MANUFACTURE  AND  PROPERTIES  OF  ANILINE  COLORS.  545 
tions  for  them.  This  work  cost  him  his  life.  Proposing  to  sep- 
arate benzol  from  the  light  coal  oils,  Mansfield  heated  these  oils 
in  a  still  with  the  head  kept  surrounded  with  water.  The  vapors 
ascending  into  the  head  became  condensed,  and  fell  back  into  the 
still ;  and  after  a  time  the  water  surrounding  the  head,  not  being 
renewed,  was  heated  to  the  boiling-point.  From  the  time  the 
water  in  the  open  jacket  reaches  a  temperature  of  80°  the  benzole 
no  longer  condenses,  but  passes  on  into  the  worm,  while  the 
other  oils  fall  back  into  the  still.  When  the  water  arrives  at  the 
boiling  point,  only  benzole  passes  over  ;  after  a  time  nothing 
passes,  and  all  the  benzole  is  separated. 
This  complete  separation  is  founded  on  the  boiling-point  of 
water,  intermediate  between  that  of  benzol,  80°,  and  that  of 
toluol,  114°. 
Mansfield  tried  to  separate  only  benzol.  The  operation  might 
easily  be  modified  so  as  to  separate  toluol  in  a  similar  manner  • 
it  would  suffice,  the  benzol  once  separated,  to  replace  the  water 
by  some  liquid — a  saline  solution,  for  instance — maintained  at  a 
constant  level,  and  with  a  boiling-point  intermediate  between 
that  of  toluol  and  that  of  xylol. 
Mansfield  also  tried  to  separate  benzol  with  the  apparatus  used 
for  the  rectification  of  alcohol.  Several  patents  have  been  taken 
out  with  the  same  idea,  amongst  which  we  will  mention  only  M. 
Ch.  Coupler's,  who  has  effected  the  separation  of  benzol  and 
toluol  by  means  of  an  ingenious  apparatus  patented  by  him.  We 
have  seen  various  products  from  his  works  at  Poissy,  consisting 
of  pure  benzol  and  aniline,  and  nearly  pure  toluol  and  toluidine. 
Some  researches,  for  the  purpose  of  previously  separating  the 
oils  of  coal-tar  in  an  exact  and  economical  manner,  are  much  re- 
quired, and  would  lead  to  great  progress  in  the  fabrication  of 
aniline  colors. 
Another  reason  for  insisting  on  this  point  is  the  considerable 
difference  in  the  manner  in  which  toluol  and  benzol  behave  with 
regard  to  nitric  acid,  when  it  is  desired  to  transform  them  into 
nitrobenzol. 
Toluol  is  attacked  with  greater  difficulty ;  mixtures  of  sulphu- 
ric and  nitric  acids  must  be  modified  before  treating  this  body. 
In  this  series,  in  proportion  as  the  equivalent  is  raised,  the 
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