PURIFYING THE ATMOSPHERE. 873 



seem to be a law of nature, that plants not only 

 supply animals with nourishment, but preserve 

 the atmosphere in a state of purity, by absorbing 

 the vast quantities of carbonic acid generated 

 during the decomposition of organic matter, the 

 respiration of animals, and by ordinary combus- 

 tion, including what is thrown into the atmosphere 

 by volcanoes and hot springs. For we learn from 

 the recent valuable work of Liebig, on the appli- 

 cation of organic chemistry to agriculture, that 

 except during the early growth of plants, they 

 receive very little carbon from the soil, and actu- 

 ally derive nearly the whole of it from the atmos- 

 phere, which contains about T -oVo-th part of its 

 weight of carbonic acid, 27 per cent, of which is 

 pure carbon. He further maintains, that as a 

 column of air, weighing 2216.66 Ibs. Hessian 

 measure, rests upon every square Hessian foot, 

 the whole atmosphere must contain 3000 billion 

 pounds of carbon in the gaseous state : that as a 

 single man consumes 45 cubic feet of oxygen in 

 twenty-four hours, or 16,425 cubic feet annually, 

 1000 millions of human beings, would increase 

 the amount of carbonic acid in the atmosphere 

 100 per cent, in 1000 years, by respiration alone ; 

 without taking into account the enormous quan- 

 tities supplied by other sources. 



For example, he estimates the yearly amount 

 of oxygen consumed by ordinary combustion, in 

 the town of Giessen, as eight times greater than 



