52 CONSTRUCTION AND MANAGEMENT OF SMALL GASWORKS. 



now no excuse for stinting the size of the vessels. They 

 should not be less than six feet square, and preferably eight. 

 Oxide of iron is usually considerably cheaper than lime, 

 and with efficient washing plant, it answers every purpose. 



A station meter is a necessary item, even in the smallest- 

 sized works, as without it there can be no proper check on 

 the make or the output. 



A usual rule in regard to storage capacity is that it 

 should be equal to twenty-four hours' maximum output. 

 This rule may well be extended to the extent of 50 per 

 cent, in small works, not so much as an increased security 

 as to leave a margin for variation in make, and thus avoid 

 idle time on the retorts. With a small storage, the make 

 must closely follow the consumption, with the result that 

 at the end of the week the supply is short, and in the 

 beginning there is no room for the gas, and one or more 

 charges must be missed. Ample storage means getting along 

 with fewer retorts under fire, and all these in full operation. 

 There should not be less than two gasholders, and pre- 

 ferably they should be of unequal size. One should be 

 large enough to take care of the night consumption without 

 necessitating change of valves, and the other may be a 

 small one for occasional use or emergency. If the storage 

 is divided between two holders of equal size, it is possible 

 that one will not last out the whole of a long winter 

 evening, and careful watching is necessary to avoid a sudden 

 stoppage in the supply to the district. Sometimes it will 

 be an advantage to couple the two holders, adding stops 

 to the top of the columns of the lighter one, to prevent it 

 from rising so high as to blow. Before adopting this plan, 

 it is well to be assured that the bases of the columns are 

 well secured to the tank, and that the brickwork is strong 

 enough to stand the strain. In a slightly built tank, I 



