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ON  ALKALINE  IODIDES  AND  BROMIDES. 
to  its  use  by  the  pharmaceutist  especially  for  extemporaneous 
application.  These  objections,  as  well  as  any  that  might  be 
raised  against  iron,  I  believe  do  not  apply  to  the  methods  given 
below,  in  which  metallic  iron  is  retained  in  its  old  place. 
PREPARATION  OF  IODIDES. 
The  alterations  which  I  have  introduced  in  the  preparation  of 
the  iodides,  and  the  bromides  as  well,  intend  to  remove  the  ne- 
cessity of  using  caustic  alkalies,  and  shorten  the  process. 
The  formulas  are  founded  on  the  following  observations : 
In  Griepenkoven's  method,  a  solution  of  ferrous  iodide  is  in 
part  oxydised  by  the  addition  of  iodate  or  hypo-iodite  of  the 
alkali,  the  precipitated  ferric  oxyd  forming  magnetic  oxyd  with 
the  ferrous  oxyd  precipitated  afterwards  by  the  addition  of 
more  alkali. 
On  the  same  principle,  when  to  a  solution  of  iodate  or  hypo- 
iodite  containing  free  alkali,  we  gradually  add  a  solution  of  a 
ferrous  salt,  there  is  at  first  a  precipitation  of  brown  ferric 
oxyd,  which  by  the  further  addition  of  ferrous  salt  changes  to 
magnetic  oxyd. 
When  ferrous  sulphate  is  used  for  this  purpose,  the  result  is 
magnetic  oxyd,  iodide  and  sulphate  of  the  alkali. 
When  ferrous  iodide  is  used,  there  results  magnetic  oxyd  and 
alkaline  iodide  only. 
Instead  of  a  ferrous  salt,  metallic  iron  can  be  used  to  reduce 
the  hypo-iodite  or  iodate.  On  bringing  together  fine  iron  filings 
with  a  solution  of  iodine  in  caustic  alkali,  containing  an  excess 
of  iodine,  and  especially  on  applying  heat,  the  iron  is  peroxy- 
dised,  as  it  would  be  by  a  solution  of  a  hypochlorite. 
To  test  for  the  presence  of  iodic  or  hypo-iodous  acid,  the  so- 
lution was  filtered  through  one  slip  of  filtering  paper  on  another, 
and  then  touched  with  an  alkaline  solution  of  iodide  potassium 
starch,  and  a  second  sample  merely  with  starch  and  a  drop  of 
hydrochloric  acid. 
When  precipitated  ferric  oxyd  is  heated  with  excess  of  iron 
filings,  water  is  decomposed,  its  oxygen  forming  ferrous  oxyd, 
which  with  the  ferric  oxyd  forms  the  denser  black,  magnetic 
oxyd,  while  the  hydrogen  it  set  free. — [Woehler  and  Preus$.~] 
If  this  action  of  metallic  iron  in  contact  with  ferric  oxyd 
