Na2B4O7 + 10H2O. 10H2O or 10Aq. is the water of crystallization.

SYSTEMS OF CRYSTALLIZATION.-The 32 possible groups, distinguished by their symmetry, are classified by crystallographers, generally, in six systems, each characterized by the relative lengths and inclinations of the axes. They are as follows:

I. Isometric System, also called Regular, Cubic, Monometric, Tesseral, and Tessular System: Three equal axes, all at right angles. The fundamental forms are the cube and the regular octahedron. Examples: Sodium chloride, potassium iodide, potassium bromide.

II. Tetragonal System, also called Dimetric, Quadratic, Pyramidal, Monodimetric, Quartenary, and Square Prismatic System: Three axes, two equal, the third longer or shorter, all at right angles. The fundamental forms are the right-square prism and the quadratic octahedron. Example: Potassium ferrocyanide.

III.-Hexagonal System, also called Rhombohedral and Monotrimetric System: Four axes, three equal, in one plane intersecting at equal angles; the fourth axis at right angles to the other three, and longer or shorter. The fundamental forms are the hexagonal prism and the double hexagonal pyramid. Examples: Iodoform, sodium nitrate, strontium bromide.

IV. Orthorhombic System, also called Rhombic, Prismatic, and Trimetric System: Three unequal axes, all at right angles. The fundamental forms are the rhombic prism and the rhombic octahedron. Examples: Magnesium sulphate, zinc sulphate, potassium and sodium tartrate.

V. Monoclinic System, also called Oblique, Hemiprismatic, Monoclinohedral, Clinorhombic, and Monosymmetric System: Three unequal axes, two obliquely inclined to each other, the third at right angles to these two. The fundamental forms are the monoclinic prism and the monoclinic octahedron. Examples: Ferrous sulphate, potassium chlorate, borax, sodium thiosulphate.

VI. Triclinic System, also called Asymmetric, Double Oblique, Triclinohedral, Clinorhomboidal, and Amorthic System: Three unequal axes, with mutually oblique intersections. The fundamental forms are the triclinic prism and the triclinic

octahedron. Examples: Copper sulphate, potassium dichro

mate.

Decantation (dē-kan-tā'shọn).-Origin.-L. de, down + (probably) canthus, side, corner.

Definition. The process of pouring a liquid from a subsided solid, or from one vessel to another.

When it is especially desired to leave the solid matter undisturbed or when the vessel is very large, a syphon may be used to advantage. Decantation is especially indicated when bulky precipitates are to be washed or when a large volume of wash water is unobjectionable.

Example. This process was officially used in the preparation of ferric hydroxide and iodide of mercury, U. S. P. VIII.

Decoction (de-kok'shọn). Origin.-L. de, from + coquere, cook, boil.

Definition. The process of extracting the desired principles of drugs by boiling them in water.

Example. The beverage, coffee, is usually prepared by this process. This process is adapted to the extraction of the hard parts of the plants, such as wood, roots, rhizomes, etc., whose medicinal principles are soluble in water and not dissipated or injured by the heating. See also Decoctions, page 295.

Decoction. The solution containing the medicinal principles derived from the drug by the process of decoction.

Decoloration (dē-kul′′o-rā'shọn). Origin.-L. de, from + color, color.

Definition. The process of removing the color from a substance. It is usually accomplished by employing oxidizing or reducing agents to destroy the coloring-matter; by precipitation with basic acetate of lead; and by absorption with animal charcoal.

Animal charcoal is frequently used to decolorize pharmaceutic preparations, but it should be used with discretion because it also absorbs many alkaloids, glucosides, and bitter principles. Deflagration (def-la-grā'shọn). Origin.-L. deflagratio, from deflagrare, to burn up.

Definition. The process of oxidizing substances so rapidly as to cause flame and detonation.

Procedure. The substance to be deflagrated is mixed with a

chemical capable of yielding oxygen, a nitrate or a chlorate, and then projected in small portions into a red-hot crucible.

Deliquescence (del-i-kwes'ens).-Origin.-L. de, down + liquere, melt, to melt down.

