The latter compound is entirely retained in the tube _D_ separated from the greater part of the arsenious acid, if this body be present, and can be brought into solution by means of a mixture of hydrochloric and tartaric acids. A fluid is then obtained which can be introduced into Marsh's apparatus, or otherwise examined for antimony. NAQUET'S APPARATUS. [Illustration: Fig. 8.] Although the separation of arsenic from antimony is the chief object in making use of the apparatus proposed by Flandin and Danger, it is evident that this result is not fully accomplished, since a small portion of arsenious acid remains in the tube _D_ (Fig. 7), together with the intermediate oxide of antimony. The following method secures the complete separation of these metals: An amalgam of sodium and mercury is introduced into the flask _A_, (Fig. 8), which is provided with two openings. The tube _B_, terminating in a funnel at its upper extremity, passes through one of these orifices. The other aperture contains a cork enclosing the small tube _C_, which is bent at a right angle and communicates, by means of a cork, with the larger tube _D_ filled with cotton or asbestus. A set of Liebig's bulbs, _E_, containing a solution of nitrate of silver, is attached to the other extremity of this tube. The apparatus being mounted, the solution under examination is slightly acidulated and introduced by means of the tube _B_ into the flask _A_: the disengagement of gas begins immediately. If arsenic and antimony are contained in the solution, arsenetted hydrogen and antimonetted hydrogen are evolved. Both gases are decomposed in passing through the solution of nitrate of silver contained in the Liebig bulbs: the arsenetted hydrogen causes a precipitation of metallic silver, all the arsenic remaining in solution as arsenious acid; the antimonetted hydrogen is decomposed into insoluble antimonate of silver. After the operation has continued for several hours, the apparatus is taken apart, the nitrate of silver solution thrown on a filter, and the precipitate thoroughly washed. An excess of hydrochloric acid is then added to the filtrate, and the precipitate formed separated from the solution by filtration, and well washed. The wash-water is added to the solution, and the whole then examined for arsenic by means of Marsh's test.