Page:Popular Science Monthly Volume 27.djvu/267

Rh about 1,200 barrels each, beneath which fires may be kindled, and urged by a strong draught until a red-heat is attained.

Petroleum consists of a great many different fluids, which range in volatility from the boiling-point of ether to nearly a red-heat. Such being the case, as soon as the oil is heated at all, the most volatile products begin to come over, at first colorless as water, but very gradually assuming a yellow tinge until the most dense distillate coming over at the last is quite dark brown in color, so that, if all the distillate were allowed to run into a tank together, it would not look very differently from the original petroleum. In the ordinary process of refining petroleum, the distillate is divided into three portions. The first is the lightest, colorless portion, nearly as volatile as ether, and is called crude naphtha, or "benzine." Like the crude petroleum, this crude naphtha may be distilled and divided into gasolene, A, B, and C naphtha, which are used in gas-machines, for mixing paints, and other similar purposes, sometimes also for burning in lamps and stoves.

The middle portion of the distillate, which is neither very light nor very heavy, and having but little color, is the crude illuminating-oil, or kerosene. As it runs from the still it has a very offensive odor, due to the decomposition of certain portions of the petroleum at the high temperature reached in the still. To remove the offensive compounds, the oil is first agitated with about five per cent of strong oil of vitriol. This combines with the offensive oils, forming a black, tarry residue that falls to the bottom of the tank as soon as the oil is brought to rest. This mixture of acid and oil is called "sludge," and is used in large quantities in the manufacture of commercial fertilizers. After the acid is drawn off and the oil washed with water, it is again washed with a strong solution of caustic soda, which removes the excess of sulphuric acid, and also some peculiar acid compounds that exist in the oil. The oil, after another washing with water, is nearly colorless, with the peculiar balsamic odor of kerosene, and possesses the slight opalescence peculiar to these oils. As usually prepared, they belong to the class known as "high-test" kerosenes, and consist almost entirely of oils that exist in the petroleum already formed, being merely separated from the lightest and heaviest portions. Such oils are called the educts of the petroleum.

The heaviest portions of the distillate contain paraffine, and are called paraffine-oils. They also are mainly educts of the original oil; they, however, contain a much larger proportion than the kerosene of the products of the decomposition of the oil. A tarry residue remains in the still, called "residuum."

In other establishments the naphtha and illuminating oil are distilled from the petroleum, and the dense oil remaining in the still, called "reduced petroleum," is drawn out and used for lubrication. A large part of this dense oil from which the naphtha and illuminating oil have been removed is "cracked," or destructively distilled, by