Add soda to molasses and beat thoroughly; add milk, shortening, ginger, salt, and flour. Enough flour must be used to make mixture of right consistency to drop easily from spoon. Let stand several hours in a cold place to thoroughly chill. Toss one-half mixture at a time on slightly floured board and roll lightly to one-fourth inch thickness. Shape with a round cutter, first dipped in flour. Bake on a buttered sheet.