30 
Oxidation  of  Nitrogen. 
(Am.  Jour.  Pharm. 
\    January,  1915. 
and  possibly  in  a  slight  degree  in  the  bombardment  of  the  higher 
strata  of  air  by  cathode  and  similar  rays,  ultraviolet  light,  and  possibly 
by  other  radiations.  The  disintegration  of  radium  and  thorium  prod- 
ucts yields  a  small  amount  of  oxides  of  nitrogen.  It  has  been  esti- 
mated that  in  this  way  about  100,000,000  tons  of  fixed  nitrogen  are 
carried  to  the  earth  every  year  by  rain  water. 
The  other  natural  method  of  fixing  atmospheric  nitrogen  is  that 
of  the  action  of  bacteria  in  the  root  nodules  of  the  clovers,  peas, 
vetches,  and  other  legumes.  The  chemical  processes  are  very  com- 
plicated and  are  at  present  unknown.  This  process  is,  however,  of 
tremendous  importance  to  the  farmer,  and  is  probably  the  cheapest 
method  now  known  of  obtaining  nitrogen  as  a  fertilizer.  This 
method  is,  however,  quite  expensive,  in  that  cloverseed  is  expensive 
and  the  raising  of  a  crop  of  clover  requires  attention,  time,  and  the 
exclusion  of  other  crops.  On  the  poor  soils  where  humus  is  the  most 
needed  it  is  found  very  difficult  to  get  clover  to  grow.  Restoration 
of  fertility  to  run-down  soils  by  this  method  is,  therefore,  slow  and 
expensive. 
The  commercial  methods  of  manufacturing  nitrogen  salts  include 
the  cyanamide  process,  the  direct  synthesis  of  ammonia,  the  various 
nitride  processes  of  making  ammonia,  and  the  electrical  methods  of 
oxidizing  nitrogen. 
A  process  that  is  being  used  commercially  is  that  of  treating  cal- 
cium carbide  with  nitrogen  gas,  thus  yielding  cyanamide,  which  itself 
makes  a  good  fertilizer.  Although  the  reactions  are  known  to  be 
complex,  they  may  be  represented,  as  regards  the  end  products,  as 
follows : 
CaO  +  3  C  ^±  CaC2  +  CO, 
CaC2  +  N2  ->  CaCN2>  C. 
The  latter  reaction  begins  at  10000  C.  or  at  even  lower  temperatures. 
The  N2  may  be  prepared  by  the  Linde  process  or  by  passing  air  over 
hot  copper.  According  to  Caro,  the  energy  consumption  for  fixing 
one  ton  of  nitrogen  (including  making  the  CaC2,  azotizing,  machine 
driving,  grinding,  charging,  air  liquefaction)  is  less  than  3  H.P.  years. 
The  direct  combination  of  nitrogen  and  hydrogen  into  ammonia 
is  very  successful  when  done  on  a  small  scale  with  pure  gases,  but,  so 
far  as  is  generally  known,  this  process  is  not  being  worked  on  a  large 
scale.  A  German  company,  however,  is  planning  to  make  large  quan- 
tities of  ammonia  by  this  process. 
