502  Commercial  Iodide  of  Potassium.         | ^'"oc^^'iSs*'""" 
Ph.  The  test  required  by  the  German  Pharmacopoeia  of  1882,  is  that 
of  our  present  pharmacopoeia^  with  all  quantities  just  one-fifth  as  large, 
but  with  dilution  to  over  twice  as  great  proportional  volume,  while  the 
time  is  the  same,  and  the  limit  is  at  opacity  instead  cloudiness.  The 
German  test,  therefore,  is  a  little  less  stringent  than  ours.  The  various 
tests  depending  upon  weight  of  silver  precipitate  obtained,  or  quantity 
of  silver  nitrate  required  for  precipitation,  or  volume  of  a  sj^andard 
mercuric  solution  for  reaction,  all  require  very  close  operations,  upon 
the  perfectly  dried  salt,  and  their  results  are  worthless  if  there  be  more 
than  one  impurity  or  defect  present.  The  effect  of  alkali  carbonate 
counterbalances  tliat  of  chloride  or  of  sodium  salt.  Traces  of  chloride 
and  bromide  are  very  difficult  to  avoid  in  manufacture.  A  quantity  of 
chloride,  larger  than  the  limit,  renders  the  article  deliquescent  in  pro- 
portion to  its  increase.  But  our  present  limit  will  no  doubt  be  found 
close  enough.  The  test-limit  admits  more  of  bromide  than  chloride, 
but  cannot  admit  enough  of  bromide  to  pass  by  proportions  of  inten- 
tional adulteration  with  this  cheaper  salt.  If  it  be  desired  to  test  for 
bromide,  the  iodine  may  be  precipitated  by  copper  sulphate,  with  a 
little  ferrous  sulphate  or  sulphurous  acid,  and  the  filtrate  treated  with 
excess  of  dilute  fresh  chlorine  water  (enough  to  oxidize  any  remaining 
iodide  to  iodic  acid),  when  the  test  may  be  completed  by  shaking  with 
carbon  disulphide,  or  chloroform,  for  the  yellow  color  of  bromine. 
(4.)  Limit  of  Sulphate. — "On  adding  to  1  gm.  of  the  salt,  dissolved 
in  30  cc.  of  water,  five  or  six  drops  of  test  solution  of  nitrate  of  barium, 
no  immediate  cloudiness  or  precipitate  should  make  its  appearance 
(limit  of  sulphate),"  U.  S.  Ph.,  1880.  20  cc.  of  a  watery  solution  (1 
to  20),  with  ten  drops  of  barium  nitrate  solution,  should  not  become 
turbid  in  five  minutes.  Ph.  Germ.,  1882.  If  the  salt  have  been  found 
alkaline,  a  drop  or  two  of  hydrochloric  acid  is  to  be  added. 
(5.)  Test  for  Cyanide. — The  solution  (1  to  20),  with  a  fragment  of 
sulphate  of  iron,  and  a  few  drops  of  ferric  chloride  solution,  warmed, 
with  addition  of  solution  of  soda,  should  not  give  a  blue  color  on  super- 
saturating with  hydrochloric  acid,  Ph.  Germ.,  1882.  A  possible  im- 
purity carried  through  the  manufacture  from  the  iodine. 
(6.)  Test  for  Sodium  M.— The  U.  S.  Ph.  and  the  Br.  Ph.,  only  de- 
mand identification  as  potassium  salt,  by  precipitation  of  the  tartrate. 
The  German  Pharmacopoeia  specifies  that  the  flame  color  shall  be  violet 
at  first,  a  quite  severe  requirement,  but  one  sometimes  justified  by  arti- 
cles in  commerce. 
