TINCTURE  OF  CHLORIDE  OF  IRON. 
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a  large  amount  of  extractive  and  gummy  matter,  a  small  amount 
of  resinous,  coloring,  and  fatty  matter,  and  a  trace  of  bassorin, 
but  no  starch  or  albumen. 
ON  TINCTURE  OF  CHLORIDE  OF  IRON. 
By  William  S.  Thompson. 
When  prepared  in  accordance  with  the  U.  S.  Pharmacopoeia, 
this  medicament  is  liable,  from  various  causes,  to  vary  in  strength 
and  other  properties.  It  is  true,  that  if  the  muriatic  acid  is 
always  of  the  officinal  specific  gravity,  and  the  subcarbonate  of 
iron  invariable  in  its  proportions  of  moisture  and  carbonic  acid, 
the  tincture  would  be  of  uniform  strength,  but  still  an  objec- 
tionable preparation,  in  consequence  of  its  tendency  to  deposit 
the  protochloride  of  iron,  and  thus  gradually  to  become  weaker. 
The  proper  strength  of  the  acid  is  that  which  has  the  officinal 
density,  for  it  dissolves  the  whole  of  the  subcarbonate,  with  the 
exception  of  a  slight  residue  of  impurity.  An  acid  of  higher 
specific  gravity  would  render  the  tincture  unduly  acid,  while  one 
of  lower  strength  would  be  too  feeble  to  take  up  all  of  the  iron. 
It  being  often  difficult,  however,  to  obtain  the  acid  of  the  exact 
specific  gravity  required,  I  feel  prompted  to  suggest,  from  my 
own  actual  experience,  the  following  means  of  making  the  success 
of  the  process,  as  well  as  the  uniform  composition  and  permanence 
of  the  product,  entirely  independent  of  the  strength  of  the  muri- 
atic acid  employed. 
The  subcarbonate  of  iron,  of  the  shops,  seems  to  consist  of  a 
mixture  of  the  carbonate  of  the  protoxide  and  sesquioxide  of  iron 
and  water,  in  variable  proportions,  depending  in  a  great  measure 
upon  its  mode  of  preparation  and  the  manner  of  drying  it.  In 
the  U.  S.  Pharmacopoeia  it  is  directed  to  be  dried  with  a  gentle 
heat,  but  neither  the  degree  nor  the  mode  of  desiccation — whether 
in  an  oven  or  over  a  water-bath— is  stated.  It  is  the  custom  with 
some  pharmaceutists  to  dry  it  in  conical-shaped  muslin  bags, 
suspended  in  a  current  of  air  at  the  ordinary  temperatures  of  the 
atmosphere ;  and,  dried  in  this  manner,  it  no  doubt  contains  a 
much  larger  proportion  of  moisture  and  protocarbonate,  than 
when  it  is  dried  "  with  a  gentle  heat ;"  by  which  plan  it  is  some- 
times made  to  nearly  resemble  the  sesquioxide  in  appearance,  and 
to  assume  a  condition  more  favorable  for  preparing  the  tincture. 
