Apparatus Proposed by Flandin and Danger
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.
The substitution of a large balloon, having a capacity of about 2 litres, in place of the small vessel of Flandin and Danger’s apparatus, is to be recommended as doing away with the necessity of evaporation; an operation which invariably causes a loss of substance. The apparatus, modified in this manner, is the most delicate in use for the detection of mercury.