84 CONSTRUCTION OF RETORTS. 



" As regards my improved mode of working off the charge, I make use of retorts about 

 twice as long as those commonly used in coal-gas works, and I prefer them made of 

 wrought iron, about half an inch in thickness, and that the transverse sections of the 

 retorts should represent the forms shown in the drawing*. The retorts are open at each 

 end, and have a mouth-piece attached to each by the usual means. These mouth-pieces 

 are each fitted up with stand-pipes, to which are fitted, as usual, bridge-pipes, dip-pipes 

 and hydraulic mains, care being taken only that one of the dip-pipes B l does not seal or 

 dip into the tar or liquid of the hydraulic main so far as does the dip-pipe B 2 ; and this 

 shorter dip-pipe is furnished with a cup-valve, or stop-cock M, capable of so closing this 

 dip-pipe by means of the lever N, as to force the gas, when required, to escape out of 

 the dip-pipe B 2 . 



" Any number of retorts found most convenient may be set up in one oven or furnace, 

 to constitute a setting of retorts. 



" I will now describe the mode of operating with retorts so arranged. 

 " Instead of putting the whole charge of coals in at one time and taking off the gas at 

 one end or mouth-piece only of the retort, my plan is as follows : 



" Supposing the retort 1 A 2 A to be empty, I charge only one half of its length, or 

 thereabout, say from 1 A to a, and leave the valve M down or open, as shown in the 

 Figure, in order that the gas may pass out at B 1 , and receive the additional heat of the 

 remaining or empty part of the retort. It will be seen that the gas must necessarily 

 take this course, because the seal B 1 is not so deep as the seal B 2 . When in this posi- 

 tion (supposing the charge to be an eight-hours' charge), then at the expiration of four 

 hours the end 2 A of the retort should be opened and the empty half of the retort from 

 2 A to a should be charged with coal and closed with coal as usual. The lever N should 

 then be acted upon so as to draw up the cup-valve M close to the mouth of the dip- 

 pipe B 1 , which cup, being deeper than the seal at B 2 , will stop the gas from continuing 

 its course out at B 1 and oblige it to pass out at B 2, thus compelling the gas evolved from 

 the fresh portion of coal to traverse over and through that portion which was first put 

 into the retort, whereby a combination is effected between the gas arising from each por- 

 tion at the expiration of eight hours from the commencement of the operation ; the lid 

 1 A of the retort is taken off, and that part of the charge between 1 A and a, which we 

 must imagine to be now nearly exhausted of its gas, is to be drawn or cleared out and a 

 fresh charge of coal put in and the lid replaced. At the same time, the cup or valve 

 attached to the dip-pipe B 1 , which was before lifted up or closed, must now be lowered 

 or opened into its original position in order to make the gas escape at B 1 , thus causing 

 the gas from the fresh charge of coals to traverse between a and 2 A in like manner as it 

 formerly traversed between a and 1 A, and with the like effects. These alternate opera- 

 tions are continued every four hours, and therefore I call my retort so arranged a Re- 

 ciprocating Retort. 



* The form of section here alluded to is shown in Plate V. 



