rapidly forced through the meshes of the sieve. This apparatus is especially useful in breaking up moistened lumps in powders which are about to be percolated. (See Percolation.)

FIG. 217.

Sifter.

The degree of fineness of powders is designated in the United States Pharmacopoeia by the number of meshes to the inch possessed by the sieve. The five different sizes are as follows:

Very fine powder should pass through a sieve having 80 or more meshes to the linear inch (30 meshes to the Cm.).

Fine powder should pass through a sieve having 60 meshes to the linear inch (24 meshes to the Cm.). Moderately fine powder should pass through a sieve having 50 meshes to the linear inch (20 meshes to the Cm.).

Moderately coarse powder should pass through a sieve having 40 meshes to the linear inch (16 meshes to the Cm.).

Coarse powder should pass through a sieve having 20 meshes to the linear inch (8 meshes to the Cm.).

In special cases powders of different degrees of fineness (e.g., No. 30,

FIG. 218.

No. 12) are directed to be taken. In every case the number of the powder indicates the number of meshes to the inch of the sieve used to make the powder. Not more than one-fourth of the powder is expected to pass

through a sieve having ten more meshes to the inch than the one designated.

For very fine powders, bolting-cloth is used for the sifting medium; and when acid substances are to be sifted, horse-hair sieves are used.

Levigation is the process of reducing substances to a state of minute division by triturating them after they have been made into a paste with

FIG. 220.

G

Slab and muller.

water or other liquid. This is effected in a shallow mortar with a flatsurfaced pestle, or upon a ground-glass slab with a flat-surfaced glass muller (see Fig. 220). The motion imparted to the muller, A, closely resembles the figure 8; this is frequently varied with that of elongated circles which intersect each other, the object being to vary the motion so that all particles of the powder may be brought under the action of the muller upon the slab G. Certain substances, like red mercuric oxide and zinc oxide, if made into a paste with alcohol or water, are more readily reduced to fine powder in this way than by the action of the mortar and pestle. The process is termed porphyrization when performed with a porphyry slab and muller.

Elutriation is the process of obtaining a substance in fine powder by suspending an insoluble powder in water, allowing the heavier particles to fall to the bottom of the vessel, and decanting the liquid containing the lighter particles into another

vessel, and there collecting them. It is water-sifting practically, wherein the superior gravity of the larger particles is used as a means of separating them from the smaller. Prepared chalk is a familiar illustration of an elutriated powder.

or

Trochiscation is the process of making the pasty mass magma obtained by elutriation into dry, conical masses. This is usually accomplished by the use

000000

FIG. 221.

Trochiscator.

of the little apparatus shown in Fig. 221. This consists of a tinnediron cone, supported in a circular wooden frame which has one short wooden leg and a handle. A slab of chalk or other porous sub

stance is provided, and after filling the cone with the pasty mass the handle is taken in the right hand and the leg of the frame is tapped gently upon the slab of chalk: the shock causes a conical mass of the substance to fall upon it, whereupon the moisture present soon becomes absorbed, so that the little cone dries quickly. A succession of taps, with a slight lateral movement, deposits the cones in regular rows, and when the slab is full the first cones are found to be dry enough to be transferred, and all will soon be in the same condition. Chalk, bismuth, lake, and other insoluble powders are formed into conical nodules in this way.

Pulverization by Intervention is the process of reducing substances to powder through the use of a foreign substance, from which the powder is subsequently freed by some simple method. No general process can be given for this method of pulverization, as the character of the substance must determine the method. The metal gold may be powdered by rubbing gold-leaf in a mortar in contact with potassium sulphate: the latter is subsequently dissolved out with water. Camphor may be pulverized through the addition of a few drops of alcohol, chloroform, or other solvent. The foreign substance in this case is disposed of through evaporation. Metallic tin may be granulated by melting it and agitating it in a box containing powdered chalk: the latter is subsequently dissolved out with diluted acetic acid. Phosphorus may be pulverized by placing it in water contained in a small flask, then heating the water gradually until the phosphorus is melted, and shaking the flask while the phosphorus is cooling: the agitation in the presence of water keeps the particles from cohering.

QUESTIONS ON CHAPTERS VII. AND VIII.

DESICCATION AND COMMINUTION.

What is desiccation?

What are the objects of desiccation?

How may roots, herbs, and leaves be conveniently dried on the large scale?
What is meant by "gruffs?"

What use is made of "gruffs?"

Why does the U. S. P. direct myrrh in substance and not in powder in

making compound iron mixture?

Table showing loss in powdering medicinal substances.

What is comminution?

