so that the knife-edge sunders the particles at an angle are greatly preferred. Fig. 193 shows a roller knife which is very serviceable. It is made by W. Weber, Evansville, Indiana. The circular blades or knives are made of the same quality of steel that is used for saws, and

are mounted upon a shaft, being separated by a series of spools or collars. The handles are of wood and mounted on the ends of the shaft, so that they are loose upon the shaft, thus permitting the handles to be grasped tightly whilst the roller knife revolves. The substances to be cut are placed upon a smooth board and the roller knife passed over them with more or less pressure. Upon the large scale drugs are cut with hay-cutters, implements usually consisting of four or more circular blades fastened to a shaft and revolving at the end of a trough, down which the substance that is to be cut is gradually fed. Sarsaparilla root is cut in this way before it is contused.

Rasping or Grating.-A half-round rasp (see Fig. 147) or a nutmeggrater is very useful at the prescription counter, as it frequently enables the pharmacist to prepare a small quantity of a powder for a prescription in case the regular stock-bottle is found empty or a very fresh powder is needed. The small pocket pepper-mills used by European travellers for grinding whole pepper at the table will be found especially useful.

Contusion, or bruising, is an operation very frequently resorted to. It may be defined as the process of reducing a drug to particles by striking it a succession of blows. The instrument generally employed is the well-known mortar and pestle, which, for contusing drugs, should be made of cast iron, bell-metal, or brass. The shape best adapted for this purpose is shown in Fig. 194, the mortar being represented on a mortar-block. The bottom of the mortar should be flat and heavy, so that it may rest firmly upon whatever base it is placed; the sides should flare slightly, but the mortar should be so deep that substances will not be easily forced out on to the floor by the blows of the pestle. A leather or wooden cover should be used upon the mortar when corrosive or irritating substances are contused. The pestle should be heavy and sufficiently flat on the under surface to permit the convexity nearly to coincide with the concave surface of the mortar. The inner surface of the mortar should be tinned, to prevent rusting and facilitate cleaning. The best support for an iron mortar is the top surface of a hard-wood post six inches in diameter and of sufficient length to pass from the top

of the floor into the cellar and rest on the ground. A turned wood mortar-block two feet high should rest upon the post; this block should have a flat iron hoop upon the top projecting half an inch above the

FIG. 194.

surface, as suggested by Dr. H. T. Cummings, whilst the bottom should have an inch hole bored up through the centre for the distance of twelve inches; an inch wooden pin, two feet long, should be firmly fixed in the centre of the post for the distance of twelve inches, which would leave twelve inches of the wooden pin projecting above the floor. Now, if the mortar-block is placed over it so that the pin enters the hole in the base, it will be found that a solid foundation is provided for resisting the blows of the pestle, and jarring and vibration, so destructive to balances and fragile apparatus, are prevented (see Fig. 194).

When for good reasons the post-support cannot be used, the next best base is a deep, strong box filled with dry sand. The principal objection to this is the constant loss of the sand and the inconvenience of having it spilled on the floor. When it is necessary to use an iron mortar and pestle for a continuous operation, for a considerable length of time, it will be found advantageous to connect the upper part of the pestle with an elastic wooden spring attached to the ceiling, so that the labor of lifting the pestle will be lessened. This spring is preferably made from a tapering hickory strip seven or eight feet long and four inches wide at the base, the rope connecting the pestle with the end of the spring being of such length that the pestle barely touches the bottom of the mortar when the spring is stretched to its utmost tension. On account of the large number of mills scattered over the country, established for grinding drugs, and the increase of facilities for grinding and powdering drugs on the large scale, the skilful use of the mortar and pestle by the pharmacist must be regarded as a lost art. The necessity for thoroughly drying drugs before subjecting them to comminution has already been mentioned. (See Desiccation.)

Mortar and pestle.

Wooden mortars and pestles are occasionally used for contusing soft bodies, like prune pulp, almonds, recent fleshy roots, substances that are affected by iron, etc. Lignum-vitæ is a very hard and suitable wood for this purpose, although boxwood is preferable when it can be procured, because it has less tendency to split.

Marble mortars are also used for operations of a similar character on a somewhat larger scale; but care must be used to avoid putting substances containing acid into such mortars, on account of the reaction upon the marble and the consequent contamination of the product.

