Sift flour with salt, soda and baking powder. Add the batter alternately with milk. Add the grated rind and 4 tablespoons of the juice.
Pour into a greased loaf pan and bake for 45 minutes or until loaf tests clean.
For the glaze, combine the remaining 2 tablespoons grapefruit juice with powdered sugar. Remove bread from pan and poke holes in it. Pour the glaze over it. Let set, then wrap in foil or plastic wrap and let stand for a day for flavors to mellow.