substance which is placed in the lower vessel A. The cover is provided with a tube and stopcock, which fits into the neck at B,

FIG. 178.

A

FIG. 179.

Hempel's Desiccator.

for connecting with a suction-pump if necessary to dry "in vacuo." Fig. 179 illustrates another form, provided with a stopcock a, which may be placed in connection with a vacuumpump and the air exhausted. The ground edges of the fittings should be greased with a little fat or petrolatum.

Vacuum Desiccator.

As material for the absorption of moisture (water), for use in desiccators, we employ usually either sulphuric acid or granulated calcium chloride; besides these we may also employ either calcium oxide (burnt lime), fused caustic potash or soda, or phosphoric oxide (anhydrous phosphoric acid).

Drying Liquids. -For removing small amounts of water from such liquids as alcohol, ether, ethyl nitrite, chloroform, volatile oils, we employ fused calcium chloride, sharply-dried potassium carbonate, or anhydrous copper sulphate. Care should be taken not to employ any substance which may react chemically on the liquid to be dried, for instance, calcium chloride cannot be employed in drying wood alcohol, benzyl alcohol or many esters, because it unites with them, forming crystalline compounds. Absolute alcohol is prepared from ordinary alcohol, by percolating it

through burnt lime, which effectually removes all but traces of

Drying Gases.-For drying (washing) gases, we employ the various forms of "wash bottles" (Fig. 180), in which the gas

cium).

passes through a layer of sulphuric acid; the tube through which the gas enters the flask, should dip from one-half to

three-quarters of an inch below the surface of the acid. For "washing gases," water or other fluids are employed. Figs. 181, 182 illustrate another form, in which the gas is dried by passing through either a U tube, or upwards through a tower, filled with granulated calcium chloride. A wad of absorbent cotton or spun glass wool is placed in the neck (Fig. 182), upon which the granulated calcium chloride rests, and another layer is placed on top just beneath the cork.

CHAPTER IX.

COMMINUTION.

The collection, drying, comminution and subsequent pulverization of drugs is at present seldom, if ever, performed by the retail apothecary. This branch has fallen entirely into the hands of the drug-miller. Crude vegetable drugs are first

reduced to coarse particles by slicing or chopping, in order to facilitate their drying and subsequent pulverization. This is called "Comminution." The slicing is done by means of chop

ping knives or rolling circular blades operated by machinery. In this condition, the drug is dried and then subjected to the operation of bruising, called "Contusion," which in other words, is pulverization by simple impact. Fig. 183 shows the operation of contusion in the row to the right; in the row on the left trituration is carried on.

In these two processes the piece that raises the pestles is a cam whose axis is fixed upon the main shaft, which is actuated by a steam engine. In order to prevent lateral action in the contusion battery, the cams revolve in a rectilinear opening in the rod of the pestle, which is seen to the right of the engraving. cam, which is a spiral, having the driving shaft as a starting point, is cut off short at 180°. On reaching this point, the wiper escapes and leaves the pestle to the action of gravity.

The

In the trituration battery, figured on the left of the engraving, the pestles must in falling turn upon themselves. To this effect the cam rubs against a wiper in the form of a horizontal circular plate that communicates, by reason of the friction, a gyrating motion to the pestle. The different positions occupied by the cam during its revolution are shown in the illustration.

In order to prevent particles from being ejected from the impact, as well as the diffusion of the dust, each mortar is covered with a leather jacket.

As soon as the drug has been thoroughly bruised it is ready for grinding.

. GRINDING is the reduction to coarse particles in properly constructed mills.

The drug-miller employs a variety of mills, for the purpose of grinding. Among these are the Chaser, Buhr-Stone, and Roller Mills, Disintegrators and other patent mills, each of which is adapted to special purposes.

A Hand Drug-Mill that answers the purposes of the pharmacist, must be so constructed, that it may be adjusted for all kinds of general work.

According to the arrangement of the grinding surfaces handmills may be divided into two classes.

1. Those in which the grinding plates are arranged vertically. 2. Those in which the grinding plates are arranged horizontally. In all of them, the grinding plates consist of teeth arranged in concentric rows, one plate fitting into the other; the distance between the grinding surfaces being regulated by means of a thumbscrew, thereby regulating the degrees of fineness of the powder.

1. Hand Drug-Mills with Vertical Grinding Plates.-Among these are the Swift, Tromner, and Enterprise mills. The latter (Fig. 184), because of the simplicity of its construction, and the case with which it is handled and cleansed, has become very popular. In this mill, the grinding plates are supported on a horizontal shaft, which is turned by two heavy fly wheels. The shaft rests between two hemispheres, enabling the operator, after opening the mill, to remove all the working parts. The various parts can be readily removed and replaced in case of fracture. The left-hand grinding plate, being geared to the shaft, revolves, while the righthand one is stationary. The fineness of the powder may be easily