PRODUCTION  OF  VERY  HIGH  TEMPERATURES.  449 
ing  ammonia-alum.  Thus  prepared  it  is  plastic,  but  shrinks 
much  on  drying.  To  prevent  this,  the  author  mixes  the  mass 
with  a  calcined  mixture  of  alumina  and  marble.  A  mixture  of 
plastic  alumina,  calcined  alumina  and  aluminate  of  lime,  in  equal 
parts,  gives  a  very  hard  and  infusible  mass,  which  softens  a  little 
at  the  melting  point  of  platinum.  Once  baked,  these  crucibles 
resist  all  tests  ;  even  sodium  has  no  action  on  them.  The  lime 
crucibles  may  be  used  whenever  the  alkali  is  not  injurious ;  the 
carbon  crucibles  have  a  more  limited  use  in  consequence  of  their 
reducing  agency.  The  alumina  crucibles  may  be  used  almost 
always  when  lime  will  not  answer.  With  respect  to  the  heat  pro- 
duced by  this  furnace  the  author  gives  the  following  details* 
Platinum  fuses  in  a  crucible  of  lime  into  a  single  well-united  but- 
ton. This  platinum  possesses  properties  very  different  from 
those  of  ordinary  platinum  condensed  from  the  sponge.  When 
copper  is  plated  with  the  fused  platinum  rolled  out  into  a  very 
thin  sheet,  nitric  acid  has  no  action  whatever,  as  it  does  not 
penetrate  the  leaf  of  metal.  A  plate  made  from  fused  platinum 
does  not  cause  the  union  of  oxygen  and  hydrogen  even  after 
several  hours.  Fused  platinum  possesses  a  perfect  softness  and 
malleability.  In  a  crucible  of  carbon,  platinum  melts  easily  but 
yields  a  brittle  alloy  of  platinum,  carbon  and  silicon.  By  rais- 
ing the  heat  above  the  temperature  required  for  fusion,  Deville 
succeeded  in  volatilizing  the  metal  with  remarkable  ease,  so  that 
it  condensed  in  small  globules.  Pure  peroxyd  of  manganese  heated 
with  carbon  from  sugar  in  quantity  less  than  sufficient  to  reduce 
the  oxyd,  gave  fused  metallic  manganese  as  a  brittle  mass,  hav- 
ing a  rose  reflection  like  bismuth  and  as  easily  reduced  to  powder. 
Its  powder  decomposed  water  at  a  little  above  the  ordinary  tem- 
perature. Chromium  as  prepared  in  a  similar  manner  was  well 
fused,  but  not  into  a  button,  at  the  temperature  at  which  plati- 
num volatilizes.  The  metal  is  brittle  and  cuts  glass  like  a  dia- 
mond. It  is  easily  attacked  by  chlorhydric  acid,  but  little  by 
sulphuric  acid,  and  not  at  all  by  nitric  acid  either  strong  or  weak. 
Metallic  nickel  fuses  to  a  homogeneous  button,  which  may  be 
forged  with  great  facility.  It  has  a  ductility  almost  without 
limit  and  is  more  tenacious  than  iron  in  the  ratio  of  90  to  60, 
according  to  Wertheim's  experiments.  This  nickel  contained 
traces  of  silicon  and  copper.    Fused  cobalt  is  as  ductile  as  nickel 
29 
