Lerrs & Buraxe—The Carbonic Anhydride of the Atmosphere. 157 
PART II. 
Section I.—Tue Amount. 
ArmosPHERIC carbonic anhydride plays such an important role in 
nature, that the question of its amount, whether in the past, pre- 
sent, or future, is one of very great interest, not only to the 
chemist, but also to the biologist, geologist, meteorologist, the 
agrioulturist, and hygienist, and to the student of nature generally. 
The reciprocal action of plants and animals on air may be said 
to fulfil three functions :—(1) to provide each with an important 
food stuff—viz. carbon and oxygen respectively ; (2) to regulate 
the condition of the atmosphere for their respective well-being; and 
(3) to keep in “ circulation ” the supply of carbon which is essen- 
tial to the existence of both, and in which each generation of either 
may be said to have a life interest only. 
If from any cause the amount of atmospherio carbonic anhy- 
dride should be largely increased, the existence of animals would 
be threatened, while, if the reverse occurred, that of vegetables 
would be jeopardized ; and animals would also stand in danger of 
eventual annihilation from the want of food which in the long run 
they derive from the synthetic processes of the vegetable kingdom. 
While the chief operations of plants and animals, as regards 
their mutual welfare, act in the sense of maintaining a state of 
balance or equilibrium in the amount of atmospheric carbonic 
anhydride, certain well recognized agencies are at work tending 
to increase its quantity. These have been called “sources of 
evolution,” and the most important are combustion, putrefaction, 
and decay, and also fermentation—all of which in one way are 
unimportant, because, even including the combustion of coal, all 
can be traced back ultimately to the operations of the organic 
kingdom. They are therefore, more or less, temporary agencies.’ 
1 The combustion of petroleum may be an exception however. If petroleum has 
been formed from carbon, originally present in the interior of the earth, the carbonic 
anhydride evolved by its combustion is of course of subterranean origin and must be 
classed in the second category, i.e., among the sources of evolution tending to per- 
manently increase the amount of atmospheric carbonic anhydride. 
N 2 
