BARIUM, one of the metallic chemical elements included in the group of the alkaline earths (symbol, Ba, atomic number 56, atomic weight 137.37 [0= i6] ). It takes its name from the Greek f3apvs (heavy) on account of its presence in barytes or heavy spar which was first investigated in 16o2 by V. Casciorolus, a shoemaker of Bologna, who found that after ignition with com bustible substances it became phosphorescent, and on this account it was frequently called Bolognian phosphorus. In 1774 K. W. Scheele, in examining a specimen of pyrolusite, found a new substance to be present in the mineral, for on treatment with sul phuric acid it gave an insoluble salt which was afterwards shown to be identical with that contained in heavy spar. Barium occurs chiefly in the form of barytes or heavy spar, and witherite, BaCO3, and to a less extent in baryto-calcite, baryto-celestine, and various complex silicates. The metal is difficult to isolate; Sir H. Davy tried to electrolyse baryta, but was unsuccessful; later attempts were made by him using barium chloride in the presence of mercury. In this way he obtained an amalgam, from which on distilling off the mercury the barium was obtained as a silver white residue. R. Bunsen in 1854 electrolysed a thick paste of barium chloride and dilute hydrochloric acid in the presence of mercury, at ioo°C., obtaining a barium amalgam, from which the mercury was separated by a process of distillation. A. N. Guntz reduced barium oxide by aluminium powder at 1200°C.; and C. Matignon reduced it in a vacuum at the same temperature by means of ferrosilicon (g5% Si), barium of 98.5% purity dis tilling over. The metal when freshly cut possesses a silver white lustre, is a little harder than lead, and is extremely easily oxidized on exposure; it is soluble in liquid ammonia, and readily attacks both water and alcohol. Its specific gravity is 3.78.
Three oxides of barium are definitely known—the monoxide, BaO, the peroxide, and a suboxide, obtained by heating BaO with magnesium in a vacuum to iioo°C. An oxide has also been described. The monoxide is formed when the metal burns in air, but is usually prepared by the ignition of the nitrate, oxygen and oxides of nitrogen being liberated. It can also be obtained by the ignition of an intimate mixture of the carbonate and carbon or barium carbide. It is a greyish coloured solid, which combines very energetically with water to form the hydroxide, much heat being evolved during the combination; on being heated in a current of oxygen it forms the peroxide, which at higher temperatures breaks up again into the monoxide and oxygen. The hydride, is obtained by direct combination at high temperatures; it is volatile and less stable than calcium or strontium hydrides.
Barium hydroxide, is a white powder that can be obtained by slaking the monoxide with the requisite quantity of water, but it is usually made on a large scale by heating heavy spar with small coal whereby a crude barium sulphide is obtained. This sulphide is then heated in a current of moist carbon dioxide, barium carbonate being formed, = and finally the carbonate is decomposed by a current of super heated steam, = Ba leaving a residue of the hydroxide. It is also made by electrolysing a barium chloride solution, using a mercury cathode. Barium hydroxide is moderately soluble in cold water, readily soluble in hot water, the solution possessing an alkaline reaction and absorbing carbon dioxide readily. The solution, known as baryta-water, finds an extensive application in practical chemistry, being used in gas analysis for the determination of the amount of carbon dioxide in the atmosphere; it is also used in organic chemistry as a mild hydrolysing agent. E. Fischer has used it as a condensing agent in the preparation of a- and /3-acrose from acrolei,n dibromide. A saturated solution of the hydroxide deposits on cooling a hy drated form, as colourless quadratic prisms, which on exposure to dry air lose seven molecules of water of crystallization. It is used as a depilatory in tanning.
