Common Water. Under this head are included the waters commonly known as rain, spring, river, well or pump, lake and marsh waters. Thomson includes ice, and snow water, spring and river water, and lake water under rain water, as it is from this source that they are chiefly supplied.

Rain Water is the purest kind of all natural waters, though subject to some variations. Thus, when collected in large towns or cities, it is less pure than when obtained in the country; moreover it is usually loaded with impurities at the commencement of a shower, but after some hours of continuous rain it becomes nearly pure; for the first water which falls brings down the various foreign matters suspended in the atmosphere. In specific gravity, it scarcely differs from distilled water. It nevertheless generally holds in solution common air, carbonic acid, carbonate of lime, chloride of lime, and a trace of nitric acid. If it be collected from the roofs of houses, after it has rained for some time, it contains sulphate of lime and occasionally carbonate of lead. The quantity of common air in rain water does not exceed 3½ cubic inches in 100 cubic inches of water; it contains more oxygen than atmospherical air; the same quantity of rain water contains one inch of carbonic acid gas.

These combinations, in the small quantities in which they exist, in no degree injure the diluent properties of rain water. It is indeed to the presence of the two elastic gases, that rain water owes the taste which renders it palatable to animals and useful to vegetables. Ice water, being destitute of these gases is extremely vapid; fish cannot live in it; and it does not seem either to quench thirst or to be so complete a solvent in the stomach as rain water. Carbonate of ammonia is also another ingredient. It is derived from the putrefaction of nitrogenous substances. When several hundred pounds of rain water were distilled by Liebig, in a copper still, and the first two or three pounds evaporated with the addition of a little muriatic acid, he found a very distinct crystallization of sal-ammoniac, the crystals having a brown or yellow color. “It is worthy of observation,” says Liebig, “that the ammonia contained in rain and snow water possesses an offensive smell of perspiration and animal excrements, a fact which leaves no doubt respecting its origin.” It is owing to the presence of carbonate of ammonia that rain water owes its softer feel than pure distilled water. According to Liebig, it is the atmospheric ammonia which furnishes the nitrogen of plants. The traces of nitric acid which have been detected in the air, are referable to the oxidation of the constituents of ammonia; and not to the direct union of the oxygen and free nitrogen of the atmosphere. Dr. Pereira states that a carbonaceous (sooty) substance, and traces of sulphates, chlorides, and calcareous matter, are the usual impurities of the first rain water of a shower. Zimmerman found oxide of iron and chloride potassium in rain water; other chemists have been able to detect no iron in it, but have found meteoric iron and nickel in dew. Brande detected in it, chloride of sodium, chloride of magnesium, sulphate and carbonate of magnesium, sulphate of lime, and oxide of manganese. The putrefaction to which rain water is subject, shows that some organic matter is present. The term pyrrhin (from πυρρος red) has been applied by Zimmerman to an atmospheric organic substance which reddens solutions of silver. Whenever rain water is collected near large towns, it should be boiled and strained before use, as it contains less saline impregnation than other kinds of natural waters, it is more apt to become contaminated with lead from roofs, gutters, cisterns, and water pipes. To purify rain water and render it useful, for the delicate purposes of chemical experiment, Morveau recommends dropping into it a little barytic water and then exposing it for some time to the atmospheric air. This combines with the carbonic acid, which being the solvent of the carbonate of lime, both it and the carbonate of baryta are precipitated as insoluble salts. Instead of exposing it to the atmosphere, it may be poured from one vessel to another; by which means not only the minute portion of barytic water is dispersed through the rain water, and brought into contact with the carbonic acid, but it involves a great portion of air in its substance, which improves both the taste and the utility of the fluid.

Snow water, as we have already stated, is destitute of air and other gaseous matters found in rain. According to Liebig, it contains ammonia. It has long been a popular, but erroneous opinion, that it was injurious to health, and had a tendency to produce bronchocele. But this malady occurs at Sumatra, where ice and snow are never seen; while, on the contrary, the disease is quite unknown in Chili and Thibet, although the rivers of these countries are chiefly supplied by the melting of the snow, with which the mountains are covered. Ice is said not to quench thirst, but on the contrary to augment it, and that the natives of the Arctic regions prefer enduring the utmost extremity of this feeling, rather than attempt to remove it by eating of snow,[8] (Captain Ross.)

