Volume 2

A system of chemistry / by Thomas Thomson.

  • Thomson, Thomas, 1773-1852.
Date:
1820
Catalogue details

Licence: Public Domain Mark

Credit: A system of chemistry / by Thomas Thomson. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    727/740 (page 715)
    formation of soap w as potash; hence we see the reason that it ciap. iv. is described by the Romans as an unguent. The oil employed v for making soft soap in this country is whale oil. A little tallow is also added, which, by peculiar management, is dis- persed through the soap in fine white spots. Some persons have affirmed that they knew a method of making hard soap with potash. Their method is this: after forming the soap in the manner above described, they add to it a large quantity of common salt, boil it for some time, and the soap becomes solid when cooled in the usual way. That this method may be practised with success has been as- certained by Messrs. Darcet, Lejicvre, and Pelletier: but then the hard soap thus formed does not contain potash but soda; for when the common salt is added, the potash of the soap decomposes it, and combines with its muriatic acid, while at the same time the soda of the salt combines with the oil, and forms hard soap : and the muriate of potash formed by this double decomposition is dissolved in water, and drawn olF along with it.* Sp. 3. Soap of Ammonia. This soap was first particularly attended to by Mr. Berthol- let. It may be formed by pouring carbonate of ammonia on soap of lime. A double decomposition takes place, and the soap of ammonia swims upon the surface of the liquor in the form of an oil; or it may be formed with still greater ease by pouring a solution of muriate of ammonia into common soap dissolved in water. It has a more pungent taste than common soap. Water dissolves a very small quantity of it; but it is easily dissolved in alcohol. When exposed to the air, it is gradually decom- posed. The substance called volatile liniment, which is em- ployed as an external application in rheumatisms, colds, &,c. may be considered as scarcely any thing else than this soap. All the alkaline soaps agree in the properties of solubility in water and alcohol, and in being powerful detergents. * Ann. cle C'liim. x\x. 32'2.