Bismuth Carbonate

The normal salt is unknown; a basic carbonate, (BiO)₂CO₃, is precipitated, however, as a white powder when sodium carbonate is added to a solution of bismuth nitrate. When dried it retains from one-half to one molecule of water. The density of the product varies with the concentration and temperature of the solutions; the product of lowest density is obtained at 45° C. The basic carbonate may also be prepared from a solution of bismuth nitrate containing mannitol. An electrolytic method has also been described. The electrolyte is a 3 per cent, solution of sodium chlorate charged with excess of carbon dioxide; the anode is of bismuth and the cathode of carbon, zinc, iron or aluminium.

It has been suggested that the composition of basic bismuth carbonate is in most cases more accurately represented by the formula CO(O.BiO)₂.

It is insoluble in water even in the presence of carbon dioxide; it is also insoluble in alkalis, but is slightly soluble in alkali carbonates. From these solutions it may be reprecipitated either by boiling, or by the addition of an alkali. It darkens in colour on exposure to light. It is used principally in medicinal preparations.

Basic bismuth carbonate occurs naturally in the minerals bismutite, basobismutite and bismutosphaerite.