CONSUMPTION AND BBSTOBATION OF CARBONIC ACID. 49 



cultivation, wodd 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 lunes at each breath, returns charged with carbonic 

 •cid. 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 

 tcid unites with the lime, and the clear lime water 

 becomes in a few moments quite milky, owing to the 

 formation of carbonate oi lime. 



2. Another source from whence carbonic acid is 

 derived in irumenseqij i^ ordinary combustion. 

 All combustible botlif-s ; tires, produce this gas 

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

 the leading combustible substance in all kinds of fuel» 

 in wood, coal, charcx)al, oil, resin, pitchy turpentine, 

 etc. While 1 ' ' * *' \v»xen, 

 iind become^ ibus- 

 tion is going on, lht!» : a. An 

 instance is to be setn acide by 

 means of burning charcoal. In trance, particularly, 

 the misguided and wicked persons who thus rashly 

 desire to take away their own lives, li^^ht a pan of 

 charcoal and shut themselves up with it in a cloM 

 room. The carlx>nic acid produced soon Alls the room, 

 and in a short time (!•- ' ii>. 6. It is easy to iM 

 that combustion mu.st ... send vast quantitieaof 

 this gas into the atiaosf»h«re. Particularly h tkis 



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