238      ON  PREPARATION  OF  ALUMINIUM  PROM  CRYOLITE. 
with  the  alkaline  fluorides,  one  of  which,  the  fluoride  of  alumi- 
nium and  sodium,  occurs  native  in  a  state  of  great  purity  as 
cryolite.  This  substance  is  not  volatile  ;  it  may  be  reduced  to  fine 
powder  with  great  ease,  is  anhydrous,  and  does  not  absorb  mois- 
ture from  the  air. 
By  heating  powdered  cryolite  mixed  with  potassium  to  bright 
redness  in  a  small  iron  crucible,  I  succeeded  in  obtaining  alumi- 
nium with  greater  ease  than  from  chloride  of  aluminium  or  its 
compound  with  chloride  of  sodium.  I  was,  however,  prevented 
by  the  scarcity  of  the  mineral  from  continuing  the  experiments, 
until  a  short  time  since,  when  I  received  from  M.  Krantz,  of 
Bonn,  a  considerable  quantity  of  it,  and  likewise  ascertained 
that  it  was  to  be  had  in  large  quantities  at  a  very  small  cost. 
A  sample  of  a  white  powder  was  given  to  me,  large  quantities 
of  which  were  introduced  into  commerce  from  Greenland,  under 
the  name  of  "mineral  soda,"  at  a  price  of  nine  shillings  a 
hundred-weight.  It  was  used  in  the  soap  factories,  where,  by 
means  of  caustic  lime,  soda  lye  was  extracted,  which  was  pecu- 
liarly adapted  for  the  production  of  certain  kinds  of  soap,  pro- 
bably on  account  of  its  containing  alumina.  This  powder  proved 
to  be  cryolite. 
Hitherto  I  have,  in  preparing  aluminium,  employed  small  iron 
crucibles  If  inch  high  and  If  inch  diameter.  The  finely  pow- 
dered cryolite  was  placed  in  layers  with  sodium,  pressed  down 
tightly,  and  covered  with  a  thick  layer  of  chloride  of  sodium. 
I  found  chloride  of  potassium  the  most  advantageous  flux.  It 
has  a  low  density,  and  facilitates  the  fusion  of  the  fluoride  of 
sodium  which  is  formed  in  the  reaction. 
The  proportions  were  equal  parts  of  chloride  of  potassium  and 
cryolite,  with  two  parts  of  sodium  for  five  of  cryolite. 
The  crucible  was  covered  with  a  well-fitting  porcelain  lid,  and 
exposed  to  strong  red  heat  for  half  an  hour.  The  contents 
were  then  perfectly  fused.  When  cold,  the  melted  mass  was 
immersed  in  water  ;  and  generally  there  was  no  evolution  of  gas, 
or,  at  most,  it  was  very  slight ;  and  in  those  instances  the  hydro- 
gen had  the  same  unpleasant  odor  as  that  evolved  during  the 
solution  of  cast-iron  in  hydrochloric  acid,  the  carbon  originating 
from  the  minute  quantity  of  naphtha  adhering  to  the  sodium 
used. 
