(1) The practice in France, as carried on near Tours, at the white lead works using the Thénard process, is to calcine the best metallic lead in reverberatory furnaces built in the rock. These furnaces are five in number, with double fireplaces, four being constantly in operation, dealing with about 4000 lb. at a charge, and using bituminous coal as fuel. Each furnace is nearly circular in shape and about 11 feet in diameter, with a fire-place on each side of the hearth. The latter is constructed of fire-brick containing as little silica as possible, and is made hollow so as to retain the metallic lead when the heat has rendered it fluid. The products of combustion from the side fire-places, having heated the hearth and its contents, pass through an aperture in front of the charging door of the hearth, and thence go to furnish heat to an upper hearth where the conversion of the oxide into red lead takes place. A period of about 12 hours is occupied in the oxidation of a charge, which is repeatedly “rabbled.” Even then a considerable amount of the metallic lead remains unoxidised and is returned to the calciner with the next charge. Half the oxide is utilised for making white lead, as described in a later chapter, and the other half is converted into red lead by the method detailed hereunder. The crude oxide is pulverised in a small mill and separated from the unconverted metal. The mill takes the form of a flat circular cast-iron plate on which rotates a cast-iron muller. Water and an agitating arrangement are also provided. As the muller revolves the material undergoes comminution, and the small particles of oxide as formed are disturbed by the agitator and kept in suspension in the water, by the overflow of which they are continuously carried away into settling pits. The residual metallic lead is not pulverised, and of course never becomes suspended in the water, consequently it accumulates at the bottom of the mill, whence it is occasionally withdrawn for re-calcination. Sufficient oxide having collected in the settling pits, it is transferred to a shallow pan heated by the waste heat from the furnaces and is there rendered almost dry. In this state it is put into small square dishes made of sheet iron, and adapted to hold about 30 lb. each. A charge consists of a hundred of these dishes, which are placed in the heated furnaces at the end of each day. The roasting is repeated several times, and the product is accordingly known as “two fires,” “three fires,” &c. The material at this stage is lumpy and coarse, and has to undergo dry pulverisation, the fine particles as they are produced being drawn off by means of a pneumatic fan, and collected.