Am.  Jour.  Pharm, 
Oct.,  1883. 
j         Commercial  Iodide  of  Potassium.  499 
macopoeia.  Primarily  we  are  to  apply  the  tests  of  the  U.  S.  Ph., 
1880,  and,  in  the  way  of  further  inquiries,  secondarily,  we  may  com- 
pare tests  of  the  U.  S.  Ph,  of  1870,  the  current  Br.  Ph.,  and  the  new 
Ph.  Germ.  Also,  we  may  consult  unofficial  tests  for  their  bearing 
upon  Pharmacopoeial  standards,  and  may  ask  discussion  as  to  the  right 
province  of  these  standards. 
The  Pharmacopoeial  requirements  are  taken  in  order  as  follows, 
believed  to  be  the  order  of  their  importance  : 
(1)  The  absence  of  iodate. — "The  aqueous  solution  of  the  salt,  mixed 
with  gelatinized  starch  and  afterward  with  diluted  sulphuric  acid, 
should  not  at  once  acquire  a  blue  color  (absence  of  iodate),'^  U.  S.  Ph., 
1880.  "Its  solution,  mixed  with  diluted  sulphuric  acid,  and  after- 
wards Avith  solution  of  starch,  gradually  assumes  a  purple  tint,  which 
at  length  becomes  blue.  When  tartaric  acid  is  freely  added  to  a  strong 
solution,  .  .  .  the  supernatant  liquid,  if  mixed  with  solution  of  starch, 
gradually  assumes  a  purple  tint,  which  at  length  becomes  blue,'^  U.  S. 
Ph.,  1870.  "The  addition  of  tartaric  acid  and  mucilage  of  starch  to 
its  watery  solution  does  not  develop  a  blue  color,''  Br.  Ph.  The 
watery  solution  (1  to  20),  .  .  .  mixed  with  diluted  sulphuric  acid,  on 
the  addition  of  solution  of  starch,  should  not  at  once  become  blue.  Ph. 
Germ.  (1882)  The  test  is  often  made  by  adding  a  crystal  of  tartaric  acid  to 
the  solution  of  the  iodide  to  be  tested.  The  results  by  a  crystal  of  tartaric 
do  not  differ  materially  from  those  by  dilute  sulphuric  acid  (provided 
the  latter  be  quite  free  from  nitrous  acid).  In  doubt  as  to  the  purity 
of  the  sulphuric  acid  at  hand,  the  tartaric  acid  crystal  may  well  be 
used.  The  test  by  color  of  the  liquid  without  starch  is  but  little  less 
delicate,  though  not  quite  sufficient  for  the  law.  Of  course  the  result 
hinges  on  the  occurrence  of  the  color  "  at  once,"  and  in  the  Ph.  Germ, 
test  the  acid  is  added  with  or  immediately  before  the  starch.  Pure 
hydriodic  acid,  it  will  be  remembered,  exposed  to  air,  and  in  water 
containing  air,  very  soon  gives  free  iodine.  All  oxysalts  of  iodine, 
hypoiodite '  as  well  as  iodate,  are  revealed  by  the  test,  and  are  fairly 
excluded  by  the  requirement  of  the  Pharmacopoeia.  Practically  the 
test  is  a  close  one,  but  does  not  effect  an  absolute  exclusion  of  iodate, 
when  no  regard  is  given  to  slight  tints  of  the  starch  short  of  the  "  blue 
color.''    Moreover,  the  test  should  not  be  applied  in  very  dilute  solu- 
^  It  has  been  inferred  that  traces  of  salt  of  hypoiodous  acid  sometimes 
result  from  atmospheric  liberation  of  hydriodic  acid,  and  impart  a  peculiar 
odor,  corresponding  to  that  of  the  chlorinated  compounds. 
