CONSUMPTION AND RESTORATION OF CARBCNIC ACID. 49 



cultivation, would be exhausted in from seven to ten 

 years. There would thus be some cause for apprehen- 

 sion on this point, could we not indicate several sources 

 which constantly tend to keep up the necessary supply. 



1. One of the most important of these is the 

 breathing of animals: the pure air that is drawn into 

 the lungs at each breath, returns charged with carbonic 

 acid, it is for this reason that the air in a close room 

 where there are many people becomes so unwholesome, 

 and after a time intolerable. The carbonic acid 

 breathed out into the air, has rendered it deleterious 

 to animal life. A direct proof of the quantity of car- 

 bonic acid breathed in this way from the lungs, may 

 be given by blowing through a tube into lime water, 

 made by pouring water upon common quicklime and 

 allowing it to settle and become clear. The carbonic 

 acid unites with the lime, and the clear lime water 

 becomes in a few moments quite milky, owing to the 

 formation of carbonate of lime. 



2. Another source from whence carbonic acid is 

 derived in immense quantities, is ordinary combustion. 

 All combustible bodies used for fires, produce this gas 

 while burning. Carbon, in one form or another, is 

 the leading combustible substance in all kinds of fuel, 

 in wood, coal, charcoal, oil, resin, pitch, turpentine, 

 etc. While burning, the carbon unites with oxygen, 

 and becomes carbonic acid. Whenever then combus- 

 tion is going on, this gas is largely produced, a. An 

 instance is to be seen in the practice of suicide by 

 means of burning charcoal. In France, particularly, 

 the misguided and wicked persons who thus rashly 

 desire to take away their own lives, light a pan of 

 charcoal and shut themselves up with it in a close 

 room. The carbonic acid produced soon fills the room, 

 and in a short time destroys life. b. It is easy to see 

 that combustion must annually send -ast quantities of 

 this gas into the atmosphere. Particularly is this 



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