146    ON  THE  PURIFICATION  OF  ESSENTIAL  OIL  OF  ALMONDS. 
acid,  sal-ammoniac  being,  of  course,  at  the  same  time  produced 
according  to  this  equation — 
Cl4H602+HC2N+HC]+2H202=NH4Cl+C14H602,C2H2P^ 
I  imagined  that  if  the  formation  of  this  substance,  this  acid, 
"which  of  course  takes  a  large  proportion  of  hydride  of  benzoyl, 
could  be  prevented  or  diminished,  this  might  prove  a  practicable 
process  for  the  destruction  of  the  hydrocyanic  acid  in  the  essence 
of  almonds.  I  have  not  succeeded,  by  any  means  that  I  have 
tried,  in  preventing  altogether  the  loss  of  hydride  of  benzoyl  in 
this  form,  but  I  think  it  may  be  effected  to  a  considerable  extent. 
The  method  I  have  pursued  is  as  follows  : — The  essential  oil  is 
mixed  in  a  flask  with  about  three  times  its  bulk  of  ordinary  hy- 
drochloric acid  diluted  with  a  small  quantity  of  water,  a  con- 
denser attached,  and  distillation  started.  As  soon  as  the  oil 
begins  to  come  over  pretty  freely,  a  quantity  of  water  is  added 
and  distillation  proceeded  with.  The  oil  is  afterwards  separated 
from  the  aqueous  portion  of  the  distillate ;  it  is  slightly  acid, 
and  to  remove  this  a  little  piece  of  quicklime  is  put  into  it, 
■which  at  the  same  time  helps  to  dry  the  oil.  If  hydrate  of 
lime  be  used  for  this  purpose,  the  essence  becomes  slightly  dis- 
colored. 
Supposing  the  change  represented  in  the  equation  above  to 
take  place  strictly  as  there  shown,  a  proportion  of  hydrocyanic 
acid  in  the  oil  amounting  to  8  per  cent,  would  cause  a  loss  of 
no  less  than  31-4  per  cent,  of  the  hydride,  in  the  form  of  the 
acid  described  ;  5  per  cent,  of  the  hydrocyanic  acid  would  re- 
move 19-6  per  cent,  of  hydride.  Such  a  deficiency  would  be, 
of  course,  out  of  the  question ;  but  I  have  made  in  the  manner 
described  two  rough  quantitative  experiments,  and  believe  that 
the  loss  on  the  large  scale  would  not  amount  to  more  than  from 
15  to  17  per  cent.,  which  would  include  hydrocyanic  acid, 
benzoic  acid,  benzoine,  and  all  the  other  impurities  of  the 
essence. 
I  now  "wish  to  describe  another  method,  which  was  suggested 
at  a  meeting  of  the  Chemical  Discussion  Association  by  my  friend 
Mr.  Broughton,  and  which  had  also  occurred  to  myself,  but  at 
that  time  I  had  no  opportunity  of  making  the  experiment. 
Chemists  have  found  that  all  the  aldehyds  with  which  we  are 
acquainted  form  definite  crystalline  compounds  with  the  alka- 
