2. Another method consists in heating the substances under examination with one half of their weight of hydrochloric acid for six hours on a sand-bath, avoiding boiling. The temperature is then increased until the liquid is in a state of ebullition, and 15 to 20 grammes of chlorate of potassa, for every 100 grammes of the suspected matter taken, added in successive portions, so that a quarter of an hour is required for the operation. The liquid is next filtered, and the resinous matter remaining on the filter well washed with distilled water; the washings being added to the principal solution. A strip of polished tin is then immersed in the liquid: in presence of a large amount of antimony the tin becomes covered with a black incrustation: if but a minute quantity of the metal is contained, only a few blackish spots are perceptible. After the tin has remained immersed for 24 hours, it is withdrawn and placed in a flask together with an amount of hydrochloric acid sufficient for its solution in the cold. If, after several hours, blackish particles are still observed floating in the liquid, they can be dissolved in a few drops of _aqua regia_. The solution may then be directly introduced into Marsh's apparatus. APPARATUS PROPOSED BY FLANDIN AND DANGER. [Illustration: Fig. 7.] This apparatus consists of a wide necked jar _A_ (Fig. 7) for the generation of the gas, the mouth of which is closed with a cork having two openings. The safety tube _S_, which is funnel-shaped at its upper extremity and has its lower end drawn out to a point, passes through one of these apertures; the other opening contains the small delivery tube _B_, open at both ends, and terminating in a point at its upper extremity: it is also provided with lateral openings, in order to prevent the solution being carried up to the flame. The second part of the apparatus is the condenser _C_, 0.03 metre in diameter, and 0.25 metre in length. This terminates at its lower extremity with a cone, and connects at the side with the tube _T_, slanting slightly downwards. In the interior of the condenser, the cooler _E_ is contained, the lower end of which is nearly in contact with the sides of the opening _O_. The combustion tube _D_, 0.01 metre in diameter, is connected by means of a cork with the tube _T_; it is bent at right angles, and encloses the tube _B_, in such a manner as to allow the evolved gas to burn in its interior. The dish _F_ is placed beneath the opening _O_. If the gas which burns in the combustion tube contains arsenetted hydrogen, water and arsenious acid are produced. A portion of this acid is retained in the tube _D_, the remainder is carried over, with the aqueous vapor, into _C_, where it condenses, and finally falls into the dish _F_. Both portions are subsequently examined by means of reactions necessary to establish the presence of the acid. If the ignited gas contains antimonetted hydrogen, water and an intermediate oxide of antimony are formed.