_Process for Organic Mixtures._—If sulphuret of arsenic be present in such mixtures in appreciable quantity, the particles, owing to their intense yellow colour, will be visible in any mass which has not the same tint. From this state of admixture they may be removed by adding caustic ammonia which dissolves sulphuret of arsenic; and the solution, on being acidulated with muriatic acid, will deposit the sulphuret sufficiently pure for undergoing the process of reduction. Sulphuret of arsenic sometimes exists in small quantity in the stomach, although the poison was given in the form of oxide; for a portion of the oxide is subject to be converted into the sulphuret by hydrosulphuric acid gas evolved in the stomach after death.[564] In every instance of the kind yet carefully examined a large proportion of the oxide has remained unacted on, although the intense colour of the mixed sulphuret makes it appear as if that were the only compound present. 7. _Arseniuretted-Hydrogen._ This compound presents the form of a colourless gas, possessing a fetid garlicky odour, a density of nearly 2·7, and great virulence as a poison. It is mentioned here, because accidental poisoning with it has happened occasionally within a few years, chiefly owing to the occasional adulteration of sulphuric acid with arsenic, and the liability of the arsenic to form arseniuretted-hydrogen when such sulphuric acid is used to prepare hydrogen gas. Dr. O’Reilly has mentioned a melancholy instance of a young chemist losing his life in this way.[565] Dr. Schlinder of Greifenberg has related another, which did not prove fatal.[566] And it is well known that the German chemist Gehlen lost his life by accidentally breathing arseniuretted-hydrogen while engaged in examining its chemical properties.[567] It is an inflammable body; and its presence in any other gas is easily detected by burning it according to the method of Marsh. SECTION II.—_Of the Action of Arsenic and the Symptoms it excites in Man._ It is now generally admitted that arsenic produces in the living body two classes of phenomena,—or that, like the narcotico-acrids, it has a twofold action. One action is purely irritant, by virtue of which it induces inflammation in the alimentary canal and elsewhere. The other, although it seldom occasions symptoms of narcotism properly so called, yet obviously consists in a disorder of parts or organs remote from the seat of its application.