Preparations: Soap Plaster - Brown Soap Plaster - Glycerite of Soap - Soap Liniment - Camphorated Soap Liniment - Liniment of Soft Soap - Compound Pills of Soap - Spirit of Soap - Compound Tincture of Green Soap
Related entries: Olea.—Oils - Adeps (U. S. P.)—Lard - Glycerinum (U. S. P.)—Glycerin
"Soap prepared from soda and olive oil"—(U. S. P.).
COMMON NAMES AND SYNONYM: Soap, White castile soap, Castile soap, Hard soap; Sapo durus, Br.
Source and Preparation.—Soaps in general are the sodium or potassium salts of the higher fatty acids (lauric, stearic, palmitic, oleic acids, etc.) occurring in fats or fixed oils, these being glycerin esters of the acids named (see Olea Fixa and Adeps). Sodium and potassium soaps are readily soluble in water, while calcium soaps and the soaps formed with heavy metals are insoluble. The latter are called plasters, e. g., lead plaster (see Emplastrum Plumbi).
Commercial soaps are broadly classed as hard soaps and soft soaps. As a rule, sodium soaps are hard soaps, while potassium soaps are soft. The nature of the higher fatty acid with which the alkali is combined, has a secondary influence on the consistency of the soap. Fats in which the solid stearic acid is preponderant, e.g., mutton and beef suet, yield a harder soap than those in which the fluid oleic or related acids are predominant, e. g., olive oil, linseed oil, fish oils. The fats from which soaps are prepared are chiefly tallow and lard, palm oil, olive oil, cocoanut oil, for hard, partly also for soft soaps, and hempseed oil, linseed oil, cotton-seed oil, and fish oils, for soft soaps; castor oil for transparent toilet soaps, and commercial oleic acid both for hard and soft soaps. In the case of oleic acid, soap-making consists simply in the neutralization of the free acid by caustic alkali or by the carbonate of an alkali. The carbonic acid evolved in the latter case is liable to be a disturbing element in the manufacture. With neutral fats, decomposition into the fatty acid and glycerin may be effected in several ways (see Glycerinum); of these, saponification by caustic alkalies is still the prevailing method of making soap. Taking stearin (glyceryl-tristearate) as a type of a solid fat, the reaction with caustic soda will be as follows: C3H5(C18H35O2)3+3NaOH=3C18H35O2Na (sodium stearate) +C3H5(OH)3 (glycerin). White castile soap is officially recognized and is made from olive oil.
HARD SOAPS.—In practical soap-making, saponification of the fat must be started with a weak lye, because soap being insoluble in strong alkali, the first soap formed would envelop the fatty particles and prevent them from being further attacked. The heating is done in copper boilers provided both with indirect and direct steam. After adding stronger lye, the mixture is boiled until a sample becomes firm on cooling; the soap is then "salted out," i. e., common salt or concentrated brine is added, in which the soap is insoluble. The latter rises to the top, while the liquid below ("spent lye") contains all the glycerin, salt solution and various impurities, but should not contain either soap or free alkali. It is drawn off, and the supernatant soap boiled with another quantity of strong soda-lye, which completes the saponification. A small quantity of weak lye is now added and the mass boiled for several hours by direct steam. This produces curd soap, composed of hard, granular particles. The soap is taken out and allowed to harden in wooden or iron frames. Mottled soap is obtained when ferrous sulphate (about 0.25 per cent) is incorporated into the cooling mass which causes greenish streaks of ferrous hydrate to form, turning red on the surface of the soap. Other substances are also used for this purpose. Yellow or resin soap, is formed by adding a certain quantity of resin (see Resina) (as much as 50 per cent and more, of the fat employed) to the mass in the soap boiler toward the end of the process; a yellow soap of uniform texture, not curdy and granular, is produced. When unbleached palm oil is saponified, the soap that is formed is also yellow.
