THE VOLATILE PART OF 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 

 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 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- 

 ijj 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. 



