1 28  Ready  Test  for  Arsenical  Compounds.  {Km^J^m- 
by  dissolving  20  grains  of  nitrate  in  an  ounce  of  distilled  water,  adding 
2  drops  of  nitric  acid,  to  render  the  solution  slightly  acid.  Exceedingly 
minute  quantities  of  arsenic  can  be  readily  detected  by  this  very  simple 
process.  Thus  one-one  thousandth  part  of  a  grain  of  arsenious  acid 
dissolved  in  1  cc.  of  distilled  water  gives  a  very  decided  effect  in  a 
few  moments,  and  even  a  smaller  quantity  can  be  detected  ;  as,  for 
example,  one  drop  of  Fowler's  solution  in  an  ounce  of  water  will  indi- 
cate in  a  little  time  by  the  blackening  of  the  silver  salt.  I  may  further 
state  that  the  presence  of  organic  matter  seems  to  interfere  but  little 
with  this  test ;  for  I  have  found  that  very  minute  quantities  of  arse- 
nious acid,  when  mixed  with  considerable  amounts  of  milk,  tea,  coffee, 
ale  or  porter,  or  flour,  could,  with  almost  the  same  facility,  be  detected 
by  this  method,  showing  the  applications  are  very  extended. 
Antimony  is  the  only  metal  which  is  capable  of  uniting  with  nascent 
hydrogen  to  form  a  gas  (antimoniuretted  hydrogen),  which,  coming  in 
contact  with  nitrate  of  silver,  produces  black  antimonide  of  that  metal  j 
and  the  blackening  of  the  silver  salt  from  the  formation  of  that  com- 
pound might  be  easily  mistaken  for  the  effect  produced  by  the  arsenical 
gas. 
The  fact,  first  pointed  out  by  Fleitmann,  that  antimoniuretted  hydro- 
gen is  not  evolved  (except,  perhaps,  as  a  mere  trace)  from  strongly 
alkaline  solutions,  though  the  conditions  may  exist  there  for  its  forma- 
tion, and  as  the  action  of  the  sodium  amalgam  is  to  render  the  mixture 
quickly  alkaline,  there  will  be  only  a  very  minute  quantity  of  the  anti- 
mony that  may  be  present  so  evolved  ;  and  by  previously  rendering  the 
mixture  strongly  alkaline,  we  may  altogether  prevent  the  evolution  of 
that  gas. 
If,  however,  we  make  the  mixture  containing  the  antimony  in  solu- 
tion first  strongly  acid,  and  then  add  the  amalgam,  or  even  acidify  after 
its  addition,  the  antimoniuretted  hydrogen  will  be  evolved  in  abun- 
dance, producing  a  deep  black  stain  on  the  paper  moistened  with  the 
nitrate  of  silver,  and,  for  the  purpose  of  this  acidification,  tartaric  acid, 
answers  very  well. 
As  the  presence  of  alkalies  in  solution  does  not  interfere  with  the 
evolution  of  the  arsenical  gas,  this  itself  is  a  means  of  distinguishing, 
the  two  metals,  arsenic  and  antimonv. 
