DETECTION  OF  ARSENIC  BY  COPPER. 
853 
corresponding  in  composition  with  the  precipitates  obtained 
by  sulphuretted  hydrogen ;  experiments  which  I  have  com- 
menced, may  clear  this  up.  The  suggestion  of  Lippert,  that 
other  metals  are  similarly  precipitated  by  copper,  appears 
probable  for  antimony,  and  perhaps  for  bismuth,  which  is  pre- 
cipitated in  crystals,  but  most  likely  not  for  silver  and  mercury; 
but  tin  and  lead,  though  enumerated  among  the  others  by  Lip- 
pert,  are  not  precipitated  at  all  by  copper  from  their  solutions 
acidulated  with  muriatic  acid. 
In  answer  to  the  objections  made  at  the  meeting  of  the  Asso- 
ciation at  Coburg,  that  all  commercial  copper  contains  arsenic, 
I  have  to  state  that  I  have  never  found  this  metal  in  the  wire 
which  I  employ  for  my  test.  The  wire  is  J  millimetre  in  thick- 
ness, and  is  invariably  heated  to  redness  for  several  hours,  en- 
closed in  a  box,  subsequently,  it  is  well  scoured.  Mere  traces  of 
arsenic  render  copper  very  brittle,  so  as  not  to  be  fit  for  fine 
wires,  and  these  I  consider  almost  pure  copper,  containing  but 
traces  of  lead,  silver  and  iron.  The  brittleness  of  sheet  copper 
even  is  generally  due  to  iron,  and  arsenic  will  probably  rarely 
be  found  in  minute  traces.  But  even  if  the  copper  should  con- 
tain arsenic,  it  could  not  be  dissolved  on  boiling  with  muriatic 
acid,  because  the  latter  metal  is  then  in  an  electro-negative  con- 
dition. However,  with  the  tests  as  proposed  by  me,  the  abso- 
lute absence  of  arsenic  is  proven  by  boiling  for  some  time  the 
copper  wire  with  the  muriatic  acid,  when  the  former  must  re- 
main bright. 
Another  objection  to  my  test  was,  that  green  colors  which 
have  recently  appeared  in  commerce,  yield  a  reaction  similar  to 
the  arsenical  colors.  Blue  or  green  ultramarine,  when  treated 
with  muriatic  acid,  disengage  much  sulphuretted  hydrogen,  and 
leave  a  gelatinous  greyish  white  mass.  If  ultramarine  was  adulte- 
rated with  a  copper  arsenic  color — the  latter,  however,  are  much 
dearer — the  color  would  not  disappear,  and  the  solution  would 
be  of  a  green  or  brown  color.  Copper  arsenic  colors  adulte- 
rated with  ultramarine  would  turn  brown,  and  evolve  with  muria- 
tic acid  sulphuretted  hydrogen.  The  solution  of  ultramarine 
in  muriatic  acid  colors  copper  blackish  blue,  sometimes  steel 
blue,  by  a  sulphur  compound,  which  is  not  decomposed  by  a 
large  excess  of  muriatic  acid  and  long  continued  boiling,  but 
23 
