Thou hollow-sounding and mysterious main?”
Let us endeavour to find out.
The first thing that strikes us is the saltness of the sea. Sea water is salt. Why? One reason is because salts are carried into it by rivers, and besides, it is more beneficial as salt water. But let us look at the facts. We know that the earth contains many “salts,” as we can see by the saline springs. We have already given the chemical constitution of sea water, but it will be useful to repeat the proportions.
| Water | 964·74372 | grains. |
| Salt (Chloride of Sodium) | 28·05948 | ” |
| Chloride of Potassium | 0·76552 | ” |
| Chloride of Magnesium | 3·66658 | ” |
| Bromide of Magnesium | 0·02929 | ” |
| Sulphate of Magnesia | 2·29578 | ” |
| Sulphate of Lime | 0·40662 | ” |
| Carbonate of Lime (with traces of Iodine and Ammonia) | 0·03301 | ” |
| 1000·00000 | ” |
Some portions of the sea are not so salt as others, or, in other words, not so dense, and the saltness of the water prevents it being frozen so quickly as fresh water, which freezes at 32°. Salt water requires to be reduced to 28° before it freezes. Besides the various constituents mentioned above, sea water has been found to contain boron, bromine, strontia, etc., and even silver, for the copper of ships has been found to be impregnated with that metal.
Fig. 697.—Going out.
If there is so much salt in the sea, it may be asked, why does it not continually become greatly saltier by additions. The reason is because tons of fresh water are continually pouring in, and though we can scarcely doubt that the sea is becoming gradually more salt as years pass away, the increase is very slight. On the other hand, evaporation is carrying water into the air and leaving the salt behind it. In seas like the Red Sea, where there is a great deal of evaporation and very little addition of fresh water in comparison, the water is extremely salt and bitter. The Baltic has little salt relatively to some parts of the Mediterranean.
Supposing that, as some allege, there are rocks of salt at the bottom of the sea, we must remember that springs of fresh water frequently bubble up to the surface of the ocean. This is a very curious phenomenon, and has been attested by Humboldt. He states that near Cuba these springs arise with considerable force, and the vessels trading on that coast get supplies of fresh water from these ocean springs. There is, or was, a similar uprising in the Gulf of Spezzia, and fresh water crustacea inhabit these localities. These occurrences prevent the sea from becoming too salt by evaporation. When salt water becomes tainted it is very offensive—much more so than fresh water. If, therefore, the ocean were not continually in movement, it would be very injurious.