330 RESOURCES OP CALIFORNIA. 



chamber, and between the latter and the condensing chamber, 

 are built with open spaces, so that the heat, smoke, and fumes 

 can pass through. The ore is placed in the ore chamber in 

 such a manner as to leave many open spaces. The heat drives 

 off the sulphur and mercury of the ore in fumes, which in 

 passing through the condensing chambers deposit the mer- 

 cury, and the smoke and sulphur escape through the chimney. 

 Three days are usually allowed for drawing off the metal 

 from each charge, and then several days are allowed for the 

 furnace to cool off before the exhausted rock can be removed, 

 and a new charge put in, so that nearly a week is devoted to 

 a charge. The rock must be made white hot before the 

 quicksilver passes off in fumes. 



The furnace patented by Knox and Osborn may be consid- 

 ered the favorite, more of that than of any other kind being 

 in use. It is upright in form, about twenty feet high, receives 

 the ore at the top, and the heat from a hearth at the side. 

 It has a capacity of twenty-five tons, and eighteen tons are 

 roasted daily, implying that the ore remains four days in the 

 heat. At the end of six months the fire is allowed to burn 

 out, and the furnace is examined to see whether repairs are 

 necessary. Two cords and a half of wood are required daily. 

 The condensers are of cast iron, seven feet long, four feet 

 high, and two feet- wide, the inner end being fourteen inches 

 higher than the outer, to allow the soot to come down easily to 

 the door. Sixteen of these are required for condensing the 

 metal from eighteen tons of ore (averaging less than five per 

 cent, of metal) daily. They are all connected into one contin- 

 uous channel by goose-neck castings, and each with its goose- 

 neck weighs 2,700 pounds. Water trickles continuously over 

 all the condensers to keep them cool. By this furnace, and 

 perhaps by several others, ore yielding one-half of one per 

 cent, of metal, can be worked with a profit at the present 

 prices. 



254. Silver. Silver ores are found at many places in 

 California, but the only productive silver mines are east of the 



