16 THE FEEDING OF ANIMALS 



exists in these in a much smaller proportion than carbon 

 or oxygen. Its source to the plant is largely water and it 

 is furnished to the animal in water and other compounds. 



12. Nitrogen and its compounds have been the 

 subject of much scientific investigation in their re- 

 lations to agricultural practice. Like oxygen, nitrogen 

 is an invisible, tasteless, and odorless gas, which, 

 according to previous determinations, forms about 77 

 per cent of atmospheric air by weight. The existence in 

 the air of newly discovered elements, such as argon, has 

 modified previous determinations. The only place in 

 nature where nitrogen or its compounds exist in large 

 quantities, outside of the air and in the tissues of living 

 organisms, is the sodium nitrate beds which are found 

 in Chile and other localities. Soil spaces contain nitrogen 

 and it is taken into solution in small proportions in all 

 natural waters. It is found in mineral and organic com- 

 pounds in the soil, but in quantities very insignificant as 

 compared with such elements as oxygen and silicon. Few 

 agricultural soils contain over }^ per cent of combined 

 nitrogen. Minute quantities of its compounds, such as 

 ammonium carbonate and ammonium nitrate, exist in 

 the atmosphere, which are being constantly carried to the 

 soil in rain-water and as constantly replaced by ammonia 

 from decomposing animal and vegetable matter and by 

 the products of oxidation of nitrogen through combustion 

 and electrical action. Although the compounds of nitro- 

 gen exist in a comparatively small proportion, they play 

 a very prominent part in agriculture, both commercially 

 and physiologically. The nitrogen balance of the farm is 

 important both to the crop-producer and the cattle-feeder. 



13. Supply of nitrogen. The available supply of 

 nitrogen compounds is often dangerously near the demand, 



