568 
Analysis  of  Essential  Oils. 
f  Ann.  Jour.  Pharrn. 
t    December,  1899. 
densation  by  the  means  of  the  laboratory.  Furthermore,  it  is  a 
peculiar  coincidence  that,  as  a  cursory  review  of  the  known  con- 
stituents of  essential  oils  shows,  no  less  than  55  per  cent,  of  those 
constituents  possess  ten  carbon  atoms  in  their  molecules,  while 
those  with  five  and  fifteen  carbon  atoms  amount  to  further  15  per 
cent.,  and  the  entire  remainder  is  only  30  per  cent.;  hereby  those 
with  ten  atoms  possess  such  a  heterogeneous  composition  as  ter- 
penes,  terpene  alcohols  and  their  aldehydes,  menthol,  camphor, 
thujone,  pulegone,  fenchone,  cineol,  carvol,  carvacrol,  anethol,  euge- 
nol,  safrol,  etc.  It  can  hardly  be  assumed  that  this  is  a  mere  in- 
cident, but,  though  I  do  not  think  that  nature  itself  believes  in 
the  decimal  system,  this  fact  seems  to  indicate  a  connection  between 
the  various  processes  by  which  these  bodies  are  generated.  Be  this 
as  it  may,  these  few  points  just  mentioned  are  sufficient  to  show 
how  many  problems  of  the  chemistry  of  essential  oils  still  are 
awaiting  their  solution,  which  probably  will  be  greatly  promoted 
by  a  careful  and  critical  study  of  the  constituents  of  a  great  number 
of  essential  oils,  and  that,  therefore,  still  for  a  long  time  the  study  of 
these  questions  will  afford  an  interesting  and  fruitful  field  for  the 
efforts  of  chemists. 
It  is  true,  however,  that  such  a  study  does  not  belong  to  the  easiest 
tasks  of  analytical  chemistry,  and  it  is,  therefore,  necessary  that  the 
chemist  who  undertakes  it  first  become  thoroughly  acquainted 
with  the  peculiar  character  of  the  respective  compounds,  if  he  wants 
to  avoid  the  most  fatal  errors  in  his  results.  The  overwhelming 
majority  of  these  compounds  contain  so-called  double  bonds,  and 
therewith  possess,  as  thermochemical  researches  have  shown,  an 
excess  of  energy,  in  comparison  to  saturated  bodies,  which  confers 
upon  them  the  tendency  to  get  transformed,  under  partial  liberation 
of  this  excess  of  energy,  into  other  more  stable  compounds.  These 
circumstances  account  for  the  great  inconstancy  of  many  of  the  essen- 
tial oils.  Even  at  ordinary  temperature  resinification  gradually  sets 
in  ;  oxygen  is  reabsorbed,  at  first  with  formation  of  ozone  or  bodies 
of  super-oxyde-like  character  which  further  on  effect  oxidations, 
by  which  the  whole  character  of  the  oil  is  changed ;  it  loses 
its  fragrance,  becomes  thicker  and  heavier,  and  more  soluble  in 
diluted  alcohol,  shows  increased  acid  and  acetylization  figures,  etc 
But  even  if  the  access  of  air  is  excluded,  changes  will  take  place* 
especially  under  the  influence  of  light ;  double  bonds  migrate,  poly- 
