TBEATMENT OF THE COMSTOCK ORES. 267 



staves of the barrels are sometimes made of six-inch stuff, without lining ; 

 sometimes, as shown in the figure, the staves are 2 or 3 inches thick, with an 

 interior lining of blocks 4 or 5 inches square, and 3 or 4 inches thick, and so 

 placed in the barrel that the wear is on the end of the grain. This lining can 

 be removed when worn out. The staves of the barrels are bound with iron 

 hoops, the ends of which are drawn together as shown in Fig. 5. The ends 

 of the barrel arc strengthened by a four-armed flange of cast iron. The bar- 

 rels are caused to revolve by cog-gearing, the teeth being put on in segments, 

 around the end of the barrel ; or by belting, or, as at Austin, by friction-gear. 

 The barrel, of which a section is shown in Fig. 3, shows a contrivance for 

 admitting steam to the pulp through the trunnion. This arrangement, not 

 very common, consists of a steam-pipe, p, Fig. 6, which enters the trunnion 

 and fits smoothly against the end of another pipe, q, that passes through the 

 end of the barrel and admits the steam to the interior. The interior pipe, q, 

 revolves with the trunnion, while the exterior pipe, p, is fixed and remains 

 without motion. The trunnion, T, is keyed to the flange already referred to. 

 The barrels are charged with about 2,000 pounds of ore, mixed with 

 water enough to make a moderately thick paste. Before adding quicksilver, 

 the charge is revolved for two or three hours in the barrel with several hun- 

 dred pounds of scrap-iron. The object of this is to effect a partial reduction 

 of the chlorides present, which would otherwise be performed at the expense 

 of the quicksilver. The chloride of silver is partly reduced by the metallic 

 iron, and is subsequently amalgamated by the quicksilver. The same is true 

 of the lead and copper. Quicksilver is added according to the richness of 

 the ore, usually varying from 250 to 600 or more pounds. The barrel is run 

 two hours, at twelve or fifteen revolutions per minute, and then examined that 

 the consistency of the paste may be ascertained. If the latter is too thin, the 

 quicksilver settles on the bottom. This condition is remedied by the addition of 

 more roasted ore ; while if too thick for the most favorable distribution of the 

 quicksilver, more water is added. The barrel is then allowed to revolve again 

 for fourteen hours, making fifteen revolutions per minute. The whole time 

 occupied from the charging to the discharging of the barrel is eighteen or 

 twenty hours. When the amalgamation is complete, the paste is thinned by 



