260 
GALLIC  ACID  FROM  CHINESE  GALL-NUTS. 
fate  with  gelatine  solution,  and  on  boiling  it  a  quantity  of  beauti- 
fully white  gallic  acid  was  obtained,  amounting  to  nearly  half  the 
weight  of  the  gall-nuts  employed. 
Another  quantity  of  Chinese  galls  in  powder  was  mixed  with 
one-eighth  of  yeast  and  left  exposed  in  the  same  manner.  The 
production  of  gallic  acid  was  rather  slower  than  in  the  last  experi- 
ment, the  astringent  matter  not  disappearing  entirely  until  the 
end  of  four  weeks  and  a  half,  but  the  quantity  yielded  was  not 
smaller. 
It  follows,  from  these  experiments,  that  the  present  theoretical 
view  of  the  production  of  gallic  acid  from  tannic  acid  is  incorrect. 
Wittstein  considers  that  the  absence  of  any  sweet  taste  in  the 
digested  mass  is  a  sufficient  proof  that  the  sugar  has  been  decom- 
posed—the question  is,  in  what  manner  ? 
Pelouze  regards  the  change  as  a  partial  oxidation,  assuming  that 
tannic  acid  takes  up  eight  equivalents  of  oxygen  from  the  atmos- 
phere, which,  combining  with  four  equiv.  of  carbon,  escape  and 
leave  two  equiv.  of  gallic  acid.  Adopting  the  old  formula  for 
tannic  acid,  C18  H8  Oi2,  this  may  be  represented  by  the  following 
equation : 
Cl8  H8  012"|       f  2  equiv.  gallic  acid     C  4  Hs  012 
08  \   ^  4equiv. carbonic  acid    C4  08 
Cis  H8  O20  J  C18  H8  O20 
An  evolution  of  carbonic  acid  certainly  takes  place,  but  Wittstein 
shows  that  it  is  in  no  way  connected  with  the  influence  of  atmos- 
pheric oxygen,  for  the  production  of  gallic  acid  takes  place  when 
a  paste  of  gall-nuts  is  allowed  to  remain  a  sufficient  time  in  a  flask 
with  a  bent  tube  dipping  under  water.  He  further  states  that  he 
has  obtained  alcohol  in  this  way,  thus  proving  that  the  change 
consists  in  a  vinous  fermentation  of  the  sugar  existing  in  tannic 
acid,  and  that  it  is  from  this  source  the  carbonic  acid  originates. 
Bracconnot  long  since  observed,  that  powdered  gall-nuts,  moistened 
with  water,  suffered  vinous  fermentation ;  but  this  statement  has 
not  hitherto  received  the  attention  it  deserved,  because  gall-nuts 
were  found  to  contain  no  (free)  sugar. 
The  author  further  expresses  his  opinion,  that  the  absence  of  the 
necessary  ferment,  in  sufficient  quantity,  is  the  only  reason  why 
an  aqueous  decoction  of  gall-nuts  yield  less  gallic  acid,  and  more 
