Soap.2

Soap is a compound of margaric and oleic acids3 with an alkaline, or an earthy, or an oxidized metallic base. The first kind is that which is employed in medicine, and has been longest known, having been invented by the Gauls at a period antecedent to historical record. Alkaline soap is of two kinds: one made with soda, and oil either animal or vegetable, or tallow, and called hard. soap; the other made with potassa and similar oily matters, and called soft soap. For medical purposes it is essential that both kinds be made from the purest materials; and therefore the soap made in countries which produce olive oil, as the south of France, Italy, Tripoli, and Spain, is preferable to the soap of this country, which is generally manufactured from grease, tallow, and other kinds of fat. The French pharmacopoeia orders medicinal soap to be prepared with fresh oil of sweet almonds; and that the soap shall not be used until it is two months old.

1 M. A. Chevalier has ascertained that paper stained with this juice is as delicate a test of the presence of alkalies and acids as litmus paper.-Journ. de Pharm. Avril, 1820.

2 The name is derived, according to Beckmann, from the old German word Sepe.-History of Inventions, iii. 239.

3 Chevreul, whose experiments have elucidated the nature of soap more than those of any other chymist, has ascertained that fixed oils and tallow consist of two substances; one solid, which he has named stearin, and the other fluid, which he has named elain. These are altered by salifiable bases, and converted in the above-named acids; vide Ann. de Chimie et de Phys.

1. Hard Soap.

Officinal. Sapo durus, Lond. Sapo durus; ex soda confectus, Edin. Sapo durus, Dub. Hard Soap. Spanish Soap.

Syn. Savon blanc (F.), Spanischc seife (G.), Spaansche zeep (Dutch), Sil-kestwal (Dan.), Sapone duro (I.), Xabon (S.), Nat Sowcarum (Tarn.), Saboon (Duk.).

Hard soap is manufactured in Spain in the following manner:-To five parts of barilla, coarsely ground to powder, one part of quicklime, rendered fluid with a small portion of water, is added; and after some time the clear liquor, which is a strong solution of caustic soda, is drawn off, and called the first ley; with the residue more water is then mixed, and drawn off after some time, and called the second ley; and a third ley is procured by another portion of water treated in a similar manner. This last ley is then mixed with a quantity of olive oil equal in weight to the barilla employed, and the mixture boiled in an iron vessel, the second ley and a portion of the first being added in a gradual manner during the boiling. The boiling mixture is constantly stirred with a wooden pole; and when it becomes tolerably thick, a small portion of common salt is added, and the boiling continued for half an hour. The fire is then damped, and after some hours the clear liquor, which has separated, is drawn off, and the half-made soap again boiled with a little fresh water and the residue of the first ley.

After the separation of the fluid of this boiling, it is again heated with a little water, and then poured into wooden vessels called frames, where it cools, and in a few days acquires a sufficient degree of hardness. Three parts of oil and three parts of soda produce five parts of firm soap.1 Castile soap is made in the same manner, except that the marbled appearance which it presents is produced by the addition of sulphate of iron to a part of the alkaline ley, after the soap is fully boiled, which gives the blue colour; and the stirring in red oxide of iron, when the soap is almost made, gives the red colour.

Qualities. - Well-made hard soap, fit for medical use, has very little odour, and a nauseous, alkalescent taste; is white, and of a firm consistence; does not feel greasy, and is devoid of any saline efflorescence on the surface. With water it forms a milky, opaque solution; and with alcohol a nearly

1 Annales de Chimie, xix. 253. T T 4 transparent, somewhat gelatinous solution.1 It is decomposed by all the acids and acidulous salts; by alum, the hydrochlorate and the sulphate of lime, and sulphate of magnesia; in fact, by all the earths and most of the metallic salts: thence hard water, which contains sulphate of lime, does not properly dissolve soap. Nitrate of silver; ammoniated copper; tincture of chloride of iron; ammoniated iron; acetate, chloride, and bichloride of mercury; acetate of lead; tartarized iron; tartar emetic; sulphate of zinc, of copper, and of iron; and all astringent vegetable solutions, decompose it. According to the experiments of Darcet, Lelievre, and Pelletier, 100 parts of newly-made soap consist of 60.94 oil, 8.56 alkali, and 30.50 water: but these proportions vary in different kinds of soap; part of the water is lost by keeping, and the soap becomes lighter.

2. Soft Soap.

Officinal, Sapo mollis, Lond. Edin. Dub, Soft Soap. Syn. Savon Mou (F.), Sapone Molle (I.).

This soap is prepared in the same manner as the former; a caustic ley of potassa, however, being used instead of the soda ley. It was this variety of soap which was originally made by the Gauls and Germans, who employed wood ashes to afford their ley; and these are still used in many places.

Qualities.- Soft soap differs from hard soap chiefly in its consistence, which is never greater than that of hog's lard.

Both soft and hard soap are often adulterated either with an excess of water, or with lime, or gypsum, or pipe clay. The first may be detected by the extent of the loss of weight in drying the soap; the other adulterations by alcohol, which dissolves the soap and leaves them.

Medical properties and uses, - Soap is regarded as purgative and lithontriptic; externally applied, it is stimulant and detergent. For internal use, the hard soap only is employed. It is occasionally ordered in habitual costiveness, and in jaundice, combined with rhubarb, or some bitter extract; but its power as a purgative is very limited, and it cannot act in any other way in relieving jaundice. It is more useful in calculous habits, in which, however, its action is altogether confined to the stomach; for, as soap is decomposed by the weakest acids, its alkaline base corrects the acidity so prevalent in the stomachs of calculous patients, and thus, at least, assists in checking the increase of the disease. Soap is also beneficial in decomposing some metallic poisons when taken into the stomach; and, as it is the antidote which can most readily be procured, should always be early resorted to. It is necessary, in this latter case, to give it in solution; of which a tea-cupful should be drunk at short intervals, till the effects expected from it be produced. In other cases it is preferable to give it in substance.

As an external remedy, soap is efficaciously used in frictions to sprains and bruises; and we have seen much benefit derived from rubbing the tumid bellies of children labouring under mesenteric fever with a strong lather of soap every morning and evening. The dose internally is from grs. iij. to 3ss. made into pills.

1 The alcoholic solution of soap is a convenient test for discovering earthy salts in mineral waters.

Officinal preparations.-Pilules Saponis composiae, L. D. Pil Scillae comp., L. D. Pil Aloet, E. Pil Aloes et Assafoetidae, E. D. Pil Colocynih. comp., D. Emplastrum Saponis, L. E. D. Ceratum Saponis, L. Linimentum Saponis comp., L. Linimentum Saponis cum Opio, E. D.