66         PREPARATION  AND  USE  OF  PERCHLORIDE  OP  IRON. 
described  in  1844,*  The  ferric  solution  would  then  be  a  prepa- 
ration which  the  surgeon  could  prescribe  of  any  strength  he  may 
desire.  The  dry  chloride  may  be  kept  for  a  long  time  without 
change ;  it  forms  a  clear  solution  with  water ;  which  also  may 
be  kept  for  a  long  time  without  any  sensible  alteration.  The 
chloride  of  iron  prepared  from  hematite  (according  to  M.  Gob- 
ley's  process  referred  to)  is  chemically  more  pure  and  more  surely 
uniform  than  that  made  from  the  hydrated  oxide.  It  also  con- 
tains a  smaller  quantity  of  free  acid.  I  believe,  indeed,  that  it 
contains  but  a  mere  trace.  If,  in  preparing  it,  the  evaporation 
be  continued  beyond  the  point  at  which  it  becomes  solid  on  cool- 
ing, I  have  observed  that  it  decomposes  into  hydrochloric  acid 
and  oxychloride  of  iron.  The  solution  which  Mr.  Burin  du 
Buisson  now  prefers  to  use  is  but  slightly  acid  when  recently 
prepared,  but  it  becomes  more  acid  after  being  kept,  from  the 
deposition  of  oxychloride.  It  is  true  that,  according  to  him, 
it  is  this  excess  of  acid  that  prevents  a  further  deposition  of  oxy- 
chloride, but  in  order  to  prevent  the  ^acidity  of  the  liquor,  would 
it  not  be  better  to  employ  a  solution  made  extemporaneously 
from  the  dry  chloride  ? 
There  is,  it  is  true,  one  difficulty  in  the  employment  of  the 
dry  salt,  namely,  that  the  quantity  of  the  solution  required  for 
an  operation  is  always  very  small,  but  I  have  surmounted  this 
difficulty  by  determining  from  experiment  the  proportions  of 
perchloride  of  iron  and  water  necessary  to  form  solutions  of  the 
strength  required  for  surgical  purposes. 
The  following  are  the  proportions  for  making  solutions  of 
certain  densities  indicated  according  to  Baume's  hydrometer: — » 
Chloride. 
Water. 
Density  of  solution. 
53.85 
46.15 
45° 
34.65 
65.35 
30<> 
21.30 
78.70 
20° 
16.35 
83.65 
15° 
The  dry  chloride  contains  about  a  fifth  of  its  weight  of  water 
it  is,  therefore,  always  easy  to  calculate  the  quantity  of  anhy* 
*  This  process  is  described  at  length  in  voL  iv.,  page  34,  of  the  Pharmsi- 
teutical  Journal* 
