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 own experience and information obtained at other works, he is satisfied the risk is very much greater among the intemperate than among sober workmen.

CHAPTER XIX.

OF POISONING WITH BARYTA.

Baryta and its salts, the last genus of the metallic irritants which requires particular notice, are commonly arranged among earthy substances, but on account of their chemical and physiological properties, may be correctly considered in the present place. These poisons are worthy of notice, because they are not only energetic, but likewise easily procured, so that they may be more extensively used, when more generally known.

I.—Of the Chemical Tests for the preparations of Baryta.

Three compounds of this substance may be mentioned, the pure earth or oxide, the muriate, or chloride of barium, and the carbonate. The pure earth, however, is so little seen, that it is unnecessary to describe its chemical or physiological properties.

The Carbonate of Baryta is met with in two states. Sometimes it is native, and then commonly occurs in radiated crystalline masses, of different degrees of coarseness of fibre, nearly colourless, very heavy, and effervescing with diluted muriatic acid. It is also sold in the shops in the form of a fine powder of a white colour, prepared artificially by precipitating a soluble salt of baryta with an alkaline carbonate. It is best known by its colour, insolubility in water, solubility with effervescence in muriatic acid, and the properties of the resulting muriate of baryta.

The Muriate of Baryta, or chloride of barium, is the most common of the compounds of this earth, having been for some time used in medicine for scrofulous and other constitutional disorders. It is procured either by evaporating the solution of the carbonate in hydrochloric acid, or by decomposing a more common mineral, the sulphate, by means of charcoal aided by heat, dissolving in boiling water the sulphuret so formed, and decomposing this sulphuret by hydrochloric acid.

It is commonly met with in the shops irregularly crystallized in tables. It has an acrid, irritating taste, is permanent in the air, and dissolves in two parts and a half of temperate water.

The solution is distinguished from other substances by the following chemical characters. From all other metallic poisons hitherto mentioned, it is easily distinguished by means of hydro-sulphuric acid, which does not cause any change in barytic solutions. From the alkaline and magnesian salts it is distinguished by the effects of the