108     AN  IMPURITY  IN  TINCTURE  OF  CHLORIDE  OF  IRON. 
be  in  the  form  of  a  yellowish  precipitate  at  the  bottom  of  the 
bottle  containing  it.  This  is  the  same,  or  a  part  of  the  precipi- 
tate called  in  the  U.  S.  P.  sesquioxide  of  iron  ;  by  some  other 
authorities,  a  basic  oxide  or  chloride  of  iron.  I  am  not  prepared 
to  say  that  the  precipitate  commonly  noticed  in  the  tincture  of 
iron,  as  obtained  by  the  subcarbonate  process,  is  not  sometimes  a 
pure  sesquioxide  of  iron,  occasioned,  as  stated  in  the  U.  S.  P., 
by  the  change  of  a  small  amount  of  protochloride  to  sesquichlo- 
ride  and  sesquioxide,  the  latter  substance  precipitating  from  a 
deficiency  of  acid.  But  I  am  satisfied  that  if  much  or  prolonged 
heat  is  employed  in  dissolving  the  iron,  the  precipitate  will  not 
be  a  pure  sesquioxide,  but  will  contain  an  appreciable  quantity 
of  the  substance  obtained  from  the  glass  of  the  vessel  used  in 
the  process.  I  feel  sure  that  this  peculiar  substance  exerts  a 
notable  influence  in  the  formation  of  the  well  known  precipitate, 
if  it  is  not  in  reality  the  cause  of  it,  as  may  be  shown  in  one 
process  of  obtaining  the  crystals  from  the  tincture  of  iron.  To 
prove  w^hether  or  not  they  were  derived  from  the  glass  of  the 
vessel,  I  made  a  gallon  tincture  of  iron  by  the  old  U.  S.  P.  pro- 
cess, adding  to  the  subcarbonate  of  iron  about  three-fourths  of 
an  ounce  of  very  finely  pulverized  glass,  before  introducing  the 
muriatic  acid.  But  to  be  plainer,  I  give  it  in  the  form  of  a 
recipe : 
Take  of  Subcarbonate  of  Iron,  12  troyounces. 
White  Glass,  in  very  fine  powder,  6  drachms. 
Muriatic  Acid  (commercial),         2J  pints. 
Alcohol,  6  pints. 
Introduce  the  subcarbonate  of  iron  and  glass  into  a  flask,  or 
any  suitable  vessel,  and  add  the  muriatic  acid.  After  efi'erves- 
cence  has  subsided  (or  nearly  so),  place  the  vessel  over  a  fire 
and  boil  gently  until  the  liquid  begins  to  be  but  slightly  muddy- 
looking,  or  until  the  sesquioxide  seems  nearly  dissolved.  (It 
will  not  be  clear.)  Have  the  alcohol  warmed,  but  not  boiling, 
and  mix  both  the  liquids  together  well.  Filter  immediately 
through  ivhite  filtering  paper  (made  stronger  than  usual).  Set 
the  clear  tincture  aside  for  three  or  four  days,  that  crystallization 
may  ta.ke  place.  At  the  end  of  this  time  a  quantity  of  small 
granular  crystals  will  be  found  on  the  bottom  and  sides  of  the 
