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PHARMACY AND PRESCRIPTION WRITING.
Pharmacy (pápuaxov, a medicament),—may be defined as the art of selecting and preserving medicines, and preparing them for administration. It may be divided into
Official or Galenical Pharmacy,-dealing with the processes and preparations of the Pharmacopoeia; and
Extemporaneous or Magistral Pharmacy,—which includes the operations of compounding and dispensing remedies as directed by the prescriptions of physicians.
PHARMACOPÆIAS AND DISPENSATORIES. A Pharmacopæia is an official list of the drugs and their preparations recognized by the medical profession of a certain country. In foreign countries the Pharmacopoeias are published under government auspices and have the force of a legal standard ; in the United States its publication is left to the medical and pharmaceutical professions and is revised every ten years by a convention called for that purpose. The principal official Pharmacopeias, with their dates of latest revision or additions, are the following, viz.
Pharmacopæia of the United States of America, 1882.
Besides the above there are the Russian (P. Rossica, 1880); the Austrian (P. Austriaca, 1869); the Swedish (P. Suecica, 1869); the Norwegian (P. Norvegica, 1879; the Danish (P. Danica, 1868, 1874, 1876); the Belgian (P. Belgica, 1881); the Swiss (P. Helvetica, 1872, 1876); the Spanish (F. Española, 1865); the (Portuguese P. Portugueza, 1876); the Hungarian (P. Hungarica, 1871); the Netherlands' (P. Neerlandica, 1871); the Roumanian (P. Româña, 1862); the Finnish (P. Fennica, 1863); the Greek (P. Hellanica, 1868); the Mexican (Nueva Farmacopea Mexicana, 1884); and the
Pharmacopæia of India, 1868, 1869. Italy, Chili and Japan are each about to issue a national pharmacopoeia.
A Dispensatory is a commentary on one or more pharmacopæias, giving in extenso the physical and medicinal history of the drugs and preparations, together with their doses, physiological action and therapeutics, and includes similar information about many drugs which are not official in any pharmacopeia, but are of occasional use or general interest. A dispensatory is a private publication, of authority according to the reputation of its author. The principal Dispensatories published in the English language are the two following, viz.—
United States Dispensatory, 15th edition, edited by Wood, Remington and Stadtler. J. B. Lippincott & Co., Philadelphia.
National Dispensatory, 3d edition, edited by Stille and Maisch. Lea Bros. & Co., Philadelphia.
American Dispensatory, King & Lloyd, Cincinnati, is the organ of the “ Eclectic” school of physicians.
Companion to the U. S. Pharmacopæia, Oldberg and Wall, William Wood & Co., New York, is an excellent commentary on official and unofficial drugs.
THE CONSTITUENTS OF VEGETABLE DRUGS.
The constituents of vegetable drugs may be classified as soluble and insoluble, the first group containing those ingredients which may be extracted by suitable menstrua, the second such as resist the action of all ordinary solvents.
THE SOLUBLE CONSTITUENTS comprise both inert and active principles, the inert being chiefly starch, gum and pectin, which may be readily separated by water. The active principles are alkaloids, acids, salts, glucosides and other neutral principles, volatile oils, resins, etc. Some few of these may be extracted by Water alone (e. g. Morphine), and in some cases the addition of acids or alkalies to the water will effect the chemical solution of many ingredients which are insoluble in water alone. As a rule, however, Alcohol is the most generally applicable of all simple solvents, but from its hardening the cell-membranes instead of softening them it prevents the osmosis of their contents. Drugs subjected to alcoholic or ethereal menstrua should have their cells thoroughly broken or torn, so that the solvent may be oht into actual contact with the principles contained in
The degree of disintegration required depends upon the the cells, ducts, tubes, intercellular spaces, etc., in which
the active principles are enclosed. A very finely powdered state is however open to objection from the packing of the particles together into an almost impenetrable mass when treated by the solvent. The average size of vegetable cells is about doof an inch, while resin cells and other cavities are larger, averaging perhaps about ido inch. The Pharmacopæia prescribes in each instance the degree of fineness of the powdered drug employed in making certain of its preparations, or its bruising, slicing, etc., when such operations will answer. [Compare the article on Comminution in the following section.]
The INSOLUBLE CONSTITUENTS are cellulose, lignin and sclerogen, which make up the cell-walls of vegetable substances, and are extremely intractable.
OFFICIAL OPERATIONS. The official operations are those processes which are directed in the pharmacopeia to be used in the preparation of medicines. Many of them are processes which are common to both chemistry and pharmacy, as precipitation and crystallization,—while others are peculiar to pharmacy, as percolation, trituration, etc. The most important of the pharmaceutical operations are briefly described below; for full details of the various apparatus used the student is referred to the more exhaustive treatises on Pharmacy.
