SECTION 1 HEATING, VENTILATION, AND POWER BY IRA N. EVANS PROPERTIES OF AIR, WATER, AND STEAM 1. Water. Water is a chemical compound composed of 16 parts by weight of oxygen and 2 parts hydrogen, or 2 volumes of hydrogen to 1 of oxygen (H2O). It is practically incompressible but its weight per cubic foot changes with the temperature (see Columns 1 and 6, Table 2). A U. S. gallon occupies 231 cu. in. and weighs, at 62 deg. F., approximately 8.33 lb., and 1 cu. ft. 7.48 gal. The boiling point of water varies with the absolute pressure upon its surface —that is, every absolute pressure has a fixed boiling point. For example, 212 deg. F. is the boiling point for a pressure of 14.7 lb. The boiling point also changes with altitude above sea level due to the reduced atmospheric pressure. The following table gives the boiling point at different altitudes: = TABLE 1.-BOILING POINTS OF WATER AT DIFFERENT ALTITUDES The specific heat of water, or the number of British thermal units (B.t.u.) required to raise the temperature of 1 lb. of pure water 1 deg. F., varies slightly with the temperature, but for all purposes of heating it may be taken at 1 B.t.u. per lb. Table 2 is a steam table which gives the boiling point for various pressures. |