Character. - An orange-red powder.

Solubility and Reactions. - It is readily dissolved by hydrochloric acid, yielding a solution which, with caustic potash added in excess, gives a yellow precipitate, and with solution of ammonia a white precipitate.

Preparation. - Triturate nitrate of mercury and metallic mercury together, and heat until nitrous fames cease to be given off. Hg(N03)2 + Hg = 2HgO + N204.

Impurity. - Undecomposed nitrate.

Test. - Entirely volatilised by a heat under redness, being at the same time decomposed into mercury and oxygen. If this be done in a test-tube,. no orange vapours are perceived.

Preparations.

B. And U.S.P

Unguentum Hydrargyri Oxidi Rubri (Ointment of Red Oxide of Mercury)

1 part in 8, B.P.; 1 in 10, U.S.P.

With soft and hard paraffin, B.P.; with ointment, U.S.P.

Uses. - The red oxide is rarely given internally. The ointment may be used in ophthalmia and conjunctivitis in the same way as the nitrate of mercury ointment, and as an application to the auditory meatus in otorrhoea occurring after scarlet fever-It is also useful in scaly skin-diseases, syphilitic sores on the skin, and in ulcers within the margin of the anus.