ON  INDIUM. 
169 
scope  is  at  98  on  the  scale,  and  the  paler  at  135,  that  is  when  the 
sodium  line  is  placed  at  50  and  the  strontium  line  at  93.  When 
the  sodium  line  is  50  and  the  strontium  104,  indium  a  will  be 
110,  and  indium  p  will  stand  at  14T.  Indium  also  gives  a  violet 
color  when  one  of  its  salts  is  introduced  into  the  flame  of  a 
Bunsen's  jet,  so  that  its  presence  can  be  recognised  without  the 
spectroscope. 
The  oxide,  when  reduced  before  the  blow-pipe  on  charcoal, 
gives  a  white  ductile  metal  resembling  tin,  but  which  marks 
paper  clearer  than  lead.  The  metal  dissolves  in  hydrochloric 
acid  with  some  evolution  of  gas,  and  a  platinum  wire,  moistened 
with  the  solution,  shows  a  very  intense  blue  line,  which,  however, 
is  very  evanescent. 
The  metal  is  easily  fusible  before  the  blow-pipe,  and  gives  a 
residue  which  is  a  dark-yellow  while  hot,  and  pale  straw-yellow 
when  cold  ;  this  residue  is  driven  off  with  difficulty  by  the  re- 
duction flame,  to  which,  in  volatilising,  it  communicates  a 
peculiar  violet  tinge. 
The  ignited  oxide  is  always  obtained  yellowish,  which  is  pro- 
bably caused  by  a  trace  of  iron  oxide. 
The  hydrated  oxide  precipitated  by  ammonia  is  always  white 
and  slimy,  so  that  it  adheres  to  the  side  of  the  beaker.  Tartaric 
acid  added  to  a  solution  of  the  oxide  prevents  its  precipitation 
by  ammonia  •  sulphide  of  ammonium  added  to  the  mixture  causes 
a  bulky  white  precipitate,  colored  pale  greenish  by  a  trace  of 
iron. 
Potash  precipitates  the  hydrated  oxide  from  acid  solutions  as 
perfectly  as  ammonia. 
Carbonate  of  soda  throws  down  a  more  crystalline  precipitate, 
and  the  white  deposit  so  obtained  at  a  boiling  heat,  after  drying, 
easily  dissolves  in  dilute  sulphuric  acid  with  effervescence,  show- 
ing that  it  is  a  carbonate  of  indium  oxide. 
The  ignited  oxide,  heated  to  redness  in  a  stream  of  dry  hy- 
drogen, forms  no  water  and  undergoes  no  change. 
When  mixed  with  charcoal,  and  heated  to  redness  in  a  tube 
in  a  current  of  chlorine,  it  form3  a  volatile  chloride,  which  con- 
denses at  the  cold  end  of  the  tube.  The  chloride  has  a  yellow  color, 
probably  from  a  trace  of  iron  ;  but  single  crystalline  scales  are 
seen,  which  appear  colorless,  and  have  a  mother-of-pearl  lustre, 
