MARINE PRODUCTS OF COMMERCE 



Table 1. Comparison of Oceanic and Fluviatile Salts.* 



cerium, zinc, yttrium, lanthanum, lead, molybdenum, thorium, caesium, arsenic, 

 scandium, uranium, selenium, mercury, silver, gold, radium, chromium, cobalt, 

 tin, and cadmium. This list merely indicates the present state of our knowledge. 

 Undoubtedly, small amounts of all the elements occur in sea water. 



Careful analytical work by many chemists has indicated the composition of sea 

 water on a water-free basis (Table 2). Many other analyses, tabulated by Clarke 

 (1924), of sea water taken from many different parts of the world correspond 

 closely to those cited in the table. Many of the differences in the analyses reported 

 are no greater than might be expected from differences in the analytical methods 

 used. 



The volume of the ocean is so great that the total quantity of a given substance 

 may be tremendous, even though the percentage seems very small. Thus, since 

 the volume of the oceans is about 331,000,000 cubic miles, they contain approxi- 

 mately 150 billion tons of a substance occurring only to the extent of one part 

 per billion. 



The essential uniformity in composition of the sea salts is evident. Inasmuch as 

 Dittmar's results (A) represent the average composition of 77 samples of sea 

 water, taken from many different parts of the ocean and drawn from various 

 depths of water, these results should be taken as the standard for comparison. 

 Dittmar (1884) found that the salinity of sea water diminishes from the surface 

 to a depth of 800 to 1,000 fathoms, and then increases to the bottom. Around the 

 poles there are areas of concentration because of the freezing of the surface 

 which removes nearly pure water and leaves a large part of the salts behind. 

 Since the rivers continually bring into the ocean small amounts of dissolved min- 

 eral matter which is derived from the decomposition of rocks by flowing and per- 

 colating waters, it is assumed that the source of the sea salts is the mineral matter 

 of rocks which have been eroded by continual weathering. 



* Clarke, F. W., "The Data of Geochemistry," U. S. Geol. Survey Bull, 770, 5th ed. 

 (1924). 



