Page:The New International Encyclopædia 1st ed. v. 14.djvu/900

* OILS. 768 OILS. the solvent used. Animal oils occur in cells of putiescible tissue and require prompt rendering or extraction to retain their quality. Rendering may be of three types, viz. : ( 1 ) Open-kettle rendering; (2) acid rendering; (3) steam ren- dering. In the lirst process the fatty tissue is chopped, heated over water until the oil or fat is melted, and tried out. The broken tissue shrivels and rises to the top, where it is skimmed oSt and pressed to remove traces of oil. On cool- ing, the oil and water stratify, and may be read- ily separated. In acid rendering, the fatty tissue is, withovit previous treatment, boiled with water and sulphuric acid, which dissolves away the tissue and liberates the oil. In steam rendering the tissue is destroyed b3- treatment with steam under ])ressure in autoclaves, the exhaust of foul- smelling gases being discharged into a chimney. The drying oils, linseed, poppy-seed, etc., ex- pressed by hot pressure, are subsequently boiled or heated with various oxidizing substances, such as the oxides of lead and manganese, in order to increase their drying or varnish-making properties. On mixing these boiled oils, which always contain some free fatty acid, with pig- ments whose base is some readily decomposable lead compound, such as white lead (basic car- bonate), a lead soap forms and dissolves in the excess of oil. The resulting product, on ex- posure for some time to the atmosphere, readily dries or forms a tough elastic coating, which acts as a protective covering to the material be- neath. Oils of the rape oil group absorb oxygen when healed, especially if air is forced through the liquid. Such are the so-called 'blown oils.' During this process the liquid becomes thicker, its viscosity and hence the lubricating Value increasing materially. The thickness is prob- ably caused by exchange of the sulphur con- tained by these oils for oxygen. The tests usually applied to fatty oils include determinations of speeifie gravity, of the amount of alkali necessary for saponification, of the amount of free fatty acids present, of the amount of volatile fatty acids, and of the amount of bromine or iodine that the oil is capaldc of ab- sorbing, as well as various color tests with acids and special reagents. E.ssEXTTAL on Volatile On.s. These are liquids which give the peculiar odor to plants. Their composition differs very widely. The vari- ous types are as follows: Ter])encs, or hydrocar- bons of the general formula (Ci„H,j)„: certain ethers, aldehydes, ketones, and |)benoIs (sub- stances composed of carbon, hydrogen, and oxy- gen) : and finally, certain substances containing sulphur or nitrogen among their elements, e.g. mustard oil. All these siilistances are solulile in nlcnliol, ether, petroleum, and certain other or- ganic solvents. Some of them have been prepared synthetically, but the greater number are still obtained from plants, by one of the following processes: (1) By distilling the plant with water; (2) by extraction of the plant with sol- vents; (.")) by pressing the plant ; (4) by macer- ating in fat; (.5) by cntlenrage, or absorption in fat. In the distillation process, the material is put into a still with a large quantity of water. During ebullition, the steam carries the oil over mechanically and separation of nil and water takes place on cooling, the oil being usually on top. Turpentine is produced by this process from the glim of the pine tree, the residue in the retort being common rosin. The processes of extrac- tion and expression require no explanation, ilaceratiou, employed in those cases in which the product would be injured by high tempera- tures, consists in gently heating the llowcrs or leaves in pure sweet tallow or lard, until ex- hausted, the product being called a pomadi-. The oil may be e-xtracted from it with alcohol. Knileurage is used in those cases in which an elevation of temperature would destroy the odor. The flowers or leaves are placeil oil glass-bot- tomed trays coated with pure tallow or lard; these trays are then stacked up and allowed to stand until the fatty matter becomes strongly charged with tlic perfume, and this is subse- quently extracted with cold alcohol. llYDiiocAKiioN Oils. Au account of the chem- istry of the hydrocarbons may be found in a spe- cial article uniler the name. Jlixtures of li^iuid hydrocarbons, or 'hydrocarbon oils,' of natural or artificial origin, are used largely as fuels, illuniinaiits, and lubricants. The main sources of these oils are petroleum, shale, and bituminous coal. Most of the native American oil comes from the Devonian and Upper Silurian. It oc- curs in sandstone or conglomerate (oil sand) between inqjervious layers of shale or slate. The Russian ])etroleiiiu deposits arc usually of Ter- tiary origin. Considerable discussion has arisen concerning the origin of petndeum. According to Berthelot it is produced by the action of steam and carbonic acid gas on alkali metals. Mendeleelf regards it as the ])roduct of the action of water on metallic carbides. According to other theories, petroleum is derived from either plant or animal matter by a slow process of destructive distillation uniler the enormous pres- sure of superincumbent strata. Since either natural gas or anthracite coal is usually found at no great distance from oil sources, it would seem that the last mentioned theories are the most plausible. American petroleum is mainly composcil of the liquid members of the marsh gas or paraflin series together with small quantities of olefins, and traces of benzenes. Russian oils consist largely of the naphlhene series, sim- ilar to the olefins. Oil fresh from the well is a thick, synijiy liquid, greenish brown to black in color and of a disagreeable odor. -Many samples are lluorescent. The specific gravity varies from 0.7S2 to 0.8.5. ^Marsh gas. ethane, ])ropane. and butane are generally found in the fresh oil. but soon escape. Sand and water are freipieiitly mixed with the oil, but are readily removed by settling in tanks. The oil is prepared for the market by :i process of fractional distillation and refining of the frac- tions with acid and alkali. The distillation ])rocess serves to siqiarate the oil into tliree ]ior- t ions, viz.; (1) Benzine distillate; ('2) burning oils; (.■?) residuum. The first portion is redis- tilled and yields very volatile products (naph- thas and gasolenes) that are used as solvents and for power in small engines. The second por- tion is likewise redistilled and yields two frac- tions, which are treated separately with strong sulphuric acid, followed by a washing with water. Ilicn treatment with caustic sodii. and a> final washing with water. By this process the oils are bleached and ]iartly deodorized. The two oils are commonly known under the name of kerosene. If the distillatinn of the crude oil has been carried on by the vacuum process, in