Science for beginners . TTT^TTPTTT^ c/ryj^x/sv Fig. 74.—An illuminating coal gas plant. has gradually increased. Gaseous fuels are commonly trans-mitted from producer to consumer in pipes. The cost ofpipes makes it unprofitable to transmit the fuel long gases, as acetylene, are transmitted under pressure inmetal tanks. The material for making acetylene, calciumcarbide, may be transmitted long distances profitably. 98. Coal Gas.—Coal gas was the first manufactured gas. GASEOUS FUELS 95 It was used for lighting the streets of London and Paris morethan 100 years ago. In 1817, the c
Science for beginners . TTT^TTPTTT^ c/ryj^x/sv Fig. 74.—An illuminating coal gas plant. has gradually increased. Gaseous fuels are commonly trans-mitted from producer to consumer in pipes. The cost ofpipes makes it unprofitable to transmit the fuel long gases, as acetylene, are transmitted under pressure inmetal tanks. The material for making acetylene, calciumcarbide, may be transmitted long distances profitably. 98. Coal Gas.—Coal gas was the first manufactured gas. GASEOUS FUELS 95 It was used for lighting the streets of London and Paris morethan 100 years ago. In 1817, the city of Baltimore beganto use it for street lighting. The gas is made by distillingsoft coal in air-tight retorts (Fig. 74). The coal containsmany hydrocarbons which leave it when the coal is hydrocarbons at the same time are broken down intosimpler compounds. The gas also contains hydrogen andcarbon monoxid. Because of the hydrocarbons in coal gas itburns with a luminous flame. The manufacture of coal gas. GENERATOR CARBURETER SUPERHEATER Fig. 75.—Water-gas apparatus. has gradually declined of late owing partly to the fact thatbut few kinds of coal are suitable for use in making it andthese are becoming more expensive, and partly to the decreasein the cost of electricity. 99. Water-Gas.—Water-gas has come to replace coal gasin many cities. When steam is passed over red-hot carbon,the former is decomposed into hydrogen and oxygen. Thecarbon then unites with the oxygen from the steam to formcarbon monoxid or carbon dioxid depending upon conditions, 96 THE PRODUCTION AND USE OF HEAT while the hydrogen from the water is set free. By propercontrol of conditions, carbon monoxid rather than carbondioxid may be formed, which, with the hydrogen set free,makes a mixture of highly combustible gases. The mixture iscalled water-gas. During the chemical reaction of the steamand the hot carbon, heat is absorbed, and consequently thecarbon soon cools to a temperature at whic
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