After the furnace has been properly heated, 100 kg. of lead melted in K₁ are poured in through the cast-iron pipe P, and after that about 200 kg. of pure, thoroughly melted galena from K₂. Ore containing 70 to 80 per cent. Pb must be used for this purpose. The blast of air is then introduced into the molten galena, and from 1000 to 3000 kg. of ore is gradually charged in through the tube A. During this operation black fume (PbS) collects in the condensation chamber. All outlets are closed against the external air. If the air blast is properly adjusted, nothing but black fume is produced; if it begins to become light colored, charging is discontinued and the blast of air is shut off. Lead is then tapped through O₂, which is about 0.2 meter above the hearth, so there is always a bath of lead in the bottom of the furnace; but it is advisable now and then to tap off some through O₁, so as gradually to heat up the bottom of the furnace. Hearth accretions are also removed through O₁. The lead is tapped off through O₂ until matte appears. The tap hole is then closed, the tuyere is lowered and the blast is turned into the lead in order to oxidize it and completely desulphurize the sulphur combinations, which is quickly done. The oxide of lead is scorified as a very fusible slag, which is tapped off through O₂, and more ore is then charged in upon the lead bath and the cycle of operations is begun again. PART VII DUST AND FUME RECOVERY FLUES, CHAMBERS AND BAG-HOUSES DUST CHAMBER DESIGN BY MAX J. WELCH (September 1, 1904) Only a few years ago smelting companies began to recognize the advantage of large chambers for collecting flue dust and condensing fumes. The object is threefold: First, profit; second, to prevent law suits with surrounding agricultural interests; third, cleanliness about the plant. It is my object at present to discuss the materials used in construction and general types of cross-section. Most of the old types of chambers are built after one general pattern, namely, brick or stone side walls and arch roof, with iron buckstays and tie rods. The above type is now nearly out of use, because it is short-lived, expensive, and dangerous to repair, while the steel and masonry are not used to good advantage in strength of cross-section.