464  Elm  Bark,  Flaxseed  and  Mustard.  {As^ptJe0mrbefhia89^ 
Put  into  a  large  test  tube  0-5  gramme  of  the  ground  mustard 
seed,  add  8  c.c.  of  water  and  1  c.c.  iodine  test  solution,  U.  S.  P. 
Boil  until  the  brown  color  has  disappeared.  Decant,  cool  the 
decanted  liquid,  and  add,  by  means  of  a  pipette,  one  drop  of  the 
iodine  test  solution,  U.  S.  P.  If  as  little  as  o-i  per  cent,  of  starch 
be  present,  a  distinct  and  quite  permanent  blue  or  greenish-blue  color 
will  appear. 
If  the  principle  of  boiling  the  infusion  of  mustard  seed  with  the 
iodine  solution  be  not  adhered  to,  the  starch  reaction  will  be  evan- 
escent, even  in  the  case  of  gross  admixtures  of  flour. 
As  the  Pharmacopoeia  demands  that  no  starch  be  present  (and  I 
can  find  none  in  pure  mustard  seed),  it  should  be  shown  explicitly 
how  the  presence  of  starch  can  be  determined. 
GENERAL  SUMMARY. 
Elm  bark  contains  starch. 
Flaxseed  and  mustard,  both  white  and  black,  free  from  admix- 
ture, do  not  contain  starch. 
The  presence  of  small  amounts  of  some  foreign  seeds  that  are 
difficult  to  separate,  and  of  grains  of  cereals,  are  common  in  both 
flaxseed  and  mustard,  and  generally  carry  sufficient  starch  to  make 
the  powder  respond  to  starch  tests,  if  properly  applied. 
In  the  case  of  elm  bark,  the  blue  coloration  disappears  very 
quickly  unless  acid  is  added.  After  this  blue  color  has  faded,  it  can 
be  partly  revived  by  the  addition  of  sulphuric  acid. 
With  mustard,  the  blue  color  also  disappears,  if  an  insufficient 
amount  of  iodine  be  added,  because  the  latter  is  readily  assimilated 
by  the  volatile  oil  of  mustard,  even  in  the  presence  of  a  large 
amount  of  starch.  Sulphuric  acid  does  not  revive  the  blue  colora- 
tion ;  but  previous  heating  with  an  excess  of  iodine  test  solution 
saturates  the  mustard  oil,  and  renders  the  starch  reaction  quite 
permanent. 
With  flaxseed,  the  blue  coloration  of  starch  remains  for  some 
time,  but  in  contradistinction  to  the  behavior  of  mustard,  an  excess 
of  iodine  must  be  avoided,  in  order  to  obtain  the  pure  blue  color  of 
iodide  of  starch.  In  commerce,  ground  flaxseed  is  not,  so  far  as  I 
know,  supplied  starch-free,  but  it  can  be  easily  obtained  without  any 
intentional  admixture.  Ground  mustard  now  and  then  is  pure,  but, 
owing  to  unintentional  contaminations,  it  usually  responds  to  the 
