Fig. 35.—Photo-micrograph of globules of
mercury obtained by Reinsch‘s process, × 50.
(R. J. M. Buchanan.)
A.—If the contents of the stomach are under examination, they should be diluted with distilled water, filtered, and the residue pressed and reserved for further examination.
The liquid thus obtained may be concentrated, and, while still warm, slightly acidified with hydrochloric acid. A slip of zinc foil, with a piece of gold foil twisted round it, is then introduced. If mercury be present, the gold will, sooner or later, lose its yellow colour, and its surface become white and silvery, while the zinc is wholly or partially dissolved. The gold being removed, separated from the zinc, washed first with water and then with ether, is divided into two equal parts. One half may be heated in a reduction tube, when it will yield a sublimate of metallic mercury, identified by the spherical form of the globules under a magnifying-glass, and their metallic reflection and complete opacity. The other half of the gold may be treated with nitric acid and heated, which will dissolve off the mercury. The resulting solution, after expelling the excess of acid by evaporation, will give a scarlet precipitate with iodide of potassium soluble in excess; and, with protochloride of tin, a black precipitate of metallic mercury.
B.—For the detection of mercury in the insoluble form, the residue from A is dried; or, if the tissues are under examination, they should be finely divided, and freed from superfluous moisture. In either case, the substance is boiled in moderately strong nitric or hydrochloric acid (about one part of acid to four of water). After digestion for some time, the liquid is filtered, concentrated, and tested as in A. When there is reason to infer the presence of corrosive sublimate in considerable quantity in an organic liquid, advantage may be taken of the solubility of the salt in ether, and the power possessed by this liquid of abstracting it from its aqueous solutions. The liquid is agitated with an equal volume of ether, the ethereal solution poured off and allowed to spontaneously evaporate, when the corrosive sublimate will be left in white silky prisms, yielding all the characteristic reactions of the salt. In obscure cases of salivation, the saliva should be examined as follows: Take about two drachms of the saliva, acidulate with pure hydrochloric acid, and immerse in the mixture a very small piece of copper gauze attached to a platinum wire, and set aside in a warm place for some hours. If mercury be present, the copper will be covered with a white coating; this should be washed and heated in a reduction tube, when globules of mercury will be formed, and examined with a lens.
C.—Mercury in solution may be detected by Reinsch‘s process. On boiling with pure copper foil after acidifying the solution with hydrochloric acid, the mercury is deposited on the copper in the metallic state, as a whitish silvery film, which can be polished to a silvery mirror surface. On washing the film in water, ether, and absolute alcohol and allowing it to dry, then subliming it in a reduction tube by the aid of heat, the mercury deposits on the cool part of the tube in the form of minute globules, which may be easily recognised through the microscope. If a small crystal of iodine be now placed in the tube and gently warmed so as to volatilise it, but not the mercury, and the tube be left to stand for a short time, the iodine combines with the mercury to form the scarlet iodide, the colour of which renders it easy of recognition.
According to Bonnewyn, the presence of an extremely small quantity of corrosive sublimate (¹/₅₀₀₀₀) in calomel may be detected by immersing a clean knife blade, moistened with alcohol or ether, in the suspected calomel. A black spot is formed on the steel very difficult of removal. No spot is formed when the calomel is pure.
LEAD
Metallic lead is not poisonous; but it appears probable that when it is acted upon by the acids of the intestinal secretions, it may become so changed as to produce unpleasant symptoms. Any salt of lead is poisonous when in a condition to be absorbed into the system.
Sugar of lead and white lead are alone important, and will therefore be briefly considered.
Sugar of Lead