BARIUM BARK 313 Davy subsequently decomposed by distillation and thus isolated tbe metal. More recently Bunsen and Matthiessen have prepared barium from the fused chloride by means of electro- lysis. Bergman introduced the word heavy spar, terra ponderosa, and Guyton de Mor- veau substituted the Greek (tapiif, heavy, from which he derived the word barote, which was afterward changed to baryta, while the metal was called barium. For the preparation of barium, anhydrous chloride of barium is mix- ed with sal ammoniac and fused in a Hessian crucible. A small porcelain crucible is then filled with the fused mass, and so attached to the poles of a battery of six Bunsen's cups as to be readily decomposed when brought to a state of fusion. The barium is obtained in a fine brass-yellow powder, which must be stored under naphtha, as it oxidizes rap- idly in the air and decomposes water at all temperatures. Alloys of barium with bis- muth, tin, and aluminum have been pre- pared ; they are crystalline, and decompose water at all temperatures, but have no appli- cation in the arts. The compounds of barium are numerous, and have extensive use in medi- cine, chemistry, and technology. The oxide has been employed as a substitute for lime in the manufacture of glass, also to prevent the fer- mentation of the molasses of sugar cane. The binoxide has been proposed as an agent for the manufacture of oxygen from the atmosphere. If the protoxide be heated in a tube and a current of air be passed over it, it absorbs oxygen, which it again gives up on raising the temperature. It was at one time thought that the process could be made continuous, but ex- perience has shown that the baryta melts and refuses to take up more oxygen. This can in a measure be prevented by previously mixing it with manganese dioxide and soda. By adding concentrated sulphuric acid to the binoxide of barium and gently warming, oxygen gas in the form of ozone is liberated. As the native sul- phate of baryta is generally too impure to be used directly in the arts, it is fused with char- coal and resin or oil, and the pure white sul- phate obtained from the dissolved residue by tbe addition of sulphuric acid. Thus prepared, sulphate of baryta is used as a permanent white, under the name of blanc Jixe, in the manufacture of paper, as a white pigment, and to adulterate white lead. As the specific gravity of heavy spar ranges from 4'3 to 4'7, it is frequently mistaken for the ore of copper or lead. Blanc fixe hardens when mixed with soluble glass, and is therefore capable of use in fresco painting. It is also used in making bril- liant white satin paper. Chloride of barium can be readily made by dissolving the native carbonate in hydrochloric acid. It is a valu- able reagent in the laboratory for the detection of sulphuric acid, and in medicine as a remedy in scrofulous complaints. Several cases of poisoning by means of this agent are on rec- ord. The chloride and the oxalate are manu- factured into anti-incrustation powders. A very good blasting powder is made of the ni- trate of baryta, which, being much cheaper than the ordinary nitre powder, has long been j employed in mines and on public works in Europe. It is not considered so dangerous as common powder, and, although slow in action, is found to be effective enough for all practical purposes. Baryta salts are used in Belgium in the preparation of citric acid, tartaric acid, and hydrocyanic acid. In the manufacture of alum it has been found that the aluminate of baryta can be very readily prepared by fusion, from which alumina salts can be easily sepa- rated. This method is employed in France, in making alum from bauxite. Prussian blue, made from potash salts, can be prepared in a ready and cheap way through the intervention of cyanide of barium. Chromic acid is more cheaply prepared by the aid of baryta than in any other way. Stearic acid, from which ada- mantine candles are made, can be combined with and afterward easily separated from this substance. Baryta is also used in the prepa- ration of starch sirup, so frequently sold as liquid honey ; spirits of hartshorn or ammonia ; a beautiful yellow paint, often employed as a substitute for chrome yellow, on account of its delicacy of tone and cheapness ; soap, and an infinite number of other substances. Some of the best English plate glass has been made by substituting carbonate of baryta for carbonate of soda. It is a clear crystal sheet, and not liable to atmospheric changes. This glass has also been found to be admirably adapted for optical instruments. The soluble salts of ba- j ryta are poisons, the readiest antidote being sulphate of soda or magnesia. BARK, the outer covering of trees and plants. It is found in its complete form only in the exogenous and gymnospermous classes, in which it consists of three portions, often quite distinct, but generally closely blended : the libel- or inner bark (endophlaum), the cellular tissue or green layer (mesophlasum), and the corky envelope (epiphlceum). The liber, or fibrous bark, consists of bast cells, long, with thick walls, formed of cellulose; liber cells, thin- walled, of ordinary parenchyma, marked with reticulated spots, and seldom if ever absent from the liber ; and laticiferous tubes, contain- ing various secretions. The cellular envelope, which usually disappears after the second year, is formed of loose parenchyma, giving the bark its green color. The suber, or corky envelope, consists of cork, formed of parenchymous cells with thin walls and rectangular section, soon dead and empty ; and periderme, of flat, thick- walled cells united in layers. The epidermis or outer skin is not permanent, but breaks away as the layers beneath it expand. The bark serves as a channel through which the sap elab- orated by the leaves descends to feed the cam- bium layer, with which the bark is continuous, and by which it grows in annual rings, as does the wood itself. The medullary rays also con-
