Am'Feb.^S^.arm•}    Mercurous  Salts  with  Silver  Salts.  87 
5  cc.  of  these  solutions  were  precipitated  by  addition  of  5  cc. 
dilute  HC1,  the  precipitate  washed  with  cold  water  (in  X  and  XI 
also  with  boiling  water),  5  cc.  water  of  ammonia  poured  over  the 
precipitate  which  had  been  loosened  from  the  filter  by  use  of  a  glass 
rod,  the  filtrate  returned  to  the  filter  and  allowed  to  run  through 
again ;  the  filtrate  was  then  acidified  with  HN03.  This  test  is 
called  the  Regular  test.  The  black  residue,  after  thorough  wash- 
ing with  water,  is  removed  as  completely  as  possible  from  the  filter 
(by  using  a  jet  of  water),  nitric  acid  added,  the  mixture  evaporated 
to  a  very  small  bulk,  diluted  with  water  and  dilute  hydrochloric  acid 
added;  this  test  is  called  the  Residue  test.  Speaking  now  of  solu- 
tions I  to  VII,  inclusive,  the  Regular  tests  for  silver  rapidly  became 
fainter  until  in  No.  IV  a  decided  turbidity  appeared,  while  in  VI 
and  VII  only  a  faint  turbidity  was  noticeable.  The  Residue  test, 
on  the  other  hand,  increases  in  quantity  of  precipitate  as  the 
Regular  test  decreases ;  in  solution  I  the  two  tests  are  nearly  alike, 
showing  that  using  the  mercurous  and  silver  nitrates  in  about  equal 
quantities,  only  one-half  of  the  silver  chloride  is  dissolved  by  the 
ammonium  hydrate,  the  other  half  remaining  in  the  residue. 
To  ascertain  if  more  dilute  solutions  give  different  or  more  favor- 
able results,  VIII  and  IX  were  made  by  diluting  I  and  V  with  four 
volumes  of  water ;  the  results  did  not  differ  much  from  those 
obtained  with  the  stronger  solutions.  In  VIII  the  Regular  and 
Residue  tests  were  of  about  equal  intensity,  while  in  IX  the  Regular 
test  gave  only  a  very  faint  turbidity. 
To  examine  the  influence  of  lead  salts  solutions  X  and  XI  were 
prepared  ;  it  will  be  noticed  that  they  correspond  to  IV  and  VII 
with  addition  of  1  per  cent.  Pb(N03)2.  The  Regular  and  Residue 
tests  did  not  differ  materially  from  those  obtained  with  IV  and  VII ; 
this  refutes  the  statement  previously  made  that  in  the  presence  of 
lead  salts,  the  silver  test  was  not  interfered  with. 
From  these  experiments  it  is  shown  that  in  the  presence  of 
mercurous  salts  the  regular  test  for  silver  is  never  in  accord  with  the 
quantity  of  silver  salt  present,  and  that  if  the  proportion  of  mercu- 
rous salt  be  to  silver  salt  as  6  or  more  to  I,  then  the  silver  may 
easily  escape  detection ;  hence  it  is  recommended  to  test  the 
ammonia  residue  as  well  as  the  ammonia  solution  for  silver. 
