576

Distilled, or Volatile Oils.

part in.

The mode of obtaining this oil, with its qualities and medi-cinal virtues, have been already noticed. The purer it is, themore soluble it is in alcohol of spec. grav. "820. (See Ricinus,Part ii.)

OLE A DISTILL AT A.

Distilled, or Volatile Oils.

Volatile Oils, as the}' are properly denominated by theEdinburgh College, are vegetable products, found in almostevery part of the vegetable body, except the cotyledons of theseeds, the part in which almost always the fixed oils are con-tained. In some plants, the volatile oil exists in distinct vesi-cles, and is obtained by simple expression, but in general it canonly be obtained by distillation; whence the name DistilledOils, given to this class of substances by the London College :and as the odour of plants generally depends on their volatileoils, the Dublin College, following the example of the olderchemists, who denominated them Essences, have adopted theterm Essential Oils. The expressed volatile oils are now re-jected from all the pharmacopoeias; and the whole of thoseused in pharmacy retained, are procured by distillation.

Volatile oil is obtained from both recent and dried plants.When fresh plants are to be employed, they require no previoustreatment; but when the plants are dry, or woods or barks areto be employed, the plants must be macerated in water forsome time, and the woods and barks be previously rasped.Thj distillation is performed in the following manner. Theplants, or the parts of them containing the oil, are to be putinto a tinned copper still, and closely pressed down; afterwhich, as much water is to be poured in as will be sufficient tocover the materials. The head of the still, which should below, is then to be luted on; the fire lighted, and so regulatedas to keep the contents of the still scarcely up to the boilingpoint; and the distillation continued, until the condensed va-pour comes over nearly insipid and inodorous. During thisprocess the volatile oil rises with the watery vapour, from whichhowever, the greater part of it again separates, after it has re-mained at rest for some hours in a cool place, and either floatson the surface of the water, or sinks to the bottom, accordingto Its specific gravity. The complete separation of the oil iseffected by an instrument called a separately (see Part i.);