PREPARATION  OF  SPIRIT  OF  NITROUS  ETHER.  331 
will  often  go  on  to  the  end  without  a  variation  of  more  than  one 
or  two  degrees  of  temperature.  When  about  twelve  fluid-ounces 
of  liquid  have  been  distilled  the  action  will  slacken,  in  conse- 
quence of  the  exhaustion  of  the  nitric  acid,  and  this  will  be  im- 
mediately indicated  by  the  disappearance  of  the  froth  on  the 
surface  of  the  liquid.  The  suddenness  with  which  this  usually 
takes  place  is  remarkable.  It  is  followed  by  a  rise  of  tempera- 
ture in  the  liquid,  if  the  applied  heat  remain  unaltered,  but  when 
the  temperature  reaches  180°  the  heat  should  be  withdrawn,  and 
the  contents  of  the  retort  allowed  to  cool.  There  will  still  be  a 
portion  of  the  spirit  left  in  the  retort,  together  with  sulphuric 
acid,  sulphate  of  copper,  and  undissolved  copper,  and  it  is  for 
the  purpose  of  converting  this  spirit  into  nitrous  ether  that  the 
remaining  half-ounce  of  nitric  acid  is  to  be  added.  When  this 
addition  has  been  made  the  distillation  is  to  be  resumed  as  be- 
fore, until  the  distilled  product  amounts  to  15  fluid-ounces.  This 
product  consists  of  a  strong  spirituous  solution  of  nitrous  ether 
containing  thirty-five  per  cent,  of  the  crude  ether.  On  mixing 
it  with  the  remaining  two  pints  of  spirit,  it  will  have  the  strength 
indicated  in  the  British  Pharmacopoeia  of  1864,  and  will  nearly 
answer  to  the  other  tests  and  characters  there  given.  The  spe- 
cific gravity  will  be  0-845.  If  it  be  mixed  with  twice  its  volume 
of  a  concentrated  solution  of  chloride  of  calcium,  from  two  to 
three  per  cent,  of  nitrous  ether  will  separate  and  rise  to  the  sur- 
face of  the  liquid.  This  indicates  the  presence  of  ten  per  cent, 
of  ether,  as  eight  per  cent,  remains  unseparated. 
Spirit  of  nitrous  ether  made  in  this  way,  is,  I  believe,  equal  in 
every  respect  to  that  produced  by  any  of  the  previously  adopted 
processes,  and  it  is  better  and  stronger  than  most  of  what  is  met 
with  in  commerce.  It  is  much  stronger  than  that  made  by  the 
London  process,  although  the  quantity  of  nitric  acid  employed 
in  its  production  is  less  than  one-half,  and  the  loss  of  spirit  is 
less  than  one-third,  what  they  are  in  that  process.  It  is  there- 
fore a  very  economical  method  of  preparing  the  product ;  in  fact 
it  surpasses  all  the  other  processes  in  this  respect,  as  there  is  no 
avoidable  loss  of  nitric  acid  or  alcohol,  and  the  copper  which  is 
dissolved  is  recovered  as  sulphate  of  copper.  Only  about  half 
the  quantity  of  copper  used,  however,  is  thus  dissolved  ;  that 
