266 
CITRATE  OF   IRON  AND  QUINIA. 
combined,  without  possessing  the  ferruginous  taste  of  many 
other  preparations  of  iron.  Several  formulas  for  its  preparation 
have  been  published,  none  of  which  seem  to  have  accomplished 
the  desirable  result  of  affording  a  preparation  easy  of  solution. 
An  investigation  of  this  preparation  having  been  one  of  the 
questions  proposed  by  the  committee  for  the  selection  of  sub- 
jects for  examination,  some  time  since,  it  was  accepted  by  me ; 
and  I  now  offer  the  accompanying  formula,  as  the  result  of  a 
number  of  experiments,  performed  at  intervals  of  leisure. 
I  first  prepare  a  solution  of  persulphate  of  iron  of  definite 
strength,  according  to  the  process  recommended  by  Wittstein  ; 
or  that  of  the  U.  S.  P.  for  preparing  the  hydrated  sesquioxide  ; 
the  strength  of  the  solution  to  be  ascertained  by  assaying  a 
portion  ;  but  to  save  this  trouble,  I  prepare  a  solution,  each 
fluid  ounce  of  which  will  yield  sixty  grains  of  anhydrous  ses- 
quioxide, by  the  following  formula  : 
Solution  of  Persulphate  of  Iron. 
Take  of  Protosulphate  of  iron,  in  crystals,  16  ounces,  troy. 
Sulphuric  acid,  commercial,    •  3 
Nitric  acid,  commercial,     •  4    "  " 
Water,  a  sufficient  quantity. 
Place  the  protosulphate  of  iron  in  an  open  dish  of  the  capacity 
of  at  least  eight  pints  and  add  24  fluid  ounces  of  water  and  the 
sulphuric  acid.  Place  the  dish  upon  a  sand-bath,  over  a  furnace 
or  other  convenient  source  of  heat,  and  after  the  protosulphate 
is  dissolved  and  the  solution  has  attained  the  boiling  point,  or 
nearly  so,  add  the  nitric  acid  in  small  portions  from  time  to  time, 
allowing  a  sufficient  interval  of  time  to  elapse  between  each  ad- 
dition of  acid  to  avoid  violent  effervescence.  These  directions 
are  essentially  the  same  as  the  U.  S.  P.,  but  it  is  better  to  com- 
plete the  process  by  the  following  directions  of  Wittstein :  "  A 
drop  is  taken  out  on  the  end  of  a  glass  rod  and  mixed  with  a 
drop  of  solution  of  ferridcyanide  of  potassium  ;  if  this  causes 
only  a  brown  coloration,  the  oxidation  of  the  iron  is  perfect, 
but  if  there  be  a  trace  of  blue,  more  nitric  acid  is  necessary." 
The  solution  is  now  reduced  by  the  addition  of  water  to  the 
measure  of  36J  fluid  ounces,  which  is  a  little  less  than  the 
