308  The  U.S.P.  Inorganic  Chemicals.      { Am jii"iSarm" 
arsine  gases  for  half  an  hour.  (Fliickiger ',  Archiv  d.  Pharm.,  27,  p.  1. 
Poleck,  ibid.,  p.  3,  and  Curtman,  Pharm.  Rundschau,  1 891,  p.  178.) 
That  is,  provided  all  of  the  arsenic  has  been  converted  into  arsine. 
Reichert  (Reichert,  Archiv  d.  Pharm.,  1880,  p.  7)  claims  the  limit  to  be 
0-0014  milligramme,  Poleck  at  0006  milligramme,  Beckurts  (Beck- 
urts,  Jahresberichte  d.  Pharm.,  1884,  p.  475)  at  0-002  milligramme, 
and  Classen  at  o-ooi  milligramme  [Analyt.  Chemie,  1901). 
This  test  is  open  to  serious  objections,  chiefly  due  to  the  extreme 
sensitive  nature  of  the  solution  of  silver  nitrate.  These  may  be 
summarized  as  follows  : — 
(a)  The  presence  of  sulfur,  sulfates,  phosphorus  or  hypophos- 
phites  in  the  reagents  or  substance  to  be  tested,  results  in  the  gen- 
eration of  sulfureted  or  phosphoreted  hydrogen,  either  of  which 
will  produce  a  black  to  brown  spot  like  that  of  arsine. 
(b)  Presence  of  coal  gas  or  traces  of  sulfureted  hydrogen  in  the 
paper  or  air  of  the  laboratory  will  likewise  produce  a  dark  stain  on 
the  paper  cap.  The  same  may  be  said  of  the  presence  of  dust  or 
the  use  of  a  poor  quality  of  filter  paper  (Curtman,  Rundschau,  1891* 
P-  33> 
(c)  The  action  of  pure  hydrogen  gas  for  a  longer  period  of  time 
will  also  cause  blackening  of  the  paper  cap ;  this  is  liable  to  happen 
when  the  reaction  is  caused  to  proceed  slowly  in  order  to  avoid  loss 
of  any  traces  of  arsenic  probably  present.  (Fliickiger,  Archiv  d. 
Pharm.,  27,  p.  1;  also  Lohmann,/%ar//z.  Ztg.,  1891,  p.  748).  Another 
objectionable  feature  must  not  be  overlooked,  and  that  is  the  rigid 
exclusion  of  the  sunlight  during  the  period  of  testing. 
{d)  Solutions  containing  antimony  produce  reactions  similar  to 
those  of  arsenic. 
The  Modified  Gutzeit  or  Mercuric  Chlorid  Test. — The  substitution 
of  mercuric  chlorid  for  silver  nitrate  was  first  proposed  by  Mer- 
c,eron  and  Bergeret  {Comptes  Rend.,  1 879,  1 1 8)  in  1 874,  The 
action  of  arsine  on  mercuric  chlorid  had  already  been  studied  and 
found  to  consist  either  of  the  yellow  compound  AsH(HgCl)2 
produced  through  traces  of  the  gas,  or  the  orange  As  (HgCl)3 
which  results  from  an  excess  of  arsine.  In  applying  this  test  it  is 
the  yellow  compound  which  is  ordinarily  observed,  since  the  tests 
are  directed  only  for  the  presence  of  traces  of  arsenic.  Alcohol 
exerts  no  effect  upon  this  reaction  ;  the  test-cap  should  be  dry  when 
the  test  is  applied.    Antimony  (Stibine  SbH3)  produces  a  dark  gray 
