dividing and suspending oil globules quite well if used in sufficient quantity. The official tincture of soap-bark may be employed in the proportion of 2 fluidrachms for each fluidounce of fixed oil, or of to 1 fluidounce for each fluidounce of volatile oil; but owing to the irritant properties of quillaja, it must be used with care, and therefore cannot be recommended for use indiscriminately.

For making from 1 to 5 gallons of emulsion, the apparatus known as the Morton patent egg-beater, or whisking machine, illustrated in Fig. 218, has been found very serviceable and satisfactory; it is made of heavily tinned iron, and supplied with a waterchamber underneath, by means of which either hot or cold water may be employed for tempering, whenever desired. The upper tank is provided with a rounded bottom, and the emulsification is effected by means of several heavy wire beaters in circular form revolving rapidly in opposite directions within each other, whereby constant cross-cutting of the mixture and most perfect dashing of the constituents are insured; to prevent dust from entering, the tank is provided with a well-fitting top. The beaters are easily removed by withdrawing the frame, and the apparatus can be quickly and thoroughly cleaned.

FIG. 218.

When emulsions are to be made on a large scale, the usual plan is to add the oil, in a thin continuous stream, to the mucilage contained in a suitable churning apparatus operated by steam power, the mixture being kept in constant agitation by rapidly revolving metallic blades frequently provided with numerous perforations. In this way 10 or 15 gallons of oil can be completely emulsified in the course of a day.

THE OFFICIAL EMULSIONS.

The Pharmacopoeia recognizes 4 emulsions: 1 made from seed, 2 from gum-resins, and 1 containing chloroform together with a fixed oil. In each case specific directions are given for manipulation, which agree with those explained elsewhere.

Emulsum Ammoniaci.-As stated on page 318, only select tears of the gum-resin should be used for this emulsion. These are crushed into a moderately coarse powder and beaten into a perfectly smooth paste with a very small quantity of water, after which more water is gradually added so as to enable the operator to produce a perfectly homogeneous mixture. In order to accomplish this it is necessary that the paste first obtained be scraped from the pestle and sides of the mortar and gradually reduced to a syrupy consistence by the use of small quantities of water. After straining the finished product through a previously moistened piece of flannel, only extraneous matter, such as sand, woody fibre, etc., should be left behind, but no particles of the gum-resin. Emulsion of ammoniac is usually of a yellowish or pale-cream color.

Emulsum Amygdala.-The Pharmacopoeia directs the almond, acacia, and sugar to be thoroughly mixed and then incorporated with the water. This is best done by first making a smooth paste with a small quantity of water, and then gradually diluting with the remainder of the water, so that a uniform liquid may result.

The acacia and sugar prescribed in the official formula are by no means essential to the formation of a perfect emulsion, although they add to the stability of the preparation. Emulsion of almond more closely resembles cows' milk in appearance than any other seed or oil emulsion made; the fixed oil present is kept suspended in a very fine state of division by means of the albuminous matter known as emulsin or synaptase, which constitutes the chief body of the seed. Blanched almonds should always be used, so that a pure white liquid may result. Almonds are best blanched by macerating them in warm water until the skin becomes loose, when it can be quickly

removed by simple pressure between the fingers.

Emulsion of almond is also known as milk of almond, and should always be made fresh when wanted. When intended as a solvent or vehicle for local applications, such as mercuric chloride, borax, zinc oxide, etc., it must invariably be made without the sugar and acacia directed in the official formula.

Emulsum Asafoetida.-This preparation is made exactly in the same manner as indicated above under Emulsion of Ammoniac. It is known also as milk of asafetida, and is sometimes prescribed by physicians under that name as lac asafoetida. The color of emulsion. of asafetida may be white, yellowish, pink, and even red, dependent upon coloring-matter unavoidably present in the gum resin.

Emulsum Chloroformi.-The official directions for preparing emulsion of chloroform are to introduce the tragacanth into a perfectly dry bottle, add the chloroform, and shake the bottle thoroughly. Then add about 250 Cc. of water and incorporate by vigorous shaking. Next add the expressed oil of almond in several portions, shaking after each addition, and after thorough emulsification of the oil add the rest of the water, also in divided portions. This method yields a stable emulsion from which neither oil nor chloroform separates, even in a week's time; but since the preparation is never kept in stock, a smaller quantity (1 Gm.) of tragacanth will prove equally efficacious and yield a more fluid but very satisfactory emulsion.

CHAPTER XXVII.

MIXTURES.

