1820.] Acnm on Coal Gas. 291 



To tlie lower extreini!y of l!;e shaft is keyed a box, or cenire piece (technically 

 called a rose centre), F, fifr. I. It is al>o been in the perpeniliciil.ir section of the 

 retort, 65. y. From (liis shaft radiate 12 ivroiiglit-iroii arms, G, G, fig. 1,* fixed in 

 sockets made in the lio.v. These arms are elevated three inches aliove the botlon 

 of the retort, and extend to nearly nilliin iis whole inner circiimferenrc. They 

 are wedge-shaped, and their oieatest diameter is at right an;;lt^ to the base of the 

 retort; so tliat the weijhi of the arms rests on the axis. They are intersected by 

 two concentric rinf;s, as will he seen on inspectinij fi;;'. 3, which exhibits the phin 

 of the retort, togeiher with the iron arms, G, (i, and concenlric ring>. The centre 

 of fig-. 3, sliov.s also the plan of the rose centre, F, fig. 1, into which the arms are 

 keyed. 



Between the arms arc placed 12 shallow iron trays or boxes, destined to contain 

 the coal from wliich the gas is to be obtained. They are formed to the segment of». 

 circle; hence the whole series of tliem, « hen arranged in the retort, exhibits a shal- 

 low circular tray, wliich, when motion is given to the shaft, may be made ta 

 revolve within the retort. 



Fig. 4, exhibits one of the shallow tr.iys, or coal boxes, in perspective. 



It will be obvious that by the motion of Ibe shall, any number of the trays, or 

 •coal-boxes, casi readily be brought fro;o the coldest into the hottest, and from the 

 Jiotlest into the coldest part of tiie retort. 



H, fig. 2, and a, fig. 1, is a per|)endieiilar pipe situated at the margin of the retort, 

 close liehind the mouthpiece, and consequently in the coldest part of the retort. 

 It serves to carry off the distillatory products evolved from the coal, and causes 

 part of the vapourous tar, which becomes condensed in it, to trickle back again 

 upon the coal in the retort, in order to become converted into gas, when the coal 

 on w.hich it falls becomessituated over liie fire-place. 



This pipe is furnished at its upperextremity with a h:/(Iraulic valve, I, fig. 2. It 

 consists simply of an inverted cup. X, applied over the upper open extremity of 

 the perpendicular pipe, 11, and submersed into a cup formed of a portion of larger 

 pipe, surrounding the pipe, H, containing tar. The smaller, or inner cup, X, is 

 represented in the design raised out of the liquid contained in the outer cup, J, to 

 show an aperture, Y, made in the smaller nr inner cup ; the use of which will be 

 mentioned herc.ifler. The inverted cup, X, is furnished with a. chain, one extre- 

 mity of « hieli is fastened to the upper extremity of the enp, the other passes over a 

 «mall wheel, and deicends through the roof of ihe building, as sliown in the design. 



K, fig. 2, is a branch pipe proceeding laterally from the pei,;endiculai- pipe, H j 

 it communicates with the hydraulic box, L. M, is a pipe v» Inch proceeds from 

 the hydraulic box, L ; it serves to carry away the gaseous and liquid products 

 to their places of destination. 



AI, fig. 2, or fig. 6, is an iron fiap table, placed level with the bottom of Ibe 

 mouth of the retort. It is convenient to hold several coal trays ready charged 

 ^ith coal in a stale fit to be introduced into the retort. 



The fire-place, Uui s, and ash-pit, of the furnace, in which the retort is fixed, aro- 

 sufiicienlly obvious, by mere inspection of fig. 2. The front elevation of the retijrt 

 is seen in fig. 6, whicli exhibits three horizontal retorts ; two of which have the 

 door of the mouth-piece slided down, and one with the door in its place, or shut. 

 The ciroilar rjng seen in this design, at the top of each retort, which rests on iron- 

 bearing bars, the extremities of which are let into the end walU of Ihe furnace, 

 serves to support the roof of the retort by means of bolts proceeding from the inner 

 side of the roof. This arrangement is likewise shown in the section, fig. 2. At 

 the bended part of the jterpcndicular pipe, II, fig. 2, is seen a bonnet, or cover, 

 which closes an opening made into the pijie, H, thriiugh which, by means of an 

 iron rod, the lower extremity of the pi|)e, 11, may, from lime to time, be examined, 

 to guard against an incrustation of d(eompiiscd tar or carhonacenus matter that 

 might happen to accumulale in that part of I'le pipe. The upper part (»f the pipe, 

 II, above llie bonne! at the bended |>arl, requires no examinalion. 

 \ b, fig. I, and b, fig. 3, is liie tlancii of the. retort; c, fig. I, the flaucli of the 

 nioiilh-picce; </, the eultiT, or«cdge, " hich draws ll-.e mouth-piece close ; e, the 

 cro.s bar, against which the cutter, il, bears, to render the nioulh-piece air-tight ; 



• In the horizontal rotary retorts at tlie Chester, Birmingham, and liri-lol g-is 

 wojU--, which are 12 feet 6 inches in diameter, tl.ere are 13 arms. At some gai 

 works, ll.carms are made of ca^t-iron. 



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