OTHER FUELS 



167 



admitted, heat is necessary also to warm this air, but the amount 

 of heat needed for this purpose is not large. If the air outside is 

 at a temperature of 32 F. (freezing point), and is to be warmed to 

 70 F., it would require about 2 pounds of coal per day to heat an 

 ample supply of air for one person (2000 cubic feet per hour). Thus 

 in heating residences an ample amount of fresh air can be allowed 

 without greatly increasing the cost of heating. 



COMPARISON OF FUELS. 



* Melting ice absorbs 143 Btu. per pound, but ice water thus formed also 

 absorbs from 15 to 20 Btu. additional before it leaves a refrigerator, making a 

 total of about 160 Btu. 



Amount of Heat Used in Cooking. In solving household prob- 

 lems it is important to know how much heat is used. It takes 

 about 180 Btu. to heat a pound of water from freezing to boiling 

 temperature, and it takes nearly 970 Btu. to boil away that amount 

 of water. " A watched pot never boils " is a saying containing much 



