IODIDE  OF  ALUMINUM. 
55 
parts  of  iodine.  At  the  ordinary  temperature  the  combina- 
tion perhaps  only  takes  place  slowly ;  the  iodine  in  contact  with 
the  aluminum  soon  adheres  slightly  to  the  walls  of  the  tube, 
and  separates  therefrom  when  struck,  leaving  behind  a  browTn  spot. 
If  the  tube  be  now  carefully  heated,  the  combination  is  affect- 
ed with  a  strong  evolution  of  light  and  heat ;  the  granules  of 
aluminum  burn  in  the  tube  with  a  beautiful  violet  light ;  the 
iodide  of  aluminum  formed  constitutes  on  cooling  a  solid  mass, 
with  a  strong  brown  color  from  the  presence  of  iodine.  If  a 
slight  excess  of  aluminum  were  employed,  all  that  is  necessary 
is  to  heat  the  tube  again  gently,  especially  at  the  point  where 
the  metal  was  placed,  and  to  drive  the  iodine  there  by  the  flame 
so  as  to  free  the  compound  from  excess  of  iodine  ;  the  compound 
then  appears  mixed  with  aluminum  as  a  dingy  white  crystalline 
mass. 
The  iodide  of  aluminum  thus  prepared  may  easily  be  col- 
lected at  the  end  of  the  tube  ;  the  tube  is  then  bent  by  the  lamp, 
(or  a  bent  tube  may  be  employed  from  the  commencement),  and 
the  iodide  of  aluminum  is  heated,  when  it  fuses,  soon  boils,  and 
sublimes  in  delicate  snow-white  laminae  into  the  cold  part  of  the 
tube. 
The  iodide  of  aluminum  thus  separated  from  free  iodine  and 
the  excess  of  aluminum  forms  dazzling  white  crystalline  laminae, 
which  fuse  into  an  extremely  liquid  fluid,  boiling  readily  when 
further  heated.  On  cooling  it  forms  a  solid,  white,  radiately 
crystalline  mass.  In  the  air  the  compound  fumes  strongly,  and 
deliquesces  into  oily  drops  by  attracting  water  ;  it  soon  colors 
paper  purple-red,  and  dissolves  in  water  with  a  strong  evolution 
of  heat.  When  heated  in  the  air,  it  is  decomposed  very  readily  ; 
iodine  separates  under  these  circumtances,  so  that  is  scarcely 
possible  to  transfer  it  when  fused  from  one  tube  to  another  with- 
out alteration,  as  the  mass  is  always  colored  brown  by  some 
separated  iodine.  If  a  few  granules  of  aluminum  be  put  into 
the  second  tube  and  first  heated,  the  whole  amount  of  free  iodine 
is  absorbed,  and  the  compound  may  then  be  again  obtained  per- 
fectly white.    Analysis  gave — 
Average 
Iodide  of  silver  2-611  2-545  2*947,  or  I  93-20  3  93  10 
Alumina  ....     0-203      0-199     0-231,  or  Al    7-12     2      6  90 
