But the _Arsenious acid_ may perchance be so mixed with various foreign matter as to render its separation by filtration difficult; in such a case, after having boiled it in distilled water, in order to procure all the soluble matter from it, the residual mass may be evaporated to dryness, care being taken that the heat applied for such a purpose never exceeds 250° _Fah._ or we shall lose the arsenic, should any be present, by volatilization. The residue thus obtained may then be submitted to a higher temperature in a subliming vessel, in order to procure the arsenious acid in its pure state. This process applies particularly to the examination of the matter vomited, or the feculent evacuations passed, by the patient. Should the arsenious acid have, in the first instance, been dissolved in oil, _Dr. Ure_ proposes to boil the solution in distilled water, and to separate the oil afterwards by the capillary action of wick threads. If the arsenious acid be mixed with resinous bodies, _Oil of Turpentine_ may be employed as their solvent, which will leave the arsenic untouched. _Dr. Black_ directed the application of alcohol for this purpose, but this is obviously improper, since arsenious acid is soluble in that fluid. If the physician be called upon to investigate the contents of the alimentary canal after death, and the arsenious acid cannot be discovered amongst the suspected matter, the stomach itself must be cut into small pieces, and in compliance with the directions of _Orfila_, boiled in ten or twelve times their weight of distilled water, which should be renewed as fast as a portion of it flies off in vapour; this liquor should be cooled and decanted, in order to put a few drops of it into the solutions of the different re-agents which we have before described. If the precipitates should indicate the presence of arsenic, we may proceed according to the directions we have already laid down; if, on the other hand, the fluid offers no indication of poison, the mass exhausted by water should be treated, according to the process suggested by _Rose_, by boiling it for some time in a solution of potass, by which means the stomach will be partly decomposed and dissolved, and the arsenious acid, with which it might have been combined, saturated by the alkali. In this state the liquor is to be filtered, again boiled, and nitric acid added, little by little, until it passes from a dark to a clear yellow colour. The object of the acid in this stage of the process being to decompose and destroy the animal matter. The excess of acid should be saturated with potass, when an _Arsenite of Potass_ will be formed, if there really existed any arsenious acid in the stomach. This _M. Orfila_ recommends us to precipitate by the _Hydro-sulphuret of Ammonia_, and a few drops of nitric acid; (_Rose_ prefers _lime water_ for the same purpose); a yellow _sulphuret of Arsenic_ will be the result, from which the whole