290 
SPIRITUS  2ETHERIS  NITRICI. 
lished.  From  this  point  the  temperature  gradually,  and  toward 
the  last,  very  slowly  rises  to  184°,  when  5J  or  6  pints  of  color- 
less distillate  will  have  passed  over.  This  distillate  is  free  from 
any  perceptible  odor  of  hyponitrous  ether,  but  has  throughout  a 
distinct  odor  of  sulphuretted  hydrogen.  The  salt  in  the  retort 
forms  a  cake  at  the  bottom,  and  the  liquid  boils  around  and  over 
it  without  any  apparent  effect  upon  it.  The  distillation  then 
slackens  somewhat,  but  no  perceptible  reaction  will  have  taken 
place  till  6  pints  of  colorless  and  odorless  (except  for  sulphuretted 
hydrogen)  distillate  has  passed  over.  An  hour  or  more  is  thus 
occupied  before  the  period  of  reaction  arrives.  The  cake  then 
commences  to  dissolve  and  break  up,  the  solution  becomes 
gradually  of  a  deeper  yellow  tinge,  faint  yellow  vapors  appear 
in  the  retort,  the  temperature  rises  slowly  to  185°  or  136p,  the 
distillation  increases,  and  the  distillate  becomes  perceptibly 
yellow.  Coincidently  with  these  changes,  and  indicating  distinct- 
ly the  full  establishment  of  etherification,  the  temperature  in  the 
retort  commences  to  fall.  When  it  has  fallen  one  or  two  degrees 
the  heat  should  be  shut  off  and  the  reaction  be  allowed  to  go  on 
spontaneously,  or  with  only  a  very  slight  heat  at  most.  As  the 
temperature  falls,  the  distillation  slackens,  till  at  170°  it  only 
comes  over  by  a  fast  dropping.  If  the  prescribed  quantity  has 
not  passed  over,  the  heating  should  then  be  cautiously  resumed, 
and  the  remainder  driven  over  at  a  temperature  not  exceeding 
180°. 
If,  on  the  contrary,  the  active  heating  should  have  been 
too  long  continued,  and  the  reaction  becomes  too  active,  so  that 
much  gas  and  uncondensed  ether  vapor  passes  over,  the  heat 
must  be  entirely  withdrawn  and  the  retort  cooled  with  water, 
copiously  applied.  This  requires  rapid  and  dexterous  manipula- 
tion to  avoid  an  undue  proportion  of  aldehyd  in  the  distillate  ; 
for,  although  aldehyd  comes  over  at  all  stages  of  the  process,  it 
comes  much  more  rapidly  as  the  temperature  and  activity  of  the 
reactions  increase.  It  is  then,  probably,  that  it  is  formed  too 
rapidly  to  be  all  of  it  fixed  by  the  secondary  reactions,  and  thus 
passes  over  with  the  distillate. 
It  is  sometimes  difficult  to  get  a  gallon  of  distillate  below  180°, 
in  which  case  the  thermometer  may  be  made  to  rise  to  182°  or 
184°.    A  temperature  of  186Q,  however,  can  never  be  exceeded 
