850 
DETECTION  OF  ARSENIC. 
ON  SOME  FAILURES  OF  MARSH'S  PROCESS  FOR  THE  DETECTION 
OF  ARSENIC. 
At  the  last  meeting  of  the  British  Association,  Dr.  Odling 
read  a  paper,  which  has  been  since  published  in  Guy's  Hospital 
Reports,  showing  that  the  presence  of  certain  organic  and  saline 
substances  prevents  the  formation  of  arseniuretted  hydrogen, 
and  consequently  destroys  the  action  of  Marsh's  test.  The 
author  had  occasion  to  examine  a  soil  which  contained  0*07  of 
arsenious  acid.  Ready  indication  of  the  presence  of  the  arsenic 
was  obtained  by  Reinsch's  process,  but,  most  unexpectedly, 
when  the  dilute  hydrochloric  or  sulphuric  decoction  was  tested 
in  Marsh's  apparatus,  no  result  could  be  obtained.  Thus,  100 
grains  of  the  dried  soil,  boiled  with  half  an  ounce  of  muriatic 
acid  and  three  ounces  of  water,  yielded  a  solution  in  which  no 
arsenic  could  be  detected  by  Marsh's  test,  yet  the  liquid  poured 
out  of  the  apparatus  and  boiled  with  copper  foil  gave  a  metallic 
deposit  from  which  crystals  of  arsenious  acid  were  obtained. 
Another  acid  decoction  prepared  in  the  same  manner,  was  dis- 
tilled to  dryness,  and  the  distillate  transferred  to  Marsh's  appa- 
ratus, when  characteristic  stains  were  obtained  with  the  greatest 
facility.  Also,  when  the  100  grains  of  soil  were  heated  with 
strong  oil  of  vitriol,  so  as  to  thoroughly  char  the  organic  mat- 
ter, then  diluted  with  water,  and  the  filtered  solution  tested  by 
Marsh's  process,  a  satisfactory  reaction  was  obtained.  One- 
fifteenth  of  a  grain  of  arsenious  acid  was  then  added  to  ordinary 
non-arsenical  soil,  and  precisely  the  same  results  obtained — 
that  is  to  say,  the  simple  dilute  acid  decoction  gave  no  evidence 
with  Marsh's  test. 
Two  different  specimens  of  grass  that  had  been  grown  upon 
arsenical  soil,  and  also  some  hay  to  which  one  fifth  of  a  grain 
of  arsenious  acid  had  been  added,  were  examined ;  the  acid 
decoctions  tested  by  Reinsch's  process  readily  furnished  arseni- 
cal deposits,  but  afforded  no  evidence  in  Marsh's  apparatus. 
Two  quantities  of  human  stomach,  each  weighing  two  ounces, 
were  boiled  for  an  hour,  one  with  dilute  muriatic,  the  other  with 
dilute  sulphuric  acid,  and  the  decoctions  filtered  off  and  mixed 
with  from  a  fourth  to  a  third  of  their  bulk  of  rectified  spirit. 
To 'about  three  ounces  of  each  decoction  0-01  of  arsenious  acid 
