562 
VARIETIES. 
metal  will  be  heard  going  on  within  the  vessel,  the  metal  being  tossed 
violently  about,  and  dashed  from  side  to  side,  shaking  the  vessel  by  the 
force  with  which  it  moves  from  the  throat  of  the  converting  vessel.  Flame 
will  then  immediately  issue,  accompanied  by  a  few  bright  sparks  ;  this 
state  of  things  will  contiuue  for  about  fifteen  or  twenty  minutes,  during 
which  time  the  oxygen  in  the  atmospheric  air  combines  with  the  carbon 
contained  in  the  iron,  producing  carbonic  acid  gas,  and  at  the  same  time 
evolving  a  powerful  heat.  Now,  as  this  heat  is  generated  in  the  interior 
of,  and  is  diffused  in  innumerable  fiery  bubbles  through  the  whole  fluid 
mass,  the  metal  absorbs  the  greater  part  of  it,  and  its  temperature  becomes 
immensely  increased  ;  and  by  the  expiration  of  the  fifteen  or  twenty  minutes 
before  named,  that  part  of  the  carbon  which  appears  mechanically  mixed 
and  diffused  through  the  crude  iron  has  been  entirely  consumed.  The 
temperature,  however,  is  so  high  that  the  chemically-combined  carbon  now 
begins  to  separate  from  the  metal,  as  is  at  once  indicated  by  an  immense 
increase  in  the  volume  of  flame  rushing  out  of  the  throat  of  the  vessel. 
The  metal  in  the  vessel  now  rises  several  inches  above  its  natural  level, 
and  a  light  frothy  slag  makes  its  appearance,  and  is  thrown  out  in  large 
foam-like  masses.  This  violent  eruption  of  cinder  generally  lasts  five  or 
six  minutes,  when  all  further  appearance  of  it  ceases — a  steady  and  power- 
ful flame  replacing  the  shower  of  sparks  and  cinder  which  always  accom- 
panies the  boil.  The  rapid  union  of  carbon  and  oxygen  which  thus  takes 
place  adds  still  further  to  the  temperature  of  the  metal,  while  the  dimin- 
ished quantity  of  carbon  present,  allows  a  part  of  the  oxygen  to  combine 
with  the  iron,  which  undergoes  combustion,  and  is  converted  into  an  oxide. 
At  the  excessive  temperature  that  the  metal  has  now  acquired,  the  oxide,  as 
soon  as  formed,  undergoes  fusion,  and  forms  a  powerful  solvent  of  those 
earthy  bases  that  are  associated  with  the  iron.  The  violent  ebullition 
which  is  going  on  mixes  most  intimately  with  scoriae  and  metal,  every  part 
of  which  is  thus  brought  into  contact  with  the  fluid,  which  will  thus  wash 
and  cleanse  the  metal  most  thoroughly  from  the  silica  and  other  earthy 
bases  which  are  combined  with  the  crude  iron,  while  the  sulphur  and  other 
volatile  matters  which  cling  so  tenaciously  to  iron  at  ordinary  temperatures 
are  drawn  off,  the  sulphur  combining  with  the  oxygen,  and  forming  sul- 
phurous acid  gas.  The  loss  in  weight  of  crude  iron  during  its  conversion 
into  an  ingot  of  malleable  iron,  was  found,  on  a  mean  of  four  experiments, 
to  be  12|  per  cent.,  to  which  will  have  to  be  added  the  loss  of  metal  in  the 
finishing  rolls.  This  will  make  the  entire  loss  probably  not  less  than  18 
per  cent.,  instead  of  about  28  per  cent.,  which  is  the  loss  on  the  present 
system.  A  large  portion  of  this  metal  is,  however,  recoverable,  by  treating 
with  carbonaceous  gases  the  rich  oxides  thrown  out  of  the  furnace  during 
the  boil.  These  slags  are  found  to  contain  innumerable  small  grains  of 
metallic  iron,  which  are  mechanically  held  in  suspension  in  the  slags,  and 
may  be  easily  recovered,  by  opening  the  tap-hole  of  the  converting  vessel, 
and  allowing  the  fluid  malleable  iron  to  flow  into  the  iron  ingot  moulds  placed 
