To determine residual carbon dioxide in baking powders resulting from sodium and calcium carbonates or unreacted sodium bicarbonate. Calcium carbonate is used as a diluent, to keep sodium bicarbonate and leavening acid separated. Generally used in combination with starch, calcium carbonate is also a source of calcium for nutritional fortification. A strong acid, e.g., sulfuric acid, is required to neutralize carbonate sources. This method can be used for single- or double-acting baking powders that contain various leavening ingredients such as sodium aluminum sulfate, sodium acid pyrophosphate, sodium aluminum phosphate, monocalcium phosphate, dimagnesium phosphate, or organic acids. In this method, baking powder is heated to cause most of the sodium bicarbonate to react with the leavening acids. Residual carbon dioxide, released by sulfuric acid, is generally associated with other carbonate sources. Therefore, excessive sodium bicarbonate, not neutralized by the leavening acids, will also contribute to the residual carbon dioxide.