Am.  Jour.  Pharm. ) 
August,  1911.  ; 
Estimation  of  Nitroglycerin. 
363 
Gunning  method  gave  8.642,  8.717,  8.732  and  8.822  per  cent,  of 
glyceryl  trinitrate, — average  8.72  per  cent.  w.v.  The  evaporation 
method  therefore  gives  high,  though  uniform  results. 
In  operating  the  Kjeldahl-Gunning  method  there  is  trouble  with 
frothing  unless  the  alcohol  is  first  driven  ofif  completely,  a  trouble- 
some matter  to  operate  without  loss  in  a  Kjeldahl  flask.  The  precau- 
tion must  also  be  taken  to  entirely  dissolve  the  nitroglycerin  in  the 
acid  before  heating,  a  matter  which  requires  a  thorough  shaking  and 
a  little  patience,  but  avoids  subsequent  loss  by  minute  explosions. 
Tested  by  the  phenoldisulphonic  acid  method  this  solution  showed 
8.3  per  cent,  w.v.,  which,  considering  the  minute  quantity  used  for 
this  test,  is  very  satisfactory. 
Two  other  samples  of  the  same  order-lot  of  solution,  but  taken 
from  different  containers,  were  tested  by  the  evaporation,  Dumas, 
Kjeldahl-Gunning,  and  the  colorimetric  methods.  The  results  follow  : 
Solution  No.  2.  Spec.  Grav.  at  26°  C.  0.8390. 
Evaporation  method  5.91  per  cent,  and  5.84  per  cent.  w.  v. 
Dumas   (combustion)   method  5.79  per  cent.  5.85  and  5.84  per  cent.  w.  v. 
Kjeldahl-Gunning  5.82  per  cent.  w.  v. 
Solution  No.  3.  Spec.  Grav.  at  25°  C.  0.8536. 
Evaporation  method  8.83  and  8.85  per  cent.  w.  v. 
Dumas  (combustion)  method  8.534  per  cent,  and  8.545  per  cent.  w.v. 
Kjeldahl-Gunning  8.42  per  cent.  w.  v. 
From  each  of  these,  dilutions  were  made  to  contain  i  gram  of 
nitroglycerin  in  loo  c.c.  of  alcohol  solution,  at  20°  C.  calculated  from 
the  Dumas  estimation,  and  these  dilutions  were  tested  by  the  colori- 
metric (phenoldisulphonic  acid)  method.  Each  of  four  solutions 
tested  I  gram  in  100  c.c.  colorimetrically. 
This  method  therefore  gives  as  accurate  results  as  a  colorimetric 
method  may,  and  for  the  estimation  of  minute  quantities  is  greatly 
to  be  preferred. 
The  method  of  a])plying  the  test  is  essentially  the  same  as  is  used 
in  water  analysis.  The  standard  solution  of  potassium  nitrate  was 
used  as  standard.  This  is  made  by  dissolving  0.722  (0.7217)  gram 
of  pure  fused  potassium  nitrate  in  sufficient  water  to  make  1000  c.c. 
One  c.c.  of  this  solution  contains  0.0001  gram  nitrogen  in  the  form 
of  nitrate  and  1.2  c.c.  of  this  solution  contains  the  same  amount  of 
nitrogen  as  i/ioo  grain  of  pure  nitroglycerin.  Of  the  alcoholic 
solutions  the  equivalent  of  0.00065  Gm.  (or  i/ioo  grain)  of  pure 
