Quinine benzoate is a sparingly soluble salt (see page 70) and may be formed by interaction, as in the following case:

Here the sodium benzoate and quinine salt in the tincture interact, quinine benzoate being precipitated, and at the same time the acid in the strychnine solution liberates a little benzoic acid from the sodium benzoate.

With Bicarbonates

When these are ordered with quinine in a prescription, the bicarbonate should be dissolved in the water, and the quinine rubbed to a fine powder and suspended in the liquid. The addition of a little mucilage has the effect in these cases of suspending the quinine and preventing it from adhering to the sides of the bottle.

With Chlorine, quinine salts generally yield yellow solutions. A familiar example of this is the late Dr. Burney Yeo's mixture (No. I.):

If No. II. is dispensed in the order given, the mixture becomes of an intensely yellow colour. It is colourless if dispensed as follows:(1 Mix the quinine sulphate with 2 ounces of camphor-water, and add the dilute acid and spirit of nitre; (2) dissolve the chlorate in 2 ounces of camphor-water, add the spirit of chloroform, mix with the quinine, and make up. Both the ethyl nitrite and the potassium chlorate appear to take part in the coloration, chlorine being liberated from the chlorate by the acid, and the fact that a few drops of ammonia added to a little of the mixture gives the green colour peculiar to thallioquin, while the same colour is produced as in the Burney Yeo mixture, shows that the chlorine is responsible for the coloration. It would, however, be wrong to assume that a chlorine derivative of quinine is formed, as it is far more likely that an oxidation-product results, cinchona alkaloids being prone, under certain conditions of oxidation, to yield a chinoline-carboxylic acid, which is of a yellow colour.

These mixtures might repay chemical investigation, and it will be useful for those interested in that direction to refer to The Chemist and Druggist, 1897, 1. 136, for reports on different methods of dispensing No. II. mixture.