On Respiration and Animal Heat. 27 
The quantity of carbonic acid gas expired 
ina day may be calculated thus: the whole 
quantity of gases expired in a day being as 
stated above =46,5lbs. troy, and 4 per cent. 
or +, of this in bulk, being carbonic acid, 
we have +£:5=1,86lbs.; but carbonic acid 
being 13 times the weight of an equal bulk 
of common air, we have 2,8 lbs. troy for the 
weight of carbonic acid gas expired in a day. 
There is a considerable diversity in different 
authors, and even in the same author at dif- 
ferent times, respecting the quantity of car- 
bonic acid, obtained by respiration. Lavoi 
sier, in his first memoir in 1789, and Davy, 
nearly coincide with the results I have given 
above from my own experience. Afterwards, 
it seems, that Lavoisier made the quantity 
much less, not one half of the above. I can- 
not conceive what could induce him to rate 
it solow. On the other hand, Dr. Menzies — 
estimates the quantity nearly 4lbs. troy; 
which, I think, must be above the medium 
for men in general. . 
The quantity of aqueous vapour exhaled 
from the lungs in a day has been variously 
estimated ; and a greater uncertainty respect- 
ing it subsists at this moment, than respecting 
any other product of respiration. Dr. Hales, 
by experiment, found that 20 oz. per day were 
D2 
