ON  fHE  CONSTITUTION  OF  TANNIN  AND   GALLIC  ACID.  51 
imbued  with  the  acid  liquor  in  which  they  are  deposited.  In 
fact,  this  sulphuric  tannin  only  contains  from  2  to  4  per  cent, 
of  sulphuric  acid  ;  and  the  muriatic  tannin,  when  placed  in  vacuo 
over  quicksilver,  loses  its  muriatic  acid  completely.  Moreover, 
these  precipitates  differ  in  no  respects  from  tannic  acid,  which 
has  been  acidulated  with  a  mineral  acid.  The  formation  of  a 
precipitate  by  a  mineral  acid  in  a  solution  of  tannin  is  therefore 
perfectly  conformable  to  the  precipitation  of  the  same  solution 
by  chloride  of  sodium  and  other  alkaline  salts,  and  even  by  ether, 
and  must  be  explained  by  a  diminution  of  the  solubility  of  the 
tannin  in  consequence  of  the  change  in  the  solvent. 
Gallic  acid,  which,  according  to  some  chemists,  contains  in  the 
formula  C11  H6  O10  4  or  2  equivs.  of  water,  is,  from  my  analysis, 
a  tribasic  acid ;  and  the  yellow  lead  salt,  regarded  by  Liebig  and 
Biichner  as  a  neutral  salt,  and  represented  by  the  formula 
4PbO.  C14  H2  O6, 
is  a  basic  salt,  which,  when  dried  at  248°  F.,  has  a  composition 
represented  by  the  formula 
4PbO .  C14  H3  O7,  or  3PbO  .  C14  H3  O7  +  PbO. 
In  fact,  five  analysis  performed  with  materials  prepared  at  differ- 
ent times  gave  75-9  to  76-1  per  cent.  PbO  ;  numbers  which  ap- 
proach much  more  closely  to  the  latter  formula  than  to  that  of 
Liebig  and  Biichner.—  Okem.  G-az.  Oct.  1854,  from  Compter 
Rendus,  July  3d,  1854,  p.  49. 
ON  THE  MOLECULAR  CONSTITUTION  OF  TANNIN  AND  GALLIC 
ACID. 
By  M.  E.  Robiquet, 
In  my  last  investigation  on  gallic  acid  fermentation,  I  have 
left  undecided  the  question  as  to  whether  tannin  is  a  simple  iso- 
mere  of  gallic  acid,  or  a  combination  of  gallic  acid  with  a  hydro- 
carbon similar  to  sugar  or  gum.  The  following  facts  which  I 
had  observed,  were  not  sufficient  to  decide  the  question.  What- 
ever method  is  adopted  for  converting  tannin  into  gallic  acid,  the 
transformation  is  never  complete  ;  a  part  of  the  tannin  is'  altered 
and  converted  into  an  amorphous/and  mucilaginous  substance  pos- 
sessing some  of  the  properties  of  the  gum.      If  we  operate  by 
