AmNo0v"'^rm"}        Preparation  of  Dialysed  Iron.  559 
iron  considerable  heat  is  evolved,  and  on  cooling  the  preparation  becomes 
gelatinized — often  so  much  so  that  the  vessel  containing  it  may  be  in- 
verted. It  is  better  to  avoid  this  result,  and  to  this  end  the  solution  of 
perchloride  must  be  diluted  until  of  a  specific  gravity  of  about  1*300. 
This  degree  may  be  nearly  enough  approached  by  diluting  two  meas- 
ures of  the  B.  P.  liquor  with  one  of  water,  or  adding  one  measure  of 
water  to  five  of  the  U.  S.  P.  preparation.  This  solution  will  gener- 
ally remain  permanently  bright  and  fluid.  The  amount  of  liq.  ammon. 
required  will  of  course  vary  with  the  acidity  of  the  perchloride.  The 
liquor  ferri  B.  P,  will  sometimes  bear  as  much  as  an  equal  volume.  A 
gelatinized  solution,  even  when  made  from  the  undiluted  liquor,  will 
often  become  fluid  when  put  upon  the  dialyser  ;  but,  as  I  have  said 
before,  it  is  better  to  work  with  bright  solutions. 
The  second  method  consists  in  adding  to  either  solution  of  the  per- 
chloride a  quantity  of  recently-precipitated  ferric  hydrate^  Mix  any 
given  quantity  of  the  liq.  ferri  with  about  five  times  its  bulk  of  water 
and  add  excess  of  liq.  amnion.,  also  diluted  with  water.  I  think  a  more 
soluble  hydrate  is  produced  when  the  iron  is  added  to  the  ammonia,  as 
remarked  in  the  case  of  the  hydrate  precipitated  from  the  persulphate  ; 
but,  in  order  to  proceed  in  this  way,  it  is  necessary  to  know,  approxi- 
mately, the  amount  of  ammonia  required.  The  precipitate  should  be 
washed  well,  by  decantation,  with  several  waters,  and  then  thrown  upon 
a  filter  to  drain  for  a  short  time.  It  may  then  be  dissolved,  by  the  aid 
of  a  gentle  heat,  in  as  much  strong  liq.  ferri  as  may  be  required  for  solu- 
tion. The  exact  quantity  cannot  be  stated,  but  in  no  case  will  it  ex- 
ceed the  volume  of  the  liquor  precipitated,  and  sometimes  only  one- 
fourth  of  this  amount  will  be  necessary.  The  solution  is  now  ready 
for  dialysis. 
With  the  majority  of  pharmacists  the  dialyser  will  have  to  be  extem- 
porized out  of  such  materials  as  may  be  at  hand.  The  hoop  may  be  a 
bell  jar,  an  inverted  glass  funnel,  or  what  is  even  simpler  and  handier, 
made  from  one  of  the  flat  hoops  of  an  ordinary  flour  barrel.  This  may 
be  smoothed  a  little  with  a  knife  or  sand  paper,  and  made  to  the  required 
diameter — 10  or  12  inches  is  a  convenient  size,  if  much  larger  the  dia- 
lytic  septum  is  liable  to  belly  in  the  center,  and  thus  make  the  layer  of 
liquid  too  deep  at  that  point. 
Parchment  paper  is  generally  used  for  forming  the  septum.  This  is 
not  the  paper  that  stationers  in  this  country  generally  supply  under  this 
