expose fresh surfaces to the dry air. On the large scale, and in the laboratory, special apparatus must be employed. Fig. 187 illustrates a portion of the interior of a laboratory drying-room. Live steam is passed through the pipes when higher temperatures are needed, but waste or exhaust steam from steam kettles is economically and properly used. Trays of suitable size, containing the substance to be dried placed on thin muslin, are set upon the shelves of the rack. Ventilators should be provided to carry off the moist air. The space immediately over the steam boiler can often be economically used for a drying-room by placing a sheet-iron floor over it to secure the radiated heat, and arranging racks and trays upon it in convenient positions, or by placing the drugs in barrels in which the heads have been replaced by wire netting, or by simply enclosing the drugs in coarse bags which permit the escape of moisture.

Fig. 188 shows a pharmaceutical drying closet which is simple, economical, and easily made: the heat from the flue of the pharmaceu

any kind, may be carried on. The sides of the closet are of thick paper, felt, or asbestos cloth, tacked to a wooden frame, and cleats at convenient intervals are arranged for the trays to slide upon. The stovepipe from the stove is connected with the flue at the bottom of the drying

closet, and the heat from the smoke and gas passing up the flue is thus utilized; the hood may be dropped over the top of the stove when the latter is not needed for other purposes, the heated air carrying the moisture from the substance to be dried, rising and escaping at the ventilators. Lozenges, crystallized salts, extracts, filters, etc., may all be dried in this cheap and simple closet. One practical point about desiccation is frequently overlooked. It is that substances which are being dried must be repeatedly turned over, so that the parts underneath shall be exposed to the external dry atmosphere. In the case of salts, crystals, and other bodies, if this is not done, a hard crust is formed upon the surface which is often difficult to break up.

A convenient drying closet, suitable for a small laboratory, is shown in Fig. 189. It was contrived by T. Edward Greenish, of London; it is heated by gas, and is intended to fit into a recess in the wall. The drying closet, B, is made of thin sheet-iron, and provided with wire shelves, C, and a tightlyfitting door, D. The closet is made of such a size that when fixed into the recess in the wall a space of about two inches is left at the back, sides, bottom, and top, the space being covered in front by the flanges a, a; these constitute, with the door, the front of the closet. E is a gas-burner supplied from the pipe, and

FIG. 189.

Drying closet (gas heat).

F, F are two air-pipes which enter at the bottom of the closet: these pipes draw their supply of air from an external source, and thus the laboratory fumes and odors cannot taint

the substances which are to be desiccated. The upper ends of these tubes are covered with a layer of sand two inches deep, forming a sand-bath.

FIG. 190.

The gas being lighted is supplied with air from the front, and the heated air, together with the products of combustion, passes around the closet through openings made for that purpose in the sides and back of the gas-chamber, up the space between the closet and the wall to a pipe, G, and thence to a chimney. The substances to be dried, or the liquids to be evaporated, are placed either upon the shelves or upon the sand-bath. The air which enters by the pipes F, F, slightly warmed by the sand, will carry up any vapor therefrom to a pipe at the top of the closet, and thence to the pipe G. In order to regulate the draught of air at the back and sides of the closet, and thereby to adjust the degree of heat, the pipe G

Drying oven.

is provided with a circular damper, and the gas-chamber also has in front of it an arrangement for regulating the supply of air to the gas, thus preventing sudden fluctuations of temperature. By these means the heat of the closet may be readily adjusted. If the temperature of the upper shelf is 82° F., the next lower will be 85° F., the next 88° F., the lower one 92° F., whilst the sand-bath will register about 130° F. A drying oven, intended for drying precipitates in analytical work, but very useful for desiccating small quantities of pharmaceutical substances, pills, lozenges, or drugs like squill, saffron, castile soap, etc., is shown in Fig. 190. Water is poured into the tubulure at the top, and a Bunsen burner furnishes the requisite heat when placed so that the flame touches the under surface, the legs of the oven being long enough to permit its use.

