Heat oven to 200 degrees. Use two 9x13-inch pans. Put half of corn in each. Mix brown sugar, butter, corn syrup and salt. Cook and stir (in saucepan) until it bubbles around the edge. Cook 5 minutes more. Add 1/2 teaspoon baking soda. Stir until foamy. Pour half over each pan. Stir until corn is covered. Bake 1 hour, stirring every 15 minutes. Variation: To make jello popcorn, omit brown sugar and add 2 small (3-ounce) boxes jello.