ITS SOURCE THE ATMOSPHERE. 45 



in the atmosphere, which scarcely amounts to ^th 

 per cent.5 sufficient for the wants of the whole vege- 

 tation on the surface of the earth, — is it possible 

 that the carbon of plants has its origin from the air 

 alone ? This question is very easily answered. It 

 is known, that a column of air of 2441 lbs. weight 

 rests upon every square Hessian foot (=0*567 square 

 foot English) of the surface of the earth; the diame- 

 ter of the earth and its superficies are likewise known, 

 so that the weight of the atmosphere can be calcu- 

 lated with the greatest exactness. The thousandth 

 part of this is carbonic acid, which contains upwards 

 of 27 per cent, carbon. By this calculation it 

 can be shown, that the atmosphere contains 3306 

 billion lbs. of carbon ; a quantity which amounts to 

 more than the weight of all the plants, and of all the 

 strata of mineral and brown coal, which exist upon 

 the earth. This carbon is, therefore, more than ade- 

 quate to all the purposes for which it is required. 

 The quantity of carbon contained in sea-water is 

 proportionally still greater. 



If, for the sake of argument, we suppose the su- 

 perficies of the leaves and other green parts of plants, 

 by which the absorption of carbonic acid is effected, 

 to be double that of the soil upon which they grow, 

 a supposition which is much under the truth in the 

 case of woods, meadows, and corn-fields ; and if we 

 further suppose that carbonic acid equal to 0-00067 

 of the volume of the air, or i^th of its weight, 

 is abstracted from it during every second of time, 

 for eight hours daily, by a field of 53,820 square feet 

 ( = 2 Hessian acres); then those leaves would re- 

 ceive 1102 lbs. of carbon in 200 days.* 



* The quantity of carbonic acid which can be extracted from the air 

 in a given time, is shown by the following calculation. During the 

 white- washing of a small chamber, the superficies of the walls and roof 

 of which we will suppose to be 105 square metres, and which receives 

 six coats of lime in four days, carbonic acid is abstracted from the air, 

 and the lime is consequently converted, on the surface, into a carbon- 

 ate. It has been accurately determined that one square decimetre re- 

 ceives in this way, a coating of carbonate of lime which weighs 0-732 

 grammes. Upon the 105 square metres already mentioned there must 



