572 
Analysis  of  Essential  Oils. 
(  A.m.  Jour.  Pharm. 
I  December,  1899. 
Some  ketones  and  aldehydes,  like  a.cetone,  acetic  aldehyde, 
vanillin,  yield,  from  the  beginning,  very  soluble  bisulphite  com- 
pounds, which  usually  do  not  crystallize  out;  the  aqueous  solution 
should,  therefore,  by  boiling  with  soda  or  sulphuric  acid,  always  be 
tested  for  the  presence  of  such  soluble  compounds;  in  the  same 
way  the  aldehydes  or  ketones  can  usually  be  obtained  from  the 
solid  bisulphite  compounds. 
Occasionally  the  latter  form  very  disagreeable  gelatinous  masses, 
which  are  almost  unalterable ;  upon  prolonged  standing,  with  occa- 
sional shaking  they  usually  are  obtained  in  the  crystalline  state; 
also  here  the  addition  of  some  alcohol  is  often  useful. 
Now  we  proceed  to  the  removal  of  acids  and  phenols  by  treat- 
ment with  a  caustic  potash  or  soda  solution.  A  very  common  mis- 
take is  here  made  in  that  an  excess  of  concentrated  alkali  is  used. 
This  is  quite  unsuitable,  because  the  alkali  salts  of  the  higher  fatty 
and  many  other  acids,  also  the  alkali  compounds  of  the  phenols,  are 
only  little  soluble  in  an  excess  of  stronger  alkali  and  will  therefore 
either  crystallize  in  masses  which  form  very  annoying  emulsions,  or 
will  chiefly  remain  dissolved  in  the  oil.  Moreover,  strong  solutions 
of  phenol-alkalies  dissolve  large  quantities  of  many  other  compounds, 
even  hydrocarbons,  so  that,  for  instance,  oil  of  bay,  which  contains 
about  60  per  cent,  of  eugenol  and  40  per  cent,  of  a  hydrocarbon,  will, 
with  the  proper  quantity  of  a  strong  aqueous  solution  of  caustic  soda, 
yield  a  perfectly  clear  mixture,  from  which  the  hydrocarbons  will  only 
separate  after  the  addition  of  much  water.  Therefore,  only  a  3  to  5 
per  cent,  solution  of  alkali  should  be  used  and  the  oil  extracted  suc- 
cessively with  small  quantities  of  the  latter,  till  a  sample  of  the 
watery  layer  no  longer  becomes  turbid  upon  acidifying.  Even  in 
such  dilution  the  phenol-alkalies  still  dissolve  notable  quantities  of 
indifferent  substances;  their  solution  must  therefore  first  be  ex- 
tracted with  ether,  which,  in  its  turn,  even  in  presence  of  an  excess 
of  alkali,  dissolves  some  phenol  (so  it  is,  for  example,  possible  to 
extract  from  an  alkaline-  solution  of  carvacrol,  by  often  repeated 
treatment  with  ether,  practically  all  of  the  phenol);  this  phenol 
must  be  extracted  from  the  ether  by  renewed  treatment  with 
alkali.  This  alternate  extraction  has  to  be  repeated  several  times  to 
effect  a  fairly  complete  separation  of  the  phenols. 
If  esters  of  phenol  acids  are  present,  they  will  likewise  form  un- 
stable alkali  compounds;  that  of  methyl  salicylate  with  soda  forms 
