Oil of peppermint differs from other oils in the variety of its colorreactions with acids, as mentioned in the Pharmacopoeia.

Oil of Pimenta or Oil of Allspice closely resembles oil of cloves in its constitution, but has a lower specific gravity. It contains eugenol, C‚Í‚Ç‚ÍOCH ̧OH, and a sesquiterpene, C1H2.

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Oil of Rose. This oil shows a marked difference in constitution from other volatile oils, in that the solid crystallizable portion consists solely of a mixture of odorless hydrocarbons, one of which has the composition CH2. The liquid portion of the oil, upon which its fragrance depends, is a mixture of geraniol, CH,,OH, with a small quantity of one or more undetermined substances of honeylike odor; it has been called rhodinol. The test given in the Pharmacopoeia for the presence in oil of rose of Turkish oil of geranium and oil of rose geranium, can be made more effective by using 5 Cc. of alcohol instead of 2 Cc., as officially directed.

Oil of Rosemary is composed of pinene, cineol, CH18O, borneol, CHOH, and camphor, C,H,,OH. The finest commercial variety is that distilled from the flowers and known as the "Eperlé" brand.

Oil of Santal. The official or East Indian oil of sandalwood is said to contain a body called santalal, CHO, and an alcoholic substance, santalol, CHO, boiling at 300° C. (572° F.) and 310° C. (590° F.) respectively. Inferior oils, produced in Australia and the West Indies, are all dextrorotatory, while the official oil is lævorotatory. Oil of cedarwood and fatty oils are readily detected by imperfect solubility of the oil in ten volumes of 70 per cent. alcohol.

Oil of Sassafras consists chiefly of safrol, CHO2, with a very small amount of eugenol and a dextrorotatory hydrocarbon, C,,H169 called safrene, probably identical with pinene. Safrol, at ordinary temperatures, is a perfectly colorless liquid of 1.108 specific gravity at 15° C. (59° F.); it is also found in Japanese camphor oil, from which it is now largely obtained. Commercial artificial oil of sassafras is not a synthetic product, but probably made from camphor oil. Oil of Savin contains pinene and the sesquiterpene, cadinene, C15H24. Oil of Spearmint differs radically in its composition from oil of peppermint, containing lævorotatory limonene and lævorotatory carvol, CHO, with possibly some lævorotatory pinene.

Oil of Tar. This oil, formed during the dry distillation of wood, is obtained from pine tar by fractional distillation. It is a complex mixture of hydrocarbons, acetic and other acids, and undetermined empyreumatic products.

Oil of Thyme. The most important constituent of this oil is thymol, CHOH, a monatomic phenol; the hydrocarbon cymene, CH, is also present, as well as very small quantities of bornyl esters. In some oils, thymol is entirely replaced by its isomer, carvacrol, whilst in others, both phenols are found present in equal

amounts.

Oil of Turpentine. The official oil, derived from American turpentine, consists almost wholly of dextrorotatory pinene, which, in the crude oil, is associated with resin and other oxidation-products depending upon age and exposure. These impurities, being removable by treatment with lime water and subsequent distillation, are therefore not present in the official rectified oil, which alone should be employed for internal use.

Oil of Wintergreen, Synthetic or Artificial. This compound is recognized in the Pharmacopoeia as Methyl Salicylate, which name at once indicates its true chemical character, a compound ether. It may be prepared by distilling a mixture of salicylic acid, methyl alcohol, and sulphuric acid, when the following reaction occurs, HC,H2O, + CH2OH + H2SO ̧ CH,C,H,O,+ H2O + H2SO, methyl salicylate being volatized and condensed in suitable receivers, while diluted sulphuric acid remains in the still. For the purpose of purification, the product is thoroughly washed with water, decanted, and redistilled.

=

The quality of this oil, as well as that of the oils of betula and gaultheria, is ascertained by means of decomposition with sodium hydroxide, as directed in the Pharmacopoeia. Sodium salicylate and methyl alcohol are formed according to the following equation, CH,C,H,O,+ NaOH= NaC,H,O,CH,OH, the former dissolving upon application of heat and subsequently yielding a precipitate of salicylic acid upon supersaturation with hydrochloric acid.

DERIVATIVES OF VOLATILE OILS. The Pharmacopoeia recognizes several compounds which, being obtained directly from volatile oils, should be considered at this point.

