Soak beans overnight in a large bowl in the water. Place beans with soaking water in a large kettle, add baking soda; bring to boiling; lower heat and continue to boil for 10 minutes.
Drain in colander over large bowl, reserving liquid. Place salt pork, onion and beans in a 2 quart bean pot or casserole. Combine molasses, sugar, dry mustard, pepper and 1 cup of the reserved liquid. Pour over beans, stir thoroughly. Add just enough reserved liquid to cover beans, maybe a cup or so.
Cover casserole. Bake in a slow oven, 300° F for 2 hours. Add remaining 1 cup liquid and stir thoroughly. Continue baking an additional 1 1/2 to 2 hours or until beans are tender and liquid is absorbed. Bake uncovered the last hour, if you wish.
Servings: 4