Barium peroxide, can be prepared as shown above, or in the hydrated condition by the addition of excess of baryta-water to hydrogen peroxide solution, when it is precipitated in the crystalline condition as These crystals on being heated to 130°C. lose water of crystallization and leave a residue of the anhydrous peroxide. In the Brin process for the manufacture of oxygen, barium dioxide was formed by heating barium monoxide with air at 700°C. under pressure, and decomposed by lowering the pressure. (This process has been superseded by the fractiona tion of liquid air.) It is a white powder which is readily decom posed by dilute acids with the production of hydrogen peroxide.
Barium carbide, is prepared by a method similar to that in use for the preparation of calcium carbide (see ACETYLENE). Barium sulphide, BaS, is obtained by passing sulphuretted hydro gen over heated barium monoxide, or better by fusion of the sulphate with small coal. It is a white powder which is readily decomposed by water with the formation of the hydroxide and hydrosulphide. The phosphorescence of the sulphide obtained by heating the thiosulphate is much increased by adding traces of uranium, bismuth or thorium salts bef ore ignition.
Barium sulphate, is the most abundant of the naturally occurring barium compounds (see BARYTES) and can be obtained artificially by the addition of sulphuric acid or any soluble sul phate to a solution of a soluble barium salt, when it is precipitated as an amorphous white powder of specific gravity 4.5. It is practically insoluble in water (about two parts per million at 15°C.), and is only very slightly soluble in dilute acids; it is soluble to some extent, when freshly prepared, in hot concentrated sulphuric acid, and on being cooled the solution deposits crystals of composition It is used as a pigment under the name of "permanent white" or blanc fixe, and with zinc sul phide in "lithopone." It is also used for weighting paper.
Barium nitride, is obtained as an orange-yellow mass by passing nitrogen over heated barium amalgam or over the metal at 26o°-600°C., or by heating the amide, in a vacuum at 400°-450°C. It is decomposed by water, and on being heated in a current of carbonic oxide forms barium cyanide (L. Ma quenne), giving ammonia and baryta. Barium amide, Ba(NH2)2, is obtained by heating the metal in a current of dry ammonia at 200°C. or from a solution of a barium salt and potassamide in liquid ammonia. Barium dissolves in liquid ammonia to give a deep blue solution of Ba(NH3)6.
Barium nitrate, is prepared by dissolving either the carbonate or sulphide in dilute nitric acid, or by mixing hot saturated solutions of barium chloride and sodium nitrate. It crystallizes in octahedra, having a specific gravity of 3.2, and melts at 597°C. It is decomposed by heat, and is largely used in pyrotechny for the preparation of green fire. Barium carbonate, occurs rather widely distributed as witherite (q.v.), and may be prepared by the addition of barium chloride to a hot solu tion of ammonium carbonate, when it is precipitated as a dense white powder of specific gravity of 4.3, almost insoluble in water. It is much more stable towards heat than calcium or strontium carbonates.
Barium and its salts can be readily detected by the yellowish green colour they give when moistened with hydrochloric acid and heated in the Bunsen flame, or by observation of their spectra. when two characteristic green lines are seen. In solution, barium salts may be detected by the immediate precipitate they give on the addition of calcium sulphate (this serves to distinguish barium salts from calcium salts), and by the yellow precipitate of barium chromate formed on the addition of potassium chromate. Barium is estimated quantitatively by conversion into the sulphate. For the relation of barium to radium, see RADIUM.
cloth made of the inner bark of trees, soaked, and beaten out with a club to the required thickness, is essentially both in origin and in use a tropical and sub-tropical ma terial, its manufacture and use being found from the Congo across Africa (including Madagascar) ; from the Malay peninsula through Indonesia and Melanesia to Easter island, reaching its highest per fection in Polynesia ; and in the tropical regions of Central and South America. It is being ousted everywhere by the introduction of native or imported cloth, and among many tribes the art of making it is already lost. There is evidence of a far wider dis tribution in former times. In India the Laws of Manu ordained that a Brahman purposing to end his life in religious meditation in the forests should clothe himself in skins or bark-cloth; it is still made in the Garo hills and before the introduction of imported cotton clothes it was the usual dress of the Vedda of Ceylon. A Kayan of Borneo reverts to a strip of bark-cloth when in mourn ing; and in the Belgian Congo, if a Bushongo woman has lost several children, she puts on a mourning robe of bark-cloth. Folk tales of the Bushongo fix the traditional date (about 78o) when bark-cloth garments superseded complete nudity. Among the Yao of Nyassaland the girls are dressed in bark-cloth during their initiation ceremonies. It was once made in New Zealand where the paper mulberry, not being indigenous, was cultivated, but both trees and industry are now dead.
