PREPARATION  OF  ALUMINIUM,  SODIUM,  ETC. 
423 
residue  in  the  retort  contained  some  alumina,  a  considerable 
amount  of  alkaline  chlorides,  and  of  the  double  chloride  of  alumi- 
nium and  potassium.  The  residue  was  washed,  mixed  with  a 
fresh  quantity  of  alumina,  and  subjected  to  the  same  treatment. 
In  working  the  process  upon  a  large  scale,  pitch  was  used  as  the 
carbonaceous  substance ;  instead  of  the  clay  retort,  an  ordinary 
gas  retort,  and,  instead  of  the  bell  vessel,  a  small  brick  chamber, 
covered  with  glazed  earthenware. 
The  ammoniacal  alum  is  calcined  upon  the  hearth  of  the  re- 
verberatory  furnace,  inVhich  the  sodium  is  prepared.  After 
having  been  heated  to  redness,  it  is  powdered  and  mixed  with 
coal  tar.  The  paste  is  introduced  into  crucibles  carefully  cov- 
ered, and  placed  in  the  reverberatory  furnace.  When  the  evolu- 
tion of  vapor  ceases,  the  crucibles  are  removed,  and,  when  it  is 
possible,  the  aluminous  carbon  is  used  while  hot. 
The  stream  of  chlorine  should  be  so  adjusted  as  to  avoid  loss 
either  by  escaping  from  the  joints  of  the  apparatus  or  by  being 
carried  up  the  chimney. 
Before  commencing  the  operation,  every  part  of  the  apparatus 
should  be  rendered  perfectly  dry  by  heating  it. 
With  regard  to  the  utilization  of  aluminium  in  the  arts,  Mr. 
Deville  considers  that  the  necessary  condition  is  its  production 
at  a  cost  considerably  less  than  that  of  silver.  Owing  to  the 
difference  in  density,  if  aluminium  and  silver  were  of  the  same 
value,  aluminium  would  be  only  one-fourth  as  dear  as  an  equal 
volume  of  silver;  and,  for  equal  masses,  the  rigidity  of  aluminium 
is  much  greater  than  that  of  silver. 
The  materials  with  which  aluminium  is  produced,  even  by  the 
methods  hitherto  employed,  are  all  obtainable  at  a  small  cost. 
Thus,  to  produce  about  half  a  hundred-weight  of  aluminium,  there 
would  be  required 
Chlorine  237  pounds,  costing    .    .  £2  14  0 
Alumina  114     «         «        .    .     0  13  0 
Carbonate  of  Soda  350     «         «        .    .     2  13  0 
£5    0  0 
Which  would  render  the  cost  of  the  materials  for  producing  a 
pound  of  aluminium  about  two  shillings. 
With  regard  to  the  actual  cost  of  the  production  of  aluminium 