Filled Soaps.—These are the cheapest soaps made. As they are not salted out they represent the total contents of the soap boiler, including the glycerin. The fats usually receive an addition of a large percentage of cocoanut oil, which has the remarkable property of being readily saponifiable with a strong soda-lye at a lower temperature producing a hard soap which can not be separated from the liberated glycerin, and in addition is capable of taking up large amounts of extraneous matters, soluble silicate of sodium being especially used for this purpose. Thus, 100 kilogrammes of cocoanut oil, 75 to 80 kilogrammes of rosin, 300 kilogrammes of waterglass, and 100 to 150 kilogrammes of tallow, yield, with 240 kilogrammes of soda-lye of 33° Beaumé, a total of 800 kilogrammes of finished soap (S. P. Sadtler, Indust. Org. Chem., 2d ed., 1895, p. 62).
Saponification of cocoanut oil, even when mixed with twice its quantity of tallow, takes place with soda-lye of the above strength at a temperature as low as 50° C. (about 120° F.) (cold process). The soap known as marine soap is made from cocoanut oil by boiling with the calculated quantity of caustic soda. It retains all the glycerin of the fat, and has the property of forming a lather with sea-water which ordinary soap does not do. Toilet soaps are prepared from grained (curd) soap, and according to the process of treatment are distinguished as transparent soaps, remelted soaps, and milled soaps. The latter are produced by slicing and drying the stock soap, grinding the material, mixing in the ingredients, e.g., perfumery, etc., and pressing into cakes. Transparent soaps maybe obtained by making an alcoholic solution of soap and distilling off the alcohol.
SOFT SOAPS.—These are made by saponifying hempseed, linseed (U. S. P.) or cotton-seed oil (Nat. Form., 1st ed.), fish oils, etc., with caustic potash. They can not be salted out with potassium chloride, hence contain glycerin and any excess of alkali that may have been employed. The U. S. P. gives the following directions for making soft soap (SAPO MOLLIS): Take of "linseed oil, four hundred grammes (400 Gm.) [14 ozs. av., 48 grs.]; potassa, ninety grammes (90 Gm.) [3 ozs. av., 76 grs.]; alcohol, forty cubic centimeters (40 Cc.) [1 fl ounce, 169 minim]; water, a sufficient quantity. Heat the linseed oil in a deep, capacious vessel, on a water-bath or steam-bath, to a temperature of about 60° C. (140° F.). Dissolve the potassa in four hundred and fifty cubic centimeters (450 Cc.) [15 fl ounce, 104 minim] of water, add the alcohol, and then gradually add the mixture, constantly stirring, to the oil, continuing the heat until a small portion of the mixture is found to be soluble in boiling water without the separation of oily drops. Then allow the mixture to cool, and transfer it to suitable vessels. The potassa used in this process should be of the full strength directed by the Pharmacopoeia (90 per cent). Potassa of any other strength, however, may be used, if a proportionately larger or smaller quantity be taken, the proper amount for the above formula being ascertained by dividing 8100 by the percentage of absolute potassa (potassium hydrate) contained therein"—(U. S. P.). (Also see formula for Sapo mollis from olive oil, Amer. Jour. Pharm., 1895, p. 485; and comment on this and the official formula, by S. A. Sieker, Pharm. Review, 1898, p. 15.)
Description, Chemical Composition, and Tests.—Dr. S. P. Sadtler (loc. cit.) broadly classifies the many commercial varieties of soaps as follows: (1) Compact soaps, including curd soaps (tallow soap or Sapo animalis, S. domesticus, and toilet soaps), mottled and yellow (palrn oil and rosin) soaps; they contain from 10 to 25 per cent of water; (2) smooth or cut soaps, which are curd soaps, allowed to take up more water; they contain from 25 to 45 per cent; (3) filled or padded soaps (see previous page), from 45 to 75 per cent of water, and glycerin, spent lye, etc.; (4) soft or potash soaps.
