20 



THE OCEAN WORLD. 



The following table shows the relative composition of the water in 

 these three interior seas : 



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

 Ural, the degree of saltness is considerably augmented. Numerous 

 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 1*10. 



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 of 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 

 in the lime, the silica, the potassa, and the iodides which are dis- 

 solved in the sea water : these mineral substances enter into their 

 textures. It is from the carbonate of lime and silica that the 

 marine animals form their solid covering, their shell or carapace. 

 The infusoria make use of the lime, silica, and potassa for the same 

 purpose. It is by the life and habits of the polypi that we explain 

 those Coral Islands found in the sea, the existence of which has been 



