the mixture is continued until it becomes transparent and somewhat tenacious, showing that no uncombined fat remains; this is necessary, as the decomposition of the fat is gradual and the newly formed soap serves as an emulsifying agent for the fat. As the process nears completion iridescent bubbles are seen to rise on the surface, consisting of soap solution. Finally common salt is added to the finished solution, whereby the soap is precipitated and can then be drained and allowed to dry in suitable moulds. This explains the fact that ordinary soap will cause no lather with sea water, a special soap made with cocoa-nut oil or resin, and known as marine soap being preferable for this purpose, since it is soluble in the solution of salt. Since all fats contain some palmitin or stearin (even the fixed oils), the consistence of the soap will depend in part upon the proportion of solid fats present, being firmest in soaps made partly with stearin fats, such as suet, tallow, etc.

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The term saponification is also used to express the decomposition of fats and fixed oils by water with the aid of superheated steam, which results in the liberation of the fatty acids and glycerin, as in the case of tallow or suet, thus: C,H,(C18H35O2)3 + 3H2O 3HC1H3O2+C,H,(OH). Chemists, not confining the process to the glycerides of fatty acids, further apply the term to the resolution of all compound ethers by an alkali into the respective acids and alcohols, which is often practised in connection with the determination of certain constituents of volatile oils. The action of potassa on aldehyde, resulting in the formation of aldehyde-resin, has also sometimes, but erroneously, been called saponification. In pharmacy, the term soap is always restricted to the alkali salts of fatty acids, obtained by treatment of a fat or fixed oil with a boiling solution of soda or potassa, which are soluble in water; the name oleate or plaster is more properly applied to those soaps which are insoluble in water or alcohol and are made with the oxides of the earths or heavy metals. Soap made wholly from animal fat is but sparingly soluble in cold alcohol and therefore to be preferred for the preparation of solid opodeldoc and similar firm liniments.

MEDICATED SOAPS. While soaps intended simply as detergents, may, without detriment, contain a very slight excess of alkali, it is desirable, when medication of the soap is intended, that prior to its application, a perfectly neutral substance be employed; it has, in fact, been found that soap containing uncombined fat is even preferable to neutral or normal soap, for not only does it render the skin softer but reaction between the soap and any medicinal agent added is also thereby avoided or at least retarded. Such soaps, containing an excess of fat, are known as "superfatted soaps" and have been largely used for the past ten years. In preparing them it is customary to add an excess of 3 or 5 per cent. of fat or fixed oil in the beginning of the operation, which then remains intimately mixed with the newly formed soap. In a few cases the excess of fat has been

incorporated with the freshly made, neutral soap while yet in a soft, pasty condition. Both olive oil and lanolin are used in the manufacture of superfatted soaps, having been found preferable to all other fats in their action on the skin and toward chemicals.

In the manufacture of medicated soaps the plan followed is identical with that prescribed on page 373 for ointments. The medicinal agent is first intimately mixed (either in the form of solution or impalpably fine powder) with a small portion of the superfatted soap, by means of suitable apparatus, which mixture is then added to such a further quantity of the same vehicle as may be necessary to establish the required percentage strength of the finished product. Among the various medications of superfatted soaps are tar 5 per cent., sulphur 10 per cent., salicylic acid 5 per cent., borax 5 per cent., carbolic acid 5 and 10 per cent., corrosive sublimate and per cent., camphor 5 per cent., and others.

OFFICIAL SOAPS. The Pharmacopoeia recognizes two varieties of soap, one by the general name soap (Latin, sapo) and the other by the general name soft soap (Latin, sapo mollis). The first is intended to be a hard soap made from olive oil and soda, as already explained. When fresh, or if kept in a damp cellar, it usually contains a large proportion of water, most of which is lost by drying in a warm, airy room and all of which can be expelled at a temperature of 110° C. (230° F.). White castile soap, the kind officially recognized, usually contains a slight excess of alkali, which should not, however, exceed 1 per cent. of sodium carbonate or 0.25 per cent. of sodium hydroxide, as indicated by the official test with oxalic acid solution. The Pharmacopoeia also demands the absence of more than 2 per cent. of matter insoluble in water.

