170 
ON  INDIUM. 
The  chloride  is  very  deliquescent,  and  when  dried  again  it  par- 
tially decomposes. 
The  chloride  shows  the  blue  line  with  the  greatest  brilliancy, 
but,  owing  to  its  volatility,  the  line  quickly  disappears.  If, 
however,  some  oxide  is  placed  on  a  platinum  spoon,  and 
moistened  with  hydrochloric  acid,  the  appearance  of  the  blue 
line  in  the  spectroscope  is  less  brilliant,  but  more  lasting,  and 
by  moistening  afresh  with  the  acid,  the  experiment  may  be  re- 
peated several  times  without  renewing  the  oxide. 
The  solution  of  the  reduced  metal  in  hydrochloric  acid,  gave, 
with  ammonia  and  sulphide  of  ammonium,  a  greyish  brown  pre- 
cipitate ;  and  further  experiments  were  necessary  to  decide 
whether  this  color  really  belonged  to  the  sulphide  of  indium  or 
was  caused  by  some  impurities. 
The  purification  of  the  oxide  by  successive  treatment  of  the 
first  solution  with  sulphuretted  hydrogen,  precipitation  by  am-, 
monia,  redissolving,  and  again  precipitating  by  potash,  gave  the 
before-mentioned  results.  It  remained  to  separate  the  iron.  By 
the  decomposition  of  the  acid  solution  with  excess  of  acetate  of 
soda,  and  heating,  the  oxide  of  iron  was  thrown  down,  and  the 
liquid  still  contained  a  good  deal  of  oxide  of  indium,  but  a  part 
of  the  latter  went  down  with  the  oxide  of  iron. 
It  is  best  to  precipitate  the  iron  by  the  cautious  addition  of 
bicarbonate  of  soda.  On  boiling  the  filtrate,  and  adding  a  small 
quantity  of  soda  salt,  the  oxide  of  indium  is  precipitated  either 
as  hydrate  or  carbonate. 
The  solution  of  the  chloride  obtained  in  the  way  before  men- 
tioned gave,  with  ferrocyanide  of  potassium,  a  white  precipitate, 
colored  bluish  by  a  trace  of  iron.  With  ferridcyanide  it  gave 
no  precipitate. 
As  oxide  of  indium  bears  much  resemblance  to  thorina — from 
which,  however,  it  may  be  distinguished  by  its  insolubility  in 
potash,  and  reducibility  on  charcoal — it  may  be  mentioned  that 
when  moistened  with  cobalt  solution  and  heated,  it  does  not  be- 
come blue,  and  ignited  in  hydrochloric  acid  it  slowly,  but  per- 
fectly dissolves.  On  adding  a  sulphate  solution  to  a  solution 
of  sulphate  of  potash  and  evaporating,  no  alum  crystals  were 
obtained. 
We  have  yet  to  discover  in  what  minerals  indium  occurs.  On 
