LAYING OUT THE DESIGN OF WORRs. 53 



have known the columns to be lifted. Both inlet and outlet 

 valves are always open, and there is some similarity to a tele- 

 scope holder, the lighter holder acting as the inner and the 

 heavier as the outer lift. In like manner, the former fills 

 first and then the other, and the reverse in emptying. 



As there is apt to be considerable variation in the quality 

 of the make from hour to hour, the inlet and outlet pipes 

 should not be too close together. If the gas can short cut 

 from inlet to outlet, this variation may be carried out into 

 the district. In one case, a defect of this kind was cured 

 by suspending a piece of wrought-iron pipe, larger in 

 diameter than the inlet, from the crown of the holder, in 

 such a manner that it fitted like a sleeve over the inlet 

 pipe. Projecting pieces were provided to keep it central, 

 and clear of a socket joint on the pipes ; and the top end 

 was about 12 inches from the crown. By this means the 

 inlet gas was delivered at the top, immediately under the 

 crown, and had to traverse the whole content of the 

 holder before reaching the outlet. 



It may be urged that a steam boiler is an advantage, 

 because hot water is sometimes required for washing out 

 foul pipes or thawing water lutes and gasholders. In cold 

 climates, where prolonged frost is experienced every winter, 

 there is something in this ; but the requirement may be 

 more efficiently and conveniently met by a small portable 

 boiler mounted on a bogey that can be moved from one 

 place to another. Under some circumstances, a fixed boiler 

 is preferable, with pipe laid on to the purifier house and the 

 gasholder tank. A very small consumption of steam, when 

 a good ejector is used to keep the water in motion, is 

 sufficient to prevent trouble in the holder tank. The plan 

 of using crowbars to break the ice is barbarous, and likely 

 to injure the plant. 



