Characters. - A heavy lemon-yellow powder, permanent in the air, odourless and almost tasteless.

Solubility. - It is insoluble in water or in alcohol, but soluble in nitric or hydrochloric acid.

Reactions. - When heated the salt turns red, becoming yellow again on cooling. At a red heat it is volatilised without residue, evolving vapours of mercury and of sulphurous acid.

Tests. - As it is a mercuric oxysulphate, it should be soluble in 20 parts of hydrochloric acid without residue (no mercurous salt).

Uses. - The yellow oxysulphate has been used under the name of Turpeth mineral as an errhine in chronic ophthalmia. It is a prompt emetic, and is sometimes preferred to other emetics in croup, as it is quick and certain, and does not produce depression nor purging. The dose for a child two years old is 2-5 grains (O.13-0.33 gm.), repeated in fifteen minutes if necessary. It may also be used as an alterative.