BA'RIUM, a peculiar metal, discovered by Davy in 1807: it is the basis of the alkaline oxide or earth barytes, from which it is ob tained by various chemical processes. It re sembles silver in appearance : it is much heavier than water. By exposure to the air it is slightly covered with a crust of barytes. It fuses before it becomes red hot, and at this temperature it acts upon glass, without being volatilized; when exposed to the air, and mo derately heated, it burns with a deep red light. It may be flattened a little, so that it is to a certain extent a malleable metal. Ba. rium has, however, as yet been obtained only in small quantities, and consequently its pro perties are but imperfectly known.
The protoxide is met with combined with sulphuric acid, forming heavy spar, or eawk, tanned chemically sulphate of barytes, and with carbonic acid, constituting the mineral termed witherite, or carbonate of barytes ; it may be procured by decomposing either of these native compounds. It is of a grayish white colour ; when moistened with water it becomes very hot, and in a short time falls into a fine white powder ; if more water is added, it becomes a crystalline and very hard mass. It is extremely poisonous, has an
acrid, alkaline, caustic taste, and requires a. high temperature to fuse it.
Barium combines with many substances to produce chemical compounds. One of the best known is sulphate of barytes, which occurs largely in many parts of the earth, especially in the lead mines of the north of England; it occurs bath amorphous and crystallized, the former state it is sometimes colourless and transparent, and frequently opaque. The crystals are often very large. It is extremely heavy, its specific gravity being about 4.7. It is unalterable by air or by water, and is scarcely affected by heat. When sulphate of barytes is only moderately heated with car bonaceous matter, a solar phosphorus is formed, which is called the Polognian Phos phorus.