Acid Drops

From 1922:

1 lb. loaf sugar, 1 cupful water, 1 tablespoonful vinegar, 1 tablespoonful lemon essence, ¼ oz. tartaric acid. Put the sugar, water and vinegar in a saucepan and boil till it snaps like glass, add a few drops of lemon essence and the tartaric acid; mix well, turn out and cut into small bullets and flatten with thumb and finger.