756 The Outline of Science 



again in the soil, or when a dead animal is buried by sexton beetles 

 and decomposes. The same result is reached when what remains 

 of a crop is ploughed in or when the stable manure is spread 

 upon the fields, and eventually takes the form of ammoniates or 

 the like, which the plants can utilise. 



On the other hand, when forests or coal-seams are burned 

 by man fixed nitrogen is lost in the combustion, and the amount 

 of free nitrogen in the atmosphere (four-fifths of the whole) is 

 increased. Combined nitrogen is similarly lost when gunpowder 

 explodes, and a small cannon shot, using up only a pound of 

 gunpowder, destroys combined nitrogen to the extent of the free 

 nitrogen in three million litres of atmospheric air. "In this sense," 

 Professor Bunge writes, "it may be affirmed that every shot from 

 a firearm kills, that it destroys life whether the ball strikes a liv- 

 ing being or not. For no life is lost by the death of the indi- 

 vidual; from the decay of the body equivalent new life arises. 

 But the destruction of combined nitrogen means the definite 

 diminution of the capital, upon the amount of which the total 

 number of living beings depends." Obviously this is taking a 

 very quantitative view of life. The vital equivalent of a lost 

 leader is not calculable! 



We see, then, that one of the farmer's main problems is to 

 keep up the supply of combined or fixed nitrogen in the soil. A 

 cheap way of doing this, referred to in the chapter on BOTANY, 

 is to cultivate Leguminous crops with root-tubercles, for by 

 means of the partner-Bacteria in the root swellings such plants 

 are able, in a way not yet understood, to capture the free nitrogen 

 of the air and fix it. If these crops are ploughed into the soil, in 

 whole or in part, they will make it rich for other and more valu- 

 able growths. But this is a slow process, and what the farmer 

 does is to manure his fields, with, in particular, a supply of nitrate 

 brought from the saltpetre fields of Chile. But Chilian nitrates 

 are expensive, and the supply is limited. Therefore we see the 

 enormous importance of the chemist's discovery that nitrates can 



