SMELTING OPERATIONS. 667 



rod-hot slag sparks fly iu every direction around the tap-bole. The tapping-pots or 

 slag-pots are then wheeled away by the slag-wheelers to the slag heap. The slag is 

 either allowed to cool completely in the pot and the cake of slag thus formed is 

 extracted bodily and broken up into fragments, or else the pot filled with molten slag 

 is tipped over the edge of the slag-heap, where the slag runs dowu like lava. 



Taking specimens of slag for assay Two or three times a day a specimen of slag is 

 taken direct from the stream flowing from the furnace by means of a very small iron 

 ladle provided with a long handle. The specimens thus obtained are forwarded to the 

 assay office, where their specific gravity aud their contents in lead and silver are deter- 

 mined. After every tapping some slag sticks to the fore-hearth aud slag-gutter, from 

 which, it is easily detached by sprinkling a little cold water over it aud knocking it off 

 with an iron bar. 



Matte and speiss iu Leadville the little speiss and irou-aud-lead matte formed dur- 

 ing smelting are run into the slag-pots. At some works speiss, matte, and slag are 

 thrown pell-mell over the slag-heap; at others the cakes of speiss or matte which have 

 settled at the bottom of the slag-pot are knocked off the slag with the hammer. Speiss 

 is kept iu a separate heap, but no treatment has been found for it. The matte, sepa- 

 rated from speiss and slag, is roasted iu heaps and resmelted afterwards with the ore. 

 In the study on mattes it will be seeu that this roasting iu heap appears to be a very 

 bad operation. 



Ladling-out of melted bullion From time to time bulliou is ladled out of the lead-pot 

 or siphon-tap by means of wrought-irou ladles, and poured into cast-iron molds placed 

 iu a row alongside the furnace on the lead-pot side. The molds bear in relief- letters 

 the name of the smelting firm, so that each bar of bullion is branded with it. When 

 cold the bars are taken out on the slag-heap, or under a shed near the engine-rooms, 

 aud then weighed, marked, and two small pieces one from top and one from bottom 

 are detached by means of hammer aud chisel aud carefully kept for assay. When a 

 car-load has been thus weighed the assay bits, all mixed up together iu a tin can or 

 copper pan, are forwarded to the assay office. 



Watching the furnace Every part of the furnace requires constant watching in 

 order to apply at a moment's notice the proper remedy for any accident that may happen. 

 The siphon-tap requires some attention and its siphon must be kept constantly clear ; 

 this is effected by the iutroductiou, from time to time, of a curved iron bar about two 

 inches thick, previously heated to redness at the curved end. This bar is represented 

 iu Fig. 8, Plate XLIV. The water-jackets form perhaps the least troublesome part of 

 the furuace, aud yet it is necessary to insure the ruuuiug of the water into them at 

 such a rate that the temperature of the water issuing from them should be as nearly 

 as possible 50 to CO (3. 



The pressure at the induction-pipe manometer must be constantly watched and 

 the pressure kept steady or modified according to momentary requirements. 



The tuyeres must be kept perfectly clear from any chilled slag by the introduction 

 of iron bars into the sliding valve, and the temperature aud condition of the zone of 

 fusion observed through the tuyeres. When black rings round the tuyeres indicate 

 a beginning of chilling, a little more fuel is added, or the charge is somewhat diminished, 

 the fuel remaining the same. If the temperature proves too high, fuel is diminished or 

 the charge is slightly increased. If semi-fluid slags or raw ore form hearth accretions 

 which do not disappear by an increase of the temperature, the blast must be shut off, 



