n  ]  LEAD    AND    ZINC    RESOURCES    OF    UNITED    STATES.  273 
indicate  that  shipments  of  spelter  rather  than  ore  are  more  likely 
be  the  final  outcome.  The  foreign  smelters  have  no  advantage  over 
e  American,  which  are  not  essentially  temporary  and  which  may 
t  be  overcome,  while  the  ore  producers  of  America  have  in  turn 
advantages  over  those  abroad,  ruder  these  circumstances  the 
rmal  law  that  products  will  be  shipped  in  the  most  concentrated 
riu  -cfiii-  likely  to  prevail.  For  the  present  it  is  by  no  means  cer- 
in  but  that  Australia  rather  than  America  affords  the  largest 
lount  of  zinc  ore  immediately  available  for  European  furnace-. 
To  meet  the  future  demands  of  the  zinc  industry  in  America  ample 
b  reserves  are  known,  no  important  districl  a>  yet  showing  any 
il  signs  of  exhaustion.  The  ore  yet  to  be  mined,  however,  is  of 
stinctly  lower  grade  than  that  marketed  in  the  past,  and  attempts 
meet  this  condition  are  already  being  made  by  improvements  in 
lelting  and  milling  practice. 
Probably  the  most  important  American  advance  in  smelting  prac- 
:e  is  the  development  of  the  direct  method  of  oxide  manufacture. 
lis  process  meets  the  situation  admirably,  except  for  the  limita- 
>ns  imposed  by  the  small  market  for  oxide  and  the  fact  that  the 
lin  increased  demand  is  likely  to  be  for  spelter.  Oxide  burning 
iy,  however,  be  used  as  a  preliminary  process,  becoming  essentially 
nethod  of  fire  concentration,  the  oxide  itself  being  reduced  to  spel- 
*  in  the  ordinary  way.  At  Pulaski,  Va.,  this  combination  of 
ocesses  is  now  in  successful  operation.  Attempts  to  smelt  iow- 
ade  ores  direct  have  been  confined  mainly  to  the  Lanyon's  work 
th  Sadtler  retorts,  though  this  line  of  investigation  is  probably 
nsidered  most  hopeful.  In  the  main  the  smelters  have  contented 
emselves  with  arranging  to  save  by-products  and  with  improve- 
ints  directed  toward  greater  furnace  economy.     They  have  thrown 
the  miners  the  main  burden  by  requiring  a  high  cleaning  of  the 
b.  Out  of  this  condition  have  come  many  improvements  in  milling 
ocesses.  particularly  the  magnetic  and  electrostatic  separating 
ichines.  but  in  any  large  advance  of  the  industry  the  smelter-  as 
dl  as  the  miners  must  be  prepared  to  take  a  large  part. 
Bull.  260—05  m IS 
