2.  The  strongest  oil  of  vitriol,  3  parts,  are
mixed  with  alcohol,  q.  s.  (about  2  parts  at  '830)
to  reduce  its  sp.  gr.  to  1'780 ;  an  object  which
may  be  easily  obtained  by  distilling  off  some
of  the  ether  if  required.  The  still  or  retort  is
then  connected  with  a  vessel  full  of  alcohol,  of
at  least  90g,  by  means  of  a  small  syphon  tube,
furnished  with  a  stop-cock ;  the  longer  limb  of
which  should  be  of  glass,  and  so  arranged  that
it  just  dips  into  the  mixture  of  acid  and  alco-
hol. Heat  is  next  applied,  and  the  contents  of
the  still  raised  to  the  boiling-point  as  rapidly
as  possible,  and  as  soon  as  full  ebullition  com-
mences the  stop-cock  ot  the  syphon  is  cautiously
turned,  so  as  to  allow  the  alcohol  to  flow  down
in  such  a  manner  as  to  keep  the  boiling  liquid
exactly  at  the  same  level ;  or,  in  other  words,
to  supply  a  quantity  of  alcohol  exactly  equal
to  that  of  the  liquid  which  distils  over.  By
careful  manipulation  the  whole  of  the  alcohol
which  enters  the  retort  passes  over  as  ether  and
water,  and  this  decomposition  pioeeeds  for
some  time,  and  would  continue  for  an  unlimited
period  did  not  the  sulphuric  acid  ultimately
become  too  weak  to  form  ether,  from  the
gradual  absorption  of  the  superfluous  water
contained  in  the  alcohol.  Were  it  convenient
or  practicable  to  use  absolute  alcohol,  a  given
weight  of  sulphuric  acid  of  the  proper  strength,
would  maintain  the  power  of  producing  ether
for  an  indefinite  period.  In  practice,  the
quantity  of  alcohol  that  may  thus  be  etherified
is  twice  or  thrice  as  much  as  by  the  common
process,  while  neither  sulphurous  acid,  sulpho-
vinic  acid,  nor  sweet  oil  of  wine  is  generated,
and  the  residual  liquid  of  the  distillation  con-
tinues limpid,  and  has  only  a  pale-brown  colour.
