A manual of elementary chemistry : theoretical and practical / by George Fownes.

  • Fownes, George, 1815-1849.
Date:
1873
Catalogue details

Licence: Public Domain Mark

Credit: A manual of elementary chemistry : theoretical and practical / by George Fownes. Source: Wellcome Collection.

    982/1062 (page 954)
    duced by the decomposition of albuminous and gelatinous sub- stances (pp. 955, 970). On heating a solution of carmine in strong sulphuric acid to 140°-150°, and then pouring it into cold water, a brown pre- cipitate is formed, consisting essentially of ricfiococcin, C10H12O8, which appears to be a derivative of dimethyl-anthracene having the composition C14H2(CH3)2(OH)4(02)''. It is insoluble in water, but dissolves in alcohol with fine yellow fluorescence.* Madder.—The root of the Ruhia tinctorum, cultivated in southern France, the Levant, &c, is the most permanent and valuable of the red dye-stuffs. In addition to several yellow colour- ing matters, which are of little importance for the purposes of the dyer, madder contains two red pigments, which are called alizarin and purpurin. These substances have been the subject of very extensive researches by Debus, Higgins, Schunck, Wolff, Strecher, Graebe, Liebermann, and Perkin. Alizarin, C14Hs04.—The aqueous decoction of madder is pre- cipitated by sulphuric acid, and the precipitate washed and boiled with aluminum chloride, which dissolves the red pigments, an insoluble brownish residue remaining behind. The solution, when mixed with hydrochloric acid, yields a precipitate consisting chiefly of alizarin—still, however, contaminated with piu-purin. The impure alizarin thus obtained may be further purified by again throwing down the alcoholic solution with aluminum hydrate, and boiling the precipitate with a concentrated solution of soda, which leaves a pure compound of alumina and alizarin behind. From this the alizarin is separated by hydrochloric acid and recrystallised from alcohol. Pure alizarin crystallises in splendid red prisms, which may be sublimed. It is but slightly soluble in water and in alcohol, but dissolves in concentrated sulphuric acid with a deep red colour. On addition of water, the colouring matter is reprecipitated unchanged. It is also soluble in alkaline liquids, to which it imparts a magnificent purple colour. It is insoluble in cold solution of alum. Alizarin is the chief colouring matter of madder : it is a feeble acid; a few of its compounds with mineral oxides have been prepared. The action of nitric acid upon alizarin gives rise to the formation of oxalic acid and phthalie acid (p. 825): CuH804 + 2H20 + O10 = 3C2H204 + C8H0O4 Alizarin. Phthalie acid. Alizarin, heated with zinc-dust (a. mixture of metallic zinc, oxide, and hydrate) is converted into anthracene: * Liebermann and Van Dorp, Journal of the Chemical Society [2], ix. 912 ; x. 706. , ■<