limate to a solution of ammonia in exaess, a compound, which, from its physical characters; is termed white precipitate, is thrown down, which is generally supposed to be a compound) of chloride with amide of mercuiy, HgCltigNII, Kane). Chloride of mercury. coagu lates albumen, and combines with the albuminous tissues generally, forming sparingly soluble compounds. IIence, in cases of .poisoning, with the salt, the white Of raw egg,s‘ is the best antidote; and for the same reason corrosive sublimate is a powerful antiseptic, and is employed to preserve anatomical preparations.
Amongst the most important tests for this substance, which is not unfrequently used as a poison, may be mentioned-1. Iodide of potassium, which, when added to a crystal or to a watery solution of chloride of mercury, gives rise to the formation of a bnglit searlet iodide of mercury. 2. The galvanic test, which may be applied in various ways, of which the simplest is the "guinea and key test," devised by Wollaston. He placed a. drop of the fluid suspected to contain corrosive sublimate on a guinea, and sirnultane ously touched it and the surface of the guinea with an iron key; metallic inercmy was. deposited on the gold in a bright silvery stain. 3. Precipitation on copper, and reduc tion. To apply this test, we acidulate the suspected fluid with a, few drops of hydro chloric acid, and introduce a little fine copper gauze, which soon becomes coated with mercury. On heating the gauze in a reduction tube, the mercury is obtained in well defined globules.
With iodine and bromine, mercury forms two iodides and bromides, corresponding in composit ion to the chlorides. Both the iodides are used in medicine; the bromides are of no practical importance. The subiodid,e (llg,I) is a green powder formed by triturating 5 parts of iodine with 8 of mercury, and is of far less interest than the zodicle (lIgI), which is most simply obtained by precipitating a solution of corrosive subliniate by a solution of iodide of potassium. The precipitate is at first salmon-colored, but soon.
changes into a brilliant scarlet crystalline deposit.
Sulphur torms two compounds with mercury—viz., a subsulphide (11g2S), a black powder of little importance, and a sulphide (ElgS), which occurs naturally as cinnabar (q.v.). Sulphide of mercury is thrown down as a black precipitate by passing sulphur eted hydrogen through a solution of a persalt of inercury (corrosive subliniate, for exainple). When dried and sublimed in vessels from which the air is excluded, it assumes its ordinary red color. The well-known pignient vermilion, is sulphide of mer cury, and is sometimes obtained from pure cinnabar, but is more frequently- an artificial product.
Mercury unites with most metals to form amalgams (q.v.), several of which are employed in the arts.
Of the numerous org,anic compounds of mercury, it is unnecessary to mention more than the fulminate (described in the article FIILMINIC ACID (q.v.), and the cyanide (IlgCy), which may be prepared by dissolving the red oxide of mercury in hydrocyanic acid, and is the best source from which to obtain cyanogen.
The uses of mercury are so numerous that a very- brief allusion to the most important of these must suffice. It is employed extensively in the extraction of gold and silver from their ores by the process of amalgamation. Its amalgams are largely employed in the processes of silveriiim and gilding, and some (as those of copper and cadmium) are employed by the dentistfor stopping teeth. It is indispensable in the construction of philosophical instruments, and in the laboratory in the form of the mercurial bath, etc, It is the source of the valuable pigment vermilion. The use of its chloride in anatomical. preparations has been already noticed; it is similarly found that wood, cordage, and. canvas, if soaked in a solution of this salt (1 part to 60 or 80 of water), are better able to resist decay when exposed to the combined destructive influence of air and moisture. The uses of mercury and its preparations in medicine are noticed in a separate article.