GALLIC  ACID  FROM  CHINESE  GALL-NUTS. 
259 
gelatine,  and  no  crystals  were  formed  on  evaporation.  The  mass 
was  therefore  boiled  with  water  and  the  clear  liquor  precipitated 
by  sulphuric  acid,  by  which  means  the  gall-nuts  yielded  barely  one- 
sixth  of  their  weight  of  rather  colored  gallic  acid. 
The  author  then  refers  to  Strecker's  researches,  which  have 
shown  that  tannic  acid  is  a  conjugate  compound  of  gallic  acid  and 
sugar,  and  consequently  that  the  production  of  the  latter  acid  in  a 
paste  of  gall-nuts  and  water  is  caused  by  a  nitrogenous  substance 
contained  in  them,  which  acts  the  part  of  a  ferment  "and  determines 
the  breaking-up  of  the  sugar  into  certain  products,  at  the  same 
time  liberating  the  gallic  acid.  He  is  further  of  opinion  that  the 
non-formation  of  gallic  acid  from  Chinese  gall-nuts,  when  treated 
in  this  way,  is  owing  to  the  absence  of  any  substance  capable  of 
acting  as  a  ferment;  and  there  certainly  does  not  appear  to  beany 
other  reason  why  the  tannic  acid  which  they  contain,  identical* 
in  every  respect  with  that  of  oak-galls,  should  not  likewise  yield 
gallic  acid  by  this  process. 
If  this  conjecture  be  in  accordance  with  fact,  it  would  follow 
that  the  production  of  gallic  acid  from  the  tannic  acid  of  Chinese 
gall-nuts  might  be  effected  by  this  process,  on  the  addition  of  a 
small  quantity  of  ordinary  galls,  perhaps  also  on  the  addition  of 
yeast;  and  experiment  proved  that  this  is  redly  the  case. 
A  quantity  of  Chinese  galls  mixed  with  one-eighth  of  its  weight 
of  ordinary  galls,  both  in  powder,  was  made  into  a  paste  with 
water,  and  left  exposed  in  an  open  vessel  at  the  ordinary  tempera- 
ture. At  the  end  of  three  weeks,  during  which  time  the  water 
was  frequently  renewed  as  it  evaporated,  the  mass  had  no  longer 
any  astringent  taste,  the  filtered  liquor  gave  but  a  slight  precipi- 
*  Hitherto  the  identity  of  the  tannic  acid  from  these  two  sources  has  been 
inferred  only  from  the  correspondence  of  their  physical  and  chemical  charac- 
ters ;  but  Wittstein  has  found  that  the  elementary  composition  is  likewise  the 
same.  The  tannic  acid  prepared  from  Chinese  gall-nuts  by  extraction  with 
ether  in  the  ordinary  manner,  and  dried  at  130°  F.,  gave,  on  combustion 
writh  oxide  of  copper  alone,  a  quantity  of  hydrogen,  which  certainly  agreed 
closely  with  the  formula  do  Hu  O2S  (=3.8  per  cent.,)  but  the  quantity  of 
carbon  was  so  small  in  proportion  to  that  required  by  theory  (  =  51.5  per 
cent.,)  that  he  concluded  it  could  not  have  been '  perfectly  burnt:  and  on 
repeating  the  analysis,  introducing  some  fragments  of  fused  chlorate  of  pot- 
ash into  the  posterior  part  of  the  tube,  so  as  to  obtain  a  supply  of  oxygen  at 
the  close  of  the  operation,  he  obtained  from  0.445  grm.  of  the  acid,  dried  at 
130°  F.,  0.164  grm.  water,  =0.01822  or  4.09  per  cent,  hydrogen,  and  0.832 
grm.  carbonic  acid,  =0.2269  or  50.99  per  cent,  carbon. 
1 
