The yield of lard oil is equal to about 60 per cent. of the weight of the lard expressed.

Oleum Amygdalæ Expressum; Expressed Oil of Almond.This oil, also commercially known as oil of sweet almond, is obtained by expression from the bitter as well as the sweet almond, the yield from the latter source being about 20 per cent. greater than from the former. The yellowish color of the commercial oil is due entirely to the colored episperm, for if blanched almonds be expressed, a colorless oil will be obtained. Expressed oil of almond is soluble to some extent in cold alcohol; it remains perfectly clear at -10° C. (14° F.), and does not congeal until cooled to -20° C. (-4° F.). The oil is largely adulterated with the oils of peach and apricot kernels, which can be detected by shaking together 1 volume each of fuming nitric acid and water and 2 volumes of the suspected oil; a whitish mixture, free from orange or reddish color, results if the oil is pure. The development of a brownish color with the same test would indicate the presence of cottonseed, groundnut, sesamum, or poppyseed oil.

Oleum Gossypii Seminis; Cottonseed Oil.-The official cottonseed oil is a refined bleached oil, for the crude product, obtained by hydraulic pressure from the seed, has a brown color and linseedlike odor, and contains considerable quantities of albuminous matter. After subsiding, the crude oil is treated with superheated steam, and finally well shaken with heated weak alkali solution. The yield of oil from cottonseed varies from 12.5 to 20 per cent. It congeals when cooled to 0° or -5° C. (32° or 23° F.), and is instantly colored dark reddish-brown on contact with concentrated sulphuric acid; it belongs to the drying oils, but shaken with nitric acid and water it gradually forms a colored semi-solid mass. The chief use of cottonseed oil is as a substitute for more expensive fixed oils, as in the case of some of the official liniments, and there is no doubt that it is extensively employed as an adulterant for almond, olive, and other oils. When heated with an acidulated alcoholic solution of silver nitrate the oil assumes a reddish-brown color, which serves as a test for its detection.

Oleum Lini; Linseed Oil.-The Pharmacopoeia demands an oil expressed without heat, which, as a rule, is not readily obtainable, since hot pressure increases the yield nearly 50 per cent. Extraction with benzin or carbon disulphide shows still better results: thus, cold pressure, 16 to 20 per cent.; hot pressure, 22 to 28 per cent.; extraction, 33 per cent. Cold-pressed linseed oil is lighter in color than the other varieties; when boiled, it darkens in color and thickens, losing about 6 to 8 per cent. in weight. The oil is quite soluble in absolute alcohol, and forms a clear mixture with an equal volume of official alcohol, but becomes turbid if the proportion of alcohol is doubled; it does not congeal above -20° C. (-4° F.). Linseed oil is always slightly acid and is readily saponified by alkalies; it is the best drying oil known, and

should not be even partially solidified if shaken with nitric acid and water for a long time, by which means the presence of nondrying oil may be detected. As linseed oil may be adulterated with paraffin oils, the Pharmacopoeia recommends shaking an aqueous solution of linseed oil soap with an equal volume of ether, which latter, after decantation, should not show a bluish fluorescence nor leave an oily residue upon evaporation.

Oleum Morrhuæ; Oleum Jecoris Aselli; Cod-liver Oil.Medicinal cod-liver oil should always be procured from fresh livers, by the aid of a gradually increased steam heat not exceeding 60° C. (140° F.); the oil is allowed to separate from the watery fluid, and after it has been frozen is expressed in canvas bags, whereby a pure, only slightly colored oil is obtained, the hard yellow residue, consisting of stearin and tissue, being rejected. Cod-liver oil thus prepared keeps well in completely filled vessels, and when cooled to 0° C. (32° F.) should deposit no solid fats; it belongs to the drying oils, and if exposed to the air soon thickens and acquires a disagreeable strong odor and taste. The color reactions with sulphuric acid mentioned in the Pharmacopoeia are due to the presence of certain biliary constituents, and are very pronounced. Cod-liver oil has a slight acid reaction which increases with age. The more probable adulteration consists of seal oil and other fish oils, which can be detected by testing with fuming nitric acid: cod-liver oil turns red, then bright rose-red, and finally lemon yellow seal oil shows at first no change of color, and other fish oils become blue at first and afterward brown and yellow.

Oleum Olivæ; Olive Oil.-The finest quality of olive oil is that obtained by cold expression from the flesh only of the ripe fruit, and is known commercially as "virgin oil"; a second quality is expressed from the residue after the same has been mixed with water. Good olive oil is of a pale-yellow or light greenish-yellow color, while the inferior grades, often expressed from fermented olives, are of a deeper green. It becomes cloudy at 10° C. (50° F.), and congeals at 0° C. (32° F.) to a whitish granular mass. Olive oil is, no doubt, sometimes adulterated with cottonseed oil, groundnut oil, poppyseed oil, and sesamum oil; when heated with an acidulated alcoholic solution of silver nitrate the oil, if pure, should retain its original pale-yellow color without becoming reddish or brown. Sesame oil is best detected by a special test given in the Pharmacopoeia, and which is characteristic for that oil. A solution of soap made from the suspected oil and potassa is decomposed with sulphuric acid, and the liberated fatty acid, freed from water, is shaken with hydrochloric acid: if the mixture turns green, sesame oil is present, and on the subsequent addition of sugar the mixture, after shaking, assumes a violet or crimson tint. This is known as Baudouin's test.

