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ELEMENTS OF MATERIA MEDICA.

—another, marbled or mottled. The soap sold in the shops as Castilesoap (sapo castiliensis) is of the latter kind : “ the marbled appearancewhich it presents is produced by the addition of sulphate of iron to apart of the alkaline ley, after the soap is fully boiled, which gives theblue colour; and the stirring in red oxide of iron, when the soap isalmost made, gives the red colour.” (Thomson’s London Dispensatory.)The marbling, or mottling, therefore, is an impurity.

(6.) Almond oil soda soap (sapo amygdalinus. Fr. Codex.)—This isthe medicinal soap ( savon medicinal) of the French ; directions for pre-paring which are contained in the French Codex .

(c.) Animal oil soda soap (sapo sebaceus, G eiger: sapo vulgaris, UnitedStates Ph.)-—Of this two kinds are in common use in this country. Thebest is that called white curd soap, and which is prepared from pure orwhite tallow and soda: when scented it constitutes Windsor soap. Thecommon or domestic soap, usually termed mottled soap, is made withrefuse kitchen grease (commonly called kitchen stuff.)

(d.) Resin soda soap. —This is the common yellow soap of the shops,and is the commonest of the hard soaps of this country. It owes its pecu-liar properties to the admixture of resin and palm oil with animal fat.

Besides the above, there are many other varieties of hard soap, termedfancy soaps, sold by perfumers. The patent silica soap consists of theusual kinds of soaps to which precipitated silica is added.

2. Of Potash Soap, (sapo potassicus: s. kalinus: s. mollis: s. liqui-dus, Pliny ?)—This kind of soap is made with caustic potash instead ofcaustic soda.

(«.) Olive oil potash soap (sapo mollis, — sapo, ex olivce oleo et potassu,confectus, Ph. L.)—No soap of this kind is made or known in London .I am informed by Messrs. Rowe, of Brentford (the most extensive ma-nufacturers of soap in the neighbourhood of the metropolis), that they areunacquainted with it. On inquiry I find that a white soft soap, made byMr. Taylor, 13, Newington Causeway, is used at Apothecaries’ Hall, inthe preparation of Ung. Sulph. Co. Ph. L.; but I have been unable to pro-cure a sample of it. Mr. Taylor tells me it is only made to order, asthere is very little demand for it, the principal consumption being atApothecaries’ Hall. He also informed me, that it w r as made from threefatty substances (olive oil, tallow', and some other oil), and two alkalies(potash and soda)—that it is white,'and has the consistence of butter, butby keeping becomes harder.

(b.) Animal oil potash soap. —This is the common soft soap of the shops,and which is made with fish oil (whale or cod), tallow and potash. (Forparticulars respecting its manufacture consult Ure’s Diet, of Chem., art.soap.)

Theory of Saponification.— Soaps are to be regarded as alkalinesalts, formed by the action of alkaline bases on fatty or resinous bodies.At one time it was supposed that they were mere compounds of fat orresin and of alkali; but it is now know r n that in the process of saponifi-cation, the organic constituents (stearine, margarine, and olein) of vegeta-ble and animal fats undergo certain chemical changes by which acids(stearic, margaric, and oleic) are produced, w'hich, combining with thebases, form the salts (stearates, margarates, and oleates) commonlytermed soaps; and at the same time a sweet substance (glycerine) is gene-rated. Thus it appears that, by the influence of an alkali, one equiva-