Within the last few years medicines have been somewhat extensively used in the form of granular effervescing powders, prepared by a peculiar process.

Their basis consists of a combination of tartaric and citric acids with bicarbonate of soda, reduced to fine powder, and then mixed and subjected to heat, by which a mass is formed capable of being passed through a coarse sieve, and the mixture is thus made to assume a granular form. The citric acid is essential to yield up its water of crystallization in order to reduce the whole to a pasty condition; frequent stirring must be employed when the mixed powder is heated.

During this process of granulation, only a small amount of carbonic acid is given off, and hence, when the prepared salts are dissolved in water, brisk effervescence ensues.

Many powerful remedial agents may be united with the mixed powder during granulation, and the following are the more important of these preparations.

The basis itself is called Citro-Tartrate of Soda; with this 25 per cent. of sulphate of magnesia is often mixed to increase the aperient action; and to the same basis the following salts may be united: -Citrate of Iron, Citrate of Iron and Quinine, Citrate of Quinine, Iodide of Iron, Carbonate of Iron, Citrate of Lithia, Nitrate of Potash, Carlsbad, Pullna, and Vichy Salts in varying proportions.