I. Mineral oil is that fluid denominated petroleum, or naphtha, of which we have already treated, under the article Bitumens.
II. Animal oils are obtained by distillation from the fat of animals, together with their volatile salts. They may also be procured from certain animal matters, by boiling and expression. Such are the train and spermaceti oils extracted from whales, porpoises, and other fish.
This class of oils is chiefly consumed in lamps; and, as they are apt to become rancid, various means have been devised to edulcorate, or restore them to their natural state. Among the most easy expedients, are those contrived by Mr. Dossie, and published some years since by the Society for the Encouragement of Arts : they deserve to be more generally known:
1. Let one ounce of chalk, finely pulverized, and half an ounce of lime, slacked by exposure to the air, be put into a gallon of fetid oil; after which they must be carefully stirred, and hah" a pint of water gradually mixed. The stirring is to be repeated after an hour has elapsed, and at other convenient intervals, for two or three successive days. At the end of that time, a pint and a half of water, in which an ounce of salt has been previously dissolved, is to be incorporated with the ingredients in a similar manner, and the agitation occasionally renewed for one or two days. The whole is then suffered to stand at rest, when the water and chalk will be precipitated, and the oil will be considerably purified, though not so completely as by the following process :
2. Let an ounce of pulverized chalk be added to a gallon of crude, fetid oil, or to a similar quantity of the fluid prepared as above directed, a nd the whole be repeatedly stirred, as before described. After it has been mixed for several hours, one ounce of pearl-ashes, dissolved in four ounces of water, is to be added, and the stirring continued, at intervals, for some hours; when a solution of two ounces of salt, in one pint of water, must be add-ed, and the agitation occasionally repeated during the next two days.- Now, the mixture ought to stand for several days, when the brine will separate from the oil, which will be greatly improved both in smell and colour. Should a greater degree of purity be required, the proportion of pearl-ashes ought to be increased; and the period intervening between the addition of the salt and water prolonged : lastly, if the same operation be repeated, and the quantity of ingredients be reduced one-half each time, the oil may be brought to a Very light colour, and its smell rendered equally sweet as the common spermaceti..—By this treatment, the coarsest cod, or seal-oil, may be made to burn ; and, though it be too putrid for use, it may be so far corrected by the first process, as to be in all respects equal to that commonly sold.
In the year 1798, a patent was granted to Mr. Collier, for a chemical process for freeing fish-oils from their impurities, in point of smell, taste, and colour : and also for improved strainers for oils and other liquids, etc. The whole is performed in the following man-ner : first, the patentee pours any quantity offish-oil, or a mixture of different kinds of oil, into a vessel, which is heated to the temperature of 110 or 120 degrees of Fahrenheit,'s thermometer; when a portion of caustic mineral alkali is added, the weight of which is equal to four parts to the hundred of the oil. The mixture is next agitated; and, after the sediment and salt have subsided, it is drawn off into another vessel, containing a sufficient quantity of finely pulverized, fresh-burnt charcoal, and a small proportion of diluted sulphuric acid. The agitation is repeated; and, when the coal, together with the saline and aqueous particles, have subsided, the oil is passed through certain strainers, and thus rendered perfectly transparent and fit" for use. Such is the patentee's process ; but, as a description of the vessels employed in edulcorating the oil, would be unintelligible, without the aid of an engraving, the reader will consult the 10th volume of the Repertory of Arts, etc.; where the patent is fully described, and illustrated with a plate.
Beside its utility for lamps, animal oil possesses a valuable property which deserves attention. If one drop be laid on a bug, fly, wasp, or earwig, it will cause the immediate death of those trou-blesome vermin ; and, even when it is damaged, it may, according to Mr. Bucknall, be advantageously applied to frail -trees, about a mouth after they have been washed with soap -suds, in order to eradicate moss..
III. Vegetable OILs are procured either by expression, infusion, or distillation.
1. Those by expression are obtained from the seed, leaves, fruit, and bark of plants; which, being pounded in a mortar, the oil is forced out by means of a press, without the aid of heat. Such are the oils of olives, almonds, beech-mast, rape, and linseed.
2. In essential oils procured by infusion or decoction, the virtues of some particular plant are ex-tracted. To this kind belong the oils of roses, chamomile, etc. ; which, however, ought to be boiled only so long as there remains any aqueous moisture ; for otherwise they will become black.
3. Other essential oils of vegetables are prepared by distillation, only from those plants, or parts of -plants, that possess a considerable odour. They contain the fragrance, warmth, pungency, and often the active powers of the substance, from which they are drawn ;; whence they have received the name of essences, or essential oils for instance, those of cloves, cin-namon etc.—See Essence.
As many of these oils are ex-sive, and frequently adulterated with alkohol, or with expressed and inferior essential oils, we shall point out a few methods by which such practices may be detected;
J. If there be reason to suspect that an essence is sophisiticated with alkihot, or rectified spirit of wine it will be advisable to pour a few drops into a glass of pure water; and, if it be actually a base mixture, the whole nil) now become milky ; and, on repeatedly agitating the glass,- all the spirituous part will be absorbed by the water, while the genuine oil w ill float on the surface.
2. If the adulteration be effected by the aid of an expressed oil, the fraud may be discovered, by simply adding a little spirit of wine to a few drops of the suspected ; oil, and" shaking them together : for- the spirit will dissolve all the essence, or that obtained by distillation, while the expressed oil will not be in the least affected.
3. Lastly, if an essential oil-should have been mixed with a; cheaper or inferior essence (which is usually effected by distilling oil of turpentine with the herbs from which the essential oil is drawn), the imposition will speedily and spontaneously appear. But there is a more expeditious mode of detecting it; namely, by dipping a piece of rag, or paper, into the suspected essence, and holding it before the fire ; when the grateful fragrance of the plant will be volatilized; and. the scent of the turpentine will remain..
On the properties or virtues of essential oils, we cannot enter in this place; for, as they correspond with those of the substances from which they are obtained, the reader will, in particular instances, resort to their alphabetical series—.See also Menstruum.
Oil. - In April, 1792, a patent was granted to Mr. Cha. Gower, for his method of depurating and improving animal oil. He directs equal quantities of oil, and of water previously acidulated with a due proportion of vitriolic acid, to be poured into a barrel or other vessel, which must be placed pear a fire, and briskly agitated, in order to unite the two fluids. The liquor is then passed into pans, with a view to complete the solution of the gelatinous parts ; and that the water may sink to the bottom; when the clear oil is decanted. Should, however, the oil intended to be purified have a turbid, or ropy appearance, the patentee directs equal parts of such liquid, and pure water, to be mixed with a little yeast, and shaken in the manner above-mentioned. When the fermentation ceases, the whole must be poured into similar pans, where all feculent particles will subside, and the pure oil float on the surface, whence it may be drawn off for use.