386         APPARATUS  FOR  PREPARING  ETHER  BY  STEAM. 
heat.  The  block  thus  made  is  turned  out  in  the  center  in  the 
form  of  a  cup  or  pan  with  flaring  sides.  Into  this  depression  a 
sheet  of  lead  of  8  lbs.  to  the  square  foot,  is  made  to  fit  accurately, 
by  hammering,  being  allowed  to  project  an  inch  above  the  sur- 
face of  the  stand. 
b.  A  length  of  15  feet  of  "  extra  strong  \  in.  lead  pipe,"  is 
next  made  into  a  worm  or  coil  of  the  form  of  a  compressed  mat- 
tress spring;  that  is,  one  flat,  or  "  flemish  "  coil  above  the  other, 
the  two  being  continuous  in  the  center.  This  coil  is  let  down 
into  the  wood  and  pan  so  that  the  entrance  and  exit  pipes  are 
held  within  the  thickness  of  the  stand,  and  so  that  the  upper 
coil  rises  but  little  above  the  brim  of  the  pan.  Where  the  en- 
trance and  exit  pipes  pass  through  the  leaden  pan,  the  lead  is 
"  chased  "  up  carefully  into  contact  with  the  pipe,  and  the  joints 
soldered  outside  the  pan.  A  piece  of  §  inch  iron  pipe  with  a 
screw  thread  on  one  end,  is  soldered  by  the  other  end  to  the 
lower  lead  pipe  for  convenience  in  connecting  the  apparatus  up 
to  the  steam  openings  from  the  boiler ;  and  a  £  inch  "  globe 
valve  "  is  attached  to  the  upper  lead  pipe  in  order  to  regulate 
the  steam  exit,  and  consequently  the  pressure  and  temperature 
in  the  coil.  The  joints  of  the  iron  and  lead  should  be  "  bolt 
joints  "  and  not  "  wiped  joints,"  as  the  latter,  though  neater  in 
appearance,  invariably  leak  under  steam  pressure.  About  13 
feet  of  coil  should  be  within  the  pan,  giving  a  surface  of  steam 
contact  for  heating,  of  say  234  square  inches. 
c.  A  piece  of  the  same  kind  of  lead  pipe  is  fitted  closely  into 
the  center  of  the  bottom  of  the  pan,  soldered  outside,  and  then 
well  caulked  or  "  burned  "  inside,  by  melting  the  lead  contact 
surfaces  together.  This  serves  both  as  a  feeding  and  discharge 
pipe  for  the  still.  For  feeding,  it  is  fitted  with  a  cork,  perforated 
with  a  small  glass  tube,  and  a  piece  of  small  india  rubber  tubing 
long  enough  to  reach  the  elevated  feeding  vessel.  This  plan  of 
introducing  the  alcohol  has  great  advantage  over  that  of  passing  it 
through  a  tube  within  the  still,  for  a  tube  within  the  still  becomes 
so  heated  as  to  vaporize  the  alcohol  within  it,  and  render  the 
feeding  irregular,  whilst  by  this  plan  the  alcohol  is  very  regularly 
delivered  in  the  bottom  and  hottest  part  of  the  still,  and 
can  only  get  to  the  surface  by  passing,  in  a  state  of  vapor,  through 
the  heated  acid. 
