28 HULLKTIN lli, lINiri:',i) STATES NATIONAL MUSEUM. 



galeua will frequently be foiiiul patches of pyrargyrite, hardly to be 

 distiuguished from the galena, except by the closest inspection. The 

 lump galena is very rich in silver, averaging about 200 ounces per ton, 

 select specimens running as high as 800 to 900 ounces per ton. The 

 average amount of lead in the ore is 2 per cent. The average amount 

 of silver in the ores treated is about 100 ounces per ton, of which HO per 

 cent, is saved in the mill, 3 ounces remain in the tailings, and 1 ounce 

 is lost in the treatment. 



In this mill the ore and salt are dried in revolving dryers and stamped 

 separately, the ore passing a No. 30 screen, and the salt a No. 16. 



There are 80 ore stamps weighing 860 pounds each, making 06 drops 

 of about 8 inches per minute, crushing 65 to 75 tons per 24 hours. 

 There are 10 salt stamps weighing 430 iiounds, making 94 drops per 

 minute. By means of an automatic discharge the proper percentage of 

 the dry stamped salt is added to the dry stamped ore as it is being ele- 

 vated in buckets from the stamps to the top of the roasting furnace. 



The roasting furnace, of the Stetefeldt pattern, is a plain square stack, 

 46 feet 6 inches high, 8 feet square at the bottom and 4 feet square at 

 the top. At one side of the stack is a fireplace for wood and the flame 

 from this fire passes into and through the stack. Near the top of this 

 main stack a return flue 3 feet square, heated by an auxiliary fire, 

 leads to a series of dust chambers. The mixed ore and salt are delivered 

 to the top of the stack into an oscillating sieve, which sifts the material 

 into the furnace. It takes about two minutes for the material to fall 

 from the top, through the flame, to the bottom. This heating sets up 

 the reactions necessary to convert the silver into the form of chloride, 

 and the reaction continues after the material has passed through the 

 flame. The roasted ore is allowed to collect in the bottom of the fur- 

 nace, and of the return flue, and is withdrawn from time to time, about 

 twice as much being taken from the latter as the former ; it is then al- 

 lowed to remain about 16 hours on the floor of the furnace house in 

 order to complete the chloridizing. At longer intervals the material 

 collected in the dust chambers is added to the piles of roasted ore from 

 the two stacks on the floor. 



The roasted ore is now taken to the pan house and mixed with hot 

 water in the pans, which are 5 feet diameter and 3 feet high. A 

 charge consists of 2,800 pounds of ore and 350 pounds of mercury, 

 to which a small amount of granulated zinc is added. The agitator is 

 revolved about sixty-five times a minute, and in about 8 hours the 

 amalgamation is complete. After the amalgamation the material is 

 run into the settlers and more water added. The settlers are 8 feet in 

 diameter and 4 feet high, and the agitator makes 14 revolutions per 

 minute. In about 4 hours the amalgam settles, so that the first portion 

 of water can be run off; more water is then added, and the washing 

 continued for about 4 hours more, so that the settlers will be ready for 

 the next charge from the pans. 



