King's American Dispensatory by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D., 1898
Syrupus Althaeae (U. S. P.)—Syrup of Althaea.
SYNONYM: Syrup of marshmallow.
Preparation.—"Althaea, cut into small pieces, fifty grammes (50 Gm.) [1 oz. av., 334 grs.]; alcohol, thirty cubic centimeters (30 Cc.) [1 fl troy ounce, 7 minim]; glycerin, one hundred cubic centimeters (100 Cc.) [3 fl troy ounce, 183 minim]; sugar, seven hundred grammes (700 Gm.) [1 lb. av., 8 ozs., 303 grs.]; water, a sufficient quantity to make one thousand cubic centimeters (1000 Cc.) [32 fl troy ounce, 391 minim]. Wash the althaea with cold water, then macerate it with four hundred cubic centimeters. (400 Cc.) [13 fl troy ounce, 252 minim] of water, previously mixed with the alcohol, during 1 hour, stirring frequently, and strain without expressing the residue. In the strained liquid dissolve the sugar by agitation, without heat, add the glycerin and enough water to make the product measure one thousand cubic centimeters (1000 Cc.) [33 fl troy ounce, 391 minim]. Mix thoroughly. Keep the syrup in well-stoppered, completely filled bottles, in a cool place"—(U. S. P.). This produces a syrup having an agreeable, but faint odor, and a yellowish color. Like syrup of acacia, it is extremely liable to ferment. The glycerin and alcohol present probably retard this change to some extent.