554  WORKING  IN  ALUMINUM. 
the  top  of  the  glass  chimney  of  an  Argand  lamp  will  suffice  for 
the  heating. 
The  elasticity  of  aluminum  is  very  much  the  same  as  that  of 
silver,  and  its  tenacity  also  about  the  same.  The  moment  after 
it  has  been  melted,  aluminum  possesses  about  the  hardness  of 
pure  silver ;  when  it  is  hammered  out,  it  almost  resembles  that 
of  soft  iron  ;  it  becomes  elastic,  acquiring,  at  the  same  time, 
considerable  rigidity,  and  emits  the  sound  of  steel  when  suffered 
to  fall  on  a  hard  body. 
A  property  which  aluminum  manifests  in  a  high  degree  is  that 
of  excessive  sonorousness.  This  property  has  already  rendered 
it  of  service  in  the  construction  of  several  musical  instruments. 
Aluminum  is  much  lighter  than  ordinary  metals.  Its  density 
is  2-56,  a  quarter  that  of  silver,  and  about  a  third  that  of  iron. 
By  the  action  of  the  hammer,  the  density  of  aluminum  increases 
sensibly,  so  as  to  become  equal  to  2-67. 
Aluminum  melts  at  a  higher  temperature  than  zinc,  and  a 
lower  one  than  silver;  to  melt  it,  an  ordinary  earthenware  cru- 
cible must  be  employed,  without  the  addition  of  any  sort  of  flux. 
Its  low  point  of  fusion,  along  with  its  slowness  of  heating,  re- 
quire that  for  melting  it  a  less  intense  fire  should  be  used,  but 
applied  for  a  longer  time  than  in  melting  silver. 
It  is  easily  melted  in  an  open  crucible,  which  facilitates  the 
removal  of  the  dust  and  other  impurities  which  appear  on  the 
surface  of  the  metal ;  and  for  the  purpose  of  stirring  the  entire 
mass,  a  clean  iron  spatula  is  used. 
Aluminum  is  easily  run  into  metallic  moulds  ;  and,  still  better, 
for  objects  of  a  complicated  form,  into  moulds  of  dry  porous 
sand,  formed  so  as  to  allow  an  easy  passage  for  the  air  expelled 
by  the  metal,  which  is  viscous  when  melted.  It  ought  to  contain 
a  greater  number  of  passage  holes,  and  should  be  so  managed  as 
to  run  it  in  one  long  and  perfectly  cylindrical  git.  When  heated 
to  a  red  heat,  it  ought  to  be  poured  out  with  tolerable  rapidity. 
A  small  portion  of  the  fused  metal  should  be  caused  to  run  into 
the  git  itself  when  full,  to  compensate  for  the  contraction  of  the 
substance  of  the  metal  at  the  moment  of  solidification. 
By  following  all  these  precautions,  castings  of  the  highest  de- 
gree of  fineness  may  be  obtained ;  but,  at  the  same  time,  to  sue- 
