34 FERTILIZERS. 



WHAT IS NITROGEN? 



The air mass which surrounds the earth for a depth of 

 about fifty miles, as it flashes through space more than 

 twenty times swifter than a cannon-ball at the highest 

 velocity, is made up of about four-fifths nitrogen and one- 

 fifth oxygen gas. This gives unnumbered thousands of 

 tons of nitrogen always right at hand, but never avail- 

 able ; for human knowledge has not as yet discovered a 

 way by which nitrogen can be economically got at for 

 plant-food. We have to depend, for our supply, wholly on 

 what plants and animals have incorporated into their 

 structure ; using their waste in the form of manure and 

 dead remains, either from land or sea, for our source of sup- 

 ply. The ammoniated liquor from the gas-works is but the 

 waste produced from the remains of ancient forests, which 

 we burn as coal. The same is true of animal life as of plant 

 life. Though over three-fourths of the air we breathe is 

 nitrogen, and it enters so largely into the composition of 

 our bodies, yet we have to obtain it from the animal 

 and vegetable food we eat. As the product of animal 

 waste in drinking-water, it sometimes causes dangerous 

 fevers. When nitrogen is combined with hydrogen, 18 

 parts of hydrogen to 82 parts of nitrogen, we have am- 

 monia, one of the most common forms in which, from the 

 waste of both animals and plants, nitrogen is fed to our 

 crops. 



The other most important source of nitrogen is nitric 

 acid. This is a combination of nitrogen with oxygen ; 

 and nitrates, of which we see frequent mention in all 

 works on manures, are a combination of the nitric acid 

 with soda, potash, and other materials, which are called 

 bases. It is .well to fix in the mind, that, in changing 

 nitrogen to ammonia in any manure analysis, we must add 



