The following are, according to M. Usiglio, who was one of a commission sent to examine the different kinds of salt water in the south of France, the component parts of one hundred gallons of Mediterranean water:—
| lbs. | |
|---|---|
| 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 circumstances, 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 Marmora, and the Yellow Sea, are less salt than the ocean. The Mediterranean 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.
The following table shows the relative composition of the water in these three interior seas:—