AmApi?r'f9hi5rm'  }   Blue  Hydrocarbon  in  Essential  Oils.  161 
-Azulene  is  readily  soluble  in  most  organic  solvents.  In  95  per 
cent,  alcohol  it  is  miscible  in  all  proportions ;  in  more  dilute  alcohol 
the  solubility  is  much  less,  but  even  50  per  cent,  alcohol  takes  up 
enough  to  be  tinted,  a  decided  blue. 
Its  solubility  in  strong  inorganic  acids,  which  makes  its  isolation 
possible,  is  especially  remarkable.  In  60  to  65  per  cent,  sulfuric  acid, 
azulene  dissolves  to  a  clear  yellow,  strongly  fluorescent  solution  ;  on 
dilution  with  water,  it  is  thrown  out  again  as  a  blue  oil,  apparently 
unchanged.  It  also  dissolves  in  50  per  cent,  sulfuric  acid,  but  less 
readily.  The  solution  in  phosphoric  acid  is  remarkable  for  its  fluor- 
escence :  reddish  yellow  by  transmitted  light,  intense  apple  green  by 
reflected  light.  These  acid  solutions  can  be  extracted  with  benzine 
without  removing  any  azulene,  and  by  repeating  several  times,  a 
product  can  be  obtained,  free  from  sesquiterpenes  or  alcohols. 
Azulene  is  strongly  resistant  to  the  action  of  even  strong  sulfuric 
acid.  When  heated  with  two  parts  of  94  per  cent,  acid  for  fifteen 
hours  on  the  water-bath,  a  dark  brown  solution  results,  which,  on 
diluting  with  water,  again  yields  the  blue  oil.  Strong  formic  acid 
dissolves  it  with  a  green  color,  but  in  acetic  acid  the  color  remains 
unchanged,  as  in  the  neutral  solvents.  On  mixing  dry  ether  solutions 
of  azulene  and  hydrochloric  acid,  no  change  in  color  was  observed. 
Nitric  acid  in  acetic  acid  solution  produces  yellow  amorphous 
substances,  not  further  examined. 
The  oxidation  of  azulene  with  permanganate  has  so  far  yielded 
only  lower  fatty  acids. 
It  is  not  attacked  by  sodium  in  hot  alcohol,  nor  does  heating  with 
strong  alkali  affect  the  color. 
By  the  action  of  acetic  anhydride  and  sulfuric  acid,  a  substance 
was  obtained,'  evidently  a  sulfonic  derivative,  which  was  soluble  in 
water.  On  adding  sodium  carbonate  in  excess  a  sodium  salt 
separated  out,  which  was  recrystallized  from  hot  water.  The  water 
solution  of  the  salt  is  colored  violet,  and  changes  to  a  light  green  on 
acidifying.  If  then  shaken  with  ether,  the  latter  becomes  violet, 
and  this  color  is  again  taken  out  by  shaking  with  alkali. 
The  sodium  salt,  on  heating,  gives  off  blue  fumes  which  con- 
dense to  a  blue  oil ;  at  the  same  time  sulfur  dioxide  is  liberated. 
On  standing  three  months  in  a  corked  bottle,  a  preparation  of 
the  sodium  salt  had  decomposed  into  a  mixture  of  oil  and  resin. 
The  water  solution  gives  blue  precipitates  with  barium  and  cal- 
cium solutions,  and  is  decolorized  by  bromine  water. 
