ITS PROPORTION IN THE ATMOSPHERE. 17 



feet of oxygen in 24 hours; 10 centners of charcoal 

 consume 58,112 cubic feet of oxygen during its 

 combustion ; and a small town like Giessen (with 

 about 7000 inhabitants) extracts yearly from the 

 air, by the wood employed as fuel, more than 1000 

 millions of cubic feet of this gas. 



When we consider facts such as these, our 

 former statement, that the quantity of oxygen in 

 the atmosphere does not diminish in the course 

 of ages*, that the air at the present day, for 

 example, does not contain less oxygen than that 

 found in jars buried for 1800 years in Pompeii, 

 appears quite incomprehensible, unless some 

 source exists whence the oxygen abstracted is 

 replaced. How does it happen, then, that the 

 proportion of oxygen in the atmosphere is thus 

 invariable ? 



The answer to this question depends upon an- 

 other ; namely, what becomes of the carbonic acid, 

 which is produced during the respiration of animals, 

 and by the process of combustion ? A cubic foot 

 of oxygen gas, by uniting with carbon so as to form 



* The air contains, in maxima, TcyBfss carbonic acid gas and 

 oxygen gas. A man consumes, in one year, 166,075 cubic feet of oxygen 

 gas (or 45,000 cubic inches in one day, according to Lavoisier, Seguin, 

 and Dary); a thousand million men must accordingly consume 166 

 billion cubic feet in one year ; this is equal to y^ of the quantity 

 which is contained in the air in the form of carbonic acid. The 

 carbonic acid in the air would thus be doubled in 1000 years, 

 and man alone would exhaust all the oxygen, and convert it into car- 

 bonic acid in 303 times as many years. The consumption by animals, 

 and by the process of combustion, is not introduced into the calcula- 

 tion. 



C 



