326  Solution  and  Tincture  of  Ferric  Chloride.  { AmvKya894.arm' 
"  Pour  the  acid  upon  the  subcarbonate  of  iron  in  a  glass  or  porcelain 
vessel,  mix  them,  and  when  effervescence  ceases,  apply  a  gentle  heat 
and  continue  it,  stirring  occasionally  until  the  carbonate  is  dissolved, 
then  filter  the  solution  and  mix  with  the  alcohol."  This  formula 
did  not  provide  for  an  excess  of  acid,  consequently  precipitation 
was  apt  to  ensue;  particularly  did  this  objection  prevail  when  inferior 
acid  was  used.  Tinctures  made  by  this  process  are  very  unreliable 
and  of  indefinite  strength.  Incessant  complaint  of  the  imperfection 
of  the  formula  resulted  in  the  adoption  of  a  new  and  much  improved 
method  in  the  Pha'rmacopceia  of  i860,  as  proposed  by  Dr.  Squibb 
and  published  in  the  American  Journal  of  Pharmacy,  1857,  p.  290. 
Pure  iron  wire  was  substituted  for  the  subcarbonate.  The  official 
directions  were :  "  When  effervescence  has  ceased  drop  in  nitric 
acid,  constantly  stirring  until  it  no  longer  produces  effervescence. 
Lastly,  when  the  liquid  is  cold  add  sufficient  distilled  water  to  make 
it  measure  a  pint  and  mix  it  with  alcohol." 
This  yielded  a  tincture  which  contained  a  little  nitric  acid,  and  all 
the  nitrous  acid  the  iron  solution  was  capable  of  holding  at  a  tempe- 
rature near  the  boiling  point.  It  is  claimed  that  such  a  tincture  has, 
in  six  months  or  a  year,  a  full  ethereal  odor  in  which  ethyl  nitrite  is 
recognizable. 
The  1870  Pharmacopoeia  again  modified  this  formula;  the  two 
steps  in  the  process  were  separated  and  two  distinct  preparations 
introduced,  one  an  acid  solution  of  ferric  chloride,  the  other  the 
tincture  which  was  made  from  the  solution 
The  committees  on  revision  of  1880  and  1890  continued  this 
plan.  Our  present  official  directions  are  :  "  After  effervescence  has 
ceased  apply  heat  by  means  of  a  sand  bath,  until  the  liquid  is  free 
from  nitrous  odor." 
This  solution  yields,  after  being  mixed  with  a  definite  quantity  of 
alcohol  and  allowed  to  stand  for  three  months,  the  official  tincture 
of  ferric  chloride.  This  tincture  does  not  possess  the  same  degree 
of  ethereal  odor  as  that  of  the  i860  tincture.  Even  after  standing: 
six  months  or  a  year,  it  does  not  possess  much  more  than  a  trace. 
The  reaction  between  the  acid  and  the  alcohol  is  very  slow,  and  the 
portion  of  acid  small  that  enters  into  combination  with  the  alcohol 
in  forming  ethers  in  the  course  of  three  months.  Therefore,  the 
U.  S.  P.  directs  it  to  stand  three  months,  although  it  is  preferable  to 
stand  a  year.   The  ethers  formed  possess  diuretic  properties.  Com- 
