Preparation

The true nitrate (ternitrate), which is crystalline, soluble, and more active and irritant than the subsalt, is formed by dissolving the metalloid in nitric acid, and when this solution is poured into a large quantity of water it is decomposed, the subnitrate of bismuth falling as a white precipitate, and the supernitrate remaining in solution.

It was known as nitrate in an earlier Pharmacopoeia, and is still sometimes described under that name (Ringer); it has been termed also tris-nitrate, and hence some confusion between the properties of really different compounds.

Characters And Tests

The subnitrate is crystalline, but when well prepared, should be in smooth and fine powder. It is heavy, whitish in color, becoming yellowish-gray on exposure to light from the formation of some sulphide, or from the presence of silver; it is insoluble in water, soluble in nitric acid. It contains sometimes such an amount of acid as to effervesce when mixed with a carbonate (Martindale). A solution of bismuth subnitrate and sodium hydrate in water and glycerin is the Lowe test for sugar in urine: it has the advantage of being stable,

and is recommended by Dr. W. G. Smith (British Medical Journal, ii., 1879).