ON  A  PROCESS  OF  FRACTIONAL  CONDENSATION.  449 
ON  A  PROCESS  OF  FRACTIONAL  CONDENSATION  :  APPLI- 
CABLE TO  THE  SEPARATION  OF  BO  DIES  HAVING  SMALL 
DIFFERENCES  BETWEEN  THEIR  BOILING  POINTS. 
By  C.  M.  Warren.* 
It  is  well  known  that  the  process  in  general  use  for  the  prox- 
imate analysis  of  mixtures  of  volatile  liquids, — viz.  :  that  of 
simple  fractional  distillation,  either  from  a  tubulated  retort  or 
from  a  flask  with  bulbs,  as  proposed  by  Wurtz,| — affords  but 
very  imperfect  and  unsatisfactory  results,  and  not  unfrequently 
leads  to  gross  errors  and  misconceptions,  except  in  those  cases 
in  which  the  boiling-points  of  the  constituents  are  widely  differ- 
ent, or  in  which  some  auxiliary  method  can  be  advantageously 
employed. 
The  want  of  a  more  efficient  process  for  effecting  such  sepa- 
rations has  long  been  recognized.  There  are  numerous  natural 
and  artificial  products,  of  the  highest  scientific  interest, — such 
as  petroleums,  essential  oils,  tars,  and  other  mixtures  of  oils  ob- 
tained by  the  distillation,  under  varied  circumstances,  of  bitu- 
minous, vegetable,  and  animal  substances, — of  which  it  may  at 
least  be  said  that  we  have  but  very  imperfect  knowledge, — I 
might  almost  say  no  knowledge,  except  such  as  could  be  derived 
from  the  study  of  very  impure  materials, — still  mixtures  of  dif- 
ferent bodies, — with  which,  instead  of  the  pure  substances  sought 
for,  chemists  have  felt  compelled  to  content  themselves,  as  the 
best  results  which  they  were  able  to  obtain  by  the  means  at  their 
command. 
In  repeated  instances,  apparently  after  persevering  and  pro- 
tracted efforts,  investigators  have  been  forced  to  assert  either 
the  impossibility,  or  their  inability,  to  obtain,  from  such  mix- 
tures, bodies  of  constant  boiling-point, — a  property  which  is 
generally  received  as  a  test  of  purity  for  liquid  bodies. 
I  may  here  specify  a  few  recent  instances  of  this  kind. 
1.  Warren  de  la  Rue  and  Hugo  Miiller,  in  their  paperj  enti- 
tled "  Chemical  Examination  of  Bur  mese  Naphtha  and  Rangoon 
*From  the  Journal  of  the  Acad.  Arts  and  Sciences,  Boston,  M  ay  10,  1864, 
f  Annales  de  Chimie  et  de  Physique,  [3],  xlii.  132. 
X  Proceedings  of  the  Royal  Society,  viii.  221. 
28 
