Air.... 0.23751 Oxygen..... 0.21751 Nitrogen... 0.2438 Hydrogen.... 3.409
 Carbonic oxide... 0.2479 Carbonic acid.... 0.217 Olefiant gas..... 0.404

The table shows that the amount of heat which would be required to raise the temperature of 1 pound of water would be sufficient to heat to an equal degree about 8 pounds of cast iron, or 30 pounds of mercury, or 4 pounds of air, which is about 54 cubic feet.

## 21. Rule 2

Rule. To find the number of B. T. U. required to raise the temperature of a body a given number of degrees, multiply the specific heat of the body by its weight in pounds and by the number of degrees rise in temperature.

Denote the number of B. T. U. required by U, the specific heat by c, the weight by W, and let t and t1 be the temperatures before and after the heat is applied, respectively.

Then, V = cW(t1 - t).

## Example

How many B. T. U. are required to raise the temperature of 13 pounds of glycerine from 63° to 80°?

## Solution

From Table 5, the specific heat of glycerine is .555; hence, U = c W{t1 - t) = .555 X 13 X (80 - 63) = 122.655 B. T. U. Ans.

## 22. Heat Contained In Water

Heat Contained In Water. The quantity of heat which will be given off by a current of hot water, in cooling through any certain range of temperature, may be found by measuring the velocity of the current and computing the weight of the water which passes through the pipe per minute. The weight thus found should be multiplied by the number of degrees through which the water is to be cooled. The product is the number of heat units which will be given off per minute by the current in question.