19. As stated in Art. 5, one B. T. U. will raise the temperature of a pound of water from 62° to 63°. The question arises, Will 1 B. T. U. raise a pound of any other substance, say mercury or iron, through the same range of temperature? Suppose two iron balls of the same weight are heated in boiling water. They will each have a temperature of 212°, and being of the same weight they must possess the same quantity of heat. Plunge one of the balls in a vessel containing, say, 10 pounds of water, and the other in a vessel containing 10 pounds of mercury. Suppose the weight of each ball is such that the temperature of the water is raised from 62° to 64° by the heat contained within the ball. Then it will be found that the mercury will be raised from 62° to 122°. That is, the same amount of heat that raises 10 pounds of water 2° raises 10 pounds of mercury 00°, or through a range of temperature 30 times as great. It is plain, therefore, that to raise a pound of mercury from 62° to 63° requires 1/80 of the heat necessary to raise a pound of water from 02° to 63°. Hence, we say the specific heat of the mercury is 1/80, or .0333.

The specific heat of a body is the ratio between the quantity of heat required to warm that body one degree and the quantity of heat required to warm an equal weight of water one degree.

Example

It is found that, to raise the temperature of 20 pounds of iron from 62° to 63°, 2.276 B. T. U. are required; what is the specific heat of iron?

Solution

To raise 20 pounds of water from 62° to 63° requires 20 B. T. U. The specific heat of the iron is, according to the above definition, the ratio between the quantities of heat required to warm the iron and the water, respectively, through 1 degree; that is, it is the ratio 2.276: 20 = 2.276 ÷ 20 = .1138. Ans.

Example

The specific heat of silver is .057; how many B. T. U. are required to raise 22 pounds of silver from 50° to 60°?

Solution

To raise the temperature of a pound of water 1 degree requires 1 B. T. U. Since the specific heat of silver is .057, only .057 B. T. U. is required to raise 1 pound of silver 1 degree. Hence, to raise 22 pounds of silver 10 degrees must require .057 X 22 X 10 = 12.54 B. T. U. Ans.

20. The specific heat of various substances is shown by the following table: