456     A  COMPOUND  OF  IODIDE  AND  NITRATE  OF  SILVER. 
A  COMPOUND  OF  IODIDE  AND  NITEATE  OF  SILVER. 
Dr.  II  of  maim  has  described,  at  a  meeting  of  the  Chemical 
Society,  a  compound  of  iodide  and  nitrate  of  silver,  which  was 
obtained  by  treating  a  mixture  of  iodide  and  oxide  of  silver  with 
nitric  acid.  He  found  that  the  iodide  fused  in  the  boiling 
liquid,  forming  an  oily-looking  stratum  at  the  bottom  of  the  ves- 
sel, which  solidified  on  cooling  into  a  crystalline  mass.  This 
salt,  when  treated  with  water,  was  resolved  into  nitrate  and 
iodide  of  silver.  Upon  further  examination  of  this  compound, 
he  found  that  its  composition  varies  according  to  the  relative 
quantities  of  its  constituents  originally  present,  and  the  amount 
of  nitric  acid  employed.  From  the  result  of  several  experiments, 
he  found  the  limits  of  combination  in  the  fusible  compound  to 
be  as  follows  : — 
# 
I.  II. 
Nitrate  of  Silver,  .  .  69.52  .  .  33.67 
Iodide  of  ditto    .    .    .      29.84    .     .  65M 
The  first  of  these  results  corresponds  to  the  formula  3(AgO, 
NO5),  Agl,  while  the  second  may  be  represented  as  2(AgO,  NO5), 
S(Agl). 
By  continued  ebullition,  the  proportion  of  iodide  of  silver  may 
be  still  further  increased,  but  the  compound  then  no  longer 
fuses  in  boiling  concentrated  nitric  acid. 
A  combination  of  iodide  and  nitrate  has  been  also  observed 
and  suspected  by  other  chemists,  although  no  analysis  or  exami- 
nation appears  to  have  been  made,  excepting  by  Dr.  Hofmann. 
Mr.  F.  Maxwell  Lyte,  in  a  recent  letter  to  the  Journal  of  the 
Photographic  Society,  alludes  to  such  a  combination  : — 
"It  is,  I  believe,  allowed  by  many,  though  not  by  all,  that 
there  does  exist  a  compound  of  the  iodide  with  the  nitrate  of 
silver ;  but  the  various  forms  and  properties  of  this  substance, 
and  the  important  part  it  plays  in  photography,  have  been  little, 
if  at  all,  separately  examined,  and  I  now  propose  to  mention  a 
few  facts  and  considerations  with  regard  to  it. 
"We  have  the  iodo-nitrate  of  silver,  if  we  may  so  call  it,  under 
three  different  forms: — First,  in  solution,  when  we  dissolve 
iodide  of  silver  in  the  negative  nitrate  bath ;  secondly,  in  the 
