THE VOLATILE PART OF PLANTS. 41 
brought to its mouth, At first a slight explosion is heard from the sudden 
purning of a mixtureof 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 ina 
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 
TL ON CUA CA TT 
Fig, 8 
ig made to stream slowly through a wide tube filled with fragnients 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, 
