GAS FURNACES

are used for a variety of industrial operations where precision and exact control are required. The high cost of gas as compared with coal or coke is offset to a,large extent by a saving in labor, and by improvement in the product due to uniformity of results, cleanline , convenience and reliability. A great many different types of furnaces are constructed, but they may be divided into two main cla es—reduction or oven furnaces and oxidizing or muffle furnaces. In the former type the products of combustion enter the furnace chamber, while in the latter, the furnace consists of a fire-clay chamber, the outside of which is heated by the burning gases. Gas furnaces are widely used in different branches of the metallurgical industries. Special furnaces for hardening steel and annealing other metals are made with a traveling carrier which pa es continuously through the furnace, carrying with it the metal under treatment. The carrier consists of an endle chain, the links forming small cast iron trucks, holding fire clay slabs. The iron trucks travel below the furnace, so that only the fireclay slabs are subjected to high temperature. Many gas furnaces are used in the United States mints for annealing gold and silver, a rotary cylindrical type being common. Steel tubes and shafts are annealed, and tools, chain links, pens, nuts, bolts, screws and springs are hardened and tempered in gas furnaces, various modifications of endle chains or rotary conveyors being used to render the work continuous. Gas furnaces or ovens are also used for soldering, brazing, a aying and japanning. In all these furnaces a blast burner, or, series of burners, is used, in which air, under pre ure inducts the gas which is thus injected into the combustion chamber mixed with the proper proportion of air to insure correct burning.