NOTE  ON  IMPURITY  IN  TR.  CHLORIDE  OF  IRON.  801 
NOTE  ON  IMPURITY  IN  TR.  CHLORIDE  OF  IRON. 
Editor  of  the  American  Journal  of  Pharmacy  : 
Dear  Sir  : — In  the  May  number  of  your  Journal  of  Pharmacy 
is  a  communication  from  Dr.  Robert  Battey,  in  answer  to  a  pre- 
vious one  from  myself,  upon  the  subject  of  an  impurity  in  tincture 
of  iron. 
He  states  that  the  silky  white  needles  that  constitute  the  im- 
purity above  mentioned,  when  tested  before  the  blow-pipe  and 
also  by  the  wet-way,  give  the  characteristic  reactions  of  sulphate 
of  lime. 
From  what  I  had  said  upon  the  subject  in  the  March  number 
of  the  Journal  of  Pharmacy,  it  would  naturally  have  been  inferred 
that  the  substance  in  question  was  some  one  of  the  salts  of  lime, 
and,  in  fact,  I  ventured  the  conjecture  that  it  was  a  silicate  of 
that  base,  but  did  not  investigate  the  matter  sufficiently  to  de- 
cide upon  its  acid  constituent,  as  I  believed  it  to  be  from  the 
glass. 
I  am  happy  to  acknowledge  the  correctness  of  Dr.  Battey's 
opinion,  and  agree  with  him  that  it  is  doubtless  sulphate  of  limey 
and  as  there  is  some  apparently  contradictory  views  between  us 
I  will  say  that  both  may  be  made  fully  to  coincide  in  most  par- 
ticulars. I  stated  that  my  conviction  was  that  the  impurity 
arose  from  the  action  of  the  acid  upon  the  glass  vessel,  and  Dr. 
B.  thought  that  it  existed  in  the  acid  employed.  In  order  to 
decide  the  matter  I  tested  my  acid  (the  same  as  I  had  used  in 
preparing  the  tincture  of  iron  when  the  crystals  were  produced.) 
I  found  that  it  contained  sulphuric  aeid  in  a  small  proportion, 
but  no  lime. 
Now  it  is  plain  that  if  commercial  muriatic  acid  be  employed, 
sulphuric  acid  will  be  a  more  probable  impurity  than  sulphate  of 
lime,  but  in  either  case  the  latter  substance  may  be  found  in  the 
tincture  prepared  from  such  acid.  If  sulphate  of  lime  does  or 
does  not  pre-exist  in  it,  when  tlie  mixture  is  heated  the  sulphuric 
acid  will  act  upon  the  glass  and  form  sulphates  of  lime,  potassa 
and  soda,  the  former  of  which  will  remain  dissolved  with  the  rest 
while  the  solution  is  warm  ;  but  will  crystallize  out  on  cooling. 
I  am  sure  that  the  reaction  is  generally  that  of  the  acid  upon 
