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Rh at the joints of the pipes. With the adoption of carefully fitted screw-joints in 1865 the pipe line gradually came into general use, until in 1891 the lines owned by the various transit companies of Pennsylvania amounted in length to 25,000 m.

The pumps employed to force the oil through the pipes were at first of the single-cylinder or “donkey” type, but these were found to cause excessive wear—a defect remedied by the use of the Worthington pump now generally adopted. The engines used on the main 6-in. lines are of 600 to 800 h.p., while those on the small-diameter local lines range from 25 to 30 h.p.

Tanks of various types are employed in storing the oil, those at the wells being circular and usually made of wood, with a content of 250 barrels and upwards Large tanks of boiler-plate are used to receive the oil as it comes through the pipe-lines Those adopted by the National Transit Company are 90 ft in diameter and 30 ft. high, with slightly conical wooden roofs covered with sheet iron; their capacity is 35,000 barrels, and they are placed upon the carefully levelled ground without any foundation.

Kerosene is transported in bulk by various means; specially constructed steel tank barges are used on the waterways of the United States, tank-cars on the railroads, and tank-wagons on the roads. The barrels employed in the transport of petroleum products are made of well-seasoned white-oak staves bound by six or eight iron hoops. They are coated internally with glue, and painted in the well-known colours, blue staves and white heads. The tins largely used for kerosene are made by machinery and contain 5 American gallons. They are hermetically sealed for transport. In Canada, means of transport similar to those already described are employ ed, but the reservoirs for storage often consist of excavations in the soft Erie clay of the oil district, the sides of which are supported by planks.

The primitive methods originally in use in the Russian oil-fields have already been described, but these were long ago superseded by pipe-lines, while a great deal of oil is carried by tank steamers on the Caspian to the mouth of the Volga where it is transferred to barges and thence at Tzaritzin to railway tank-cars. The American type of storage-tank is generally employed, in con]unction with clay-lined reservoirs.

Natural gas is largely used in the United States, and for some time, owing to defective methods of storage, delivery and consumption, great waste occurred. The improvements introduced in 1890 and 1891, whereby this state of affairs was put an end to, consisted in the introduction of the principle of supply by meter, and the adoption of a comprehensive system of reducing the initial pressure of the gas, so as to diminish loss by leakage. For the latter purpose, Westinghouse gas-regulators are employed, the positions of the regulators being so chosen as to equalize the pressure throughout the service. The gas is distributed to the consumer from the wells in wrought-iron pipes, ranging in diameter from 20 in. down to 2 in. Riveted wrought-iron pipes 3 ft. in diameter are also used. The initial pressure is sometimes as high as 400 ℔ to the sq. in., but usually ranges from 200 to 300 ℔. The most common method of distribution in cities and towns is by a series of pipes from 12 in. down to 2 in. in diameter, usually carrying a pressure of about 4 oz. to the sq. in. To these pipes the service-pipes leading into the houses of the consumers are connected.

Refining of Petroleum.—The distillation of petroleum, especially of such as was intended for medicinal use, was regularly carried on in the 18th century, and earlier. V. I. Ragozin states in his work on the petroleum industry that Johann Lerche, who visited the Caspian district in 1735, found that the crude Caucasian oil required to be distilled to render it satisfactorily combustible, and that, when distilled, it yielded a bright yellow oil resembling a spirit, which readily ignited. As early as 1823 the brothers Dubinin erected a refinery in the village of Mosdok, and in 1846 applied to Prince Woronzoff for a subsidy for extending the use of petroleum-distillates in the Caucasus. In their application, which was unsuccessful, they stated that the had taught the Don Cossacks to “change black naphtha into white,” and showed by a drawing, preserved in the archives of the Caucasian government, how this was achieved. The used an iron still, set in brickwork, and from a working charge of forty “buckets” of crude petroleum obtained a yield of sixteen buckets of “white naphtha.” The top of the still had a removable head, connected with a condenser consisting of a co per worm in a barrel of water. The “white naphtha” was sold at Nijni Novgorod without further treatment.

Some of the more viscous crude oils obtained in the United States are employed as lubricants under the name of “natural oils,” either without any treatment or after clarification by subsidence and filtration through animal charcoal. Others are deprived of a part of their more volatile constituents by spontaneous evaporation, or by distillation, in vacuo or otherwise, at the lowest possible temperature. Such are known as “reduced oils”.

In most petroleum-producing countries, however, and particularly where the product is abundant, the crude oil is fractionally distilled, so as to separate it into petroleum spirit of various grades, burning oils, gas oils, lubricating oils, and (if the crude oil yields that product) paraffin. The distillates obtained are usually purified by treatment, successively, with sulphuric acid and solution of caustic soda, followed by washing with water.

