kerr's  solution  of  pernitrate  of  iron. 
171 
KERR'S  SOLUTION  OF  PERNITRATE  OF  IRON.* 
By  T.  and  H.  Smith. 
Many  pharmaceutists,  as  well  as  ourselves,  must  have  found 
the  process  for  preparing  Kerr's  solution  of  pernitrate  of  iron 
very  unsatisfactory,  from  the  unstableness  of  the  product  yielded  ; 
in  a  longer  or  shorter  time  it  begins  to  lose  its  transparency  and 
becomes  unsightly,  or  through  the  production  of  nitrous  gases  of 
a  more  or  less  condensible  nature  the  stopper  may  be  thrown  out 
or  the  bottle  burst. 
Kerr's  solution  being  made  by  the  action  of  nitric  acid  on 
metallic  iron  in  the  cold,  contains  a  varying  proportion  of  pro- 
toxide of  iron,  depending  upon  variations  of  temperature  and 
other  circumstances ;  hence  arise  after  changes.  Lower  oxides 
of  nitrogen  and  possibly  even  free  nitrogen  may  be  produced 
from  the  continued  action  between  the  protoxide  of  iron  and 
nitric  acid ;  part  of  the  nitric  acid  being  thus  destroyed,  the 
quantity  necessary  for  the  solution  of  the  metallic  oxide  becomes 
deficient.  In  this  way  gases  are  liberated,  and — from  the  pro- 
duction of  a  basic  compound — the  liquid  becomes  cloudy.  It 
cannot  have  been  intended  that  the  compound  should  be  a  pro- 
topernitrate,  such  a  preparation  being  a  medicine,  whose  compo- 
nents are  in  a  state  of  gradual  change  ;  further,  the  British 
Pharmacopoeia  views  it>  as  a  nitrate  of  the  peroxide.  With  a 
view  to  remedy  these  inherent  defects,  we  were  led  to  adopt  a 
method  which  has  for  a  considerable  time  been  satisfactorily  pro- 
secuted. We  have  little  doubt  that  the  process  may  have  already 
occurred  to  some,  and  may  have  been  advantageously  applied  by 
them.  With  the  hope,  however,  that  an  approved  method  would 
not  be  unacceptable  to  such  as  have  experienced  the  uncertain 
results  of  the  recognized  formula,  we  publish  the  following  pro- 
cess : — 
In  making  Kerr's  solution,  instead  of  acting  directly  on  metal- 
lic iron  with  nitric  acid,  we  dissolve  the  pulpy  precipitate  of  per- 
*  The  authors  do  not  appear  to  be  familiar  with  the  solution  of  the  if. 
S.  Pharm.  made  by  forming  a  protonitrate  from  a  given  portion  of  nitric 
acid  and  peroxidizing  it  afterwards  by  the  proper  addition  of  NO5.  The 
process  has  been  used  here  for  ten  years,  and  affords  a  permanent  solu- 
tion.— Ed.  Am.  Jour.  Pharm. 