Vaporization includes the various operations by which volatile matters are separated from fixed substances or from other matters which are less volatile, heat at varying temperatures being the agent used. The operations under this head are—Evaporation, Distillation, Desiccation, and Sublimation.
EVAPORATION in Pharmacy is the process by which the more volatile constituents of a liquid are driven off by heat for the purpose of reducing its volume or of purifying it, as in the preparation of extracts and fluid extracts, the crystallization of salts, etc. The vessels used should be shallow so as to expose a large surface of the liquid to the atmosphere. The heat used may be regulated by a water-bath, a steam-bath or sand-bath, and ordinarily should be kept below but near to the boiling point of the liquid treated. As organic substances are usually injured by long heating, small portions only of vegetable preparations should be
Sibjected to this process, and the liquid should be frequently Stirred in order to hasten the operation. In large laboratories vacuum-pans are employed to remove the atmospheric pressure, enabling the evaporation to be accomplished at a much less degree of heat than if the liquid were exposed to the air. Ebullition or Boiling is a form of evaporation.
SPONTANEOUS EVAPORATION is the evaporation of a liquid without the direct application of strong heat, but at the temperature of the room or closet used for the purpose. It is especially applicable to cases in which the residue is liable to injury or loss from much heat, or to secure finer crystals than can be obtained by quick evaporation of their solution.
Distillation consists of two processes, (1) the evaporation of a liquid, (2) the condensation of the vapor into a liquid in a separate vessel. The agent used in the first part of the operation is heat, in the second part cold. Its object is to separate mixed volatile and fixed substances, or to combine volatile substances which cannot otherwise be mixed, as in the preparation of some of the official Waters. The apparatus used is of great variety, from the simple retort and receiver to the elaborate and costly stills.
DESTRUCTIVE OR DRY DISTILLATION is a process of decomposing an organic substance by heat into volatile products which are collected in a sep. arate vessel, the residue being said to be carbonized. It is only employed by large manufacturers, for the preparation of Acetic and Succinic Acids, Oil of Amber, Wood-tar, etc.
FRACTIONAL DISTILLATION is the separation by distillation of substances which are volatile at different temperatures, each being separately driven over and received in a vessel by itself. Different degrees of heat are successively employed in accordance with the volatilizing points of the substances to be obtained.
Sublimation is the distillation of a volatile solid, the product being termed a sublimate. Its objects are to purify volatile solids from impurities, and to collect such as result from chemical action at high temperatures. The operation is carried on in iron, glass or stoneware retorts, and results in cake sublimates or powder sublimates according as the temperature of the condensing surface is high or low.
Desiccation is the process of removing moisture from solids, and has for its object either the preservation of the substance, the reduction of its bulk or the facilitation of its comminution. The operation should be conducted at as low a temperature as possible. Roots, leaves and seeds are generally dried by being placed in trays of wire net-work and exposed to a uniform temperature in a room heated by steam. A better method is to suspend organic substances from the ceiling of an attic during warm weather; a slow process, but one which does not result in much loss of the active volatile principles. Crystals and precipitates require a higher temperature and are usually dried on a water-bath. When the water of crystallization is to be expelled, as in desiccating Alum and Sulphate of Iron, a temperature of about 400° F. is required. In absorbing water from alcohol Carbonate of Potassium and slaked Lime heated are employed, and in several instances Sulphuric Acid is the active desiccator used.
Fusion is the process of liquefying solids by the application of high heat without the use of a solvent. It is employed in making ointments, plasters, etc., in purifying resins, and for the purpose of decomposition. The degree of heat required varies from a temperature of 90° F., sufficient to melt lard in an open vessel, to one of 800° F., employed in fusing Zinc in an earthen crucible ; and may be regulated by the aid of the water-, steamor sand-bath. The two former appliances limit the degree of heat applied, while the sand-bath prevents sudden changes in the temperature. Oil-baths and glycerin-baths are employed in fractional distillation on a large scale.
Exsiccation or Calcination is the process of depriving a solid of its moisture or other volatile constituents by the application of heat without fusion. The term Exsiccation is usually applied to the vaporization of the water of crystallization from a crystalline body, Calcination, to such operations as the expulsion of carbonic acid and water from carbonates, as in the manufacture of Lime, Magnesia, etc.
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.
Incineration is the heating of organic substances with access of air until the carbon is consumed, the ash remaining being the product desired.
Ignition in pharmacy means the process of strongly heating solids or semi-solid substances, the residue left being the product desired. It is used in the official quantitative tests for Phosphoric Acid, Phosphate of Ammonium and purified Sulphide of Antimony.
Deflagration is the heating of an inorganic substance with another which yields oxygen (usually a nitrate or a chlorate), the