66l3 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



distributed iu the center and ou the sides of tho fuiuace, the lower ]iarl ot the shaft 

 wouUl reach a higher temperature and prevent the formation of these accretious, which 

 constitute the only real difficulty with which the smelters have to contend. The analyses 

 which have heeu made of these products, (see Section IV) show that they are formed 

 of sublimated substances volatilized in the zones of higher temperature and deposited 

 in the first cool zones which they encounter as they ascend in the form of vapor. Should 

 the modification in the mode of charging which has been proposed prove practical, 

 accretions would still be formed, but in the higher zones of the shaft, from which they 

 could be detached oftener and with much more facility. In any case, they would inter- 

 fere much less with the working of the furnace, wliich depends a great deal ou the regu- 

 larity with which the charges desceud the shaft, and the dreaded hangiug (i. e., the lall 

 of the fuel to the tuyere-holes and suspension of the charge ou the sides) would be iu 

 great part avoided. 



Barring-out or barring-down of the furnace As it is, OUCe per shift Or OUCe in 2-1 hourS, 



as the case may be, or eveu ouce iu two or three days, the furnace is barred out or 

 down, i. e., the accretions are forcibly detached from the walls of the shaft by uieaus 

 of bars and sledges. The charges are allowed to descend to the level of the accretions, 

 the blast is turned off, and long chisel pointed bars a little shorter than the height of 

 the shaft are introduced from the feed-holes between the accretions and the walls by 

 means of the sledge, and the accretions thus removed are left iu the charge, by which 

 they are fluxed down. When this operation is over the blast is turned ou agaiu, the 

 charging of the furnace continues, and smelting is resumed. (The chisel pointed bars 

 used in barring down the furnace are represented in Fig. 7, Plate XLIV.) 



Smelting of flue and chamber dusts — Flue aud chamber dusts are mixed in general with 

 lime, and the mixture, either molded into bricks or not, is spread over the ore-beds, so 

 that a little flue-dust enters into the composition of the smelting charges. This is evi- 

 dently the best way of disposing of this rather troublesome product, and in the discus- 

 sion of chamber-dust it will be shown that the admixture of lime is the best plau that 

 can be devised for its treatment. 



Running with dark top — Iu Leadville, furuaces are always made to run with a dark 

 top, and this is one of the best indications that the furnace is running properly. By 

 this is meant that the zone of the throat is perfectly dark; that no flame issues from it; 

 that the top part of the charge s'.iows no signs of incandescence; aud that all that is 

 seen is a thick, black smoke ascending the chimney. 



Tapping of slag — As sooii as the furnace begius to work with regularity it becomes 

 necessary to draw out periodically the molten slag from the furuace. This is done ou 

 an average every flfteeii or twenty minutes. To effect this, slag-))ofs, mounted ou wheels 

 and made entirely of cast iron (see Plates XXIII and XXX VI I for the two styles of 

 slag-pots used iu Leadville), are brought close to the fore-hearth of the furuace aud 

 l)laced under the slag gutter. A tap-hole is perforated at the middle of the base of 

 the tymp stone by means of a pointed steel bar about an inch thick, which is forced 

 into the clay by gentle strokes of a light hammer. This operation is generally per- 

 formed by the head smelter's assistant. The slag runs over the steep or clay with 

 which the fore-hearth is covered, then along the slag-gutter, and thence into the slag- 

 pot. As soon as the slag-pot tills, the head-smelter dexterously jilugs the ta])-hole with 

 a small lump of soft tapping clay stuck to the end of the peculiar iron rod shown in 

 Fig. G, Plate XLI\'. and calleil the tapping-rod. Duiing this operation showers of 



