86 CONSTRUCTION AND MANAGEMENT Of SMALL GASWORKS. 



in the hand, but not too wet to lie lightly in the box. And 

 some limes are improved by admixture with fine coke 

 ashes that have been through a J-inch mesh. This course is 

 preferable, if the lime is apt to give a heavy back pressure, 

 to reducing the thickness of the layers, which must neces- 

 sarily shorten the working life of each charge. The slaking 

 must be thoroughly complete, and the lime quite cool, before 

 being laid in ; and some limes continue to heat for a long 

 time after the first violence of the action has passed away. 

 If the lime is put in warm, it will continue to swell in the 

 box, and then up goes the back pressure. With attention 

 to these points, and assuming that the gas reaches the inlet 

 of the purifiers properly condensed and free from tar, there 

 should be no trouble from back pressure. 



Some limes are apt to be extremely offensive when 

 removed from the box, and continue so for several hours, 

 or even days. To minimize this nuisance, the material 

 should be spread thinly, so as to avoid heating up, and all 

 lumps should be broken. The spent lime is usually in 

 demand for agricultural purposes, and it should be 

 thoroughly well weathered by exposure before being used. 



If lime is fairly cheap, and the spent fetches a decent 

 price, there are many reasons for preferring it to oxide. A 

 charge of lime is more effective than a similar bulk of oxide, 

 so the latter requires somewhat larger boxes than the 

 former. But if lime is costly or the spent is a nuisance, 

 oxide may be preferable. There should be a sufficient supply 

 of oxide to leave at least two charges outside for revivifying ; 

 and it must be remembered that oxide does not come round 

 properly, especially when it begins to get old, without 

 turning and watering. It is a mistake to suppose that 

 directly it changes colour it is completely revivified. If a 

 few small lumps are cut through and examined under a 



