[978] Barium carbonate and sulphate are usually enumerated as occasional adulterants of bread, but there is no modern authentic instance of this.
§ 903. Chloride of Barium, BaCl22H2O 208 + 36; anhydrous, Ba, 65·86 per cent., Cl, 34·14; specific gravity, 3·75, is in commerce in the form of white, four-sided, tabular crystals; water dissolves about half its weight at ordinary temperatures, three-fourths at 100°. Its solution gives a white precipitate with sulphuric acid, quite insoluble in water and nitric acid.
The salt imparts a green hue to an otherwise colourless flame; viewed by the spectroscope, green bands will be visible. We may note that chloride of barium gives two different spectra—the one at the moment of the introduction of the salt, the other when the substance has been exposed for some time to a high temperature. This is caused by a rapid loss of chlorine, so that the first spectrum is due to BaCl2, with a variable mixture of BaCl, the second to BaCl alone.
§ 904. Baric Carbonate, BaCO3 = 197; specific gravity, 4·3; BaO, 77·69 per cent., CO2, 22·31, in its native form termed Witherite, is a dense, heavy powder, insoluble in pure water, but dissolving in acetic, nitric, and hydrochloric acids, the solution giving the reactions of barium.
A rat-poison may be met with composed of baric carbonate, sugar, and oatmeal, flavoured with a little oil of aniseed and caraway.
§ 905. Sulphate of Barium, BaSO4; specific gravity, 4·59; BaO, 65·66 per cent., SO3, 34·34 per cent., is a pure white powder when recently precipitated, absolutely insoluble in water, and practically insoluble in cold dilute acids. It is quite unalterable in the air at a red heat; on ignition with charcoal, it may be converted almost entirely into sulphide of barium; and by ignition with CaCl2 into chloride.
§ 906. Effects of the Soluble Salts of Barium on Animals.—One of the early notices of the poisonous characters of barium compounds was by James Watt,[979] who found that witherite, given to dogs, produced vomiting, diarrhœa, and death in a few hours. Sir Benj. Brodie[980] administered barium chloride, and noticed its paralysing effect on the heart. Orfila[981] made several experiments, and observed that 4 grms. of the carbonate produced death in dogs in periods varying from one to five hours; but in these experiments the gullet was tied. The later investigators have been Gmelin, Onsum, Cyon, and Böhm.[982] Gmelin found barium carbonate and barium chloride act in a very similar manner; and, indeed, it is improbable that barium carbonate, as carbonate, has any action, but, when swallowed, the hydrochloric and other acids of the stomach form with it soluble compounds. J. Onsum made eight experiments with both barium carbonate and chloride on animals. The respiration was quickened and, at the same time, made weak and shallow; the heart’s action was accelerated; the animals became restless: and there was great muscular prostration, with paralytic symptoms; convulsions did not occur in any one of the eight animals. He found, on post-mortem examination, the right side of the heart full of blood from backward engorgement; he describes a plugging of the small arteries with little fibrinous coagula, having an inorganic nucleus, with constant hæmorrhagic extravasations. Onsum seems to have held the theory that the baryta salts circulated in the blood, and then formed insoluble compounds, which were arrested in the lungs, causing minute emboli, just in the same way as if a finely-divided solid were introduced directly into the circulation by the jugular vein.
[979] Memoirs of the Literary and Philosophical Society of Manchester, 1790, vol. iii. p. 609.