232 Native Bitumens and the Pitch Lake of Trinidad. (April, 
A little study of these figures will make it clear that all these 
different hydrocarbons may be produced, theoretically at least, by 
removing from cellulose, which represents all woody matter, vari- 
able proportions of carbonic anhydride (CO,), marsh gas (CH,), 
and water (H,O); and this is, in many cases, the course that nature 
pursues. Under ordinary conditions decaying wood is attacked 
by the oxygen of the air and burned up to carbonic anhydride, 
water and ashes as completely as if thrown into a furnace; but if 
kept out of contact with the atmosphere, as when lying beneath 
the water and mud of a marsh, or buried in deposits of sand or 
clay, the wood is still subject to decomposition, though the decay 
is of a very different order and much less complete. The oxygen 
is the most active element of the wood, and the first to leave; 
but it never goes alone, always taking with it some of the hydro- 
gen in the form of water, or of carbon as carbonic anhydride. 
Afterwards other portions of the carbon and hydrogen unite and 
make their escape as the inflammable gaseous substance known 
as marsh gas. The presence of this gas in most swamps and 
marshes attests that nature’s laboratory for the manufacture of coal 
and bitumen is still in operation. Both these species of decom- 
position, whether in the air or out of it, go on much more rapidly 
in the presence of heat; the first process being exemplified in 
every stove and furnace, and the second by the charcoal pit; for 
anthracite, the ultimate product of slow decomposition out of 
contact with the air, is simply a mineral charcoal. 
A further inspection of our formulas will make it evident that 
to transform cellulose or wood into the average bitumen we must 
remove all the oxygen, some carbon and but little hydrogen ; 
while for the conversion of vegetable matter into coal, the oxygen 
is less completely removed, and the hydrogen suffers much greater 
loss than the carbon. In the one case the escaping volatile pro- 
ducts of the decomposition are mainly carbonic anhydride with 
some marsh gas; and in the other case the loss has occurred 
chiefly in the form of water, the carbon remaining largely intact. 
This is an important difference, and one which would be more 
obvious if our series included all the varieties of coal. The fact 
is this series is not a very natural one after all. It represents 
fairly well the changes resulting in the production of the different 
bitumens, viz: a complete abstraction of the oxygen and a 
gradual diminution of the hydrogen; but the coals are generated 
