Syn. Aqua (Lett.), (Greek), Eau (F.), Agua(s.), Acqua (Ital.), Aae

(Dan.), A (Swed.), Ea, Eha (old Sax.), Awe (Pers.), Aw (Welsh), Aa (Low Germ., Islandic), Ab (Shans.), Abh (Gaelic), Immek (Esquimaux), Tannee (Tarn.), Panic (Duk.), Mah (Arab.), Watoora (Cyng.), Ayer (Malay), Panicura (Sans.), Hai (Tonquinese), A (Gothic), Inki (Bornou), Mane (Begharmi), Gowah (Mandara), Hary (Timbuctoo).

WATER is an agent of great importance, independent of (he part it sustains in the magnificent operations of nature. Its efficacy in the cure of disease is indubitable; yet it is not admitted into the list of materia medica of any of the British Pharmacopoeias, either in its ordinary state, or in form of mineral water. Under both of these forms it is necessary that its qualities and effects should be known to the medical practitioner.

I. Common Water

The usual appearance of water is too well known to require description. It retains its fluidity under the ordinary pressure of the atmosphere, at any degree of temperature between 32° and 212° 1, Fah. : under 32° it crystallises, becomes solid, and is changed into ice; above 212° 2 it becomes steam, expanding to 1698 times its ordinary bulk. One cubic inch of pure water at 60°, and under a pressure of the atmosphere indicated by 30° of the barometer, weighs 252.42 - grains, or nearly 1/15 part of a grain less than two hundred and fifty-two grains and a half.

Although water is almost universally diffused over the surface of the earth, yet it is not found perfectly pure in any place; which is owing to its great solvent powers enabling it to take up a portion of many things with which it comes into contact in its natural state. These impregnations, however, are not sufficient in general to give it any very sensible taste or odour, or to render it unfit for the ordinary purposes of life; and it is in this state that common water is usually obtained. Common water varies considerably according to the source whence it is derived, and other circumstances; but all the varieties may be reduced under the three following heads: -

1. Rain water - Aqua pluvialis.

2. Spring Water - Aquafontana.

3. River Water - Aquajluviatilis.

1. Rain Water is the purest kind of natural water; nevertheless, in every 100 cubic inches, it contains in solution about 3 1/2 cubic inches of air, rather more oxygenous than common atmospherical air, and about one cubic inch of carbonic acid gas, besides minute portions of carbonate of lime and sulphate of lime. Its specific gravity scarcely differs from that of distilled water; it is sufficiently pure for most pharmaceutical purposes.3 "When rain water, however, is collected in towns, or from the roofs of houses, besides the small portion of sulphate of lime, it contains soot and other impurities, and requires to be boiled and filtered.

1 This degree varies according to the pressure of the atmosphere. Thus, in Gemmilaro's hut, on the side of Etna, about 11,332 feet from the level of the sea, Dr. Irvine found that water boiled at 191°. Vide Letters on Sicily, 8vo. p. 153.

2 Gay Lussac.

3 Morvcau, Annates de Chimie, xxiv. 320.

Snow Water, when newly melted, is destitute of air, which is the reason that fish cannot live in it; but when allowed to remain for some time exposed to the atmosphere, it does not differ in its qualities from rain water.

2. Spring Water, if it have not filtered through a very soluble soil, is almost as pure as rain water. The best springs are those which rise through sand or gravel at a small depth.1 It generally contains, besides the ingredients which are found in rain water, a small portion of chloride of sodium.

Well or Pump Water, which is spring water obtained by digging to a considerable depth, is by no means so pure. It is commonly distinguished by a property named hardness, implying an incapability of dissolving soap 2, which is owing to its containing many earthy salts, the principal of which is sulphate of lime. It also contains more carbonic acid gas than common spring water. Many of the foreign ingredients contained in hard water are simply suspended in it; for pump water is rendered softer and purer by only passing it through a filtering stone. The best mode of freeing hard water of its earthy salts, is first to boil it; then, after it has cooled, to drop into it an alkaline carbonate; and, lastly, to filter it. It cannot be employed for pharmaceutical purposes.

3. River Water, when the stream is rapid, and runs over a pebbly channel, is as pure as soft spring water; but when the current is slow, and the bed clayey, it approaches nearer to the nature of well water, and frequently contains putrefied vegetable and animal matters, as is generally the case in the water of lakes.

Such are the foreign ingredients contained in common water: distillation in glass vessels frees it entirely from these ingredients, and it is obtained almost perfectly pure, transparent, colourless, insipid, and inodorous.

The varieties of waters enumerated above may be almost indiscriminately employed as diluents, the small proportion of foreign ingredients they contain occasioning no difference in their diluent properties. When the quantity of sulphate of lime and aluminous matter, however, is very considerable, as is the case in the water of many pumps, there is some reason for concluding that deleterious effects may arise from the use of the water; although it may be doubted whether the scrofulous and glandular swellings, peculiar to some populous towns, can be justly ascribed to this cause.3 Even a few of the waters which are regarded as mineral waters owe more to the diluent property of the water for their efficacy than to the impregnations they contain. This is particularly the case with the Malvern spring, which has been found to contain very little foreign matter. The diluting power of water is much modified by temperature; warm or tepid water being a much better diluent than cold water.