ISABYTA, or BARY'TES, or Oxide of Barium (q.v.)—symbol BaO—is the earth present in the minerals witherite (carbonate of B.) and heavy spar (sulphate of B.), It may be prepared in several ways: 1. By acting upon the carbonate of B. (Ba0CO3) by nitric acid (NO.), which causes the disengagement of the carbonic acid and the nitric acid combining with the B. forms the nitrate of baryta (Ba0N06). On evaporating the latter substance to dryness, and igniting the residue, the nitric acid volatilizes, and leaves the baryta (BaO). 2. Another mode of preparing the same substance is to act upon a solution of sulphuret of barium (BaS) by the black oxide of copper (CuO), when an interchange of elements occurs, the sulphur uniting with the copper, producing sulphuret of copper (CuS), and the oxygen with the barium, forming B. (BaO), which remains dissolved in the water, and, on evaporation, deposits crystals in the hydrated condition (BaO, 110). B. belongs to the group of alkaline earths, and has the property of acting like an alkali (q.v.) on coloring matters. It has a very harsh taste, is highly caustic, and is very poisonous. A solution of B. is used by the chemist as the best indication of the presenc3 of carbonic acid gas in the atmosphere, for when a plate or other vessel containing the solution is exposed to the air, the carbonic acid floating across the surface combines with the B., and forms a film of white carbonate of baryta (BaO,CO2). Other wise, B. possesses little interest, as it is not put to any commercial or medicinal use. The compounds of B. are, however, of considerable importance. The sulphate of B. (Ba0S03), otherwise called ponderous or ham' spar, is found in the mineral kingdom, diffused in fissures or cracks, passing through other rocks, especially in Cumberland, Durham, and Westmoreland, and in theisland of Arran, At the latter place, an exten sive mine of heavy spar has been worked for many years.
In its native condition, the sulphate of B. occurs of a crystalline texture, is sometimes found pure and white, but generally presents a flesh-red color, from the red oxide of iron (rust) incorporated in it. The rust can be got quit of by reducing the sulphate of B. to a fine powder under rollers or traveling-wheels, and subjecting the pulverized material to the action of dilute sulphuric acid, which dissolves the red oxide of iron, and leaves the sulphate of B. as a white dense powder. The principal use of heary spar is as a pigment under the name of permanent white; but having little opacity, it cannot die employed by itself, but only when mixed with ordinary white lead. When added, to the latter, however, it must be regarded as an adulteration, for the little opacity it possesses renders it of service only as an increaser of the bulk of the white lead. Several mixtures of sulphate of B. and white lead are manufactured, and are known in commerce. Venice white contains 1 part sulphate of B., and 1 part white lead. Hamburg white contains 2parts sulphate of B., and 1 part white lead. Date* white contains 3 parts sulphate of B., and 1 part white lead. The native sulphate of B. has been. employed by the celebrated potter Wedgwood in the manufacture of jasper ware, and for the formation of white figures, etc., on colored jars and vessels. The carbonate of B. found native as witherite, and the nitrate of B., have been previously referred to in this article and that on BARIUM.