The soft soap of the Pharmacopoeia is directed to be made by the action of potassa on linseed oil. Commercially, it is generally known as green soap, which was formerly also the official title; the color is, however, by no means green, being yellowish-brown. On account of the unsightly appearance and disagreeable odor of the official preparation, the use of olive in place of linseed oil has been recommended, yielding a more satisfactory product. The value of the official soft soap is partly due to its greater alkalinity. In the German Pharmacopoeia this soap is known as sapo kalinus.

Lead plaster is sometimes spoken of as lead soap, and, in its manufacture, a process similar to that used for the official hard soap is employed, finely divided lead oxide being allowed to act upon heated olive oil, in the presence of water, forming lead oleate (oleopalmitate) and liberating glycerin, which latter is removed by subsequent washing with warm water. The use of water is essential, as it not only keeps the temperature down to that of boiling water, thus preventing decomposition of the olive oil at a higher heat, but also very materially aids in the reaction between the oil and lead oxide, as shown by the equation, 2C,H(C18H33O2)3 + 3PbO + 3H2O =

3Pb(CH [33O2)2 + 2С2Н,(OH). The finished product, which is a normal lead oleate mixed with small quantities of lead palmitate, owing to the palmitin in the olive oil, should not be sticky or greasy to the touch, and should dissolve completely in warm oil or turpentine, showing the absence of free oil and uncombined lead oxide.

The name diachylon plaster, which is still applied to lead plaster, was given to it during the middle ages, when mucilage of linseed, althæa and similar substances, was added to the mixture before heating, with the view of retarding the evaporation of water and possibly also to increase the plastic condition of the finished product. The term diachylon is derived from the Greek words dá, through or with, and quλóg, juice.

GLYCERIN. As already stated, the basylous radical found in nearly all fats and fixed oils is glyceryl, the hydroxide of which is glycerin, C,H,(OH),, a triatomic alcohol. Its manufacture, on a commercial scale, has been explained on page 195. While glycerin is unaffected by cold nitric or sulphuric acid separately, a mixture of the two acids forms with it a definite chemical compound, glyceryl or propenyl trinitrate, C,H,(NO3)3, commonly but wrongly called nitroglycerin and also known as glonoin and trinitrin.

Glyceryl trinitrate is prepared by adding a mixture of 100 parts of anhydrous glycerin and 3 parts of sulphuric acid spec. grav. 1.835, gradually and in small portions at a time, to a well-chilled mixture of 280 parts of nitric acid spec. grav. 1.5, and 300 parts of sulphuric acid spec. grav. 1.835, the vessel being kept surrounded by ice. This mixture is afterward poured into six times its volume of cold water, washed free from acid, and finally dried over sulphuric acid. The reaction may be illustrated as follows: C,H,(OH), + 3HNO3 + H2SO1 = C2H,(NO3)3 + 3H,O+H,SO,, the sulphuric acid simply serving to withdraw the water eliminated in the formation of the compound ether.

The product is a slightly yellowish, oily liquid, insoluble in water but soluble in alcohol. It has a sweet, aromatic taste, and is very poisonous.

In the form of a 1 per cent. alcoholic solution, glyceryl trinitrate is recognized, in the Pharmacopoeia, as Spirit of Glonoin; tablet triturates and chocolate tablets containing 0.00065 and 0.0013 Gm. (Cate and grain) of glonoin each are also used by physicians; mixed with three parts of infusorial earth (kieselguhr), it constitutes dynamite, a well-known blasting agent.

PETROLEUM PRODUCTS. Pharmaceutically closely allied to the fats, but chemically entirely distinct are those mixtures of hydrocarbons of the paraffin series obtained by purification of the residuum from the distillation of American petroleum. They are recognized in the Pharmacopoeia by the name "Petrolatum," in three varieties, as liquid, soft, and hard ; a still firmer variety is recognized

in the British and German Pharmacopoeias as "hard paraffin." These substances are fat-like in appearance and extensively employed as vehicles for the application of numerous remedial agents; commercially they are known as vaseline, cosmoline, albolene, petrolina, etc.

The existence of petroleum in the earth has not as yet been satisfactorily explained; several theories have been advanced, the most acceptable of which is that petroleum is the result of dissociation of large quantities of fatty matter (derived from marine animals), while under long-continued pressure, at a moderate temperature, with entire exclusion of air.

