NITROGEN IN AGRICULTURE. 301 



of the air-cells, and is expelled as nitrogen, without diminu- 

 tion of volume, or an}^ chemical change whatever. 



The volume of free nitrogen in the air is immense ; and its 

 weight, as it rests upon the earth's crust, can only be under- 

 stood by a consideration of the figures which approximately 

 represent it. The nitrogen of the air can be separated from 

 the oxygen and other gases and vapors present over the 

 earth's surface, and weighed. One thousand pounds of air 

 contains of 



Pounds. 



Nitrogen 7.55 



Oxygen 2.34 



Carbonic acid ......... .01 



Aqueous vapor 10 



10.00 



The whole weight of the nitrogen contained in the gaseous 

 envelope of our planet may approximately be stated to be 

 3,994,592,925,000,000 tons. 



The commercial value of nitrogen, as presented in the esti- 

 mates of chemists who make analyses of fertilizers, is about 

 twenty cents a pound. Apply this price to the great vol- 

 ume of nitrogen around us, and the value would reach a 

 point almost beyond the reach of figures to demonstrate. 

 For crop purposes, the nitrogen of the air is valueless to the 

 farmer; for, although it comes in direct contact with his soils, 

 mingles with them to considerable depths, the spongioles of 

 plants, penetrating everywhere, are not endowed with the 

 power of appropriating it to their uses, or combining it with 

 their structures. It also comes in direct contact with the 

 surfaces of plants above ground ; but this contact is produc- 

 tive of no combination or assimilation : vital plant-structures 

 and dead nitrogen, when brought together, do not permit 

 of the play of chemical affinities which result in chemical 

 unions. From a careful and candid consideration of the 

 experiments which have been made towards ascertaining 

 whether there is any absorption of nitrogen by the leaves 

 or other external organs of plants, I have no hesitation in 

 saying that they must be regarded as complete failures. The 

 affirmative results which some experimenters state to have 

 been reached are totally unreliable ; and the question stands 

 to-day a settled one, and that in tlie negative. 



