Dissolve soda in buttermilk, stirring well.
Place 2 cups cornmeal in a medium mixing bowl. Add buttermilk mixture, 2 tablespoons bacon drippings, beaten egg, and salt, mixing well.
Place remaining bacon drippings in an 8-inch cast-iron skillet; heat in a 425° oven 2 minutes or until very hot. Pour batter into hot skillet. Bake at 425° for 30 minutes or until golden brown. Cut into wedges, and serve hot.