This form of preparing medicines is the simplest, and perhaps the least objectionable; but it is not applicable to all the articles of the materia medica. Those remedies, which are very unpleasant to the taste; those which deliquesce rapidly when exposed to the air, or are very volatile; and those which require to be given in large doses, or which are not diffused readily in water, cannot with propriety be administered in the form of powder. Some substances cannot be reduced to powder, unless they be very much dried; and the heat necessary for that purpose alters their properties; even the impalpable form given to powders is injurious to some resinous substances; and we cannot be surprised that a great alteration should be effected in a short time by the action of the air on so great an extension of surface as takes place in the operation usually adopted for reducing drugs to fine powder. Cinchona, rhubarb, ipecacuanha, and guaiacum, operate much less powerfully in the state of impalpable powder, than when reduced to that degree of fineness only, which can be effected by simply beating them in mortar, and passing them through a coarser sieve than is employed in the former case.

As powders are generally affected by the action of the air and light, all powders should be kept in opaque or green glass bottles. The effect of light on the majority of powders is rendered obvious by the labelled sides of clear bottles containing them, which are always turned to the light, becoming encrusted with the powder changed in its colour, while the other side remains clear and transparent.

In forming compound powders, it is necessary to sift the mixture after it has been well triturated. The following general rule for the formation of powders.is given by the Dublin College: - "Let the substances, to be powdered be first dried1, and then beaten in an iron mortar; then separate the finer powder by shaking it through a hair sieve, and preserve it in close vessels."

1 Mr. Battley, a respectable druggist in London, has proposed the following method of drying narcotic plants for powders: -

Previous to the process of drying the leaves of plants, the same rules must be carefully observed in reviving them, which were recommended previously to their being pressed for extracts.

The leaves being in a high state of preservation, and entirely freed from the stalks, and as much as possible from external moisture, must belaid in thin layers in baskets of willow stripped of its bark, in a drying room, from which the light is

Abstract of the Table of MM. Henry and Guibourt, showing the loss in powdering certain substances.

1000 Parts of