OUR COAL SUPPLY 109 



the different parts of the apparatus, the heat produced by the 

 fuel may be determined. 



TABLE V. HEAT VALUE OF FUELS (APPROXIMATE) 



Calories per pound B.t.us. per pound 



Carbon 3,672 14,544 



Hydrogen 15,664 62,032 



Wood, Ash 2,141 8,480 



Wood, Beech 2,161 8,591 



Wood, Oak 2,100 8,316 



Wood, Pine 2,311 9,153 



Wood, Elm 2,150 8,510 



Charcoal 3,227 12,780 



Peat 1,800 to 2,300 7,200 to 9,000 



Lignite 1,800 to 3,000 7,200 to 11,700 



Coal, Bituminous 3,000 to 3,600 11,700 to 14,400 



Coal, Semi-anthracite 3,000 to 3,600 11,700 to 14,400 



Coal, Anthracite 3,400 to 3,900 13,500 to 15,300 



Coke 3,450 to 3,700 13,700 to 14,500 



Petroleum , . about 5,000 about 20,000 



VIII. OUR COAL SUPPLY 



123. Development of Coal Production. The first coal 

 produced in the United States was mined and marketed in 

 1820. The records show that 365 tons, an average of 1 ton 

 per day, were produced that year. For many years the pro- 

 duction of coal increased slowly. During recent years the 

 increase in production of coal has been very rapid, till in 1910 

 about 500,000,000 tons were mined and used. The diagram, 

 Fig. 84, shows that on the average the production of coal in 

 the United States has doubled about every ten years. If this 

 rate of increase in the use of coal continues in the future, we 

 shall be consuming in 1920 about 1,000,000,000 tons; in 

 1930 about 2,000,000,000 tons; in 1940 about 4,000,000,000 

 tons, and so on. At this rate of increase, how many tons will 

 we require in the year 2000 ? How many tons in the year 2040 ? 



124. Waste in Mining of Coal. In mining coal, it has gener- 

 ally been found necessary to leave large columns of coal to 

 support the roof of the mine. In the anthracite fields of 



