muriatic acid gas, and may be collected in proper vessels. The arseniac
acid is entirely freed from the other acids employed during the process
by heating it in a crucible till it begins to grow red; what remains is
pure concrete arseniac acid.
Mr Scheele's process, which was repeated with great success by Mr
Morveau, in the laboratory at Dijon, is as follows: Distil muriatic acid
from the black oxyd of manganese, this converts it into oxygenated
muriatic acid, by carrying off the oxygen from the manganese, receive
this in a recipient containing white oxyd of arsenic, covered by a
little distilled water; the arsenic decomposes the oxygenated muriatic
acid, by carrying off its supersaturation of oxygen, the arsenic is
converted into arseniac acid, and the oxygenated muriatic acid is
brought back to the state of common muriatic acid. The two acids are
separated by distillation, with a gentle heat increased towards the end
of the operation, the muriatic acid passes over, and the arseniac acid
remains behind in a white concrete form.
The arseniac acid is considerably less volatile than white oxyd of
arsenic; it often contains white oxyd of arsenic in solution, owing to
its not being sufficiently oxygenated; this is prevented by continuing
to add nitrous acid, as in the former process, till no more nitrous gas
is produced. From all these observations I would give the following
definition of arseniac acid. It is a white concrete metallic acid,
formed by the combination of arsenic with oxygen, fixed in a red heat,
soluble in water, and capable of combining with many of the salifiable
bases.
SECT. XXIV.--_Observations upon Molybdic Acid, and its Combinations with
Acidifiable Bases[43]._
Molybdena is a particular metallic body, capable of being oxygenated, so
far as to become a true concrete acid[44]. For this purpose, one part
ore of molybdena, which is a natural sulphuret of that metal, is put
into a retort, with five or six parts nitric acid, diluted with a
quarter of its weight of water, and heat is applied to the retort; the
oxygen of the nitric acid acts both upon the molybdena and the sulphur,
converting the one into molybdic, and the other into sulphuric acid;
pour on fresh quantities of nitric acid so long as any red fumes of
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