14 OF THE ASSIMILATION OF CARBON. 



pie, does not contain less oxygen than that found in jars buried for 

 1800 years in Pompeii — appears quite incomprehensible, unless 

 some cause exists capable of replacing the oxygen abstracted. 

 How does it happen, then, that the proportion of oxygen in the 

 atmosphere is thus invariable ? 



The answer to this question depends upon another, namely 

 what becomes of the carbonic acid produced during the respira- 

 tion of animals, and by the process of combustion ? A cubic 

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

 acid, does not change its volume. The billions of cubic feet of 

 oxygen extracted from the atmosphere, are immediately supplied 

 by the same number of billions of cubic feet of carbonic acid. 



The most exact and trustworthy experiments of De Saussure, 

 made in every season for a space of three years, have shown 

 that the air contains on an average 0-000415 of its own volume 

 of carbonic acid gas ; so that, allowing for the inaccuracies of the 

 experiments, which must diminish the quantity obtained, the pro- 

 portion of carbonic acid in the atmosphere may be regarded as 

 nearly equal to -foVo" P art °f lts weight. The quantity varies 

 according to the seasons ; but the yearly average remains cor- 

 tinually the same. 



We have reason to believe that this proportion was much 

 greater in past ages ; and nevertheless, the immense masses of 

 carbonic acid which annually flow into the atmosphere from sc 

 many causes, ought perceptibly to increase its quantity from year 

 to year. But we find that all earlier observers describe its 



yearly consumes 9505*2 cubic feet. 1000 million men yearly consume 

 9,505,200,000,000 cubic feet (Parisian). 



Without exaggeration we may suppose that double this quantity is con- 

 sumed in the support of respiration of the lower animals, and in the pro- 

 cesses of decay and combustion. From this it follows, that the annual con- 

 sumption of oxygen amounts to 2*392355 cubic miles, or in round numbers 

 to 2"4 cubic miles Thus, every trace of oxygen would be removed from 

 the atmosphere in 800,000 years. But it would be rendered quite unfit for 

 the support either of respiration or combustion in a much shorter time. 

 When the quantity of oxygen in the air is diminished 8 per cent., and the 

 oxygen thus abstracted is replaced by its own volume of carbonic acid, the 

 latter exerts a fatal action upon animal life, and extinguishes the combus- 

 tion of a burning body. 



