Bismuth Salts and Iodides are sometimes prescribed together, with the result that patients and some dispensers become alarmed by the changes that occur in the appearance of the mixtures owing to the formation of bismuth oxyiodide - a brownish-red substance, which, happily, is a therapeutic agent, and may act quite as well as the ingredients from which it is formed. The following are examples of prescriptions in which the change occurs:

The formation of bismuth oxyiodide is slow, being hindered by the mucilage in I., and doubtless it is proportionate to the amount of bismuth subnitrate which gets into solution. Mist, bismuthi sedativa is a Guy's Hospital preparation (see IV.).

The powders in IV. are mixed together in a mortar and made into a thin cream with a little water, allowed to stand for two hours, and the morphine solution added. At this stage the mixture is well stirred, and the potassium iodide (in a drachm of water) and tincture of belladonna added as soon as effervescence ceases. No. III. is a South African prescription of recent date, and a new combination. It makes quite a pretty mixture in this way: Make a mucilage with 12 grains of tragacanth and about 6 ounces of the chloroform-water and with this rub down the bismuth salicylate perfectly smooth; then add, in three or four portions, the potassium iodide dissolved in about 1 ounce of the chloroform-water, shaking well after each portion has been added; finally add the remaining ingredients, and make up. The bismuth oxyiodide, slowly formed, is very fine, and easily shaken up and uniformly distributed.

Bismuth Salicylate is one of a class of compounds (salol is another) which do not mix readily with water. They are best dealt with by placing in a dry mortar and triturating with sufficient undiluted mucilage of acacia to make a thin cream, then gradually stirring in the water. If any spirit is available, mix it with the bismuth salicylate.

In No. I. rub the salicylate very fine in a mortar, making it into a smooth cream with the spirit of chloroform, thinning it with the water. Separately dissolve the bromide in half the water, and to this add fresh mucilage of acacia equivalent to the powder ordered; pour in the salicylate mixture, shake, and make up. Bismuth salicylate is soluble in ammonium-citrate solution, so that No. II. is a 'smooth'mixture.

Liquor Bismuthi

The original of this preparation is a solution of bismuth citrate in a slightly alcoholic aqueous solution of ammonium citrate. The 1867 B.P. liquor contained ammonium nitrate and citrate, and was much stronger in bismuth than the original; a change was made in 1885, the solution becoming one of ammonio-citrate of bismuth; and in 1898 the manner of making the solution was altered, its composition remaining the same, substantially, there being no excess of ammonium citrate. Yet there is a difference, for the solution frequently turns quite milky, owing to separation of bismuth citrate, hence manufacturers are inclined to modify the preparation so as to make it permanently clear. These facts account for some of the differences which are reported in the appearance of bismuth mixtures.

On compounding this prescription with the B.P. 1898 solution freshly prepared, the result was a mixture containing a copious white deposit of bismuth carbonate. This result cannot be avoided. With the 1867 liquor a clear mixture was obtained, because the excess of citrate of ammonium in it prevents the precipitation of bismuth citrate.

Bicarbonates do not affect Schacht's liquor, yet mixture a rapidly becomes perfectly thick, although neither ammonium carbonate or hydrate nor potassium bicarbonate has this effect immediately. The following reaction appears to take place:

2AmHO + 2KHCO3 = Am,CO3 + K,CO3 + H2O.

This is followed by interaction between the dissolved bismuth citrate and the potassium carbonate, with precipitation of bismuth oxycarbonate. Even aromatic spirit of ammonia produces a precipitate in Schacht's solution in the course of a few days, and ammonium carbonate has a similar effect; but ammonium carbonate and ammonia solution produce a faint opalescence in Schacht's liquor in an hour or two. More ammonium citrate prevents this. Mixture b becomes milky at once, and the precipitation is most abundant with dispensing solution of bicarbonate because it contains carbonate.

No. I. is substantially bismuth hair-dye. On compounding it there is nothing abnormal-looking about it, but at the end of a day a yellowish-brown precipitate begins to fall, and this becomes darker on exposure. The precipitate is bismuth sulphide. No. II. mixture turns greenish in colour, owing to the presence of black bismuth sulphide, which doubtless arises from some sulphuretted compound in the glycerin of pepsin reacting with the bismuth precipitated. The opium dose is excessive.

This can be made into a clear mixture by first mixing the tinct. ferri perchlor. with the phosphoric acid in a glass measure, then adding the two tinctures; afterwards gradually adding the liq. bismuthi, constantly stirring with a glass rod; and, lastly, adding the potassium bromide in fine powder.