METHOD  OP  FORMING  AMMONIA-IODIDES  OF  METALS.  57 
ON  A  NEW  METHOD  OF  FORMING  AMMONIO-IODIDES 
OF  METALS. 
By  the  Rev.  J.  B.  Reade. 
It  is  only  within  the  last  few  years  that  the  attention  of 
chemists  has  been  directed  to  the  compounds  of  metals  with 
iodine  and  ammonia.  The  fifth  edition  of  Brande's  Chemistry, 
published  in  1841,  is  silent  on  the  subject.  At  the  Oxford 
Meeting  of  the  British  Association,  in  1847,  I  exhibited  the 
ammonio-iodide  and  per-iodide  of  gold,  and  since  that  time  other 
experiments  on  other  metals  have  furnished  me  with  results 
which  perhaps  may  be  of  some  interest  to  the  Chemical  Section. 
Solution  of  Iodine  in  Ammonia.  Perhaps  the  best  mode  of 
dissolving  iodine  in  ammonia  for  the  purpose  in  question,  is  to 
place  about  50  or  60  grains  of  iodine  in  an  evaporating  dish, 
hold  it  over  the  spirit-lamp  till  thoroughly  warm  and  the  vapor 
arises,  and  then  add  a  few  drops  of  liquor  ammoniae,  which  will 
be  immediately  charged  with  a  large  excess  of  iodine  in  solution. 
This  may  be  poured  into  a  bottle  and  more  iodine  and  ammonia 
added,  until  the  requisite  supply  is  obtained. — Ammonio-iodide 
of  Gold.  Gold-leaf  when  placed  in  the  iodine  solution  instantly 
turns  black,  (a  purple  if  the  solution  is  diluted),  and  immediately 
dissolves,  like  sugar  in  water.  If  left  to  evaporate  spontaneously 
in  some  quantity,  we  obtain  black  four-sided  prisms  of  the  am- 
monio-periodide,  which  readily  dissolve  in  water  ;  and  if  a  very 
weak  solution  be  exposed  for  some  months-  to  the  direct  action 
of  the  sun's  rays,  a  slight  precipitate  appears,  and  a  drop  or  two 
of  the  clear  solution  furnishes  a  most  striking  microscopic  object 
both  as  to  crystalline  arrangement  and  richness  of  tint  when 
placed  in  polarized  light.- — Ammonio-iodide  of  Silver.  Gmelin 
says  of  the  ammonio-iodide  of  silver,  that  "  unfused  iodide  of 
silver  absorbs  with  evolution  of  heat  3.6  per  cent,  of  ammonia, 
and  forms  a  white  compound,  which  on  exposure  to  the  air  gives 
off  ammonia  and  turns  yellow  again."  The  phenomena  are  far 
more  interesting  when  silver  leaf  is  added  to  the  ammonia  solu- 
tion of  iodine.  The  metallic  silver  is  dissolved,  and  when  a  few 
drops  are  placed  on  a  slip  of  glass  beautiful  brushes  of  prismatic 
crystals  shoot  out  in  all  directions,  which  may  be  mounted  as  a 
microscopic  object  in  Canada  balsam  after  the  excess  of  iodine 
is  spontaneously  evaporated.    Under  polarized  light  the  colors 
