48 THE OCEAN 



principally carbonates, which make up 57-7 

 per cent., sulphates 11-4 per cent., silicates 9-9 

 per cent., common salt only 2-2 per cent., with 

 small quantities of other salts and organic 

 matter. 



The dissolved salts in sea- water are princi- 

 pally chlorides and sulphates of sodium, 

 magnesium, potassium and calcium. Common 

 salt makes up 77-8 per cent, (more than three- 

 fourths of the whole), sulphates 10-8 percent., 

 but silicates do not exceed 004 per cent., 

 and calcium carbonate forms only 0-345 per 

 cent. This difference leads to the conclusion 

 that sea-water is not merely a concentrated 

 solution of river-water discharged from the 

 land-surfaces throughout the geological past, 

 but that changes have taken place due to 

 chemical reactions between the various salts 

 in solution and to the action of living organ- 

 isms. In addition to the main constituents, 

 sea-water holds in solution traces of nearly 

 every known chemical element, but in such 

 small proportions as to be negligible in quan- 

 titative chemical analyses ; the presence of 

 gold in sea- water has been repeatedly verified, 

 and the possibility of its economic recovery 

 suggested. 



Average Composition of Sea-Salts. — The 

 results of W. Dittmar's well-known analyses of 

 77 samples of sea-water collected by the 



