The water of the sea is essentially salt, of a peculiar flavour, slightly acrid and bitter, and a little nauseous. It has an odour perfectly sui generis, and is slightly viscous. In short, it includes a great number of mineral salts and some other compounds, which give it a very disagreeable taste, and render it unfit for domestic use. It contains nearly all the soluble substances which exist on the globe, but principally chloride of sodium, or marine salt, and sulphate of magnesia, of potassium, and of lime.
Pure water is produced by a combination of one volume of oxygen and of two volumes of hydrogen, or in weight, 100 oxygen and 12·50 hydrogen. Sea water is composed of the same; but we find there, besides, other elements, the presence of which chemistry reveals to us. In 1000 grains of sea water the following ingredients are found:—
| Water | 962·0 |
| Chloride of sodium | 27·1 |
| Chloride of magnesium | 5·4 |
| Chloride of potassium | 0·4 |
| Bromide of magnesia | 0·1 |
| Sulphate of magnesia | 1·2 |
| Sulphate of lime | 0·8 |
| Carbonate of lime | 0·1 |
| Leaving a residuum of | 2·9 |
| —— | |
| 1000 |
consisting of sulphuretted hydrogen, hydrochlorate of ammonia, iodine iron, copper, and even silver in various quantities and proportions, according to the locality of the specimen. In examining the plates of copper taken from the bottom of a ship at Valparaiso, which had been long at sea, distinct traces of silver were found deposited by the sea. Finally, we find dissolved in the ocean a peculiar mucus, which seems of a mixed animal and vegetable nature, and is evidently organic matter proceeding from the successive decomposition of the innumerable generations of animals which have disappeared since the beginning of the world. This matter has been described by the Count Marsigli, who designates it sometimes under the name of glu, and sometimes as an unctuosity. It is the "ooze" of marine surveyors, and consists chiefly of carbonate of lime, ninety per cent. of which is formed of minute animal organisms. Its mealy adhesiveness results from the pressure of the superimposed water. The numerous salts which exist in the sea can neither be deposited in its bed, nor exhaled with the vapour, to be again poured upon the soil in showers of rain. Particular agents retain these salts in solution, transform them, and prevent their accumulation. Hence sea water always maintains a certain degree of saltness and bitterness, and the ocean continues to present the chemical characters which it has exhibited in all times, varying only in certain localities where more or less fresh water is poured into the sea basin from rivers: thus the saltness of the Mediterranean is greater than that of the ocean, probably because it loses more water by evaporation than it receives from its fresh-water affluents. For the opposite reason, the Black and the Caspian Seas are less charged with these salts. The Dead Sea is so strongly impregnated with salt that the body of a man floats on its surface without sinking, like a piece of cork upon fresh water. The supposed cause is excessive evaporation and the absence of rivers of any importance.
The saltness of the sea seems to be generally less towards the poles than the equator; but there are exceptions to this law. In the Irish Channel, near the Cumberland coast, the water contains salt equal to the fortieth of its weight; on the coast of France, it is equal to one thirty-second; in the Baltic, it is equal to a thirtieth; at Teneriffe, a twenty-eighth; and off the coast of Spain, to a sixteenth. Again, in many places the sea is less salt at the surface than at the bottom. In the Straits of the Dardanelles, at Constantinople, the proportion is as seventy-two to sixty-two. In the Mediterranean, it is as thirty-two to twenty-nine. It is also stated that as the salt increases at a certain depth, the water becomes less bitter. At the mouth of the great rivers it is scarcely necessary to add that the water is always less saline than on shores which receive no supplies of fresh water; the same remark applies to sea water in the vicinity of polar ice, the melting of which is productive of much fresh water. A recent analysis of the water of the Dead Sea by M. Roux gives about two pounds of salt to one gallon of water. No mineral water, if we except that of the Salt Lake of Utah, is so largely impregnated with saline substances; the quantity of bromide of magnesia is 0·35 grammes to the litre. The water of the Dead Sea is, according to these proportions, the richest natural depository of bromide, which it might be made to furnish abundantly. The waters of the great Lake of Utah and Lake Ourmiah in Persia are both highly saline. In Lake Ourmiah, as in the Dead Sea, the proportion of salt is six times greater than in the ocean. Many of our fresh-water lakes were probably salt originally, but have by degrees lost their saline properties by the mingling of their waters with those of the rivers which traverse or flow into them. Among the lakes which appear to have been divested of their saline properties may be mentioned the great lakes of Canada and the Sea of Baikal, in all of which seals and other marine animals are still found, which have become acclimatized as the water gradually became fresh.
The saltness of sea water increases its density, and at the same time its buoyancy, thus adapting it for bearing ships and other burdens on its bosom; moreover, to abbreviate slightly Dr. Maury's remark, "the brine of the ocean is the ley of the earth." From it the sea derives dynamical power, and its currents their main strength. It is the salt of the sea that imparts to its waters those curious anomalies in the laws of freezing and of thermal dilatation, that assist the rays of heat to penetrate its bosom; the salts of the sea invest it with adaptations which fresh water could not possess. In the latter case, the maximum density would be thirty-nine degrees two seconds F. instead of twenty-seven degrees two seconds F., when the dynamical force of the sea would be insufficient to put the Gulf Stream in motion. Nor could it regulate those climates we call marine.
We have said that sea water contains nearly all the soluble substances which exist in the globe. Nevertheless its exhalation is comparatively pure. "The water which evaporates from the sea," says Youman, in his "Chemistry," "is nearly pure, containing but very minute traces of salts. Falling as rain upon the land, it washes the soil, percolates through the rocky layers, and becomes charged with saline substances, which are borne seaward by the returning currents. The ocean, therefore, is the great depository of all substances that water can dissolve and carry down from the surface of the continents; and, as there is no channel for their escape, they would constantly accumulate, were it not for the creatures which inhabit the seas, and utilize the material thus brought within their reach." These substances are chloride of sodium or marine salt, sulphates of magnesia, potassa, lime, and other substances which the water of various seas is found to contain.
In the year 1847, I made an analysis of water taken a few leagues from the coast at Havre, which gave the following result, from one litre (1 pint·760773):—[2]
| Grammes. | |
|---|---|
| Chloride of sodium | 25·704 |
| Chloride of magnesium | 2·905 |
| Sulphate of magnesia | 2·462 |
| Sulphate of lime | 1·210 |
| Sulphate of potassa | 0·094 |
| Carbonate of lime | 0·132 |
| Silicate of soda | 0·017 |
| Bromide of sodium | 0·103 |
| Bromide of magnesium | 0·030 |
| Oxide of iron, carbonate and phosphate of } | Only |
| magnesia, and oxide of manganese} | traces. |
| ——— | |
| 32·657 |
The water of the Mediterranean contains more salts than that of the ocean.