22 
NITROGEN.— CARBON. 
deposites, and gushing forth to fertilize and beautify 
the surface of the globe, again to be evaporated and 
again to fall, constitutes no small item in the aggre- 
gate amount. 
The amount of hydrogen contained in coal, lig- 
nite, and peat, is by no means inconsiderable. Some 
varieties of coal, as the Cannel and others, contain 
as much as 21 per cent, of hydrogen ; this, com- 
bined with carbon, forms the gas used for lighting 
cities. 
In many places, especially where coal and rock- 
salt are found, hydrogen issues in a constant stream 
from the earth, as at Bristol, Honeoye, &c. ; and 
many places in the western part of New- York, and a 
village on Lake Erie, are lighted by this means. The 
phenomenon of burning springs, of which almost 
every country, particularly China, furnishes numer- 
ous examples, is owing to the same cause. 
Nitrogen gas, or azote, is chiefly important as con- 
stituting 80 per cent, of the atmosphere. It neither 
supports combustion nor animal life. It abounds in 
animals and vegetables, being obtained, doubtless, 
from the atmosphere ; some have supposed that it 
also exists in rocks which contain animal organic 
remains. Some species of bituminous coal contain 
15 per cent, of nitrogen. 
Carbon abounds not only in living animal and ve- 
getable substances, but also in fossil vegetables and 
limestone. It forms the largest proportion of every 
species of coal, bituminous coal containing from 50 
to 75 per cent., and anthracite often as much as 90 
per cent, of carbon. Diamond is pure carbon. It 
also enters into the composition of many of the me- 
tallic minerals, as iron, lead, zinc, and copper. De 
la Beche remarks, that if carbonic acid be compo- 
sed of equal volumes of the vapour of carbon and 
oxygen, the volume of the vapour of carbon con- 
densed in the calcareous strata must be very great. 
Taking the specific gravity of pure limestone at 2.7, 
