352 
PURIFICATION  OF  ESSENCE  OF  ALMONDS. 
a  metal  still  of  the  proper  dimensions,  the  oil  is  rarely  purified. 
These  considerations  acted  forcibly  on  myself,  and  induced  me 
to  attempt  the  purification  of  the  essence  by  means  within  the 
reach  of  all ;  and  I  think  1  have  succeeded  in  doing  so.  TIk 
process  is  not  altogether  novel,  being  a  modification  of  the  well- 
known  iron-test  for  prussic  acid.  I  at  first  mixed  with  the 
essence  a  solution  of  the  proto  and  perchlorides  of  iron,  which 
are  both  soluble  in  spirit,  then  a  slight  excess  of  liq.  potassse, 
and  finally  sufficient  dilute  sulphuric  acid  to  neutralize  that 
excess.  I  found  this  to  separate  considerable  quantity  of  Prussian 
blue,  but  that  it  did  not  remove  the  whole  of  the  prussic,  although 
the  proportions  of  the  ingredients  were  varied  very  many  times. 
I  at  last  prepared  three  quantities,  in  the  first  of  which  the  acid 
predominated,  the  second  was  neutral,  the  third  strongly  alkaline. 
All  three  were  exposed  in  small  flasks  in  the  laboratory  window, 
and  agitated  occasionally  for  two  days.  In  the  meantime  the  first 
had  assumed  a  bright  blue,  which  had  increased  from  the  first, 
and  gave  promise  of  complete  purification  ;  the  second  and  third 
were  of  an  olive-green.  As  therefore  the  protoxide  was  just  dis- 
appearing, and  fearful  that  oxidation  would  commence,  they  were 
rendered  neutral  by  sulphuric  acid,  and  after  a  short  time  filtered. 
The  third  was  the  only  one  found  to  be  quite  free  from  prussic 
acid,  viz.,  that  in  which  the  alkali  had  been  in  excess.  From  my 
experiments  I  deduce  the  following  formula. 
Make  a  solution  of  protochloride  of  iron  by  adding  an  excess 
of  iron  wire  to  the  dilute  hydrochloric  acid  of  the  Pharmacopoeia ; 
when  the  solution  has  become  neutral,  add  one  drachm  of  it  to  an 
ounce  of  the  essence  (containing  one-tenth  by  measure  of  essen- 
tial oil,)  and  then  twenty-five  grs.  of  potass  (the  commercial 
potassa  fusa  answers  the  purpose)  dissolved  in  one  drachm  of 
distilled  water.  Shake  them  well  together,  and  keep  the  mixture, 
shaking  and  opening  the  vessel  occasionally,  until  it  has  acquired 
an  olive-brown  color,  then  neutralize  with  dilute  sulphuric  acid, 
and  after  a  short  time  filter.  About  six  drachms  will  come 
through  without  attention,  and  a  further  quantity  by  tapping 
with  the  finger  the  funnel  containing  the  filter.  Let  the  filter 
then  be  washed  with  spirit,  until  the  required  quantity  be  ob- 
tained. Nearly  the  whole  of  the  water  will  be  retained  on  the 
filter  by  the  hydrated  oxides  and  the  cyanide. 
