Quinine salts are not compatible with mercuric chloride except under certain conditions, such as the absence of free acids. Mercuric chloride is an alkaloidal precipitant, but the precipitates formed are usually dissolved by hydrochloric acid, as in the next example.

The best way to compound this is to dissolve the quinine hydrochloride in 2 ounces of water and 1 drachm of the dilute acid, and add to the liq. hydrarg. perchlor.; dissolve the barium and calcium chlorides in 1 ounce of water, add the rest of the acid and the arsenic solution, mix with the quinine solution, and make up.

With Tannin

We have already remarked that tannin precipitates alkaloids. Here are good instances:

In No. I. there is a very copious precipitate of quinine tannate, and in No. II., after a time, a faint scum is observed, which is due to the same cause. The tannin in No. I. comes from the rose-petals, in No. II. from the cinnamon of tr. card, co., which was part of tr. chlorof. co., B.P. 1885. Filtration in the first case is unjustifiable; in the second the quantity of active material removed is so slight, and the gain in appearance so great, that filtration is advisable. A similar mixture with a little tincture of nux vomica and tr. card. co. showed a considerable precipitate, but with a purchased tr. card. co. none, the explanation being that the latter tincture was made with cinnamon oil instead of bark.

With Salicylates quinine salts form a precipitate of salicylate of quinine. The following are good examples:

In this case dissolve the citrate in an ounce of chloroform-water, and the salicylate and iodide in the rest contained in a measure or mortar, then add the citrate solution gradually to it, stirring assiduously in order to break up the precipitate thoroughly. Or place the three salts in a mortar, triturate with a little chloroform-water, then gradually add the remainder with continued trituration. The precipitate formed is diffusible though bulky.

The hydrobromic acid acts on the salicylate of sodium, precipitating salicylic acid. Salicylate of quinine is also formed if the quinine has been dissolved with the acid. The following is a good method of procedure: Dissolve 90 grains of the salicylate in 4 ounces of water in a mortar, and to this add the hydrobromic acid gradually, stirring constantly. Rub the quinine to fine powder, mix an ounce of water with it, dissolve the rest of the salicylate in 2 ounces of water, and add both to the mixture in the mortar.

In this case also a precipitate of salicylate of quinine is formed which is not dissolved by the addition of acids. These examples might be indefinitely multiplied. The dispenser should remember that in most cases where salicylates in aqueous solution are to be mixed with quinine or cinchona preparations it is desirable that a little mucilage should intervene to prevent the precipitated quinine salicylate from aggregating and adhering to the bottle. With 1 1/2 grain of quinine sulphate per ounce of mixture no precipitate of salicylate is formed, with 2 grains there is a slight precipitate.