Abstract: According to the instant invention fine and very fine granular zinc- and lead-containing oxidic byproducts are mixed with thermally inert additives and are hot briquetted with caking coal as a binder at a temperature of 490.degree..+-.40.degree. C. using sufficient carbon to reduce all of the metallic components in the byproducts. Then this mixture is briquetted and heated to more than 700.degree. C. and is maintained at this high temperature for a predetermined time to reduce, that is deoxidize, most of the oxidic components of the briquets, especially zinc, lead, and iron oxides. When the byproducts are not dry, which is standard with a wet scrubbing system for cleaning stack gases, the resultant slurry must be dried before it can be treated according to this invention. The carbon according to the invention is added as fine-granular caking coal in portions of at least 20% by weight. Preferably the portion is between 25% and 35% and up to 40%.

Abstract: The reducing power of gases liberated at the top of the charge of an industrial furnace is determined by a method wherein the energy radiated from the charge in the range, for example between 1 and 6 microns, covering the radiant energy emitted by the compounds CO.sub.2, CO, H.sub.2, and CH.sub.4 is continuously measured in a multiplicity of detection points distributed over the entire upper surface of the charge and outputs are formed corresponding to the energy radiated at each of the points. An energy image of the energy radiated at the points in the range is formed from the outputs. This energy image is converted into respective specific images for the compounds by isolating from the energy image for each detection point the radiant energy emitted by the compounds. The concentration of each of the compounds at each of the points is calculated from the intensity of the respective specific image.