58       METHODS  OF  FORMING  AMMONIA-IODIDES  OF  METALS. 
of  the  crystals  are  brilliant  in  the  extreme. — Ammonio-iodide  of 
Mercury.  The  phenomena  in  forming  this  compound  are  varied 
and  interesting.  Mercury  is  added  to  the  iodine  solution,  and 
after  the  application  of  heat  and  the  addition  of  a  little  water,  a 
few  drops  on  a  slip  of  glass  give  bundles  of  permanent  prismatic 
crystals,  similar  to  those  of  silver,  and  acted  on  with  the  same 
energy  by  polarized  light.  If  ammonia  be  added  to  these  crys- 
tals, they  are  immediately  covered  with  tufts  of  snowy  whiteness, 
and  by  degrees  they  are  converted  into  ruby-colored  hexagonal 
prisms,  which  are  also  permanent. — Ammonio-iodide  of  Cobalt, 
Brande  observes  that  "  no  precipitate  is  produced  in  solutions  of 
cobalt  either  by  hydriodic  acid  or  iodide  of  potassium,  or  by 
iodic  acid  or  iodate  of  potassa."  I  find,  however,  that  cobalt 
yields  to  the  action  of  the  ammonio-iodide  solution  after  some 
hours'  digestion  and  a  little  heat  and  water.  As  might  be  ex- 
pected, it  exhibits  very  strongly  the  sympathetic  properties  of 
the  chloride,  for  when  placed  on  paper  and  gently  heated  it  be- 
comes a  brilliant  green,  which  of  course  vanishes  as  the  paper 
cools. — Ammonio-iodide  of  Titanium.  As  titanium,  which  re- 
sists every  direct  method  of  attack  in  the  laboratory,  yields  after 
a  period  of  digestion  in  the  iodine  solution,  it  is  probable  that 
other  of  the  scarcer  metals,  which  are  with  difficulty  reduced  by 
the  ordinary  methods,  might  be  exhibited  in  the  form  of  am- 
monio-iodides,  and  thus  throw  additional  light  on  their  respective 
equivalents.  The  crystals  of  ammonio-iodide  of  titanium  which 
I  have  obtained  were  from  a  pure  specimen  of  the  metal  obtained 
by  Mr.  Waterhouse,  of  Halifax,  from  the  slag  of  the  neighbor- 
ing iron-furnaces  at  Low  Moor  Ammonio-iodide  of  Aluminum. 
In  forming  this  compound  I  did  not,  as  on  other  occasions,  use 
the  pure  metal,  but  alumina  only,  precipitated  in  the  usual  way. 
After  allowing  the  alumina  to  digest  for  some  time  in  the  iodine 
solution,  the  whole  was  boiled  in^a  little  water,  which  dissolved 
the  new  compound,  and  upon  evaporation  and  the  proper  mea- 
sure of  heat  to  volatilize  the  excess  of  iodine  and  ammonia,  a 
white  semi-metallic  substance  remained,  as'  in  the  case  of  silver. 
It  is  soluble  in  dilute  hydrochloric  acid,  and  yields  a  blue  pre- 
cipitate on  the  addition  of  yellow  prussiate  of  potash.  Whether 
any  use  can  be  made  of  this  process  towards  obtaining  the  pure 
metal  is  of  course  a  problem  for  practical  men. — London  Phar- 
maceutical Journal,  October,  1857. 
