588 GAS, COAL 



the column of water which would press tho gas within the gasometer, were no counter- 

 weight employed ; it consists as follows : 



9. for the highest position = - ; 



56 



10. for the lowest = 2 ' 72y ; 



50 



For the case when the height of tho gasholder is different from its semi-diameter, 

 let this height = mx ; then the height of the water-level is 



11. for tho highest position = p 



56 



12. for the lowest - 



13. the counterweight = * x* (p (1 + 2 m)-^^ 



112 



14. the weight of tho equalising chain = -- p ir m x-. 



830 



For example, let the diameter of the gasholder be 30 feet, the height 15 (the con- 

 tents in cubic feet will bo 10,597), .p = 4 Ibs. ; then the counterweight for a height of 

 1- inch of water-pressure = 3, 53 2 Ibs. ; tho weight of the chain for a length of 15 feet 

 = 395 Ibs. Were no counterweight employed, so that the gasholder pressed with its 

 whole weight upon the gas, then the height of the equivalent column of water in its 

 highest position = 2'56 inches ; and in its lowest, 2'33. Tho counterweight may hcnco 

 be lessened at pleasure, if the height of the pressing water column, n, be increased. 

 The weight of the equalising or compensating portion of the chain remains the same. 

 When n = 2 inches, for instance, the counterweight =1,8 86 Ibs. 



The velocity with which the gas passes along the mains for supplying the various 

 jets of light may be further regulated by opening the main cock or slide valve in a 

 greater or less degree. 



Gasholders whose height is greater than their semi-diameter are not only more 

 costly in the construction, but require heavier counterweights and equilibration 

 chains. 



The above estimate is made on the supposition of the gas in the gasholder being 

 of the same specific gravity as the atmospherical air, which would be nearly true with 

 regard to oil-gas under the ordinary pressure. But coal-gas, whose specific gravity 

 may be taken on an average at about 0'5, exercises a buoyancy upon the top of the 

 gasholder, which of course diminishes its absolute weight. Supposing the cubic foot 

 of gas to be = 0'0364 Ibs., the buoyancy will be = 3'0364 wa: 3 Ibs., a quantity which 

 deserves to be taken into account for large gasometers. Hence, 



15. the weight of the gasholder in its highest position = 3p ir X s O'l 143 or 1 ; 



16. the counterweight =*x*(3p - 



17. the weight of the chain for the length x, = * 2 Q-1143** . 



800 pit 2 



18. the weight of the water-pressure from the highest position, without tho counter- 



0-1143ar 



19. the same for tho lowest position = in feet. 



The preceding values of p and x, are, 



(16)=*3147; (17) -304; (18) =2-44 inches; (19) =2-33 inches. 



The water-columns in the highest and lowest situations of the gasholder here diftl-r 

 about 0-1 of an inch, and this difference becomes still less when p has n smaller value, 

 for example, 3 Ibs., or when the diameter of tho gasholder is still greater. 



It would thus appear that for coal-gasholders, in which the height of tho gas- 

 holder does not exceed its semi-diameter, and especially when it has a considerable 

 size, neither a compensation chain nor a counterweight is mrrssary. Tho only tiling 

 requisite is to preserve the vertical motion of tho gasholder by a sufficient inn, 

 guide rods or pillars, placed either within the water cistern or round about, it. Should 

 the pressure of the gas in tho pipe proceeding from the gasholder be less than iu the 



