880  Manufacture  of  Chloramine—T.  {AmD{°cUT\g^vm- 
is  very  important,  as  upon  it  depends  the  time  necessary  to  complete 
the  sulphonation.  This  reaction  was  carried  out  in  a  flask  fitted 
with  a  reflux  condenser,  and  only  a  small  loss  of  toluene  vapour  took 
place,  sulphonation  being  complete  in  about  thirty  minutes  with  very 
little  charring.  Under  these  conditions  about  75  per  cent,  of  the 
toluene  is  converted  into  the  />-sulphonic  acid,  the  remainder  being 
a  mixture  of  0-  and  m-acids.  If  this  mixture  of  acids  was  isolated, 
converted  into  dry  sodium  salts,  and  treated  with  phosphorous  penta- 
chloride,  the  /^-chloride  could  be  obtained ;  but  as  the  other  chlorides 
would  be  useless  there  would  be  a  considerable  waste  of  material. 
We  therefore  made  use  of  Lange's  discovery  (Ger.  Pat.  57,  391) 
that  if  water  is  added  so  that  the  mother  liquid  consists  of  only 
66  per  cent,  sulphuric  acid,  then  on  cooling,  the  crystals  that  separate 
consist  only  of  the  ^ara-acid  which  separates  almost  completely — the 
mother  liquid  retaining  the  0-  and  m-isomers  in  solution.  In  order 
to  carry  this  out,  45  Cc.  of  'water  is  added  to  the  reaction  mixture 
after  sulphonation  as  above  and  the  liquid  poured  out  and  cooled. 
The  liquid  rapidly  crystallises  and  sets  to  a  crystalline  cake,  and  on 
filtering  over  an  asbestos  mat  (as  in  a  Gooch  crucible)  nearly  the 
whole  of  the  mother  liquid  can  be  drained  away,  leaving  a  white 
crystalline  mass  which  proves  to  contain  only  small  amounts  of 
0-  and  ^-impurities.  The  crystals  that  separate  appear  to  be  the 
monohydrate,  C7H7S03H,  H20,  and  correspond  to  about  75  per 
cent,  of  the  toluene  taken.  Hence  about  25  per  cent,  of  the  toluene 
is  either  lost  as  vapour  or  is  contained  in  the  mother  liquor  in  the 
form  of  the  0-  and  m-acids.  The  separation  by  crystallisation  is, 
however,  not  very  sharp,  and  the  mother  liquid  on  standing  con- 
tinually deposits  further  crops,  which,  however,  are  nearly  free 
from  the  par a-acid. 
The  0-  and  7/z-acids  being  useless  to  us,  experiments  were  made 
by  Mr.  C.  L.  Carter  at  my  suggestion,  to  see  how  completely  the 
toluene  could  be  recovered  by  the  action  of  superheated  steam.  It 
was  found  that  if  the  liquor  were  heated  to  about  1700  and  then 
a  brisk  current  of  steam  at  2000  were  blown  through  it  the  bulk  of 
the  toluene  was  rapidly  evolved,  the  distillate  containing  at  first  as 
much  as  20  per  cent,  toluene.  When  the  percentage  fell  below  5  per 
cent,  the  operation  was  stopped,  as  further  continuance  was  hardly 
profitable  (Armstrong,  /.  Chem.  Soc,  1884,  45,  148).  The  total 
amount  thus  recovered  was  about  14  per  cent.,  leaving  11  per  cent. 
