Adeps (U. S. P.)—Lard.
"The prepared internal fat of the abdomen of Sus scrofa, Linné (class Mammalia; order Pachydermata), purified by washing with water, melting, and straining. Lard should be kept in well-closed vessels impervious to fat, and in a cool place "—(U. S. P.).
SYNONYMS: Prepared lard, Hog's lard, Axunge.
Source and Preparation.—Lard should preferably be prepared from "leaf fat" obtained from the omenta, mesenteries, and kidneys of the common hog killed during the winter or early spring months. The fat should be thoroughly cleansed from extraneous material, as dirt, blood, etc., and the outer membranous portion of the leaf torn off, after which the perfectly fresh fat should be suspended in the air for a short time. It must then be beaten in a stone mortar until the fibrous, vesicular walls of the cells are broken and the mass becomes uniform throughout, and then heated in a water-bath to 54.4° C. (130° F.). Separate the remaining membranous parts, and strain through flannel or linen, after which it may be filtered through paper in a warm atmosphere. It should then be put into impervious containers, cooled, covered with waxed or varnished paper, and kept in a dark, cool, dry place, preferably a cellar, otherwise by the action of the atmospheric oxygen it will speedily become unfit for medicinal use.
Description and Chemical Composition.—Lard used for medicinal purposes should not contain salt; when good it is white, somewhat translucent, of granular appearance, smooth to the touch, somewhat of the consistency of butter, having a faintly-sweetish taste, and a faint, but not rancid, odor; but by exposure to the air it absorbs oxygen, and acquires an unpleasant odor and rancid properties. It is bland to the taste. Water does not dissolve it, and alcohol but slightly; ether, chloroform, benzin, benzol, and carbon disulphide are solvents of it, and so are the essential oils. The concentrated acids decompose it, and caustic alkaline solutions form soap with it, when boiled together. "Specific gravity about 0.932 at 15° C. (59° F.). It melts at 38° to 40° C. (100.4° to 104° F.) to a perfectly clear liquid, which is colorless in thin layers, and which should not separate an aqueous layer. At or below 30° C. (86° F.) it is a soft solid"—(U. S. P.). When melted it combines with resins, wax, and fixed oils, forming ointments, liniments, etc., as may be required. When heated in close vessels, it undergoes a process of destructive distillation, by which palmitic, oleic, acetic, and probably benzoic acids are formed, together with other less important modifications of its constituent fatty principles-i. e., glycerides of oleic, stearic, and palmitic acids; these are found in most animal oils and fats, whose hardness or softness is owing to the relative quantity which they contain of each of these principles (see Soap).
OLEIN, or the Glyceride of oleic acid, is the liquid principle of oils, and is unknown in the native state. It is an oily fluid, devoid of color, taste, and odor, of specific gravity about 0.900, is partially dissolved by alcohol, but not by water, readily so by ether, and becomes solid at -6.6° C. (20° F.). It is convertible by saponification into glycerin and oleic acid. Its formula is C3H5.3(C18H33O2). it is said to be used to adulterate olive oil.
STEARIN (C3H5.3[C18H35O2]), or Glyceride of stearic acid, is a crystalline solid somewhat resembling cetaceum, is sufficiently friable to admit of pulverization, freely dissolved by ether at 35.5° C. (96° F.), but is completely separated again on cooling, is insoluble in alcohol and water, melts at 62.2° C. (144° F.), and is convertible by saponification into stearic acid and glycerin. It may be obtained from lard or mutton tallow, by washing either of these with ether until they suffer no more loss; the stearin remains behind, and may be collected in flakes by boiling it in alcohol and then allowing it to cool. This substance should not be confused with the stearin used in the making of stearin candles, which consists mainly of free stearic and palmitic acids, to which some wax is added to prevent crystallization.
