450  ON  A   PROCESS  OF  FRACTIONAL  CONDENSATION. 
Tar,"  after  detailing  the  preliminary  treatment  by.  distillation  in 
a  current  of  steam,  add  that  "  A  further  separation  of  the  va- 
rious products  was  effected  by  repeated  fractional  distillations ; 
but  no  absolutely  constant  boiling-points  could  be  obtained,  not- 
withstanding the  great  number  of  distillations  and  the  large 
quantity  of  material  at  command.  It  is  true  that  considerable 
portions  of  distillates  could  be  collected  between  certain  ranges 
of  temperature,  tending  to  indicate  a  constant  boiling-point ; 
nevertheless,  it  soon  became  evident  that  distillations  alone 
could  not  effect  the  separations  of  the  various  constituents,  and 
that  recourse  must  be  had  to  other  processes."  The  other  pro- 
cesses resorted  to  were,  treatment  with  sulphuric  and  nitric  acids, 
either  separately  or  mixed  ;  but  still  with  very  imperfect  results. 
This  acid  treatment,  which  was  first  proposed  by  De  la  Rue,  and 
subsequently  employed  by  C.  Greville  Williams,*  Schorlemner, 
and  others,  will  be  further  noticed  below. 
2.  Frankland,f  in  speaking  of  a  mixture  of  the  hydrocarbons 
of  the  formulae  Cn  Hn  andCnHn_j_j  (now  generally  considered 
as  Cn  Hn_|_2),  which  have  a  difference  of  6°  to  7°  C.  between  their 
boiling-points,  says,  "  The  separation  of  two  such  bodies  by  dis- 
tillation alone  is  impossible;"  and  suggests  that  the  employment 
of  anhydrous  sulphuric  acid  may  accomplish  the  object  by  dis- 
solving out  the  body  of  the  formula  Cn  Hn . 
3.  And  so  recently  as  1862,  Schorlemner,^  in  his  first  paper 
"  On  the  Hydrids  of  the  Alcohol-Radicals  existing  in  the  Pro- 
ducts of  the  Destructive  Distillation  of  Cannel  Coal,"  remarks 
that  "  it  was,  however,  found  impossible  to  obtain  a  product  of 
constant  boiling-point  by  repeated  fractional  distillations  and 
he  also  had  recourse  to  the  acid-treatment  above  referred  to. 
4.  Pebal,§  after  an  elaborate  research  on  the  petroleum  from 
Galicia,  in  which  Wurtz's  bulbs  were  employed,  and  also  Eisens- 
*  Philosophical  Transactions,  1857,  447. 
f 'Quarterly  Journal  of  the  Chemical  Society,  1851,  3,  43. 
X  Journal  of  the  Chemical  Society,  xv.  419. 
\  Annalen  der  Chemie  und  Pharmacie,  cxv.  20,  asserts  the  11  Un- 
moglichkeit,  das  Gemeage  durch  fractionirte  Destillationen  zu  entwir- 
ren." 
