 constituents, recalculated to the unit we are using, mole per liter 

 of ocean water, and rounded off to 0.01 mole. For each element 

 amounts derived from primary rock and present in sediments and 

 sea water are given. Some volatile elements, especially H, C, CI, 

 and S, are found in greater quantities in sea water than would 

 correspond to their concentration in igneous rock. Hence, they 

 must have come chiefly from the interior of the earth and con- 

 centrated at the surface by distillation, for instance through 

 volcanic activity, which may set free H2O, HCI, HBr, HF, CO2, 

 SO2, and B(0H)3. 



In the following we will use Goldschmidt's figures; other 

 estimates give somewhat different numbers but do not seem to 

 change the main features of the picture. 



