Water-gas Tar--Water-gas tar, or gas-house tar, is a by-product of the coal used in the manufacture of water gas. It is slightly heavier than crude oil and has a comparatively low flash point. In burning, it should be heated only to a temperature which makes it sufficiently fluid, and any furnace suitable for crude oil is in general suitable for water-gas tar. Care should be taken where this fuel is used to install a suitable apparatus for straining it before it is fed to the burner. [Illustration: Babcock & Wilcox Boilers Fired with Blast Furnace Gas at the Bethlehem Steel Co., Bethlehem, Pa. This Company Operates 12,900 Horse Power of Babcock & Wilcox Boilers] GASEOUS FUELS AND THEIR COMBUSTION Of the gaseous fuels available for steam generating purposes, the most common are blast furnace gas, natural gas and by-product coke oven gas. Blast furnace gas, as implied by its name, is a by-product from the blast furnace of the iron industry. This gasification of the solid fuel in a blast furnace results, 1st, through combustion by the oxygen of the blast; 2nd, through contact with the incandescent ore (Fe_{2}O_{3} + C = 2 FeO + CO and FeO + C = Fe + CO); and 3rd, through the agency of CO_{2} either formed in the process of reduction or driven from the carbonates charged either as ore or flux. Approximately 90 per cent of the fuel consumed in all of the blast furnaces of the United States is coke. The consumption of coke per ton of iron made varies from 1600 to 3600 pounds per ton of 2240 pounds of iron. This consumption depends upon the quality of the coal, the nature of the ore, the quality of the pig iron produced and the equipment and management of the plant. The average consumption, and one which is approximately correct for ordinary conditions, is 2000 pounds of coke per gross ton (2240 pounds) of pig iron. The gas produced in a gas furnace per ton of pig iron is obtained from the weight of fixed carbon gasified, the weight of the oxygen combined with the material of charge reduced, the weight of the gaseous constituents of the flux and the weight of air delivered by the blowing engine and the weight of volatile combustible contained in the coke. Ordinarily, this weight of gas will be found to be approximately five times the weight of the coke burned, or 10,000 pounds per ton of pig iron produced.