Barium, Phosphate of. Ba(PO4)2. Prep. In a similar manner to the oxalate, which it resembles in being an almost insoluble white powder.
Barium, Sulphate of. BaSO4. Syn. Sulphate of baryta, Heav′y spar, Bolo′′gnian s., Cawk (mi); Bary′tæ sul′phas (Ph. E. & D.), Spa′thium pondero′sum, &c., L.; Sulfate de baryte, Spath pesant, &c., Fr.; Schwefelsaures baryt, Schwerspath, &c., Ger. This salt is found native, often in beautiful tabular crystals, but more frequently in white or reddish-white masses. It is also occasionally prepared artificially, as a pigment and chemical, by decomposing a solution of chloride of barium with dilute sulphuric acid, or with a solution of sulphate of sodium; the resulting precipitate being collected, well washed, and dried.
Prop., &c. When pure, or free from iron, its powder is white. It is insoluble in water, and nearly insoluble in all other menstrua; before the blowpipe it decrepitates, fuses with great difficulty (by which it is distinguished from the sulphates of strontium and calcium), and ultimately melts into a hard, white enamel. Mixed with charcoal, and heated to redness in a covered crucible, it is reduced to sulphide of barium. It is readily decomposed by fusion with alkaline carbonates; also very slightly so by their cold solutions; but ultimately completely, though slowly, by their boiling solutions. Sp. gr. 4·3 to 4·75.
Uses. Chiefly as a pigment (PER′MANENT WHITE), and to adulterate white-lead; for which purposes the native sulphate is commonly well washed, first in very dilute sulphuric acid, and afterwards in pure water, to remove any iron which may contaminate it, and impair its whiteness. It is also used to form sulphide of barium; and, in pyrotechny, instead of the more expensive nitrate.
Barium, Sulphide of. BaS. Syn. Sul′phide of barium, Sul′phuret of baryta; Ba′′rii sulphure′tum, &c., L.; Sulfure de baryum, &c., Fr. Prep. Sulphate of barium, well dried and in fine powder, 3 parts; powdered charcoal or powdered coal, 1 part; the mixture is pressed tightly into an earthen crucible, and the cover being fitted on, it is exposed for 11⁄2 to 2 hours, to a bright red heat; after it has cooled, the black mass thus obtained is powdered, and boiled in water, and the resulting solution allowed to crystallise. Some authorities recommend forming the mixed powders into a stiff paste with oil, or oil of turpentine, before calcination; but this is not at all necessary.
Prop., Uses, &c. Crystals, thin and nearly colourless plates, containing combined water; very soluble in hot water, less so in cold water; and rapidly decomposed by exposure to the air. It is principally used to form the BARIUM SALTS, and in organic analysis. Care should be taken in its preparation to expose the solution to the air as little as possible. Sulphides of a higher grade may be formed by boiling this compound with sulphur; but they possess little practical interest.
Barium, Sulphite of. BaSO3. Syn. Sul′phite of baryta. Prep. By testing a soluble barium salt with sodium sulphite, and washing the precipitate. Insoluble.
Barium, Tartrate of. BaC4H4O6. Syn. Tar′trate of baryta. Prep. Like that of oxalate of barium. White powder. Slightly soluble.
BARK. [Eng., Dan.] Syn. Cor′tex, L.; Écorce, Fr.; Baumrinde, Rinde, Ger. The rind or exterior covering of vegetables, corresponding to the skin of animals. It consists of the—cu′ticle or epiderm′is—cellular substance, containing colouring matter, &c., and—li′ber, the inner or true bark. The last is formed of woody fibre in great quantity, intermixed with cellular tissue. At the commencement
of the annual growth of a tree, the bark separates spontaneously from the wood, in order to make room for the new matter forming beneath. It thus increases by yearly layers, and gradually perishes on the outside, owing to distension, from the growth of the interior portion. Its physiological uses are numerous and important. It is the depository of many of the secretions of plants, and it acts as a living filter, separating secretions from each other, and allowing a part of them to pass off horizontally through the medullary processes on their way to the centre of the tree. But its principal offices appear to be to act as a protection to the tender wood, and as a channel for the sap in its descent from the leaves. “True bark only exists in exogens and gymnosperms; in endogens its place is supplied by cortical integuments, which cannot be separated from the adjacent wood, without violence.” (Lindley.)