57°  Analysis  of  Essential  Oils. 
the  reason  of  such  differences  can  be  accounted  for.  It  is  therefore 
desirable  to  state:  (i)  Genus  and  species  of  the  plant  which  fur- 
nished the  material ;  (2)  what  parts  of  the  plants  have  furnished 
the  oil;  (3)  in  what  stage  of  growth,  respectively  at  what  time  was 
the  material  collected ;  (4)  how  was  the  distillation  effected  (on  dry 
or  fresh  material,  after  fermentation  or  not,  with  water  or  with  steam, 
etc.);  (5)  how  and  how  long  had  the  oil  been  kept  between  prepara- 
tion and  analysis;  (6)  specific  gravity;  (7)  optical  rotation,  refraction 
and  dispersion ;  (8)  solubility  in  alcohol  of  various  strength  ;  (9)  sa- 
ponification and  esterification  numbers.  Some  of  these  data  furnish 
indications  which  will  greatly  facilitate  the  identification  of  the  bodies 
resulting  from  subsequent  fractionation.  So,  for  instance,  a  specific 
gravity  below  0  84  indicates  the  presence  of  large  quantities  of  ali- 
phatic compounds,  like  methyl-nonylketone  in  oil  of  rue,  hexyl-  and 
ethyl-alcohol  and  their  esters  in  oil  of  heracleum.  A  specific  gravity 
above  0-9  betrays  the  presence  of  oxygenated  compounds,  above 
1*0,  that  of  aromatic  bodies,  etc.  Insolubility  in  70  or  80  per  cent, 
alcohol  indicates  hydrocarbons;  insolubility  in  larger  quantities  of 
90  per  cent,  alcohol,  parafrines,  sesqui-  and  polyterpenes.  From 
the  saponification  figure  before  and  after  acetylization  the  amount 
of  esters,  lactones  and  alcoholic  bodies  may  be  estimated. 
After  this  preliminary  work,  we  may  proceed  to  the  proper  analy- 
sis of  the  oil.  It  is,  however,  a  useful  rule  never  to  use  the  whole 
of  the  oil  at  command  for  this  analysis,  but  to  reserve  a  good  deal 
of  the  same,  both  for  later  reference  or  for  the  case,  occurring  even 
at  the  most  careful  work,  that  some  fractions  are  lost  by  accident 
or  decomposition  from  improper  treatment.  All  processes  to  which 
the  oil  is  subjected  should  first  be  tried  with  a  small  quantity,  and 
only  if  the  treatment  is  successful  and  results  in  the  isolation  of  the 
supposed  compound,  the  bulk  of  the  oil  should  be  subjected  to  the 
same  process. 
It  has  already  been  said  that  it  is  impossible  to  construct  a  general 
scheme  for  the  analysis  which  would  in  all  cases  lead  to  the  detec- 
tion of  all  the  constituents  of  the  oil,  and  the  result  therefore 
largely  depends  on  the  practical  experience,  the  skill  and  the 
divinatory*  faculties  of  the  chemist.  As  most  of  the  components 
of  essential  oils  possess  a  more  or  less  pronounced  odor,  it  is  espe- 
cially the  sense  of  smell  which  greatly  lacilitates  such  kind  of  work, 
the  more  so,  the  better  it  has  been  developed  by  proper  training. 
