"^""jan'VsSi"'"'"}  ^^^^  Essential  Oils.  19 
3d.  Is  the  oil  in  each  case  a  mixture^  in  which  one  ingredient  is 
present  in  variable  quantity  in  the  different  plants  ? 
4th.  Do  the  oils  of  spearmint  and  peppermint  bear  any  chemical 
relation  to  each  other  ? 
5th.  Which  species,  containing  the  oil  of  peppermint^  yields  the 
largest  quantity  and  which  the  most  valuable  one  for  medicinal 
purposes  ? 
To  recapitulate :  The  writer  would  recommend  that  for  convenience 
the  name  of  Mentha  arvensis  f.  piperascens  should  be  retained  for  the 
Japanese  peppermint  plant  and  that  of  Mentha  arvensis  f.  glahrata  for 
the  Chinese  one. — Fhar,  Jour,  and  Trans.,  Nov.  11,  1882. 
ON  THE  ESSENTIAL  OILS. 
By  Dr.  August  Belohoubek. 
Freshly  distilled  oil  of  turpentine  contains  no  oxidized  products,  and 
hence  no  resinous  matters,  for,  owing  to  their  slight  volatility,  they 
remain  behind  in  the  retort ;  while  an  oil  that  has  been  kept  in  open 
vessels  absorbs  oxygen  from  the  air  and  hence  contains  a  resin. 
Various  observations  have  forced  us  to  the  view  that  substances 
composed  of  carbon,  hydrogen,  and  oxygen  mix  with  other  liquids — 
that  is,  mutually  dissolve  each  other  more  easily  the  more  similar  they 
are  chemically.    The  exceptions  to  this  rule  are  very  few. 
If  we  apply  this  rule  of  the  mutual  solvent  power  of  allied  sub- 
stances to  the  oil  of  turpentine  recently  distilled,  we  can  predict  that, 
being  a  hydrocarbon,  it  will  dissolve  easily  in  other  hydrocarbons ;  and 
the  more  readily  the  more  nearly  the  hydrocarbon  series  to  which  they 
belong  are  related  to  each  other,  and  the  less  they  differ  in  the  number 
of  carbon  atoms  in  the  molecule. 
But  how  will  it  be  with  the  old,  oxidized,  and  hence  resinous  oils 
which  contain  but  a  few  per  cent,  of  resin.  Such  resin  differs  from  the 
oil,  CioHjg,  in  containing  one  or  two  atoms  more  of  oxygen,  and  one  or 
two  molecules  of  water,  so  that  it  is  tolerably  similar  to  the  pure  oil 
and  soluble  in  it;  but  it  differs  considerably  from  other  hydrocarbons, 
especially  if  they  contain  but  little  carbon  and  comparatively  more 
hydrogen  in  the  molecule,  and  therefore  do  not  readily  mix  with  it. 
This  supposition  was  confirmed  by  experiment.  I  selected  as  a  cheap 
reagent  the  petroleum  ether  which  boils  at  about  104°  Fahr.  (40°C.), 
and  is  a  mixture  of  pentanes,  C5II12,  etc.    Fresh  oil  of  turpentine  mixes 
