290 
TINCTURA  FERRI  CHLORIDI. 
in  strength,  the  preparation  will  not  remain  clear  ;  for  the  officinal 
subcarbonate  always  contains  a  little  carbonate  of  protoxide, 
which  latter  forms  protochloride  at  first.  This  protochloride  is 
afterward  gradually  decomposed,  and  forms  sesquichloride  and 
sesquioxide,  when,  through  the  deficiency  of  acid,  the  oxide  is 
deposited  as  a  sediment. 
The  filtering  of  the  solution  of  chloride  of  iron  of  the  Pharma- 
copoeia process  is  very  tedious  and  troublesome,  and  cannot  be 
rendered  less  so  by  any  ordinary  management ;  so  that  although 
the  process  is  in  principle  unobjectionable,  it  is  yet  so  difficult 
and  troublesome  in  practice  that  perhaps  very  few  follow  it  with 
success. 
If  the  subcarbonate  be  replaced  by  magma  of  hydrated  sesqui- 
oxide, the  saturation  of  the  acid  is  easily  accomplished  ;  but,  with 
the  slightest  excess  of  magma  the  filtering  becomes  more  difficult 
than  before,  or  is  almost  impossible.  In  the  use  of  this  substitute 
for  some  time,  the  difficulty  in  the  filtration  was  in  great  mea- 
sure avoided  by  subtracting  one  thirty-second  part  of  the  pre- 
scribed acid,  then  saturating  the  remainder  as  nicely  as  practi- 
cable, and  finally  restoring  the  portion  of  acid  separated,  and 
digesting  before  filtration.  In  this  way  an  excellent  preparation 
was  obtained,  having  the  strength  of  the  acid  for  an  index  of 
strength  and  uniformity. 
A  much  better,  because  a  much  easier,  more  simple  and  more 
direct  process  is  that  now  adopted.  This  is  a  mere  adaptation 
of  the  old  process  for  obtaining  pure  sesquichloride'of  iron,  and  is 
used  as  follows,  the  quantities  being  five  times  greater  than  those 
of  the  officinal  formula. 
Take  of  Iron  filings  or  card  teeth,  18g  =llb.  4oz.  Av. 
Muriatic  acid,  (s.  g.  1*16)  5  pints=51bs.  14oz. 
Nitric  acid,  (s.  g.  142)     Q.  S.  say  4ff.f.  =:7Joz. 
Alcohol,  (s.  g.  -835)  15  pints. 
Distilled  water,  3  pints. 
To  the  iron  filings  placed  in  a  ten  pint  flask  add  3  pints  4  Jf.3. 
=31bs.  14oz.  av.s  of  the  muriatic  acid  and  8f.f.  of  the  distilled 
water.  When  the  spontaneous  reaction  has  subsided,  boil  gently 
for  four  hours,  add  one  pint  of  distilled  water,  heat  again  to  boil- 
ing, and  strain  off  the  hot  solution.  Wash  the  flask  and  residue 
with  8f.g.  of  distilled  water,  and  rinse  the  strainer  through  with 
ble  subcarbonate,  if  the  acid  be  in  the  smallest  degree  deficient 
