THE SEA 11 



serious losses, we can also estimate the age of the 

 ocean if we know the amount of sodium added 

 annually by the rivers. Dr. F. W. Clarke has care- 

 fully considered, all the information at hand, and has 

 concluded that the age of the ocean, since the earth 

 assumed its present form, is somewhat less than a 

 hundred million years. 



Sea salt is not almost pure sodium chloride, such 

 as the salt we use as a condiment, but is a mixture 

 of a large number of compounds of which common 

 salt, Glauber's salt, Epsom salt, gypsum, and potas- 

 sium chloride and sulphate are the principal 

 components. Approximately three fourths of the 

 saline matter is sodium chloride or common salt, and 

 it is in the preparation of this important substance 

 that sea-water finds its principal use. In nearly all 

 warm dry countries salt has been prepared from 

 sea- water since prehistoric times. Even in this coun- 

 try, in the State of California, salt is prepared on 

 a large scale from sea-water. 



In addition to the compounds named above, sea- 

 water contains appreciable amounts of bromine, 

 iodine, iron, silicon, carbonates, and phosphates. 

 The presence of the following elements has also been 

 demonstrated: fluorine, nitrogen, arsenic, boron, 

 lithium, rubidium, caesium, strontium, manganese, 

 barium, aluminium, copper, zinc, silver, lead, cobalt, 

 nickel, gold, and radium. 



The total amount of any of these elements occur- 

 ring in the entire ocean is stupendous even though 

 it may be present in an extremely small proportion. 

 Iodine exists in sea-water to the extent of only about 



