This Drug is to be chosen by Colour, Smell and Taste; the best Sort is of a Reddish-Brown; that which is deepened to Blackness, being fit only for external Use, as we may expect it to be mixed with some other narcotic Extract. To the Smell it should be pungent, almost to Volatility, without Fœtidness. When it proves very powerfully acrimonious to the Tongue (which the Opium we use, too often does) the inward Use of it should be rejected. The Right Sort is very bitter, and as such will be pungent to the Tongue, but will not leave a Soreness behind, in the Manner of corrosive Bodies; it should not be chosen heavy, lest it should be mixt with Sand, to increase the Weight; nor very dry, as some of its finer Powers might be then lost; and when cut in thin Slices, it may, by holding it to the Light, be easily discovered, if drossy. Burning it, in order to try the Purity, is recommended by some Authors; the best, emitting a clear Flame; to which let me add, that being a resinous Body, it may, if pure, be moulded by Heat into any Form, and answers the Characteristic observed of it by _Pliny_, Lib. 20. Cap. 18. _Sed maxime mirum, Æstivo sole deprehendi. Syncerum enim sudat, & se diluit, donec succo recenti simile fiat._ All authors agree, that Opium is very volatile, which Volatility must be the Cause of its immediate action on the Stomach; this is likewise manifest, by the following simple Experiment: "Take a Portion of Opium, either sliced or grated, place it before the Fire, near enough to dry without scorching; after remaining some time, you will find the Strength of it considerably abated." This Process was directed by the Ancients, to deprive it of its supposed poisonous Quality, but that is left behind in the grosser Body. The effects of it, thus managed, would not be so sudden, though used in large Doses, yet would prove, for Reasons given in a former Page, more severe and permanent; by this Means, the fixt Salts and Fæculæ remain, and the volatile Spirit, which occasions the soft refreshing Sleep, is in a great Measure, evaporated.