Am.  Jour.  Pharm.  \ 
Aug.,  1878.  J 
Notes  on  the  Tannins, 
393 
If  the  various  kinds  of  tannin  were  all  glucosides,  it  might  be  possi- 
ble to  arrive  at  some  sort  of  valuation  by  determining  the  amount  of 
glucose  which  they  are  capable  of  yielding.  It  was  this  idea  that  led 
to  the  experiments  detailed  in  the  paper. 
Strecker  stated  that  ordinary  gallotannic  acid  (from  gall-nuts)  was  a 
glucoside,  splitting  up  when  boiled  with  dilute  acid  as  follows  : 
C27H22017+4H20=3C7H605+C6H1206, 
but  H.  Schiffhas  recently  shown  that  tannic  acid  as  ordinarily  prepared 
is  only  digallic  acid,  splitting  up  thus,  CuH10O9+H2O=2C7H6O5 ;  and 
this  view  has  been  confirmed  by  Stenhouse  in  a  study  of  the  action  of 
bromine  upon  tannin.  SchifF,  however,  expresses  the  opinion  that  the 
unaltered  natural  tannin  of  gall-nuts  may  probably  be  a  glucoside,  not 
of  gallic  acid,  but  of  digallic  acid,  and  that  it  is  to  some  extent  decom- 
posed by  the  mode  of  preparation  (comp.  foot  note,  "Ann.  Chem. 
Pharm.,"  clxx,  175).  In  that  case  its  decomposition  would  be  repre- 
sented by  the  equation — 
C31H28O22+2H2O=C6H,2O6+2CuHI0O9. 
These  statements  of  Schiff  led  us  to  examine  a  number  of  com- 
mercial samples  of  tannin,  by  boiling  them  with  dilute  acids  and 
examining  the  products  for  glucose.  The  solution  thus  obtained 
reduced  Fehling's  solution,  although  in  everv  case  it  was  found  to  be 
quite  free  from  sugar,  and  to  contain  only  gallic  acid.  Moreover,  the 
freedom  of  the  original  samples  of  tannin  from  any  glucoside  was 
shown  by  the  fact  that  they  gave  no  purple  coloration  with  strong  sul- 
phuric acid  alone,  although  when  sugar  was  added  the  coloration  came 
out  strongly.  This  result  is  in  accordance  with  the  circumstance, 
mentioned  by  SchifF  in  a  supplementary  note  to  his  paper,  that  tannic 
acid  is  now  prepared  commercially  with  dry  ether,  and  not  with  ether 
containing  water  or  with  a  mixture  of  ether  and  dilute  alcohol.  It 
seems,  therefore,  to  be  a  matter  of  some  doubt  whether  tannin  is  after 
all  a  glucoside  even  in  its  natural  state,  because  if  it  were  so,  a  process 
sufficient  to  effect  its  decomposition  so  far  as  to  eliminate  glucose,  would 
scarcely  stop  at  that  stage,  but  would  also  presumably  give  gallic  acid 
and  not  digallic  acid. 
As  we  could  find  nowhere  any  statements  regarding  the  constituents 
of  cutch  and  mimosa  bark  extract,  further  than  that  they  both  yield  a 
peculiar  acid  named  mimotannic  acid,  some  experiments  were  made  also 
with  these  materials. 
