elongated funnel, the spout of which delivers the material immediately upon the path of the stones. The height of the curb is increased by pasting heavy paper around it, and the fineness of the powder is influenced by the height of the curb. The revolution of the chasers produces an upward current of air; this carries over the lighter particles, which fall outside the curb and are subsequently collected as a fine powder; those particles which are larger are of course heavier and cannot rise to the height of the curb, but fall back under the stones to be reground : in this way refractory substances can be reduced to very fine powder. Chasers are more largely employed in making "dusted" or very fine powders than any other form of pulverizing apparatus.

Mills with Iron Grinding Surfaces. Many mills have been constructed from time to time to suit special purposes: these cannot be noticed at length in a work having the scope of the present one. Barrelmills have been used. These consist of strong barrels lined with sheetiron, supported by strong iron shafts attached to the heads. The substance to be comminuted is placed in the barrel, and large round iron balls, like cannon-balls, are introduced: upon revolving the barrel rapidly, disintegration is effected. This principle is used also in pulverizing dried extracts and friable substances. A hollow circular iron ring, having a diameter slightly larger than that of the cannon-ball which is placed inside with the charge of substance to be powdered, is made to revolve rapidly; the inertia of the cannon-ball and the friction render its speed less than that of the ring, and the substance is quickly ground. The "Bogardus" mill is constructed on a very ingenious principle: the grinding surfaces are two horizontal chilled-iron plates, the lower one revolving, the upper one stationary; both have corrugations having sharp edges, arranged concentrically. The peculiarity of this mill is that the centres of the grinding-plates are not directly over each other as in buhr-stone mills, but the centre of the lower plate is placed a few inches to one side: by this arrangement the substance to be ground is caught by the ring-edges of the revolving plate and dashed against the cutting-edges of the stationary upper plate at an angle, the effect being to incise it as if cut with scissors and crush it at the same

time.

Mead's Disintegrator differs from the mills thus far considered in the principle of construction, in the character of the grinding surfaces, and in its method of operation. The grinding is effected by hardened steel beaters riveted to a steel disk, which revolves vertically between corrugated rings; the beaters are placed on the side of the disk nearest to the feeding-trough, and catch the material as it enters the mill, beating it with great force against the corrugated rings until it is fine enough to pass between the disk and the face of the rings; as soon as it passes here, it is on the side of the mill from whence it is discharged, and all that is fine enough is immediately driven out by the beaters on the back of the disk. That portion of the substance which is not fine enough is caught by the beaters and beaten against the screens until sufficiently fine to pass through. The screens are two inches in width, and extend around three-fourths of the diameter of the mill: they are made of square steel bars, and present a grinding surface to the beaters,

FIG. 200.

FIG. 201.

but there is sufficient space between them to permit the passage of fine particles. The substance, as it is ground, falls into a receiving-box below the mill, or is discharged through the floor into a room below. One prime requisite in running this mill is high speed: the disk must make three thousand revolutions a minute. The disintegrator is capable of grinding one hundred and fifty pounds of Ignatia bean, or six hundred pounds of wild-cherry bark, in one hour. Fig. 200 gives an illustration of the mill, whilst Fig. 201 shows an enlarged view of the revolving disk, and a section of the screens immediately above. Hand-Mills. It is more difficult to construct a drug-mill for the general use of the pharmacist than one for the special purposes of a drug-miller. The latter has the choice of a buhr-stone mill, chaser, disintegrator, iron mill, etc., which he can adjust to suit the character of the substance he desires to grind. The pharmacist's drug-mill, on the other hand, is expected to do all kinds of work rapidly and well. It must, therefore, be capable of ready adjustment, possess durability, and have cutting surfaces not quickly dulled, and working parts not liable to get out of order.

Mead's disintegrator.

Revolving disk and screens.

It is not easy to realize that every medicinal substance has an individuality of its own, but he who neglects the study of the physical characters of the substances of the materia medica can never expect to overcome successfully the obstacles which stand in the way of disintegration. Hand drug-mills may be divided into three classes: 1. Those having vertical grinding surfaces. 2. Those having horizontal grinding surfaces. 3. Those having conical grinding surfaces. They have the following points in common: iron is the principal material of construction, the grinding surfaces are of hardened iron or steel and consist of teeth arranged in concentric rows, and the regulation of the fineness of the powder is effected by a screw or screws, by which the plates are made to approach or recede from each other.

1. HAND DRUG-MILLS WITH VERTICAL GRINDING SURFACES.Swift's Mill (old style).-This hand-mill has been in use longer than any other in the American market. Its introduction marked an era in the history of pharmacy, and, although superseded now by greatlyimproved mills, it is still remembered with grateful feelings by those of the present generation, who had been previously accustomed to laborious mortar practice. In this mill there are two vertical grinding-plates, one of which is stationary, whilst the other is connected with the horizontal revolving shaft; a conical breaker is also attached to the shaft, and when in position it is immediately below the lower opening of the hopper; a fly-wheel with a handle is bolted to the outer

end of the horizontal shaft, and furnishes the power required. The teeth are of iron and arranged in concentric rows, and the plates are made to approach each other or to separate by an adjusting-screw. The supports of the mill are of ash or oak, and are durable and firm. The principal disadvantages of this mill are the difficulty of cleaning it, its slow action, its liability to become clogged, and the absence of a tight box or drawer to receive the ground drug. Two improvements have been made in the Swift's new-style mills: in one the fly-wheel has been made larger and heavier, in the other a double fly-wheel has been attached. Troemner's Mill, whilst constructed upon the same principle as Swift's, is much more thorough in its action, and requires less labor to operate it, than Swift's mill (old style). It has vertical plates, a thumb-screw to regulate the fineness of the powder, a heavy fly-wheel, and a close-fitting drawer to receive the powdered drug. It is not so easily cleaned, however, as the next mill to be mentioned.

