Place yeast m hot water & let dissolve.
Jombine sugar, salt & 4 cups of flour in bowl, add sourdough starter & yeast water, mix & stir well.
Let rise until almost twice the bulk.
Mix baking soda and enough of remaining flour to make a stiff dough.
Knead on a floured dough board, add flour if needed.
Knead until smooth & satiny.
Shape into loaves on greased tins.
Let rise to double in size, brush with water.
Bake at 400 degrees for about 40-45 minutes.