Page:International Library of Technology, Volume 93.djvu/61

 will be found that the lead ball is the hottest. Since all the balls are in a position to absorb equal amounts of heat, it is evident that the lead ball requires less heat to raise its temperature to a given point than the other balls. Different substances require different amounts of heat to raise equal weights of those substances 1°, water requiring more than most other substances. Hence, it is taken as a standard of comparison. Thus, This ratio is always expressed as a decimal. Hence, if the specific heat of a certain substance is said to be .1375, it is understood that the amount of heat required to raise a given weight of that substance 1° is only .1375 times the amount of heat required to raise the same weight of water 1°. 59. In Table II are given the specific heats of a number of substances.

60. Calculations involving the specific heats of various substances may be worked out by means of the following rules:

Rule I. —

in which

— How many British thermal units are required to raise 20 pounds of lead from 50° F. to 400° F., the specific heat of lead being .0314?

— Substituting values in formula 1,