Fire and Heat 145 



The weight of a unit measure of common fuels is as follows : coke 

 and coal, 2000 Ibs. per ton ; wood, 4000 Ibs. per cord ; petroleum, 

 6.5 Ibs. per gallon; kerosene, 6.1 Ibs. per gallon; gasoline, 4.9 Ibs. per 

 gallon ; wood alcohol, 6 Ibs. per gallon ; charcoal, 30 Ibs. per bushel. 



The heat value of artificial gas varies with the kind of gas. 

 The range is from 150 to 700 B. T. U. for a cubic foot. A cubic 

 foot of coal gas has a value of about 700 B. T. U. If it costs 80 

 cents per thousand cubic feet, it means that 80 cents purchases 

 700,000 B. T. U. of heat. You may compute the cost of an 

 equal quantity of heat from coal, and then compare the cost of 

 the two fuels, coal and gas. 



Electricity is utilized in many sections of the country both for 

 cooking and for heating, as well as for lighting. It is instructive 

 to compare the cost of a given amount of heat from electricity 

 with an equal amount of heat from any of the fuels. A kilo- 

 watt hour is estimated to furnish about 3400 B. T. U. The cost 

 per kilowatt hour varies greatly in different sections. If it 

 costs two cents per kilowatt hour, it will be found to be some- 

 what more expensive than gas at 80 cents per thousand cubic 

 feet ; but it has advantages which are not afforded by any 

 other source of heat supply. What are some of the advantages 

 of gas as a fuel for cooking ? For heating ? Of electricity 

 for these purposes? Compare with coal. 



SUMMARY 



Coal, although measured by the ton, is bought for the amount of heat 

 it yields. 



Heat is measured by the amount required to raise one pound of 

 water one degree Fahrenheit. This is called the British Thermal Unit 

 (B. T. U.). In the metric system the unit of heat is that required to 

 raise one kilogram of water one degree Centigrade, called the Calorie ; 

 or one gram of water one degree Centigrade, called the gram calorie. 



The heat value of a fuel depends upon its chemical composition. 

 Fuels vary greatly in heat value. 



Good coal has a 'heat value of about 14,000 B. T. U. per pound; 

 coal gas 700 B. T. U. per cubic foot ; and electrical energy 3400 B. T. U. 

 per kilowatt hour. 

 L 



