TINCTURA  FERRI  CHLORLDI. 
291 
the  washings,  receiving  them  into  the  original  solution.  To  the 
strained  solution,  in  a  flask,  add  the  remainder  of  the  muriatic 
acid  and  heat  the  mixture.  Then  add,  by  small  portions,  the 
nitric  acid  until  it  falls  into  the  hot  mixture  without  effervescence, 
boil  for  half  an  hour  and  set  aside  to  cool.  When  cold  make 
up  the  measure  to  five  pints  with  distilled  water,  and  add  the 
solution  to  the  alcohol. 
The  yield  of  finished  tincture  is  19i  pints ;  and  the  s.  g.  .992. 
One  fluid  ounce  =456  grains  of  this  tincture  yields  32*04 
grains  =7  per  cent,  of  sesquioxide  of  iron,  or,  64-8  grains  = 
14.2  per  cent,  of  sesquichloride  of  iron. 
If  the  acid  be  of  the  prescribed  strength  the  proportion  indi- 
cated dissolves  15|  oz.  of  the  iron,  leaving  a  residue  of  4J  oz. 
A  calculation  upon  this  basis  gives  63«94  grains  as  the  propor- 
tion of  Fe2Cl3  in  solution  in  each  fluid  ounce,  thus  verifying  the 
direct  experiments  within  -86  grain. 
The  flask  is  best  heated  on  a  sand  bath  during  the  saturation, 
and  the  point  of  saturation  is  determined  within  practical  limits 
by  removing  the  flask,  and  observing  that  when  the  boiling  has 
completely  ceased  but  few  bubbles  of  hydrogen  rise  from  the 
residuary  iron.    The  time  required  for  saturation  varies,  that 
named  being  the  maximum.    The  solution  is  now  of  a  beautiful 
deep  green  color,  and  contains  protochloride  of  iron  free  from 
sesquichloride,  in  proportion  as  the  iron  used  was  free  from 
sesquioxide,  and  in  proportion  as  access  of  air  has  been  prevented, 
but  it  is  so  concentrated  that  it  deposits  crystals  of  FeCl+4Ho, 
as  soon  as  it  begins  to  cool.    Hence  the  necessity  for  adding  the 
pint  of  distilled  water,  and  heating  up  before  attempting  to 
strain.    The  straining  (through  »muslin)  is  easily  and  quickly 
effected,  and  with  little  loss.    The  strained  solution  need  not  be 
heated  to  boiling  before  the  additions  of  the  nitric  acid  are  com- 
menced ;  and  the  additions  should  be  cautiously  and  carefully 
made  at  first,  that  the  violence  of  the  reaction  may  not  cause  loss 
of  liquid  with  the  extricated  vapors,  and  toward  the  close  that  an 
excess  of  nitric  acid  may  be  avoided.    As  soon  as  the  acid,  added 
in  drops,  falls  quietly  into  the  surface  of  the  hot  solution  the 
purpose  is  fully  accomplished.    The  half  hour  after  boiling  is 
useful  in  driving  off  the  oxides  of  nitrogen  that  may  have  been  dis- 
solved, but  should  be  shortened  or  omitted  altogether  in  operating 
