Notes  on  the  Tannins. 
J  Am.  Jour  Pharm. 
X      Aug.,  1878. 
In  our  case  at  the  Paris  Exhibition  are  shown  crystalline  specimens 
of  meconoiosin,  both  in  the  pure  and  in  the  impure  form. — Pbar.  Jour, 
and  Trans.  [Lond.],  June  8,  1878. 
NOTES  ON  THE  TANNINS. 
By  B.  H.  Paul,  Ph.D.,  and  C.  T.  Kingzett. 
In  a  paper  recently  published  by  Mr.  H.  R.  Proctor  he  has  shown 
that  no  two  processes  for  the  estimation  of  tannin  give  similar  or  com- 
parable results,  although  when  the  same  process  is  tried  against  pro- 
ducts of  the  same  nature,  the  results  obtained  by  each  process  are 
tolerably  constant,  that  is  to  say,  cutch  may  be  compared  with  cutch, 
mimosa  with  mimosa,  and  tannin  with  tannin,  so  long  as  the  same  pro- 
cess is  employed  ;  but  even  in  this  case  tannin  cannot  be  compared 
with  cutch. 
In  the  course  of  professional  practice  we  have  had  occasion  to 
examine  various  tanning  materials,  in  such  a  way  as  to  enable  us,  if 
possible,  to  value  one  kind  of  material  against  another  ;  and,  to  make 
a  long  story  short,  it  may  be  said  our  results  fully  sustained  Mr.  Proc- 
tor's statements.  We  could  compare  cutch  with  cutch,  but  not  with 
ordinary  gallotannic  acid,  as  it  is  called,  and  even  when  each  kind  of 
substance  was  re-examined  by  different  processes,  varying  results  were 
obtained.  Thus  a  sample  of  tannic  acid  (sold  as  pure)  showed  with 
Gerland's  antimonial  process  76  per  cent,  of  pure  tannin  ;  by  the  vol- 
umetric process,  employing  lead  acetate  and  using  potassium  ferricyanide 
as  an  indicator,  179  per  cent.;  and  by  the  indigo  process  it  showed 
(using  the  figures  worked  out  by  Neubauer)  135  per  cent,  tannin,  which 
figure,  corrected  for  admixed  gallic  acid  by  the  gelatin  and  salt  treat- 
ment, became  93  per  cent,  real  tannin 
A  number  of  perfectly  unmeaning  results  were  therefore  obtained, 
and  the  difficulty  was  made  still  greater  when  cutch  and  extract  of 
mimosa  bark  were  similarly  compared. 
Although  the  term  iL  tannin"  appears  to  indicate  that  the  astringent 
character  of  different  plants  is  due  to  the  presence  of  a  common  sub- 
stance, this  supposition  is  not  only  erroneous  to  a  large  extent,  but  it 
becomes  delusive  when  an  attempt  is  made  to  base  analytical  methods 
upon  it.  The  commercial  value  of  different  materials  can  so  far  be 
ascertained  only  by  the  practical  tanner. 