2. Spring Water. Rain water, when it falls on high grounds, enters the soil and filtrates through it, until it is stopped by some natural obstacle, when it pushes upwards, and welling out upon the surface, forms springs; the water is therefore merely a modification of rain water. During its passage, however, it almost always takes up some soluble matters, which of course vary according to the nature of the soil. It is purest when it passes through sand or gravel; in a limestone region, it always contains more or less of the sulphate and carbonate of lime, and it generally contains a trace of common salt, and the usual proportions of air and carbonic acid gas. The presence of these is detected by subacetate of lead, which displays the smallest portion of carbonic acid or a carbonate, and nitrate of silver, which detects the muriates by the formation of muriate of silver.

Water from melted ice is perfectly wholesome, and is drunk during the summer season, wherever the climate will admit of its being collected and preserved at a moderate expense. In this form, it is a luxury—almost a necessary—in the middle states of this country more particularly, “where,” Dr. Dunglison remarks, “there is not a tavern on the road, on the eastern side of the Blue Ridge, that does not furnish ice to the traveller in any abundance.” When sea-water freezes, the ice does not contain the salts. Consequently, when melted, it affords fresh water, and according to the voyagers in high northern and southern latitudes, the water has been found sweet, soft, and wholesome.

River Water. This is a mixture of rain and spring water, and when deprived of the matters which it frequently holds in suspension, is generally of considerable purity. Mountain streams, which generally issue from siliceous rocks, and run over stony or pebbly beds, are, for the most part, comparatively pure and soft. The river water of New-England, and the other hilly portions of the United States, is usually of this description, though in the time of floods, and after heavy rains, they contain much sedimentary matter. River water gradually deposits much of its earthy salts as it flows, and becomes purer by exposure; it therefore generally contains less calcareous matter than spring water; its specific gravity is less, and its taste more vapid. It, however, more or less partakes of the nature of the soil over which it flows; consequently some rivers, whose waters were pure and excellent at their source, lose these properties before they mingle with the sea. The water of the Thames, for example, in England, which is originally very soft and pure, becomes so loaded with animal and vegetable matter from the towns and villages on its banks, that after being kept a month or two in a closed cask, on opening it, a quantity of sulphuretted hydrogen gas, of the most offensive odor escapes, and the water is so black and nauseous as to be unfit for use. But on racking it off, it clears, depositing a quantity of slimy mud, and becomes remarkably clear, sweet and palatable. As the matters deposited in such rivers are merely mingled with the body of the water, which is too large, and too changing, to admit of any permanent taint from solution, filtration, or even the natural deposition of the ingredients fits them for every domestic and medicinal purpose.

* * * * *

The following Table shows the solid contents of the Thames water[9] London, and of the Croton water[10] in the city of New-York.

QUANTITY OF WATER.
1 Gallon = 10 lbs. Avoirdupois,
at 62° Fah., or 70, grs. Avoirdupois.		THAMES WATER.CROTON WATER.
Brentford.
Source of the
Grand Junction
Water Works
Company.		Chelsea.
Source of the
Chelsea
Water Works
Company.		At its source,
Croton Lake.		In the City of
New-York
as it issues from
the pipes.
Grains.Grains.Grains.Grains.
Carbonate of Lime, 16·00016·5001·421·52
Sulphate of Lime,} 3·400 2·900 ·00 ·44
Chloride of Sodium,}
Oxide of Iron, }very minute
portions		Ditto.
Silica, }
Magnesia, } ·34 ·46
Carbonaceous Matter, }
Chloride of Magnesium,} ·86 ·90
Chloride of Calcium, }
Carbonate of Magnesia, ·70 ·84
Solid matter held in solution, 19·40019·4002·983·70
Mechanical impurity, 0·368 0·238 ·34 ·46
Total solid matter, 19·76819·6383·324·16