to compute the theoretical heating powers of these fuels. In the case of methane, CH_{4}, the formula is not true, but the error is not great enough to seriously affect the result. This gives for the combustion of one pound of: Anthracite 14,500 Br. Heat Units. Bituminous 14,200 " " " Petroleum 20,300 " " " Coal gas 20,200 " " " Generator gas 3,100 " " " Water gas 8,500 " " " Reducing the above to terms of pounds of water evaporated from 212° F., we have: POUNDS OF WATER EVAPORATED FROM 212° F. Anthracite 15.023 Bituminous 14.69 Petroleum 21.00 Coal gas 20.87 Generator gas 3.21 Water gas 8.7 The results of experiments show the efficiency of fluid-burning furnaces to be about ninety per cent., while with coal sixty per cent. may be taken as a good figure. The great difference in the efficiencies is due to the fact that fluid fuels require for combustion very little air above the theoretical quantity, while with the solid fuels fully twice the theoretical quantity must be admitted to dilute the products of combustion. Correcting our previous results for these efficiencies, we have: POUNDS OF WATER ACTUALLY EVAPORATED FROM 212° F., PER POUND OF FUEL. Anthracite 9.0 Bituminous 8.8 Petroleum 18.9 Coal gas 18.8 Generator gas 2.9 Water gas 7.8 These figures agree closely with the results of experiments. We will now consider the subject of cost. The following cities have been selected, as manufacturing centers, termini of railroads, or fueling ports for steamers. In the case of petroleum, as it is rarely shipped in the crude state, an approximation is made by adding to the cost at the nearest shipping port the freight charged on refined petroleum, and ten per cent. to cover duties and other charges. Owing to the difficulty of obtaining prices, in some of the cities, there may be some errors. COSTS. MARCH, 1884. Anthracite Bituminous Coal gas per ton of per ton of per 1,000 2,240 lb. 2,240 lb. cubic feet.