6615 GEOLOGY AND MINING INDUSTRY OF LEADV1LLE. 



distributed iu tho center and on the sides of tho furuace, the lower part ol the shaft 

 would reach a higher temperature and prevent the formation of these accretions, which 

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

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

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

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

 the modification iu the mode of charging which has beeu proposed prove practical, 

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

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

 fere much less with the working of the furuace, which depends a great deal ou the regu- 

 larity with which the charges descend the shaft, and the dreaded hanging (i. e., the fall 

 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, OUCC per shift Or OHCC ill 24 hours, 



as the case may be, or even ouce in 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 means 

 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 in 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 dowu the furnace are represented i:i Fig. 7, Plate XLIV.) 



Smelting of flue and chamber dusts Flue and chamber dusts are mixed iu general with 

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

 that a little tine-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 plan that 

 call be devised for its treatment. 



Running with dark top In Leadville, furnaces 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 noflaine issues from it; 

 that the top part of the charge s'uows no signs of incandescence; and that all that is 

 seen is a thick, black smoke ascending the chimney. 



Tapping of slag AS soon as the furnace begins to work with regularity it becomes 

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

 an average every fifteen or twenty minutes. To effect this, slag-pots, mounted on wheels 

 and made entirely of cast iron (see Plates XXIII and XXXVII for the two styles of 

 slag-pots used iu Leadville), are brought close to the fore-hearth of the furmu-e and 

 placed under the slag-gutter. A tap-hole is perforated at the middle of the base of 

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

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

 ibrmed 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 plugs the tap-hole with 

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

 Fig. G, Plate XLIV. and called the tapping-rod. Dining this operation showers of 



