GASHOLDERS. 



167 



lower part of the " bird fountain," or vessel for supplying water 

 to birds in cages, the bulk of the water being prevented from 

 escaping by the pressure of the atmosphere, whilst some can escape 

 now and then when required, bubbles of air entering to supply its 

 place. The delivery tube of a gas generator evolving the gas to be 

 stored in the holder is then passed into the drum through this short 

 slanting tube ; the bubbles of gas rise into the drum, and watei 

 flows out until the drum is filled with gas and emptied of water 

 (which is known by means of the gauge), when the delivery pipe 

 is withdrawn, and the plug 

 inserted again. 



Fig. 75 represents a model of 

 the kind of gasholder used in 

 gas works and chemical factories. 

 A large reservoir is constructed 

 of sheets of iron bolted together, 

 and is suspended by chains pass- 

 ing over pulleys and counter- 

 balanced by weights, so that it 

 can rise and fall as required. 

 Gas is led into the reservoir by 

 the pipe a leading from the 

 generators, and passes out 

 through the pipe b. If & be 

 closed by turning off the valve 

 connected therewith, the gas 

 entering in by the pipe a accu- 

 mulates in the reservoir, and by 

 and by raises it up out of the 

 cylindrical basin of water in 

 which it rides up and down; 

 thus the reservoir is filled. In 

 order to force the gas out, as for 

 example when a town is to be 

 supplied with coal gas, the 

 counterpoising weights c, c are 

 partly removed, so that the 

 weight of the reservoir partly 



Fig. 75. Model Gasholder. 



presses on the contained gas, and forces it out through the tube 

 5, when the valve therewith connected is opened. 



For laboratory experiments and for producing the " limelight ' 

 in theatres, &c. (Expt. 211), gases are often stored in india-rubber 

 bags, filled by directly connecting them with the delivery tubes of 

 gas generators, and emptied by placing a board with weights on it 



