166 



GENERAL SCIENCE 



Heating Values of Fuels.* The heat required for heating, 

 cooking, and other purposes may come from any one of several 

 sources, and the one chosen should depend upon the cost and con- 

 venience of the heat supplied by these different sources. The table 

 below gives the approximate amount of heat produced by burning 

 several different kinds of fuel, as determined by the Bureau of 

 Standards; also the number of gallons of water which could be heated 

 from 32 to 212 F. (0 to 100 C.) for one cent, if no heat were lost. 



These figures apply to the cost of the heat actually supplied 

 to the water, but the true cost of any operation, like heating a kettle 

 of water or baking a loaf of bread, will depend also upon what pro- 

 portion of the heat is utilized, and this again will depend upon the 

 nature of the fuel. For instance, a coal fire must be kept burn- 

 ing for a long time in a stove of considerable size because much of 

 the heat from the fuel is used in heating the stove, and still more is 

 radiated from the heated surface of the stove, while perhaps only a 

 very little heat is actually used in cooking. A gas burner, on the 

 other hand, may be lighted and turned out quickly, and because 

 there is no large amount of metal to heat, much less heat is wasted. 

 For this reason gas, which costs six times as much as hard coal for 

 each heat unit, may still be cheaper to use than coal when heat is 

 needed for only a short time. 



Heating of Rooms. The proper heating of a residence is a 

 matter of the utmost importance, as upon it depend the comfort 

 and health of the occupants. Two essentials are a supply of heat 

 and a supply of fresh air. The supply of heat is usually given some 

 attention, while the supply of air is often sadly neglected. 



When fuel is burned in a furnace, stove, or grate for heating 

 purposes, part of the fuel is usually left unburned, part of the heat 

 produced passes off up the chimney, and part may be lost from hot 

 water, steam, or air pipes running to the several rooms. The 

 remainder is utilized in heating the air in the room, and in supplying 

 the loss of heat through the walls, doors, and windows. 



The Amount of Heat Required to Warm Fresh Air. A certain 

 amount of heat is, of course, required to keep a house warm in cold 

 weather, even if no fresh air is admitted; and if cold fresh air is 

 * From the Bureau of Standards. 



