438  Black  and  White  Mustard  Seed.  {^Se^SS1- 
the  researches  of  Dr.  Gadamer  (5)  and  his  predecessors  sufficiently 
explain.  Yet,  with  powdered  white  mustard  seed  containing 
starch,  the  starch-iodine  color  also  disappears,  but  less  rapidly  than 
it  does  with  black  mustard  seed. 
Fortunately,  we  find  that  the  use  of  solution  of  iodide  of  potas- 
sium with  white  mustard  likewise  checks  the  evanescence  of  the 
starch  reaction,  when  it  is  employed  in  the  manner  directed  for 
black  mustard  seed  under  Test  III.  Indeed,  when  applied  to  white 
mustard  seed,  the  test  is  even  more  sensitive  by  far  than  with  black 
mustard,  for  by  means  of  it  we  can  detect  the  presence  of  as  little 
as  0-05  per  cent,  starch  with  certainty. 
TESTING  WHITE  MUSTARD  FOR  STARCH. 
Solutions. — (1)  Potassium  Iodide  Solution  (5  per  cent.),  5  grammes 
of  crystallized  pure  potassium  iodide  are  dissolved  in  water  to  make 
100  c.c. 
(2)  Iodine  Test  Solution,  U.S.P.  (2  per  cent.). 
Directions. — Put  I  gramme  of  the  powdered  white  mustard  seed 
into  a  perfectly  dry  test  tube,  add  10  c.c.  of  the  above  potassium 
iodide  solution  and  boil.  Cool  and  carefully  add  to  the  surface  of 
the  bright  yellowish  liquid  one  drop  of  iodine  test  solution,  U.S. P., 
taking  care  in  adding  iodine  to  allow  it  to  flow  down  the  side  of  the 
tube,  upon  the  surface  of  the  liquid.  The  contrast  in  color  between 
the  iodized  upper  part  and  the  lower  liquid  is  plainly  visible  with  as 
little  as  005  per  cent,  starch,  in  which  case  the  coloration  of  the 
upper  part  is  decidedly  bluish  and  is  permanent  for  a  reasonable 
length  of  time. 
Summary  for  Powdered  While  Mustard  Seed. — (a)  If  not  more 
than  1  per  cent,  of  starch  (in  the  form  of  starch-bearing  seeds,  etc.) 
is  considered  admissible  in  white  mustard  of  commerce,  the  Pharma- 
copoeia should  demand  that  : 
The  sample  be  mixed  thoroughly  with  twenty-four  times  its 
weight  of  powdered  white  mustard  seed  previously  ascertained  to 
be  free  from  starch ;  the  mixture,  if  submitted,  in  the  quantity  of 
1  gramme,  to  the  test  indicated  under  white  mustard,  should  not 
give  a  plain  blue  starch  reaction. 
(b)  If  a  lower  limit  is  desired  by  the  Pharmacopoeia,  a  corre- 
spondingly smaller  amount  of  starch-free  white  mustard  seed  should 
be  employed  in  making  the  dilution. 
