ON  CATECHU  AND  ITS  ACIDS. 
329 
first  crystallization  was  reddish  brown,  precipitated  gelatin,  and 
therefore  contained  the  tannin.  The  other  mother  liquors  had 
a  yellowish  color,  which,  after  standing  24  hours,  changed  to  a 
red,  like  that  of  the  first ;  they  also  precipitate  gelatin.  The 
mother  liquors  were  evaporated  by  means  of  a  water-bath,  when 
gradually  they  became  turbid  and  the  reaction  with  gelatin 
stronger ;  after  evaporation  to  dryness,  a  shining,  cracked, 
spongy  mass  remained,  easily  yielding  a  cinnamon-brown  pow- 
der like  that  of  catechu.  Now  it  was  only  partly  soluble  in 
water  ;  the  brown  filtered  solution  immediately  precipitated  gela- 
tin ;  when  treated  in  the  percolator  like  catechu,  it  still  yielded 
a  considerable  quantity  of  catechin ;  the  ether  had  a  slightly 
yellowish  color ;  alcohol  dissolved  nearly  all  the  residue. 
Snow  white  catechuic  acid  was  now  dissolved  in  water,  the 
solution  had  a  yellowish  tinge  and  did  not  precipitate  a  clear 
'filtered  solution  of  gelatin;  it  was  boiled  in  an  open  dish  for 
three  hours,  when  it  had  become  turbid  and  of  a  yellowish  brown 
color,  and  after  evaporation  it  dissolved  with  a  dark  color  in 
water,  leaving  a  reddish  brown  residue.  The  solution  now  im- 
mediately precipitated  a  clear  filtered  solution  of  gelatin,  a  fact 
observed  already  by  Wackenroder. — [Ann.  d.  Oh.  and  Pliarvn. 
xxxvii.,  376.) 
This  is  a  strong  proof  for  the  allegation  that  pure  catechuic 
acid,  under  the  influence  of  heat  and  the  air,  is  converted  into  a 
substance  which  must  be  looked  upon  as  a  tannin.  Btichner 
(Geiger's  Pharm.  i.,  864)  says  that  catechuic  acid,  when  heated 
until  it  becomes  brown,  changes  to  a  tannic  acid.  But  to  en- 
tirely effect  this  change  through  the  influence  of  heat  and  air  is 
very  difficult. 
Catechuic  acid  was  now  prepared  by  the  process  recommended 
by  Berzelius  ;  catechu  was  first  exhausted  by  cold,  afterwards 
by  boiling  water,  this  last  solution  precipitated  by  sugar  of  lead 
as  long  as  a  colored  precipitate  was  formed ;  the  pale  yellow  fil- 
trate was  freed  from  the  lead  by  hydrosulphuric  acid,  filtered 
while  still  hot,  and  yielded  on  cooling  nearly  white  catechuic 
acid,  which  was  recrystallized  and  washed  with  cold  water. 
The  following  are  the  results  of  the  elementary  analysis  : 
