Am.  Jour.  Pharm.) 
April,  1920.) 
Assay  of  Iron  Filings. 
247 
reduced  to  a  few  seconds,  lessening  the  chance  of  oxidation  and 
mechanical  loss.  But  filtration  must  be  thorough,  and  no  trace  of 
precipitate  must  be  allowed  to  remain  in  the  solution,  for  it  has  a 
strong  reducing  action  on  the  permanganate.  Wash  with  about 
100  Cc.  of  cold  water,  add  sulphuric  acid,  and  titrate  as  usual. 
This  treatment  appears  to  get  rid  of  the  phosphine.  Either  it  is 
volatilized  as  formed,  or  it  is  completely  precipitated  at  the  boiling 
temperature  by  the  excess  of  copper  sulphate.  Brisk  boiling  also 
aids  interaction  by  keeping  the  particles  from  massing  together 
There  is  no  fear  of  oxidation  while  boiling,  as,  in  the  narrow  beaker 
the  liquid  is  covered  with  an  atmosphere  of  steam.  The  originators 
of  the  process  official  in  the  German  Pharmacopoeia  may  have  had 
the  effect  of  such  impurities  in  mind  when  they  devised  the  method 
which  is  as  follows: 
I  Gm.  of  ferrum  pulveratum  is  dissolved  in  about  50  Cc.  of  dilute 
sulphuric  acid  and  made  up  to  100  Cc.  with  water.  10  Cc.  of  this 
solution  is  treated  with  V2  per  cent,  solution  of  potassium  perman- 
ganate, sufficient  to  produce  a  faint  pink.  The  solution  is  then  de- 
colorized by  means  of  tartaric  acid,  2  Gms.  of  potassium  iodide  are 
added.  The  stoppered  flask  is  allowed  to  stand  one  hour,  and  the 
liberated  iodine  is  then  titrated  with  N/10  sodium  thiosulphate. 
The  iron  and  such  impurities  as  phosphorus  and  sulphur  are  fully 
oxidized.  The  final  oxidation  products  of  the  phosphorus  and  sul- 
phur have  no  effect  on  the  potassium  iodide,  whereas  the  ferric 
sulphate  is  reduced  to  ferrous  sulphate,  which  liberates  the  equivalent 
of  iodine.  The  process  is  required  to  yield  97.7  per  cent,  of  total 
iron.  The  same  process  is  used  for  ferrum  redactum,  which  is  re- 
quired to  indicate  96.6  per  cent,  of  total  iron.  It  must  not  be  for- 
gotten, however,  that  a  standard  base  on  the  total  iron  is  sufficient 
to  ensure  a  minimum  of  the  free  metal  being  present  when  the  figure 
approaches  100  per  cent.,  as  in  the  German  test.  But  it  fails  to 
give  a  measure  of  the  free  metal,  and  is,  therefore,  only  a  check  on  a 
prearranged  standard.  Clearly,  filings  from  a  cast-iron  at  95  per 
cent,  or  less  would  be  rejected  by  the  German  Pharmacopoeia  test, 
and  only  filings  from  steel  or  wrought  iron  which  indicate  98  per 
cent,  to  99  per  cent,  free  iron  are  considered  suitable.  Such  a 
standard  determined  with  the  precautions  indicated,  secures  medic- 
inal preparations  with  full  iron  content. 
The  work  in  connection  with  this  note  was  carried  out  in  the 
laboratory  of  Messrs.  Evans  Sons,  Lescher  and  Webb,  Liverpool. 
