BINIODIDE OF MERCURY.

483

retains some biniodide of mercury in solution. It is better, however, tohave a slight excess of iodide of potassium, in order to obtain the mer-curial biniodide free from corrosive sublimate.

Properties. —It is a scarlet red powder, whose sp. gr. is 632. It isinsoluble in water, but soluble in alcohol, some acids, alkalies, and solu-tions of iodide of potassium, chloride of sodium, and of many of the mer-curial salts. From its solution in boiling rectified spirit it is deposited,on cooling, in rhombic prisms. When heated it fuses, forming a ruby-red liquid, sublimes in crystals, which are at first yellow but afterwardsbecome red, and furnish a scarlet-red powder. It combines with otheralkaline iodides (as iodide of potassium) forming a class of double salts,called the hydrargyro-iodides.

Characteristics. —Heated with potash in a tube it yields metallicmercury, which is volatilized : the residue is iodide of potassium, recog-nisable by the tests before described (p. 280.) From the protiodide ofmercury it is distinguished by its colour and its solubility in a solutionof chloride of sodium. The effects of heat on it, and its solubility iniodide of potassium, are other characters which serve to recognise it.

Composition. —Its composition is as follows :—

Eq. Eq.Wt. Per Cent.

Mercury. 1 . . . 202 . . . 44*5

Iodine. 2 . . . 252 . . . 55*5

Biniodide of Mercury . 1 . . . 454 . . . 100*0

Purity. —The presence of bisulphuret of mercury in it may be recog-

nised by fusion with caustic potash in a glass tube, by which a mixtureof sulpliuret and iodide of potassium is obtained : the existence of sul-phur may be proved by the evolution of hydrosulphuric acid on the addi-tion of a mineral acid.

Physiological Effects, (a.) On animals. —A scruple killed a rabbitin twenty-four hours: the stomach was found pretematurally reddened.Ten grains, dissolved in a solution of iodide of potassium, and given toa dog, caused vomiting, pain, tenesmus, and depression : in four or fivedays the animal was well (Cogswell, Essay on Iodine , p. 164). Maillet{Journ. de Chim. Med. iii. 543, 2 de - Serie) has also made some experi-ments with it.

(b.) On man .—It is a powerful irritant and caustic. It is nearly as }powerful as the bichloride of mercury; indeed, Payer ( Treatise on SkinDiseases , by Hr. Willis, p. 79) considers it more active than the latter.Applied to ulcers, in the form of ointment, I have known it cause excru-ciating pain. Left in contact with the skin for a while, it induces, saysPayer, a most intense erysipelatous inflammation. When administeredinternally, it must be done with great caution. Like other mercurialcompounds, its repeated use causes salivation.

Uses. —It has been employed in the same cases (i. e. syphilis andscrofula) as the protiodide of mercury, than which it is much more ener-getic. Brescliet (O’Shaughnessy’s Transl. of Lugol's Essays, p. 204)applied it, in the form of ointment, with great success in a case of obsti-nate ulceration (thought to have been carcinomatous) of the angle of theeye. In the form of a dilute and thin ointment (composed of biniodideof mercury, gr. ii.; cerate, 3ii.; and almond oil, 3i.) it has been used inopacity of the cornea (Graefe and Walther’s Journ. f. Chir. Bd. 13). In