There are two Sulphurets of Arsenic: the yellow variety known in
commerce under the name of _Orpiment_, and the red sulphuret, termed
_Realgar_. The bodies, as they occur _native_, do not appear to be
endowed with the virulent powers which distinguish the other compounds
of arsenic. _M. Renault_[264] gave as much as two drachms of the native
orpiment to dogs of different sizes, from which they experienced no
inconvenience. _Hoffman_[265] also offers his testimony of the inertness
of this substance. The same observations apply to the _Realgar_. It is
not a little singular that while these native sulphurets of arsenic
should be so harmless, those which are produced by artificial fusions,
are extremely virulent in very small doses. _M. Renault_ supposed that
this remarkable difference of effect was owing to the arsenic being
oxidized in the latter compound, and in its metallic state in the
former. This explanation, however, is not considered as satisfactory by
_M. Orfila_, who states that it does not embrace all the varieties of
the case, for that the _sulphuret_, which is artificially obtained by
pouring the arsenious acid into a solution of sulphuretted hydrogen, is
as inert as the native compounds; besides which, chemical analysis has
proved that there is no oxygen in any of these _sulphurets_, and that
they only differ from one another, by a greater or less proportion of
their two ingredients. This apparent anomaly induced _M. Orfila_ to
institute a series of experiments for its investigation, but the results
which he has obtained are too unsatisfactory to enable him to decide the
question.
The presence of an _Arsenical Sulphuret_ is to be sought for by
calcination with caustic potass, in a small glass tube. The sulphuret is
decomposed in a few seconds, yielding its sulphur to the potass, while
its metallic element is volatilized with the usual phenomena.