This is prepared by mixing solutions of nitrate of bismuth and carbonate of soda, and washing and drying the resulting precipitate. By double decomposition between the two salts, nitrate of soda and carbonate of bismuth are produced; the former, which is soluble, being retained in solution, and the latter thrown down. The process would seem to be very simple; but, on the contrary, as given in the U. S. Pharmacopoeia, it is very complex, being rendered so by the necessity of providing against the presence in the preparation of a portion of arsenic, which is often contained in the metal as found in commerce.

Subcarbonate of bismuth is in the form of a white or yellowish-white powder, inodorous and tasteless, of the sp. gr. of about 4, and insoluble in water. It should not give evidence of the presence of arsenic, when mixed with sulphuric acid, and treated by Marsh's test.

It was introduced into the practice of medicine as a substitute for the subnitrate, the virtues of which it possesses, with less tendency to disturb the stomach. It is thought by M. Fannon, of Brussels, to have the advantage over the subnitrate of being more readily dissolved by the gastric juice; but this might be a doubtful recommendation when large doses are given, especially in an acid state of the gastric liquids, as a highly irritant salt might thus be substituted for a perfectly bland powder. The probability is that, as in the case of the nitrate, its efficacy in the complaints of the stomach and bowels, in which chiefly it is given, depends on this very insolubility, which, with its weight, cause it to spread over the mucous surface, and give to this a protective coating against the irritant liquids of the primae vise. The dose is from fifteen to forty grains, given three times a day before meals, and gradually increased if deemed advisable. It should not be administered in connection with acids.