PALMITIN, or Glyceride of palmitic acid, is a solid constituent found in the oily portion of the fat. Its formula is C3H5.3(C16H31O2). When lard is subjected to pressure at the temperature of 0° C. (32° F.) palmitin and stearin may be separated. The remaining fluid is then known in commerce as lard oil. Lard contains from 32 to 40 per cent of solid constituents. Margarin is a mixture of stearin and palmitin.
By incorporating with lard, while hot, a small amount of benzoin or benzoic acid, and stirring until cold, rancidity is prevented. Poplar buds, various balsams, and some volatile oils have the same effect. Pure benzoic acid should not be used, but rather the ordinary acid prepared from the gum, which still retains balsamic qualities.
Adulterations and Tests.—Lard is sometimes treated with common salt to prevent its becoming rancid. Again, for the purpose of yielding a whiter lard and to render the incorporation of water with it less difficult, salt of tartar is added to it by dishonest dealers. Boiling with water, and again fusing the lard, repeating the process if necessary, will remove these impurities. The most largely employed adulterant of lard, however, is cotton-seed oil. When heated, if the lard contains it, the foreign admixture may be detected by its odor. The U. S. P. indicates the following tests of the purity of lard: "Distilled water boiled with lard, should not acquire an alkaline reaction (absence of alkalies), nor should another portion be colored blue by iodine T.S. (absence of starch). A portion of the water when filtered, acidulated with nitric acid, and treated with silver nitrate T.S., should not yield a white precipitate soluble in ammonia (absence of chlorides). If 10 Gm. of lard be dissolved in chloroform, and the solution mixed with 10 Cc. of alcohol and 1 drop of phenolphtalein T.S., it should not require more than 0.2 Cc. of normal potassium hydrate V.S. to produce a pink tint after strong shaking (limit of free fatty acids). If 5 Cc. of melted and filtered lard be, while warm, intimately mixed, by agitation, in a test-tube with 5 Cc. of an alcoholic solution of silver nitrate (made by dissolving 9.1 Gm. of silver nitrate in 10 Cc. of deodorized alcohol and adding 2 drops of nitric acid), and the mixture then heated for 5 minutes in a water-bath, the liquid fat should not acquire a reddish or brown color, nor should any dark color be produced at the line of contact of the two liquids (absence of more than about 5 per cent of cotton-seed fats)"—(U. S. P.).
Ɣ ADEPS BENZOINATUS (U. S. P.). Benzoinated lard.
Preparation.—"Lard, one thousand grammes (1000 Gm.) [2 lb. av., 3 oz., 120 grs.]; benzoin, in coarse powder, twenty grammes (20 Gm.) [309 grs.]. Melt the lard by means of a water-bath. Tie the benzoin loosely in a piece of coarse muslin, suspend it in the melted lard, and, stirring frequently, continue the heat for 2 hours, covering the vessel and not allowing the temperature to rise above 60° C. (140° F.). Lastly, having removed the benzoin, strain the lard, and stir occasionally while it cools. When benzoinated lard is to be kept or used during warm weather, 5 per cent (or more, if necessary) of the lard should be replaced by white wax"—(U. S. P.).
Action and Medical Uses.—Lard is emollient, and is a convenient article for the formation of ointments, plasters, and liniments. It is also used, without addition, to discuss tumors, by friction, or with cataplasm—(Ed.). Sometimes it is added to purgative injections, As an enema it is soothing in colitis. Being difficult of digestion it is occasionally used as a laxative for children. Good effects are obtained from it in inunction in scarlatina and other eruptive diseases, in which it allays itching and burning and improves the skin. Applied to the bridge of the nose with friction it alleviates the unpleasantness of coryza. When applied to blistered or excoriated parts, it will be apt to cause ulceration, unless it be free from rancidity, As a lubricating material for manual examinations and operations, it is preferable to petrolatum, as it does not readily mix with fluids. Many of the vegetable alkaloids are soluble in oleic acid (the red oil of soap and candle manufactories), and form with it useful and readily absorbed external applications.