PLANT OF SMELTER D. 679 



The lighter portions of the fumes are carried away into the air and fall back occasion- 

 ally on the roof of the building, which is covered with an impalpable yellowish-white 

 dust. In each section of the chambers is a door for the extraction of the dust, which 

 is moistened with water before being wheeled away. 



Treatment of flue-dust From four to five tons of flue-dust are collected weekly in 

 the chambers just described. The dust is mixed with milk of lime and molded into 

 bricks in the molds represented in Figs. 9 and 10, Plate XLIV, which are also used for 

 common bricks. The bricks thus obtained are then dried under a shed and after- 

 wards on driers ; they are then laid on the ore-beds and resmelted. 



One of these bricks was examined to determine the actual quantity of lime with 

 which they are mixed. Their contents in lime and magnesia are : Lime, C.9 per cent.; 

 magnesia, 5.1 per cent., or 12 per cent, in all ; but the original dust contained already 

 4 per cent, of a mixture of lime and magnesia, leaving 8 per cent, for the lime and 

 magnesia thus introduced. 



Treatment of mattes and accretions Mattes and accretions are placed in heaps in 

 alternate layers with wood, and thus slowly roasted by slow combustion; but it will 

 be seen in the study of mattes and accretions that this is a very imperfect mode of 

 treatment, by which a great deal of silver is lost. Speiss is kept separate from other 

 products at smelter C, but is not treated. It will be seen in the analytical study on 

 speiss that this, as well as all the other speiss at the camp, contains a small quantity of 

 molybdenum, which is entirely concentrated there. 



Steam-power The boiler is worked at a pressure of 60 pounds to the square inch, 

 and the engine is of 50 horse-power. The machinery driven by this engine consists of 

 two No. 5.J Baker blowers, three Blake crushers, and the pumps feeding the water 

 tanks. 



The blast arrangement adopted at this smelter is the one chosen for the general 

 description at the commencement of this section, to which the reader is referred. The 

 normal pressure used is eight-eighths to nine-eighths inch of mercury. It will be seen 

 in the discussion of the blast furnace that the weight of atmospheric air needed to 

 work in the best conditions is about four-fifths the weight of the smelting charges; 

 it -will also be seen that the volume of blast in Leadville is much greater than at lower 

 altitudes. 



Smelter C, with two furnaces, smelts from 80 to 100 tons of ore per 24 hours. 



SMELTER D. 



Smelter D is a neat and compact little smelter situated on the northern bank of 

 California gulch, and so like the similarly situated smelters just described, in its gen- 

 eral arrangement, that its description will not be given in detail. The pressure of 

 steam in the boilers is 65 pounds to the square inch; they supply a 40 horse-power 

 engine, which drives two No. 5 Baker blowers, 1 Blake crusher, one set of Cornish rolls, 

 and the pumps feeding the water tank, which supplies the water-jackets of two fur- 

 naces. The diameter of the pipe supplying both is 2 inches. The pressure of blast 

 used at this smelter is the lowest in the camp and averages from four-eighths to six- 

 eighths inch of mercury. 



Furnaces. The two furnaces used at this smelter, and which are equal in dimen- 

 sions and capacity, are represented in elevation (Fig. 1) and in vertical section (Fig. 2, 



