The unit of heat that is used in the industries and shops of England and America is the British thermal unit (B. T. U.) It is the quantity of heat required to raise 1 lb. of water to a temperature of 1° F. Therefore, the heat required to raise 5 lbs. of water through 15° F. is
5 X 15 = 75 B.T.U.
Similarly 72 lbs. of water require, to raise its temperature
72 X 1/2 = 36 B.T.U.
The unit that is used on the Continent and in scientific circles in America is the metric system unit called a calorie.
A calorie is the amount of heat necessary to raise 1 g. of water 1° C,