Until a comparatively recent time, coal has been sold by weight and reputation alone; but conditions are rapidly approaching, which will require it to be sold according to its composition and heating value. Among manufacturers and others using large quantities of fuel, the practice of contracting for coal by specification is becoming increasingly common. The determining factors are the amounts of moisture, ash, sulphur, carbon, and volatile matter the coal contains, as well as the size of the pieces and freedom from dust. In a few of the most progressive cities, coal dealers are required to supply coal for schools and other municipal uses, which'has been subject to the approval of the City Engineer. The time is not far distant when dealers will be required to submit samples of all fuel, for sale to the public, to the examination of the municipal authorities.

The following table of the heating values of various fuels is taken from Benson's " Industrial Chemistry."

British Thermal Units for One Cent from Different Fuels

Acetylene, from carbide at 10 cents per pound......

600

Denatured alcohol, at 40 cents per gallon.........

2,000

Air gas (from gasoline, 80°Be at 25 cents per gallon)......

3,000

Water gas, at $1 per 1000 cubic feet.......

3,000

Coal gas, at $1 per 1000 cubic feet........

6,500 7,500

Gasoline, at 20 cents per gallon.............

Kerosene, at 15 cents per gallon............

11,000

Natural gas, at 50 cents per 1000 cubic feet............

18,000

Charcoal, at 10 cents per bushel (15 pounds).........

20,000

Petroleum at 5 cents per gallon.............

30,000

Producer gas, from anthracite, $7 per ton...............

30,000

Producer gas, from coke, $5 per ton............

36,000

Anthracite, at $7 per ton............

46,000

Producer gas, from soft coal, at $3 per ton.............

50,000

Coke, at $5 per ton...........

54,000 65,000

Mond producer gas from soft coal, at $3 per ton..............

Soft coal, at $3 per ton..................

80,000