i6 
Ammonium  Benzoate. 
J  Am.  Jour.  Pharm 
\    January,  1910. 
Several  grams  of  ammonium  benzoate,  through,  which  a  slow 
current  of  air  was  drawn  for  eighteen  hours,  lost  an  amount  of 
ammonia  corresponding  to  about  2  per  cent,  of  ammonium  benzoate, 
and  it  appeared  that  the  alteration  had  all  taken  place  at  the  point 
where  the  current  of  air  first  met  the  sample.  Of  five  samples  of 
ammonium  benzoate  kept  in  an  ordinary  desiccator,  over  H2S04 
for  two  and  one-half  months,  four  lost  ammonia  corresponding  to 
about  5-8  per  cent,  of  ammonium  benzoate.  The  fifth,  however,  lost 
an  amount  corresponding  to  20.7  per  cent.  Under  diminished  pres- 
sure, as  might  be  expected,  the  loss  of  ammonia  is  very  rapid,  as 
will  be  seen  by  reference  to  the  last  four  analyses  given  in  Table  I, 
and  to  the  experiment  described  in  connection  with  the  melting- 
point  determinations. 
The  Pharmacopoeial  Litmus  Paper  Test. — On  applying  this  test 
to  a  number  of  samples  containing  varying  per  cent's  of  benzoic 
acid,  it  was  found  that  even  as  high  as  8  per  cent,  of  the  latter 
produced  no  distinct  change  in  blue  litmus  paper ;  with  samples  con- 
taining 12  per  cent,  benzoic  acid,  however,  the  change  could  be 
detected.  It  is  therefore  apparent  that  the  litmus  paper  test  is 
valueless  as  an  indication  of  the  partial  deterioration  of  ammonium 
benzoate  within  the  limit  stated. 
Melting  or  Decomposition  Point  of  Ammonium  Benzoate. — The 
specifications  under  ammonium  benzoate,  in  the  Pharmacopoeia, 
contain  the  following  statement:  "The  salt  fuses  at  1930  to 
1940  C.  (379.40  to  381. 20  F.)  with  decomposition  ..."  Con- 
sidered in  connection  with  the  purity  rubric  of  98  per  cent.,  this 
statement  would  doubtless  be  generally  construed  to  mean  that  if 
a  sample  of  ammonium  benzoate  fuses  with  decomposition  at  193 0 
to  1940  C,  it  may  be  considered  to  be  98  per  cent,  pure  or  very 
nearly  so.  Upon  this  assumption  and  in  connection  with  an  inves- 
tigation now  being  conducted  in  this  laboratory  upon  the  melting 
points  of  Pharmacopoeial  compounds,  the  decomposition  point  of  four 
samples  of  ammonium  benzoate  had  been  determined,  with  results 
that  were  practically  concordant  for  the  different  samples  and  with 
the  U.S. P.  requirement,  thereby  indicating  a  purity  of  at  least  98 
per  cent.,  which  subsequent  analyses  confirmed.  The  analytical 
data  for  the  different  samples,  however,  showed  a  variation  as  great 
as  1  per  cent.,  with  no  corresponding  variation  of  the  decomposition 
point.  Another  sample  which  had  been  kept  in  a  vacuum  desiccator 
for  a  short  time  and  was  found  upon  analysis  to  contain  only  94 
