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 undergo dissociation, as shown by the experiments of Thorpe and Young, into specifically lighter hydrocarbons of lower boiling points, and the yield of kerosene from ordinary crude petroleum may thus be greatly increased. A large number of arrangements for carrying out the cracking process have been proposed and patented, probably the earliest directly bearing on the subject being that of James Young, who in 1865 patented his “Improvements in treating hydrocarbon oils.” In this patent, the distillation is described as being conducted in a vessel having a loaded valve or a partially closed stop-cock, through which the confined vapour escapes under any desired pressure. Under such conditions, distillation takes place at higher temperatures than the normal boiling-points of the constituent hydrocarbons of the oil, and a partial cracking results. The process patented by Dewar and Redwood in 1889 consists in the use of a suitable still and condenser in free communication with each other—i.e. without any valve between them—the space in the still and condenser not occupied by liquid being charged with air, carbon dioxide or other gas, under the required pressure, ind the condenser being provided with a regulated outlet for condensed liquid. An objectionable feature of the system of allowing the vapour to escape from the still to the condenser through a loaded valve, viz: the irregularity of the distillation, is thus removed, and the benefits of regular vaporization and condensation under high pressure are obtained. In the American petroleum refineries it is found that sufficient cracking can be produced by slow distillation in stills of which the upper part is sufficiently cool to allow of the condensation of the vapours of the less volatile hydrocarbons, the condensed liquid thus falling back into the heated body of oil.

In the earlier stages of the development of the manufacture of mineral lubricating oils, the residues were distilled in cast-iron stills, and the lubricating properties of the products thus obtained were injured by overheating. The modern practice is to employ horizontal cylindrical wrought-iron or steel stills, and to introduce steam into the oil. The steam is superheated and may thus be heated to any desired temperature without increase of pressure, which would be liable to damage the still. The steam operates by carrying the vapours away to the condenser as fast as they are generated, the injury to the products resulting from their remaining in contact with the highly-heated surface of the still being thus prevented

In order to separate the distillate into various fractions, and to remove as much of it as possible free from condensed steam, it is now usual to employ condensing appliances of special form with outlets for running off the different fractions.

The process of distillation of lubricating oils under reduced atmospheric pressure is now in very general use, especially for obtaining the heavier products. The vapours from the still pass through a condenser into a receiver, which is in communication with the exhauster.

The products obtained by the distillation of petroleum are not in a marketable condition, but require chemical treatment to remove acid and other bodies which impart a dark colour as well as an unpleasant odour to the liquid, and in the case of lamp-oils, reduce the power of rising in the wick by capillary attraction. At the inception of the industry kerosene came into the market as a dark yellow or reddish-coloured liquid, and in the first instance, the removal of colour was attempted by treatment with soda lye and lime solution. It was, however, found that after the oil so purified had been burned in a lamp, for a short time, the wick became encrusted, and the oil failed to rise properly. Eichler, of Baku, is stated to have been the first to introduce, in Russia, the use of sulphuric acid, followed by that of soda lye, and his process is in universal use at the present time. The rationale of this treatment is not fully understood, but the action appears to consist in the separation or decomposition of the aromatic hydrocarbons, fatty and other acids, phenols, tarry bodies, &c., which lower the quality of the oil, the sulphuric acid removing some, while the caustic soda takes out the remainder, and neutralizes the acid which has been left in the oil. This treatment with acid and alkali is usually effected by agitation with compressed air. Oils which contain sulphur-compounds are subjected to a special process of refining in which cupric oxide or litharge is employed as a desulphurizing agent.

Testing.—A large number of physical and chemical tests are applied both to crude petroleum and to the products manufactured therefrom The industry is conducted upon a basis of recognized standards of quality, and testing is necessary in the interests of both refiner and consumer, as well as compulsory in connexion with the various statutory and municipal regulations.

In the routine examination of crude petroleum it is customary to determine the specific gravity, and the amount of water and earthy matter in suspension; the oil is also frequently subjected to a process of fractional distillation in order to ascertain whether there has been any addition of distilled products or residue. Petroleum spirit is tested for specific gravity, range of boiling points, and results of fractional distillation. To illuminating oil or kerosene a series of tests is applied in order that the colour, odour, specific gravity and flash-point or fire-test may be recorded. In the testing of mineral lubricating oils the viscosity, flash-point, “cold-test,” and specific gravity are the characters of chief importance. Fuel oil is submitted to certain of the foregoing tests and in addition the calorimetric value is determined. Paraffin wax is tested for melting point (or settling-point), and the semi-refined product is further examined to ascertain the percentage of oil, water and dirt present.

