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above. The following list of acids and salts comprises most of the solids which are best adapted for use in liquid form, by reason of their solubility in water.

A few require the use of viscid substances as vehicles or correctives. They are as follows:

Ammonii Carbonas.
Plumbi Acetas.

Potassa.
Potassii Cyanidum.

Hydrargyri Chloridum Corrosivum.

Certain salts are best ordered by prescribing such agents as will when in solution together react upon each other and produce the desired salt. Instances of this may be found in the pharmacopoeial processes for most of the official Liquores; the salts so produced being the following:

Ammonii Acetas.

Magnesii Citras.

Potassii Citras.

Ferri Citras,

Ferri Acetas.

Ferri Chloridum.

Hydrargyri Nitras.

Ferri Nitras.
Ferri Phosphas
Potassii Arsenis.
Potassii Hydras.
Sodii Hydras.

Soda Chlorata.
Zinci Chloridum.

Arsenii et Hydrargyri Iodidum.

Certain other substances require the addition of other agents in order to form eligible solutions. Such are the following:—

Quinine Sulphas,-requires acidulated water for its solution, the acid used being generally Sulphuric diluted, or the Aromatic Sulphuric. This method of prescribing this salt develops its bitter taste to the utmost, and is often avoided by ordering the drug to be suspended in a viscid liquid, such as Pulv. Acacia in Syrup of Ginger. In such a case an officious dispenser anxious to

show his smartness may add some dilute Sulphuric Acid to dissolve the Quinine and thus defeat the object of the prescriber.

Sulphate of Quinine may be prescribed with Aromatic Spirit of Ammonia, Spirit of Nitrous Ether, Tinctures or other alcoholic preparations together with Glycerin or Syrup and Water. In such cases the salt should be first dissolved in the alcoholic portion of the prescription; then the glycerin or syrup, and finally the aqueous portions should be added gradually. It may also be ordered with dilute Sulphuric Acid and some vegetable infusion containing Tannin, in which case a precipitate of Tannate of Quinine will be produced. This of course should not be filtered, but should be dispensed with a "Shake-label." Chinoidin, Cinchonine Sulphate and Quinidine Sulphate,-also require the addition of dilute mineral acid for their solution in aqueous mixtures. Iodine,-requires the addition of Iodide of Potassium for its solution in a convenient quantity of water, as in the case of the official Liquor Iodi Compositus.

Red Iodide of Mercury,-requires the addition of Iodide of Potassium or Mercuric Chloride for its aqueous solution.

Potassii Bitartras, Cream of Tartar,-requires the addition of Borax or Boric Acid for its solution in water.

Benzoic Acid,-requires the addition of Borax to aid its solubility in water, an equal part of the latter making it 5 times more soluble than when alone. Lime, is more soluble in sweetened water than in plain water, the sugar aiding its solution.

EXCIPIENTS are substances which give form and consistence to prescriptions, and serve as vehicles for the exhibition of the other ingredients. Some of the excipients are diluents, or agents which effect the dilution or division of the active ingredients; while others act in the double capacity of diluents and flavoring agents. The excipients most generally used in mixtures may be tabulated as follows, viz. :

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Compounding the Mixture is a matter of no slight importance, and one which is best learned at the dispensing counter, though a few directions may not be out of place. In the case of the simplest form of mixture, where two or more fluid preparations are prescribed together, the only operations required are the measuring of the several ingredients and pouring them into the designed vial. In doing this the compounder should pursue a regular and definite order of procedure. Taking in his left hand a graduate of sufficient capacity to hold the whole quantity prescribed, he should walk along the shelves, and with the right hand pour from the stock-bottles the requisite quantity of each ingredient in the order in which they are entered on the prescription. A skilful clerk will hold the graduate between the thumb and first finger, the prescription between the second and third fingers, and the stopper of the stock-bottle between the little finger and the hand, leaving his right hand free for the manipulation of the bottles. containing the ingredients.

When an actively poisonous agent is ordered it should always be the last thing put into the mixture. Attention to this rule will prevent the danger of the toxic substance being put in twice.

The order in which the ingredients are put together is not of so much importance in compounding a simple mixture as in the case of an emulsion, and the order of the prescription can usually be followed, with the exception noted in the preceding paragraph. Still, when several alcoholic preparations, syrups and waters are ordered together, it is good practice to first mix the alcoholic fluids, then to add the syrups and finally the water, so as to avoid the precipitation of resinous principles which would occur if the alcoholic solutions were added to the water. Distilled water should always be used, in order to insure uniformity in taste and appearance, and also as a matter of purity and cleanliness. All mixtures should be well shaken before being labelled.

