\ 
328  ON  CATECHU  AND   ITS  ACIDS. 
influence  of  the  air,  was  oxydized  to  catechuic  acid.  Several 
chemists  believe  in  this  behaviour,  and  Delffs  asserts,  that  an 
aqueous  solution  of  catechu-tannic  acid,  left  to  a  spontaneous 
evaporation  in  a  shallow  vessel,  fills  with  white  crystals  of  cate- 
chuic acid,  which  take  the  place  of  the  gallic  acid  on  exposure 
of  gallo-tannin ;  and  that?  catechu  contains  catechin  (catechuic 
acid)  only  as  a  product  of  decomposition  of  the  tannin  during 
the  process  of  inspissation.  To  gain  some  light  on  this  assertion, 
another  quantity  of  catechu  was  exhausted  with  ether,  which 
had  been  previously  saturated  with  water.  This  solution  had 
only  a  tinge  of  red ;  it  was  divided  into  three  parts,  one  of  which 
was  evaporated  in  vacuo  above  sulphuric  acid,  the  second  at  a 
moderate  heat,  and  the  third  spontaneously  in  the  open  air ;  all 
left  a  resin-like,  little  colored  mass,  resembling  gallo-tannic  acid. 
The  residues  were  all  dissolved  in  very  little  water,  the  solutions 
heated  to  expel  the  ether,  filtered  and  placed  over  sulphuric  acid, 
where  all  on  cooling  stiffened  to  a  mass  of  crystals,  which  under 
the  microscope  proved  to  be  very  fine  needles,  the  former  result 
not  altered  by  the  use  of  ether  saturated  with  water,  or  by  evapo- 
ration in  vacuo.  The  crystals  were  purified  by  recrystallization 
from  water,  wrapped  in  paper  and  dried  in  the  air.  The  mother 
liquors  from  the  first  crystallization  necessarily  must  contain 
the  tannin  with  some  catechuic  acid  ;  it  was  left  in  an  open  vessel 
to  the  action  of  the  atmosphere  for  six  months,  without  its  show- 
ing even  traces  of  crystallization1. 
By  the  above  methods,  a  mixture  of  catechuic  and  catechu- 
tannic  acids,  with  a  small  quantity  of  colored  matter  (chlorophylj 
is  obtained,  at  it  would  seem  that  the  catechuic  acid  is  not 
formed  by  the  action  of  the  air  on  the  tannin,  but  that  it  exists 
in  the  catechu,  from  which  it  is  extracted  by  ether,  as  Nees  von 
Esenbeck  already  stated,  and  Delffs  observed  the  crystallization 
of  catechuic  acid  only  from  a  diluted  solution.  The  author  now 
prepared  a  larger  quantity  of  catechuic  acid,  by  exhausting 
catechu  with  watery  ether,  distilling  off  the  ether  in  an  atmo- 
sphere of  carbonic  acid,  and  towards  the  end  in  vacuo  near  oil 
of  vitriol,  dissolving  by  a  moderate  heat  in  water,  filtering,  re- 
crystallizing  twice,  washing  with  cold  water,  and  after  pressing 
the  white  crystals,  drying  them  at  the  ordinary  temperature 
wrapped  in  much  bibulous  paper.    The  mother  liquor  from  the 