Camphor. This term is applied to compounds having the composition CHO, which occur in a number of essential oils and are solid at ordinary temperature. They are no doubt the result of oxidation of hydrocarbons in the plant, and stand in the relation of a ketone to the alcohol borneol, CHOH. Official camphor is derived solely from the wood of the camphor tree of China and Japan. When camphor wood is heated in the stills the camphor volatilizes and sublimes in the form of small grains which come to this country as crude camphor. It is accompanied, as a by-product, by oil of camphor, a liquid of complex composition, containing not less than four hydrocarbons, pinene, phellandrene, dipentene, and cadinene, besides five oxidized bodies, cineol, camphor, terpineol, safrol, and eugenol.

The term artificial camphor has been given by some to terpin hydrate, but it is generally applied to terpene hydrochloride, CHHCl, obtained by saturating oil of turpentine, dissolved in twice its volume of carbon disulphide, with dry hydrochloric acid gas. The compound forms a white, plastic, crystalline mass, melting at 125° C. (257° F.) and possessing the odor and appearance of ordinary camphor. If terpene hydrochloride be heated with potas

sium stearate in a sealed tube, solid terecamphene, C10H16, is formed, which, when boiled with potassium dichromate and dilute sulphuric acid, takes up oxygen and is converted into camphor, C1HO.

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Menthol, CHOH. This body, forming the chief constituent of oil of peppermint, is obtained now almost altogether from the Japanese oil, by simple refrigeration, and is then purified by recrystallization. Its chemical character is that of a secondary alcohol, yielding by moderate oxidation with potassium dichromate and sulphuric acid a ketone, menthone, C1HO, and combining with organic acids to form compound ethers, such as menthyl acetate, benzoate, butyrate, formate, etc. By means of dehydrating agents, menthol is converted into the hydrocarbons menthene and dimenthene.

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Monobromated Camphor. This compound is obtained by heating camphor and bromine together in a flask or retort (preferably with the addition of water or chloroform) until reaction ceases, then allowing the yellowish solution to crystallize, heating until the mass becomes white, and recrystallizing from alcohol or benzin. The reaction involves the formation of camphor dibromide, CHOBг2, which splits up into camphor monobromide and hydrobromic acid, CHOBг. =C10H1BrO + HBr, the latter distilling over with the water or chloroform."

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Terebene. This preparation is obtained by the action of concentrated sulphuric acid on oil of turpentine, the acid being gradually added to the oil; the mixture is allowed to stand for a day, after which the supernatant layer is removed, neutralized with chalk, and distilled. Careful investigations by Power and Kleber (1894) have shown that the statements in the Pharmacopoeia regarding terebene are erroneous, and that, in its chemical properties, it does not resemble oil of turpentine. While the latter oil, as before stated, consists almost wholly of dextrorotatory pinene, true terebene consists chiefly of the hydrocarbons dipentene and terpinene, with some cymol and camphene, and is optically perfectly inactive; the latter is an important test for the presence of unaltered oil of turpentine. The specific gravity of terebene is about 0.855 instead of 0.862 at 15° C. (59° F.) and its boiling point between 170° and 185° C. (338° and 365° F.) instead of 156°-160° C. (312.8°-320° F.).

Terpin Hydrate, CH(OH)2 + H2O. This compound may be obtained by allowing a mixture of four parts of rectified oil of turpentine, 3 parts of 80 per cent. alcohol, and 1 part of nitric acid to stand in large, shallow dishes for several days; the crystals which have separated may then be drained, dried between filter paper, and recrystallized from 95 per cent. alcohol rendered slightly alkaline to remove adhering acid. The yield is about 12 per cent. of the weight of the oil of turpentine used, and the operation should always be performed in the cold, as, during hot weather, resinification of the oil will occur in place of the formation of crystals. Terpin hydrate, when fused or rendered anhydrous over sulphuric acid, yields terpin, CH(OH)2, a diatomic alcohol, which, when distilled with moder

ately dilute sulphuric acid, loses water and is changed chiefly into terpineol, CH,OH, a substance largely employed in perfumery on account of its very fragrant odor, resembling that of fresh lilacs.