Two classes of medicinal soaps are recognized by the U. S. P.: I. SAPO (U. S. P.), Soap; White castile soap.—This soap, prepared from olive oil, is also known as Hard soap (Sapo durus), Sapo oleaceus, Sapo venetus, Sapo Hispanicus, or Spanish soap. As described by the U. S. P., it is "a white or whitish solid, hard, yet easily cut when fresh, having a faint, peculiar odor free from rancidity, a disagreeable, alkaline taste, and an alkaline reaction. Soluble in water and in alcohol, more readily with the aid of heat"—(U. S. P.).
Soap is insoluble in petroleum ether; this permits the quantitative extraction of any unaltered fat that may be present in soap. Soap is incompatible with all acid liquids, with the salts of heavy metals, with alum, and the solutions of the alkaline earths and their salts, e.g., with lime-water, chloride of calcium, sulphate of magnesium, etc. Hard waters do not form a lather with soap, because soap forms granular compounds with the calcium salts of the water. Previously boiling the water with sodium carbonate will precipitate the calcium salts, and the water thus purified will foam with the soap. Or, sodium or potassium carbonate incorporated with the soap, is said to produce the same effect.
The U. S. P. directs the following tests for hard soap: "On placing a small, weighed portion of soap, together with about 10 Cc. of alcohol, in a tared beaker containing sand, evaporating the resulting solution of the soap to dryness, and drying the residue at 110° C. (230° F.), the loss of weight should not exceed 36 per cent (absence of an undue amount of water). A 4 per cent alcoholic solution of soap should not gelatinize on cooling (absence of animal fats). An aqueous solution of soap should remain unaffected on the addition of hydrogen sulphide or ammonium sulphide T.S. (absence of metallic impurities). On dissolving 20 Gm. of soap in alcohol, with the aid of heat, transferring the undissolved residue, if any, to a filter, and washing it thoroughly with boiling alcohol, it should, after drying, weigh not more than 0.6 Gm. (limit of sodium carbonate, etc.); and at least 0.4 Gm. of this residue should be soluble in water (limit of silica and other accidental impurities). If a solution of 5 Gm. of soap in 50 Cc. of water be mixed with 3 Cc. of decinormal oxalic acid V.S., the subsequent addition of a few drops of phenolphtalein T.S. should produce no pink or red tint (limit of alkalinity)"—(U. S. P.). The presence of free alkali in soap may be qualitatively ascertained by adding to a concentrated solution of the soap either calomel or solution of mercurous nitrate. A black precipitate is formed if free alkali is present.
The adulterants that have been found in hard soap are China clay, fuller's earth, chalk, pumice stone, gypsum, sand, bran, etc. They all remain undissolved when the soap is treated with alcohol or water.
II. SAPO MOLLIS (U. S. P.), Soft soap, Sapo viridis (Pharm., 1880), Green soap."A soft, unctuous mass, of a yellowish-brown or brownish-yellow color. Soluble in about 5 parts of hot water to a nearly clear liquid; also in 2 parts of hot alcohol, without leaving more than 3 per cent of insoluble residue"—(U. S. P.). This soap has been found adulterated with starch to the extent of 25 per cent. The adulteration may be recognized by iodine in slightly acidulated solution. (For a tabulated scheme of systematic soap analysis, we refer the reader to S. P. Sadtler, Handbook Indust. Org. Chem., 2d ed., 1895, p. 82; or to A. H. Allen, Commercial Organic Analysis, 3d ed., Vol. II, Part 1, 1899, p. 277. An interesting account of the analysis of five samples of castile soap and four samples of soft soap, with comment on the above U. S. P. requirements, is given by F. A. Sieker, Pharm. Review, 1898, pp. 15, 94, and 267; also see S. R. Knox, Proc. Amer. Pharm. Assoc., 1894, p. 174; and article by Alfred Smethan, on "Soap Manufacture and Soaps of Commerce," in Pharm. Jour. Trans., Vol. XIV, 1883-84, p. 534.)
