Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/803

Rh OILS 743 In addition to the use of bisulphide of carbon claimed under 3iis patent of 1855 (English patent 1856), E. Deiss enumerates as solvents chloroform, ether, and benzin or benzol. In 1863 an English patent was secured by Messrs Richardson, Lundy, and Irvine for obtaining oil from crushed seeds, or from refuse pressed cake, by the solvent action of &quot;volatile hydrocarbons from petro leum, earth oils, asphaltum oil, coal oil, or shale oil, such hydro- Carbons being required to be volatile under 212 Fahr. &quot; Since that time the development of the American petroleum industry and improvements in the apparatus employed have raised this system of extraction to the rank of a competing practical method of oil production. The most approved apparatus for this method of ex traction at present in use is that of Vohl. In the separation of oil from oil-seeds by means of light petroleum spirit heat is required. Vohl uses a light petroleum spirit boiling at not more than 60 C., which he calls canadol, and by a very ingenious arrangement of ex tractors, boiling and collecting kettle, and condenser, all brought into connexion by a system of pipes, he percolates the crushed .seed in the extractor cylinders with heated canadol, which passes down into the kettle laden with extracted oil. Here the volatile canadol is distilled off by steam heat, and passes into the condenser, whence it again goes into the extractors, still further exhausting the seed and carrying an additional portion of fixed oil into the kettle. In this way the original charge of canadol keeps circulat ing till it completely exhausts the charge of seed in the extractors. The canadol is then distilled off from the fixed oil collected in the kettle, the condensed spirit going this time into a separate receiver, .and finally the oil is perfectly freed from canadol by having steam blown through it. As pure petroleum spirit extracts neither resinous nor gummy matters from the oil-seed, and moreover takes up little or no colouring matter, the oil obtained by this solvent is remarkably pure, and the process is quite adapted for extracting even the oils used for food and for pharmaceutical purposes. The extraction of oils by means of ether, although presenting many advantages, has never been successfully undertaken on a com mercial scale, chiefly through the apparently insurmountable waste of the costly menstruum. Refining. The refining of vegetable oils is generally carried on as a separate industry. A kind of clarification of an expressed oil takes place by simple settling in oil-tanks, but the action is too tedious and the result too imperfect for practical purposes. The all but universal method of oil-refining now practised was invented and patented by Charles Gower in 1792. It consists of treating the oil with a small percentage of sulphuric acid, which, owing to the avidity with which it takes up water, acts on the suspended impurities by depriving them of the water they contain, and then carbonizes the substances themselves, which precipitate in dark- coloured flocky masses. To a certain extent also the acid influences the oil itself, liberating fatty acids and combining with the freed glycerin ; and these new products remain dissolved in the oil. It is thus of great importance to use no more than that proportion of sulphuric acid which is capable of separating the impurities. The ordinary operations of refining are briefly as follows. The oil is placed in a large tank, within which is a coil of pipe for heating by steam. When the oil is sufficiently hot, sulphuric acid is slowly added to the extent of from J to 1 per cent, of commercial acid, according to the nature and impurities of the oil. After the con tents of the tank have been in vigorous agitation for about an hour, it is left at rest for about five hours to allow the charred impurities to collect and precipitate. The oil is then conveyed into a washing vat, where it is mixed with about 20 per cent, of boiling water, with the addition of a little soda, and kept briskly stirred for an hour. From this the mixture passes to clearing tanks, in which the oil is allowed to rest about a week in order to thoroughly separate the remaining water. The addition of about 5 per cent, of common salt, by increasing the specific gravity of the water, considerably hastens this separation. Finally the oil is passed through a filter composed of alternate layers of tow, dried moss, canvas, and similar porous substances. Numerous modifica tions of the above sequence and other processes of refining have been introduced, and more or less adopted. One of the best distinct processes is that of Bareswil, which consists in heating the oil and adding to it 2 to 3 per cent, of caustic soda. Thereby a corresponding proportion of soap is formed, which, rising to the surface as a strong frothing scum, brings with it the impurities which are rendered insoluble. The scum is subsequently allowed to precipitate, in doing which it perfectly clarifies the oil. The coagulum so formed is used as a lubricant. Rudolph von Wagner proposed the use of concentrated chloride of