452        NEW  PROCESS  FOR  PREPARING  POWDER  OF  IRON. 
iron.  Water  digested  on  the  powder  should  not  precipitate  with 
solution  of  nitrate  of  silver ;  that  would  indicate  that  all  the 
cyanide  of  potassium  had  not  been  washed  out. 
The  chemical  decompositions  which  take  place  in  this  process 
1  believe  to  be  as  follows  :— Two  atoms  of  ferrocyanide  of  potas- 
sium 2  (2  K  Cy  -f-  Fe  Cy),  and  two  atoms  of  carbonate  of  potash 
2  (KO,  CQ2)  being  fused  together  yield  five  atoms  of  cyanide  of 
potassium  5  (K,  Cy),  one  atom  of  cyanate  of  potash  (KO  -f  Cy, 
0),  two  atoms  of  metallic  iron,  and  two  atoms  of  carbonic  acid 
gas,  which  are  given  off  in  effervescence.  The  five  atoms  of  cy- 
anide of  potassium  thus  formed  now  acting  on  three  atoms  and 
one-third  of  the  peroxide  of  iron,  decompose  the  peroxide,  giving 
rise  to  five  atoms  of  cyanate  of  potash  5  (KO,  Cy,  0),  and  setting 
free  the  iron  in  a  finely  divided  condition,  thus  we  obtain  all  the 
iron  contained  in  the  materials  used,  both  that  of  the  ferro-cyanide 
and  that  of  the  peroxide. 
The  proportions  in  the  process  detailed  above  do  not  exactly 
agree  with  the  atomic  quantities  just  mentioned.  According  to 
the  above  explanation,  the  quantity  of  peroxide  of  iron  required 
should  be  2,144  grains  instead  of  four  ounces,  or  1,750  grains, 
directed  to  be  used.  But  as  Wittstein  has  remarked  (in  speaking 
of  Liebig's  process  for  obtaining  the  mixed  cyanide  of  potassium 
and  cyanate  of  potash,  by  fusing  ferrocyanide  of  potassium  and 
carbonate  of  potash  together  in  the  proportions  adopted  in  the 
process  which  has  been  detailed)  that  some  of  the  cyanide  is  de- 
composed during  the  exposure  to  heat,  the  product,  instead  of 
being  five  atoms  of  cyanide  of  potassium  to  one  atom  of  cyanate 
of  potash,  as  by  theory  should  be  the  result,  consists  of  cyanide 
and  cyanate  in  the  proportion  of  seven  of  the  former  to  five  of 
the  latter ;  it  was  therefore  necessary  to  allow  for  this  decompo- 
sition, and  also  further  to  reduce  the  amount  of  oxide  used,  so  as 
to  maintain  a  considerable  excess  of  cyanide  of  potassium  to  pro- 
tect the  metal  already  reduced  from  oxidation  by  exposure  to  the 
heat  and  air. 
This  process,  affording  an  easy  and  certain  method  of  preparing 
an  article  which  promises  to  be  of  some  value  as  a  therapeutic 
agent,  and  of  obviating  the  use  of  a  difficult  and  uncertain  pro- 
cedure, I  have  been  induced  to  make  known  in  the  hopes  that  it 
may  turn  out  of  some  value  to  the  pharmaceutical  chemist — Ann. 
of  Pharm.,  July,  1854,  from  Dublin  Medical  Press. 
