. WATER, a universally diffused liquid, the true nature of which was not discovered till' toward the close of the 18th century. In 1781 Cavendish carried out a series of experiments by detonating mixtures of common air and hydrogen or dephlogisticated air, as it was termed. He showed that by regulating the rela tive quantities talmost the whole of the inflam mable and dephlogisticated air is converted into Pure water' Although Cavendish showed ex perimentally that water is produced by bringing together oxygen and hydrogen, yet to Lavensiee, who received information regarding Cavendish's experiments, roust be assigned the merit of in terpreting aright the experimental results, and of proving that water was a compound subs stance —a compound of hydrogen and of oxy gen.
Water may be produced by exploding ,a mixture of two volumes of hydrogen with one volume of oxygen at a temperature above 1190° F. that tomperatbre the gases will not unite. It may also be produced by passing hydrogen over the heated oxidei of several of the metals—and in various other ways. It exists, although never in a Parfet-4 pure state, in immense quantities in nature. The com position of water has been determined by two distinct methods: (1) by volumetric synthesis; (2) by gravimetric synthesis. In volumetric synthesis of water measured voltages of pure dry hydrogen and of pare dry oxygen are mitred and the Mature is exploded 'by the elec tric spark while standing over mercury; the residual volume of gas is then measured; it is found that two volumes of tycliogen Invariably unite with one volume of oxygen. In the sec ond method a weighed quantity of a metallic oxide (usually cupric oxide) is decomposed by means of pure dry hydrogen at a high tem perature and the water which is produced is weighed. The decrease in weight of the oxide gives the quantity of oxygen in the water formed; while the difference between the total weight of water and the weight of 'the oxygen gives the weight of hydrogen used. It is found that 16 parts by weight of oxygen are always united with two parts by weight of hydrogen to form 18 parts by weight of water. In the scale in which 16 is adopted as the atomic weight of oxygen the formula of water is H20. The molecular weight of water has been variously decided upon; first as 18, later as 36, and it is now accepted as probably 72.
Water is a tasteless, inodorous liquid, under usual coaditions, colorless; but when a great thickness of it is examined, as in looking end wise through a pipe filled with it, it is found to have a distinctly blue tint. At all tempera tures below 32' i F. it is a solid and at all tem peratures above zlr F. it is a gas. When water at is heated it contracts until it reaches the temperature of 392°, after which it expands; conversely, when water at 212° is cooled it contracts until it reaches the temperature of 392', after which it expands; 2' F. is
called the point of maximum density of water ; the specific gravity of water is greater at this than at any other temperature. The fact that water expands on cooling from 392° to 32' is a most important me. If a sheet of fresh water be cooled, the upper layers become more and more dense; they, theretore, tend to sink, and so fresh surfaces are exposed to the cooling influences. But when the temperature of the mass of water has reached 392• further cool ing of the surface causes an expansion of the upper layers, which continues until these solidify into ice; these layers of cold water consequently float upon the warmer water underneath ; hence it is impossible for the mass of water to sud denly freeze throughout. When water passes from the liquid to the solid state it expands to the amount of about 1-11h of its volume; that is, one volume of water forms 1.0908 vol ume of ice. This expansion is sufficient to bring about a large quantity of mechanical work and to it the bursting of water-pipes during frost is to be largely traced. When solid water becomes or when liquid water becomes gaseous, a considerable quantity of beat is absorbed and disappears, or, as the expression is, is rendered 'latent' Steam is suing from boiling water is no hotter than the water itself ; water formed when ice is melting is no hotter than the ice itself ; yet heat is being communicated to the ice and to the water. The latent heat of water is 79 thermal units; the latent heat of steam is 536 thermal units, although by the thermometer the tem perature remains unchanged. In other words, to order to convert unit weight of ice at 32' into water at 32' a quantity of heat must be communicated to the ice, which, if communi cated to unit weight of water at 32°, would raise its temperature to 79' C. In order to con vert unit weight of water at 212' into steam at 212' such a quantity of beat must be com municated to the water as would suffice to raise the temperature of that weight of water through 536' C., or 536 times that weight of water through 1' C. Before water can become steam the upward pressure of its vapor must overcome the downward pressure of the at mosphere; hence it follows that the boiling point of water is conditioned by the atmospheric pressure. Water boils at a much lower tem perature on mountain tops, where the pressure is comparatively small, than in the valleys. Water is almost incompressible_ At 32• it is diminished in volume only by the fraction .0000462 for each atmosphere (1.5.7 pounds) of pressure added.