"Protiodid of mercury," HGI, formerly also called "Green iodid of mercury."

Properties : Mercurous iodid is a bright yellow, amorphous powder, odorless and tasteless. By exposure to light it becomes darker, in proportion as it undergoes decomposition into mercuric iodid and metallic mercury. It is almost insoluble in water and wholly insoluble in alcohol.

Incompatibilities: Mercurous iodid is incompatible with oxidizing agents, alkalies and the haloid salts of the alkali metals (chlorids, bromids or iodids), which tend to decompose it with the formation of mercuric salts. Alkali iodids decompose mercurous iodid with formation of metallic mercury and soluble alkali mercuric iodid.

Action and Uses: Mercurous iodid is used to secure the constitutional effects of mercury, especially in the treatment of syphilis. Its effects are much the same as those of calomel, although it is not so likely to produce diarrhea or salivation as the latter preparation.

Dosage: In syphilis mercurous iodid is best given in pill form in doses gradually increasing until slight toxic symptoms appear in the form of pain in the abdomen, diarrhea, salivation, etc. During its administration careful attention should be given to cleanliness of the mouth and skin. The teeth should be kept in good order, and soreness of the gums should be the signal for interrupting temporarily the administration of the remedy. The initial dose should not exceed 0.015 gm. or grain in the form of tablets, pill or powder, three times a day after meals, and this should be increased by the addition of 0.008 or 1/8 grain daily to the limit of tolerance.

Hydrargyri Iodidum Rubrum. —Red Mercuric Iodide, U. S. P.

"Biniodid of Mercury," HgI2.

Properties : Mercuric iodid is a scarlet-red powder, odorless and tasteless, and permanent in the air. It is nearly insoluble in water, but slightly soluble in alcohol (1:116). It is rendered soluble in the presence of soluble iodids, such as an equal weight of potassium iodid with formation of potassium mercuric iodid.

Incompatibilities: Red mercuric iodid is incompatible with alkalies and their carbonates and alkaloids and their salts.

Action and Uses: Mercuric iodid is used as an antiseptic and germicide. It is more powerfully antiseptic than mercuric chlorid It may be applied in potassium iodid solution. It is also used for the internal administration of mercury. A solution of mercuric iodid in sodium iodid (mercuric iodid 1 gm., sodium iodid 3 gm., water to make 100 c.c.) has also been used as a means of administering mercury by intramuscular injection.

Dosage: 0.003 or 1/20 grain three times a day. It is frequently formed for internal administration by the prescription of a mixture of corrosive chlorid of mercury and potassium iodid.

Gm. or c.c.

Aquae...........................                100| [M.]