PLANT OF SMELTER A. 671 



of cast iron. This principle is a bad one, owing to tbe unequal expansion and con- 

 traction of tbe two metals, and should be avoided; whenever this plan is adopted the 

 water-jacket system frequently gets out of order. Each jacket is provided with a 

 feeder, R, in which exists an outlet for the hot water, and a hole, n, for the introduction 

 of the nozzle of a tuyere. Fig. 2 shows the disposition of the six tuyeres and of the 

 jackets; the space between the water-jackets and the masonry above is filled as usual 

 by fire-bricks, b. The pillars P have their capitals flange-shaped at 0". This flange 

 rests on the pillars by means of brackets t. The main cast-iron plate-support is also 

 flanged at o (Fig. 4), and these flanges are connected with the circular and vertical 

 flange 0' of the plate by means of the brackets r. The masonry and stack are en- 

 tirely surrounded by a wrought-iron casing or jacket, J', surrounded at the base by 

 the flange 0'. 



There is only one feed-hole, H, at the throat, but this feed-hole is twice as high as 

 it is in most furnaces, and is divided into two sections by two hinged wrought-iron 

 doors, S' S". The upper door is only opened to bar out the furnace. The damper G of 

 the stack is not s'ugle, as in all the other furnaces, but is made of two halves, G G'. 

 The walls ' of this furnace are much thicker than the walls of most circular blast- 

 furnaces. 



The induction-pipe Jis made, as usual, of galvanized sheet iron. It has a pecu- 

 liar shape; it forms a ring around the furnace, and this ring is square in vertical section, 

 but the branch pipes J are cylindrical, as is always the case. Each furnace smelts from 

 17 to 20 tons in twenty-four hours; produces from 4 to 5 tons of bullion and from 13 to 25 

 tons of slag. 1 The length of run of these furnaces is about six months ; they are barred 

 out every twelve hours, at the beginning of each shift. The chief defect is that the 

 diameter of the water-jackets at the tuyeres is rather too large. Contrary to the plan 

 adopted at all tbe other smelters, periodical tapping of slag is not done here. The 

 slag is allowed to flow in a constant stream, and the gutter in the steep of the fore- 

 hearth and its projection are covered with live charcoal to prevent the chilling of the 

 slag. The slag-pots used at these works are indicated by B B'; they are independent 

 of the car D', by means of which they are wheeled to the slag-heap. 



The quantity of speiss resulting from the smelting of 10,241 tons of ore during 

 the year ending June, 1880, was about 20 tons, assaying 49 ounces of silver to the ton 

 and containing 980 ounces of silver; consequently the quantity of speiss formed 

 amounts to about 0.2 of 1 per cent, of the ore. 



Condensing chamber lu Plate XXV the general disposition of the dust-chamber 

 and its connection with the furnaces are seen in perspective. In Fig. 3, Plate XXIV, 

 the same chamber is seen in horizontal section, divided into three parts by means of 

 partition walls, TF', the arrows indicating the circulation of the fumes. Fig. 2, Plate 

 XXIV, is a vertical section of the same chamber. Both sections are drawn to scale, and 

 a glance at them is all that is necessary to understand its construction and its working. 

 About 150 tons of dust were collected in this chamber in the space of six months. 



Roasting-furnace This furnace is represented in elevation (Fig. 1, Plate XXIV), 

 chiefly with a view of giving its dimensions, for it presents no peculiarity in construc- 

 tion. Its width (not indicated in the sketch) is 12 feet. The sketch shows the system 

 of bracing by rails, the hinged cast-iron doors d, and the dotted lines indicate the in- 

 1 The mnuicipality of Leadville uses most of this slag to macadamize the roads. 



