NITRATE  OF  AMMONIA  AND  NITROUS  OXIDE.  409 
cial  nitrate  of  ammonia ;  but  if  the  solution  is  rendered  only 
turbid,  without  affording  an  immediate  precipitate  with  the  above 
reagents,  it  is  sufficiently  pure. 
The  various  effects  of  increasing  heat  upon  nitrate  of  ammonia 
are  shown  by  the  following  table : 
At  226°  F.  fuses  perfectly. 
At  302°  F.  emits  white  fumes,  condensing  in  drops. 
At  347°  F.  effervesces  slightly. 
At  356°  F.  boils  without  decomposition. 
At  437°  F.  effervesces  rapidly. 
At  460°  F.  begins  to  evolve  gas. 
At  482°  F.  evolves  gas  in  abundance. 
Above  500°  F.  nitric  oxide  is  given  off. 
To  determine  the  temperature,  thermometers  have  been  pre- 
pared which  may  be  passed  through  the  cork  and  into  the  retort, 
marking  the  following  degrees  :  226°,  356°,  460°,  482°,  500°  F. 
To  obtain  the  largest  amount  of  gas,  the  nitrate  should  first 
be  melted  in  the  retort  at  a  temperature  just  sufficient  (226°  to 
250°  F.)  When  melted,  the  heat  may  be  at  once  carried  up  to 
the  point  of  decomposition,  460°  F.  If  a  gradually  increasing 
heat  is  used  after  the  salt  is  melted,  a  portion  of  it  will  sublime 
unchanged  until  the  temperature  reaches  460°  F.  The  heat 
should  never  be  allowed  to  rise  above  482°  F.,  for  beyond  that 
noxious  products  are  generated.  After  the  gas  has  begun  to 
come  over  briskly,  the  appearance  of  copious  white  fumes  in  the 
retort  is  an  indication  that  the 'heat  is  too  great.  The  nearer 
the  heat  can  be  kept  at  the  point  necessary  to  generate  nitrous 
oxide,  the  purer  will  be  the  gas. 
After  the  decomposition  has  fairly  commenced,  the  heat  must 
be  lowered  rather  than  increased,  as  by  that  time  the  sand,  re- 
tort, and  the  salt  itself  have  accumulated  enough  heat  to  carry 
on  the  generation  of  gas  for  some  time,  even  if  the  flame  were 
entirely  withdrawn. 
A  sand-bath  should  always  be  used  to  protect  the  retort  from 
the  direct  heat,  which  may  be  supplied  by  means  of  a  suitable 
gas-burner,  or  by  an  alcohol  or  kerosene  lamp. 
The  retort  must  be  of  glass  ;  no  other  practical  material  has 
yet  been  found  to  answer  the  purpose.    The  retort  is  usually 
