B A SILICON 295 



BARYTA, CARBONATE OP. The composition of tho native carbonate of 

 biirya, called Witheritc, after Withering, who described it ('Phil. Transactions,' 1784), 

 may bo regarded as baryta, 77'39, and carbonic acid 22-41. It is found in Shropshire, 

 Cumberland, Westmoreland, and Northumberland. Tho carbonate of baryta is em- 

 ployed in our colour-manufactories as a base for some of tho more dolicate colours ; it 

 is also used in tho manufacture of plate-glass, and of Wedgwood-ware ; and, in France, 

 it is much used in the preparation of beet-root sugar. 



A small quantity only of carbonate of baryta is now produced in this country ; in 

 1870 about 2,613 tons, 19 cwt, were raised in Northumberland; a few tons were sold 

 from Alston Moor, and from Snailbeach, in Shropshire. 



BARYTA, NITRATE OP. This salt is used in pyrotechny for making green 

 frc. The best mixture is nitrate of baryta 77 parts, sulphur 13 parts, chlorate of potash 

 5 parts, metallic arsenic 2 parts, charcoal 3 parts. Tho nitrate is prepared by dis- 

 solving carbonate of baryta in nitric acid. 



BARYTA, SULPHATE OP. This compound occurs native, forming the 

 mineral-species known variously as baritc, baryte, or barytas. Its comparatively high 

 density for a non-metallic mineral (4'7) led to its recognition by the older minera- 

 logists as spathum ponderosum, or terra ponderosa, and it is still commonly known as 

 heavy spar. The mineral frequently occurs in large crystals, usually tabular in form. 

 Massive varieties, common in many of tho lead-mines worked in the mountain lime- 

 stone of Derbyshire and Shropshire, are usually termed cawk ; certain columnar 

 varieties from Saxony are known to German mineralogists as Stangenspath ; and a 

 peculiar form occurring, near Bologna, in nodules which present a radiated struc- 

 ture, is called Bologna stone. This Bologna spar is notable for the phosphorescence 

 which it exhibits when heated ; the so-called ' Bologna Phosphorus ' was made by 

 powdering this stone, and cementing the powder into tho form of sticks, by means 

 of gum. 



Sulphate of baryta is composed of baryta Co - 63, sulphuric acid 34'37i with some- 

 times a little iron, lime, or silica. 



This salt of baryta is very extensively spread over various parts .of the British 

 islands. It might be obtained in very large quantities in Devonshire, Cornwall, and 

 other places, if tho demand for it sufficiently increased the price, so as to render the 

 working of it profitable. It is worked in Derbyshire, Yorkshire, Shropshire, the Isle 

 of Arran, and in Ireland. 



Cawk, or massive sulphate of baryta, was introduced by Josiah Wedgwood as an 

 important ingredient in his celebrated ' jasper ware,' and is still employed by the 

 potter in producing a similar fine paste. But the mineral is chiefly used as a pigment, 

 or rather for adulterating other pigments. 



The white varieties are ground after being heated and thrown into water, and the 

 heavy white powder is employed in adulterating white lead. On this account it is 

 very difficult to obtain correct returns. Tho production of 1871 was : 



Tons Cwts. 



Derbyshire 2,189 5 



Shropshire 595 1 



Northumberland 1,690 



Isle of Arran 400 



Cumberland . . . . . 57 15 



B ARYTES. Heavy spar, or native sulphate of baryta. 



BAS AliT. One of the most common varieties of trap-rock. It is a dark green 

 or black stone, composed chiefly of augite and labradorite-felspar, very compact in 

 texture, and of considerable hardness, often found in regular pillars of three or more 

 sides, called basaltic columns. Eemarkable examples of this kind are seen at the 

 Giant's Causeway in Ireland, and at Fingal's Cave, in Stiffa, one of the Hebrides. 

 Messrs. Chance (brothers), of Birmingham, at one time adopted the process of melting 

 the Rowley rag, a basaltic rock forming the plateau of the Rowley hills, near Dudley, 

 South Staffordshire, and then casting it into moulds for architectural ornaments, tiles 

 for pavements, &c. Not only the Rowley rag, but basalt, greenstone, whinstone, or 

 any similar mineral, might bo used. The material was melted in a reverberatory 

 furnace, and when in a sufficiently fluid state poured into moulds of sand encased in 

 iron boxes, these moulds having been previously raised to a red heat in ovens suitable 

 for tho purpose. The object to be attained by heating the moulds previous to their 

 reception of the liquid material is to retard tho rate of cooling; as the result of slow 

 cooling is a hard, strong, and stony substance, closely resembling the natural stone, 

 while tho result of rapid cooling is a dark brittle glass. 



BASZXiZCOir. Tho name given by the old apothecaries to a mixture of oil, wax, 

 and resin, which is represented by the Cerat reeina of the present day. 