American petroleum consists of a mixture of hydrocarbons of the fatty or marsh gas series from methane upward to those richest in carbon, together with small and varying proportions of aromatic hydrocarbons. Upon subjecting the crude petroleum to a refining process by fractional distillation, benzin or naphtha, illuminating oils, and a residuum largely composed of paraffins are obtained. All fractions are then further purified by treatment with sulphuric acid and subsequently with alkalies, after which they are subjected to further fractional distillation. The benzin recognized in the Pharmacopoeia also as petroleum benzin or petroleum ether, is collected between 50° and 60° C. (122° and 140° F.) and should be free from sulphur compounds. Its chief components are the hydrocarbons, pentane (C,H,2), and hexane (CH1). Official benzin is a valuable solvent for fats, caoutchouc, and some alkaloids, and, as such, is extensively employed; it must not be confounded with benzene, CH, a coal tar derivative (see page 555). Benzin is highly inflammable, and its vapor, like that of ether, is explosive when mixed with air and ignited. Upon distilling the purified residuum from the crude petroleum at higher temperatures, paraffin oils" are obtained together with a residue of pitch. These paraffin oils are filtered, while hot, through freshly burned bone-black, for the purpose of removing odor and color, and then subjected to distillation until the desired consistence or melting-point of the residuary portion is obtained. The three official varieties of petrolatum differ from each other simply in the graded removal of lower hydrocarbons.

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Petrolatum is not saponifiable and not subject to rancidity. It properly purified, it consists only of hydrocarbons, which are not af fected at all by cold acids and alkalies and only slightly by hot acids; hence the name paraffins has been given to the products, from the words parum, too little, and affinis, allied, on account of their lack of affinity for other substances.

Hard paraffin is obtained partly as a residue from the abovementioned paraffin oils and also largely by the purification with sulphuric acid, etc., of ozokerite or mineral (earth) wax. It occurs as a white, crystalline, odorless, wax-like body, having a melting-point varying from 65° to 80° C. (149°-174° F.), according to its source. Ceresin is a yellow variety of purified earth wax, often used to adulterate yellow beeswax.

CHAPTER LVII.

VOLATILE OILS AND RESINS.

VOLATILE oils form a very important class of pharmaceutical plant products. Their physical properties and the mode of obtaining them have already been fully considered on pages 196-204. Chemically, volatile oils differ radically from fats and fixed oils, as they are not capable of saponification and contain no glycerin. Moreover, by exposure to air, they undergo resinification, but do not become rancid. They may be said to consist of hydrocarbons of the aromatic series, usually associated with oxygen derivatives, alcohols, aldehydes, compound ethers, acids, ketones, and phenols. While some volatile oils are complex mixtures, others are of very simple composition. The hydrocarbons found in volatile oils all belong to one of the following groups: terpenes of the composition CH169 which include pinene, camphene, dextrorotatory limonene (known also as hesperidine, citrene, or carvene), lævorotatory limonene, dipentene or cinene, sylvestrene, and phellandrene; sesquiterpenes of the composition C1H; diterpenes of the composition C20H32; polyterpenes of the composition (C10H16).×

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Chemists must rely largely upon fractional distillation for separation of the different constituents, in addition to which the examination of volatile oils is materially aided by determination of their optical rotation by means of the polariscope, as explained on pages 512-514 of the Pharmacopoeia.

The behavior of volatile oils with acids, alkalies, and other reagents must naturally vary greatly, owing to the diversity in their constitution. Those oils composed almost wholly of terpenes form either solid or liquid compounds with hydrochloric acid. Other oils are oxidized and converted into resin-like bodies by nitric acid, while sulphuric acid thickens some volatile oils and completely chars others. Color reactions also occur between some of the oils and sulphuric and other acids. Alkali carbonates are without much effect on volatile oils unless the latter contain acids, but alkali hydroxides, in both aqueous and alcoholic solution, are more active, removing phenols, saponifying compound ethers, etc. Acid alkali sulphites, when added to volatile oils containing aldehydes, combine with the latter to form crystalline compounds. Iodine reacts violently with some oils, and bromine forms crystallizable tetrabromides with others.

The study of the chemistry of volatile oils is a very comprehensive subject, and, while a full treatment thereof cannot be attempted