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.

    136/768 (page 124)
    grees of facility. Some, as arsenic and manganese, suffer it with facility at common temperatures; others, as lead and copper, slowly, and not without the presence and ope- ration of moisture. In general, it is necessary to raise the temperature considerably ; and to many of them it is necessary to apply very intense heats. Some are oxidated at the temperature at which they melt; others, even when in perfect fusion, undergo no change; some are oxidated when the heat is raised sufficiently high to convert them into vapour; and others, as gold or platina, resist oxida- tion at either temperature, and cs>n scarcely be made to undergo it from the action ot oxygen in its elastic form. The application of heat, in promoting metallic oxidation, is to be explained on the same principles as its agency in favouring in general chemical combination. It acts by lessening the cohesion of the metal, which is an obstacle to the combination : this is counteracted, however, to a certain extent, by its necessarily augmenting the elasticity of the oxygen gas; and hence, where the mutual affinity^ between the metal and the oxygen is weak, the combina- tion is not affected. The phenomena which accompany the combination of a metal with oxygen are various. In general, it takes place slowly, and hence there is scarcely any sensible evo- lution of light, and no such extrication of caloric as to enable the combination to proceed independent of the continued application of heat. In some, however, the oxidation is so rapid as to give rise to the phenomena of combustion : thus zinc and iron burn vividly at a tem- perature a little higher than that of ignition ; copper, tin, and arsenic, burn at the same temperature, with a more feeble flame; and at more intense heats, nearly all the metals suffer combustion. The substances formed by the combination o'f oxygen