96 
Benzoic  Acid  from  Urine. 
j  Am.  Jour.  Pharm. 
{       Feb.,  1884. 
a  free  outlet  being  always  allowed  for  the  less  readily  condensible 
vapors. 
Before  the  end  of  the  operation  all  these  vapors  will  have  passed 
away  and  the  temperature  may  be  raised  even  to  230°  C.  without  any 
risk  of  contaminating  the  acid. 
The  second  test  is  to  prove  the  absence  of  cinnamic  acid,  and  depends 
on  the  fact  that  the  odor  of  oil  of  bitter  almonds  is  evolved  when 
cinnamic  acid  is  warmed  with  an  oxidizing  agent.  It  is  difficult  to 
get  benzoic  acid,  which  has  been  sublimed  directly  from  gum,  always 
free  from  cinnamic  acid ;  for  all  varieties  of  benzoin  occasionally 
co u tain  this  acid,  and  sometimes  it  has  been  said  no  benzoic  acid  ('  Phar- 
macographia ') ;  and  it  is  only  by  the  lime  extraction  method  that  the 
cinnamic  acid  could  be  got  rid  of,  as  it  sublimes  in  the  same  way  as 
benzoic  acid. 
The  third  test  is  to  prove  the  presence  of  volatile  hydrocarbons,  and 
depends  on  the  fact  that  known  quantities  of  styrol  and  vanillin  and 
some  other  liquid  hydrocarbons  reduce  a  known  quantity  of  solution 
of  permanganate  of  potassium  in  a  certain  time.  This  test  is  also 
faulty,  for  if  a  few  drops  of  permanganate  solution  be  added  to  a 
crystallized  solution  of  the  impure  urine-benzoic  acid,  decolorization 
occurs  in  a  very  short  time,  although  no  styrol  or  other  aromatic 
hydrocarbon  is  present.  Almost  any  organic  matter,  indeed,  will  effect 
this  change. 
The  United  States  Pharmacopoeia  implies  that  benzoic  acid  must  be 
made  from  benzoin  by  extraction  with  lime,  for  the  acid  is  to  be  white 
and  to  have  only  a  faint  aromatic  odor  of  benzoin.  It  is  not  to  have 
the  smell  of  oil  of  bitter  almonds  or  stale  urine,  thus  preventing  the 
use  of  benzoic  acid  prepared  from  toluene  or  from  urine. 
Two  additional  tests  are  given. 
1.  A  solution  of  benzoic  acid  in  pure  cold  sulphuric  acid,  when 
gently  warmed,  should  not  turn  darker  than  a  light  brown.  This  is  a 
good  test  for  the  absence  of  organic  impurity. 
2.  Benzoic  acid  mixed  with  freshly  ignited  and  moistened  cupric 
oxide  should  not  yield  a  green  coloration  to  the  flame  when  applied  on 
a  platinum  wire.  This  test  is  meant  to  prove  the  absence  of  chloro- 
benzoic  acid,  which  may  occur  as  an  impurity  if  the  benzoic  has  been 
made  from  toluene.  It  must  be  performed  with  great  care,  for  if  the 
mixture  be  allowed  to  get  too  hot,  the  cupric  oxide  combines  with  the 
benzoic  acid,  and  colors  the  flame  an  intense  green.    The  mass  then 
