EXTRACTION  OF  THALLIUM. 
47 
of  thallium  are  then  placed  in  the  dish,  and  water  poured  over 
to  cover  the  salt.    Heat  is  applied,  and  in  the  course  of  a  few 
hours  the  whole  of  the  thallium  will  be  reduced  to  the  state  of  a 
metallic  sponge,  which  readily  separates  from  the  plates  of  zinc 
on  the  slightest  agitation.    The  liquid  is  poured  off,  the  zincs  re- 
moved, and  the  spongy  thallium  washed  two  or  three  times.  It 
is  then  strongly  compressed  between  the  fingers,  and  preserved 
under  water  until  it  is  ready  for  fusion.    The  fusion  of  the  metal 
is  readily  effected.    An  iron  crucible  is  placed  over  a  gas-burner, 
and  a  tube  is  arranged  so  that  a  constant  stream  of  coal  gas  may 
flow  into  the  upper  part  of  the  crucible.    Lumps  of  the  com- 
pressed sponge  are  then  introduced,  one  after  the  other  as  they 
melt,  until  the  crucible  is  full  of  metal.    It  is  then  stirred  up 
with  an  iron  rod,  and  the  thallium  may  either  be  poured  into 
water  and  obtained  in  a  granlated  form,  or  cast  into  an  ingot. 
Thirty  or  forty  fusions  have  been  performed  in  the  same  cruci- 
ble without  the  iron  being  acted  upon  in  the  least  by  the  melted 
thallium.    The  products  of  these  fusions  were  ultimately  melted 
together  and  cast  in  an  iron  mould.    The  result  is  the  accompa- 
nying bar  of  thallium,  weighing  a  quarter  of  a  hundredweight. 
Thallium  contracts  strongly  on  cooling.  The  coating  of  tar- 
nish which  it  acquires  while  hot  is  instantly  removed  by  water, 
which  renders  the  surface  perfectly  bright.  The  liquid  metal  in 
the  crucible,  when  protected  by  the  stream  of  coal  gas,  can 
scarcely  be  distinguished  from  mercury.  Thallium  is  not  abso- 
lutely identical  in  color  with  any  other  metal,  but  approaches 
nearest  to  cadmium  and  tin.  It  has  perfect  metallic  lustre.  Its 
specific  gravity  is  11-9.  It  is  very  malleable,  but  not  very  duc- 
tile. It  can  only  be  drawn  into  wire  with  great  difficulty,  but 
by  the  operation  technically  known  as  squirting,  thallium  wire 
may  be  formed  most  readily.  Thallium  is  very  soft,  being  only 
exceeded  in  this  property  by  the  alkali  metals.  A  point  of  lead 
will  scratch  thallium  with  the  greatest  readiness.  Thallium  pos- 
sesses the  property,  in  common  with  soft  metals,  of  welding  by 
pressure  in  the  cold.  Rubbed  on  paper,  it  gives  a  dark  streak, 
having  a  yellow  reflection,  which  in  a  short  time  nearly  fades 
out,  but  may  be  restored  with  an  alkaline  sulphide.  Thallium  is 
strongly  diamagnetic,  being  in  this  respect  nearly,  if  not  quite, 
equal  to  bismuth.    It  melts  at  550°  F.,  and  distils  at  a  red 
