=Comparative Value of Coal to Other Fuels.=--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°Bé 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 Gasoline, at 20 cents per gallon 7,500 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 Mond producer gas from soft coal, at $3 per ton 65,000 Soft coal, at $3 per ton 80,000 =Price of Coal.=--The value of coal as a fuel will depend on the amount of heat it is capable of producing when burned; its price should therefore be determined by the heating value per pound of fuel as purchased. Secondary determining factors in price are those of convenience of handling and the difficulty in burning the fuel such as the size and uniformity of the pieces, the formation of clinkers, smoke and accumulation of soot. Soft coals, containing a large amount of volatile matter, usually produce much soot and smoke and as a consequence sell for a lower price than coals that produce little smoke.