386  Some  Official  and  Non-Official  Iodides.  {A^St,u£fm" 
yellow  magma  of  plumbic  iodide  was  formed.  This,  after  being 
washed  and  dried,  fell  short  by  about  one-twelfth  of  the  amount  theo- 
retically required.  The  powder  was  neither  iridescent  or  crystalline. 
"When  boiled  with  water  the  undissolved  portion  appeared  unchanged. 
The  solution  gave  a  large  residue  of  yellow  crystals  which  a  half- 
inch  power  revealed  as  a  beautiful  collection  of  hexagonal  plates  and 
truncated  pyramids.  The  ferrous  acetate  resulting  from  the  reaction 
in  which  this  iodide  was  formed,  appeared  to  exercise  no  special  solvent 
power  since  the  remarkable  solubility  of  the  powder  in  pure  water  was 
very  striking.  The  presence  of  much  acetic  acid,  however,  consider- 
ably augments  its  solution.  The  simply  aqueous  solution  gives  with 
potassium  iodide  a  faint,  white  flocculent  precipitate.  The  addition  of 
acetic  acid  to  this  mixture  produces  immediately  a  more  abundant  iri- 
descent precipitate  of  plumbic  iodide.  The  same  result  is  obtained 
when  the  potassic  salt  is  added  after  the  acetic  acid ;  an  incomparably 
more  intense  iridescence  results  when  the  iodide  of  potassium  is  added 
in  the  solid  form  to  the  filtrate  which  contains  the  resulting  ferrous 
acetate,  together  with  the  excess  of  plumbic  acetate  and  the  dissolved 
plumbic  iodide.  The  profuse  precipitate  of  plumbic  iodide  when 
stirred  about  in  the  liquid,  forms  satiny  wavy  striae,  having  a  decep- 
tive crystalline  aspect.  Under  the  microscope,  however,  even  with  a 
quarter-inch  power  and  higher  eye-pieces,  the  precipitate  is  amorphous. 
The  results  would  indicate  that  plumbic  iodide  can  assume  three  char- 
acteristic states,  namely,  an  extraordinary  amorphous  and  rather  solu- 
ble form ;  an  ordinary  amorphous,  and  a  crystalline  form.  "Whether 
the  iridescent  precipitate  represents  still  another  distinct  form,  or  is 
only  a  mixture  of  the  second  and  third,  cannot  be  positively  stated. 
The  writer  believes  that  the  extraordinary  amorphous  iodide  is  the 
proper  medicinal  salt.  The  following  formula  represents  its  produc- 
tion. The  dissolved  portion  may,  however,  be  separately  secured  in 
the  ordinary  form  by  the  addition  of  acetic  acid  and  excess  of  potassic 
iodide  : 
Iron  in  fine  wire  240  grains. 
Iodine  508 
Plnmbic  acetate  757  " 
Acetic  acid  
Water  of  each  sufficient. 
Upon  the  iron  wire  pour  three  fluidounces  of  water,  add  the  iodine 
and  shake  the  mixture  at  frequent  intervals  until  the  iodine  is  all  com- 
