Fold in a white paper one drachm of Rochelle salts. In a blue paper a mixture of twenty grains of tartaric acid, and twenty-five grains of carbonate of soda. They should all be pulverized very fine. Put the contents of the white paper into a tumbler not quite half full of cold water, and stir it till dissolved. Then put the mixture from the blue paper into another tumbler with the same quantity of water, and stir that also. When the powders are dissolved in both tumblers, pour the first into the other, and it will effervesce immediately. Drink it quickly while foaming.