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ON  SOME  VARIETIES  OF  TANNIN. 
The  Tannin  in  Tea. 
The  tannin  both  of  green  and  black  tea  is  invariably  accom- 
panied by  a  small  quantity  of  gallic  acid,  which  does  not  arise 
from  the  decomposition  of  the  tannin  in  the  tea,  as  is  the  case 
with  nut-galls,  sumach,  or  Chinese  galls.  On  treating  a  strong 
decoction  of  tea,  when  cold,  with  nearly  half  its  bulk  of  sulphu- 
ric acid,  the  tannin  falls  as  a  dark  brown  precipitate.  This  was 
collected  on  a  cloth  filter,  strongly  compressed,  and  washed  with 
a  little  cold  water  to  free  it  as  much  as  possible  from  adhering 
impurities.  The  precipitated  tannin,  when  boiled  with  dilute  sul- 
phuric acid,  did  not  yield  a  trace  either  of  grape-sugar  or  gallic 
acid,  but  was  changed  into  a  dark  brown  substance  nearly  in- 
soluble in  water.  It  dissolved  pretty  readily  in  alcohol,  forming 
a  dark  brown  solution,  from  which,  however,  no  crystals  could 
be  obtained. 
Oak-bark  from  Quercus  pedunculata. 
A  decoction  of  oak-bark  gave  a  dark  brown  precipitate  with 
acetate  of  lead.  This  was  decomposed  by  sulphuretted  hydrogen. 
The  filtered  solution,  when  boiled  with  sulphuric  acid,  yielded 
grape-sugar  and  a  reddish  brown  precipitate,  but  no  gallic  acid. 
The  reddish  brown  precipitate  dissolved  with  difficulty  in  spirit 
of  wine,  but  gave  no  crystals  on  standing.  Rochleder  has  stated 
that  tea  and  oak-bark  contain  the  same  species  of  tannin.  They 
certainly  resemble  each  other  in  their  general  characters  ;  but  as 
the  tannin  of  oak-bark  yields  sugar  when  boiled  with  dilute  sul- 
phuric acid,  while  that  of  tea  does  not  yield  a  trace  of  sugar,  it 
is  clear  that  the  two  tannins  are  not  identical. 
Valonia,  the  aeorn  of  the  Quercus  JEgilops. 
This  species  of  tannin,  which  has  a  bright  yellow  color,  when 
treated  in  the  way  already  described,  yielded  sugar,  but  no 
gallic  acid. 
The  tannin  of  pomegranate  rind  also  gave  abundant  indica- 
tions of  sugar,  but  no  gallic  acid. 
The  tannin  of  Myrobalans,  the  fruit  of  Terminalia  Chebula, 
gave  similar  results. 
Tannins  which  give  green  precipitates  with  per  salts  of  Iron. 
Salix  triandra  and  Salix  undulata  (the  willows  generally  used 
for  basket  making)  A  quantity  of  the  bark  of  these  two  wil- 
