204 MIKING mDUSTRT. 



length, is the fire-place and ash-pit. Above it is an arch, from the top of which 

 the flues, y^ lead to the stack. Some retorts are set in such manner that tempo- 

 rary brick-work may be built up in front of the door during the sublimation to 

 prevent the escape of heat. Dampers are so arranged that the heat may be 

 applied more or less vigorously to the front, back, or middle of the retort 

 according to its requirements. 



The retort is furnished with amalgam trays, illustrated by Fig. 4, Plate 

 XVIII, having a semi-circular shape adapted to the bottom of the cylinder. 

 There are usually several of these, and they are of a size convenient for handling 

 when loaded with amalgam. In many mills, however, they are not used, the 

 amalgam being charged directly upon the bottom of the retort. Before intro- 

 ducing the amalgam into the tray or the retort the surface of the latter is covered 

 with a thin wash of clay or slime, such as is produced in stamping, to prevent 

 the metal from adhering to the iron. Whiting, wood ashes, or paper are some- 

 times used for this purpose and recommended as being less likely to choke the 

 pores of the bullion. The amalgam being placed in the retort and the door 

 properly adjusted and luted with clay, the fire is lighted and heat is applied, at 

 first very gently and afterward gradually increased. If heated too strongly 

 at first the surface of the bullion in contact with the retort is liable to fuse 

 and prevent the escape of quicksilver from the central part. The charge 

 for a cylinder of the dimensions above described is about 1,200 pounds. The 

 firing usually occupies about eight hours. When quicksilver ceases to vola- 

 tilize, the retort is gradually cooled down and the bullion withdrawn. A bout 

 one-sixth of the original charge usually remains, or 200 pounds of crude bul- 

 lion from 1,200 pounds of amalgam. This retorted amalgam is broken up, 

 melted, and cast in ingots ready for market. The melting furnace commonly 

 used for this purpose is shown in Figs. 5 and 6 on Plate XVIII. Fig. 5 is a 

 front elevation of a double furnace. The cover of the left-hand furnace is re- 

 moved, showing the size and position of the flue. Fig. 6 is a transverse 

 section on the line A B in Fig. 5. Fig. 12 shows the tongs for removing the 

 melting pot. Fig. 10 shows the form of ingot mold usually employed. The loss 

 of \\ eight in melting the retorted amalgam, or crude bullion, is between two and 

 three per cent. The ingots, when obtained, are assayed, and their fineness, ex- 

 pressing the proportions of gold and silver contained in thousandths, as well as 



