" Take of water, ten pounds; pure subcarbonate of potassa, one ounce. Dissolve, and expose the solution to a current of carbonic acid gas, arising from carbonate of lime in powder, three ounces; sulphuric acid, three ounces; and water, three pounds; gradually and cautiously mixed. The chymical apparatus of Dr. Nooth is well adapted for this preparation. But if a larger quantity of the solution be required, an apparatus which will admit of a sufficiently great pressure should be employed. The solution must be preserved in well-stopped vessels."

This solution is seldom sufficiently impregnated with the acid when made on a small scale; but in the great way, and with an apparatus from which a much greater pressure is obtained, a solution is prepared for sale, which contains a very large quantity of uncombined carbonic acid.

Qualities. - When properly prepared, it has a pungent, acidulous taste, and reddens tincture of litmus; is perfectly transparent, sparkles when poured into a glass, and effervesces violently with all the acids.

1 Annales de Chimie, t. xv. p. 33.

Medical properties and uses. - This solution of the acidulous bicarbonate is tonic and diuretic. It has also been regarded as lithontriptic, and is much used in calculous cases; but its properties as a solvent of calculi, if it possess any, must depend upon the potassa it contains, and, thence, the more completely it is impregnated with carbonic acid, the more its lithontriptic powers must be diminished. There is, however, reason for believing that even pure potassa when taken into the stomach exerts no influence on ready-formed calculi, and consequently its operation, even as a palliative or preventive, is confined to the stomach, where it neutralizes the acid that always prevails there in calculous affections, and relieves many of the uneasy symptoms it occasions. In this view the' solution of the acidulous bicarbonate is a grateful mode of exhibiting potassa, as its acrimony is destroyed by its combination with the acid, which is nevertheless so weak as not to interfere with its operation as an alkali. On the same principles it proves beneficial in dyspepsia and gout, and forms with lemon-juice an effervescing draught still preferable to that prepared with the bicarbonate.

The dose in calculous affections is f viij. taken three or four times a day.