Manganese, or Magnesia nigra, a dark-coloured native mineral, found in a more or less impure state, both in iron-mines, and in the lead-mines of Mendip-hills, in the county of Somerset.

Common manganese is very heavy, moderately hard, and of a deep dusky grey, approaching to black, but sometimes of an iron-brown cast. It emits sparks with great difficulty, when stricken against steel; nor does it effervesce with acids, though the latter make a partial solution of it when calcined.

Considerable quantities of manganese are employed in glass-works for purifying glass ; as it destroys the effects of colouring substances, and renders vitrified matters perfectly clear; from which property it has received the appellation of Soap of Glass. Farther, it imparts to a large quantity of glass, in a state of fusion, a purplish or reddish tinge, that disappears if continued in the fire: these colours may, according to Cronstedt, be easily effaced by the calces of arse-tiic or tin.—Manganese likewise communicates various tints to warm water, such as green, purple, red, blue, etc. which change on agitating that fluid.—When distilled with the muriatic acid, or spirit of salt, this mineral yields the oxygenated muriatic acid, or Bleaching Liquor of Bertholeet.—It is also employed for glazing earthen-ware, which thus acquires a black colour.—After being calcined in a Strong fire, it has been recommended medicinally, as an astringent ; of which, however, we have had no experience.