As used in this subpart, all terms not defined herein shall have the meaning given them in the Act and in subpart A of this part.

(a) Primary lead smelter means any installation or any intermediate process engaged in the production of lead from lead sulfide ore concentrates through the use of pyrometallurgical techniques.

(b) Sintering machine means any furnace in which a lead sulfide ore concentrate charge is heated in the presence of air to eliminate sulfur contained in the charge and to agglomerate the charge into a hard porous mass called sinter.

(c) Sinter bed means the lead sulfide ore concentrate charge within a sintering machine.

(d) Sintering machine discharge end means any apparatus which receives sinter as it is discharged from the conveying grate of a sintering machine.

(e) Blast furnace means any reduction furnace to which sinter is charged and which forms separate layers of molten slag and lead bullion.

(f) Dross reverberatory furnace means any furnace used for the removal or refining of impurities from lead bullion.

(g) Electric smelting furnace means any furnace in which the heat necessary for smelting of the lead sulfide ore concentrate charge is generated by passing an electric current through a portion of the molten mass in the furnace.

(h) Converter means any vessel to which lead concentrate or bullion is charged and refined.

(i) Sulfuric acid plant means any facility producing sulfuric acid by the contact process.