Grinding and Pulverizing.-The former term is applied to the reduction of a substance by mechanical means to coarse particles, the latter to the production of fine particles. These processes are the most important of any grouped under comminution. At present they are

very largely carried on by drug-millers. It is necessary for the pharmacist to be familiar with the methods employed, however, if intelligent judgment is to be exercised in the subsequent treatment of the vegetable and mineral substances of the materia medica. Before pulverizing a substance it must be dried, and the desired fineness of the powder determines the character of the preliminary treatment. In order properly to grind or powder substances upon the large scale, special knowledge and experience are required; previous acquaintance with the methods best suited to accomplish the object on the small scale, whilst useful to some extent, will be found inadequate. If a drug is to be coarsely ground, the necessity for thoroughly drying it is generally not so pressing as when a fine powder is to be made of the substance; drugs containing volatile oils are apt to be rendered worthless if they are dried sufficiently to enable them to be ground to a fine powder. Myrrh,

cloves, cubebs, nutmegs, etc., afford good illustrations of this: hence these drugs are preferred when coarsely powdered. Within the last few years an important change in pharmaceutical practice in this respect has been effected, and preparations in which formerly very fine powders were directed are now ordered to be made from coarse powders: the processes for extracting the soluble principles having been greatly improved, the

necessity no longer exists for using the very fine powders, and hence volatile principles are not sacrificed.

DRUG-MILLS.

The Buhr-stone Mill is very extensively employed in drug-milling. There are two kinds, termed respectively under-runners and upperrunners. The principle upon which this mill operates is that of reducing the substance to particles by the friction and contusion that follow the delivery of the substance in the contracted space formed by a rapidlyrevolving stone disk, brought in nearly close contact with a similar disk which is stationary. In the under-runners the upper stone is stationary and the lower stone revolves, the upper store having a central circular opening through which the substance is fed, as shown in Fig. 195, the under stone being connected with the shaft. In the upperrunners the lower stone is stationary, the upper stone being perforated as in the under-runners. In both, the stones revolve horizontally. The

FIG. 196.

Buhr-stone.

stone used must be very hard. The best buhrmillstone is obtained from the old and celebrated quarries of La Ferté-sous-Jouarre, in France. The surfaces of the millstones are crossed with "furrows," which pass from the centre to the circumference, as shown in Fig. 196. The object of the furrows is to provide a means for the passage of the ground particles to the outer circumference and to the trough this is accomplished through the centrifugal force and current of air caused by the rapid revolution of

the stone in motion. The fineness of the powder is regulated by raising. or lowering one of the stones, this of course increasing or decreasing the space between them; the character of the powder is also influenced by the dressing of the stone. Fig. 195 illustrates one of the best of the modern buhr-stone mills,-Munson's under-runner.

Roller-Mills operate by crushing, or crushing and cutting, the substance. In their simplest form they consist of two smooth-faced iron rollers revolving in opposite directions, which can be brought into close contact by regulating screws. The principle has been extended and improved in modern milling, so that for grinding certain drugs this mill gives excellent results. The rollers are now made of steel, chilled iron,

or biscuit (porcelain), and are corrugated or ribbed to suit special purposes. The sections of these corrugations are serrated, undulated, or

crenated. The rollers

revolve in the same direction or in opposite directions, and at equal or different speeds. Fig. 197 shows the position of the grooved rollers, and Fig. 197a shows a sectional view of the same. A roller drugmill, operated by steampower or by hand, is made by W. Schroeder & Co., of Leipsic, Ger

many. The rollers have sharp oblique furrows upon their surfaces, and extra rollers are supplied to suit special purposes for grinding very fine powders, etc. (N. R., 1878, p. 336.) Allaire, Woodward & Co., of Peoria, Illinois, use with great success a corrugated roller-mill in grinding nux vomica.

FIG. 198.

FIG. 199.

Chaser-Mills are so called because two heavy granite stones, mounted like wheels and connected by a short horizontal shaft, are made to revolve or chase each other upon a granite base (see Fig. 198). The stones are discoid, and the grinding surfaces are the circumferential edges of the stones and the surface of the granite base; an iron cylinder, called a "curb," surrounds the circular base, and a "scraper," made of iron and adjusted at an angle, is connected with the shaft. It is evident that if the substance to be powdered is delivered upon the granite base in the path of the rapidly-revolving stones it must speedily be reduced to powder, not only on account of the crushing weight of the heavy stones, but also because of the attrition caused by the outer edge of the stone travelling through a longer distance than the inner edge. In some mills the stones having flat, grinding surfaces have been replaced by stones having curved surfaces, and the flat base by a circular gutter curved to correspond with that of the surface of the stone: in this way the grinding surfaces have been greatly increased and rapid pulverization facilitated. Fig. 199 shows the shape of

Chasers.

Chasers (curved grinding surface).

the stones of this form in use in Dr. Squibb's laboratory. In practice the chasers are enclosed in a tight box or small room, closed with airtight doors, and the substance to be powdered is fed in from the top by an