THE term "mixture" in pharmacy, and more particularly in dispensing operations, is applied to liquid medicines which either contain insoluble substances in suspension or are composed of two or more liquids, with or without the addition of saline or other material in solution; in its more restricted application the term is applied to such medicines as are intended for internal administration. In only a few cases, in which the stability of the preparation for a considerable length of time can reasonably be assured, are mixtures kept in stock; hence the extemporaneous preparation of mixtures is a matter of constant occurrence, as it is a favorite method of administering medicines with physicians, because more extended use can be made of excipients and flavoring agents, with a view of improving the mixture pharmaceutically and therapeutically. Considerable skill and judgment are frequently necessary in the preparation of mixtures, so that the object of the prescriber may be fully attained and each fraction of the mixture contain an aliquot part of all the ingredients. All insoluble or only partly soluble substances, particularly those of a vegetable nature, should be brought to the condition of smooth and uniform suspension by trituration in the form of very fine powder with the liquid in the mortar; this is best done by first rubbing into a smooth paste with a portion of the liquid and then diluting this with the remainder, constantly stirring. Calcined magnesia or magnesia and charcoal can best be brought into a uniform mixture with water, by stirring at once with sufficient water to overcome the tendency of the magnesia to "set" in a gelatinous mass; a small quantity of water added to calcined magnesia also causes it to become gritty and difficult to mix. Some prefer to add the magnesia to the water and diffuse by agitation. In all cases the mixture should be passed through a loosely textured cloth. All powerful remedies, such as mercuric chloride, arsenous acid, the salts of morphine, strychnine, etc., should always be brought to a state of perfect solution before they are added to the other ingredients of a mixture, so as to insure a uniform distribution throughout the liquid. Substances which are readily diffusible in the liquid by agitation of the bottle do not, as a rule, require the addition of an excipient to insure their uniform suspension; but other insoluble substances which are relatively much heavier than water, or are inclined to float on the surface of the liquid, demand the addition of some mucilaginous or other body to increase the density. Syrup, glycerin,

or honey is frequently preferable to acacia or tragacanth, especially in the case of heavy metallic salts, liable to form, with the gum, a compact mass, which cannot be readily suspended by agitation.

Formerly emulsions were recognized among the mixtures, but they are now considered as a distinct class of preparations, the characteristics of which have been described in the preceding chapter.

In connection with the preparation of mixtures, it becomes necessary to consider the subject of incompatibility; this term is applied to the antagonism or disability of harmonious coexistence, which is exhibited by numerous substances when brought into contact with certain other substances. Liquids which are not mutually intersoluble, although they can be brought into homogeneous mixture with the aid of excipients, are often said to be incompatible with each other, as in the case of fixed oils and water, chloroform and glycerin, etc.; but, strictly speaking, the term incompatibility in pharmacy refers to the relation existing between two or more bodies by reason of which they cannot be mixed without undergoing or producing some change of a physical or chemical nature. Three kinds of incompatibility exist-pharmaceutical, chemical, and therapeutic— of which the pharmacist must take note, and for the proper understanding of which he must rely upon his knowledge of the physical, chemical, and medical properties of drugs.

The

Pharmaceutical incompatibility is such as affects the physical properties of substances, and is chiefly confined to their solubility; it may result in the partial or total separation of matter held in solution, which may include valuable constituents of the mixture, or it may cause simply a separation of liquids from each other. changes due to pharmaceutical incompatibility, being entirely of a physical character, can often be avoided or overcome by judicious manipulation or by the addition of some suitable excipient or protective agent. The mixture of strongly alcoholic liquids with solutions of acacia-of acid or neutral aqueous liquids with resinous tinctures of alcoholic or ethereal solutions of volatile oils and other substances with aqueous liquids-the admixture of solids which undergo liquefaction by reason of intersolubility, as in the case of camphor with solid fats, chloral hydrate, thymol, salol, menthol, etc. -the addition of certain metallic salts to vegetable solutions, causing gelatinization, as in the case of tincture of ferric chloride and mucilage of acacia-are all instances of pharmaceutical incompatibilities. İn many cases of physical incompatibility the trouble may be averted by appropriate dilution before mixing, as, for instance, when spirit

of nitrous ether or tincture of ferrie chloride is to be mixed with a strong mucilage of acacia: a perfectly uniform mixture, free from precipitate or gelatinization, can be prepared if the mucilage as well as the spirit or tincture be first largely diluted with water, and such should be the invariable rule when these substances are prescribed together. When tinctures of asafetida, guaiac, lupulin, myrrh, and similar substances are ordered in combination with