the mineral barite or barytes (also called cawk, cauk or eaulk). It is found in England, as in Derbyshire and Shropshire; also in Eu- rope, and in the United States at various locali- ties, but chiefly in ilissouri, Tennessee, North Carolina, and Virginia. It is a heavy, ^vhite mineral, with a specific gravity of 4.48, and is found crystallizing in the orthorhombic system, and massive. The better grades are used in the manufacture of pigments, as a cheap substitute for, or as an adulterant of, white lead; in manu- facturing reagents, and in pyrotechny; also as a makeweight in the paper manufactures; while the lower grades are use.d l)y pork-packers in the preparation of canvas for their products. Barium sulphate was an important constituent of the white body used by Wedgwood in his jasper-ware. It is made artificially by adding dilute sulphuric acid to a solution of barium chloride; the resulting white precipitate, after being well washed and dried, constituting the pig- ment called hhmc fixe, or permanent ichile. In 1899, 41,894 short tons of barytes. valued at $139,,')28, were produced in the United States.
Barium chloride, made by treating the native carbonate, witherite, with hydrochloric acid, is used in chemistry as a reagent, in the preparation of the artificial sulphate or permanent white, and for preventing incrustation in boilers.
Barium nitrate is prepared commercially by dissolving the native carbonate in dilute nitric acid and crystallizing the barium nitrate. It is largely used in pyrotechny, in the preparation of green fires, and in the manufacture of explo- sive compounds, as a substitute for potassium nitrate.
Barium salts, when brought into a non-lumi- noxis flame, burn with a yellowish-green color.
BAR'JE'SUS. See Eltmas.
BARK (akin to Sw. and Dan. bark, LG.
horke; possibly related to AS. beorgan, Ger.
hergen, to cover). In the stems of perennial
woody plants, the portion which lies outside the
wood', and can be easily separated from it, par-
ticularly at certain times. The term is also often
applied to the corresponding part of annual
stems, especially to those which contain textile
fibres, such as flax, hemp, etc. But this is
more properly called the cortex (q.v.), and the
word 'bark' should be used only of shrubs and
trees. European and English botanists, and con-
sequently English translations of foreign works,
iise the "term 'bark' for the dead and dry outer
portions only of what is known in this country
as bark.
The bark of a one-year-old twig consists of three concentric zones"; (1) The inner is the phloem (q.v.), or bast, vhose work is the con- duction (q.v.) of foods; (2) the outer is the skin (epidermis) and the layers of cork begin- ning to develop near it; (3) between these lies the green zone, whose cells are still capable of making food. See Piiotosyxthesis.
The green zone does not usually exhibit further growtli ; the others increase in thickness. The inner bark receives additions to its inner face season after season from a layer of actively dividing cells, known as the cambium (q.v.), which lies between it and the wood. The outer zone increases because a layer of similar cells, the phellogen (q.v.), develops from the epider- mis (q.v.), or some of the cells of the cortex. This cork cambium, as it is otherwise kno>vn, gives rise by division of its cells, chiefly in a tangential plane, to layers of cork and other tissues. The corky lajcrs, being almost im- pervious to water, cut off all tissues outside them from nutriment ; these tissues consequently die and dry up. If the cork cambiiun continues its activity year after year, the tissues it pro- duces become thicker and thicker. By drying and weathering, the outside becomes rough and irregularly seamed, the internal increase in di- ameter tending to make the longitudinal furrows and ridges the more conspicuous. In this case the green layer loses its color wholly, or retains it only beneath the deep furrows.
If the activity of the first cork cambium ceases and new phellogen layers are formed, deeper por- tions of the green zone are continually involved, and finally the whole of it comes to lie outside the newest cork ; wherefore it perishes. The new phellogen layers may next invade the phloem, so that the bark may come to consist only of the phloem and the tissues produced by the cork cambium. The corky la.yers are lines of weak- ness. Warping, due to drying and wetting, cracks these layers, and the outermost sheets or flakes of bark are loosened and fall off. If the corky layers are very close together and concen- tric, a bark such as that of the paper birch or sycamore results; but in most barks the flakes are irregular.
Tanning. The bark of many trees is capable of being used for tanning, but that is pre- ferred which particularly aboimds in tannic acid. Oak bark is principally used in Great Britain and throughout Europe, as well as in North America, where hemlock, however, is more ex- tensively employed. In Spain the inner layer of the bark of the cork oak, or cork tree, is em- ployed. The bark of the chestnut is also much valued for this purpose. Larch and willow are used in preparing some kinds of leather. The bark of the birch and that of the alder are also employed, birch bark being, however, more esteemed for steeping fishermen's nets and cord- age, to preserve them from rotting, than for the preparation of leather. Different species of Acacia (q.v.) and of Eucalyptus (q.v.) furnish harks used for tanning in Australia, some of which have, to a small extent, become articles of commerce.
The barking of trees can be accomplished with facility only in spring, when the sap has begim to circulate. The tree being felled, the rough, external lifeless parts of the bark are removed as useless ; the smaller branches are cut into lengths of about two feet, and their bark is loosened by beating with a mallet, and easily taken off; the bark of the trunk and main branch<'S is cut by a chisel-like instrument or with an axe into similar lengths, each of which is divided longitudinally, and finally stripped oft' by the aid of mallets," chisels, etc. The bark is sometimes dried in sheds, being placed on narrow shelves or frames in such a way that there may be a free circulation of air about it; sometimes in the open air, when it is very generally made to rest in a sloping position against trunks of trees placed horizontally at a little distance from the ground, the larger pieces of bark being placed so as to protect the smaller botli from sim and rain. Great care is necessary in the drying of liark. as it is much damaged if allowed to get moldy, and is liable to suffer injury from ram
