BENZOIN  AND  BENZOIC  ACID. 
407 
2*2,  2*5  and  2*4  grm.  benzoic  acid  were  obtained  ;  therefore,  an 
oxidation  of  the  resin  to  benzoic  acid  does  not  take  place  on 
fusion  in  atmospheric  air. 
30  grm.  of  benzoin  were  dissolved  in  95  per  cent,  of  alcohol 
and  the  filtered  solution  mixed  with  an  alcoholic  solution  of 
caustic  soda.  A  red  brown  sediment  had  occurred  after  48 
hours,  which  was  well  Avashed  upon  a  filter  with  alcohol,  dis- 
solved in  water  and  decomposed  by  boiling  with  muriatic  acid ; 
an  amorphous  precipitate  separated,  which,  after  filtering,  yielded 
benzoic  acid  on  being  heated.  If  free  benzoic  acid  had  been 
contained  in  the  resin,  it  would  have  entered  the  soda  precipitate 
and  been  separated  in  crystals  by  the  muriatic  acid  ;  since,  how- 
ever, it  is  obtained  from  the  amorphous  precipitate  only  by  heat, 
the  author  concludes  that  benzoic  acid  as  such  was  not  present. 
The  filtrate  from  the  soda  precipitate  was  distilled ;  the  amor- 
phous residue  dissolved  in  water,  yielded  with  muriatic  acid,  a 
resinous  precipitate,  giving  a  copious  sublimate  of  benzoic  acid, 
while  the  acid  filtrate  on  concentration  yielded  only  small  quan- 
tities of  crystalline  benzoic  acid.  The  author  concludes  from 
this  experiment  that  at  least  a  portion  of  benzoic  acid  does  not 
exist  ready  formed  in  the  resin. 
A  portion  of  benzoin  was  dissolved  in  alcohol,  the  solution  at 
the  boiling  point,  precipitated  with  water,  the  alcohol  distilled 
off,  and  the  aqueous  solution  decanted  from  the  sediment ;  this 
was  treated  four  times  in  the  same  manner,  at  last  the  alcohol 
was  not  distilled  off,  but  was  removed  with  the  water.  The 
resin  thus  purified,  behaves  towards  soda  and  muriatic  acid  es- 
sentially like  the  crude  benzoin.  The  aqueous,  faintly  alcoholic 
solutions  did  not  yield  crystals  of  benzoic  acid  on  evaporation ; 
a  small  quantity  of  it,  however  was  present,  its  crystallization 
being  prevented  by  the  presence  of  a  resinous  body. 
These  results  led  the  author  to  the  conclusion  that  some  free 
benzoic  acid  is  present  in  the  resin,  but  that  the  greater  portion 
is  generated  on  heating,  from  one  of  the  proximate  principles 
contained  in  benzoin. 
Of  all  the  different  apparatus  recommended  for  the  sublima- 
tion of  benzoic  acid,  the  author  prefers  that  of  Molir,  but  recom- 
mends a  steady  temperature  of  170°  C.  A  flat  vessel  of  iron 
or  copper  is  connected  with  a  glass  tube  bent  upwards,  into 
