WATER 311 WATER BRASH of the earth's surface; in the solid state it exists permanently in the form of ice or snow in the polar regions; and as a vapor is a constituent of the aerial en- velope of the earth, and the exhalations of volcanoes and boiling springs. It oc- curs in combinations in many mineral substances, and also in organic bodies, animals, and plants containing from 80 to 90 per cent. Water is the most effici- ent of all solvents, there being few sub- stances which are not, to some extent, affected by it, hence natural waters never occur absolutely pure, but contain in solution more or less of the constitu- ents of the strata through which they have passed. Rain water contains sub- stances derived in minute quantities from the atmosphere, such as ammonia, nitrate of ammonia, carbonic acid, ni- trous and sulphurous acids. Spring water always contains a much larger proportion of dissolved substances than rain water. When this is so highly charged with saline or gaseous constitu- ents, as to have a peculiar taste or smell, and is unfitted for ordinary use, it is called Mineral Water {q. v.), and when the amount of these constituents does not sensibly affect its taste, etc., it is described as fresh water. Sea water is essentially a mineral water, its saline constituents consisting of the chlorides and sulphates of sodium, potassium, magnesium, and calcium, together with minute quantities of silica, bromine, io- dine, phosphoric acid, etc. The total solid contents of sea water in mid-ocean varies from 30 to 40 grammes per liter, being largest near the equator and smallest near the poles. A cubic inch of fresh water at 42° weighs .036126 pounds. A cubic foot weighs 62.231 pounds. A cubic foot contains 6.2321 gallons. One gallon weighs 10 pounds. A ton comprises 35.943 cubic feet. Salt water is slightly heavier than fresh. The term water is applied to the color or luster of a diamond or pearl, and oc- casionally of other precious stones; as, a diamond of the first water — i. e., one perfectly pure and transparent. In chemistry, H2O. Water was long re- garded as an element, but toward the end of the 17th century it was shown by Lavoisier to be a compound, and to con- sist of 2 parts by weight of hydrogen to 16 of oxygen, or two volumes of hydrogen to one of oxygen. When pure it is free from taste and smell, and at ordinary pressure is liquid between 0" and 100°, boils at 100°, and freezes at 0°C., expanding to the extent of one- eleventh of its volume. The quantity of heat absorbed in the melting of ice is sufficient to raise the temperature of an equal weight of water 79.2°, and the quantity of heat rendered latent by water at 100°, becoming vapor, would raise the temperature of water 5.37 times as much as from 0° to 100° C. Water is 825 times heavier than air, and when converted into steam expands to nearly 1,600 volumes. One cubic centi- meter at 4°, and under a pressure of 760mm. of mercury, weighs 15.432349 gi-ains, or one gramme, the unit of weight in the metric system. WATER BED, a device that orig- inated with Dr. Neil Arnott, one of Queen Victoria's physicians. It consists of a trough of the dimensions of a wide sofa or a bed, having six or seven inches depth of water in it, and over it a caout- chouc covering on which clothes and pil- lows are laid as in a common bed. A more convenient and portable contri- vance is the water mattress, consisting of a coutchouc or waterproof bag of the size of an ordinary mattress, which may be filled with water of any degi-ee of temperature, or with air, as may be de- sired. The water bed is exceedingly use- ful in many diseases, but it is frequently a considerable time before the patient can become accustomed to its use, and some can never be reconciled to it. WATER BEETLES, beetles which live on or in the water, especially the some- what similar Amphizoidss, Haliplidse, Dytiscidse, and Gyrinidse, and also the quite different clavicorn Hydrophilidas. WATER BEETLH AND LARVA The Dytiscus, common in stagnant water, is olive-green above, and oval in shape. The respiratory organs of the per- fect insect are not adapted to obtaining air from the water; the creature must therefore come occasionally for air to the surface of the water, where it lies on its back, the openings of its airtubes, which are in the last segment of the abdomen, being exposed. WATER BRASH, an affection of the stomach, the result of a general func* tional debility of that organ, by which
