12 THE WEALTH OF THE SEA 



two parts per million. Yet the entire ocean contains 

 some sixty billion tons of iodine. Science has not 

 developed a profitable method of extracting this 

 iodine from sea- water, but nature has. Many sea- 

 weeds extract iodine from the sea-water in their life 

 processes. By burning the seaweed and extracting 

 the ash, we obtain iodine commercially. 



Gold, silver, and radium are contained in sea- 

 water. The amounts of these extremely valuable ele- 

 ments are very small, and are ordinarily listed as 

 traces; nevertheless their presence has attracted 

 much attention. From time to time, various schemes 

 have been devised for obtaining the gold and silver 

 from sea-water. Many of these processes are suc- 

 cessful in obtaining the precious elements, but no one 

 has ever been able to do the trick profitably. The 

 amounts of gold found vary from a tenth of a grain 

 to a grain per ton of sea-water. The man who first 

 succeeds in profitably obtaining gold from this source 

 will revolutionize gold mining. 



The composition of sea salt has been the subject 

 of many elaborate investigations which have shown 

 that, although ocean water varies considerably in 

 concentration, the composition of its saline matter 

 is remarkably uniform. 



Dittmar, of the Challenger expedition, made a 

 large number of analyses of sea-water from many 

 parts of the globe, and found that the density, and 

 therefore the salinity, of ocean water diminishes 

 from the surface to a depth of 800 to 1000 fathoms, 

 and then increases to the bottom. Around the poles 

 there are areas of concentration because of the 



