94 CONSTRUCTION OF RETORTS. 



round the jointed edge, into which the fire-clay with which they are set is 

 compressed, this serving effectually to keep the ovens gas-tight. 



B is a cast-iron plate secured against the front of the oven by wrought-iron 

 bolts, built into the general brickwork at a a . . and jointed with a channel 

 running round the mouth of the retort, as shown at b b, Fig. 3. When heated, 

 this joint is slightly compressed by the expansion of the oven against the 

 plate ; for the rods by which it is secured, being comparatively cold, will re- 

 tain their original length, and consequently prevent the advance of the plate. 



C is the mouth-piece, bolted on to the cast-iron plate B, and jointed with 

 iron-cement in the usual manner. The lid, being considerably larger than 

 those used on ordinary retorts, is secured by two screw-bars, S S., Figs. 4. 

 and 5, and when removed is supported by a small crane T turning in a 

 socket cast on to the side of the mouth-piece. 



D is the furnace communicating with the flues FF through the openings 

 E E . . The arrangement will be sufficiently explained by the engraving. 



G is the stand-pipe, furnished at its upper end with an hydraulic valve. 

 When the retort is in action, the lever H (Fig. 6.) is acted upon, and the cup 

 I raised above the surface of the fluid contained in the larger cylinder, so that 

 the gas passes away by the outlet-pipe K without being obstructed in the least 

 degree. When the charge has to be drawn, the cup is let down into the posi- 

 tion shown in the figure, sealing the stand-pipe by a head of ten inches. 



The reason assigned by Mr. Spinney for the use of this kind of valve, in- 

 stead of the ordinary hydraulic main, is that the retort may not be exposed 

 to any pressure ; and as the charge is only drawn once in twelve hours, the 

 inconvenience of having to attend this valve is not felt as formerly when used 

 with iron retorts. 



L L . . are plugs covering sight-holes, through which the heat of the flues 

 and oven is examined. 



The first cost of the erection of one of these ovens, complete, is 90, the 

 annual wear and tear is about 5. 



The usual charge for these retorts is five cwt. of Welsh coal, from which, 

 Mr. Spinney informs me, he can produce 2400 cubic feet of good gas in twelve 

 hours. The quantity of coke obtained from a ton of coal is from fourteen to 

 fifteen cwt. 



The fuel required for heating the retort is 50 per cent, of coal on the quan- 

 tity distilled. If coke is used as fuel, three-fourths of the quantity made is 



