Degrees Specific Weight B.T.U.’S B.T.U.’S Beaumé Gravity per gal. per lb. per gal. Gasoline 67.2 .7125 5.932 21120 125,284 Heavy naphtha 64.6 .7216 6.011 20527 123,388 Kerosene 48.8 .7848 6.538 20018 130,877 W. Virginia crude 40.0 .8251 6.874 19766 135,871 Penn. fuel oil 31.9 .8660 7.215 19656 141,818 Kansas crude 29.0 .8816 7.345 19435 142,750 Fuel oil 22.7 .9176 7.645 19103 146,042 California crude 22.5 .9248 7.710 18779 144,786 California crude 15.2 .9646 8.036 18589 149,381 Alcohol, 95% 41.9 .816 6.798 10500 71,380 It will be noted that the petroleum products contain an enormous amount of heat energy, nearly 25% more than that of the same weight of pure carbon. It will also be noted that the lighter products such as gasoline, kerosene, etc., have more heat per pound but less per gallon than the heavier oils. This is rather confusing at first, but as will be seen after deliberation that the heavier fuel is the most economical since the least is used per horse-power, and is bought by the gallon. The calorific values given in the table are obtained by a calorimeter, and are burnt in the open air, and consequently have a different heating value when under compression in the cylinder of the engine. In all cases the liquids are vaporized before being introduced in the cylinder, the more volatile liquids such as gasoline being converted into vapor at atmospheric temperature, and the heavier non-volatiles by being sprayed into a heated vessel or preheated air. The percentage of liquid fuel contained in a cubic foot of air vapor mixture depends on the temperature, the boiling point of the liquid and upon the pressure and humidity. Gasoline consists principally of compounds of the methane series, the one representative of gasoline being Hexane (C_{6}H_{14}). It requires 15.5 pounds of air for combustion theoretically and about 10 per cent. more in practice. The formation of gasoline vapor produces a drop in temperature of 50°F, and should be heated 100°F above the atmosphere for the best results. The volume of air required for the combustion is about 192 cubic feet. With alcohol at 20 cents per gallon and gasoline at 12½ cents the number of B.T.U.’s for one cent in the case of alcohol is 3594 and 9265 in the case of gasoline. In the engine the difference is not so great owing to the difference in compression pressures. (18) Tar for Fuel. Because of the increasing interest in the Diesel type engine and the low grade fuels that it has made possible, we quote the specifications laid down by Dr. Rudolph Diesel, the inventor, before the English Institution of Engineers.