SALTNESS OF THE SEA. 19 



Ibs. 



Chloride of sodium 29*524 



Chloride of potassium 0*405 



Chloride of magnesium 3'219 



Sulphate of magnesia 2-477 



Chloride of calcium 6*080 



Sulphate of lime 1-557 



Carbonate of lime . 0'114 



Bromide of sodium 0*356 



Protoxide of iron . . 0*003 



Total . . . 43*735 



We conclude, from the quantity of sea salt contained in the water 

 of the ocean, that, if it were spread over the surface of the globe, it 

 would form a layer of more than thirty feet in height. 



The salt contained in sea water gives it a greater density than fresh 

 water; its average specific weight is 1*027. The density of the 

 water of the Mediterranean is, according to M. Usiglio, 1*025 when 

 at the temperature of seventy degrees. But the saltness of the sea 

 varies very much under the influence of a great many local circum- 

 stances, among which we must count principally currents, winds 

 favourable to evaporation, rivers coming from the continents, &c. 



It has been remarked that the sea is less salt towards the poles 

 than at the equator ; that the saltness increases, in general, with the 

 distance from land, and the depth of the water ; that the interior seas, 

 such as the Baltic, the Black Sea, the White Sea, the Sea of Mar- 

 mora, and the Yellow Sea, are less salt than the ocean. The Mediter- 

 ranean is an exception to this last rule ; it is, as we have seen, salter 

 than the ocean. This difference is explained by the fact that the 

 quantity of fresh water brought into it by rivers is less than that lost 

 by evaporation. The Mediterranean must therefore grow salter with 

 time, unless its water is discharged into the ocean by a counter 

 current, which would run under the current coming from the Atlantic 

 by the Straits of Gibraltar. 



The Black Sea, on the contrary, the water of which has a density 

 of only 1*013, receives from rivers more fresh water than it loses by 

 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. 



c 2 



