Chapter LXXVII: Section 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 hydrosulphuric acid, which does not cause any change in barytic solutions. From the alkaline and magnesian salts it is distinguished by the effects of the alkaline sulphates, which have no visible action except on the barytic solution, and cause in it a heavy white precipitate, insoluble in nitric acid. From the chlorides of calcium and strontium, it is to be distinguished by evaporating the solution till it crystallizes. The crystals are known not to be chloride of calcium, because they are not deliquescent. The chloride of strontium (which resembles that of barium in many properties, but which must be carefully distinguished, as it is not poisonous), differs in the form of the crystals, which are delicate six-sided prisms, while those of the barytic salt are four-sided tables, often truncated on two opposite angles, sometimes on all four,—by its solubility in alcohol, which does not take up the chloride of barium,—and by its effect on the flame of alcohol, which it colours rose-red, while the barytic salts colour it yellow. The chloride of barium is known from other soluble barytic salts, by the action of nitrate of silver, which throws down a white precipitate.

Vegetable and animal fluids do not decompose the solution of chloride of barium, except by reason of the sulphates and carbonates which most of them contain in small quantities. But the action of its tests may be distinguished, although the salt has not undergone decomposition. In that case the most convenient method of analysis is to add a little nitric acid, which will dissolve any carbonate of baryta that may have been formed,—to filter and then throw down the whole baryta in the form of sulphate, by means of the sulphate of soda,—and to collect the precipitate, and calcine it with charcoal for half an hour in a platinum spoon or earthen crucible, according to the quantity. A sulphuret of baryta will thus be procured, which is to be dissolved out by boiling water, and decomposed after filtration by muriatic acid. A pure solution is thus easily obtained. Orfila has lately proposed a process more complex in its details, but the same in principle.[1380]