Am.  Jour.  Pharm. ) 
'     Feb.,  1884.  J 
Benzoic  Acid  from  Urine. 
95 
acid  is  then  added  in  excess,  and  the  hippuric  acid  which  separates  is 
washed  and  recrystallized  and  sometimes  further  purified  and  decolor- 
ized. The  purified  hippuric  acid  is  then  heated  with  strong  hydro- 
chloric acid  and  the  mixture  kept  at  its  boiling  point  till  the  hippuric 
acid  has  entirely  disappeared  and  dark  oily  drops  of  benzoic  acid  have 
begun  to  form.  On  cooling  and  adding  water  the. benzoic  acid  crystal- 
lizes out  in  the  form  of  flattened  plates,  which  are  washed  and  dried. 
f  (CH2-(NH-C7H50)  ,   f  H   _  f  CH2NH2  ,    f  C7H50  Qr  f  C6H5 
tCO-OH  +\OH-\COOH     +\OH  or\COOH 
Benzamidoacetic  Acid,  ,     Water  =  Amidoacetic  ,  Benzoic  Acid, 
or  Hippuric  Acid.    4_t~  Acid 
or  Glycocine. 
Benzoic  acid  thus  obtained  has  that  peculiar  urine-like  odor  which 
quite  unfits  it  for  use  in  medicine. 
I  have  found,  however,  that  when  this  impure  acid  is  carefully  sub- 
limed, it  can  be  obtained  in  a  state  of  perfect  purity  and  in  beautiful 
crystals,  which  recrystallize  from  water  in  a  form  different  from  that 
in  which  the  acid  crystallizes  before  sublimation,  but  identical  with 
that  in  which  benzoic  acid  obtained  from  gum  crystallizes. 
Tests. — The  only  test  in  the  British  Pharmacopoeia  for  benzoic  acid 
is  that  of  smell ;  benzoic  acid  is  to  have  an  agreeable  aromatic  odor 
resembling  that  of  benzoin.  As  gum  benzoin  differs  very  much  in 
smell,  some  specimens  containing  styrol,  and  others  vanillin,  while 
others  have  no  particular  odor,  as  the  specimen  of  Palembang  gum 
from  the  Museum  of  the  Pharmaceutical  Society,  there  is  much  com- 
mercial benzoic  acid  which  does  not  answer  to  this  test,  and  has  not 
the  aroma  which  it  is  understood  gum  benzoin  should  have. 
In  the  German  Pharmacopoeia  there  are  three  tests.  The  acid  is  to 
have  the  smell  of  benzoin  and  also  an  empyreumatic  odor,  and  is  to  be 
of  a  yellowish  or  yellow-brown  color.  This  is  to  ensure  the  acid 
being  prepared  by  direct  sublimation  of  the  gum.  However,  benzoic 
acid  thus  made,  if  the  operation  be  performed  with  care  and  at  a  low 
temperature,  may  be  quite  colorless.  It  is  a  pity  that  the  acid  should 
be  required  to  be  contaminated,  simply  to  prevent  adulteration  with 
acid  obtained  from  other  sources.  In  order  to  obtain  it  colorless  a 
temperature  of  160°  C.  is  quite  high  enough  for  the  sublimation  of  the 
whole  of  the  acid.  At  first  water  and  dark  colored  hydrocarbons 
volatilize  together  with  some  benzoic  acid ;  these  must  be  allowed  to 
escape  for  two  or  three  hours.  The  benzoic  acid  may  then  be  collected, 
! 
