makes the oil less valuable. The sulphur oils, besides being heavier, require a more expensive treatment, in order to produce a first-class illuminating oil, and, consequently, are not so desirable to the refiner.
When an oil contains very small percentages of gasoline and burning oil, and, in consequence, has a high fire-test and is free from sediment and wax, it may be of a much higher value as a lubricant, requiring no refining. Such oils are sold as natural lubricating oils.
55. The refiner generally attempts to produce all, or a part, of the compounds given in Table X by fractional distillation and subsequent purification with sulphuric acid, caustic soda, steam, and such other chemicals as the distillate may require.
The specific gravity being carefully taken, a given quantity of the crude oil is heated to 120° F. and poured into a graduated cylinder to settle. After standing for 10 or 12 hours, the amount and nature of the sediment is determined. Another sample of definite quantity of the crude oil is weighed and then dried for 24 hours over sticks of chloride of calcium. The difference in weight is ascribed to the loss of water, from which the percentage of water can readily be calculated.
The presence of certain offensive sulphur compounds may be detected by the odor, and they will be sure to appear in the distillates. The condition of these compounds is best determined by chemical treatment of the distillate.
COMPARISON OF GASOLINE AND KEROSENE
56. The two products of petroleum chiefly used in internal-combustion engines are kerosene and gasoline. Of these, the latter is by far the simpler to use, owing to the ease with which it may be vaporized. Commercial gasoline, as has already been pointed out, is not a homogeneous com- pound, but a mixture of lighter and heavier products. It is rated according to its density, common stove gasoline being usually from 71° to 72° Baumé. Owing to evaporation and
