CARBONIC ACID OF TOWNS. 57 
some millions of cubic feet of the gas, whose 
connexion with the world of plants has de- 
tained us for the last few pages — carbonic- 
acid. One healthy adult man, in the course 
of a day of twenty-four hours, pours from his 
lungs about fifteen thousand cubic inches of 
the same gas, containing, upon calculation, about 
six ounces of solid carbon. So that, if we 
consider London to contain two millions of 
inhabitants, this number of human beings every 
twenty-four hours casts up, in the form of gas 
from their lungs, the astonishing amount of 
upwards of three hundred and thirty tons of 
carbon. If we could reduce this to a solid 
form, and suppose the products of London 
respiration for one day stored up as charcoal, 
or coke, and now grant that a family uses 
twenty tons of fuel in a year, then the breathing 
of the population of London for twenty-four 
hours would furnish one such family with house- 
hold fuel for sixteen years and a half, and would 
demand a coal-cellar as great as two or three 
houses put together. 
These facts are mentioned, not to excite an 
unreflective curiosity, but to impress upon the 