Solids which are comparatively insoluble or only slowly soluble require to be rubbed up in a mortar with one or more of the fluid ingredients. Glass mortars are much employed for this purpose, and many compounders mix all the ingredients in such a mortar before transferring them to their vial. Vegetable powders (as) Rhubarb, Ipecac, etc.), or finely pulverized inorganic substances, are often ordered in intimate mixture with water, thickened with mucilage or syrup. In such cases the mixture should be made in a porcelain or wedgwood mortar, enough mucilage or syrup being added at first to make a thick paste, and after this is rubbed smooth the water may be gradually added during the continued

process of mixing. This process will answer for all inorganic substances in powder, except Magnesia, which is best mixed by being thrown on the surface of the water, and after it has sunk to the bottom as a uniform sediment the other ingredients may be added, and the whole well shaken. Froth upon the surface of the liquid, which often arises after agitation, and may prevent the corking of the bottle, will quickly subside on the addition of a few drops of alcohol.

The following are samples of prescriptions for medicines to be administered in mixture form:

Emulsions (Emulsiones),-are mixtures containing an oil or a resinous substance in a state of minute subdivision, and suspended in water by the aid of some viscid excipient, as gum, soap, alkali, or yolk of egg.

NATURAL EMULSIONS comprise two classes of substances,—(1) those emulsions which exist ready formed in nature, as milk, yolk of egg, the milky juices of plants, etc.; and (2) the mixtures formed by rubbing up gum-resins (as Ammoniacum, Myrrh, Asafetida) with water. Each of the latter substances contains, together with its resin, enough gum to make a perfect emulsion when triturated with water The manufactured emulsions are simply imitations of the natural ones, sufficient gum being added in case of a resinous substance to cause its suspension in the aqueous diluent.

Emulsification consists in the division of the oily or resinous substance into very minute globules, and surrounding each globule with a thin envelope of the excipient. If properly done the globules will remain mechanically suspended in the water, without any tendency towards recombination. Milk is the best illustration of a natural emulsion, its butter existing in the aqueous portion as very minute globules, each surrounded by a thin film of casein. Yolk of Egg is a dense emulsion, consisting of oil suspended in water by means of albumen.

THE EXCIPIENTS which may be used for emulsification are the following, arranged in the order of their most frequent employment, viz. :—

Mucilage of Acacia,-used for oils and resins. Powdered Acacia is even better, being made into a mucilage by the process of emulsification; such a mucilage having the advantage of being perfectly fresh when incorporated

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with the other ingredients. To give uniformly good results the following proportions in parts by weight should be used, viz. :—

Mucilage of Tragacanth,—may also be used for oils and resins, but it has not proved so satisfactory as the preceding. The same may be said of powdered Tragacanth.

Vitellus, Yolk of Egg,—is an excellent agent for emulsifying oils, but mixtures made with it must be used within a few days, as they will not keep long. One yolk will emulsionize an ounce of fixed oil, and is about equal to half an ounce of Acacia. It is best suited to emulsions of cod-liver oil intended for immediate administration. The official Mistura Chloroformi is an emulsion made with yolk of egg. Glyceritum Vitelli or Glyconin is an official preparation consisting of glycerin and yolk of egg. (See ante, page 392.) One ounce of it will emulsify three ounces of fixed oil.

Liquor Potassæ,→may be used for oils, the resulting compound being however a soap rather than an emulsion. Copaiba is usually emulsified by using both a gum and an alkali; a similar process being employed for many of the fixed oils. Tincture of Senega,-will emulsify fats and oils very efficiently, and even in very small quantities, mx emulsifying an ounce of fixed oil.

Tincture of Quillaia (Soap-bark),-is a good emulsifier for oils, and is much used in Europe for this purpose.

Milk,-is used to emulsify Scammony in the Mistura Scammonii, which is official in the British Pharmacopœia.

Syrups, Confections and Extracts,—may be used in making emulsions, but are rarely so employed.

Soap,-is occasionally used for emulsifying Oil of Turpentine.

THE METHOD of preparing an emulsion which experience has shown to be the best, is as follows:-Add the oil, resin, etc., to a proper quantity of the excipient, and mix both thoroughly in a wedgwood mortar. Then add enough water to equal one-half the weight of the previous mixture, and triturate the whole rapidly and unceasingly until the emulsion is homogeneous and of a whitish color. Next, add the remainder of the water slowly, with continual stirring; finally incorporating the other ingredients, if any.

Emulsions are sometimes flavored and at the same time colored, with such a preparation as the Compound Tincture of Cardamom; but they present a better appearance when perfectly white. Alcoholic preparations should not be added in large quantity to emulsions made with Acacia or Yolk of Egg, as alcohol will precipitate the emulsifying agent. Volatile Oils require admixture with a fixed oil before being made into an emulsion. Soluble salts should never be prescribed with emulsions of oils. Acids are incompatible with mixtures which have been emulsified by an alkali. Mucilage used for emulsions should always be freshly prepared.