BARIUM, a metallic element, strongly re sembling calcium in its chemical properties. The mineral barite (q.v.) was the first com pound of barium to be examined. In 1750 Marggraf showed that barite contains sulphu ric acid, and the subsequent labors of Scheele and Gahn proved that it also contains a pre viously unrecognized earth, which Bergmann called terra ponderosa, or ("heavy earth?' In 1779 Guyton de Morveau proposed the name ((barotex' (Greek, ((heavy))) for this earth, and Lavoisier modified the word to ubaryta,* in which form it still survives. Subsequently ba ryta was found to be the oxide of a new metal, which was isolated by electrolysis in 1808 by Berzelius and Pontin, and afterward by Davy, and named ((barium.* When absolutely pure, barium is a silver-white metal with the density of 3.78. It is a little harder than lead, melts at 1580° F., and vaporizes at 1760° F. It oxidizes rapidly in the air, and decomposes water read ily. It is ductile and somewhat malleable. Powdered barium talces fire spontaneously. Its atomic weight is 137.4 (0 16), and its chemi cal symbol is Ba. Its specific gravity appears to be between 3.75 and 4.00. Banum occurs in nature in all primary rocks and in some min eral waters. The most common sources of barium compounds are the carbonate and sul phate, which occur native as witherite and barite (qq.v.), respectively. The nitrate is prepared by acting upon the native carbonate with nitric acid. It is a soluble salt, with the formula Ba(NO2)2 The nitrate decomposes upon being strongly heated, the nitric acid be ing expelled, while barium monoxide (or baryta), Ba0, is left behind as a gray, porous mass, strongly caustic and alkaline. When gently heated in air, barium monoxide takes up another molecule of oxygen and forms the dioxide, Ba02; and on being more strongly heated, the dioxide gives up the extra atom of oxygen again, and returns to the monoxide. It was long ago proposed to make use of this curious property for isolating pure oxygen from the air, by alternately heating the dioxide at a high temperature, and collecting the oxy gen given off as it returns to the monoxide and then submitting it, at a lower temperature, to the action of a current of air until it has again passed into the state of dioxide. It was found, however, that the process would work only for a short time, after which a fresh supply of baryta was required. Recent investigations have gone far toward discovering the cause of this loss of activity, and it is now likely that oxygen will sometime be made on a com mercial scale by this most ingenious process. Baryta absorbs water with considerable evolu tion of heat and the formation of a hydrate, Ba(OH)2, which crystallizes with eight mole cules of water. Barium hydrate is also made,
in large quantities and at a low price, at Niagara Falls, by the electrolysis of soluble salts of barium. The hydrate is used in refin ing sugar, being much superior to lime for this purpose. With cane sugar it forms an insoluble compound from which the sugar may after ward be set free by a current of carbon diox ide gas. The hydrate is also likely to be of great use, in the near future, for preventing the formation of boiler scale,. by precipitating the carbonates and sulphates in the feed water, in the form of insoluble barium compounds. The value of barium hydrate for this purpose has long been known, but until the development of the electrolytic method of manufacturing it, the expense involved was prohibitive. Barium sul phate (barite) is thrown down as a precipitate whenever a soluble barium compound is added to a solution of any sulphate; and for this reason soluble barium salts are much used by the chemist in testing for sulphuric acid and sulphates. The chloride (BaC12) is the salt most commonly employed as a reagent for this purpose. Bartuni sulphate is one of the most insoluble salts known. The native sulphate, when ground up, was formerly used to adulter ate white lead. The artificial sulphate was also used for this purpose and is itself used as a paint, under the name of *permanent white,* or blanc fise. The artificial sulphate is said to be superior to the natural mineral for use as a paint, as it has more *body.° In ready-mixed paints, white, ground and hydrate barite is em ployed as a pigment. With 30 per cent of zinc sulphate, 70 per cent of barite is mixed to form the white pigment called *lithopone,D which is used extensively as a Mat° wall paint. Barite is also used in the manufacture of glazed and coated paper. When baritun sulphate is heated with coal it loses its oxygen, and becomes reduced to the sulphide BaS, a salt which is highly phosphorescent, and is known as Bologna phosphorus. After ex posure to sunlight or to a strong artificial light, barium sulphide shines for hours with a bright, golden light. It is used in the manufacture of luminous paint. The sulphide may be heated in an earthenware retort through which moist carbomc acid gas is being passed, and baryta caustic thus obtained. Barium is readily rec ognized by the spectroscope through a number of characteristic green lines. Its volatile salts communicate a green color to non-luminous flames, and are used (especially the nitrate) in pyrotechny.