Examples in U. S. P.: Oleum Amygdala Expressum, Gossypii Seminis, Lini, Morrhuæ, Olivæ, Ricini, Tiglii.

Fats are fixed oils which are solid at ordinary temperatures owing to their larger content of palmitin and stearin, C3H5(C18H31O2)3; if extracted by expression, sufficient heat to melt them must be used. Examples in U. S. P.: Oleum Theobromatis, and Adeps.

The same definitions will apply to fixed oils and fats of animal origin.

Waxes are chiefly composed of fatty acids combined with monohydric alcohols homologous with methyl alcohol. They contain no glyceryl, however, and are brittle at low temperatures.

Volatile or Essential Oils are those peculiar principles to which, in a majority of instances, the odor of plants is due. They may preexist in the plant and be obtained by distillation, e.g., Oleum Terebinthinæ, or by expression, e.g., Oleum Limonis; some are the result of enzyme action upon certain constituents of the plant, e.g., Oleum Sinapis Volatile. They do not leave a greasy mark on paper, and resemble fixed oils only in being soluble in the same media. They do not become rancid, but on exposure to light and air may change to resins. They are mostly inflammable, and mostly lighter than water. They are highly odorous and aromatic, and sufficiently soluble in water to impart their odor and taste to it. Most are prepared by distillation-that is, by passing a current of steam through the substance from which they are extracted; the steam is condensed, and the oil either floats to the top or sinks to the bottom of the water. Their composition varies greatly and is often complex. They are of four classes:

(a) Terpenes, which consist of carbon and hydrogen; e.g., Oleum Terebinthinæ.

(b) Oxygenated, containing oxygen, e.g., Oleum Eucalpyti.

(c) Sulphurated, containing sulphur; e.g., Oleum Sinapis Volatile.
(d) Nitrogenated, containing nitrogen; e.g., Oleum Amygdala Amaræ.

They may contain aldehydes, phenol derivatives, ethers or ethereal salts, alcohols or ketones, generally associated with terpenes of varying composition.

Resins are of very indefinite composition. They are among the products of oxidation of volatile oils, being usually oxidized terpenes. They are solid, mostly uncrystallizable, fusible, not volatile, combustible, insoluble in water, mostly soluble in alkalies and

volatile oils, and also in one or more of the following: alcohol, ether, chloroform, and fixed oils. Since they are insoluble in water, but not in alcohol, they may be prepared by extraction with alcohol and precipitation with water. Those which combine with alkalies form resin soaps. When occurring naturally, there are usually two or more resins mixed.

Those in the U. S. P. are Resina Jalapæ, Podophylli, and Scammoniæ.
Oleoresins are natural solutions of resins in volatile oils.

Those in the U. S. P. are Oleoresina Aspidii, Capsici, Cubebæ, Petroselini, Piperis, and Zingiberis.

Balsams are resinous or oleoresinous exudates. The U. S. P. articles are liquid or soft products and contain an odorous principle, which is benzoic, or cinnamic acid, or both.

Those in the U. S. P. are Balsamum Peruvianum and Tolutanum, and Styrax. Not all substances having a balsamic odor are balsams; e.g., Benzoinum is a resin and Copaiba, sometimes known as Balsam of Copaiba, is an oleoresin. Resins containing benzoic or cinnamic acids are sometimes called solid balsams.

Gums are exudations from plants, having an insipid taste, insoluble in ether and alcohol, and in water either dissolving to form a mucilage or swelling to form an adhesive jelly. They consist of one or more of the following:

(a) Arabin or soluble gums, e.g., Acacia.

(b) Bassorin or partially soluble gums, e.g., Tragacantha.

(c) Cerasin or insoluble gum.

Gum-resins are exudations from plants consisting of a natural mixture of one or more gums and oleoresins. When they are rubbed with water the gum dissolves and the resin remains mechanically suspended in the solution, forming an emulsion.

The U. S. P. gum-resins are Asafoetida, Cambogia and Myrrha.

PHARMACEUTICAL PROCESSES

Many of these, as filtration, precipitation, need no explanation. Carbonization is the heating of organic substances without exposure to the air until the volatile constituents are driven off and the residue assumes the characteristic appearance of carbon.

Clarification is a process for making liquids transparent by separating from them, without the use of filters or strainers, such solid substances as render them turbid. It is most commonly effected by the application of heat, though filtration or decantation must always be subsequently resorted to for removing the separated matter. Other means employed for clarifying are: By increasing the fluidity of the liquid, by the use of egg-albumin, gelatin, milk, or paper-pulp; by subsidence through long standing (often applied to fixed oils); and by fermentation (as in the case of fruit juices).

