350      PURIFICATION  OF  THE  ESSENTIAL  OIL  OF  ALMONDS* 
After  this  crystalline  deposit  has  been  formed  it  is  sometimes 
dissolved  and  again  re-deposited,  in  which  respect  it  differs  from 
what  occurs  in  the  case  of  oil  of  sassafras.  I  have  never  found, 
if  the  ste'aroptene  of  sassafras  is  dissolved  in  the  oil  from  which 
it  was  deposited,  that  it  is  deposited  again,  nor  have  I  been  able 
to  crystallize  it  after  it  has  been  liquefied. 
We  know  that  benzoic  acid  is  instantly  and  largely  dissolved 
by  essential  oil  of  almonds,  and  again  deposited  with  change  of 
temperature  ;  and  I  have  placed  on  the  table  some  of  the  crystal- 
line deposit  thus  formed.  It  will  be  observed  that  the  appear- 
ance of.  the  crystals  is  different  from  that  of  the  crystals  which 
are  formed  spontaneously  in  oil  of  bitter  almonds.  The  latter 
appears  to  me  more  nearly  to  resemble  the  crystalline  product 
obtained  from  balsam  of  tolu,  which  by  Thompson  and  others  has 
been  designated  benzoic  acid,  but  which  has  subsequently  been 
shown  to  consist  principally  of  cinnamic  acid.  This  cinnamic 
acid  is  said  to  be  formed  by  the  oxidation  of  hyduret  of  cinnamyle, 
just  as  benzoic  acid  is  produced  from  hyduret  of  benzoyle.  I 
have  observed  that  during  the  formation  of  the  crystalline  deposit 
in  oil  of  bitter  almonds,  water  is  at  the  same  time  produced, 
which  floats  upon  the  oil,  a  fact  which  supports  the  opinion  of 
the  crystalline  matter  being  benzoic  acid. 
Although  the  crude  oil  of  bitter  almonds  contains  a  large  but 
variable  quantity  of  hydrocyanic  acid,  yet  the  hyduret  of  ben- 
zoyle is  found  to  be  insoluble  in  hydrocyanic  acid,  at  least  in  the 
aqueous  acid.  Whether  it  be  so  in  the  anhydrous  acid,  as  was 
hinted  by  Dr.  Stenhouse,  is  an  interesting  subject  for  inquiry. 
I  may  here  notice  the  impropriety  of  employing  the  water  ob- 
tained in  the  distillation  of  the  essential  oil  of  almonds  for  culin- 
ary purposes.  The  quantity  of  hydrocyanic  acid  contained  in 
this  water  varies  very  considerably,  and  the  strength  of  it  is 
sometimes  such  as  to  render  it  highly  dangerous.  The  solution 
of  the  essential  oil  in  spirit,  called  essence  of  almonds,  as  com- 
monly sold,  is  also,  as  I  conceive,  unnecessarily  strong.  It  is 
usually  prepared  of  the  strength  of  one  part  of  oil  and  seven  of 
spirit.  If  made  in  the  proportions  of  three  fluid  drachms  of  oil 
to  sixteen  fluid  ounces  of  spirit,  it  would  afford  a  better  flavor, 
and  be  much  safer. — Ibid. 
