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Chap. XXXVI. Of Powders.

605

gummy resins as stand in need of it to give them an apparentdegree of purity, should not be admitted into the shop of theapothecary. Besides, many of the impurities which theyusually contain are easily separated, in compounding the pre-parations or extemporaneous prescriptions into which theyenter.

Styrax puiuficata. Lond.Purified Storax.Dissolve storax in rectified spirit of wine, and filter; after-wards reduce the balsam to a proper thickness, by distill-ing off the spirit with a gentle heat.

Dub.

Digest the storax in water, with a low heat, until it get soft;then express it between iron plates, heated with boiling wa-ter ; and, lastly, separate it from the water.

Storax is a balsam, or combination of resin and benzoicacid, both of which are soluble in alcohol, and neither of themvolatile in the heat necessary for evaporating alcohol. TheLondon process for purifying it is therefore not liable to anychemical objections. The method now directed by the Dub-lin college is certainly more economical, but must be attend-ed with loss of benzoic acid.

Chap. XXXVI.—POWDERS.

This form is proper for such materials only as are capableof being sufficiently dried to become pulverizable, without theJoss of their virtue. There are several substances, however,of this kind, which cannot be conveniently taken in powder;bitter, acrid, fetid drugs are too disagreeable ; emollient andmucilaginous herbs and roots are too bulky ; pure gums co-here, and become tenacious in the mouth ; fixed alkaline saltsdeliquesce when exposed to the air; and volatile alkalies ex-hale. Many of the aromatics, too, suffer a great loss of theirodorous principles when kept in powder, as in that form theyexpose a much larger surface to the air.

The dose of powders, in extemporaneous prescription, hgenerally about half a drachm ; it rarely exceeds a wholedrachm; and is not often less than a scruple. Substances