Am.  Jour.  Pharni./ 
January,  1910.  f 
Ammonium  Benzoate. 
17 
per  cent,  of  ammonium  benzoate,  also  showed  a  decomposition  point 
practically  identical  with  that  of  the  pure  material.  These  results 
led  us  to  a  more  extended  and  systematic  investigation  of  the  effect 
of  the  presence  of  benzoic  acid  upon  the  decomposition  point  of 
ammonium  benzoate. 
Since  benzoic  acid  is  the  impurity  which  results  when  ammonium 
benzoate  is  partially  decomposed,  we  approached  the  problem  from 
the  two  extremes  of  ammonium  benzoate  and  benzoic  acid,  obtain- 
ing two  series  of  samples  which  gradually  approached  each  other  in 
composition.  The  first  series  was  obtained  by  subjecting  pure 
ammonium  benzoate  to  continual  desiccation  in  the  presence  of 
sulphuric  acid  in  a  Hempel  desiccator  under  diminished  pressure 
(about  50  mm.),  portions  being  removed  at  irregular  intervals  for 
analytical  and  melting-point  determinations.  In  this  way  we 
obtained  six  samples,  varying  in  composition  from  98.6  per  cent, 
to  57.5  per  cent,  ammonium  benzoate.  The  last  sample  (57.5  per 
cent.)  exhausted  the  supply  of  material  we  started  with  in  that 
experiment.  The  second  series  was  obtained  by  mechanically  mix- 
ing benzoic  acid  and  ammonium  benzoate  in  proportions  varying 
from  50  per  cent,  each  at  the  one  extreme  to  pure  benzoic  acid  at 
the  other,  six  samples  being  prepared  in  this  way. 
The  melting  or  decomposition  points  determined  for  the  different 
samples  of  both  series,  together  with  the  duration  of  desiccation 
required  to  produce  the  varying  degrees  of  decomposition  indicated 
in  the  first  series,  will  be  found  in  the  following  table.  The  samples 
of  the  first  series  have  been  designated  by  Roman  numerals  and 
those  of  the  second  by  letters.  The  method  used  for  determining  the 
melting  points  is  one  recently  adopted  in  this  laboratory,  according 
to  which  the  material,  within  certain  limits,  is  heated  at  a  definite 
rate  (30  per  minute  within  200  or  25 0  of  the  melting  point).  A 
standard  thermometer  was  used  and  the  observed  reading  was  cor- 
rected for  emergent  stem. 
.  It  would  seem  to  require  only  casual  consideration  of  the  tabu- 
lated data  to  lead  to  the  very  definite  conclusion  that  the  decom- 
position point  of  ammonium  benzoate  is  quite  useless  as  a  test  of 
purity — at  least,  in  the  presence  of  benzoic  acid,  even  to  the  extent 
of  nearly  50  per  cent. — and  that,  therefore,  the  statement  previously 
quoted  from  the  Pharmacopoeia  relative  thereto  should  either  be 
modified  so  as  to  insure  against  misinterpretation  or  should  be 
omitted.     The  melting-point  results  of  the  mixtures  shown  in 
