^""'DrcTisso?"""}  Examination  of  Solution  of  Chloride  of  Iron.  599 
ti^n  to  be  complete,  when  the  reading  on  the  burrette  showed  17*8  cc. 
of  the  standard  solution  to  have  been  used.  The  strength  of  the 
solution  of  potassium  permanganate  had  previously  been  estimated  with 
pure  iron  wire,  and  i  cc.  of  the  solution  oxidized  o  004936  gram  of 
iron  from  ferrous  to  ferric  form,  or  was  equal  to  0*004936  gram  of  iron  ; 
hence  ly  S  cc.  =  0  08786  gram  of  irom.  Deducting  0'000735  gram, 
the  amount  of  iron  already  present  in  the  zinc  used,  we  have  left 
0*0871  gram,  the  amount  of  iron  in  1926  gram  of  the  solution  of 
chloride  of  iron,  or,  expressed  in  percentage,  4  52  per  cent.  ;  and  as 
112,  the  molecular  weight  of  iron,  is  to  325,  the  molecular  weight  of 
anhydrous  ferric  chloride,  so  is  4*52,  the  per  cent,  of  iron  found,  to  the 
percent,  of  anhydrous  ferric  chloride,  which  is  13*1  per  cent. 
To  find  the  per  cent,  of  iron  in  the  officinal  solution,  we  quote  the 
Pharmacopceia,  which  gives  the  following  description  and  tests  for 
liquor  ferri  chloridi  : 
"A  reddish-brown  liquid,  having  an  acid  and  strongly  styptic  taste, 
and  the  specific  gravity  i'355.  Two  fluidrachms  of  the  solution, 
diluted  with  water  and  treated  with  ammonia  in  excess,  yields  a  pre- 
cipitate of  sesquioxide  of  iron,  which,  when  washed,  dried  and  ignited, 
weighs  28*25  grains." 
From  these  figures  the  percentage  of  iron  and  anhydrous  ferric 
chloride  is  calculated  as  follows:  As  160,  the  molecular  weight  of 
sesquioxide  of  iron,  is  to  112,  the  molecular  weight  of  iron,  so  is 
28  25,  the  number  of  grains  of  sesquioxide  yielded  by  two  fluidrachms 
of  the  solution  to  the  number  of  grains  of  iron  in  two  fluidrachms, 
which  we  find  to  be  19*775  grains.  Also,  two  fluidrachms  of  the 
solution,  having  a  specific  gravity  of  1*355,  weighs  154*36  grains,  and 
as  just  stated,  contains  19*775  grain  of  iron,  or,  expressed  in  per 
cent.,  12*8  per  cent.  Now,  as  the  molecular  weight  of  iron,  112,  is 
to  the  molecular  weight  of  anhydrous  ferric  chloride,  325,  so  is  the 
percentage  of  iron  in  the  officinal  solution,  12*8,  to  the  percentage  of 
anhydrous  ferric  chloride,  which  is  37*1  per  cent.  Comparing  these 
results,  we  have  in  the  solution  analyzed  4*52  per  cent,  of  iron  ;  in  the 
officinal  solution  I2*8  per  cent,  iron,  and  13*1  per  cent,  of  anhydrous 
ferric  chloride  instead  of  37.1  per  cent,  in  the  officinal  solution,  prov- 
ing this  solution  to  be  very  deficient  in  strength,  which  is  also  indicated 
by  its  light  color. 
Although,  as  will  be  seen  by  this  method  of  estimation,  the  total 
amount  of  iron  contained  in  the  preparation  was  estimated,  yet  a  portion 
