GENERAL AEExiNGEMENT OF FURNACES. 661 



vaiiized sbeet-iroii, provided witdi sliding valves, I, used to observe the interior of tbe 

 furuaee, and also as safety-valves, for tiiey are left partially opened. Tbe front jackets 

 are always provided witb an open space, F, varying- in sbape and dia-ensions, and 

 closed witb a plug of tapping clay. Tbis plug is called tbe tympstone. The tap-hole 

 Z is perforated through tbe tynip stone for the exit of molten slag. 



Circular furnaces (Plate XXVIl). — Tbe circular furnaces are constructed on the 

 same principles as tbe srpiare ones, differing only in that their masonry is always 

 bidden froui view by a wrougbt-iron casing or jacket, J', painted black. Tbis jacket is 

 made of riveted wrougbt-iron plates about one-fourth inch thick. The round furnaces, 

 like the square ones, are made of two iudepeudent parts ; tbe masonry supported on a 

 cast-irou plate, 0, resting on cast-iion pillars, P ; and tbe crucible or hearth A, upon 

 which rest the circular water-jackets B, always made of wrought-lron plates riveted. 

 The interval between the water-jackets andthe masonry is also filled in with fire-brick, b. 

 The main cist iron i)late sui)port is provided with a circular vertical fiange, 0', and with 

 four projecting horizontal flanges, 0", corresponding to the pillars. These horizontal 

 flanges are supported by brackets r ; they rest on the flanges (designated also by 0") 

 of the capitals of the pillars, supported by brackets t. The masonry jacket J' (Fig. 3) 

 is incased by the flange 0' of the main cast-iron plate support 0, and rests on this 

 plate, as does the masonry C. The wall C" is made of fire-V>ricks. The stack U, a con- 

 tinuation of the jacket J', is not lined with fire-bricks. A wooden hood, TF, and chimney, 

 W, are placed in front of the furnace, above the slag-gutters. Tbe hexagonal induction 

 blast-pipe /supplies tbe branch pipes J- and the tuyeres N with the blast. iTrepre- 

 sent.s the canvas hose or wind-bags connecting the branch pipes J wih the tuyeres N. 



The hearth or crucible A and fore-hearth X are made of strong cast-iron plates, 

 firmly bound together and covered with a cast-iron plate, d. Tbe lead pot, which i ro- 

 jects from the crucible, is framed in a wrougbt-iron or cast-iron box. Tbe fore-hearth is 

 provided with two slag-gutters, U. The hearth A', fore-hearth X', and lead-pot L are 

 made of steep. The lead pot and crucible communicate, as in the case of square fur- 

 naces, by means of the siphon L'. Tbe circular water-jackets are made of two sections, 

 flrmly bound together. Each section is provided with a water supply pipe, J/, at base, 

 and an outlet, M', at top, to carry off hot water. In these jackets no other feeders are 

 used. 



Holes in the jackets allow the iutroduction of the tuyeres. The horizontal section 

 (Fig. 2) through the tuyeres shows the disposition of the blast apparatus in the furuaee. 

 The deflecting elbow or sheet-iron flue F' forms the conuectiou between the chimney 

 D and the dust-condensing chamber D'. The stack E is provided with a damper, G. 

 The furnace has but one feed-hole, ff, with its sliding door <S'. 



Blast apparatus — The blast apparatus in general use in Leadville consists of rotary 

 positive blasts, driven by steam power; of galvanizediron pipes, for the distribution 

 of the blast; and of thin galvanized-iron tuyeres, connected with the branches of the 

 blast-pipes by means of canvas hose or wind- bags. The blower mostly adopted is 

 Baker's rotary forced-blast blower, but at one smelter Root's forced-blast blower is 

 also in use. The average pressure of the blast introduced in the furnaces is one inch 

 of mercury. The following table gives the character, capacity, etc., of the blowers 

 used at each smelter: 



