PHOSPHORUS    ORE    AT    MOUNT    HOLLY    SPRINGS,  PA.  479 
In  the  Wing  process  the  charge  of  bone  ash  or  pulverized  rock 
phosphate  and  silica  is  moistened  and  made  into  balls,  and  is  placed 
in  the  cupola  in  layers,  alternating  with  coke  or  coal,  which  furnish 
incandescent  carbon  to  reduce  the  phosphoric-acid  fumes.  The  silica 
releases  the  phosphoric  acid  from  the  phosphate  in  the  form  of  the 
anhydride  P205,  which  is  reduced  by  the  incandescent  carbon  and  a 
reducing  flame  to  phosphorus.  The  fumes  pass  off  to  depositing 
chambers,  kept  at  a  temperature  of  500°  F.,  where  most  of  the  phos- 
phorus is  deposited  in  the  red  form  and  the  remainder  is  caught  in 
a  water  chamber  as  yellow  phosphorus.  The  process  is  made  con- 
tinuous by  feeding  the  charge  from  the  top,  dumping  the  residuum 
from  the  grate  below,  and  using  two  depositing  chambers  alternately. 
With  only  the  ordinary  furnace  at  command  this  method  was 
found  impracticable  on  account  of  the  high  degree  of  heat  required 
to  smelt  so  refractory  a  charge.  Electricity  as  a  powerful  heating 
agent  had  been  known  for  some  time  aud  was  expected  to  furnish 
the  solution  of  the  problem,  but  only  recently  has  the  invention  of 
the  electric  furnace  made  it  commercially  feasible.  It  has  now  been 
generally  introduced  throughout  Europe  and  America  in  the  produc- 
tion of  phosphorus  on  a  profitable  basis. 
The  Headman  patent  (1889)  is  the  process  which  has  come  into 
commercial  use  in  most  countries.  Bone  ash  or  crude  phosphoric  acid 
is  mixed  with  powdered  coal  or  charcoal,  or,  if  mineral  calcium  phos- 
phate is  used, it  is  roasted, crushed,  and  mixed  with  charcoal  and  silica 
or  some  basic  salt.  The  mixture  is  reduced  in  a  continuously  operated 
electric  furnace  in  a  reducing  atmosphere,  by  passing  the  current 
from  carbon  electrodes  through  the  mass,  which  acts  as  a  resistant 
conductor  and  is  heated  to  incandescence.  The  silica  combines  with 
the  calcium  to  form  calcium-silicate  slag.  The  phosphorus  and  car- 
bon monoxide  distill  off  as  before.  Distillation  begins  at  1,150°  C. 
and  requires  1,400°  to  1,500°  C.  to  complete  the  process.  The 
chemical  reaction  is — 
2Ca3(P04)2  +  6SiO,  +  10C  =  6CaSi03  +  10CO  +  P4. 
In  Harding's  patent  (1898)  pulverized  rock  phosphate  is  boiled 
with  sulphuric  acid,  and  the  phosphoric  acid,  free  from  lime,  is  filtered 
out  and  boiled  down  to  a  sirup.  This  is  mixed  with  granulated  carbon 
heated  in  a  reverberatory  furnace,  and  then  smelted  in  an  electric 
furnace  by  electric  arcs  between  the  electrodes  and  the  mass.  A 
hydrogen  atmosphere  is  obtained  by  spraying  gasoline  into  the 
furnace. 
In  the  Gibbs  furnace,  which  was  devised  especially  for  the  manufac- 
ture of  phosphorus,  instead  of  the  electricity  discharging  through  the 
mass,  it  passes  through  a  continuous  highly  resistant  medium,  such 
