When Smithson's pile is employed, the organic substances are most advantageously decomposed by means of chlorine. It is advisable to operate with as small a quantity of fluid as possible, for, owing to the volatility of bichloride of mercury, a portion of this salt may be lost by the evaporation of aqueous, alcoholic, and even etherial solutions, and the detection of minute quantities rendered impossible. APPARATUS PROPOSED BY FLANDIN AND DANGER. [Illustration: Fig. 9.] This apparatus consists of a stand _S_, (Fig. 9) supporting a balloon _A_, which serves as the reservoir of the suspected solution, and a funnel _B_, into which the neck of the balloon is dipped. The funnel _B_ is bent at a right angle and is drawn out at its lower end under which the dish _C_ is placed for the reception of the escaping fluids. A fine wire of pure gold, forming the negative electrode of a Bunsen's battery, passes through the lower extremity of the funnel. The end of this wire nearly comes in contact with a second wire, inserted in the upper part of the funnel, and connected with the positive pole of the battery. If the balloon filled with the solution is inverted and immersed in the funnel _B_, its neck will be submerged at first; soon, however, it becomes uncovered, owing to the depression of the level of the fluid caused by the escape of the latter through the tapering extremity of the funnel: a bubble of air then passes in the balloon and expels a drop of the solution. This process is repeated at short intervals, causing a continuous flow of the fluid, the rapidity of which is easily regulated by elevating or lowering the balloon, thus raising or depressing the level of the liquid. The apparatus having been mounted in this manner and the battery set in action, the disengagement of gas commences. Should mercury be contained in the solution under examination, this metal will be deposited upon the negative wire. When the operation is completed this wire is detached from the apparatus, washed with ether, and dried. It is then introduced into a small tube provided with a bulb, and the mercury volatilized by means of the blow pipe flame: the metal condenses in the bulb of the tube in globules which are readily recognized. They can also be dissolved in nitric acid, and the presence of a mercurial salt in the solution confirmed by further tests. The solution to be examined in the preceding apparatus, is prepared as follows: The suspected organic matter is treated with cold sulphuric acid of 66° _B._ until liquefied, and hypochlorite of lime, and distilled water then added: if necessary, the evolution of chlorine can be accelerated by a further addition of sulphuric acid. As soon as the liquid becomes clear, it is filtered, concentrated and examined as described above. The solution contains the mercury in the state of bichloride, a salt soluble in water and well adapted to the above test.