Latent Heat of Steam

—Insensible heat; in heating water a certain proportion of the heat which has been absorbed, is not shown by the thermometer or by touch. There are two sorts or conditions of heat in the proce of steam production operating upon water: (1) sensible heat; (2) latent or insensible heat; hence the constituent, or total heat of steam consists of its latent heat in addition to its sensible heat. In generating water into steam there is absorbed about five and one half times as much heat as is required: under atmospheric pre ure, to raise the temperature of the water from freezing point, 32° Fah., to boiling point, 212° Fah., an amount of heat which if the water were a fixed solid would, it is said, render it red hot by daylight. Tested by a thermometer the steam will show only 212°, but by experiment 965.7 heat units have been added, which is stored up in some unaccountable way and is called the latent heat of steam. In some steam tables, such as Buel’s, the latent heat of steam is divided into two elements, as follows: (1) The heat required to evaporate the water at the temperature of the steam, called internal latent heat; (2) the external work done by the steam in making room for itself against the pre ure of the atmosphere (or surrounding steam if enclosed in a boiler), called the latent heat of volume.