NITROGEN FROM THE AIR. 96 



that our knowledge and powers are so limited, but 

 we have to take things as we find them. 



It has been found, however, that Nature does con- 

 tribute a small amount to the nitrogen fund of the 

 soil; and this, although too little for any perceptible 

 effect on our crops, is perhaps enough to slowly im- 

 prove a poor piece of ground, when left uncropped. 



The ammonia escaping from different sources 

 diffuses itself through the atmosphere; nitric acid 

 is formed by the electric spark passing through the 

 air during thunder showers. The rains absorb it 

 and carry it down to the ground. It is then utilized 

 by plant growth, or washed into the streams. 



This free contribution of nitrogen from the air 

 may help the poor owner or tiller of poor soil to 

 continue his unprofitable style of poor farming 

 until it lands him in the poor-house; but it is by 

 far too miserly to be of much use to the good farmer 

 whose crops are provided with liberal rations of 

 nitrogen by the free use of manures, and who, con- 

 sequently, has large and paying yields. 



I do not know but what it would be just as well, 

 practically, to forget entirely that nature grants us 

 this pitiful allowance, and to depend altogether on 

 our own facilities for supplying the soil with the 

 needed nitrogen in one of the various forms of ni- 

 trogenous manures. 



There is one way, however, in which we can draw 

 on the nitrogen supply of the air, and make it avail- 

 able at least to some extent. This is by means of 

 clovers and other leguminosse, which seem to have 

 the power of deriving their nitrogen from the air, 

 when they cannot get it from the soil or subsoil. Of 

 this I will speak in a later chapter. 



In nitrate of soda we probably have the cheapest 



