arseniate, mixed with black flux, will, like white arsenic, furnish a metallic sublimate, when heated in a glass tube. THE SULPHURETS OF ARSENIC. 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. MERCURY. Mercury, or Quicksilver[266], was known in the earliest ages. Its external characters are too familiar to require any particular description in this place. Its specific gravity is 13·568.[267] In its metallic state it exerts no action on the living system, except that which may depend upon its mechanical properties, although a different opinion has been entertained, (see _Pharmacologia_, art. Hydrargyrum.) Several of the combinations of this metal are, however, highly destructive in small doses, and are consequently objects of forensic interest. CORROSIVE SUBLIMATE. _Oxy-muriate of Mercury. Bi-chloride of Mercury._