The following table, from Dr. S. P. Sadtler's Handbook, p. 73, gives the results of some analyses performed by M. Dechan (Pharm. Jour. Trans., Vol. XV, 1884-85, p. 870), of the soaps chiefly employed in pharmacy:
|NAME OF SOAP.||Fatty acids.||Combined Alkali.||Free Alkali.||Silica.||Sulphates and Chlorides.||Insoluble Matter.||Water.||Insoluble in Alcohol.|
|Hard soap (Sapo durus)||81.5||9.92||.08||.00||.28||0.20||10.65||0.50|
|White castile soap||76.7||9.14||.09||.00||.36||0.90||13.25||0.60|
|Mottled castile soap||68.1||8.9||.19||.15||.63||0.80||21.70||1.30|
|Tallow soap (Sapo animalis)||78.3||9.57||.28||.00||.47||0.40||12.50||1.10|
|Soft soap (Sapo mollis)||48.5||12.6||.38||.17||.93||1.00||39.50||1.60|
Action, Medical Uses, and Dosage.—Soap taken internally is slightly laxative, and, externally, it is detersive. Its action is very much like that of the alkalies, but less energetic; hence it may be administered in considerable doses without producing inflammation, though it readily disturbs digestion. As an antacid, it is useful in strong solution, in cases of poisoning by mineral acids, and also in acid conditions of the stomach. It has likewise been found serviceable in those cases of gravel in which uric acid prevails, but it does not dissolve the uric acid formations. In cases of poisoning by acids, it may be used until more effective agents can be procured, as chalk, lime, magnesia, or the alkaline bicarbonates. It is seldom used alone as a purgative, but is usually combined with aloes, gamboge, resin of podophyllum, or other resinous cathartics, whose irritating properties are thereby modified. United with rhubarb, it forms a pill of much service in obstinate costiveness and biliary derangements. It lessens the astringent action of rhubarb. Externally, it has been found serviceable in tinea capitis, itch, boils, and other cutaneous diseases, and as a discutient in glandular enlargements, abscesses, contusions, etc., in which it is used either in form of liniment or plaster. Soft soap, especially, has been found efficient in these cutaneous affections, used either alone, or in combination with other suitable agents. An excellent injection is formed by making a strong soap-water from soft soap, which will be found useful in obstinate costiveness, or where it is desirable to produce a prompt discharge from the bowels. In the preparation of pills, liniments, or plasters, we must be particular not to add agents which are chemically changed by the soap. Soap may be administered in a dose of 5 to 30 grains, and is commonly used in the pilular form; in poisoning by mineral acids, ½ pint of a strong solution should be promptly administered and be repeated every few minutes, if necessary.
Special Soaps.—As such we consider soaps containing certain ingredients intended to impart to the soap special medicinal or economic characters. This includes the multitude of medicated soaps. The following special soaps may be mentioned:
TRANSPARENT GLYCERIN SOAP may be made by melting together 10 kilogrammes of tallow, 10 kilogrammes of cocoanut oil, 6 kilogrammes of castor oil, 10 kilogrammes of glycerin, heating to about 50° C. (122° F.), adding 13 kilogrammes of soda-lye of 40 per cent, and 12 kilogrammes of 96 per cent alcohol, stirring the mixture until the soap becomes transparent, then add sugar solution (2 kilogrammes of sugar boiled with ½ kilogramme of water), 100 grammes of cassia oil, 50 grammes of bergamot oil, and pour the finished soap into tin molds (Amer. Jour. Pharm., 1879, p. 566). It is stated by Dr. Sadtler, however, that the addition of sugar is harmful to sensitive hands.
OPODELDOC is the camphorated soap liniment (Linimentum Saponato Camphoratum) of the German Pharmacopoeia (also see p. 1143).
SAPO MEDICATUS of the German Pharmacopoeia (which enters into the composition of the preceding) is a neutral soda soap, prepared on the steam-bath, with the aid of alcohol, from a mixture of equal amounts of lard and olive oil.
SAPO JALAPINUS (Ger. Pharm.).—Dissolve jalap resin (4 parts) and medicinal soap (4 parts) in diluted alcohol (8 parts), evaporate on the steam-bath to 9 parts, with constant stirring.
