THE VOLATILE PART OP PLANTS. 41 



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 

 ve=sel ; 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 extinguished ; on low- 

 ering it again, it will be relighted by the burning gas; finally, if the bot- 

 tle be suddenly turned mouth upwards, the light hydrogen rises in a 

 sheet of flame. 



In the above experiment, the hydrogen burns only where 

 it is in contact with atmospheric oxygen ; the product of 

 the combustion is an oxide of hydrogen, the universally dif- 

 fused compound, water. The conditions of the experiment 

 do not permit the collection or identification of this wa- 

 ter ; its production can, however, readily be demon- 

 strated. 



EXP. 14. The arrangement shown in fig. 8 may be employed to ex- 

 hibit the formation of water by the burning of hydrogen. Hydrogen 

 gas is generated from zinc and dilute acid in the two-necked bottle. 

 Thus produced, it is mingled with vapor of water, to remove which it 



Fig. 8. 



is made to stream slowly through a wide tube filled with fragments of 

 dried chloride of calcium, which desiccates it perfectly. After air has 

 been entirely displaced from the apparatus, the gas is ignited at the up- 

 curved end of the narrow tube, and a clean bell-glass is supported over 

 the flame. Water collects at once, as dew, on the interior of the bell, 

 and shortly flows down in drops into a vessel placed beneath. 



In the mineral world we scarcely find hydrogen occur- 

 ring in much quantity, save as water. It is a constant in- 

 gredient of plants and animals, and of nearly all the 

 numberless substances which are products of organic life. 



