Baryta

Baryta, or BARYTES, or Oxide of Barium (q.v.)—symbol BaO—is the earth present in the minerals witherite (carbonate of barium) and heavy spar (sulphate of barium). It may be prepared in several ways: (1) By acting upon the carbonate of baryta, BaCO₃, by nitric acid, HNO₃, which causes the disengagement of the carbonic acid, CO₂, and the nitric acid combining with the baryta forms the nitrate of barium, Ba₂NO₃. On evaporating the latter substance to dryness, and igniting the residue, the nitric acid volatilises, and leaves the baryta, BaO. (2) Another mode of preparing the same substance is to act upon a solution of sulphide of barium, BaS, by the black oxide of copper, CuO, when an interchange of elements occurs, the sulphur uniting with the copper, producing sulphide of copper, Cu₂S, and the oxygen with the barium, forming baryta, BaO, which remains dissolved in the water, and, on evaporation, deposits crystals in the hydrated condition, BaH₂O₂·8H₂O. Baryta belongs to the group of alkaline earths, and has the property of acting like an Alkali (q.v.) on colouring matters. It has a very harsh taste, is highly caustic, and is very poisonous. The presence of carbonic acid gas may be detected by exposing a solution of baryta to the air, when carbonic acid combines with the baryta and forms a film of white carbonate of barium, $\backslash text\{BaCO\}\_3$. Baryta exposed to air or oxygen absorbs oxygen, forming peroxide of barium. On this being heated, oxygen is liberated and baryta again produced. Till lately it was found impossible to procure oxygen by this simple method, as the action became weak when the process was repeated. But recently it has been found that by carefully removing all carbonic acid gas and water from the air before passing it over the barium, the difficulty is removed, and oxygen is thus economically produced. The sulphate of baryta, $\backslash text\{BaSO\}\_4$, otherwise called ponderous or heavy spar, is found in fissures or cracks in other rocks. It is crystalline, and is sometimes found pure and white, but generally presents a flesh-red colour, from the red oxide of iron (rust) incorporated in it. The rust can be got quit of by reducing the sulphate of baryta to a fine powder under rollers or travelling-wheels, and subjecting the pulverised material to the action of dilute sulphuric acid, which dissolves the oxide of iron, and leaves the sulphate of baryta as a white dense powder. The principal use of heavy spar is as a pigment under the name of permanent white; but having little opacity, it cannot be 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 baryta and white-lead are manufactured, and are known in commerce. Venice White contains 1 part sulphate of baryta and 1 part white-lead. Hamburg White contains 2 parts sulphate of baryta and 1 part white-lead. Dutch White contains 3 parts sulphate of baryta and 1 part white-lead. The native sulphate of baryta has been employed by the celebrated potter Wedgwood in the manufacture of jasper ware, and for the formation of white figures, &c. on coloured jars and vessels. The carbonate of baryta found native as witherite, and the nitrate of baryta, have been previously referred to in this article and that on BARIUM.