The essences or essential oils sold for general use are or ought to be obtained by distillation; but for many purposes they may be obtained equally as good, and, in some cases, superior, without. As these are often adulterated with olive or nut oils, or with spirits of wine, the fixed oils may be detected by pouring some of the suspected essence on a piece of clean writing paper, and holding it before the fire; the quantity of fixed oil it contains will remain, leaving a greasy mark, whereas the pure essential oil will evaporate without leaving any appearance; if spirits of wine be added, pour a little water or oil of turpentine into the adulterated sample, and it will turn milky, as the two will not unite without producing this effect. It is often sophisticated with the oil of turpentine, which is the lightest of all essential oils; in this case, rub a drop over the hand and hold it by the fire, when it may be recognized by the smell, or if burnt it will give out adense black smoke.

Rectified spirits of wine dissolve the volatile oil and resin of vegetables (their taste and smell most frequently reside in these), whilst water acts on the saline and mucilaginous parts. Proof spirit, which is a mixture of both these, extracts all their virtues, and through this we are enabled to obtain the essence or tincture of any vegetable, of superior quality to that generally sold, and at considerably less expense. The essential oil of lemons or oranges is obtained by rubbing off the yellow rind on the rough surface of a piece of loaf sugar, which is much superior for flavour to that produced by any other means. Scrape off the sugar after it has imbibed the oil, and dry it in a gentle heat, put it into small glazed pots, and tie them over with bladder; it will keep any length of time unimpaired. The same observation holds good as regards all fruit whose flavour or essential oil resides in its peel.