460 
TINCTURA  FERRI  CHLORIDI. 
the  article  usually  known  as  sub-carbonate  of  iron,  and  -VThich 
is  sold  in  the  market  at  about  25  cents  per  pound.  From  the 
samples  above  given,  the  variation  in  sesqui-oxide  strength,  it 
will  be  observed,  is  only  five  per  cent.  The  sub- carbonate  has 
evidently  been  exposed  to  just  sufiicient  heat  to  free  it  from  its 
carbonic  acid,  without  affecting  its  water  of  hydration,  so  that 
in  composition  it  approaches  very  nearly  hydrated  oxide,  (Fcg 
03+2110=98,)  which  contains  81"63  per  cent,  sesqui-oxide. 
One  equivalent  or  80  grs.  sesqui-oxide  of  iron,  (Fe2  O3,)  re- 
quires for  conversion  into  sesqui-chloride,  three  equivalents,  or 
106*5  grs.  chlorine  (01. ),  which  amount,  basing  the  calculation 
on  the  table  given  in  the  U.  S.  Dispensatory,  is  contained  in 
282*19  grs.  muriatic  acid  1*16.  Six  troyounces  of  a  sub-carbonate 
like  e.  g.y  No.  2,  would  give  2390*40  grs.  sesqui-oxide,  and  would 
require  20  troyounces  and  245  grs.  of  the  same  acid,  80 : 
282*19::2390*40:10,025.  Practically,  however,  a  somewhat 
larger  quantity  is  necessary  to  effect  complete  solution,  and  as 
an  excess  of  acid  in  the  tincture  is  considered  desirable,  a  little 
more  than  enough  simply  to  dissolve  the  sub-carbonate  should  be 
used.  In  the  experience  of  the  writer  the  following  formula  has 
proved  successful : 
R.  Ferri  Sub-carb.       .        .       six  troyounces. 
Acid  Muriat.,  C.  P.  sp.  gr.  1*16    twenty-three  troyounces. 
Introduce  the  sub-carbonate  into  a  quart  flask,  add  the  muri- 
atic acid,  and  having  allowed  the  mixture  to  stand  for  a  few 
hours,  apply  heat,  and  hoil  for  a  few  seconds,  then  add  sufficient 
nitric  acid  (more  or  less,  according  to  the  quantity  of  proto- 
chloride  present,  usually  about  half  a  fluiddrachm,)  to  sesqui- 
chloridize  the  small  quantity  of  proto-chloride  present,  or  till  the 
solution  ceases  to  give  either  a  blue  or  green  coloration  with  ferri- 
cyanide  of  potassium.  When  the  solution  has  cooled,  add  to  it  suffi- 
cient stronger  alcohol  to  make  the  measure  up  to  eighty  fluidounces. 
This  tincture  has  the  sp.  gr.  995,  and  is  permanent.  By  calculation 
it  would  yield  29*88  grs.  sesqui-oxide  to  the  fluidounce,  and  is 
therefore  a  little  stronger  in  iron  than  the  officinal.  Were  it 
prepared  from  either  of  the  other  samples  of  sub-carbonate  the 
variation  would  be  a  little  [greater ;  but  even  then  so  slight,  as 
