disk and the face of the ring; as soon as it passes here it is on the discharge side of the mill, and all that is fine enough is immediately

driven out by the beaters on the back of the disk. What is not fine enough to discharge is caught by these back beaters and beaten against the screens until fine enough to pass through. The screens are made of square steel, and present a grinding surface to the beaters and a discharging surface between each bar; they are two inches in width and extend around three-fourths of the diameter of the mill, thus giving a large discharging surface without diminishing the grinding surface. The material, as it is ground, falls into the box or room below. The most effective work is achieved with the disintegrator running at high speed, three thousand revolutions per minute; under such conditions, six hundred pounds of wild cherry bark can be finely crushed in an hour.

Side view.

FIG. 80.

The production of very fine powders of section of corrugated ring; c. drugs has long since passed into the hands

Steel disk with beaters attached.

of the drug-miller, and even the coarser powders intended for percolation are to-day prepared by only a small number of pharmacists. For the latter purpose the drug mills shown in Figs. 81 and 82 will be found very desirable In the New B Swift Mill the grinding is done between plates placed horizontally, while in the Enterprise Mill they are placed vertically. The grinding surfaces of both mills consist of circular chilled-iron castings studded with concentric rows of sharp teeth, those of one plate fitting between those of the other. The teeth decrease in size toward

the centre, and the fineness of powder is regulated by a pair of screws, by means of which the plates are made to approximate each other. One of the plates is stationary while the other revolves. Separate sets of plates for coarse and for very fine grinding can be had for the mills. Care should be taken to thoroughly clean the mill after each operation, else the remaining dust will surely contaminate the drug next ground. The simplest method of cleaning is to run sawdust through the mill repeatedly, then loosen the screws and remove the grinding plates, so as to wash these with hot water, if necessary, and dry quickly. A great mistake often made by the inexperienced is the attempt to produce fine powders at once by screwing the plates close together, instead of grinding the drug coarsely at first and gradually tightening the mill; the first plan is apt to cause the material to become heated and cake, while the second plan will achieve the desired end more perfectly, with far less

plates, which possess the advantage over the usual styles of not allowing any material to pass through the mill unground (this some

times happens with vertical plates), and of not holding any of the ground material too long, whereby clogging may sometimes be caused with the horizontal plates. The mill is provided with an iron support, or may be had without it, to be mounted on a heavy block or box. For grinding small quantities at the dispensing counter the No. 450

Enterprise Mill (Fig. 84) is admirably adapted; it is constructed on the same principle as the larger Enterprise Mill shown before. All the before-mentioned hand-mills can be opened horizontally, as shown in the cuts, by means of a thumb-screw and hinge; thus the interior may be readily exposed to view for examination or cleaning. The material is supplied through a capacious hopper, with its base specially arranged for crushing the drug into coarse particles. The

apidity with which the material should be fed to the mill depends ntirely upon the character of the drug, as some drugs will soften inder the influence of heat and pressure, while others are not affected it all. Substances like vanilla, which cannot be heated before powdering, on account of the rapid loss of the aromatic principle, must be reduced in the soft condition; and, although the old method

Cutter for vanilla.

of grinding with sugar or clean sand is still largely in use, it is decidedly inferior to the process of cutting. Grinding or powdering vanilla has a tendency to press out the soft pulp, which soon retards the reduction of the tough fibre and requires the expenditure of much time and labor. If vanilla be reduced to the requisite degree of fineness for percolation by means of a rapid-acting cutter it retains practically its original condition, no pulp being expressed, and a powder is obtained far superior to that by grinding with sand or sugar. Fig. 85 represents the American mince-meat chopper, an apparatus admirably adapted to the cutting of vanilla, and first suggested for this purpose, I believe, by Mr. N. H. Jennings, of this city. The large knife-blade with which the cutting is effected must be kept well sharpened. As the cylinder revolves with each turn of the lever, fresh particles of the material are continually presented to the knife, and disintegration is rapidly achieved, while the aroma and virtue of the vanilla are kept intact.

The grinding of drugs on a large scale, and particularly into very fine powder, is accomplished either in buhr-stone mills, iron mills, such as the Bogardus Eccentric Mill, or stone "chaser" mills. In the first-named mill, grinding is effected between two large stone disks placed horizontally and provided with numerous furrows to facilitate the passage of the ground drug from the centre to the circumference; one of the disks is stationary-in some mills the upper, and