Chap- IV. Earths and Earthy Sails.

373

count of the very strong attraction which subsists between thesulphuric acid and baryta.

The sulphate of baryta may be decomposed,

1. By compound affinity, by means of carbonate of pot-ass or muriate of lime.

Carbonate of potass is capable of effecting this decomposi -tion, either in the dry or humid way. Klaproth boils sixteenounces of finely powdered sulphate of baryta with 32 ouncesof purified carbonate of potass, and five pounds of water, foran hour in a tin kettle, constantly agitating the mixture, andrenewing the water as it evaporates. He then allows it tosettle, pours off the fluid, which is a solution of sulphate ofpotass, and edulcorates the precipitate with plenty of water.He next dissolves the carbonate of baryta, which it contains,hi muriatic acid. The portion of sulphate which is not de-composed, may be treated again in the same manner.

On the other hand, Van Mons mixes equal parts of sul-phate of baryta and carbonate of potass with one-fourth oftheir weight of charcoal, all in powder, and heats the mixtureto redness in a crucible. When it cools, he washes out thesulphate and sulphuret of potass, with water, then boils theresiduum with a little potass, and washes it again. The car-bonate of baryta thus obtained he dissolves in muriatic acid.

But by these methods of decomposing the sulphate ofbaryta, we do not get rid of the metallic substances which it of-ten contains, and which render the muriate thus prepared unfitfor medical use. The metalline muriates may, however, beexpelled, according to Westrumb, by heating the salt to red-ness as Jong as any fumes arise. The pure muriate of barytais then to be dissolved in water, and crystallized. Gbttling,with the same intention, of getting rid of metalline substances,chooses sulphate of baryta, perfectly colourless, and treats itwith muriatic or nitro-muriatic acid before he proceeds to de-compose it.

La Grange has proposed a new method of decomposing thesulphate of baryta, by means of muriate of lime, which heprepares from the residuum of the decomposition of muriateof ammonia by lime, by dissolving it in a small quantity ofhot water, and evaporating it to dryness. He mixes equalparts of this muriate with sulphate of baryta in powder, andprojects it by spoonfuls into a crucible previously heated toredness. When it is all in complete fusion, he pours it outupon a polished stone previously heated. The matter, whichcracks as it cools, has a whitish-grey colour, and is very hard 3