Am.  Jour.  Pharm.") 
September,  1894.  J 
On  American  Isinglass. 
447 
ON  AMERICAN  ISINGLASS  AS  A  SUBSTITUTE  FOR 
GELATIN-PRODUCING  TISSUE  IN  THE  QUANTI- 
TATIVE ESTIMATION  OF  TANNIC  ACID. 
By  Prof.  W.  T.  Wenzeu,. 
The  absorption  of  tannic  acid  by  means  of  gelatin-producing 
tissue,  such  as  hide  powder,  bone  and  horn,  has,  of  late,  obtained 
the  most  general  recognition  in  the  estimation  of  tannic  acid  by  the 
method  known  as  that  of  Lbwenthal.  This  method,  which  was  found 
to  be  more  convenient,  expeditious  and  productive  of  uniformity  as  to 
results,  having  superseded  the  precipitation  of  tannic  acid  by  means 
of  isinglass  or  gelatin  solutions,  consists  essentially  in  the  titration 
of  a  tannic  acid  solution  mixed  with  an  indigo  solution  acidu- 
lated with  sulphuric  acid,  by  means  of  a  solution  of  potassium  per- 
manganate standardized,  either  pure  tannic  acid  or  oxalic  acid. 
Aside  from  these  reagents  there  is  also  a  substance  required 
which  possesses  the  property  of  absorbing  or  withdrawing  tannic 
acid  from  its  solutions,  in  order  to  determine  in  the  liquid,  after  the 
withdrawal  of  the  tannic  acid,  the  amount  of  other  substances  capa- 
ble of  oxidation  by  the  permanganate  solution,  and  designated  sim- 
ply by  the  name  of  non -tannins.  The  titre  of  the  permanganate 
solution  should  be,  according  to  Professor  von  Schroeder,  of  such 
strength  that  one  cubic  centimetre  equals  0  0OT747  grams  of  tannic 
acid. 
It  is  not  within  the  province  of  the  writer  to  enter  into  the  details 
regarding  the  subject  under  consideration,  as  ample  directions  will 
be  found  touching  the  method  of  Lbwenthal  in  a  report  from  Dr. 
C.  Councler  in  the  transactions  of  a  commission  appointed  to  inves- 
tigate critically  and  devise  a  uniform  method  for  the  determination 
of  tannic  acid. 
The  object  of  this  paper  is  simply  to  draw  the  attention  of 
chemists  to  a  substance  which  is  readily  obtained  and  easily  pre- 
pared, and  is  par  excellence  in  every  way  a  desirable  substitute  for 
the  various  gelatin-producing  tissues  at  the  present  time  in  use. 
This  substance,  called  American  Isinglass,  or  occasionally  ribbon 
isinglass,  occurs  in  thin  ribbons  several  feet  long,  and  from  an  inch 
and  a  half  to  two  inches  in  width.  It  is  less  soluble  than  the  Rus- 
sian. It  is  obtained  from  the  air  bladder  of  the  common  hake 
(Gadus  merluccius).    This  is  thrown  into  water  to  macerate  for  a  little 
