ON  THE  COMPOSITION  OP  TANNIC  ACID. 
49 
may  be  estimated  by  simpler  methods.  Yet  it  is  valuable  as 
applied  to  acetic  acid,  a  quantitative  determination  of  which  is 
often  a  matter  of  great  difficulty.  Its  applicability  to  this  has 
been  proved  by  direct  experiment.  The  process  is  identical  with 
that  previously  described.  The  plan  suggested  does  not  involve 
any  new  principle,  but  is  brought  forward  merely  as  a  fair  mode 
of  overcoming  one  of  the  most  common  practical  difficulties  in 
analytical  chemistry. — Ohem.  G-az*  Oct.  1854. 
ON  THE  COMPOSITION  OF  TANNIC  ACID. 
By  A.  Strecker. 
It  appears  from  my  experiments,  that  tannic  acid  and  the 
tannins  in  general  are  much  more  complex  bodies  than  is  gene- 
rally supposed.  In  fact,  by  the  action  of  mineral  acids,  of  alka- 
lies, or  of  ferments,  they  are  resolved  into  glucose  and  a  new 
acid  by  fixing  the  elements  of  water.  This  resolution,  which  I 
announced  two  years  ago,  has  served  me  as  a  starting-point  in  the 
determination  of  the  molecule  of  tannic  acid. 
According  to  the  analyses  of  Pelouze,  Liebig  and  Berzelius, 
the  molecule  of  tannic  acid  is  expressed  by  the  formula  C18  H8 
O12,  and  it  is  supposed  that  in  its  neutral  salts  3  equivs.  of  water 
of  this  formula  are  replaced  by  3  equivs.  of  metallic  oxide.  There 
is  nevertheless  only  one  tannate  (that  of  lead)  which  appears 
from  analysis  to  contain  the  carbon  and  metal  in  the  proportion 
of  18  :  3  equivs. 
Perceiving  from  the  splitting  of  tannic  acid  into  glucose  (C1* 
H12  O12)  and  gallic  acid  (C14  H6  O11)  that  the  above  formula  could 
not  express  the  molecule  of  acid,  I  undertook  a  series  of  experi- 
ments to  determine  the  true  formula  of  tannic  acid :  of  these  I 
now  lay  the  results  before  the  Academy. 
To  obtain  tannic  acid  in  a  pure  state,  I  purified  the  acid  pre- 
pared by  the  method  of  M.  Pelouze,  in  two  ways ;  one  portion 
was  dissolved  in  pure  ether  and  the  solution  precipitated  by  water, 
the  other  portion  was  dissolved  in  water  and  precipitated  by  ether. 
Under  these  conditions  two  or  three  distinct  strata  are  obtained, 
of  which  the  heaviest  consists  of  tannic  acid,  dissolved  in  the 
etherial  fluid.    This  syrupous  liquid  was  dissolved  in  water  and 
4 
