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, sucu as white lead (basic car bonate), a had soap forms and dissolves in the excess of oil. The resulting product, on ex posure for some time to the atmosphere, readily dries o• 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 heated, especially if air is forced through the liquid. Such are the so-ealbal 'blown oils.' During this process the liquid becomes thicker, its viseosity 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 specifie gravity. of the 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 capable of ab sorbing. as well as various odor tests with acids and special reagents.
on Voitrfix. Otis. These arc liquids which give the peculiar odor to plants. Their composition differs very widely. The vari ous types are as follows: Terpenim, or hydrocar bons of the general formula (C,,dlm)„: certain ethers, aldehydes, ketones, and phenols (sub stances composed of hydrogen, and oxy gen) : and finally, certain suhstanees containing sulphur• or nitrogen among their elements, e.g. mustard oil. All these substances are soluble in alcohol. 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: (I) By distilling the plant with water: (2) by extraction of the plant with sol vents; 131 by pressing the plant ; (4) by macer ating in fat ; (5) by euttIvuiage, Or absorption in fat. In the distillation process, the material is put into a still with a large quantify of water. During 1.1)ffilitinn, the steam carries the oil over merlin n iea 1 ly and eat ion of (di mend water takes place on cooling. the oil being usually on top. Turpentine is produced by this proves, from the gnu, of the pine tree. the residue in the retort being common rosin. The processes of extrac
tion and expression requite no explanation. :Maceration, employed in those eases in which the product would be injured by high tempera tures, consists in gently beating the flowers or leaves in pure sweet tallow or lard, until ex hausted, the product being called a pomade. The oil may he extracted from it with alcohol. Entleurage is used in those cases in which an elevation of temperature would destroy the odor. The flowers or leaves are placed on 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 the perfume, and this is subse quently extracted with cold alcohol.
IlvoitueAneox OrLs. An account of the chem istry of the hydrocarbons may be found in a spe cial article under the name. Mixtures of liquid hydrocarbons, or 'hydrocarbon oils,' of natural or artificial origin, are used largely as fuels, illuminants, 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 impervious layers of shale or slate. The Russian petroleum deposits arc usually of Ter tiary origin. Considerable discussion has arisen concerning the origin of petroleum. According to Berthelot it is produced by the action of steam and carbonic acid gas on alkali metals. Mendel&fr regards it as the product of the action of water on metallic earbides. According to other theories, petroleum is derived from either plant or animal matter by a slow process. of destructive distillation under the enormous pres sure of superineumbent strata. Since either natural gas o• 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 composed of the liquid members of the marsh gaS or paraffin series together with small quantities of olefins, and traces of benzenes. Russian oils consist largely of the naphthol(' series, sim ilar to the olefins. Oil fresh from the well is a thick, syrupy liquid, greenish brown to black in color and of a disagreeable odor. Many are fluorescent. The specific gravity varies from 0.782 to 0.85. 3l.•nsh gas, ethane. propane. and butane are generally found in the fresh oil, but soon escape. Sand and water are frequently mixed with the oil. but are readily removed by settling in tanks.