OX  CATECHU  AND   ITS  ACIDS. 
327 
a  relation,  similar  to  the  above,  existing  between  catechu-tannic 
and  catechuic  acids.  The  author  attempted  to  prepare  the 
catechu  tannic  acid  bj  tho  process  of  Berzelius,  to  precipitate 
the  aqueous  tincture  of  catechu  by  sulphuric  acid,  decompose 
the  precipitate  by  carbonate  of  lead,  and  evaporate  the  liquor  in 
vacuo  above  oil  of  vitriol.  But  evenr  a  strong  solution  of  cate- 
chu extracted  by  its  own  weight  of  cold  water,  yields  but  a  slight 
precipitate  with  sulphuric  acid,  which  remains  suspended  in  the 
liquid,  and  does  not  settle  after  standing  or  moderately  heating. 
A  warm  or  hot  prepared  solution  is  instantly  precipitated  by 
sulphuric  acid,  caused,  however,  chiefly  by  the  then  dissolved 
catechuic  acid,  which  I  found  instantly  yields  a  yellow  floccu- 
lent  precipitate  with  it.  Berzelius  experimented  on  catechu- 
tannin  in  1828,  and  used  a  warm  prepared  aqueous  solution, 
thus  obtaining  also  catechuic  acid  in  solution,  which  was  disco- 
vered in  1832  by  Nees  von  Esenbeck.  Having  thus  failed  in 
preparing  catechu  tannic  acid,  the  author  tried  the  second  method 
given  by  Berzelius,  that  of  exhausting  catechu  in  a  percolator 
by  ether.  The  yellowish  solution  did  not  separate  into  two  strata, 
and  was  evaporated  to  dryness  partly  above  oil  of  vitriol,  an- 
other part  in  the  water-bath.  A  porous  brownish  mass  remained 
behind  which,  to  separate  it  from  a  little  ether,  was  dissolved  in 
a  little  water,  and,  after  Strecker's  recommendation,  slightly 
heated  in  the  water-bath  for  a  short  time.  The  solution  soon 
lost  its  smell  of  ether,  but  contained  some  green  insoluble  flocks, 
which  were  separated  by  filtration  ;  the  solution,  on  cooling  over 
oil  of  vitriol,  crystallized  in  fine  white  needles,  which  after  fil- 
tration were  recrystallized  from  warm  water.  The  darker  mother 
liquor  precipitated  gelatin,  and  did  not  yield  any  more  crystals ; 
these,  from  the  following  reactions  and  the  elementary  analysis, 
proved  to  be  catechuic  acid : 
Heated  with  concentrated  sulphuric  acid  it  assumed  a  purple 
violet  color,  with  solution  of  caustic  soda,  a  brown  color  ;  the 
watery  solution  was  instantly  precipitated  by  acetate  of  lead 
(white  ;)  sesquichloride  of  iron,  at  first  a  green  color,  afterwards 
a  dirty  green  precipitate  ;  gelatin  was  not  precipitated,  but  sul- 
phuric acid  instantly,  (yellowish.) 
As  these  methods  failed  to  yield  catechu-tannic  acid  in  some 
quantity,  it  might  have  been  possible  that  this  tannin,  under  the 
