356  Contributions  from  the  School  of  Pharmacy ,  etc.  {AVu°gTi87h6a.rm' 
CONTRIBUTIONS  FROM  THE  SCHOOL  OF  PHARMACY  OF  THE. 
UNIVERSITY  OF  MICHIGAN. 
Communicated  by  Prof.  Albert  B.  Prescott. 
I.  The  Preparation  of  Liquor  Ferri  Nitratis.    By  F.  T.  Bower,  Ph.C. 
This  solution,  made  by  the  U.  S.  P.  process,  is  variable  in  two  par- 
ticulars, namely,  in  the  proportion  of  iron  to  the  solution,  and  in  the 
proportion  of  acid  to  iron.  From  the  last-named  variation  the  ferric 
salt  may  be  more  or  less  basic  or  possibly  normal.  As  with  other  ferric 
salts,  the  more  basic  the  darker  its  color ;  the  normal  salt  in  solution 
of  U.  S.  P.  strength  being  very  light  in  color,  and  in  presence  of  free 
nitric  acid  almost  colorless.  The  "  Pharmacopoeia  "  specifies  its  color 
as  pale  amber  ;  but  if  the  iron  be  dissolved  in  strict  compliance  with 
the  directions,  the  finished  solution  is  darker  than  pale  amber — and  this 
is  true  of  the  solution  commonly  in  use.  By  the  addition  of  nitric  acid 
it  can  be  made  pale,  in  proportion  to  the  amount  added.  The  causes 
of  the  variation  lie,  firstly,  in  the  uncertain  action  of  iron  on  the  cold 
dilute  nitric  acid  ;  slight  differences  in  temperature  and  differences  in 
the  equilibrium  of  the  nitric  acid  change  the  decomposition  products  of 
the  acid  and  the  proportion  of  ferrous  nitrate  it  can  make.  Even  if 
the  direction  to  avoid  red  fumes  be  so  strictly  obeyed  that  no  trace  of 
nitric  oxide  is  formed,  we  may  have  the  acid  breaking  up  in  at  least 
three  different  ways,  as  follows  : 
4Fe+i0HNO3=4Fe(NO3)2+NH4NO3+3H2O 
4Fe+ioHN03=4Fe(N03)2+N20+5H20 
Fe+  2HNOs=  Fe(NOs)2+2H 
Again,  the  action  of  the  second  portion  of  nitric  acid,  added  to  change 
the  ferrous  to  a  ferric  salt,  will  be  varied  by  conditions.  The  chief 
decomposition  product  is  undoubtedly  nitric  oxide,  but  other  products 
may  occur  to  some  extent.  In  using  nitric  acid  to  make  ferric  solu- 
tions of  sulphate  and  chloride,  we  know,  by  experience,  that  the  only 
exact  direction  is  to  add  sufficient  nitric  acid,  and  afterward  expel  any 
excess  ;  but  here,  with  a  variable  quantity  of  ferrous  nitrate  to  act  upon 
(to  oxidize  and  then  make  normal),  we  have  no  guide  but  to  heat  to  1300 
and  add  the  two  troyounces  of  nitric  acid. 
The  "  Pharmacopoeia  "  directs  that  one  fluidounce  of  the  solution 
shall  furnish  "  from  eight  to  ten  grains  "  of  ferric  oxide.  Five  sam- 
ples of  the  solution  were  assayed,  the  first  two  obtained  at  drug  stores,. 
