86  A  Basic  Reaction  of  Aldehydes.  {^ebrn^f™' 
obtained.  If  citral  is  not  found  to  be  the  predominating  aldehyde, 
the  results  would  be  of  little  value  except  as  comparative. 
For  oil  of  lemon,  5  or  10  grammes  are  weighed  into  an  Erlen- 
meyer  flask,  and  after  neutralization,  25  or  50  c.c.  of  a  20  per  cent, 
sodium  sulphite  solution,  depending  upon  the  amount  taken,  is  added. 
Before  adding  the  sulphite  solution,  however,  it  is  neutralized  with 
a  little  N / 2HCI,  after  being  heated  by  immersion  in  a  water  bath. 
The  sulphite  solution  used  in  these  experiments  required  about  75 
c.c.  of  N/ 2HCI  to  neutralize  at  boiling  temperature,  with  rosolic 
acid  as  an  indicator.  When  the  solutions  were  mixed  a  red  color 
formed  at  once  in  the  aqueous  layer.  This  was  discharged  from 
time  to  time  with  N / 2HCI.  The  flask  is  then  heated  and  agitated 
frequently.  The  reaction  is  complete  in  about  half  an  hour,  if  kept 
hot,  and  the  layers  mixed  frequently.  When  the  color  is  all  dis- 
charged, or  all  but  a  very  faint  pink,  which  is  not  appreciably 
affected  by  a  few  drops  more  acid,  the  number  of  cubic  centimetres 
of  standard  acid  is  noted.  An  emulsion  forms,  due  to  the  neutral- 
ized resins,  but  that  does  not  interfere  with  the  reaction,  if  care  is 
exercised. 
The  reaction,  as  written  by  Tiemann,  is  : 
C9H15COH  +  2H20  +  2N3SO3  =  C9H17COH 
(NaHS03)2  +  2NaOH 
and  is  probably  correct,  as  the  amount  of  citral  and  sulphite  is  shown 
below  to  be  in  the  ratio  of  1  to  2. 
The  amount  of  standard  hydrochloric  acid  used  expressed  in 
terms  of  citral,  in  the  above  ratio  of  one  molecule  of  citral  to  two 
molecules  of  HC1,  divided  by  the  weight  of  oil  taken,  gives  the 
percentage  of  citral. 
Analyses  of  citral  in  lemon  oil,  by  this  method,  gave  in  two  de- 
terminations : 
Per  Cent. 
1  5'24 
II  5'29 
I  believe  results  within  one  or  two  tenths  of  a  per  cent,  can  be 
gotten  in  every  case,  with  a  little  practice,  by  this  method. 
To  check  the  accuracy  of  this  reaction,  I  made  some  known  mix- 
tures of  citral,  which  was  kindly  furnished  by  Dr.  Harry  F.  Keller, 
and  separated  lemon  oil  terpenes,  previously  freed  from  citral. 
Calculated.  Found. 
1  8-68  8-85 
