Crude oil, a natural product, is the base of the fuels most commonly used in internal combustion engines, especially in the smaller sizes. From this compound the following derivatives are obtained by the process of distillation, a separation possible because of the different boiling points of the various oils. As each derivative or =DISTILLATE= has a different boiling point, the temperature of the crude oil is maintained at the boiling point of that product that is desired, and the resulting vapor is condensed. The following list is not anywhere near complete for there are several hundred distinctly different distillates, but it contains those that are of the most interest to the engine man. 1. Crude Oil. 2. Gasoline. 3. Naphtha. 4. Solar Oil. 5. Kerosene. The specific gravity of the crude oil as obtained in the field will range from 12° to 56° Beaumé scale. The crude from Pennsylvania will average 40° Beaumé while that from Texas will average 20°. The accompanying table will give the calorific values and general properties of the principle liquid fuels. It should be noted that the weight or density of the liquids is given in terms of specific gravity or Beaumé scale, in which the =SPECIFIC GRAVITY= of the fuel is the ratio of its weight per unit volume to the weight of an equivalent volume of water. The specific gravity of a liquid is generally determined by an instrument known as a =HYDROMETER= which consists of a glass tube sealed at both ends carrying a graduated scale on the upper portion of the stem, and a ballast weight of shot or mercury at the bottom. The hydrometer is floated in the liquid to be tested, and the lower the specific gravity, the lower the hydrometer sinks, and vice versa. The specific gravity of the liquid is read directly from the graduation on the stem that are on a level with the surface of the liquid under test. As in the case of thermometers, hydrometers are all graduated in two different scales, the specific gravity scale and the Beaumé scale. The specific gravity scale reads at 1.00 when floated on distilled water, and the Beaumé at 10.00 when floated on the same liquid. A difference in temperature affects the density of a liquid, hence all hydrometers are graduated for a standard temperature of 60°F unless otherwise specified. For a difference of 10°F there is a variation of one degree gravity in the Beaumé scale, and for a difference of 20°F in temperature there is a change of one degree on the specific gravity scale. If the temperature differs from 60°F, the corresponding correction should be made in the reading. To convert the Beaumé reading (B) to terms of the specific gravity scale (S) use the following formula: 140 S = ——————— = specific gravity. 130 + B 140 B = ——— = Beaumé scale. S PROPERTIES OF OILS