Calomel, or the subchloride of mercury, is not used as a poison. In large doses it may act as an irritant poison, and death has not infrequently occurred even from comparatively small doses. Profuse salivation and gangrene of the mouth have resulted from its use, and cases are recorded of death resulting from these. In many cases idiosyncrasy appears to modify, more or less, the action of this preparation of mercury. The poisonous effect of calomel has been attributed to—(1) Adulteration with corrosive sublimate. (2) Conversion of the calomel into corrosive sublimate by the action of the hydrochloric acid of the gastric juice.
N.B.—The free acid of the gastric juice is probably in too small a quantity to materially alter the composition of the calomel.
Ammonio-Chloride of Mercury
White precipitate may, if taken in large doses, produce alarming effects, but it cannot be regarded as an active poison. Pavy‘s experiments on rabbits indicate that it is a more powerful poison than was formerly thought to be the case. Its action is that of an irritant, accompanied with, in some cases, severe salivation.
Red Precipitate
Red oxide of mercury possesses poisonous properties, but it is seldom employed as a poison. The symptoms most frequently present are vomiting, coldness of the surface of the body, stupor, pain in the abdomen, and cramps of the muscles of the lower extremities. The vomited matters are generally mixed with some of the red oxide.
Cinnabar. Vermilion
A compound of sulphur and mercury in the form of a dark red crystalline mass is known as cinnabar; and to the same substance reduced to a fine powder the name vermilion has been given. It is used as a red pigment. It can scarcely be considered as a poison, Orfila asserting that it is not poisonous. The vapour of this substance appears, however, to be capable of producing severe symptoms, and in one case, profuse salivation resulted from the application of the vapour to the body.
Cyanide of Mercury
This substance, though an active poison little inferior to corrosive sublimate, is seldom used as such, probably from its being better known to chemists than to the general public. It differs from corrosive sublimate in having no local corrosive action. It has been supposed, but proof is wanting, that its injurious effects are due to its decomposition by the acids of the stomach and the formation of prussic acid. Death has occurred in nine days from a dose of ten grains. It acts as an irritant. The sulphocyanide of mercury is used in the manufacture of the toy known as Pharaoh‘s serpents.