CHAPTER VII 



THE NITROGEN REQUIRED BY PLANTS 



IN the last chapter we found that the air is a 

 mixture of two gases nitrogen and oxygen and 

 that nitrogen forms four-fifths of the air. 



This gas is found combined with other substances 

 in both plants and animals, and can easily be recog- 

 nised. 



One of the simplest compounds containing 

 nitrogen is ammonia, which has a peculiarly 

 pungent smell. (For instance, take a little sal- 

 ammoniac and mix it in a mortar with lime. 

 Ammonia is at once set free, and we can notice 

 the peculiar smell of the gas.) 



If, then, we find that any substance can be made 

 to yield ammonia, we may take that as a proof that 

 it contains nitrogen combined with other substances. 



Now take some seeds of corn, and mix them with 

 a little soda-lime, and heat them strongly in a test- 

 tube. Ammonia is set free, and we can smell it 

 coming from the tube. 



