Am,juryr;i894arm"}  Solution  and  Tincture  of  Ferric  Chloride.  325 
liar  with  the  fact  that  the  medicinal  qualities  largely  depend  upon 
the  quantity  of  hydrochloric  acid  present.  When  deficient  it 
reduces  the  percentage  of  iron  and  deprives  the  tincture  made 
therefrom  of  the  ethereal  odor,  and  when  added  in  excess  it  is  very 
deleterious  insomuch  that  it  affects  its  therapeutic  properties,  becom- 
ing injuriously  irritating  to  the  stomach  and  often  producing  second- 
ary effects  which  are  very  undesirable.  References  have  been  made 
to  various  works  and  text-books  on  chemistry  with  a  view  of  finding 
some  satisfactory  method  for  making  this  determination,  but  with 
unsatisfactory  results ;  in  consequence  of  which  a  new  and  original 
method  (suggested  by  Prof.  W.  Simon)  was  employed,  proving  to 
be  very  applicable,  simple  and  accurate,  giving  perfect  satisfaction 
in  all  its  details. 
Take  i-o  gram  of  the  solution,  dilute  with  100  cc.  of  water,  neu- 
tralize with  seminormal  solution  of  potassium  hydroxide,  using  litmus 
as  an  indicator,  transfer  it  into  a  flask  and  add  enough  water  to 
make  250  cc.  Titrate  50  cc,  of  the  supernatent  liquid  v/ith  deci- 
normal  solution  of  silver  nitrate,  after  the  addition  of  a  few  drops  of 
neutral  potassium  chromate.  From  the  number  of  cc.  of  silver 
nitrate  solution  required,  determine  total  amount  of  hydrochloric 
acid  present.  From  the  percentage  of  Fe.2Cl6  already  ascertained  in 
the  sample,  calculate  the  amount  of  absolute  acid  represented,  and 
deduct  from  the  total ;  the  result  will  be  the  free  acid  present. 
In  case  an  excess  of  KOH  solution  is  added  titrate  back  with  sul- 
phuric acid  solution. 
The  official  solutions  should  contain  27-43  Per  cent,  of  hydro- 
chloric acid,  allowing  1-95  per  cent,  for  free  acid.  It  will  be  readily 
observed  that  the  solutions  are  generally  deficient  in  hydrochloric 
acid.  This  is  due  to  a  weaker  acid  than  the  official  being  used  in 
making  the  preparatipn,  causing  considerable  oxychloride  to  be' 
formed  during  the  process,  which  is  not  always  detected.  The  5 
per  cent,  of  official  acid,  directed  to  be  added,  is  partly  taken  up  by 
the  oxychloride,  thereby  reducing  the  amount  of  free  acid.  The 
excess  is  accounted  for  by  reason  of  insufficient  time  allowed  for  the 
acid  to  act  on  the  iron.  Nos.  3  and  9  are  examples  of  the  latter. 
The  percentage  as  stated  in  the  column  is  absolute  acid. 
Prior  to  the  publication  of  the  Pharmacopoeia  of  1870,  tincture 
ferric  chloride  was  made  either  directly  from  iron  wire  or  from  the 
subcarbonate  of  iron.    The  pharmacopceial  directions  of  1850  were  : 
