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.

    728/740 (page 716)
    SECT. II. OF EARTHY SOAPS. Book u. The earthy soaps differ essentially from the alkaline in their iivision ii. properties. They are insoluble in water, and incapable of being employed as detergents. They may be formed very rea- dily by mixing common soap with a solution of an earthy salt: the alkali of the soap combines with the acid of the salt, while the earth and oil unite together and form an earthy soap. Hence the reason that all waters holding an earthy salt are unfit for washing. They decompose common soap, and form an earthy soap insoluble in water. These waters are well known by the name of hard waters. Hitherto the earthy soaps have been examined by Berthollet and Chevreul only. Sp. 1. Soap of Lime. This soap may be formed by pouring lime-water into a so- lution of common soap. It is insoluble both in water and al- cohol. Carbonate of fixed alkali decomposes it by compound affinity.* It melts with difficulty, and requires a strong heat. Soap of barytes and of strontian resemble almost exactly the soap of lime. Sp. 2. Soap of Magnesia. This soap may be formed by mixing together solutions of common soap and sulphate of magnesia. It is exceedingly white. It is unctuous, dries with difficulty, and preserves its whiteness after desiccation. It is insoluble in boiling water. Alcohol and fixed oil dissolve it in considerable quantity. Water renders its solution in alcohol milky. A moderate heat melts it; a transparent mass is formed, slightly yellow, and very brittle.f Sp. S. Soap of Alumina. This soap may be formed by mixing together solutions of alum and of common soap. It is a flexible soft substance, which retains its suppleness and tenacity when dry. It is in- + Thouvencl. f Bcrthullet, Mem. Par. 1780, or Nicholson's Jour. j. 170.