The making of bark-cloth depends on several factors—the need of clothing, the existence of trees with suitable fibrous inner bark, and the discovery that this could be beaten out into "cloth." In Central America bark-cloth is common on the Mosquito coast ; it provides loin-cloths for the men, skirts for the women and long sleeveless mantles for both sexes as waterproofs. In Brazil the "shirt tree" (a Lecythis allied to the "monkey-pot") provides a bark which needs little or no preparation. A length of the stem four or five feet long is cut off, the bark is peeled off in one piece, soaked, and with two holes cut for the arms, the shirt is made. But the typical bark-cloth trees are absent from the South Amer ican forests; the less civilized natives wear no clothing, while among the more civilized cotton weaving is universal. In Africa there are numerous kinds of Ficus which have suitably fibrous bark. Bark-cloth was the natural clothing and an important indus try in Uganda up to the middle of the 19th century. It was man's work to plant and cultivate the bark-cloth trees and make the cloth, which was used both for their ample garments and for draping the house walls, and for fines. A thick kind was also used for bed—clothes; several layers one on the top of the other two or three feet high made excellently springy beds for kings and chiefs. The "paper mulberry" (Broussonetia papyri/era), which is extensively cultivated in the East for paper making, grows wild in Burma, China and most of Oceania, and various kinds of Ficus (F. prolixa, F. tinctoria, F. bengalensis, the banyan tree, and F. religiosa, the "sacred fig tree") as well as the breadfruit tree (Artocarpus incisa) are used for making bark-cloth in the islands of the Indian and Pacific oceans.
The method of making bark-cloth differed very little in the various islands. A suitable length of branch or sapling was cut, the outer bark was scraped with a shell, and the inner strips, sev eral feet long and an inch to a few inches wide, were left to soak in water. When thoroughly soaked the strips were beaten out on a flat, hollow log with a grooved wooden mallet, frequent wetting and continuous beating felting the fibres together (occasionally gum was used) until a piece of the required size was made. In Tahiti a bale was often 2ooyd. long, and a yard wide, and the wealth of a chief was estimated by the number of bales hanging from his palace roof. In Fiji a man would wind 2ooyd. round and round his body as a display of wealth. The cloth was variously coloured according to the bark used, Ficus becoming dark brown, breadfruit lighter brown, and paper mulberry beautifully white when dried and bleached. The common cloth was often dyed with Casuarina bark, but the better kinds were decorated with patterns, either sketched out and painted on by the artist, impressed by pressing leaves or flowers in the dye (Tahiti), or (in Samoa and Fiji) printed with printing boards, or by blocks made of strips of cane or midribs of palm leaves stitched on to the piece of leaf. Stencilling was found in Fiji alone. The making of tapa was woman's work, from princess to peasant.
In Uganda, the bark was peeled off the living tree, the third or fourth barks being usually the best, though a tree would continue to provide fresh barks for 3o or 4o peelings. There it was exclu sively men's work, and though the beating on a hollow log was similar the beater was of a different shape. Moreover, the pat terns so characteristic of Polynesian tapa do not occur in Africa, where any decoration is rare, though the women sometimes added patterns, the princesses of Toro tracing designs with their own blood. Different trees yielded differently coloured cloth, the com mon kind, when exposed to the sun, colouring light brown and better kinds terracotta. A special tree was grown to provide pure white bark-cloths to be used at the king's coronation.