16 The Feeding of Animals 



of living organisms in a much smaller proportion than 

 carbon or oxygen. Plants obtain it largely from water, 

 and it is furnished to the animal body in water and in 

 other compounds. 



Nitrogen. Probably no element has been given 

 more attention in its relations to agriculture from the 

 scientific and practical standpoints than has nitrogen 

 as such and in its compounds. Like oxygen it is an 

 invisible, tasteless, and odorless gas which forms in the 

 free state a large part of the earth's atmosphere. The 

 air has been considered to be approximately 77 per 

 cent free nitrogen by weight, but the discovery of the 

 new element, argon, which has heretofore passed as 

 nitrogen, will slightly modify previous determinations. 



Nowhere outside of the air and the tissues of living 

 organisms does nitrogen exist in any form in compara- 

 tively large quantities. The soil spaces contain it and 

 it is taken into solution in small proportions in all 

 natural waters. It is found in the mineral, as well as 

 organic compounds of the soil, but in quantities which 

 seem insignificant as compared with other elements, 

 such as oxygen and silicon. Few agricultural soils 

 contain over one -half of one per cent of combined 

 nitrogen. Minute quantities of its compounds exist in 

 the atmosphere which are being constantly carried to 

 the soil in rain-water and as constantly replaced by the 

 ammonia from decomposing animal and vegetable mat- 

 ter and by the products of the oxidation of nitrogen 

 through electrical action and combustion. Notwith- 

 standing this comparatively small supply of nitrogen 

 compounds, they play a prominent part in agriculture. 



