168 SCIENTIFIC AMUSEMENTS. 



on the bags (fig. 76), so that the pressure of the weights forces the 

 gas out in a current through an attached pipe leading to wherever 

 the gas is required. For experiments on the small scale, an ordinary 



Fig. 76. Gas Bags. 



ox bladder used in the same kind of way answers very welL To fill 

 the bladder, it should be softened and made pliable by dipping in 

 water, and when soft should be blown full of air, and then well 

 rubbed with glycerine ; the air should then be squeezed out and 

 the bladder connected with the gas generator, preferably by fixing 

 in the mouth of the bladder a piece of brass tubing with a tap 

 attached, and tying the bladder firmly round the tube, so that when 

 the tap is turned off no gas can escape, whilst when turned on it 

 can pass in and out through the tube. 



Instead of bags or gasholders, gases are often stored in strong 

 iron cylinders, into which the gas is pumped under great pressure, 

 so that by slightly opening a valve the gas issues forth spontane- 

 ously; owing to the great diminution in the bulk of the gas 



thus occasioned such cylin- 

 ders are far more conveni- 

 ently portable than large 

 india-rubber bags (fig. 77). 



Fig. 77. Cylinder of Compressed Gas. n Ex P t 17 * * prepare 



Oxygen and Quicksilver 

 by heating a Solid. In Expt. 176, where oxygen is prepared by 



