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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 of an inch, while resin cells and other cavities are larger, averaging perhaps about inch. The Pharmacopoeia 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 PHARMACY.

OFFICIAL OPERATIONS.

The official operations are those processes which are directed in the pharmacopoeia 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 separate 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

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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 Anti

mony.

Deflagration is the heating of an inorganic substance with another which yields oxygen (usually a nitrate or a chlorate), the

result being the decomposition of the body, with violent and sudden combustion.

Torrefaction or Roasting is the application of heat, in a less degree than for carbonization, to an organic substance for the purpose of modifying some of its constituents, as in the roasting of coffee and rhubarb. The latter substance when subjected to this process, loses its cathartic properties but retains its astringency, and is known as Torrefied Rhubarb.

Comminution is the process by which the aggregation of the particles of a solid body is overcome, and the body is reduced to pieces of varying sizes. Its object is to increase the surface exposed to the action of solvents, and it includes the mechanical operations of cutting, rasping, grating, crushing, stamping, grinding, pulverizing, triturating, levigating, elutriating, granulating, etc. Apparatus of various kinds, as cutters, mortars and pestles, mills, etc., are used for the comminution, while spatulas are employed to loosen the particles, and sieves to sift the coarser from the finer. These last-named contrivances are of five sizes, designated by the number of their meshes to the inch, 80, 50, 60, 40 and 20, respectively permitting the passage of powders termed very fine, fine, moderately fine, moderately coarse and

coarse.

Trituration is the comminution of a solid to an extremely fine powder by continued rubbing in a wedgwood mortar with an inert and gritty powder, Sugar of Milk being the substance directed to be used. The product is called a Trituration (see that title under OFFICIAL PREPARATIONS). The surfaces of the mortar and pestle-head should coincide closely, and the thorough comminution of the trituration is best accomplished by a circular motion of the pestle in gradually increasing circles, until the side of the mortar is reached, then reversing the motion, and gradually lessening the circles until the pestle reaches the centre again. The process is greatly facilitated by having the pestle attached to a long handle playing in an opening made in a piece of wood which is nailed at a convenient height. A weight may be fixed on top of the handle if a greater degree of friction be desired.

PULVERIZATION BY INTERVENTION is only another name for trituration when performed in a mortar and with solid bodies, the foreign substance used being subsequently removed. Potassium Sulphate may be employed as the medium for the pulverization of Gold, and is then dissolved out with water. Alcohol or Chloroform may be added to Camphor to aid its pulverization, and then removed by evaporation. Phosphorus may be pulverized by placing

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441 it in water, gently heating the latter until the phosphorus is melted, and agitating the whole while cooling.

LEVIGATION is trituration of a substance made into a paste with water or some other liquid, and resembles the old process of grinding oil-paints by hand on a slab of stone. This process is used for coarse materials, as chalk, etc., where the refuse is rejected, or for such substances as Red Oxide of Mercury, Oxide of Zinc, etc. When performed with a porphyry slab and muller it is termed Porphyrization.

ELUTRIATION is a water-sifting process for separating the coarser particles of insoluble substances from the finer. The substance is mixed with water and after the larger particles have fallen to the bottom, the liquid is decanted into another vessel, in which the light and powdery particles are collected.

Solution is the dissolving of a solid or a gaseous substance in a liquid, and may be simple when the substance undergoes no alteration, being recovered unchanged on evaporation, or chemical, when the dissolved body is chemically altered by the solvent or some other substance present, and cannot be recovered on evaporation. Simple Syrup is an instance of simple solution, the Syrup of Lime one of chemical solution. The liquid employed is termed a solvent before the substance is added to it, after the operation is completed the combined preparation is called a solution. If fully charged with the dissolved substance so that it will retain no more, it is known as a saturated solution. One liquid may be dissolved in another, or a gas may be dissolved in a liquid. The solution of solids is greatly facilitated by pulverization and by stirring the menstruum. Heat generally aids solution, most substances being more soluble in hot liquids than in cold ones. A saturated solution of one substance may still be capable of dissolving others. Rapid solution of solids without chemical change causes reduction of temperature, while chemical solution produces elevated temperature. Circulatory Solution is performed by suspending the substance to be dissolved near the surface of the solvent in a gauze bag or on a porous shelf. The portion first acted on descends and produces a circulatory movement in the fluid, facilitating the solution of the whole.

SOLVENTS employed are chiefly Water, Alcohol, Glycerin, Acids and Oils. Others less frequently used are Ether, Chloroform, Benzin and Carbon Disulphide.

Washing is a simple mechanical process for separating soluble from insoluble matter, by pouring upon it a liquid which will dissolve the soluble portion. Various methods of doing this are in vogue and are often dignified with very high-sounding terms, as Lotion, Affusion, Ablution, etc. An ordinary wash-bottle, with the two glass tubes perforating the cork, is a convenient implement for directing a continuous stream upon a precipitate,

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