Many of these, as filtration, precipitation, etc., need no explanation, but the following require a few words.

Dialysis

The process of separating crystalloids from colloids by bringing them in a mixed solution, into contact with one side of a membrane, such as a bladder, parchment or a parchment paper, which has water in contact with its other side, and resulting in the passage into the water of the crystalloid to form the "diffusate," the remainder constituting the "dialysate." In this way dialysed iron is prepared by diffusing the excess of the crystalloid acid solution.

Displacement

Another name for Percolation.

Elutriation consists in diffusing an insoluble powder in water, letting the heavier part settle, then decanting the supernatant fluid. The heavier powder in this is allowed to settle, the fluid decanted, and so on until a fluid containing powder of the required fineness is obtained.

Levigation consists in reducing a drug to powder by triturating it with a little water and drying the resulting paste.

Lixiviation consists in the extraction with water of the soluble matter of the ashes of anything which has been ignited, the solution being called a "lye."

Maceration

The extraction of the soluble portions of a substance which is not wholly soluble in the menstruum, by prolonged contact therewith.

Percolation

The extraction in a suitable vessel (the "percolator") of the soluble constituents of a powder by the descent through it of a solvent (the "menstruum"), the resulting solution being called the "percolate." The marc is the material after its exhaustion by maceration or percolation. Percolation enters into the manufacture of a great majority of the official preparations of organic drugs.

Repercolation consists in using the liquid obtained by a substance as the menstruum for percolating a second portion of the same substance, and using the liquid from this second percolation as a menstruum for percolating a third portion of the same substance, and so on as often as may be desired.

Scaling

Scale preparations are made by drying concentrated solutions of drugs on glass plates. The solid left behind forms a thin film on the plate, and this film is broken up. Some preparations of iron are obtained by scaling.

Standardizing

Specifying an upper or lower limit, or both, of the active constituent which a drug or its preparation must contain in order to be official, and prescribing an appropriate process for its determination. Satisfactory processes for standardizing are extremely difficult to establish, and have been adopted for the following only:

Cinchona, not less than 5 per cent. of total alkaloids.

Cinchona rubra, " 5 " " "

Extractum nucis vomicae, 15 " " "

Extractum nucis vomicae fluidum, 1.5 per cent. of total alkaloids.

Tinctura nucis vomicae, 0.3 per cent. of total alkaloids.

Opium, not less than 9 per cent. of crystallized morphine. Opii pulvis, not less than 13 nor more than 15 per cent. of crystallized morphine.

Extractum opii, 18 per cent. of crystallized morphine.

Tinctura opii, Tinctura opii deodorati, Vinum opii,

1.3 to 1.5 per cent. of crystallized morphine.