Combine first 4 ingredients in a large mixing bowl; mix well. Cut in shortening with a pastry blender until mixture resembles coarse meal.
Dissolve soda in buttermilk. Sprinkle buttermilk mixture evenly over flour mixture, stirring until dry ingredients are moistened . Turn dough out onto a lightly floured surface; knead lightly 2 to 3 times.
Pat dough to 1/4-inch thickness; cut biscuits with a 2-inch biscuit cutter. Place in 2 lightly greased 8-inch round cake pans. Bake at 450° for 10 minutes or until lightly browned .