\WATER VAPOR, OR GASEOITS WATER. This is a normal constituent of the atmosphere (q.v.). The passage of one gram of liquid water into steam at 100° C. (212° F.) involves the absorp tion of as much as 536 calories of heat. At every temperature water-vapor can only exist below a certain maximum of pressure, viz. the vapor tension of water at that temperature. Under that pressure the vapor is said to be 'saturated.' Stronger pressure causes liquefaction, unless the temperature is above the critical point, which, according to Nadejdin, is about 25S° C. (about 496.5° F.). (See CRITICAL. Poryr.) Water vapor is colorless and perfectly transparent, unless it is allowed, in the saturated state, to escape into the cold air, when condensation causes the forma tion of minute bubbles that produce the char acteristic appearance of steam.
BIBLIOGRAPH Y. 1)6116111i IL Etudes pour scruir ei l'histoirc de in chimic. La th'eourerte de la composition de. l'eau (Paris, 1800) ; Nichols, Water Supply (New York, 1882) ; Davis, A Treatise on Steam-Boiler Incrustation, and Meth ods for Prcrenting Corrosion and the Formation of Scale; also a Complete List of all American Patents -issued by the Dorernment of Doc United Stales from 1790 to July 1, for Compounds and Mechanical Devices for Purifying Water, and for the Incrustation of Steam Boilers (Philadelphia, 1884) ; Davis, Ele mentary Handbook on Potable Water (Boston, 1891) ; Wanklyn and Chapman, Water Analysis (London, 1891) ; Greenwell and Curry, 'hater Supply (London, 1895) : Masun, Water Supply (New York, 1896) ; Thresh, Water and ll'a ter Supplies (London, ; Fuentes. 'a ter
and Public Health (New York, 1897) ; Water and Its Purification (Loudon, 1897) ; Crook, The Mineral Waters of the t'nited States (New York, 1899) ; Lehmann, Examina tion of Water for Sanitary and Technical Pur poses (4th ed., Philadelphia, 1899). See WATER PURIFICATION; WATER SUPPLY; WATER-WoRK WELL-SINKING, etc.; together with the accom panying bibliographies.