PREPAKATION  OF  ALUMINIUM,    SODIUM,  ETC. 
421 
When  this  operation  is  well  conducted,  the  sodium  obtained  is 
quite  pure,  and  is  not  accompanied  by  those  carbonaceous  sub- 
stances that  are  so  troublesome  in  the  preparation  of  potassium. 
The  operation  should  be  conducted  so  rapidly  that  a  charge 
of  five  pounds  of  the  mixture  may  be  worked  off  within  about  two 
hours. 
The  temperature  requisite  for  the  reduction  of  carbonate  of 
soda  by  means  of  carbon  is  not  so  high  as  has  hitherto  been  sup- 
posed ;  and,  according  to  the  opinion  of  Mr.  Rivot,  is  not  greater 
than  that  of  the  retorts  in  the  centre  of  the  zinc  furnaces  at  the 
Vieille-Montagne. 
From  the  ease  with  which  the  operation  is  conducted,  it  might 
be  supposed  that  by  increasing  the  dimensions  of  all  parts  of  the 
apparatus  used,  much  larger  quantities  of  sodium  may  be  obtain- 
ed. However,  Mr.  Deville  has  found  that  there  are  practical 
objections  to  this  course ;  and,  after  many  unsuccessful  attempts 
to  work  large  receivers,  he  has  found  that  it  is  preferable  to  use, 
with  a  reduction  apparatus  five  times  as  large  as  the  mercury 
bottle,  receivers  of  the  same  dimensions  as  in  that  case. 
In  operating  with  large  reduction  vessels,  the  calcination  of 
the  mixture  becomes  more  advantageous,  if  not  indispensable. 
When  the  operation  is  made  continuous,  the  mixture  may  be 
calcined  as  it  is  required,  and  introduced  into  the  reduction  ves- 
sel red  hot. 
The  vessels  used  for  the  continuous  operation  are  drawn  iron 
tubes,  four  feet  long,  six  inches  internal  diameter,  and  about  | 
inch  thick.  One  end  is  closed  by  a  f  inch  plate  of  iron,  with  a 
hole  near  one  side,  into  which  is  screwed  the  discharge  tube  that 
fits  into  the  receiver.  The  other  end  of  the  cylinder  is  closed  by 
a  moveable  iron  plug,  0,  with  a  handle  ;  it  is  at  this  end  that  the 
mixture  is  introduced. 
These  tubes  must  be  covered  with  a  refractory  lute,  and  an 
exterior  envelope  of  baked  clay,  so  as  to  be  entirely  protected 
from  the  direct  action  of  the  fire. 
The  furnace  in  which  the  operation  was  conducted  was  an  ordi- 
nary reverberatory  furnace,  in  which  the  fireplace  was  divided  into 
two  parts  by  a  small  wall  upon  which  the  cylinders  rested  in  the 
middle,  while  their  ends  were  level  with  the  outer  walls  of  the 
furnace.    The  fuel  was  introduced  through  two  lateral  openings 