The Enterprise Mill.-The introduction of this mill, in 1875, gave an impetus to the manufacture of hand drug-mills which is still felt the application of several new principles, and the extension and improvement of some valuable old ones, at once gained the attention of practical pharmacists. The great advantage possessed by this mill over those in the market at the time it was introduced was the ease with which the interior and the working parts could be reached. The principle of sup

porting the grindingplates upon a horizontal shaft, to the extremities of which heavy flywheels were attached, and providing a means for lifting all the working parts out of the interior to facilitate their cleaning, were novel features. Fig. 202 so thoroughly illustrates this mill that it is hardly necessary to dwell upon

its other features. The left-hand grinding-plate revolves, being geared to the shaft, whilst the one on the right hand is stationary: when in position for grinding they are, of course, nearly in The opening

contact.

of the interior is effected

by simply turning the thumb-screw in front. A smaller mill is shown in Fig. 203. It is very conveniently used at the dispensing counter. 2. HAND DRUG-MILLS HAVING HORIZONTAL GRINDING SURFACES.-Thomas's Mill.-This was one of the first hand drug-mills

FIG. 203.

made upon this principle. There are two horizontal grinding-plates, the lower one revolving and the upper one stationary. A vertical shaft, which is geared to a horizontal shaft by bevel-wheels, communicates the power to the lower plate upon revolving the flywheel. The absence of a closed receptacle, and the difficulty of quickly cleaning the grinding surfaces, are the principal objections to this mill.

Swift's B Mill.-This is a comparatively new mill, very different in appearance from the old Swift's mill, and different in principle. The grinding-plates are horizontal, the lower one revolving, whilst the upper one is stationary and forms the lower part of the hopper. It has two fly-wheels, but the receptacle for the powder is an open one. A valuable feature of the Enterprise mill is present here,-i.e., that of opening horizontally in the centre. The fineness of the powder is regulated by raising or lowering the lower plate by the thumb-screw.

3. HAND DRUG-MILLS HAVING CONICAL GRINDING SURFACES. -The principle of construction in these mills is probably the best, because it avoids the fault of those constructed on the vertical-plate principle, that of permitting particles to drop into the receptacle before they are finely ground, and also the fault of the horizontal-plate mills, which may hold the ground particles too long, often until clogging results. The conical-plate mill, if properly constructed, leaves little to be desired.

Hance's Mill is made on this principle. Formerly, the objection to this mill was the loss of time and labor consumed in getting it apart: this has been obviated by the introduction of the principle of opening it horizontally with the same kind of thumb-screw and hinge that is used in the Enterprise mill. The Hance mill is better adapted for heavy work than any other of the hand drug-mills, and, if desired, a belt and pulley can be attached for steam-power. The lower plate is conical in shape, the summit being elongated into a breaker; the teeth are arranged in consecutive rows, a scraper being attached to the under surface of the lower plate; the upper grinding surface is situated upon the lower surface of the hopper, and corresponds in shape and in the arrangement, number, and size of teeth with the surface of the lower plate. The revolving-plate is attached to the upright shaft by a simple key; this permits the easy removal of the plate when the mill is to be cleaned, yet holds it securely when in operation. Power is communicated by means of two shafts at right angles, geared with bevel cog-wheels. The fineness of the powder is regulated by a thumb-screw at the base, which elevates the revolving-plate. The support to the mill is a strong iron frame, which is cast in one piece, and, although the mill has but a single fly-wheel, this is partially compensated for by the length of the bearing for the horizontal shaft. Fig. 204 shows the

form which is mounted on a stand and is designed to be bolted to the floor; the new form, in which the mill is mounted on a box-stand, may

FIG. 204.

be preferred by some. Fig. 205 shows the upper grinding-plate, and Fig. 206 the lower plate with a feeder, which is fastened to the upper portion with a set-screw, so that seeds and similar drugs may be automatically fed to the mill.

General Rules for Operating Hand-Mills. -Much of the dissatisfaction experienced in operating hand-mills has arisen from improper methods of using them, or from failure to measure accurately the degree of resistance to disin

Hance's drug-mill.

tegration possessed by the substance to be ground. One of the first requisites, as before mentioned, is to dry the substance as perfectly as its physical character will permit without injuring it. If coarse, bulky, fibrous roots, barks, or similar substances are to be ground, they must first be cut or bruised. Most substances are ground with less labor if they are passed through the mill first with the coarse adjustment, returning the portion which is sifted out for regrinding, after setting the plates more closely together: this plan is repeated until the whole is ground. Care should be taken not to feed the substance into the hopper faster than it can be ground. The desire to get through quickly is the most frequent cause of clogging the mill, and when this occurs much time is lost, and the operator is strongly reminded of the well-worn proverb about undue haste. If a considerable quantity is to be ground, two persons can operate the mill more economically than one,-one feeding the mill carefully, the other supplying the physical labor, and, after the expiration of a given time, exchanging places. Good judgment is necessary in determining the rapidity with which substances can be fed into the hopper. Resinous or oily drugs, or substances which soften by heat, require very careful treatment and cannot be fed rapidly; dry ligneous barks or roots, on the other hand, can be fed as rapidly as the extent of grinding surface of the mill and the muscle of the operator will permit. The mill should be thoroughly cleaned after each operation, particular attention being given to the grinding-plates. In the case of substances which form hard lumps by heating or clogging upon the plates, the quickest way is to use boiling