576 
Analysis  of  Essential  Oils. 
/Am.  Jour.  Pharm . 
\  December,  1899. 
easily  obtained  by  a  good  water  jet  pump,  is  the  most  recommend- 
able  arrangement,  but  also  a  pump  of  minor  efficiency  will  render 
good  service.  Especially  in  the  beginning  of  the  fractionation  the 
temperature  of  the  boiling  liquid  is,  in  consequence  of  the  presence 
of  bodies  of  higher  boiling  point,  so  much  higher  than  the  true 
boiling  point  of  the  more  volatile  parts  of  the  distillate,  that  the 
latter  are  very  apt  to  undergo  changes  from  overheating,  even  if  in 
their  pure  state  they  are  distillable  without  decomposition  under 
ordinary  pressure.  Thus,  for  instance,  it  is  sometimes  impossible, 
with  oils  that  give  a  strong  phellandrene  reaction,  to  find  this  hydro- 
carbon in  any  part  of  the  distillate  after  some  fractionating  under 
ordinary  pressure ;  it  has  completely  disappeared  by  isomerization. 
Under  the  same  condition  pinene  will  partly  be  transformed  into 
dipentene,  myrcene  will  for  the  greater  part  be  polymerized  to  diter- 
penes,  which  boil  under  decomposition  only  at  a  very  high  tempera- 
ture, etc.  In  spite  of  the  evident  great  advantages  of  the  vacuum 
distillation,  it  is  not  used  in  the  laboratory  as  much  as  it  deserves, 
because  many  chemists  consider  the  taking  of  fractions  under  a 
vacuum  very  incommodious,  on  account  ot  the  interruption  of  the 
vacuum,  though  many  forms  of  apparatus  have  been  constructed 
which  allow  to  change  the  receiver  without  such  an  interruption.  It 
is,  however,  true  that  many  of  these  constructions  are  either  expensive 
or  inconvenient,  as  they  are  very  apt  to  break,  difficult  to  be  kept  air- 
tight, or  provided  with  glass  cocks  which  refuse  to  turn  and  rubber 
connections  which  stick  fast  or  get  dissolved  by  the  vapors.  It 
might,  therefore,  perhaps,  not  be  useless  here  to  describe  an  appara- 
tus which  I  have  had  in  use  over  twelve  years  and  the  construction  of 
which  is  so  simple  that  it  can  be  made  by  any  one  with  a  little 
skill  in  glass  blowing,  from  materials  which  are  found  in  every 
laboratory  ;  the  apparatus  is  likewise  so  handy  that  it  can  be 
used  to  advantage  even  for  fractionation  under  ordinary  pressure. 
An  ordinary  glass  tube  (a,  Fig.  i)  and  a  good  round  glass  rod 
(b),  both  about  the  thickness  of  a  pencil,  are  soldered  together,  and 
a  bulb  (c)  blown  out  from  the  former,  about  I  inch  in  diameter,  and 
the  latter  provided  with  a  hole  {d).  Now  the  upper  half  of  the 
bulb  is  heated  before  the  gas  blast  until  soft  and  then  forced  down, 
so  that  a  kind  of  double- walled  cup,  with  a  hole  in  the  bottom  of 
the  inner  wall,  is  formed  {Fig.  2).  Now  we  insert  a  glass  tee  (e) 
(about  y2  to  yA  inch)  into  the  upper  tube  of  an  ordinary  bitubular  . 
