Am.  Jour.  Pharm.  \ 
August,  1884.  j 
Ferric  Chlorides. 
407 
FERRIC  CHLORIDES. 
By  E.  Rother. 
The  Pharmacopoeia  was  never  very  successful  in  the  selection  and 
construction  of  its  iron  compounds.  The  tendency  towards  an  unat- 
tainable degree  of  definiteness  and  purity  was  perhaps  the  main  cause 
of  this  failure.  In  pharmacy  excessive  purity  and  accuracy  is  in  most 
cases  wholly  unwarranted.  Extreme  concentration  is  another  charac- 
teristic whose  undesirable  features  are  conspicuously  manifested  in  at 
least  two  prominent  directions.  The  one  leads  on  to  certain  forms  of 
dense  solutions  whose  high  degree  of  strength  is  inimical  to  permanence. 
The  other,  however,  which  comprises  the  most  vicious  system  of  the 
two,  embodies  a  class  of  preparations  whose  exalted  medicinal  power, 
irrespective  of  physical  concentration,  is  their  principal  danger.  With- 
out citing  the  very  numerous  instances  so  readily  at  hand,  let  the  case 
of  tincture  of  opium  suffice.  This  preparation,  already  four  times  too 
strong  for  general  safety,  has  recently  had  its  strength  augmented  by 
50  per  cent.  All  of  these  powerful,  especially  liquid,  compounds  call 
for  a  systematic  and  universal  dilution. 
In  order  to  reach  a  highly  definite  result  and  simultaneously  secure 
a  superior  grade  of  purity,  the  Pharmacopoeia,  in  its  process  for  solu- 
tion of  ferric  chloride,  uses  an  excess  of  iron.  This  surplus  of  iron  is 
intended  to  exclude  contaminating  metals  and  insure  the  perfect  satura- 
tion of  a  certain  quantity  of  acid.  Since,  however,  a  practically  pure 
quality  of  iron  is  easily  obtainable,  and  since  the  acid  itself  is  never 
definite,  these  troublesome  precautions  are  wholly  gratuitous.  To 
facilitate  the  solution  of  the  metal  under  these  adverse  conditions  the 
Pharmacopoeia  has,  however,  improved  the  process  by  adding  water  to 
the  acid.  As  100  parts  of  the  solution  shall  contain  37#8  parts  of  ferric 
chloride,  it  must  represent  13  parts  of  metallic  iron,  thus : 
FeCl3,  162-1  :  Fe,  55'9  ::37'8  :  13-03. 
This  amount  of  iron  in  the  condition  of  normal  ferric  chloride  repre- 
sents 80  parts  of  chlorhydric  acid,  thus : 
FeCl3,  162-1  :  3(HC1),  3  X  36'4     -319  ::  37-8  :  79'82. 
Officinally  86  parts  of  the  acid  are  directed. 
Now,  since  under  ordinary  circumstances  80  parts  are  sufficient,  it 
follows  that  the  6  superfluous  parts  must  be  counted  as  impurity.  Yet 
