310  Spirit  of  Nitrons  Ether.  {^'A^l'S:™' 
encountered  in  this  method.  One  of  these  difficulties  attended  the 
assaying  of  samples  of  the  spirit  which  were  acid  in  reaction  ;  it 
consisted  of  a  decomposition  between  the  acid  spirit  and  the  potas- 
sium iodide,  with  evolution  of  nitrogen  dioxide  before  the  normal 
sulphuric  acid  was  added.  Spirit  of  nitrous  ether  is  usually  acid;  of 
the  sixteen  samples  examined  during  the  course  of  this  work,  not  one 
was  neutral,  but  most  of  them  were  very  acid.  To  overcome  the 
difficulty  referred  to,  the  sample  to  be  assayed  was  neutralized  by 
mixing  it  with  one-fifth  its  volume  of  an  alcoholic  solution  of  potas- 
sium hydrate.  Six  c.c.  of  this  mixture  instead  of  5  c.c.  of  the  origi- 
nal sample  were  then  taken  for  each  estimation. 
The  following  figures  show  the  results  which  were  obtained  by 
the  official  method  on  the  same  sample,  before  and  after  neutral- 
izing : 
Sample  A.  Acid.  Neutralized. 
(1)  5  c.c.  gave  22*0  c.c.  NO  and  21*0  c.c.  NO. 
(2)  5  "      "    24-0  "     "     "    20-4    (C  " 
(3)  5  "      "    24-4  "      "     "    20-4    "  " 
The  other  difficulty  encountered  in  the  official  assay  process  was 
the  displacement  of  air  from  the  aqueous  solution  of  potassium 
iodide  when  this  liquid  was  let  into  the  burette  of  the  nitrometer 
containing  the  spirit  on  top  of  the  brine.  Any  inaccuracy  which 
might  arise  from  this  cause  could  be  prevented  by  raising  the  level 
tube  and  then  opening  the  stopcock  so  the  air  could  pass  out.  But 
this  could  not  be  done  unless  the  sample  was  free  from  acid,  on 
account  of  the  premature  reaction  which  takes  place  between  the 
potassium  iodide  and  the  spirit  in  the  presence  of  acid.  To  obviate 
this  difficulty,  I  tried  using  a  saturated  alcoholic  solution  of  potas- 
sium iodide  in  place  of  the  aqueous  solution,  as  directed  by  the 
United  States  Pharmacopoeia.  The  results  were  satisfactory,  as  but 
little  or  no  air  bubbles  collected  in  the  burette.  In  order  to  supply 
the  required  amount  of  potassium  iodide,  which  is  not  so  soluble  in 
alcohol  as  in  water,  20  c.c.  of  a  saturated  alcoholic  solution  were 
used  instead  of  the  10  c.c.  of  aqueous  solution  of  potassium  iodide. 
Three  samples  were  neutralized  with  the  alcoholic  solution  of 
potassium  hydrate,  and  submitted  to  the  official  method  of  assay 
with  the  nitrometer,  the  alcoholic  solution  of  potassium  iodide  being 
used  in  place  of  the  aqueous  solution  ordered  by  the  Pharmacopoeia. 
The  results  were  as  follows  : 
