18 



THE OCEAN WORLD. 



evaporation. The saltness of this interior sea is only half as intense 

 as that of the ocean. 



The Sea of Azov and the Caspian Sea are still less salt than the 

 Black Sea. 



The following table shows the relative composition of the watei 

 in these three interior seas : 



In some lakes without any outlet, as the Dead Sea and the Lake 

 of Ural, the degree of saltness is considerably augmented. Nume- 

 rous experiments have proved that the water of the Dead Sea is six 

 times salter than that of the ocean. MM. Boutron and O'Henry 

 analysed, in April, 1850, after the rainy season, some water of the 

 Dead Sea, taken at about two leagues from the mouth of the Jordan ; 

 its density was then no. 



The saltness of sea water makes it more fitted to float ships, 

 because its density is increased by the salts which are dissolved in it. 

 Besides this, these salts contribute to prevent the water becoming 

 contaminated with decomposed organic matter. 



By the table representing the composition of the water of the 

 ocean and that of the Mediterranean, we see that salts of lime and 

 potassium, as well as iodine and silica, are only found in infinitely 

 small quantities. Nevertheless, the lime and silica contained in the 

 sea water are of very great importance ; for these quantities, which 

 appear to us so small in the table of a chemical analysis, become 

 enormous in the entire extent of the ocean. The marine plants take 

 up the lime, the silex, the potassium, and the iodides which are dis- 

 solved in the sea water, and these mineral substances enter into 

 their textures. It is from the carbonate of lime and silex that the 



