and petroleum, have almost superseded the fat oils for lubricating purposes. They have no chemical action on the ordinary metals, and are not affected by cold. The lightest of these comparatively heavy oils are used for spindles, or other kinds of rapid machinery; the heaviest for the bearing parts of heavy machinery; and those of an intermediate character for such things as printing-presses, agricultural steam-engines, &c. In America and on the Continent this oil is also used for making gas. The firm of Whitmore and Craddock is favorably known for the manufacture and purification of these machinery oils. See Oil, Belmontine (above), and Oil, Paraffin (below).
Oil, Pa′raffin. Syn. Paraffine oil. This name was given by Mr Young to the oil produced by the distillation of cannel coal, Boghead coal, &c., at a temperature considerably lower than that employed in the manufacture of illuminating gas. The following is a brief outline of Mr Young’s process:—
Manuf. (Young’s patent.) Boghead coal, broken into small fragments, is introduced into perpendicular tubes or retorts, about eleven feet in height, by conical hoppers at their upper extremities. Four of these tubes constitute a set, being built into one furnace, and charged by a single workman. They pass completely through the furnace, and are closed below by dipping into shallow pools of water, while the openings into the hoppers above may be shut by spherical valves. The coal in each tube is gradually heated as it descends to that part which passes through the furnace, and when it reaches the bottom of the tube it has parted with its volatile constituents, and is raked away as refuse, the coal from above descending as it is removed. Thus, the action of these perpendicular retorts is continuous, and the distillation goes on uninterruptedly both day and night. The vapours produced are conducted by iron tubes to the main condensers, which consist of a series of syphon pipes freely exposed to the air. The quantity of incondensible gas formed is inconsiderable; and it is this result, so different from that obtained in the ordinary gasworks, that marks the great value of Young’s process. The crude oil, a dark-coloured, thick liquid, is then distilled to dryness in large iron cylindrical stills, and is thus freed from the excess of carbon which is left behind as coke. The oil, after distillation, is further purified by being acted upon by strong sulphuric acid (oil of vitriol), which chars the principal impurities, and causes them to subside in the form of a dense black, heavy acid tar. To separate the remaining impurities, and that portion of the sulphuric acid which remains in the oil, it is next subjected to the action of caustic soda. As thus purified, the paraffin oil contains four distinct commercial products. To effect their separation, the process of fractional distillation is first employed.
The first elevation of temperature drives over the lighter and more volatile portions, which, when purified by a subsequent distillation, yields the fluid known as ‘paraffin naphtha,’ ‘petroleum spirit,’ ‘benzoline.’ This product is used as a substitute for ‘turps,’ as a solvent for india rubber for cleaning gloves, and for burning in those naphtha lamps so much employed by costermongers, and workmen in railway tunnels and similar situations. On the perfect separation of this naphtha the safety of the burning oil depends. This burning oil, the ‘paraffin oil’ of commerce, comes over at a much higher temperature than the naphtha. It is a perfectly safe lamp oil, and has a greater illuminating value than any other oil in the market. Its properties are noticed below. The third product in point of volatility is a comparatively heavy liquid (machinery oil), largely used for lubricating purposes in the Lancashire factories. From this oil, and others which come over at a very high temperature, the fourth commercial product is separated by the action of artificial cold. This last product is the beautiful translucent solid, paraffin, now much used as a candle material.[60] (See Oil, Paraffin, Petroleum.)
[60] For a detailed account of the processes carried on at the Bathgate works, see Mr Tegetmeier’s paper in ‘England’s Workshops,’—Groombridge and Sons.
In the preparation of paraffin oil, from native petroleum, the oil is obtained by direct distillation from the petroleum, and subsequently separated from the more or less volatile hydrocarbons (the paraffin naphtha, the lubricating oils and the solid paraffin) that are associated with it by fractional distillation as in Young’s process; whereas, when procured from bituminous minerals, it is derived from the tar or crude oil, which has to be previously extracted from the bituminous matters by destructive distillation. There are various methods for obtaining this tar or crude oil, which, although differing in detail, are in general principles very similar to that described in Young’s patent. Thus, whilst in many works closed horizontal retorts are employed, in other establishments vertical ones, to the bottoms of which are attached receptacles for the receipt of the exhausted coal or other material as it falls from the retort, the same as in Young’s apparatus, are extensively adopted. When horizontal retorts are employed they are made of cast iron, and vary in length from 8 to 10 feet, being from 28 to 34 inches wide and from 9 to 14 inches deep. The charge is introduced by an opening in the end of the retort, by which aperture the exhausted residue is removed when necessary. This aperture is closed by a tightly fitting cast iron cover while the distillation is going on. At the other end of the retort is a pipe for carrying off the products of distillation. This communicates with a larger pipe, and this latter with the condensing apparatus.
A number of these retorts are set together in a row, with a furnace at one end, and flues extending beneath the retorts, while the upper parts of the retorts are covered with brickwork, to prevent the oil vapours from being decomposed by the heat of the waste furnace gas passing to the chimney through the flues above the retorts.
The gaseous products of the distillation of the tar, leaving the retort by the exit tube already described, are cooled by being made to pass through a number of iron pipes exposed to the air, or surrounded by water, and thus becoming condensed pass into a reservoir in the form of the oil, which forms the material from which the various hydrocarbons are separated by fractional distillation. Accompanying the oil vapours are certain uncondensable gases; these escape through a properly contrived outlet which is made in the condensing pipes; in some works these escaping gases are utilised as fuel, and in others for purposes of illumination.
In other works superheated steam is driven into the retorts during the process of distillation; but although this has the effect of sweeping the oil vapour more quickly out of the retort into the condenser, it is questionable whether this advantage covers the extra cost of the production of the steam.[61]
[61] Payne’s ‘Industrial Chemistry.’ Edited by Dr Paul.