SOAP, a composition of fixed alkaline salt, in a state of combination with animal or vegetable oil: it is sometimes dry and hard, at others soft and liquid; being manufactured in various ways, with and without heat; but, as these depend on the same principle, we shall state only the common methods.
Where large quantities of soap are to be formed, heat becomes indispensable. For this purpose, a ley is made of soda and quick-lime, in the proportion of four parts of the former to one of the latter; and which is sufficiently strong to bear an egg. Equal parts of such ley, and of some tallow, or oil, are next poured into a copper, placed over a gentle fire, and stirred continually, till they begin to unite; when the rest of the ley is added, and the agitation continued, till the ingredients be completely incorporated. The mixture is next cast into proper vessels, at the bottom of which a little pulverized chalk is spread, to prevent it from adhering: and, in a few days, the soap acquires a sufficient degree of consistence, to be taken out, and formed into oblong squares.
Such is the process by which the various kinds of soap are manufactured; the only difference being in the oils employed in the composition. Thus, the common hard soap is prepared from the caustic ley above-mentioned, with the addition of tallow. The Venice, Alicant, or Spanish Soap, with olive-oil; Green Soap with that of rape, hemp, or linseed; Black Soap with train-oil; and, lastly, the ordinary Soft Soap is formed by using pot-ash as a substitute for soda, together with tallow, or train-oil; to which is added a large quantity of common salt.—The perfumed compounds, known under the names of Palm, Violet, Almond, or other Soaps, are prepared in a similar manner; the oils of such vegetable substances being employed, instead of those of the usual kind.
The vegetable oils, as well as the fat of animals, generally consumed in the manufacture of soap, raising this article to a high price, experiments have successfully been made, with a view to substitute fish-oil. The only objection to its general use, is a disagreeable smell, of which it cannot be easily divested.—With a similar design, Chaptal has proposed to employ wool. He directs ("Annales de Chimie," vol. 21) the ley to be prepared in the usual manner, and made boiling hot; when shreds or rags of any kind of woollen cloth are to be gradually thrown in, and they will be speedily dissolved.—Fresh portions are then to be sparingly added; the mixture must be constantly agitated: when no more of the woolly substance can be dissolved, the soap will be ready; and, when cool, is fit for use.—This compound has been tried in washing, and found to answer the same purposes as common soap: we therefore conceive, it might be advantageously substituted for that expensive article, in numerous families; provided the rags could be obtained in sufficient quantities, and at a reasonable price.
As various frauds are practised by the manufacturers, and especially by the retailers of soap, by adding ingredients that increase its weight, but diminish its value, we deem it our duty, to give a few hints for detecting such impositions. The liquor, generally employed for such nefarious purpose, is a strong brine made of common salt and water, which may be added to soap formed of tallow (the ingredient principally used in the manufactories of Britain), without rendering it softer, or less consistent. In order to prove this adulteration, it will be sufficient to expose a piece of the suspected soap to the air, for several days, when the water will evaporate, and the quantity thus fraudulently added, may be accurately ascertained, by the diminished weight of the soap. Several other methods have been contrived for corrupting this article, but these being neither so lucrative as that before stated, nor generally known, we are not disposed to propagate such knowledge. Hence, we shall proceed to review the principal patents that have been granted to speculators in this article; and next explain the uses to which soap may be applied.
In November, 1790, Mr. Samuel Pugh obtained a patent, for a method of preparing oils for manufacturing hard soap, either with, or without, the aid of any tallow, or other grease, at a cheaper than the usual rate. His process, however, is too complex to be understood, excepting by manufacturers: the inquisitive reader will, therefore, consult the 2d vol. of the Repertory of Arts, &c. where a diffuse specification is inserted.
In July, 1800, a patent was granted to Mr. John Crook, for a method of making soap, by means of the volatile, mineral, and vegetable alkalies, &c. His invention consists in extracting the volatile alkali from urine, either by distillation, or in its raw state; and rendering it caustic by means of unslacked lime, in the proportion of one pint to eight of raw urine. These are poured into a cask for 6 or 8 hours, when the clear liquor is drawn off, and incorporated with the common materials for making soap. The patentee likewise employs such alkaline ley, and also the raw urine, for the purpose of strengthening the ordinary soap, so as to impart to it greater clearness and solidity. He farther observes, that such urinous lixivium may be profitably applied to the cleansing of raw goods from the unctuous matter with which they are impregnated; by boiling the liquor, and causing the steam that arises from the volatile alkali in a state of vapour, to pass into close vessels, in which such goods are suspended.
Soap is one of the most valuable articles in domestic economy: its uses in various manufactures require no description. The ashes, refuse, or waste, remaining after this compound is made, furnish an excellent manure. (See vol. i. p. 27.) The suds, or water, in which soap has been dissolved, are of great service to gardeners; as they effectually destroy insects in hot-houses. (See also vol. ii. p. 496, and vol. iii. p. 232.) Farther, it appears from a patent granted, in June, 1780, to Mr. Samuel Unwin, and which is now expired; that soap-suds, after being used in scowering, washing, &c. may be rendered sufficiently strong to serve the same purposes, repeatedly, and even for the re-production of soap. He directs any quantity of the suds (when rendered useless by the foul or greasy matters they may hold in solution) to be boiled over a brisk fire; in consequence of which, a scum of grease, oil, &c. will rise to the surface. This must be saturated or dissolved, by the gradual addition of pot-ash, or similar alkaline salt; the whole being stirred, till the scum disappear. The soap-suds, thus corrected, are now to boil for two hours, when the fire must be discontinued, in order that all feculent or earthy particles may subside. The liquor will then be found sufficiently purified, and may again be employed for scowering, &c. every time repeating the process before described. In order to make soap of such rectified suds, the patentee directs any quantity to be drawn off into shallow vessels, in which it must be evaporated over the fire, till it acquire a due consistence; and, by adding the usual proportion of sea-salt, the mixture will become hard, and possess all the properties of saponaceous matter.
Soap is also of considerable utility in medicine: for this purpose, however, it is prepared without the aid of heat; the ley being filtred and concentrated by evaporation, to such a degree, that a phial capable of holding an ounce of water, will contain one ounce and 216 grains, or nearly 112 oz. of such lixivium. One part of the latter is then mixed with two parts of the oil of sweet-almonds, or of olives, in a stone vessel; the ingredients are occasionally stirred; and, in the course of a week, a firm white soap will be obtained.—This compound is reputed for its efficacy in dispelling calculi, or stones, in the human body; and, when dissolved in ale, it has with advantage been administered in the jaundice. Boerhaave always prescribed it with resinous pills; as it contributes to decompose them in the stomach. But, of late years, soap has fallen into disrepute, and is now seldom employed in medicine; though we are informed by M. Bellot, that soap-water has been given, with the happiest effects, to persons bitten by mad animals.
There are numerous vegetables, that may afford proper substitutes for soap, in its various applications to domestic uses; but, as many of these have already been pointed out; and others will occur in the subsequent pages; we refer the reader to our General Index of Reference.