[ 199  ] 
XI.  On  the  Constitution  of  the  Essential  Oil  of  Rue. 
By  C.  Greville  Williams,  Lecturer  on  Chemistry  in  the  Normal  College^  Swansea. 
Received  February  15, — Read  March  18,  1858. 
The  essential  oil  procured  by  distillation  of  the  rue  plant  with  water,  has  already  been 
examined  by  several  chemists.  It  was  analysed  many  years-ago  by  Will*,  who  deduced 
from  his  analyses  the  expression  O®.  But  at  that  time  far  too  little  was  known 
about  the  oxygenated  essential  oils  to  permit  of  their  accurate  investigation.  A more 
minute  series  of  experiments,  made  by  Gerhardt  in  1848f,  led  him  to  conclude  that 
oil  of  rue  consisted  principally  of  the  capric  aldehyde,  contaminated  by  a small  quantity 
of  some  hydrocarbon.  This  \dew  was  considered  to  be  confirmed  by  the  production  of 
capric  acid  when  the  oil  undenvent  oxidation  by  means  of  nitric  acid.  But  the  pro- 
duction of  an  acid  containing  merely  rendered  it  probable  that  the  rue  oil  did  not 
contain  less  than  20  equivalents  of  carbon;  it  was  no  proof  that  it  did  not  contain  more. 
In  fact,  the  action  of  nitric  acid  varies  with  its  concentration. 
Guided  by  ideas  which  need  not  now  be  detailed,  I made  in  1853  some  experiments, 
with  the  intention  of  obtaining  from  oil  of  rue  certain  bodies  of  the  capric  series,  but 
they  only  served  to  conGnce  me  that  the  views  then  entertained  regarding  the  consti- 
tution of  the  oil  were  erroneous.  Some  curious  reactions  were  observed,  but  the  expe- 
riments diverging  into  other  channels  have  not,  as  yet,  been  renewed.  Previous  to 
recommencing  them,  it  has  been  thought  necessary  to  make  a fresh  examination  of  the 
oil;  the  results  form  the  subject  of  this  communication. 
On  examination  of  Gerhardt’s  numbers,  it  will  be  found  that,  while  two  of  his 
analyses  agree  exactly  with  the  formula  the  vapour-density  (5‘83)  exceeds  the 
theoretical  number  (5-398)  to  a degree  much  greater  than  can  be  accounted  for  by  an 
error  of  experiment;  the  number  obtained  being  almost  the  correct  value  for  the 
homologue  above  the  capric  aldehyde.  Moreover,  the  fluid  analysed  was  purified 
by  distillation  only. 
In  this  investigation  use  has  been  made  of  the  invaluable  reagent  for  the  isolation 
and  purification  of  aldehydes  (and  bodies  of  more  or  less  analogous  constitution),  placed 
in  the  hands  of  chemists  principally  by  the  researches  of  M.  Bertagnihi.  By  its  aid  a 
perfect  separation  has  been  made  of  the  aldehydes  in  oil  of  rue,  enabling  their  nature 
to  be  clearly  determined. 
On  submitting  the  crude  oil  to  about  a dozen  fractional  distillations,  distillates  were 
obtained  from  160°  to  238°.  On  treating  them  with  the  bisulphites  of  soda  or  ammonia, 
* Ann.  der  Chem.  und  Pharra.  xxxv.  235. 
t Ann.  de  Chim.  et  de  Phys.  [3]  xxiv.  103. 
