The total heat of the water is the number of British thermal units needed to raise one pound of water from 32° F. to the boiling point, under the given pressure., The latent heat of steam is the number of British thermal units (965.7) required to con vert one pound of water, at the boiling point, into steam of the same temperature. This is also the unit of evaporation.
The total heat of saturated steam is the num ber of heat units required to raise a pound of water from 32° F. to the boiling point, at the given pressure, plus the number required to evaporate the water at that temperature.
The specific heat of steam is the quantity of heat required to raise the temperature of one pound of steam through one degree of tempera ture. In British units and near the saturation temperature, it equals, at constant pressure, 0.48.
The specific gravity of steam at any tem perature and pressure, as compared with air of same temperature and pressure, is approxi mately 0.622. One cubic inch of water evapo rated into steam at 212° F. becomes 1,646 cubic inches—that is, nearly one cubic foot.
Water in contact with saturated steam has the same temperature as the steam itself. Water introduced into superheated steam will be vapor ized until the steam becomes saturated, and its temperature becomes that due to its pressure. Cold water, or water at a lower temperature than that of the steam, introduced into saturated steam, will condense some of it, thus lowering both the temperature and pressure of the rest until the temperature again equals that due to its pressure.
Heat. Unit of heat is a standard or term (B. T. U., British Thermal Unit) for measuring the amount of heat absorbed or emitted during any operation by any body or substance. It is
the quantity of heat required to raise one pound of water 1° in temperature, Fahr., at sea-level.
Specific heat is the capacity of a substance for heat. It is the number of heat units neces sary to raise the temperature of the body 1° F.
Latent heat is the heat absorbed daring evaporation, or it is the heat necessary to change water at 212° into steam at that temperature.
Transmission of heat: First, by radiation, that is, the heated body giving out its heat in rays; second, by convection, the heat being con veyed from the heated body by currents or flues, etc.; third, by conduction, the heat passing from the heated body to the colder one when in contact.
A unit of temperature is 1° F., or part of distance between freezing point, 32°, and boiling point, 212°, on Fahrenheit scale.
A thermometer is an instrument for indicat ing the intensity (not quantity) of heat. The thermometer scale upon which the intensity of the heat is indicated, is an arbitrarily chosen scale. The two scales in most general use are the Fahrenheit and the Centigrade.
The Fahrenheit scale is used most generally in domestic, commercial, and industrial fields.
Its lowest point, zero (0°), designates the lowest point to which mercury will fall in a tube when surrounded by a mixture of salt and ice. The point at which water freezes—called the freez ing point (32°)—is noted, and the point at which water boils under normal conditions is noted as 212°; the distance between is divided into 180 equal divisions called degrees.
The Centigrade scale is divided into 100 equal divisions called degrees between the freezing point of water (0°) and its boiling point (100°) under normal conditions. These points and di visions are calibrated or marked upon a glass tube, containing mercury, the expansion of which by the heat indicates the number of degrees, or the temperature.
The distance from 32° (freezing point) to 212° (boiling point), or 180° Fahrenheit, is equal to the distance 0° (freezing point) to 100° (boil ing point) on the Centigrade scale; or each de gree on Fahrenheit thermometeris 100/180 or of a degree on the Centigrade. Therefore to convert Fahrenheit temperatures to Centigrade temperatures, it is necessary to subtract 32 (de grees), and multiply by V,. To convert Centi grade temperatures to Fahrenheit temperatures multiply by and then add 32 (degrees).
Temp C.= (Temp. Temp. F.=(Temp. C X9/5)+32°.