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ELEMENTS OF MATERIA MEDICA.

of mercury, may be readily recognised. Sulphuretted hydrogen pro-duces, with mercurial solutions, a black precipitate.

Solutions of the protosalts of mercury yield, with caustic potash orsoda, a grey or black precipitate; and, with iodide of potassium, agreenish or yellow precipitate.

Solutions of the persalts yield, with caustic potash or soda, a yellowor reddish precipitate; and, with iodide of potassium, a scarlet one.

Purity. —-The purity of this metal is ascertained by its brilliancy andgreat mobility. Mechanical impurities—such as adhering dirt or dust—are instantly detected, and may be separated by straining through flannel,or by filtering through a small hole in the apex of an inverted cone ofpaper. The presence of lead, tin, zinc, or bismuth, may be suspected bythe rapidity with which the metal tarnishes in the air, and by its smallparts tailing, instead of preserving a spherical form. These impuritiesmay be got rid of by distillation in an earthen retort.

Physiological Effects. 1. Of Metallic Mf.rcury. (a.) Onvegetables. —Mercurial vapours are fatal to plants (Decandolle, Phys. Veg.1332).

(/;.) On animals. —From the experiments of Moulin {Phil. Trans, for1691, No. 192), Haighton (Beddoes , On Pulmonary Consumption, 1799),Viborg (quoted by Wibmer, Wirkung d. Arzneim, iii. 88), and Gaspard(Magendie, Journ. de Physiol, i.), it appears that when injected into theveins, mercury collects in the small vessels of the neighbouring organs,and acts as a mechanical irritant. Thus, if thrown into the jugular vein,peripneumonia is excited; and, on examination after death, littleabscesses and tubercles have been found in the lungs, in each of whichwas a globule of quicksilver as the nucleus.

(c.) On man. — Some difference of opinion exists as to the effects ofliquid mercury when swallowed; one party asserting that it is poisonous,another that is innocuous. The truth I believe to be this : so long as itretains the metallic state it is inert; but it sometimes combines withoxygen in the alimentary canal, and in this way acquires activity.Avicenna, Fallopius, and Brasavola , declared it harmless; Sue {Mem.de la Facult. Med. d’Emulat. 4th year, p. 252) states that a patient tookfor a long time two pounds daily without injury; and I could refer to theexperience of many others who have seen it employed in obstructions ofthe bowels, without proving noxious ; but the fact is so generally knownand admitted, as to require no further notice. In some instances, how-ever, it has acted powerfully, more especially where it has been retainedin the bowels for a considerable time ; no doubt from becoming oxidized.Thus Zwinger {Miscell. Curiosa Decur. 2 nd \ Ann. 6, 1688) states thatfour ounces brought on profuse salivation four days after swallowing it.Laborde {Journ. de Med. i. 3) also tells us, that a man who retainedseven ounces in his body for fourteen days, was attacked with profusesalivation, ulceration of the mouth, and paralysis of the extremities; andother cases of a similar kind might be quoted.

Dr. Christison considers the question set at rest by the Berlin Collegeof Physicians, and that the metal is innocuous.

Applied externally, liquid mercury has sometimes produced bad effects.Dr. Scheel has related a fatal case, attended with salivation, brought onfrom wearing at the breast during six years a leathern bag, containing a