THE VOLATILE PABT OF PLANTS. 



35 



that has been weighed, being fourteen and a half times 

 lighter than common air. It is hence 

 )used in filling balloon s. Another property 

 is its combustibility ; it inflames on contact 

 with a lighted taper, and burns with a 

 flame that is intensely hot, though scarcely 

 luminous if the gas be pure. Finally, it 

 is itself incapable of supporting the com- 

 ^'g- ''• bustion of a taper. 



Exp. 13.— AU these characters may he shown by the following single 

 experiment. A bottle full of hydrogen is lifted from the water over 

 which it has been collected, and a taper attached to a bent wire, Fig. 7, 

 Is brought to Its mouth. At first a slight explosion is heard from the 

 sudden burning of a mixture of the gas with air that forms at the mouth 

 of the vessel ; then the gas is seen burning on its lower surface with a 

 pale flame. If now the taper be passed Into the bottle it will be extin- 

 guished ; on lowering it again, it will be relighted by the burning "gas ; 

 finally, if the bottle be suddenly turned mouth upwards, the light hy- 

 drogen rises in a sheet of flame. 



In the above experiment, the hydrogen burns only 

 where it is in contact with atmospheric oxygen ; the pro- 

 duct of the combustion is an oxide of hydrogen, the lini- 

 versally diffused compound, water. The conditions of 

 the last experiment do not permit the collection or iden- 

 tification of this water ; its production can, however, 

 readily be demonstrated. 



Exp. 14.— The arrangement shown in Fig. 8 may be employed to exhibit 



Fig. & 



the formation of water by the burning of hydrogen. Hydrogen gas is 

 generated from zinc and dilute acid In the two-necked bottle. Thus 



