334  Gleanings  from  the  European  Journals.  {kHu*™\m¥*' 
GLEANINGS  FROM  THE  EUROPEAN  JOURNALS. 
By  the  Editor. 
The  constitution  of  Tannic  Acid. — Hugo  Schiff  gives  a  critical  re- 
Tiew  of  the  researches  on  this  subject,  particularly  since  the  investi- 
gations of  Strecker,*  and  from  these  as  well  as  his  own  experiments 
arrives  at  the  conclusion  that  the  presence  of  glucose  is  entirely  un- 
important for  the  reactions  generally  ascribed  to  tannic  acid,  and 
that,  therefore,  this  compound,  if  perfectly  pure,  is  not  a  glucoside. 
Gallic  acid  was  slowly  heated  with  oxychloride  of  phosphorus  to 
between  115  and  120°  C,  and  kept  at  this  temperature  for  several 
hours  ;  during  this  process  only  hydrochloric  acid  gas  was  evolved; 
The  residue  in  the  flask  was  purified  from  gallic  and  phosphoric  acids 
by  washing  with  absolute  ether,  dissolving  in  cold  water,  filtering  and 
precipitating  by  table  salt.  After  further  purification  an  amorphous 
and  inodorous  mass  was  obtained,  possessing  all  the  chemical  reactions 
of  tannic  acid,  and  which,  by  boiling  with  dilute  muriatic  or  sulphuric 
acid,  was  completely  converted  into  gallic  acid,  from  which  tannic  acid 
was  again  obtained  by  treatment  with  phosphor-oxychloride.  This 
reconversion  of  one  substance  into  the  other  was  repeated  three  times  ; 
the  wash  waters  collected  in  the  proceess  contained  neither  glucose 
nor  any  other  saccharine  body.  Ultimate  analysis  gave  results  agree- 
ing with  the  formula  (CuH10O9)  for  tannic  acid,  and  it  is  accordingly 
formed  from  gallic  acid  by  the  abstraction  of  water  (2C7H605 — H20) ; 
being  the  first  anhydride  of  two  molecules  of  gallic  acid,  it  is  digallic 
acid. 
The  same  result  was  more  easily  obtained  when  gallic  acid  was 
treated  with  arsenic  acid,  which  is  not  reduced  thereby.  Commercial 
tannin  contains  glucose  ;  on  dissolving  it  in  a  solution  of  acetanhydride 
in  an  equal  volume  of  glacial  acetic  acid,  heating  to  boiling  and  then 
pouring  into  water,  triacetylglucose  is  dissolved  and  pentacetyltannic 
acid  precipitated.  The  latter  yields,  by  recrystallization,  white  wart- 
like crystals,  from  which  the  digallic  acid  may  be  obtained  by  plumbic 
hydrate. 
The  tannin  of  galls  appears  to  be  C34H28022,  that  is  C6H1206  (glucose) 
-{-  2CuH10O9  (digallic  acid)  —  2H20.  This  compound  is  readily  sol- 
uble in  ether  diluted  with  water  and  alcohol ;  but  if  absolute  ether 
containing  little  alcohol  is  employed,  the  gallotannin  is  decomposed, 
See  American  Journal  of  Pharmacy,  1855,  49. 
