124 
ON  ALUMINIUM. 
By  these  means  the  greater  portion  of  the  metal  is  united  in 
one  mass,  the  other  portion  of  the  metal  in  small  globules  remains 
with  the  slag,  which  can  be  removed  mechanically,  or  by  first 
digesting  in  water ;  there  will,  however,  remain  about  ten  per 
cent,  with  the  slag.  This  will  be  explained  by  the  following  data. 
Theoretically : 
250  parts  of  metallic  Sodium  produce 
100    "  "      Aluminium  ; 
70  parts  are  obtained  in  one  metallic  mass  ; 
20    "  "       in  metallic  globules ; 
90  "  being  the  nett  produce. 
10     "  remain  with  the  3coria. 
Total,  100 
The  alkaline  scoria  contains  large  quantities  of  the  chloride 
of  sodium,  that  can  easily  be  extracted  by  water,  leaving  an 
insoluble  residue  from  which  the  fluoride  of  aluminium  can  be 
extracted  by  volatilization.  The  scoria  containing  the  fluoride 
and  the  metallic  aluminium  is  economically  used  by  introducing 
it  again  with  a  new  charge  of  the  double  chloride  of  aluminium 
and  sodium,  and  metallic  sodium,  and  by  that  means  the  loss  of 
the  metal  is  rendered  very  small. 
Aluminium,  when  carefully  removed  from  any  slag,  is  readily 
fused  in  a  crucible  by  itself:  when  in  fusion  (which  is  at  a  lower 
point  than  that  required  to  fuse  silver)  the  whole  is  stirred  with 
a  rod,  and  all  the  globules  of  metal  are  united  in  one  mass  with 
the  greatest  facility ;  at  this  point  nitrate  of  potash  can  be  added, 
(the  stirring  continued.) 
All  other  metals  are  oxidized  by  this  process ;  the  refining  is  • 
finished  when  the  metal  has  a  pure  white  color.    It  can  now  be 
poured  into  a  mould  of  any  shape. 
Impure  aluminium  may  be  whitened  by  plunging  it  into  caustic 
potash  or  soda,  washing  it  quickly  with  distilled  water,  plunging 
it  again  into  pure  nitric  acid,  again  washing  quickly  and  tho- 
roughly. The  surface  then  has  the  color  of  fine  aluminium,  which 
it  retains  unless  afterwards  polished.    This  operation  has  for  its 