Crude petroleum was experimentally distilled in the United States in 1833 by Prof. Silliman (d. 1864), and the refining of petroleum in that country may be said to date from about the year 1855, when Samuel M. Kier fitted up a small refinery with a five-barrel still, for the treatment of the oil obtained from his father's salt-wells. At this period the supply of the raw material was insufficient to admit of any important development in the industry, and before the drilling of artesian wells for petroleum was initiated by Drake the “coal-oil” or shale-oil industry had assumed considerable proportions in the United States. Two large refineries, one on Newtown Creek, Long Island, and another in South Brooklyn, also on Long Island, were in successful operation when the abundant production of petroleum, which immediately followed the completion of the Drake well, placed at the disposal of the refiner a material which could be worked more profitably than bituminous shale. The existing refineries were accordingly altered so as to adapt them for the refining of petroleum; but in the manufacture of burning oil from petroleum the small stills which had been in use in the distillation of shale-oil were at first employed.

In the earlier refineries the stills, the capacity of which varied from 25 to 80 barrels, usually consisted of a vertical cylinder, constructed of cast- or wrought-iron, with a boiler-plate bottom and a cast-iron dome, on which the “goose-neck” was bolted The charge was distilled almost to dryness, though the operation was not carried far enough to cause the residue to “coke”. The operation was, however, completely revolutionized in the United States by the introduction of the “cracking process,” and by the division of the distillation into two parts, one consisting in the removal of the more volatile constituents of the oil, and the other in the distillation (which is usually conducted in separate stills) of the residues from the first distillation, for the production of lubricating oils and paraffin.

Various arrangements have been proposed and patented for the continuous distillation of petroleum, in which crude oil is supplied to a range of stills a fast as the distillates pass off. The system is largely employed in Russia, and its use has been frequently attempted in the United States, but the results have not been satisfactory, on account, it is said, of the much greater quantity of dissolved gas contained in the American oil, the larger proportion of kerosene which such oil yields, and the less fluid character of the residue.

In the United States a horizontal cylindrical still is usually employed in the distillation of the spirit and kerosene, but what is known as the “cheese-box” still has also been largely used. American stills of the former type are constructed of wrought-iron or steel, and are about 30 ft. in length by 12 ft. 6 in. in diameter, with a dome about 3 ft. in diameter, furnished with a vapour-pipe 15 in. in diameter. The charge for such a still is about 600 barrels. The stills were formerly completely bricked in, so that the vapours should be kept fully heated until they escaped to the condenser, but since the introduction of the “cracking process,” the upper part has usually been left exposed to the air. The cheese-box still has a vertical cylindrical body, which may be as much as 30 ft. in diameter and 9 ft. in depth, connected by means of three vertical pipes with a vapour-chest furnished with a large number, frequently as many as forty, of 3-in. discharge-pipes arranged in parallel lines.

The stills employed in Russia and Galicia are usually smaller than those already described.

The “cracking” process, whereby a considerable quantity of the oil which is intermediate between kerosene and lubricating oil is converted into hydrocarbons of lower specific gravity and boiling-point suitable for illuminating purposes, is one of great scientific and technical interest. It is generally understood that the products of fractional distillation, even in the laboratory, are not identical with the hydrocarbons present in the crude oil, but are in part produced by the action of heat upon them. This was plainly stated by Professor Silliman in the earliest stages of development of the American petroleum industry. An important paper bearing on the subject was published in 1871, by T. E. Thorpe and J. Young, as a preliminary note on their experiments on the action of heat under pressure on solid paraffin. They found that the paraffin was thus converted, with the evolution of but little gas, into hydrocarbons which were liquid at ordinary temperatures. In an experiment on 3500 grams of paraffin produced from shale (melting point 44.5° C.) they obtained nearly 4 litres of liquid hydrocarbons, which they subjected to fractional distillation, and on examining the fraction distilling below 100° C., they found it to consist mainly of olefines. The hydrocarbon C20H42, for example, might be resolved into C5H12+C15H30, or C6H14+C14H28, or C7H16+C13H26, &c., the general equation of the decomposition being—

&emsp;CnH2n+2 (paraffin) = Cn−pH2(n−p)+2, (paraffin) +CpH2p (olefine).

The product actually obtained is a mixture of several paraffins and several olefines.

The cracking process practically consists in distilling the oils at a temperature higher than the normal boiling point of the constituents which it is desired to decompose. This may be brought about by a distillation under pressure, or by allowing the condensed distillate to fall into the highly heated residue in the still. The result of this treatment is that the comparatively heavy oils