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Distilled, or Volatile Oils.

PART III.

ilous proportions. From their solubility in alcohol, they areicmetimes adulterated with that fluid; but the fraud may bedetected by agitating some of the suspected oil with water;when if the oil contain alcohol, an increase of temperaturewill be indicated by the thermometer, but not if the oil bepure. 1 The more expensive oils are also occasionally adul-terated with the cheaper, particularly with oil of turpentine,which however is readily discovered by its peculiar odour, if apiece of paper be dipped in the suspected oil and dried with agentle heat. They are also sometimes adulterated with castoroil; and as the mixture, when the ingredients are in equal pro-portions, is soluble in alcohol, the fraud cannot be detected bythat test; but it is rendered obvious by the adulterated oilleaving a greasy stain upon paper, which has been touched withit, and held before the fire, whereas no stain is left by thegenuine oil.

Volatile oils unite with sulphur, in a temperature sufficientou,to melt it, and form brown-coloured foetid mixtures, whic^^have been denominated balsams of sulphur. The alkalies andearths combine imperfectly with them, and constitute a classof bodies which the French chemists have denominated sapo-nules. The action of the acids is much more violent than on thefixed oils: and several of them detonate when rubbed withoxymuriate of potash.

As medical agents, volatile oils are stimulant and aromatic.They are chiefly employed to remove nausea and flatulence, tQcorrect the griping qualities of some purgatives, and the dis-agreeable taste of other remedies. They may be given, tritu-rated with water and mucilage; or dropped first on a lumpof sugar, and through its medium diffused in water, forminga solution of what has been denominated oleum saccharum.The quantity of sugar must be more than ten times the weightof the oil; and when they are well triturated together the oilbecomes thus completely soluble in water, and may be dilutedto any extent.

Some of the more stimulant of these oils are added to em-brocations to be used as rubefacients in cases of numbness,pains, and paralytic affections of the joints.

The three British Colleges give the following general rulesfor the preparation of volatile oils.

1 Maiqucion, Annates de Chimie, xlviii. 26?.