TANNIN SOAP.—Saponify cocoanut oil (9 kilogrammes) with soda-lye (4.5 kilogrammes); add solution of tannin (250 grammes) in alcohol; finally add balsam of Peru (30 grammes), oil of cassia, oil of cloves (each, 1 10 grammes).
IODINE SOAP.—Cocoanut Oil (10 kilogrammes), lye of 38° Beaumé (5 kilogrammes), potassium iodide (500 grammes), dissolved in water (250 grammes).
GALL SOAP.—Cocoanut oil (25 kilogrammes) is mixed with galls (1.5 kilogrammes) and saponified in the cold with 12.5 kilogrammes of soda-lye of 38° Beaumé. The soap is colored with 350 grammes of ultramarine green, and perfumed with 75 grammes each of oil of lavender and caraway.
CAMPHORATED SULPHUR SOAP.—Cocoanut oil (12 kilogrammes), soda-lye of 38° Beaumé (6 kilogrammes), potassium sulphide (1 kilogramme), dissolved in water (0.5 kilogramme); camphor (160 grammes) is to be dissolved in melted cocoanut oil (Amer. Jour. Pharm., 1882, p. 64).
PETROLEUM SOAP.—Heat white beeswax (40 parts), petroleum (50 parts), alcohol of 90 per cent (50 parts) on a water-bath; when melted, add hard Marseille soap (100 parts), agitate and pour into molds. The soap is said to be firm, emulsifies easily and does not leave the washed parts impregnated with petroleum (Amer. Jour. Pharm., 1889, p. 287).
SAND SOAP may be prepared from curd soap and cocoanut oil soap, each, 7 pounds; sifted sea-sand, 28 pounds; oils of thyme, cassia, caraway, and French lavender, each 2 ounces.
ASEPSIN SOAP is a milled tallow soap medicated with asepsin and borax (also see Asepsin).
ANTISEPTIC SOAP (ethereal, Johnston) is a medicinal soap in liquid form introduced and manufactured by Parke, Davis & Co., Detroit.
SHAVING CREAM.—The Pharm. Jour. Trans., Sept. 19,1896, p. 248, recommends the following formula: Curd soap, 2 ounces; fresh butter, 4 drachms; tincture of quillaja, 2 ounces; carbonate of potassium, 2 drachms; otto of rose, 10 minims; oil of lavender, 10 minims, oil of myrcia acris, 5 minims. Dissolve the soap, shredded fine, in 10 ounces of water by the aid of heat; melt the butter, and mix in a warm mortar with the carbonate of potassium dissolved in 1 ounce of water; gradually add the soap solution, and stir until a paste is formed, then add the quillaja tincture in which the oils have been dissolved.
MOLLIN.—An ointment base in use in German dermatological practice, and is classed as a soft soap containing 17 per cent of free fat. It is a smooth, soft, yellowish-white, non-rancid body not easily altered in the air, and readily washed from the skin with water, hot or cold. To prepare it, fresh fat, or cocoanut oil, 100 parts is first saponified with caustic potash solution (specific gravity 1.145), 40 parts. Glycerin, 30 parts, is then intimately mixed with it and carefully heated.
PULVERULENT MEDICINAL SOAPS.—This form of soap is recommended by Dr. P. J. Eichhoff. A neutral soap-powder base (anhydrous, hygroscopic) is obtained from beef tallow; superfatted soap powder is obtained from the preceding by adding oleic acid (2 per cent) and lanolin (3 per cent). An alkaline soap-powder base is obtained by adding to the neutral base potassium and sodium carbonates (2.5 per cent of each). A number of medicinal soaps have been prepared from the three bases named, by incorporating with them certain medicinal constituents, e.g., sulphur (10 per cent), balsam of Peru, chrysarobin, chlorinated lime; or carbolic acid, salicylic acid, pyrogallol, iodoform, aristol, quinine sulphate, etc, etc. (see Amer. Jour. Pharm., 1893, p. 68, from Pharm. Zeitung, 1892; also see Amer. Jour. Pharm., 1891, p. 360).