170 
ACTION  OE  REAGENTS  UPON  IODIDE  OF  POTASSIUM. 
order  to  develop  it  by  itself,  the  chemical  transformation  corres- 
ponding to  it  would  take  place  with  remarkable  precision  and 
simplicity. 
I  shall,  in  a  short  time,  give  a  new  instance  of  this,  in  de- 
scribing the  organized  ferment  proper  to  the  fermentation  termed 
^'viscons.' ' —Lond.  Pharm.  Journ.  fromCompt.  Rend.  Mai,  1860. 
ON  THE  ACTION  OF  VARIOUS  REAGENTS  UPON  IODIDE  OF 
POTASSIUM. 
By  G.  Ubaldini. 
When  nitrate  of  ammonia  and  neutral  iodide  of  potassium  are 
intimately  mixed  at  the  ordinary  temperature  and  in  contact 
with  the  air,  the  mass  acquires  a  yellow  color,  and  starch-paste, 
which  acquires  a  blue  tint,  indicates  free  iodine  in  the  mixture. 
The  boracic  acid  of  commerce  acts  in  the  same  way.  These  two 
reagents  acting  upon  a  concentrated  solution  of  iodide  of  potas- 
sium at  the  temperature  of  ebullition,  set  free  iodine. 
By  the  action  of  contact  aided  by  heat,  operating  with  dry 
substances  in  a  glass  tube  closed  atone  end,  iodide  of  potassium 
is  decomposed  with  evolution  of  violet  vapors  of  iodine,  not  only 
by  nitrate  of  ammonia  and  boracic  acid,  but  also  by  sulphate, 
oxalate,  carbonate,  and  muriate  of  ammonia,  by  phosphorus 
salt,  sulphate,  phosphate,  nitrate  and  borate  of  soda,  chloride  of 
sodium,  chlorides  of  potassium  and  calcium,  sulphates  of  potash 
and  magnesia,  nitrate  of  lime  and  silicic  acid. 
The  decomposition  of  iodide  of  potassium  by  the  above  men- 
tioned substances,  does  not  always  take  place  at  the  same  tem- 
perature ;  thus  whilst  silicic  acid  only  decomposes  the  iodide  at 
the  temperature  of  fusion  of  glass,  boracic  acid,  chloride  of 
sodium,  nitrate  of  ammonia,  and  nitrate  of  soda  cause  the  evolu- 
tion of  the  violet  vapors  at  a  low  temperature.  Oxalate  of 
ammonia  decomposes  the  iodide  when  it  begins  to  decompose 
itself ;  carbonate  and  muriate  of  ammonia,  when  gently  heated 
with  iodide  of  potassium,  fuse  with  it,  forming  a  yellow  liquid 
which  evolves  vapors  of  iodine  in  contact  with  the  air;  lastly, 
phosphorus  salt,  nitrate  of  lime,  chloride  of  calcium,  sulphate  of 
ammonia,  sulphate  of  magnesia,  and  sulphate,  phosphate  and 
