398  Preparation  of  Nitrous  Oxide.  { "'"'isss''''"" 
PREPARATION  OF  NITROUS  OXIDE. 
By  p.  Cazeneuve. 
The  explosions  which  sometimes  take  place  in  the  preparation  of 
this  gas  on  the  large  scale,  are  explained  by  the  fact  that  the  decom- 
position of  ammonium  nitrate  is  an  exothermic  reaction,  and  that  the 
large  quantity  of  heat  thus  liberated  added  to  that  directly  applied,  is 
capable  of  causing  the  sudden  decomposition  of  the  whole  mass  of  the 
salt.  The  process  is  often  slow  in  beginning  on  account  of  the  con- 
tained moisture,  and  hence  the  operator  is  apt  to  apply  undue  heat  at 
first.  Therefore,  the  salt  should  previously  be  dried  in  a  capsule  at  a 
temperature  below  200°,  and  the  retort  should  be  heated  slowly  until 
the  disengagement  of  gas  begins,  when  only  a  very  gentle  heat  will  be 
required,  and  tlie  operation  should  not  be  pushed  too  far  towards  the 
end.  That  the  recently  prepared  gas  has  an  irritating  odor  and  causes 
symptoms  of  asphyxia,  whilst  after  standing  for  some  days  in  the  gas- 
holder it  becomes  easier  to  l)reathe,  is  due  to  the  well-known  difficulty 
of  completely  removing  small  quantities  of  one  absorbable  gas  from 
another,  even  when  the  absorbing  solution  is  very  energetic  in  its 
action.  The  author  found  that  nitrous  oxide  even  after  slow  passage 
through  solutions  of  ferrous  sulphate  and  of  sodium  hydrate,  retained 
this  irritating  odor,  which  he  traced  to  the  presence  of  a  little  hyponi- 
trous  acid.  But  when  the  gas  was  several  times  shaken  up  in  a  test- 
tube  with  a  solution  of  ferrous  sulphate,  the  irritating  odor  was  at  once 
removed,  and  the  same  effect  was  produced  by  allowing  it  to  remain 
24  liours  in  the  gasholder.  The  author  reconmiends  that  the  gas  should 
in  all  cases  be  prepared  a  sufficient  time  beforehand.  The  diminution 
in  the  anaesthetic  properties  of  the  gas  after  remaining  for  a  time  in  the 
gasholder,  is  due  to  the  fact  that  the  nitrous  oxide  always  contains  a 
little  free  oxygen  and  free  nitrogen,  and  that  during  a  prolonged  stay 
in  the  gasholder,  the  water  gradually  absorbs  the  protoxide;  the  rela- 
tive proportions  of  oxygen  and  of  nitrogen  are  thereby  so  increased 
that  the  anaesthetic  property  of  the  gas  is  sensibly  diminished. 
The  author  has  examined  the  liquefied  nitrogen  protoxide,  prepared 
in  Paris  by  Duflos,  and  in  London  by  Barth,  and  sold  in  cast-iron 
bottles.  He  finds  these  products  are  chemically  pure,  and  therefore 
their  employment  in  dental  practice  offers  great  advantages. — Jour. 
Chem.  Soc,  May,  1885,  p.  613;  from  J.  Pharm.,  [5],  XI,  67-73. 
