Ebullition —The temperature of ebullition of any liquid, or its boiling point, may be defined as the temperature which exists where the addition of heat to the liquid no longer increases its temperature, the heat added being absorbed or utilized in converting the liquid into vapor. This temperature is dependent upon the pressure under which the liquid is evaporated, being higher as the pressure is greater.
Total Heat of Evaporation —The quantity of heat required to raise a unit of any liquid from the freezing point to any given temperature, and to entirely evaporate it at that temperature, is the total heat of evaporation of the liquid for that temperature. It is the sum of the heat of the liquid and the latent heat of evaporation.
To recapitulate, the heat added to a body is divided as follows:
| Total heat | = | Heat to change the temperature + heat to overcome the molecular cohesion + heat to overcome the external pressure resisting an increase of volume of the body. |
Where water is converted into steam, this total heat is divided as follows:
| Total heat | = | Heat to change the temperature of the water + heat to separate the molecules of the water + heat to overcome resistance to increase in volume of the steam, |
| = | Heat of the liquid + internal latent heat + external latent heat, | |
| = | Heat of the liquid + total latent heat of steam, | |
| = | Total heat of evaporation. |
The [steam tables] given on pages [122] to [127] give the heat of the liquid and the total latent heat through a wide range of temperatures.
Gases —When heat is added to gases there is no internal work done; hence the total heat is that required to change the temperature plus that required to do the external work. If the gas is not allowed to expand but is preserved at constant volume, the entire heat added is that required to change the temperature only.
Linear Expansion of Substances by Heat —To find the increase in the length of a bar of any material due to an increase of temperature, multiply the number of degrees of increase in temperature by the coefficient of expansion for one degree and by the length of the bar. Where the coefficient of expansion is given for 100 degrees, as in [Table 6] , the result should be divided by 100. The expansion of metals [Pg 87] per one degree rise of temperature increases slightly as high temperatures are reached, but for all practical purposes it may be assumed to be constant for a given metal.
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