New Outlines of Chemical Philosophy. 251 
According to M. Lavoisier, carbonic acid gas consists of 28 
parts of charcoal united with 72 parts of oxygen, and that car- 
bonic acid gas is composed of these two bodies combined in that 
proportion. 
_ Example. Suppose Q = 100. 
Then a+l=100 = the given quantity of oxygen gas; conse- 
quently a+c=100 = the quantity of carbonic acid gas expelled 
from the lungs in respiration. 
a= 72 oxygen. 
¢ = 28 charcoal. 
a-+c¢= 100 carbonic acid gas. 
On Animal Heat. 
I believe that it has never been explained, in a satisfactory 
manner, how animal heat is generated, although different hypo- 
theses have been inyented to account for this wonderful effect. 
It is, however, generally supposed that heat is generated in the 
lungs. Indeed, from the construction of the lungs, and the 
change which takes place in the air in respiration, there remains 
little reason to doubt of the truth of this supposition. 
The internal surface of the lungs in man is estimated by Dr. 
Keil to be about ten times the external surface of the whole 
body, or about 150 square feet*. On this surface the blood is 
exposed in respiration ;-and part of the thermogen contained in 
the air being attracted by the phetogen in the blood, heat is 
generated by their union, in the same manner as in all other 
processes which cause an increase of temperature. The heat 
thus generated is carried through the whole animal system by 
means of the circulation of blood, to supply that heat which is 
constantly flying off from the surface of the body. 
On the Renovation of the Atmosphere. 
I¢ has been ascertained in the most satisfactory manner, that 
the atmosphere is depraved by the living functions of animals 
and vegetables, by combustion, and by various other processes ; 
and yet it has been found by Dr. Priestley and other chemical 
philosophers, that the air in crowded cities contains as much 
oxygen gas as that of any other places. Dr. Priestley supposed 
that the purity of the air was preserved by the living functions 
of vegetables: but this hypothesis is highly objectionable ; for 
the air is as pure in winter when all Europe is covered with 
snow, as in summer when vegetation is in the utmost perfection. 
It appears, however, an obvious truth, that if the oxygen gas 
which is withdrawn from our atmosphere, by entering into new 
* Tentam. Med, Phys. p. 80. 
: combinations, 
