THE   ESSENTIAL  OIL   OP   BITTER  ALMONDS. 
S45 
of  the  oil  with  abundance  of  milk  of  lime  and  caustic  potash, 
and  subsequent  distillation,  appeared  to  be  quite  effectual ;  but 
as  the  addition  of  a  salt  of  iron  does  no  harm,  and  does  not  add 
materially  to  the  expense,  and  as  this  method  has  succeeded  well 
with  him,  he  was  disposed  to  prefer  it.  The  essential  point 
seemed  to  be  that  the  agents  employed,  should,  by  careful  and  suffi- 
ciently prolonged  agitation,  be  brought  into  perfect  contact  with 
the  oil.  Dr.  Maclagan  said  that  it  had  been  suggested  that  perhaps 
one  distillation  might  be  saved  by  adding  the  lime  and  potash  to 
the  marc  of  the  almonds  when  the  oil  was  first  distilled.  This 
appeared  to  him  a  priori  to  be  unlikely,  from  the  facility  with 
which  both  the  amygdalin  and  the  emulsin  of  the  bitter  almond 
were  acted  on  by  alkalies,  and  accordingly  he  had  found  on  ac- 
tual trial,  that  under  these  circumstances,  no  oil  was  separated, 
but  only  an  ammoniacal  liquor  distilled  over. 
Dr.  Maclagan  insisted  on  the  absolute  necessity,  whatever 
process  of  purification  was  followed,  of  carefully  testing  the  pro- 
duct for  hydrocyanic  acid.  This  was  best  done  by  agitating  the 
oil  briskly  with  aqua  potassse,  passing  through  a  wetted  filter, 
and  applying  the  iron  test  in  the  usual  way  to  the  filtrate.  It 
was  to  the  neglect  of  sufiicient  agitation  with  aqua  potassae  that 
he  ascribed  the  fact,  that  in  oil  in  which  no  hydrocyanic  acid 
had  been  detected,  it  had  sometimes  on  subsequent  trials  been 
readily  found.  It  had  been  suggested  that  possibly  the  hydro- 
cyanic acid  might  not  really  exist  in  newly  rectified  oil,  but 
might  be  re-developed  in  process  of  time.  Dr.  Maclagan  showed 
that  this  was  not  the  case,  by  a  specimen  of  the  rectified  oil,  but 
prepared  by  himself  twelve  months  ago,  still  being  quite  free 
from  all  trace  of  hydrocyanic  acid,  and  moreover,  not  giving, 
under  Lassaigne's  potassium  test,  any  trace  of  nitrogen,  without 
which,  of  course,  hydrocyanic  acid  could  not  be  re-developed. 
In  relation  to  the  more  immediate  question,  whether  or  not 
the  pure  hydruret  of  benzule  was  poisonous,  the  author  recapi- 
tulated the  views  and  contradictory  statements  that  had  been 
made  on  the  subject,  and  noticed  the  statement  made  in  the  post- 
humous volume  of  Dr.  Pereira's  Materia  Ifedica,  on  the  autho- 
rity of  Mitscherlich,  that  the  pure  oil  was  a  poison.  He  then 
recounted  his  own  experiments  on  animals,  giving  the  preference 
for  this  purpose  to  dogs  over  rabbits,  as  being  more  fitted  to  test 