Comminution is the process of reducing drugs to particles, or breaking up their state of aggregation. It is effected by cutting, slicing, chopping, the use of drug-mills, etc.

Decoloration of liquids is usually effected through the agency of animal charcoal.

Dialysis is 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 parchment paper, which has water on its other side, and resulting in the passage into the water of the crystalloid to form the "diffusate," the remainder, the colloid, constituting the "dialysate."

Displacement is another name for Percolation.

Elutriation is a process for obtaining a substance in fine powder by diffusing an insoluble powder in water. The larger and heavier particles having sunk to the bottom of the vessel, the supernatant fluid is decanted into another vessel, where the lighter particles are collected. The process may be repeated, if necessary. To facilitate the drying of the powder thus obtained, the soft mass, or magma, after having been drained, may be formed into small conical masses on warm porous tiles. Prepared chalk is an example of an elutriated powder.

Expression is the forcible separation of liquids from solids by means of pressure. Hand-pressure through straining-cloths may be employed, but mechanical processes are more efficient.

Fusion is the process of liquefying solid bodies by the application of heat, as in the melting of wax and the preparation of moulded silver nitrate.

Granulation is a process by which certain substances soluble in water are obtained in the form of coarse powder by simple evapora

tion of their solution, with constant stirring, until all moisture is dissipated.

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

Lixiviation is the practice of exhausting substances, which have been incinerated, as, for instance, wood-ashes, of their soluble constituents by pouring water upon them after their introduction into a conical-shaped vessel; the resulting solution being called a "lye."

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

Massing is the important step in the preparation of pills by the formation of a proper mass, which should consist of a firm, consistent paste, sufficiently plastic to admit of being moulded without adhering to the moulds and sufficiently firm to prevent the pills from losing shape. Some substances, such as gums and resinous drugs, possess the requisite adhesiveness in themselves but need the addition of a liquid-water or alcohol-in order to develop it. Others have no inherent adhesive properties, and with them it becomes necessary to impart tenacity by the addition of some liquid or solid material, which is called the excipient. Excipients must be added judiciously, so that the constituents of the mass may not be modified in their action or the bulk be unnecessarily increased; and after each addition the mass should be well kneaded. In order to insure homogeneity of the mass, and also the subsequent accurate division of doses, all the constituents should, whenever possible, be reduced to a fine powder. Small quantities of potent remedies, such as alkaloids or narcotic extracts, are preferably triturated with a little sugar of milk before. mixing them with the other ingredients, to facilitate uniform distribution.

Percolation consists of 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 from a sub

stance as the menstruum for percolating successive portions of the same substance.

Pulverization is the reduction, by mechanical means, of a substance into fine particles. Like grinding, applied to the production of coarse particles, it is very largely carried on by drug-millers. Before pulverizing, a substance must be dried, and the desired fineness of the powder determines the character of the preliminary treatment. Thus, drugs containing volatile oils are apt to be rendered worthless if they are dried sufficiently to enable them to be ground very finely, and hence they are preferred when coarsely powdered. The processes for extracting the soluble principles having been very greatly improved, the necessity no longer exists for using the very fine powders, and therefore the volatile principles are not sacrificed. 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.

Scaling is the drying of concentrated solutions of drugs on glass plates; after which the solid film, the scale, thus left is broken up. Some preparations of iron are obtained by scaling.

Separation of liquids which do not mix with each other is a mechanical process accomplished with pipettes or with funnels having stopcocks in their necks. Special forms of receivers are used for the separation of volatile oils from the water accompanying them during distillation.

Solution is the process by which a solid, gaseous, or liquid substance, when brought into contact with a liquid, becomes molecularly blended with it in such a way that a permanent homogeneous fluid results; and the resulting fluid is known as a solution. The liquid employed for effecting solution is termed a solvent or menstruum. In cases where it is incapable of entirely dissolving a substance the solution is called a saturated one when all of the substance that is possible for it to dissolve has been taken up. A substance which altogether resists solution is said to be insoluble. It should be noted that when certain solids are brought together by means of trituration, solutions result. This effect is seen, for instance, when camphor is rubbed up with menthol or with hydrated chloral. Solution is facilitated by agitation, and in most cases by the application of heat. Solution may be either simple or chemical. In the first the substance dissolved undergoes no change except as