with them, being by preference formed in a chamber in connection with the flue, by introducing a solution of chloride of sodium in spray, and by providing a sufficient excess of sulphurous acid beyond that required for forming the sulphite of lead. Air is also present, and a well known reaction takes place, yielding hydrochloric acid and sulphate of soda, the operation taking place at a part of the flue near enough to the furnace to be always at a red heat. The hydrochloric acid thus mixed with the gases and sublimate causes the formation of chloro-sulphite of lead, or other combinations of lead, sulphur, oxygen, and chlorine of variable constitution, depending on the proportions of the several constituents, but in most cases the product is a body which forms a white pigment of extremely good quality. Fig. 18 is an elevation of their improved cupola furnace; Fig. 19 is a corresponding vertical section; and Fig. 20 is a horizontal section as at the level of the principal tuyeres. This cupola furnace is formed with a deep hearth _a_ (like the American lead smelting cupola) having a siphon outlet _b_, for withdrawing molten lead when necessary. At a level a little above the siphon outlet _b_, an outlet _c_ for slag and scoria is provided, and the main blast tuyeres _d_ enter at about the same or a slightly higher level. With this arrangement, a considerable depth of melted lead is constantly maintained, and the choking of materials is thereby avoided at the level of the tuyeres. For a short distance above the main tuyeres _d_, the interior of the furnace is made with the sides _e_ moderately and gradually widening upwards, and is afterwards continued upwards of uniform diameter or width. The charging door _f_ is between 3 and 4 feet above the main tuyeres _d_, and the space above the charging door is crossed by two or more arched diaphragms _g h_, of brickwork, having irregular openings in them, there being doors _i k_ in the side of the furnace above each diaphragm, for inspection and cleaning. The purpose of these diaphragms is to cause the air, gases, and sublimate to become thoroughly intermixed and to ensure the complete combustion of any black smoke and the oxidation of any sulphide of lead that may be present.