In civilized countries provision is made by law for the testing of the flash-point or fire-test of lamp-oil (illuminating oil or kerosene), the method of testing and the minimum limit of flash-point or fire-test being prescribed (see below, Legislation).

The earliest form of testing instrument employed for this purpose was that of Giuseppe Tagliabue of New York, which consists of a glass cup placed in a copper water bath heated by a spirit lamp The cup is filled with the oil to be tested, a thermometer placed in it and heat applied, the temperatures being noted at which, on passing a lighted splinter of wood over the surface of the oil, a flash occurs, and after further heating, the oil ignites. The first temperature is known as the flash-point, the second as the “fire-test.” Such an apparatus, in which the oil cup is uncovered is known as an open-test instrument. In Saybolt’s Electric Tester (1879) ignition is effected by a spark from an induction-coil passing between platinum points placed at a fixed distance above the oil.

Before long, however, it was found that the open-cup tests (though they are employed in the United States and elsewhere at the present time) were often very untrustworthy. Accordingly Keates proposed the substitution of a closed cup in 1871, but his suggestions were not adopted. In 1875 Sir Frederick Abel, at the request of the British Government, began to investigate the matter, and in August 1879 the “Abel test” was legalized. This apparatus has an oil cup consisting of a cylindrical brass or gun-metal vessel, the cover of which is provided with three rectangular holes which may be closed and opened by means of a perforated slide moving in grooves; the movement of the slide causes a small oscillating colza- or rape-oil lamp to be tilted so that the flame (of specified size) is brought just below the surface of the lid. The oil-cup is supported in a bath or heating-vessel, consisting of two flat-bottomed copper cylinders, to contain water, heated by a spirit lamp, and provided with an air-space between the water-vessel and the oil-cup. Thermometers are placed in both oil-cup and water-bath, the temperature of the latter being raised to 130° at the commencement of the test, while the oil is put in at about 60° F. Testing is begun when the temperature reaches 66° by slowly drawing the slide open and reclosing it, the speed being regulated by the swing of a pendulum supplied with the instrument. It has been found that variations in barometric pressure affect the flash-point and accordingly corrections have to be made in obtaining strictly comparative results at different pressures. The Abel-Pensky instrument, used in India and in Germany, differs only in being provided with a clockwork arrangement for moving the slide. Numerous other forms of open-test and close-test instruments have from time to time been devised, some of which are in use in the United States and in other countries.

It is still customary to determine the open flash-point and fire-test of lubricating oils, but the close flash-point is also usually ascertained, a modification of the Abel or Abel-Pensky apparatus, known as the Pensky-Martens, having been devised for the purpose. This instrument is so constructed that the higher temperature needed can be readily applied, and it is fitted with a stirrer to equalize the heating of the contents of the oil cup.

For the testing of the viscosity of lubricating oils the Boverton Redwood standardized viscometer is generally employed in Great Britain. By means of this instrument the time occupied in the flow of a measured quantity of the oil through a small orifice at a given temperature is measured.

Uses.—Petroleum has very long been known as a source of light and heat, while the use of crude oil for the treatment of wounds and cutaneous affections, and as a lubricant, was even more general and led to the raw material being an article of commerce at a still earlier date. For pharmaceutical purposes crude petroleum is no longer generally used by civilized races, though the product vaseline is largely employed in this way, and emulsions of petroleum have been administered internally in various pectoral complaints; while the volatile product termed rhigolene has been largely used as a local anaesthetic.

For illuminating purposes, the most extensively-used product is kerosene, but both the more and the less volatile portions of petroleum are employed in suitable lamps. Petroleum products are also largely utilized in gas manufacture for, (1) the production of “air-gas,” (2) the manufacture of oil-gas, and (3) the enrichment of coal-gas. For heating purposes, the stoves employed are practically kerosene lamps of suitable construction, though gasoline is used as a domestic fuel in the United States. The use of petroleum as liquid fuel is dealt with under, as is the employment of its products in motors, which has greatly