zinc, instead of sul phuric acid, in refining ; and various other mineral acids as well as salts and tannin have also been suggested and tried. The most recent process of refining, and certainly the simplest and most ex peditious if experience demonstrates its sufficiency, is that intro duced by Mayer of the Hernalser Actien - Oelfabrik. It consists simply in submitting oil direct from the press to the action of a centrifugal machine. Thereby the albuminoid, mucilaginous, and Other impurities are driven against the sides of the drum, on which they deposit as a solid coating, leaving the oil pure and clear. The effect is, of course, due to the difference in density between the oil and its suspended impurities. Animal Fat tendering. The animal fats, butter only excepted, are liberated from the cells in which the fatty matter is enclosed by the agency of heat alone. The heat applied melts the fat, and by thereby causing its expansion as well as by acting on the moisture in the tissue it bursts the cell membrane and allows the liquid fat to flow together. The process is a noxious and disagreeable one owing to the intolerable stench given off by the putrefying animal matter while under the influence of heat ; and it is practically im possible to have the fatty matter heated on a large scale in its pure and sweet condition. It becomes an object of importance, therefore, to prevent the escape of such disagreeable fumes into the air, and the apparatus used is principally modified with that view. The simplest method of tallow-rendering consists in cutting the fatty matter by hand or machine into small fragments, which are placed in a copper vessel, with a small quantity of water, over an open fire. While the fire is applied the mass is kept stirring, and gradually the oil exudes and collects as the membraneous matter greaves or cracklings becomes shrunken and shrivelled. The fat is then ladled out of the boiler and strained through a sieve or filter, and the greaves, placed in a hair or woollen bag, are submitted to press ure, by which a further portion of tallow is separated. The pressed greaves are useful for dog s food or for feeding swine, &c., or they may be still a source of tallow, which can be obtained by treating them with bisulphide of carbon or with petroleum spirit. An im proved method of rendering tallow consists in crushing the suet under a pair of edge-stones, whereby the cells are ruptured, and heating the product over an open fire with about one-fifth part of water acidified with from two to seven parts of strong sulphuric acid added in the boiler. The means, however, of most effectually separating animal fat and at the same time avoiding the pollution of the air consists in the use of air-tight cylinders or kettles heated by steam. According to certain methods of working, superheated steam is forced into the kettle and acts direct on the shred suet, &c. ; in other cases the steam circulates in a coiled pipe within the vessel ; and a third way consists in the use of steam -jacketed rendering vessels. Strained tallow, however prepared, is further purified or refined before using by melting and thorough washing with hot water, after which it is allowed to cool slowly, so as to throw down impurities with the separating water. The same effect is also pro duced by blowing steam through molten tallow (comp. LARD, vol. xiv. p. 312). Classification and Enumeration of Oils and Fats. There is no strictly systematic plan upon which oils and fats can be satisfactorily classified and arranged. The scheme which follows brings the various commercial pro ducts into convenient groups, the distinctions of which are of prominent importance. I. Fluid Oils. a. Non-drying or greasy oils, containing chiefly olein. b. Drying oils, containing linolein. c. Fish or train oils, containing physetolein. II. Fats and Waxes. a. Solid glycerides, principally palmitin and stearin. b. Non-glycerides or waxes. In a pure condition the non-drying oils undergo little change through the influence of the atmosphere, but by degrees a process of slow fermentation is set up by the agency of the natural impurities they contain, developing an offensive rancid smell, and rendering the oils thick and greasy. Even in very thin layers, however, they never dry. Under the influence of nitrous acid and mercuric nitrate the olein of non-drying oils undergoes a molecular change into elaidin, and the oil becomes solid. Castor oil, the characteristic glyceride of which is ricinolein, occupies an intermediate position between drying and non-drying oils. The influence of nitrous acid on ricinolein changes the molecular constitution of the body forming ricinclaidin, with simultaneous solidification, as in the case of olein. The drying oils are those which contain as principal con stituents linolein or analogous glycerides. They absorb oxygen from the atmosphere with much rapidity, giving off at the same time carbonic acid and water, whereby the composition of the oil is modified, the proportion of oxygen much increased, and the physical properties of the oils changed. They do not solidify under the influence of nitrous acid. The fish oils do not dry on exposure to the