30 



BULLETIN 42, UNITED STATES NATIONAL MUSEUM 



Flue dust. 



(1) First chamber. (55709.) 



(2) Secoud cLutnber. (.35710.) 



(3) Third chamber. (55711.) 



(4) Fourth chamber. (.55712.) 



(5) Fifth chamber. (.5.5713.) 



(6) Sixth cliamber. (.55714.) 



(7) Seventh chamber. (.55715.) 

 (d) Ninth chamber. (55716.) 

 (9) Tenth chamber. (55717.) 



(10) Eleventh chamber. (.5.5718.) 



(11) Twelfth chamber. (55719.) 



MILL i;AAIFLE.S. 



(1) Mercury, used in the pan to amalgamate the silver. (51117.) 



(2) Silver amalgam, taken from the strainer. (55720.) 



(;}) Tailings, containing three ounces of silver per ton; thrown away as waste. 

 (55723.) 



(4) Silver bullion, about 700 tine, (55721.) • 



(5) Model of ingot No. 11998, containing 1,551.50 ounces of bullion 646 hue. (55722.) 



MOULTON MILL. 



The process followed is the same as at Park City, bat it varies in its 

 details, partly on account of the general difference in the character of 

 the ores treated, and partly because ores from different mines with 

 varying characters are treated. TheMoulton ores carry their silver in 

 the form of native silver, argentite, and ruby silver, together with 

 argentiferous sulphurets. The main difference between the two ores 

 being the large percentage of pyrite and manganiferous minerals, and 

 smaller percentage of blende in the Moulton ores. In the ores from the 

 lower levels, the carbonate of manganese (rhodochrosite) is quite abun- 

 dant, but in the upper levels this has been altered to various oxides of 

 manganese, which consume and waste large amounts of salt in the roast- 

 ing operation. 



In the mill the ore and salt are mixed before drying, and are then 

 spread over hot plates to dry ; after drying they are stamped and 

 roasted. The roasting takes place in a revolving cylinder of the How- 

 ell pattern ; this consists of a hollow irou cylinder lined with firebrick, 

 set at an angle and slowly revolved. The ore is fed into the cool end, 

 as it descends toward the hot end successive portions are exposed 

 to the action of the flames, and in this way the roasting is accom- 

 plished. A much larger portion of the ore ])asses through the furnace 

 than in the Stetefeldt roaster, consequently less fine ore is carried oft' 

 by the draft, and fewer chambers are required to catch the dust. At 

 the Moulton mill some of the dust chambers are emptied only at long 

 intervals. After roasting the ores are allowed to stand from three to 

 five days on the floor, and from that stage of the process until the melt- 

 ing of the bullion the process is the same as at the Ontario mill. 



The collection was made by the writer with the assistance of Mr. J. 

 K.Clark, general superintendent, in September, 1884, and includes — 



