r fats may likewise be obtained, by boiling and expression, from certain animal-substances; for the membranes which contain the fat, being chopped small, and set in a pan over the fire, become fit for the canvas bag, and, by pressure, afford a large quantity of fat; as we see in the art of chandlery, which thus extracting the oily matter, leaves a cake-behind, commonly called grease.

As to the essential oils of vegetables, they are obtained by distillation with an alembic and a large refrigeratory. Water must be added to the materials, in sufficient quantity, to prevent their burning; and they should be macerated or digested in that water, a little time before distillation. The oil comes over with the water; and either swims on the top, or sinks to the bottom, according as it is specifically heavier or lighter than water.

This process is applicable to the distilling of the essential oils from flowers, leaves, barks, roots, woods, gums, gums, and balsams, with a slight alteration of circumstances, as by longer digestion, brisker distillation, &c., according to the tenacity and hardness of the subject, the ponderosity of the oil, &c.

Essential oils may be divided into two classes, according to their different specific gravities; some floating upon water, and others readily sinking to the bottom. Thus, the essential oils of cloves, cinnamon, and sassafras, readily sink, whereas those of lavender, marjoram, mint, &c., float in water; the lightest of these essential oils is, perhaps, that of citron-peel, which even floats in spirit of wine; and the heaviest seems to be oil of sassafras.

For obtaining the full quantity of the more ponderous oils from cinnamon, cloves, sassafras, &c., it is proper to reduce the subjects to powder; to digest this powder for some days in a warm place, with thrice its quantity of soft river-water, made very saline by the addition of sea-salt, or sharp with oil of vitriol; to use the strained decoction, or liquor left behind in the still, instead of common water, for fresh digestion; to use for the same purpose the water of the second running, after being cleared of its oil; not to distil too large a quantity of these subjects at once; to leave a considerable part of the still, or about one fourth, empty; to use a brisk fire, or a strong boiling heat, at the first, but to slacken it afterwards; to have a low still-head, with a proper internal ledge and current leading to the nose of the worm; and, finally, to cohobate the water, or pour back the liquor of the second running upon the matter in the still, repeating this once or twice.

The directions here laid down for obtaining the ponderous oils to advantage, are easily transferred to the obtaining of the lighter; so that we need not dwell particularly upon them.

Many of the essential oils being dear, it is a very common practice to adulterate or debauch them several ways, so as to render them cheaper both to the seller and the buyer. These several ways seem reducible to three general kinds, each of which has its proper method of detection, viz. 1. With expressed oils. 2. With alcohol. And, 3. With cheaper essential oils.

If an essential oil be adulterated with an expressed oil, it is easy to discover the fraud; by adding a little spirit of wine to a few drops of the suspected essential oil, and shaking them together; for the spirit will dissolve all the oil that is essential, or procured by distillation, and leave all the expressed oil that was mixed with it, untouched.

If an essential oil be adulterated with alcohol, or rectified spirit of wine, it may be done in any proportion, up to that of an equal quantity, without being easily discoverable either by the smell or taste: the way to discover this fraud, is to put a few drops of the oil into a glass of fair water; and if the oil be adulterated with spirit, the water will immediately turn milky, and, by continuing to shake the glass, the whole quantity of spirit will be absorbed by the water, and leave the oil pure at top.

Finally, if an essential oil be adulterated by a cheaper essential oil, this is commonly done very artfully: the method is to put fir-wood, turpentine, or oil of

Oil. Old.

turpentine, into the still, along with the herbs to be distilled for their oil, such as rosemary, lavender, origanum, &c., and by this means the oil of turpentine distilled from these ingredients comes over in great quantity, and intimately blended with the oil of the genuine ingredient. The oils thus adulterated always discover themselves in time, by their own flavour being overpowered by the turpentine-smell: but the ready way to detect the fraud, is to drench a piece of rag, or paper, in the oil, and hold it before the fire; for thus the grateful flavour of the plant will fly off, and leave the naked turpentine-scent behind.

The virtues of oils, being the same with those of the substances from whence they are obtained, may be learned under their several articles, to which we refer.

We have this account of different oils in the island of Madagascar in the Universal History.

Oils are of different sorts; the most common are those of menach-tanhetanhe, menach signifying oil, menachil, menach-chouivau, menach-mafoutra, menach-vourave, menach-apocapouc, menach-vintang, and menach-arame. Menach-tanhetanhe is drawn from a particular plant, called, in the language of the country, tanbetanbe, and known in Europe by the name of palma Chriflii, or Ricinus. Menachil is an oil from the seed of sassafras, which they call woonacaze; a great quantity whereof is made in the valley of Amboule. Menach-chouivau is drawn from a fruit of the size of an almond, extremely good in liquors or meats. Menach-mafoutra is drawn from nuts, the fruit of the tree which produces dragon’s blood. Menach-vourave is drawn from a fruit named fonsfi. Menach-apocapouc is squeezed from the fruit apocapouc, extremely poisonous. Menach-vintang is an oil from large acorns, or mast. Menach-arame is drawn from nuts, the fruit of the tree from which the gum tacamahaca is produced.

Rock Oil. See Petroleum.

Essential Oil of Roses. See Roses.

Method of Purifying Rancid Oils. See Chemistry, p. 1431.