Loss in Drying Medicinal Substances.-When drugs are pow dered, loss is always experienced. This arises partly from the escape of fine particles, but principally from loss of moisture in drying. Again, in powdering almost all drugs, a portion remains which resists disintegration. This is called by the miller "gruffs," and is usually worthless and should be thrown away: the gruffs are frequently kept, however, and sent with the next lot of the same drug to be ground at the mill. The dose of a powdered drug is usually somewhat less than that of the same drug before it was pulverized, because the weight it has lost generally represents inert matter, water, etc. Powdered ipecac is a good illustration of this. The active principle emetine resides in the starchy cortical portion of the root; the internal ligneous cord constitutes the "gruffs" of ipecac, and is inert. The exception to this is the case of those drugs containing an active volatile constituent, like the aromatics, cloves, cinnamon, nutmeg, or like asafetida, myrrh, cubeb, etc. These drugs, when powdered, generally contain less of their active constituents than they did before they were ground: the volatile oils to which their virtues are due are driven off to a greater or less extent by the amount of heat necessary to make them brittle enough to be readily pulverized. The U. S. Pharmacopoeia recognizes the importance of this fact by directing myrrh, and not powdered myrrh, in the compound iron mixture; asafetida, and not powdered asafetida, in the asafetida mixture; and in the compound tincture of cardamom by the direction to mix the unpowdered drugs, cardamom, cinnamon, caraway, and cochineal together, and reduce the mixture to powder, in preference to mixing the separate powders of these drugs. If care is exercised in desiccating, the powders of most drugs possess all their medicinal properties, and in many cases they will retain indefinitely these properties unimpaired if they are properly preserved and not unduly exposed to air, light, or moisture.

The practice of some drug-millers of establishing a loss in the weight of a drug as a regular standard, and then making up the deficiency by adding the same amount of some inert substance, is reprehensible. That the amount of moisture present in different lots of the same drug varies greatly may be seen by a glance at the following table, compiled by Mr. T. J. Covell from accurate records obtained from Dr. E. R. Squibb's drug-mills. The table is valuable because it represents the loss in powdering considerable quantities of drugs:

CHAPTER VIII.

COMMINUTION.

COMMINUTION is the process of reducing drugs to particles, or breaking up their state of aggregation.

Medicinal substances in their natural state require to be mechanically divided in order to facilitate the action of menstrua or solvents, or to permit their administration per se in the form of fine powders.

A simple illustration is offered in the case of alum. A solid lump of alum weighing one ounce, if added to a pint of water, will not dissolve nearly so quickly as will one ounce of the same alum in the same quantity of water if finely powdered. Vegetable substances offer very variable degrees of resistance in powdering, owing to the proportion and toughness of their ligneous fibre and the amount of cellular tissue.

Under the head of comminution will be grouped the various mechanical operations used in pharmacy by which the surface of solid substances is increased, whether by cutting, rasping, grating, chopping, crushing, rolling, stamping, grinding, powdering, triturating, levigating, elutriating, granulating, or similar processes.

By far the greater number of substances employed in medicine belong to the vegetable kingdom, and, whilst many of the processes of comminution used for these are also applicable to the chemical substances of the materia medica, it will be necessary in the following chapter to note the apparatus specially adapted to each class.

Cutting, Slicing, and Chopping.-This process is used principally in bringing roots, barks, leaves, herbs, etc., to the proper condition for

FIG. 192.

Herb-cutter.

treating with suitable solvents. For very small operations either the pruning-knife or pruning-shears answers a good purpose. The tobacco-knife or herb-cutter shown in Fig. 192 is well adapted for the purpose. It should be

observed, however, that the principle upon which a knife operates successfully should be carefully carried out in constructing apparatus designed for cutting: direct pressure without a slight drawing or sawing motion is not effective; therefore those knives which have guides arranged