IODINE  IN  MINERALS,  PLANTS  AND  ANIMALS. 
445 
in  his  Memoirs,  that,  with  a  liquid  containing  rather  more  than 
one  millionth  of  iodine,  nitric  acid  produced  a  very  characteristic 
blue,  while  sulphuric  acid  gave  only  a  slight  violet,  and  as  I  ob- 
tained only  a  faint  violet  color  by  the  application  of  pure  nitric 
acid  to  a  liquid  containing  a-i_  of  iodide  of  potassium,  there  is 
some  reason  for  the  suspicion  that  this  nitric  acid  contained 
iodine. 
2.  By  the  test  proposed  by  Grange  5-^0  of  iodide  of  potassium 
may  be  detected. 
Overbeck,  who  recommends  this  test,  adds  concentrated  nitric 
acid  to  a  small  quantity  of  starch  or  sugar,  in  a  test-tube,  and 
applies  the  heat  of  a  spirit  lamp  until  a  brisk  evolution  of  gas 
commences.  The  gas  is  passed  into  the  liquid  to  be  tested  for 
iodine  which  has  been  previously  mixed  with  starch  paste.  He 
states  that  a  blue  color  is  immediately  produced  by  one  millionth 
of  iodide  of  potassium,  and  that  subsequently  the  starch  compound 
separates  in  the  form  of  a  tangible  precipitate.  I  have  not  been 
able  to  confirm  this  degree  of  sensibility  for  a  quantity  less  than 
go-oVo iodide  of  potassium. 
3.  Lassaigne's  test,  precipitation  with  nitrate  of  palladium, 
produces,  in  the  presence  of  ^  iodide  of  potassium,  an  intense 
color,  and  after  some  time,  a  precipitate  of  iodide  of  palladium ; 
with  5^0  a  decided  yellow  color  is  produced,  but  no  precipitate. 
4.  Rabourdin's  method — treatment  with  a  mixture  of  nitric 
and  sulphuric  acid  and  addition  of  chloroform — indicates  ~0  of 
iodide  of  potassium  by  a  distinct  violet  color ;  with  —~0  the  color 
appears  only  after  some  time. 
5.  Marchand's  process — treatment  with  chlorate  of  potash, 
hydrochloric  acid  and  dry  starch — indicates  g~  by  a  faint  violet 
color,  which  is  somewhat  more  distinct  than  that  produced  by 
Grange's  test. 
6.  Price's  method — treatment  with  nitrite  of  potash,  hydro- 
chloric acid  and  starch — indicates  of  iodide  of  potassium  by 
the  production  of  a  violet  red  color,  which  is  almost  as  intense  as 
that  produced  with  JL_  by  the  method  of  Grange.  This  test  has 
therefore  the  advantage  of  being  the  most  sensitive  of  all. 
Some  experiments,  made  with  a  view  to  the  quantitative  esti- 
mation of  chlorine,  bromine  and  iodine,  by  means  of  Grangers 
method,  showed  that  it  was  well  adapted  for  this  purpose. 
