Elements of chemistry, in two volumes / by John Murray.

  • Murray, John.
Date:
1828
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry, in two volumes / by John Murray. Source: Wellcome Collection.

    146/768 (page 134)
    OF METALS, than when the mutual action is favoured by heat. 3d, 1 he oxidation of the metal may at first be at the mini- mum, but it may pass to a higher degree, from exposure to the air, oxygen being absorbed; or a similar change may be produced from a farther decomposition of the acid in the combination, especially if heat is applied. 4th, The affinity of the metallic oxide to the acids changes as the oxidation varies, being in general strongest to protoxides, and becoming less strong as the degree of oxidation is greater: hence the peroxide of a metal may be insoluble in an acid in which the protoxide is readily soluble; hence, too, metallic solutions, from exposure to the air, and sometimes from exposure to heat, may suffer a par- tial decomposition, a portion of precipitate being thrown down ; this consists of the metal in a higher state of oxida- tion, which, from being in this state, exerts a weaker affi- nity to the acid, and hence the whole of it cannot be re- tained in solution, but a portion of it is precipitated, re- taining a little of the acid combined with it. To this al- so is it owing, that some metallic oxides in a high state of oxidation are insoluble in sulphuric or nitric acid, but are dissolved by sulphurous, nitrous, or muriatic acid ; the latter acids abstracting a portion of the oxygen of the oxide, and, in conformity to this law, allowing the more powerful affinity to be exerted. Nevertheless, though the peroxides of metals form the least stable combinations with the acids, yet they unite with larger quantities of these acids than the protoxides; and this is one reason, why peroxides are partially precipitated from their solu- tions, that a larger quantity of acid would be necessary to saturate them. Lastly, From this greater affinity of pro- toxides than of peroxides to bases, one metallic oxide may precipitate another from its combination with an acid ; the action of the one, at a low state of oxidation, being more