678 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



fluxed down without serious stoppings and blowings-out. Even the dreaded sows float 

 on the lead bath, remaining constantly at the same level, exposed to the oxidizing influ- 

 ence of the blast and to the sulphurizing influence of mattes and unreduced sulphurets ; 

 they thus rather assist than hinder the completion and perfection of smelting, and very 

 soon disappear, being fluxed down in this way. 



Sampling of bullion The chisel used to detach pieces of bullion from each bar at 

 smelter C is represented in Fig. 14, Plate XLIV. It is a hollow conical chisel or 

 punch, provided with two apertures, a and b. Samples of lead or assay bits (Fig. 15, 

 Plate XLIV) are obtained from the top and bottom of eacli bar by hammering the 

 chisel perpendicularly to the bar. The punch being driven by the hammer into the 

 surface of the bar, the cylinder of lead is forced in at b and out through a, being detached 

 by striking the butt-end of the punch. 



Slags. -A uniform treatment of slags has been adopted at smelter C, which pre- 

 sents two advantages. The slag is left in the pot until a solid crust about two inches 

 thick is formed on the sides and surface of the mass. The upper crust is pierced by 

 two holes, the slag-pot is reversed on the slope of the slag-heap and its molten con- 

 tents poured out. The thin shells of slag thus obtained are broken up and kept for 

 smelting. It will be seen in the assays of slag that the side shell is a little richer in 

 silver than the portion of the slags poured out; but that the upper crust is poorer in 

 silver than either the poured out portion or the side shell, so that this portion of the 

 slag might be thrown away as useless. 



Bars of bullion At smelter C the bars of bullion weigh about ninety -eight pounds. 

 They have the shape and dimensions indicated in Figs. 3 and 4, Plate XLV. 



Length of run The average length of run of the admirable furnaces above de- 

 scribed is 12 months, and runs of even 13 months have been obtained. The remarka- 

 ble length of these campaigns is due not only to the mechanical perfection of the 

 apparatus, but also to the great care bestowed upon every detail of the smelting opera- 

 tions. 



Dust-chambers The dust-chambers are built of small blocks of limestone (Lead- 

 ville dolomite), cemented hy a mortar of sand and lime. They were constructed at a 

 time when limestone was less expensive than bricks. They form a parallelopipedic 

 construction 75 feet long, 15 feet high, and 25 feet wide, with walls about one foot 

 thick, and are placed immediately below the feeding-floor at the rear of the furnace, 

 In Plate XXX are seen the vertical sections (Fig. 1) and the horizontal sections (Fisr. 

 2) of these chambers. Figs. 6, c. d, e, /, g represent elevations of the partition walls 

 W, showing the disposition of the apertures a through which the fumes circulate. At 

 the time this report was made the chambers were connected with only two furnaces, 

 although they are constructed to condense the fumes from three; this explains the 

 unequal allowance of condensing space provided for each furnace. The first furnace 

 is connected with a chamber divided into two sections, A and B, by a wall, IV 7 , provided 

 with an aperture, a (see also Fig. g) ; the fumes enter the chambers at F 1 and reach the 

 sheet-iron stack through G". The second furnace is connected by the flue F" with the 

 chamber, divided into sections (7, D, E, G. The fumes circulate alternately up and down 

 and from right to left, until they reach the flue 6", which takes them to the stack F. 



The whole arrangement is far from perfect, but the fumes are made to strike 

 walls, and this seems to be one of the conditions essential to deprive them of their dust. 