Thymol, CHO or CH.CH.CH2OH. This body, chemically known as methyl-propyl phenol, occurs in several volatile oils, and is obtained by treating the residue left upon distilling the oils below 200° C. (392° F.) with solution of soda, whereby thymol is dissolved as sodium-thymol, CH,ONa. When the solution has become clear by subsidence, thymol is liberated by means of hydrochloric acid and purified by distillation and crystallization; if necessary, it is also decolorized by treatment with animal charcoal.

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Resins.

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Comparatively little is known as yet regarding the chemical composition of resins which occur in plants either alone or in combination with volatile oils as oleoresins or with gums as gum resin3. Investigations are now in progress in the hands of Prof. Tschirch of Berne, Switzerland, and his colaborers, and no doubt, in the course of a few years, much light will be shed upon this now rather obscure subject. This much has already been established, that resins are largely composed of organic acid esters or compound ethers of certain alcohols, to which latter the general name resinol has been applied; some of these alcohols give reactions similar to those characteristic of the tannins and have therefore been designated as resinotannols. Thus we have benzoresinol, storesinol, peruresinotannol, toluresinotannol, etc. Some resins have decidedly acid properties, while others are known to be anhydrides, as in the case of common pine resin or colophony, which is chiefly composed of abietic anhydride, CHO; one of the resins found in copaiba is a crystalline acid, called copaivic acid, having the elementary composition, C2H3O2; the resin obtained from guaiacum wood and officially recognized as guaiac, consists largely (70 per cent. and over) of guaiaconic acid, C1H2O5, to which the well-known color reactions of guaiac with oxidizing agents are due. Resin of Scammony consists almost wholly of scammonin, C3H6O16, the anhydride of scammonic acid, which behaves like a glucoside. Jalap resin consists of two distinct resins which can be separated from each other by ether, the one insoluble in that menstruum, and constituting about 70 per cent. of the official resin, consists almost entirely of convolvulin, C3H50O16, an anhydride possessing glucosidal properties and being colorless when pure. The official resin of podophyllum is a complex mixture, containing an acid called podophyllinic acid, insoluble in ether, and a substance to which the name podophyllotoxin has been given; the latter, which constitutes about 50 per cent. of the official product, is said to be the active purgative principle. Both these substances are soluble in chloroform, and may be separated by addition of ether to the chloroformic solution, which precipitates podophyllinic acid; upon evaporation of the ethereal solution podophyllotoxin is obtained.

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CHAPTER LVIII.

ORGANIC ACIDS.

Of the large number of compounds termed organic acids, only the few that are of special interest in pharmacy have been officially recognized. Organic acids are considered as derived from hydrocarbons or their alcohols, by replacement of hydrogen or hydroxyl by the univalent group carboxyl, CO2H, and vary in their basicity as one, two, or three carboxyl groups may have been taken up, carrying with them one, two, or three atoms of replaceable hydrogen, as in the case of inorganic acids. The official organic acids are acetic acid, benzoic acid, citric acid, gallic acid, lactic acid, oleic acid, salicylic acid, stearic acid, tannic acid, and tartaric acid. Diluted hydrocyanic acid, although usually reckoned among the inorganic acids, is preferably considered at this point, since cyanogen is a carbon compound probably derived from hydrocarbons by substitution of nitrogen for hydrogen. Oxalic and valerianic acids, although not officially recognized, are both of interest to pharmacists, as is also meconic acid.

ACETIC ACID, HC2H2O2 or CH,CO2H. This acid has already been considered in connection with the derivatives of cellulose on page 549.

2

BENZOIC ACID, HC,H,O2 or CH,CO,H. Several methods are in use for obtaining this acid from benzoin, the balsamic resin from which it takes its name.

Both a dry and a wet process are employed for extracting the acid from the resin, in which it exists in a free state. The former is by sublimation, benzoin in coarse powder, which has been dried over lime, being heated in shallow iron pans covered with a porous diaphragm and connected with a suitable condenser, carefully regulated sand-bath heat being used so as to avoid contamination of the acid with other products, partly the result of decomposition, which volatilize at a temperature approaching 200° C. (392° F.). The yield of acid by this method ranges from 6 to 8 per cent. of the weight of benzoin used, the fused resin retaining a considerable portion which can be recovered by the wet method; sublimed acid is never chemically pure, being always accompanied by a volatile oil to which the peculiar odor of the acid is due.

The wet method consists in treating powdered benzoin for some time with warm milk of lime, and finally boiling the mixture and filtering while hot. The filtrate is supersaturated with hydrochloric