PREPARATION  OF  SALTS  OF  NICKEL. 
403 
tated  by  a  stream  of  sulphuretted  hydrogen,  the  solution  filtered 
to  separate  the  sulphuret  of  copper,  and  gently  boiled  to  expel 
hydro-sulphuric  acid.  The  solution  of  the  sulphate  may  then 
be  set  aside  to  crystallize  by  spontaneous  evaporation,  or  the 
carbonate  or  oxide  immediately  precipitated  by  an  alkali  or 
alkaline  carbonate ;  caustic  ammonia,  or  its  carbonate,  are  not 
suitable,  as  an  excess  dissolves  the  precipitate. 
The  oxide  may  then  be  dried  with  a  gentle  heat,  which,  if  in- 
creased, will  expel  water  of  hydration  and  leave  anhydrous  oxide. 
If  an  attempt  be  made  to  accelerate  the  crystallization  of  the 
sulphate  by  concentrating  the  solution  by  heat,  a  change  occurs 
similar  to  that  of  the  corresponding  salt  of  manganese,  (viz.) 
the  formation  of  an  insoluble  subsulphate  of  a  greenish  white 
color,  into  which  the  sulphate  will  change  entirely  by  continued 
ebullition ;  more  or  less  of  the  subsalt  is  formed  during  the 
spontaneous  crystallization  of  the  neutral  subsulphate.  It  adheres 
slightly  to  the  crystals,  but  may  be  washed  away  by  agitation 
with  a  little  water.  Metallic  nickel  is  readily  oxidated  by  nitric 
acid  with  the  production  of  a  nitrate.  The  solution  of  the 
nitrate  gradually  changes  by  exposure  to  the  air  more  quickly 
at  an  elevated  temperature,  and  an  insoluble  gelatinous  sub- 
nitrate  is  formed,  more  difficult  to  separate  from  the  neutral  salt 
than  the  corresponding  subsulphate. 
But  it  is  objectionable  to  form  a  nitrate  from  the  metal,  on 
account  of  the  difficulty  in  separating  iron,  if  it  should  be  present, 
which  not  being  thrown  down  by  sulphuretted  hydrogen,  cannot 
be  precipitated  as  in  the  sulphate  by  carbonate  of  lime,  without 
the  production  of  a  nitrate  of  lime  more  difficult  to  dispose  of 
than  the  iron  salt. 
A  better  plan  is  to  oxidize  the  metal  by  mixing  it  in  powder, 
with  two  parts  of  nitre  and  one  of  carbonate  of  potash,  then 
fusing  them  together  in  a  crucible  at  a  red  heat,  until  nitrous 
acid  fumes  cease  to  be  given  off.  The  mass,  when  cold,  is 
powdered  and  washed  to  separate  the  potash  and  any  arsenical 
compounds,  and  the  oxides  dissolved  in  dilute  sulphuric  acid, 
treated  with  carbonate  of  lime  to  separate  the  iron,  with  sul- 
phuretted hydrogen  to  precipitate  copper,  and  then  either  pre- 
cipitate the  nickel,  or  crystallize  by  spontaneous  evaporation. 
From  the  precipitated  oxide  all  the  salts  of  Nickel  may  be 
obtained. 
