GASOMETERS. 133 



L are receivers, in which the tar or water collects from the mains, being pumped 

 out by a small hand-pump, of which a and b represent the suction-pipes. 



The well, down which these pipes are conducted, may be about seven feet 

 diameter, built of brickwork in mortar, and well puddled, and as much lower 

 than the tank of the gasometer as to allow the top of the receiver to be below 

 the bottom of the tank. The tank of the gasometer may also be built of 

 brickwork in mortar ; in good ground the dimensions marked in the engra- 

 ving, with a counterfort every ten feet, projecting eighteen inches, will be 

 strong enough. Care must be taken, however, to have good, sound, and well- 

 burned stock-bricks. The outside of the tank, to the thickness of two feet, 

 must be well puddled. In getting out the ground the method pursued will vary 

 so much under even 7 different circumstance that little can be said about it here. 

 In very bad marshy ground, abounding in land-springs, and otherwise disad- 

 vantageous, it will often be found less expensive to construct an iron tank. 



At Chester, Mr. Clegg found so firm a bed of red rock that no brickwork 

 was necessary, the tank being simply fashioned with the pick, and a few land- 

 springs stopped. The earth-work in the centre of the excavation may be left, 

 with a sufficient slope, and a " berm" half-way down ; to guard against slips ; 

 and may in some cases be hurdled, or staked and osiered, whichever may be 

 found the least expensive ; the angles of these slopes will also vary according 

 to the nature of the ground ; a good gravel will stand at the slope shown in 

 the engraving. The slopes of porous earth, such as the last-named, must 

 be puddled, and made water-tight. 



In tanks, whose diameter does not exceed fifty-five or sixty feet, the earth, 

 if requiring puddle or other finishing, may be got out entirely, as it will be 

 found cheaper to do so. In rock, stiff clay or chalk, the centre portion may 

 be left in for much smaller diameters. 



I have not noticed the counter-weights, or specific gravity-apparatus, as 

 they are termed by some, because I consider them (when applied to such gas- 

 ometers as I have just attempted to explain) productive of evil rather than of 

 good. If gasometers are counterbalanced, while the pressure opposed to the 

 entrance of the gas may be decreased, it is also decreased when the gas is re- 

 quired to flow from them, and the weights must be removed, which will be 

 attended with labour, and often with difficulty. It will generally be found 

 that gasometers require weighting rather than balancing, as the pressure ne- 

 cessary for forcing the gas through the street- mains usually exceeds that given 



