142  Solution  of  Perchloride  of  Iron.      { AmMa^u^!7h9arIn• 
rate  of  potassium)  be  followed,  the  operation  may  be  performed  with 
comparative  comfort,  but  the  introduction  of  a  salt  of  potassium  or 
sodium  is  an  insuperable  bar  to  the  general  application  of  the  method. 
The  process  may  also  be  rendered  much  pleasanter,  but  at  the  sacri- 
fice of  time,  by  following  the  suggestions  I  made  some  years  ago  (1873), 
and  allowing  the  mixture  of  acidified  iron  solution  and  nitric  acid  to 
stand  a  day  or  two  at  ordinary  temperatures,  or  at  the  heat  of  a  water- 
bath.  In  this  way  the  use  of  expensive  vessels  may  be  avoided,  and 
the  whole  operation  conducted  in  earthenware.  I  have,  however,  for 
the  past  four  or  five  months,  pursued  another  plan,  which  was  sug- 
gested to  me  by  Mr.  S.  Cox,  a  practical  chemist  working  under  my 
direction,  and  which  is  so  great  an  improvement  on  former  methods, 
and  which  answers  the  purpose  so  admirably,  that  I  feel  jastified  in 
recommending  it  very  strongly. 
It  consists  in  reversing  the  ordinary  operation — adding  the  iron  solu- 
tion to  the  nitric  acid  instead  of  the  acid  to  the  iron.  If  the  specified 
■quantity  of  nitric  acid  be  placed  in  a  dish  or  pan,  and  the  iron  solution, 
mixed  with  the  proper  quantity  of  hydrochloric  acid,  be  allowed  to 
trickle  slowly  into  it,  the  oxidizement  is  instantaneous  in  the  cold,  and 
the  frothing  very  slight.  The  change  from  blackish-green  to  reddish- 
brown  is  very  marked,  and  any  deficiency  in  the  quantity  of  nitric  acid 
can  be  at  once  seen.  On  the  large  scale  the  liquor  may  be  best  added 
with  a  syphon.  With  a  bent  glass  tube  of  five-sixteenths  of  an  inch 
an  diameter,  the  liquor  from  ten  pounds  of  iron  may  be  run  in  safely  in 
twenty-two  minutes,  and  requires  no  attention  whatever,  save  in  getting 
the  syphon  in  operation.  With  pharmacopoeial  quantities  of  material, 
the  process  of  oxidizement  may  be  concluded  in  almost  as  many 
seconds. 
The  final  concentration  may  be  performed  in  a  water-bath,  and  in 
this  case  earthenware  vessels  may  be  used,  but  of  course  the  evapora- 
tion is  much  more  rapid  with  the  naked  flame  or  a  sand-bath  ;  but  a 
high  degree  of  heat  is  not  at  all  necessary  in  making  this  preparation. 
I  think  this  plan  of  reversing  the  order  of  mixing  may  be  applied  to 
many  similar  preparations,  and  shall  be  glad  to  learn  the  experience  of 
others  on  this  point. — Can.  Pbar.  Jour.,  Feb.,  1879. 
