Volume 2

The elements of experimental chemistry / by William Henry.

  • Henry, William, 1774-1836.
Date:
1815
Catalogue details

Licence: Public Domain Mark

Credit: The elements of experimental chemistry / by William Henry. Source: Wellcome Collection.

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

    173/586 (page 155)
    S. The composition of thewhite oxide of arsenic, or arsenous acid, has been investigated by several chemists, with the fol- bwing results. It consists, Arsenic. Oxygen. Arsenic, Oxygen. Accordino- to Proust, of.. .75.2 . .24.8 100 . .32.979 Thenard, of 100..34.69* . Berzelius, of 74.48 . .25.52 ,.. .100 . .34.263 Do.corrected 69.63 . .30.37 100 . .43.616 , Thomson, of 100..34.930 It has been justly observed, however, by Dr. Thomson *, that the result, which Berzelius considers as the most correct, is probably the least so; not only on account of its want of accordance with other determinations, but on account of the comphcated process, by which it was obtained. On the whole, it appears probable, that 100 parts of arsenic, to be- come the white oxide, combine with between 34 and 35 parts of oxygen. 4, Oxide of arsenic combines with the pure alkalis to saturation; and hence it fulfils one of the principal functions of an acid. It has therefore been called arsenous acid, and its compounds arsenites. They may be formed by simply boiling the arsenous acid with the respective bases and a sufficient quantity of water ,• or by double decomposition. Thus arsenite of lead may be prepared, by mixing the solu- tions of nitrate of lead and arsenite of potash; and the fine green pigment, called ScheeWs green, by mixing the solu- tions of arsenite of potash and sulphate of copper. 5. The arsenous acid, or rather the arsenic which it con- tains, by distillation with sulphur, affords either a yellow substance, called orpiment, or a red one, termed realgar. The oxygen, uniting with sulphur, escapes in the form of sulphurous acid. Both these compounds are sulphurets of arsenic, varying in the proportion of their components. Orpiment contains three parts of sulphur and four of arse- nic ; and realgar one part of sulphur and three of arsenic. Hence realgar, by fusion with an additional quantity of * Annals, iv. 171.