Baryta.

Syn. Baryte (F.), Baryterde, Schwerede (G.), Barite, (I.).

This mineral substance does not exist, as far as we know, in an uncombined state; and its native combinations hitherto discovered are very few. It is found,

A. combined with carbonic acid:

Sp. 1. Carbonate of baryta, or Witherite.1

B. combined with sulphuric acid:

2. Sulphate of baryta, or Heavy spar.

Baryta is obtained by decomposing these fossils. It is not a simple substance, but a compound of a peculiar metallic base, . named barium by Sir H. Davy2, and oxygen, in equal proportions, making the equivalent 76.7.

1. Carbonate of Baryta.

Officinal. Barytae Carbonas, Lond. Carbonas Barytae,

Edin. Carbonate of Baryta.

Syn. Spath pesant, Carbonate de Baryte (F.), Schwerspath, Kohlonsaure Baryterde (G), Ossicarbonato di Barite (I.).

This fossil is found native in Sweden, Scotland, and Cumberland, but in greatest abundance at Anglesark, in Lancashire. It usually occurs massive in veins, which traverse the independent coal formation: and sometimes, although rarely, it is found crystallized. It is well known under the name of Witherite. The crystals are small, and their primitive form is yet undecided.

1 So named by Werner, after Dr. Withering, who discovered it native on Alston Moor, in Cumberland, in 1783.

2 Mr. Murray proposes barytum instead of barium. - Syst. of Chym. ii. 205.

Qualities. - Carbonate of Baryta is inodorous and insipid, but it is nevertheless poisonous. Its colour is white, or yellowish grey: it is translucent, with a shining, somewhat resinous lustre; and breaks in one direction with a fracture intermediate between radiated and foliated, and in another uneven: the fragments wedge-shaped. The lustre of the principal fracture is glimmering, that of the cross glimmering and resinous. Its specific gravity is 4.338. When heatea it becomes opaque; and is fused into a white enamel by the blowpipe; and, when pulverized, its powder phosphoresces when thrown on burning coals. It is nearly insoluble, requiring for its solution 4300 times its weight of cold water, and 2300 of boiling water. It dissolves with effervescence in diluted nitric acid, although the strong acid exerts no action on it. Carbonate of Baryta consists of 76.7 or 1 equivalent of Baryta and 22.12 or 1 equivalent of carbonic acid, making the equivalent of the salt 98.82.

Use.-It is only used for preparing the chloride. It may, however, be exhibited as a poison: it produces slight inflammation of the stomach; but acts chiefly on the brain, spine, and voluntary muscles1: and in this case the antidote is diluted sulphuric acid, as the sulphate which is thus formed is an inert salt.

Officinal preparation. - Barii Chloridum, L. Murias Barytae, E. D.

2. Sulphate of Baryta.

Officinal.-Sulphas Barytae, Edin. Dub. Sulphate of Baryta.

Syn. Sulfate de Baryte (F.), Schwefelsaures Baryterde( G. ),Tungspat(Swed.), Ossisolfato di Barite (I.).

This combination of Baryta, which was formerly named Ponderous spar, is found native at Freyburg in Germany, and in many parts of the world. It is found almost always in veins; but sometimes it occurs in beds. It is occasionally obtained in powder, frequently in amorphous masses, and often in crystals.

Qualities. - Sulphate of Baryta is inodorous and insipid. Its colour is white, with shades of yellow, red, blue, or brown.

1 Professor Gmelin found that, in animals poisoned by the soluble salts of Baryta, the voluntary muscles lose their contractility; but the heart continues to contract for many minutes, even without the application of stimuli. - Versuche uber die Wirkungen, etc. 1824.

It occurs transparent, semi-transparent, or only translucent; and is hard, brittle, and heavy, its specific gravity being from 4.448 to 4.865. The varieties of form of its crystals are numerous; but the primitive form is a right rhombic prism, the bases of which are rhombs with angles of 101° 30' and 78° 30'.1 The most common varieties of its crystals are the octahedron with oblique summits, the six or four sided prism, the hexangular table with bevelled edges; sometimes they are needle-form.2 It breaks with a straight foliated fracture: the fragments are nearly rhomboidal, and have a shining, pearly, almost vitreous lustre. It is fused by the blow-pipe, and converted into the sulphuret; and is soluble in sulphuric acid only, from which it is precipitated by water. It consists of one equiv. of Barytarr76.7 + one of acidr = 40.l, making the equivalent of the salt = 116.8.

Use. - This barytic salt is unncessarily introduced into the list of materia medica. It is merely used as a substitute for preparing the chloride of barium, when the carbonate cannot be procured.

Officinal preparation.-Baryta Murias, D. E.