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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 cloggiug 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 bopper, with its base specially arranged for crushing the drug into coarse particles. The
rapidity with which the material should be fed to the mill depends entirely upon the character of the drug, as some drugs will soften under the influence of heat and pressure, while others are not affected at 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. X. 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, wbile the aroma and virtue of the vapilla 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
in others the lower—while the other revolves, the material being fed through an opening in the centre of the upper stone. By suitable approximation of the stone disks, powders of various degrees of fineness can be produced.
The portable Bogardus Eccentric Mill (Fig. 86) is a great favorite with drug-millers, as it can be driven at a high rate of speed without
becoming heated, and discharges the ground material promptly without danger of choking. Both grinding plates revolve in the same direction, on centres which are about one or two inches apart from each other, hence the name eccentric; this arrangement causes the material between the plates to be moved about in every conceivable manner, to be acted upon by the plates at every point, and subjected to a peculiar twisting, cutting, and grinding motion, whereby it is rapidly disintegrated, with large results in quantity ground and the expenditure of but little power. In mills with single revolving plates (the other being stationary), one plate continually describes the same circle on the other, so that mate
rial ground in these mills is subject to Bogardus eccentric mill. motion in one direction only, hence
greater power and more time are necessary to accomplish the desired result than if the material were acted upon in various directions and by different motions. The rate of feeding the mill is controlled by an adjustable slide attached to the hopper, and the degree of fineness of powder is regulated by means of a screw and lever controlled by a weight.
The so-called Chaser Mill is preferred when large quantities of material, such as cinnamon, ginger, pepper, mustard-seed, and the like, are to be reduced to impalpable powder. Fig. 87 shows a sectional view of a large chaser mill in use at the drug mills of Messrs. Gilpin, Langdon & Co., of this city. It consists of two large stone disks, or granite wheels, connected by a short metallic axle with a revolving shaft, which compels them to travel in fixed lines on a base of granite. The name chaser mill is derived from the motion of the disks—called chasers—which appear to chase each other in their travels over the stone base. The grinding of any material supplied to the mill is effected between the granite base and the outer edge of the chasers ; by means of iron scrapers appropriately fastened to the revolving shaft, the material is continually brought under the grinding edges again. As seen in the illustration, the base is surrounded
MECHANICAL SUBDIVISION OF DRUGS.
by a curb, to prevent the coarsely-ground particles from mixing with the finer powder, which, by means of the draught created by the rapid revolution of the chasers, is carried upward and over the sides of the curb. The whole mill is enclosed in a dust-proof compartment, which is frequently provided with a series of shelves for the purpose of allowing the fine particles of powder to be deposited for subsequent convenient collection. The feeding of the mill is accomplished through the top of the box, by means of a long funnel delivering the material directly upon the stone base.
SIFTING. In order to produce powder of uniform fineness, the ground substance should be subjected to the separating action of some perforated medium, whereby division into coarser and finer particles is readily effected. The construction of ordinary sieves is too well known to require special description. The perforated material or netting used may be made of iron, brass, or tinned wire, hair-cloth for substances affected by metal, and silken cloth for very fine or dusted powders. Different degrees of fineness of powder are designated in the U.S. Pharmacopoeia by numbers, which refer to the number of meshes to the linear inch in the material of which the sieve is made; thus, very fine or No. 80 powder should pass through a sieve having 80 meshes to the linear inch (or 30 meshes to the centimeter); fine or No. 60 powder should pass through a sieve having 60 meshes to the linear inch (or 24 meshes to the centimeter); moderately fine or No. 50 powder should