Science for beginners . in about 120 years, or about theyear 2030. We therefore see how necessary it is that weavoid as far as possible all waste of coal. At the present time a much larger portion of our coal isbeing wasted than is being used for the benefit of two chief sources of loss are: 1. Only about one-half of the coal is being removed fromthe mine; the other half is being left in such a condition thatit probably can never be recovered. OUR COAL SUPPLY 101 2. We have seen in the preceding pages of this chapter,that only a small portion of the energy in the coal bnrned isnow
Science for beginners . in about 120 years, or about theyear 2030. We therefore see how necessary it is that weavoid as far as possible all waste of coal. At the present time a much larger portion of our coal isbeing wasted than is being used for the benefit of two chief sources of loss are: 1. Only about one-half of the coal is being removed fromthe mine; the other half is being left in such a condition thatit probably can never be recovered. OUR COAL SUPPLY 101 2. We have seen in the preceding pages of this chapter,that only a small portion of the energy in the coal bnrned isnow being utilized. 106. The Coal Fields of the United States.—The map,Fig. 77, shows the location of the more important coal fieldsof the United States. The large eastern field extending fromPennsylvania to Alabama yields chiefly anthracite, semi-anthracite and semi-bituminous coals. The central fields,consisting of the Illinois, Indiana, Kentucky, Iowa, and Mis-souri fields yield chiefly bituminous and cannel coals. The. Fig. 77.—Distribution of coal fields in the United States. large northwestern field of the Dakotas, Montana, and Wyom-ing yields bituminous and lignite coals. The fields of Col-orado yield bituminous and semi-anthracite coals (see TableII, Art. 91, Composition of Solid Fuels, for the distinctionin different kinds of coals). IX. DEVELOPMENT OF HOUSE HEATING107. The Roman Hypocaust.—The houses of the Romanswere heated by hypocausts. These were fire rooms con- 102 THE PRODUCTION AND USE OF HEAT structed in the cellars (Fig. 78). From these rooms claypipes led to various rooms of the house above. Through thesepipes all of the smoke and heat from the burning wood passedto the rooms above. This method of heating would seemvery disagreeable to us, especially when the volatile matterwas distilling from the wood. Crude as this method ofheating was, it was the best method known until compara-tively recent times. The use of the hypocaust perished withthe civilization
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