Definition. The property, possessed by certain chemical compounds, of liquefying through absorption of moisture from the air. Substances possessing this property are said to be deliquescent. They should be carefully protected from the air. Deliquescent Substances:

Desiccation (des-i-kā'shọn).—Origin.-L. desiccatio, from desiccare, dry up.

Definition. The process of depriving substances of moisture, drying.

Example. The drugs thyroid and suprarenal glands of the U. S. P. are prepared by desiccation.

Procedure. The substances are usually exposed to a current of warm air. The temperature may range from 40° to 200° C., but for most organic medicinals the temperature should not exceed 40° C. unless it is positively known that a higher temperature is unobjectionable.

Drugs whose active principles are volatile, or are easily injured by heat, suffer considerable loss during desiccation. The following of this class are deserving of special mention: Aro

matic drugs, like cardamom, cinnamon, cloves, nutmeg, etc.; certain gum-resins and resins, like ammoniacum, asafetida, and myrrh, and certain alkaloidal and glucosidal drugs, such as conium, aconite, and digitalis.

Objects. To reduce bulk, to aid in preservation, and to facilitate comminution.

Bibulous Paper.—A thick, unsized paper (blotting-paper), used for drying crystals and precipitates.

Dialysis (di-al'i-sis).-Origin.-Gr. dia, through + lysis, a loosing.

Definition. The process of separating soluble crystalline substances (crystalloids), from glue-like substances (colloids) by taking advantage of the unequal rate of diffusion through natural or artificial membranes.

Example.-Dialysed iron is prepared by this process. See Dialysates, page 446.

Procedure. The liquid containing the substance to be separated is placed in a parchment-paper bag or a dialyser and floated in distilled water. The crystalloids pass through the moist membrane into the surrounding water very readily; the colloids remain behind.

Dialyser. A shallow vessel with a bottom of parchment paper or animal membrane, used in dialysis.

Dialysate. The product removed from a solution by dialysis. The term "dialysate" is usually restricted to the liquid containing the colloids which remains in the dialyser.

Dialysates. See page 446.

Diffusate. The solution containing crystalloid substances which have been removed by dialysis.

Diffusion (di-fu'zhọn).-Origin.-L. dis, away + fundere, pour. Definition. A process of extraction which consists of remaceration. It is used principally in the extraction of sugar from sugar-cane and the sugar beet, and is carried out in a manner similar to Repercolation, see page 71.

Diffusion, when applied to fluids, refers to the spontaneous molecular mixing which occurs when they are placed in contact one with the other.

Digestion (di-jes'tyon).-Origin.-L. dis, apart + gerere, to

carry.

Definition. A process of partial extraction wherein the substance is allowed to remain in contact with the menstruum at an elevated temperature for a considerable time. The temperature, unless otherwise indicated, usually ranges from 38° to 45° C.

Displacement Washing. See Lotion, page 67.

Distillation (dis-ti-la'shọn). Origin.-L. de, from + stillare, to drop.

Definition. A process of separation which consists in vaporizing the liquid and subsequently condensing the vapor.

Example. Water is freed from mineral impurities by distillation, as in the preparation of the official distilled water.

Apparatus.-Adapter.-A tube (usually of glass) with ends differing in size, used to connect two other tubes or pieces of apparatus.

Alembic.-An ancient form of distillatory apparatus, usually made of copper or glass. It consisted of a gourd-shaped bottom part for the reception of the liquid, surmounted by a dome-like condensing chamber.

Capitol. The condensing chamber of an alembic; the dome or head.

Condenser. See Condensation, page 48.

Cucurbit. The body or boiling chamber of an alembic.

Grommet. A ring of rope, rubber tubing, or straw, used to support a round-bottomed flask, or to keep a heated glass vessel from contact with a cold surface.

Helm. The tube leading from condensing chamber of an alembic.

Retort. A flask-shaped vessel, used in distilling, which has a long tapering neck bent at an acute angle with the body of the flask. Retorts are usually made of glass, but may also be made of either metal or porcelain. Retorts which have an opening in the top through which the substance may be introduced are called tubulated retorts, and the short tube-like opening is known as a tubulure.

Still.—The complete distillatory apparatus-boiler, condenser, and sometimes the receiver.

Worm. A term applied to a condenser which consists of a coil of tubing, usually of copper or tin, placed in a jacket of running water.