Tlie    Chemical   Relations   of   the   Element   Nitrogen.  —  In

compounds  with  hydrogen  and  the  metals  nitrogen  is  trivalent,
while  in  those  containing  oxygen  and  other  negative  elements,  it  is
frequently  quinquivalent.  It  is  a  non-metal,  for  its  oxides  are  acidic
(p.  272).  The  compounds  of  nitrogen  are  often  extremely  active
and  interesting.  Those  of  them  which  we  have  to  discuss  in  inor-
ganic chemistry  are  ammonia  NH3  and  nitric  acid  HN03,  and
several  related  substances.
Occurrence  and  Preparation.  —  Free  nitrogen  is  present  ir
the  air.  The  nitrates  of  potassium  and  sodium  are  found  in  Bengal
and  Peru  respectively.  Natural  manures,  such  as  guano,  contain
large  quantities  of  nitrogen  compounds,  and  owe  part  of  their  value
as  fertilizers  to  this  fact.  Nitrogen  is  an  essential  constituent  of
vegetable  and  animal  matter.  The  albumins,  for  example,  contain
on  an  average  about  15  per  cent  of  combined  nitrogen.
Nitrogen  containing  about  one  per  cent  of  argon  (q.v.)  is  obtained
by  burning  phosphorus  in  air,  or  by  passing  air  over  heated  copper.
Pure  nitrogen  is  prepared  by  heating  ammonium  nitrite :

NH4NO2  ->  2H20  +  N2.
In  practice,  strong  solutions  of  ammonium  chloride  and  sodium
nitrite  are  mixed,  a  double  decomposition  results  in  the  formation  of
ammonium  nitrite,  NH4C1  +  NaN02  <=»  NH4NO2  +  NaCl,  and  this
breaks  up  when  heat  is  applied,  giving  nitrogen.
279


280  COLLEGE    CHEMISTRY

We  may  also  prepare  nitrogen  by  the  oxidation  of  ammonia  (NH3) ,
by  passing  the  latter  over  heated  cupric  oxide  (see  p.  282),  or  by  the
reduction  of  nitric  oxide  (NO)  by  passing  this  gas  over  heated
copper.
