160  Blue  Hydrocarbon  in  Essential  Oils.  {Am-^;^Jm- 
Fifty  grams  of  a  very  blue  fraction,  freshly  steam  distilled,  were 
shaken  with  10  g.  of  63  per  cent,  sulfuric  acid,  and  the  mixture 
allowed  to  settle  over  night.  The  acid  layer  was  then  drawn  off, 
diluted  with  water,  and  extracted  with  petroleum  benzine  until  no 
more  blue  color  was  taken  up.  The  benzine  solution,  dark  blue  in 
color,  was  then  shaken  out  with  85  per  cent,  phosphoric  acid  until  no 
longer  blue,  the  dark  red  acid  solution  drawn  off,  diluted  with  water, 
and  extracted  with  ether.  The  residue  from  the  evaporation  of  the 
ether  amounted  to  0.141  g.,  or  0.28  per  cent.  This,  redissolved  in 
50  g.  of  a  pale  yellow  oil,  gave  a  mixture  with  about  the  same  tint  as 
the  original,  showing  that  there  was  no  appreciable  loss  in  the 
preparation. 
Larger  quantities,  isolated  in  this  way,  were  further  purified  by 
distillation  with  steam,  and  finally  in  vacuo.  The  substance  thus 
obtained  was  a  slightly  viscid  liquid,  intensely  blue  in  thin  layers, 
black  in  quantity,  with  a  weak  phenolic  odor,  suggesting  thymol, 
especially  when  warm. 
Subst.,  0.21 18  and  0.2294  g.  gave  CO2  0.7054  and  0.7587  g. ;  H20,  0.1478  and 
0.1903  g. ;  calc.  for  GsHis :  0  =  90.84;  H=:9.i5;  found:  0  =  90.83  and  90.20; 
H  =  9.23  and  9.28. 
The  molecular  weight  determination  was  made  by  Dr.  Earl  F.  Farnau  of 
New  University,  by  the  cryoscopic  method,  using  benzene  as  solvent.  Found : 
187.2  and  193.4  (av.,  190.3)  ;  calc.  for  G5H12:  1.98. 
The  compound  is,  then,  a  hydrocarbon,  having  most  probably  the 
formula  C15H18,  and  for  it  the  writer  would  preserve  the  name 
"  azulene,"  proposed  in  1863  by  Piesse,10  one  of  the  earliest  investi- 
gators, for  the  blue  fraction  which  he  obtained  from  oil  of  worm- 
wood. 
The  specific  gravity  at  25 0  is  0.9738,  when  freshly  steam-distilled. 
Exposed  to  light  and  air,  it  is  gradually  converted  into  a  brown  resin. 
Distilled  at  atmospheric  pressure,  the  boiling-point  rises  from  295 0 
to  300 °,  leaving  a  tarry  residue,  soluble  in  ether  with  a  brown  color. 
At  about  25  mm.  azulene  distils  from  1850  to  1950,  leaving  a  brown 
residue  of  about  5  per  cent.  Since  the  product  had  been  previously 
distilled  with  steam,  this  shows  that  it  cannot  be  distilled  without 
change  under  these  conditions.  When  evaporated  on  the  water-bath 
in  an  open  dish,  a  brown  resin,  amounting  to  10  per  cent,  or  more, 
remains. 
Compt.  rend.  57,  1016  (1864). 
