Of all the salts of quinine the sulphate is most used. It is one of the least soluble of the salts. Other salts are prescribed either owing to their combination with a special acid (such as valerianic acid) or because the prescriber has some special reason for preferring them. It may be useful to summarise here the properties of the more important salts of the alkaloid:

Quinine, C20H21N2O2,3H2O. Practically insoluble in water.

Acetate. Soluble in water, but, like caffeine citrate, hydrolyses with separation of quinine hydrate. Contains 84 per cent, of quinine. Arsenate. Soluble in hot, sparingly soluble in cold, water. Contains 69.4 per cent, of quinine. Benzoate. Soluble 1 in 373 of water. Contains 72 1/2 per cent, of quinine. Carbolate. The salt generally sold as such is a sulphocarbolate containing 75 1/2 per cent, of quinine. More soluble than the sulphate. Chlorhydrophosphate. Soluble I in 2 of water. Contains 50 per cent. of quinine. Chlorhydrosulphate. Soluble in a little over its own weight of water.

Contains 74.2 per cent, of quinine. Citrate. Two salts- (1) neutral or dibasic is less soluble in water than the sulphate (about 1 in 1,000 or less), and contains 72 1/2 per cent, of quinine; and (2) the acid or monobasic citrate, soluble 1 in 650 of water. The former is the commercial salt. Glycerophosphate. Soluble 1 in 353 of water. Contains 6 per cent. of quinine. Hydriodide or Iodide. (1) Neutral, soluble about I in 900 of water ;

(2) acid, soluble 1 in 20 of water. Hydrobromide. (1) Neutral (the commonly used salt), soluble 1 in 45 of water, contains 76 per cent, of quinine ; (2) acid salt, soluble 1 in 7, contains 60 per cent. Hydrochloride. (1) Neutral, soluble I in 36 of water, contains 82 per cent, of quinine ; (2) acid salt, soluble less than 1 in 1 of water, and contains 72 per cent, of quinine. Hypophosphite. Soluble 1 in 250 of water. Lactate. Soluble about 1 in 10 of water. Contains 78 per cent, of quinine. Phosphate. The English salt contains 76 per cent, of quinine, the German contains 79 per cent.- i.e., 1 of phosphoric acid to 2 of quinine, the English being 2 to 3. The English is soluble 1 in 420 of water, the German 1 in 784. Salicylate. Soluble 1 in 225 of water. Contains 70 per cent. of quinine. Sulphate. (1) Neutral or B.P. (the 'quinine' of the public), soluble (into which the former is converted on mixing with sulphuric acid and water), soluble 1 in 11 of water, and contains 59 per cent of quinine. Tannate. Insoluble in water, therefore tasteless.

Contains 20 per cent. of quinine.

1 in 800 of water, contains 73.5 per cent, of quinine ; (2) acid salt Tartrate. The commercial or neutral tartrate is less soluble in water than the sulphate, but the acid tartrate is very soluble. Valerianate. Soluble I in 110 of water. Contains 51 per cent, of quinine.

For the dispensing-counter it is a good plan to rub down quinine sulphate in a mortar, so as to get it into smaller bulk, when it is more easily weighed. Dispensing-solutions should not be made stronger than 4 grains in 1 fluid drachm, 4 minims of dilute sulphuric acid being used to dissolve the sulphate.

If a prescription contain nothing which will dissolve the quinine sulphate, the salt should merely be rubbed down, suspended in the water, and a 'shake the bottle' label used. If you know that the prescriber wishes acid to be added, add it and note the fact on the prescription. Never dissolve quinine sulphate with hydrochloric acid if that acid is not ordered : such a solution is not fluorescent, and if the prescription happens to have been dispensed before with sulphuric acid, the patient may notice the difference.

Quinine sulphate is soluble 1 in 40 of glycerin, and this combination has been suggested as a means of getting over the acid difficulty, also to give the dose in sweet spirit of nitre, an ounce of which dissolves 20 grains of quinine sulphate. This latter combination is used in fevers. Such suggestions are now out of date, as the readily soluble hydrochloride is better pharmaceutically and therapeutically.

Quinine salts are prescribed on the Continent in combination with extract of liquorice. In this case first dissolve the extract in ten times its weight of water, then add the solution of quinine, as both the alkaloid and the acid tend to throw out a dirty-looking precipitate of glycyrrhizin.