What are the objects of comminution?

How may roots, barks, etc., be conveniently cut?

How upon the large scale?

How may drugs be most conveniently bruised or contused?

When it becomes necessary to use an iron mortar and pestle for a considerable

length of time, how may the labor of lifting the pestle be lessened?

For what purposes are wooden mortars used?

For what purposes are marble mortars used?

In using marble mortars, what precautions are necessary?
What is the difference between grinding and pulverizing?
What drugs are most injured by drying?

mills?

What is a buhr-stone mill?

What two varieties are there, and what are they called?

What is the peculiarity of each ?

What are roller-mills?

What are the rollers usually made of?

What is the form of the rollers?

What are chaser-mills?

How are the stones arranged?

How are powders of greater or less degrees of fineness obtained from chaser

What are barrel-mills?

How is the "Bogardus" mill constituted, and what is its peculiarity ?

What is Mead's disintegrator?

What is requisite in running this mill?

What three classes of hand-mills are there?

Describe Swift's mill (old style).

What improvements have been made in the new-style Swift's mill?
Describe Troemner's mill.

Describe the Enterprise mill.

What are its advantages?

Describe Thomas's mill.

What are the principal objections to this mill?

Describe Swift's B mill.

Describe Hance's mill.

Is Hance's mill best adapted for light or heavy work?

What are the most usual difficulties met with in operating hand-mills?
How may these be obviated?

What is a good method of cleaning a mill after an odorous drug has been

ground?

What is trituration?

What shaped mortars and pestles are best adapted to the purpose of trituration?
What objection is there to the ordinary pestle of porcelain or wedgwood
How is this best remedied?

mortars?

Is the hard-rubber handle any better, and if so, why?

What preparation, called a "trituration," has been made official in the U. S. P.?

Describe a device for facilitating trituration.

What is the objection to glass mortars and pestles?

Which are most useful,-mortars and pestles of porcelain, white glass, or green glass, and why?

What is a spatula, and what is its best form?

For what are spatulas covered with hard rubber useful?

How is the process of sifting accomplished?

How are the degrees of fineness of powders designated in the U. S. P. ?

How many degrees of fineness are so designated?

What is meant by a very fine powder? Fine powder? Moderately fine

powder? Moderately coarse powder? Coarse powder?

In some special cases other degrees of fineness than these five are designated.

as, for example, No. 30 and No. 12: what is meant by these numbers?

What is levigation?

What is meant by porphyrization? By elutriation?

Give an example of an elutriated powder.

What is trochiscation?

What is pulverization by intervention?
Give an example of this process.

CHAPTER IX.

SOLUTION.

Solution. In pharmacy this term is applied to the process whereby any substance is liquefied or made to disappear when brought in contact with a liquid: the particles of the substance being uniformly diffused through the liquid, no separation takes place upon standing. The liquid used to effect this change is called a solvent, and, after its combination with the dissolved substance, a solution; if the liquid has exercised its powers as a solvent to its utmost extent, and is incapable of retaining any more of the dissolved substance, it is termed a saturated solution. A substance which is not acted on by a solvent is said to be insoluble.

Solution of Solids.-This is an operation which is very frequently performed by the pharmacist: in this place only the methods of effecting the solution of solid bodies which can be entirely dissolved in the solvent will be noticed. This excludes the operations of Infusion, Decoction, Percolation, Maceration, etc., which will be considered at length in subsequent chapters. Solution may be of two kinds: 1, Simple; 2, Chemical.

1. Simple Solution is where the solid suffers no alteration on being dissolved, except that which depends upon its external form, and where, if the reverse operation of evaporation is applied, the solid substance is recovered unchanged. The making of simple syrup is an example.

2. Chemical Solution is where the properties of the dissolved body are changed by the chemical action of the solvent or some of the substances added, and the simple process of evaporation results in the production of a body having different properties, as, for example, in the official solution of mercuric nitrate.

Effects of Pulverization and Agitation.-The solution of solids may be facilitated by pulverizing them and stirring the mixture, thus increasing their extent of surface and promoting the frequent contact of the surfaces with fresh portions of the solvent. This is easily illustrated, as already noted under Comminution, by placing half an ounce of lump alum and half an ounce of powdered alum each in a pint of water at the same time: a few vigorous stirs will soon cause the latter to dissolve, whilst the former will require a much longer time.

Effect of Heat.-The application of heat generally favors solubility, for nearly all substances are more soluble in hot liquids than in cold ones. In addition to this, the convection currents in the liquid caused by heat hasten the solution by constantly bringing fresh surfaces into