Oleum Ricini; Castor Oil.-This well-known oil is produced in very large quantities in this country in the city of St. Louis; in order to increase the yield of the oil the seed is frequently heated

to about 60° C. (140° F.) before expression, and the oil afterward heated with water to remove albuminous matter. The yield of oil by cold expression is about 25 to 30 per cent., and by hot expression 38 to 45 per cent. Castor oil when cooled to 0° C. (32° F.)

becomes turbid, but does not congeal until the temperature has been reduced to -18° C. (--0.4° F.); it is soluble in all proportions in absolute alcohol or in glacial acetic acid, and in 3 times its volume of a mixture of 19 volumes of alcohol and 1 volume of water, which distinguishes castor oil from other fixed oils. Castor oil is rarely adulterated, and is readily saponified by alkalies.

Oleum Sesami; Sesame Oil; Benne Oil; Teel Oil.-Sesame oil is obtained both by cold and hot expression to the extent of about 50 per cent. of the weight of the seed. It congeals at -5° C. (23° F.) to a yellowish-white mass, and is converted into a browni-h-red jelly when mixed with concentrated sulphuric acid. When shaken with an equal volume of concentrated hydrochloric acid it assumes an emerald-green color, which, upon addition of sugar and further shaking, changes to blue, violet, and finally deep crimson. Sesame oil is sometimes found as an admixture in olive oil and expressed oil of almond.

Oleum Theobromatis; Oil of Theobroma; Butter of Cacao. -Oil of theobroma is the only fixed oil recognized by the Pharmacopoeia which is solid at ordinary temperature; it is brittle at 15° C. (59° F.), and melts at from 30° to 33° C. (86° to 91.4° F.). The oil is obtained to the extent of about 40 per cent. by heating the shelled seeds to 70° C. (158° F.) and expressing between hot iron plates. Adulterations with stearin, tallow, wax, and paraffin can be quickly detected on account of the low fusing-point and high congealing-point of the pure oil. The Pharmacopoeia requires that 1 Gm. of oil of theobroma dissolved in 3 Cc. of ether at 17° C. (63° F.), and plunged into water at 0° C. (32° F.), shall neither become turbid nor deposit a granular mass in less than three minutes ; if the mixture, after congealing, be warmed to 15° C. (59° F.), it should gradually form a perfectly clear liquid.

Oleum Tiglii; Croton Oil.-Croton oil is obtained by expression, and does not congeal until cooled to -16° C. (3.2° ̊F.). solubility in alcohol increases with age, and according to H. Senier, of England, the portion insoluble in alcohol contains the purgative principle, while the vesicating principle is soluble in alcohol. Croton oil is a non-drying oil, but differs from other non-drying oils in remaining liquid if vigorously shaken with fuming nitric acid and water, and allowed to stand for one or two days; this behavior serves to detect adulterations.

VOLATILE OILS.

Volatile oils are those peculiar principles to which, in a majority of cases, the odor of plants is due; they do not all pre-exist in the

plant, some being the result of fermentative action between certain constituents of the plant in the presence of water, and others being produced by destructive distillation. Volatile oils may exist in every part of the plant from the root to the seed, and when several oils are present in different parts of the same plant they will generally be found to differ in physical as well as chemical properties; as, for instance, the oils of orange obtained from the leaf, flower, and rind. Volatile oils usually occur in separate cells, as glands in the herbaceous portion and rinds of many fruits, or distributed throughout the interior tissue, or forming distinct oil tubes, as in the fruit of fennel, anise, etc. The odor of volatile oils, while in some instances due to their particular composition, in others appears to be due to atmospheric influences, since oil of turpentine and other oils when rectified in an atmosphere of carbon dioxide have been found devoid of all unpleasant odor, and yet, when again exposed to the air, they soon acquired their characteristic odor. With few exceptions, volatile oils are lighter than water, and their solubility in water is very variable; their specific gravities at 15° C. (59° F.) range from 0.850 to 1.185. Absolutely pure volatile oils are colorless, but the commercial varieties are frequently colored yellow, green, blue, red, and brown; the color in most instances disappears when the oil is brought into solution. Many volatile oils are completely soluble in glacial acetic acid, and all are soluble in alcohol, but in proportions varying from less than an equal volume to ten or more. They have but few properties in common with fixed oils, but like these are soluble in ether, chloroform, and carbon disulphide. Freshly prepared volatile oils are generally freely soluble in benzin, but after exposure they gradually lose this property, and often form turbid mixtures when shaken with the same. When dropped upon filtering paper they cause a stain somewhat resembling that of fixed oils, but which is dissipated upon the application of heat; the stain produced by old or partly resinified volatile oils frequently cannot be removed by heat, but can be readily distinguished from the stain of fixed oils by its shining, varnish-like appearance and by its complete removal with the aid of warm alcohol, the stain from fixed oils being devoid of lustre and insoluble in alcohol. Volatile oils are inflammable, and burn with a bright but sooty flame; exposed to air and light they are more or less rapidly oxidized, being gradually converted into a viscid oil, and finally even into a solid resin. They never become rancid in the sense mentioned under fixed oils, and do not contain glycerin. Owing to the changes which volatile oils undergo through exposure to light and air, they should be preserved in well-stoppered bottles in a dark place; amber- or yellow-colored glass is best adapted for oil containers, as it intercepts the actinic rays of light. The addition of deodorized alcohol or Cologne spirit will also preserve the fine aroma of such oils as lemon and orange, not more than 5 per cent. by volume being necessary. Resinified oils may

be restored by redistillation with water or weak alkali, or, if in small quantities, by Cuvier's method, which consists in shaking the oil for fifteen or twenty minutes with a magma formed of animal charcoal and a solution of borax, whereby the resinified portion is united to the borax and the oil becomes limpid. The whitening of

Distillation of oil of star-anise in Tonquin, Asia.

corks in bottles containing volatile oils is due to the presence of ozone produced by the gradual oxidation of the oil.

The adulterations to which volatile oils are subjected are fixed oils, alcohol, and highly rectified petroleum; frequently, also, the higher-priced oils are mixed with cheaper and inferior oils. Fixed