484

ELEMENTS OF MATERIA MF.DICA.

obstinate ophthalmia tarsi, with thickening of the meibomian glands, itlias also been successfully employed.

Administration. —It should be given in doses of one-sixteenth of agrain, gradually increased to one-fourth of a grain. It may be exhibitedin the form of pills, or dissolved in alcohol or ether.

Unguentum IIydrargyri Biniodidi, Ph . L. (biniodide of mer-cury, 3j.; white wax, 3ij.; lard, 3vj. M.)

Hydrar'gyri Bisulphure turn. — Bisul'phuret of Mer'cury.

History. —It is mentioned in the Old Testament ( Jerem . xxii. 14).Theophrastus {De Lapidibus) says that cinnabar {iciwdjlafn) was acci-dentally discovered, by Callius, about ninety years before the magis-tracy of Praxibulus, of Athens—that is, 494 years before Christ. Geiger(Handb. d. Pharm., by Liebig) found it in the colouring matter of the oldEgyptian tombs. It was formerly called minium. It is commonly termedred sulphuret of mercury, and, when in powder, vermilion.

Natural History. —The principal repositories of native cinnabar{cinnabaris nativa) are Idria, in Carniola, and Almaden, in Spain . Itoccurs both massive and crystallized; the primary form of its crystalsbeing the acute rhombohedron.

Preparation. —Artificial cinnabar ( cinnabaris factitia ) is prepared bymixing two pounds of mercury, with five ounces of melted sulphur, inan iron pot over a fire; and, as soon as the mass begins to swell, it is tobe removed from the fire, and covered, to prevent inflammation. Whenlarge quantities of sulphur and mercury are heated together, a slightexplosion and flame are produced. When cold, it is rubbed to powderand sublimed in earthen pots {Ann. Chim. iv.; Aikin’s Dictionary ofChemistry).

In this process the heat enables the mercury and sulphur to combine,and form the bisulphuret.

Properties. —Artificial cinnabar has, in the mass, a dark reddishbrown crystalline appearance; but, when reduced to a fine powder, is ofa beautiful scarlet-red colour, and is then termed vermilion. It is taste-less, odourless, insoluble in water or alcohol, and unalterable in the air.It is fusible and volatile. It burns in the air with a blue flame, the sul-phur uniting with oxygen to form sulphurous acid, while the mercury isdissipated in a vaporous form.

Characteristics. —Heated in a glass tube, with potash, it evolvesmercurial vapour, which condenses into liquid globules of this metal.The residue, wdiich is sulphuret of potassium, gives out hydrosulphuricacid on the addition of hydrochloric acid. The colour of cinnabardeepens under the influence of heat.

Composition. —Its composition is as follows:—

Eq. Eq.Wt. Per Cent. Guibourt. Sefstrnm.

Mercury. 1 .... 202 .... 86*32 .... 86.21 .... 86*29

Sulphur . 2 .... 32 .... 13*67 .... 13*79 .... 13*71

Bisulphuret of Mercury 1 .... 234 .... 99*99 .... 100*00 .... 100*00

Purity. —Pure cinnabar is totally evaporated by heat, and is insolublein nitric or hydrochloric acid. If minium or red lead be intermixed, wemay recognise it by boiling in acetic acid, by which acetate of lead is