AmApiT'i£5arm'}   Blue  Hydrocarbon  in  Essential  Oils.  159 
Semmler  and  Jakubowicz  8  obtained  blue  oils  by  heating  the  gur- 
junene  sesquiterpenes  in  autoclaves  filled  with  air  or  oxygen. 
So  far  as  the  writer  knows,  no  connection  has  as  yet  been  assumed 
between  the  blue  oils,  and  the  striking  color  reactions  which  have 
frequently  been  observed  when  oils  consisting  largely  of  sesqui- 
terpenes or  sesquiterpene  alcohols  are  treated  in  dilute  solutions  with 
mineral  acids.  An  experiment  seems,  however,  to  indicate  that  such 
connection  may  exist.  If  oil  of  gurjun  balsam  be  dissolved  in  acetic 
anhydride,  and  a  small  amount  of  sulfuric  acid  added,  the  mixture 
becomes  intensely  blue,  and  on  diluting  with  water  and  distilling  the 
oil  in  a  current  of  steam,  a  deep  blue  distillate  is  obtained. 
Very  many  oils  containing  sesquiterpenes  and  related  compounds 
give  strong  color  reactions  when  dissolved  in  acetic  anhydride  con- 
taining a  trace  of  sulfuric  acid.  Of  the  oils  examined  in  this  labor- 
atory, those  of  gurjun,  amyris,  and  guaiac-wood  give  strong  blue  or 
violet  colors  under  these  conditions ;  santal  and  cedar-wood,  none. 
This  test  may  be  used  to  advantage  to  detect  adulterants  in  some  oils, 
such  as  santal. 
As  to  the  nature  of  this  blue  constituent,  nothing  whatever  has 
so  far  been  definitely  ascertained,  for  the  reason  that,  as  already 
indicated,  it  has  not  been  isolated  in  a  state  of  even  approximate 
purity.  A  remarkable  fact  is  that  a  substance  with  such  intense  color 
should  possess  a  comparatively  low  boiling-point,  indicating  a  simple 
molecule.  Semmler 9  suggests  the  possibility  of  a  bimolecular 
structure,  closely  related  to  the  sesquiterpenes,  which  on  distillation 
dissociates,  and  on  condensing,  again  forms  a  bimolecular  compound, 
with  a  group  similar  to  that  in  indigo:  >C  :  C<.  As  a  rule,  how- 
ever, the  assumption  has  been  made  that  the  blue  substance  is  an 
oxygenated  compound  of  alcoholic  nature. 
The  following  work  describes  the  isolation  of  this  body  in  a  state 
of  purity,  as  shown  by  the  analysis  and  reactions.  As  a  pure  sub- 
stance, its  remarkable  properties  become  even  more  striking  than 
before.  The  analysis  shows  it  to  be  a  highly  unsaturated  hydro- 
carbon, but  the  peculiar  grouping  of  atoms  to  which  it  owes  its 
unique  properties  is  more  difficult  to  speculate  upon  than  ever. 
The  property  which  was  utilized  to  isolate  the  substance,  and 
which  has  heretofore  not  been  noted,  is  its  solubility  in  mineral  acids 
of  certain  strengths.    The  method  of  preparation  was  as  follows : 
*  Ber.  47,  2252-9  (1914). 
9  Aetherischen  Ole,  3,  p.  266. 
