The Sub-oxide of Mercury, Hg2O, called also the Oxide, the Grey and the Black Oxide of Mercury, is a compound of Mercury 96.15, Oxygen 3.85, in 100 parts.

Med. Prop. and Action. The least irritating of the Salts of Mercury; is rarely employed internally, on account of the varying proportion of the mineral. Occasionally it is used as a fumigation (gr. lx. - gr. cxx.), or in the form of ointment (gr. lx. ad Adipis gr. ccxl. - ccclx.). It is also used in the form of Black Wash, or Lotto Nigra (Calomel, gr. lx., Aq. Calcis Oj.), a mild, unirritating, useful application.

Dose, gr. i - gr. iij.

1496. Therapeutic Uses

To Chancres and Syphilitic Sores of all kinds, the Black Wash (ut supra) is a most serviceable application. It should be applied fresh on linen or lint several times a day, and the mixture should be well shaken before each* application.

1497. In Cancrum Oris, the Black Wash, locally applied, is occasionally signally beneficial. It should be used chiefly in the earlier stage of the disease, and the ulcer should be frequently cleansed with the lotion.