The barrel of crude petroleum of commerce is 42 gallons, weighing six and one-half pounds per gallon, and it is customary to consider roughly that three and three-quarters barrels are equivalent to one ton of coal.
The requirements of a desirable fuel oil are: high calorific value — at least 18,000 B. T. U.; specific gravity within 0.85 to 0.97 at 60° F.,• high flash point— not lower than 150°• and if for shipboard use, not lower than 175°, and 200° preferred; viscosity low enough to remain liquid at 32° and to flow freely with one foot head in a four-inch pipe; freedom from water (2 per cent highest exception) ; freedom from sulphur (1 per cent highest exception) ; free dom from dirt; and freedom from acid (one twentieth of 1 per cent highest exception).
Tar Tar fuels are of two classes: the high temperature tars and the low tempera ture tars. The former are products of the horizonal gas retorts, are quite viscid and con tain a high percentage of the objectionable naphthalene, and about 19 per cent of free car bon. Low temperature tars are the products of vertical gas retorts and blast furnaces manu facturing coalite and coke. The latter produce tars which are quite fluid, contain but small percentages of napthalene and anthracene and almost no free carbon. The tar from the verti cal gas retorts is of the same general character, but has a larger proportion of naphthalene and about 3 per cent of free carbon. In some cases the tars are first distilled to secure their benzol content.
As fuel, tar is much less desirable than the oils because of its content of oxygen com pounds (carbolic acid, cresylic acid, etc.), which not only reduce its calorific value but evolve noi some fumes. The average composition of tar is about as follows: carbon, 78 per cent; hydro gen, 6 per cent; sulphur, 1 per cent; nitro gen, 1 per cent; oxygen, 14 per cent. Its
calorific value is about 15,800 B. T. U. per pound. The flash point of tar varies from 100° to 115° F. for vertical retort tar to to 190° for horizontal retort tar.
Benzol appears upon the market in two grades —90 per cent benzol and 50 per cent benzol ; also in mixtures of the two. The 90 per cent grade is the only one used to any ex tent as a fuel and this use is confined almost wholly to internal combustion motors, where it very successfully takes the place of the higher priced gasoline and yields about 12 per cent more heat gallon for gallon - and with out any change in the motor. The calorific value of benzol is 17,500 B. T. U. per pound (156,700 B. T. U. per gallon).
Alcohol.- It has been truly said of alcohol that, in the present state of the world's knowl edge, it is the only fuel which man is able to manufacture in unlimited quantities and within a reasonable time, without drawing upon the reserves of natural fuels; and this is especially important as to those parts of the earth where there are no natural fuel deposits. Alcohol is easily produced from any form of vegetable growth containing sugar or fermentable starch and at a cost of about 21 cents per gallon from such relatively costly material as the sugar cane and the sugar beet- which may be grown in four months. The so-called gasoline motors run readily on 84 per cent alcohol (a higher degree has been found of no advantage) with out material change in the mechanism. The only difficulties to be overcome are those of starting from the cold, and the necessity of a more abundant supply of fuel than with gasoline. The calorific value of fuel alcohol is about 11,500 B. T. U. per pound (91,100 B. T. U. per gallon). With alcohol, internal combustion motors show a somewhat higher efficiency than with gasoline and run with much less noise.