Lead oxid is regenerated from the basic lead carbonate obtained by heating in retorts to a little above 260°, and the carbon dioxid evolved can also be used again in the technical process. =253. Commercial Glucose and Grape Sugar.=—The commercial products obtained by the hydrolysis of starch are known in the trade as glucose or grape sugar. The former term is applied to the thick sirup obtained by concentrating the products of a partial hydrolysis, while the latter is applied to the solid semi-crystalline mass, secured by continuing the hydrolyzing action until the intermediate products are almost completely changed to dextrose. In this country the starch employed is obtained almost exclusively from maize, and the hydrolyzing agent used is sulfuric acid.[208] The products of conversion in glucose are chiefly dextrins and dextrose with some maltose, and in grape sugar almost entirely dextrose. When diastase is substituted for an acid, as the hydrolytic agent, maltose is the chief product, the ferment having no power of producing dextrose. In the glucose of Japan, known as midzu ame dextrin and maltose are the chief constituents.[209] Commercial glucose is used chiefly by confectioners for manufacturing table sirups and for adulterating honey and molasses. Commercial grape sugar is chiefly employed by brewers as a substitute for barley and other grains. In Europe, the starch which is converted into glucose, is derived principally from potatoes. The method employed in conversion, whether an acid or diastatic action, is revealed not only by the nature of the product, but also by the composition of its ash. In the case of diastatic conversion the ash of the sample will contain only a trace of sulfates, no chlorin, and be strongly alkaline, while the product of conversion with sulfuric acid will give an ash rich in sulfates with a little lime and be less strongly alkaline. The process of manufacture in this country consists in treating the starch, beaten to a cream with water, with sulfuric acid, usually under pressure, until the product shows no blue color with iodin. The excess of acid is removed with marble dust, the sirup separated by filtration, whitened by bleaching with sulfurous acid or by passing it through bone-black and evaporated to the proper consistence in a vacuum. The solid sugar, consisting mostly of dextrose, is made in the same manner, save that the heating with the acid is continued until the dextrin and maltose are changed into maltose. The product is either obtained in its ordinary hydrated form or by a special method of crystallization secured as bright anhydrous crystals. Solutions of dextrose, when first made, show birotation, but attain their normal gyrodynatic state on standing for twenty-four hours in the cold, or immediately on boiling.