ON  SOME  VARIETIES  OF  TANNIN. 
255 
lows,  when  boiled  with  water,  yielded  a  dark  brown  solution. 
This,  when  treated  with  acetate  of  lead,  gave  a  copious  precipi- 
tate of  a  brownish-yellow  color.  This  lead-salt  was  decomposed 
by  sulphuretted  hydrogen;  and  the  clear  filtered  liquid,  when 
boiled  with  sulphuric  acid  and  then  neutralized  with  chalk,  gave 
abundant  indications  of  grape-sugar.  Another  portion  of  the 
solution  from  the  decomposed  lead-precipitate,  when  digested 
with  nitric  acid,  yielded  only  oxalic  acid. 
When  a  decoction  of  willow-bark  is  boiled  with  dilute  sulphu- 
ric acid,  the  brown  colored  liquid  becomes  very  red,  and  a  floccu- 
lent  brownish-red  precipitate  falls,  which  is  nearly  insoluble  in 
water,  but  dissolves  pretty  readily  in  hot  spirit  of  wine  and  alka- 
line leys.  The  brownish  red  precipitate,  when  dissolved  in  spirit 
of  wine  and  left  to  spontaneous  evaporation,  did  not  crystallize, 
but  formed  a  dark  brownish  resin.  It  consisted  chiefly  of  im- 
pure saliretine,  resulting  most  probably  from  the  decomposition 
of  salicine  in  solution.  When  it  was  digested  with  nitric  acid, 
it  yielded  a  good  deal  of  nitropicric  acid.  Willow-bark,  there- 
fore, is  a  tolerably  good  source  of  this  acid. 
Alder-bark  (Alnus  glutinosa). — Alder  bark  yields  a  dark  red 
decoction  with  water.  It  was  precipitated  with  acetate  of  lead, 
and  the  lead-salt  decomposed  with  sulphuretted  hydrogen.  It 
formed  a  dark  red  solution,  which  on  digestion  with  sulphuric 
acid  yielded  no  sugar. 
Catechu. — It  was  the  light-colored  cubical  variety  of  catechu 
that  I  employed.  The  tannin  from  this  astringent  substance, 
when  digested  with  dilute  sulphuric  acid,  yielded  no  sugar,  a  re- 
sult which  corresponds  with  Neubauer's  experiments  [Ann.  der 
Chem.  und  Pharm.,  vol.  xcv.,  p.  103.) 
Larch-bark  (Pinus  larix,  Linn.). — The  bark  of  the  larch  is  em- 
ployed in  Scotland  to  some  extent  in  tanning,  though  the  leather 
made  with  it  is  inferior  in  quality.  Larch-bark  contains  a  good 
deal  of  a  peculiar  tannin,  which  yields  olive-green  precipitates 
with  salts  of  iron.  The  aqueous  solution  of  larch-bark  is  strongly 
acid  to  test  paper,  and  has  at  first  a  pale  yellow  color,  which  ex- 
posure to  the  air  renders  brownish-red.  Acetate  of  lead  threw 
down  a  copious  yellow  precipitate  ;  this  was  decomposed  by  sul- 
phuretted hydrogen  and  boiled  with  dilute  sulphuric  acid,  when 
the  liquid  assumed  a  fine  scarlet  color,  like  infusion  of  Brazil- 
