IMPURITIES  OF  COMMERCIAL  ZINC. 
407 
ed  from  these  two  zincs,  and  that  their  freedom  from  arsenic  was  a 
property  shared  by  the  whole  sample,  and  not  an  accidental  peculiarity 
of  a  particular  fragment.  At  sundry  times  we  therefore  repeated  again 
and  again  the  long  and  careful  test  for  arsenic  above  described  with  these 
two  samples  of  spelter,  and  invariably  arrived  at  the  same  conclusion  ; 
namely,  that  no  deposit  of  any  kind  could  be  obtained  in  the  reduction 
tube  from  these  zincs  and  purified  sulphuric  acid." 
The  authors,  by  adding  infinitessimal  quantities  of  arsenious 
acid  to  these  zinc  and  acid  mixtures,  say  that  they  could  easily 
detect  a  proportion  of  arsenic  less  than  the  ten  millionth  part  of 
the  zinc  used. 
The  authors  subsequently  applied  the  test  to  the  other  zincs 
of  the  list,  and  all  of  them,  including  the  New  Jersey  zinc,  were 
found  to  contain  various  minute  quantities  of  arsenic.  The 
authors  finally  remarked  that  the  purest  of  all  the  zincs  they 
have  analyzed,  is  that  manufactured  at  the  Pennsylvania  and 
Lehigh  zinc  works,  Bethlehem,  Pa.  This  spelter  dissolves  in 
dilute  sulphuric  acid  without  leaving  any  appreciable  residue, 
and  therefore  contains  no  lead  ;  indeed,  a  trace  of  cadmium  is 
the  only  impurity,  whose  presence  in  the  zinc  we  could  con- 
fidently assert.  The  ore  from  which  this  spelter  is  made  is  the 
hydrated  silicate  of  zinc  (electric  calamine)  and  it  is  not  surpris- 
ing that  this  mineral  should  yield  zinc  of  singular  purity,  if  the 
ore  be  carefully  selected.  We  have  stated  above,  that  our 
first  sample  of  this  zinc  was  free  from  arsenic,  but  a  second 
sample  was  not  pure  in  this  respect.  At  these  works  the  oxide 
of  zinc  is  manufactured  as  well  as  the  metal,  and  we  learn  from 
a  letter  addressed  to  Prof.  Brush,  by  Mr.  Wharton,  the  director 
of  the  works,  that  the  crust  from  the  oxide  furnaces  has  now  and 
then  been  worked  into  spelter,  and  that  the  ore  used  in  making 
the  oxide  is  less  carefully  selected  than  that  which  goes  to  the 
spelter  furnaces,  and  is  much  more  likely  than  the  latter  to 
contain  both  blende  and  pyrites.  This  fact  may  account  for  the 
occurrence  of  arsenic  in  some  specimens  of  this  spelter  while  the 
greater,  part  of  it,  manufactured  from  carefully  selected  silicate 
of  zinc,  is  perfectly  free  from  that  impurity.  There  seems  to  be 
no  reason  why  zinc  of  uniform  purity  should  not  be  obtained 
from  this  excellent  ore. 
