(From comminuo, to break in pieces). Comminution. Contritio. It is the reduction of any solid body into finer particles, and is of two kinds, viz. contusion, or pulverisation, and leviga-tion, or trituration; which differ, however, only in degree.

Subsequent to pulverisation, where extremely fine powders are required, two secondary processes are necessary, viz. searching and elutriation: the first is the passing of any pounded matter by agitation through the interstices of cloth of different fineness, stretched across a cylinder, covered with a similar one. The latter is by diffusing the powdered substance in a proper quantity of water; then decanting the liquor with the lightest part of the powder, as directed in the preparation of crude antimony.

In powdering any substance, care should be taken to accommodate the substance to the instruments: such medicines as will dissolve metal should be prepared in stone or glass mortars; very hard bodies will abrade soft marbles: to prevent then the mixture of the instruments made use of with the medicine that is prepared by them, such mortars, stones for levigating on, must be chosen, as cannot be affected by the uses they are employed in.

Light dry substances, resins, roots of a tenacious texture, are more easily pulverised if the mortar is previously rubbed with oil; camphor and cortex require a little water: tough substances may be grated or rasped: hard minerals, as flint, calamine, or stone, should previously undergo an extinction; that is, should be made red hot, and then quenched in water; the alkaline and calcareous stones should be converted into lime by this process.

Some metals, if heated to a proper degree, arc rendered brittle, and then by agitation are easily powdered: of this kind is tin. This comminution of metals is called granulation.

Simple as this pharmaceutic operation is, its importance is considerable in medicine; resinous purgatives, when well triturated, are more easily soluble in the animal fluids, and operate more briskly with less irritation: antimony, finely powdered, discovers but little efficacy; but exquisitely levigated, is said to be a powerful alterative. Mercurials, and many other medicines, owe their virtue in part to comminution.

Roots, and such other articles as consist of different parts, viz. a resinous, ligneous, etc. should be completely powdered, and then the whole powdered substance should be well mixed together; for, without this precaution, one part which yields more easily to the pestle than another, as more friable, will be too active, and another too inert.

In levigating, some fluid must generally be added. Earthy and other hard bodies, that are not soluble in water, must first be finely powdered in a mortar, then levigated with water on a hard marble stone, and afterward dried on a chalk stone. Bezoar should be levigated with spirit of wine.