WATER (HO). (Chemistry.) Water, as it occurs in nature, has already been treated of in the NATURAL HISTORY DIVISION of this Cyclopnelia ; its physical properties in the three states of gas [STEAM; VAPOUR, OPALESCENT]; liquid [WATF.R, following article] ; and solid [Ice]; have also been separately described in the present Division; so that it is now only necessary to consider it from what may be termed a chemical poiut of view.
Water is a chemical combination of the two elements oxygen and hydrogen. When a jet of hydrogen is burnt in an atmosphere of oxy gen, or rice vend, water is formed, and condenses on and trickles down any cool surface that may be near. A compound of hydrogen, when burned in the air, also eliminates that element in the form of aqueous vapour. A cold plate held for a few moments in or over the flame of a candle, oil-lamp, or gas-jet, is soon bedewed with moisture, which may be collected and proved to be water. Conversely, water may he made to yield up its elements. Exposed to a temperature above the melting point of platinum, it is resolved into its elements. Passed in the state of steam over red-hot iron, it parts with its oxygen to the metal, and its hydrogen is evolved as gas. Submitted to the action of the electric' force, its two constituents are respectively evolved, and may be coRectel in quantity, from the two terminals of the battery ; that from the negative pole; hydrogen, occupying twice the bulk of that from the positive pole, oxygen. A given bulk of hydrogen being only ono-sixteenth the weight of an equal bulk of oxygen, it follows from the fact just mentioned that', the respective proportions by weight of hydrogen and oxygen In water are one of the former to eight of the latter. 3lany other experiments might be described demonstrating both epithetic:ally and analytically that water is the protoxide of hydrogen ; that It contains one equivalent of hydrogen (II = 1) and one equivalent of oxygen (0 es 8).
Water acts upon other bodies with four different degrees of intensity. Chemically, it unites to form, first, hydrates ; in these the water is most intimately combined, and can only be separated in many cases by a temperature approaching redness : slaked lime is such a hydrate. Secondly, water combines with crystalline bodies, as seen in sulphate of magnesia, which contains six equivalents (MgO, SO,, + 6Aq.), carbonate of soda, which has ten (NaO, 10 Aq.), &c. This water is generally termed water of cristallisation, to distinguish it from the former, or water of hydration. Thirdly, water, acting chemico-mecha nically, is a more or less powerful solveut for most bodies. On its uses in this respect it is scarcely necessary to enlarge. Its capacity for dissolving oxygen and carbonic acid enables it to support the life of fishes and sub-aquatic plants, and without which it would be unpleasant and mawkish as a beverage. Chlorine, sulphurous acid, and sulphuretted hydrogen gases are re-agents whose chemical value would be much restricted if they could not be obtained in the state of solution in water. Its property of dissolving solids enables it to be used as a vehicle for the conveyance of organic and inorganic matter to the tissues of animals and plants, and as an indispensable medium in nearly all arts and manufactures. When water has taken up as much of a body as it can dissolve, it is said to be satu rated ; and if at this point some of it be removed by spontaneous or artificial evaporation, the dissolved solid is again deposited, either in an amorphous state or in beautiful geometrical forms called crystals. The
fourth action of water is purely mechanical ; it is seen in the gradual wearing away of solid insoluble matter, and is largely concerned in the formation of the channels of streams, be.
From what has been said regarding the solvent powers of water, both upon gaseous and solid matter, it is obvious that pure water is never met with in nature. If we trace water from the moment when it assumes the liquid condition to the time when it finally makes its way to the ocean, we find it gradually accumulating impurities of various kinds. At the moment of condensation It exerts its solvent power and absorbs gases from the air. When it falls to the earth it percolates through strata more or leas soluble and more or less pervious to water, and dissolves, according to circumstances, various quantities of the solid matters which it there meets with. If the surface of the earth where it falls be very hard and insoluble, the water becomes only very slightly contaminated with solid matter. Loch Katrine, for instance, contains only 24 grains of solid matter in a gallon of the water ; the Dee. at Aberdeen, contains 4 grains ; and the Tay, at Perth, contains 5 grains. Frequently, also, when the strata through which the water percolates are pervious, supposing they are at the same time compara tively insoluble, very little solid matter gets into solution. Such is the case with the green sand formation, where the water is very free from mineral matters of a solid kind. Generally, however, water MN is with more conatituents,than those just indicated, and the quantity varies from 5 to 50 grains per gallon. When the latter quantity is exceeded, the water frequently acquires a taste, and may be regarded as abseental water. The water of the ocean is in this condition. The riven which flow into the sea carry with them matters dissolved, and leave them there, for the solid matters are not carried back by evepo. ration. Therefore, the sea contains a larger proportion of these sub stances than is contained in the water of rivers; and we get this effect on a still more exaggerated scale when, in hot climates, rivers empty themselves into lakes which have no outlet. This is the case with the Dead Sea. The river Jordan, which is constantly flowing into it, contains 75 grains of solid matter in the gallon; and none of this matter is returned again into the atmosphere, or no practical amount : there fore, there is a constant accumulation of the saline matters going on there, and in this Dead Sea we have no leas than 2600 grains of solid constituents to the gallon of water. The same effect takes place in a lake in the north of Australia, discovered a few months ago. It is highly charged with saline matters, and is known to possess no outlet. There is a similar instance in the celebrated Elton Lake in Russia, which is 11 miles long, 8 miles broad, and on an average only 15 inches deep. In summer it appears to be covered with snow, in consequence of the evaporation of the water forming a crust of saline matter. No less than 200,000 tons of salt are yearly extracted from this lake.