To Powder Substances - Place the substance in the mortar and strike it gently with direct perpendicular blows of the pestle, until it separates into several pieces, then remove all but a small portion, which bruise gently at first, and rub the pestle round and round the mortar, observing that the circles described by the pestle should gradually decrease in diameter, and then increase again, because by this means every part of the powder is subjected to the process of pulverization. (See 3101.)

2665. Some substances require to be prepared in a particular manner before they can be powdered, or to be assisted by adding some other body. For example, camphor powders more easily when a few drops of spirits of wine are added to it; mace, nutmegs, and such oily aromatic substances are better for the addition of a little white sugar; resins and gum resins should be powdered in a cold place, and if they are intended to be dissolved, a little fine well washed white sand mixed with them assists the process of powdering, Tough roots, like gentian and columba, should be cut into thin slices; and fibrous roots, like ginger, cut slanting, otherwise the powder will be full of small fibres. Vegetable matters require to be dried before they are powdered, such as peppermint, loose-strife, senna, etc.

2666. Be careful not to pound too hard in a glass, porcelain, or Wedge-wood's-ware mortar; they are intended only for substances that pulverize easily, and for the purpose of mixing or incorporating medicines. Never use acids in a marble mortar, and be sure that you do not powder galls or any other astringent substances in an iron mortar.

2667. Sifting is frequently required for powdered substances, and this is usually done by employing a fine sieve, or tying the powder up in a piece of muslin and striking it against the left hand over a piece of paper.

2668. Filtering is frequently required for the purpose of obtaining clear fluids, such as infusions, eye-washes, and other medicines; and it is therefore proper that you should know how to perform the simple operation. We must first of all make the filter-paper; this is done by taking a square sheet of white blotting paper, and doubling it over, so as to form an angular cup. We next procure a piece of wire, and twist it into a form to place the funnel in, to prevent it passing too far into the neck of the bottle. Open out the filter-paper very carefully, and having placed it in the funnel, moisten it with a little water Then place the wire in the space between the funnel and the bottle, and pour the liquid gently down the side of the paper, otherwise the fluid is apt to burst the paper. (See 3085.)

2669. Maceration is another process that is frequently required to be performed in making up medicines, and consists simply in immersing the medicines in cold water or spirits for a certain time.

2670. Digestion resembles maceration, except that the process is assisted by a gentle heat. The ingredients are placed in a flask, such as salad-oil is sold in, which should be fitted with a plug of tow or wood, and have a piece of wire twisted round the neck. The flask is held by means of the wire over the flame of a spirit lamp, or else placed in some sand warmed in an old iron saucepan over the fire, care being taken not to place more of the flask below the sand than the portion occupied by the ingredients.

2671. Infusion is one of the most frequent operations required in making up medicines, its object being to extract the aromatic and volatile principles of substances that would be lost by decoction or digestion; and to extract the soluble from the insoluble parts of bodies. Infusions may be made with cold water, in which case they are weaker, but more pleasant. The general method employed consists in slicing, bruising, or powdering the ingredients first, then placing them in a common jug (which should be as glob-ular as possible), and pouring boiling water over them; cover the jug with a cloth folded six or eight times, but if there is a lid to the jug so much the better; when the infusion has stood the time directed, hold a piece of very coarse linen over the spout, and pour the liquid through it into another jug.

2672. Decoction, or boiling, is employed to extract the mucilaginous or gummy parts of substances, their bitter, astringent, or other qualities, and is nothing more than boiling the ingredients in a saucepan with the lid slightly raised. Be sure never to use an iron saucepan for astringent decoc-tions, such as oak bark, galls, etc, as they will turn the saucepan black and spoil the decoction. The enamelled saucepans are very useful for decoctions, bat an excellent plan is to put the ingredients into a jar and boil the jar, thus preparing it by a water bath, as it is technically termed.

9678. Extracts are made by evaporating the liquors obtained by infusion or decoction, but these can be bought much cheaper and better of chemists and druggists, and so can tinctures, confections, cerates, plasters, and syrups; but as every one is not always in the neighbourhood of druggists, we shall give recipes for those most generally useful, and the method of making them.