166 SCIENTIFIC AMUSEMENTS. 



the other only communicates with the top. If the taps in each 

 pipe are both turned on, water will run down the first of these 

 pipes, and force out the gas through the other, causing it to bubble 

 up through the water in the reservoir, and thus enabling jars, &c., 

 to be filled just as when working with the pneumatic trough. If 

 the first tap be turned on, and the other turned off, the pressure 

 of the water can be made to force gas out through a side tube on 

 turning on the tap connected therewith ; so that by connecting 

 this tap with a bladder, as represented in the diagram, this may be 

 filled with gas ; or if connected with any required apparatus by 



Fig. 74. Gasholder. 



means of an india-rubber tube, a stream of gas can be passed con- 

 tinuously through the apparatus, as long as there is any in the 

 gasholder to force out. 



In order to fill the gasholder with gas in the first instance, all 

 three taps are turned on, and water poured into the reservoir until the 

 drum is quite full of water, and all air originally in it is displaced 

 by the water. The three taps are then turned off, and the plug at the 

 bottom unscrewed ; the short bit of slanting piping fixed into the 

 side of the drum, and ordinarily closed by the plug, acts like the 



