112 PURIFIERS. 



has to be lifted, this arch-pipe must be removed, and any other kind of joint 

 would be troublesome. 



E is the lid of the purifier, also sealed by a water-joint ; e e are round 

 f rods, keyed at one end into the keep-ring k, and riveted to each corner of 

 the lid at the other ; a chain is hooked on to the ring k, and passed over a 

 pulley to a balance-weight, by which, and the rods just mentioned, the lid is 

 lifted. 



FF are blank flanches or bonnets, through which, when removed, the 

 pipes are cleared from any deposited impurity. 



G G are clamps, to keep the lid of the purifier in its place. The general 

 arrangement of the purifiers will be more fully explained by reference to 

 Plate XIII., where the two sets are shown with their several pipes and valves. 



A is the pipe leading from the wash-vessel into one partition of the hydraulic 

 valve, which I shall describe immediately. 



B is the pipe leading to the three purifiers C D E in action, and rising into 

 the same partition of the valve as B. 



F is the pipe leading the purified gas back to another partition of the valve. 



G is the pipe conveying this gas to the meter and gasometers ; the connexion 

 between the two last-named pipes is formed in the same way as that between 

 the pipes A and B. It will be evident that the lime contained in the first 

 purifier will be spent or saturated before the other two, and that contained in 

 the third will be comparatively untouched. At the expiration of twenty-four 

 hours C D and E must be shut off, by changing the divisions of the hydraulic 

 valve to the situation shown by the dotted lines in the figure representing that 

 valve, and turning the gas through HIK, having previously been put in 

 readiness ; at the instant of turning the valve the gas will pass through both 

 sets of purifiers, all the communications being open. 



When the covers of C D and E are taken off, remove the screens from C, 

 and place those from E in their stead. The lime from C is quite expended, 

 and must be either heated to sublime the sulphur, or laid aside until it can 

 meet with a sale as manure, or be otherwise disposed of. That from D may 

 be spread for a time in the open air (if there be room in the works), and in 

 a week or two it will be fit to use in the first purifier. After renewing the 

 lime in the second and third purifiers, replace the covers, and they are again 

 ready for action. The same operation is repeated when H I and K are spent. 



The annexed woodcut represents the hydraulic valve just mentioned. 



