PREPARATION  OF  HEAVY  CALCINED  MAGNESIA. 
195 
ing  to  dry  the  precipitate  it  fell  into  granules,  very  hard  and  gritty, 
which  could  not  be  reduced  even  by  long  trituration  to  a  fine  con- 
dition. 
(/.)  Having  experienced  much  difficulty  in  the  experiments  with 
Epsom  salts,  on  account  of  the  iron  which  it  contained  contami- 
nating the  products  of  its  decomposition,  I  tried  in  the  last  process, 
(e),  to  free  it  from  that  impurity  by  the  following  method.  I  first 
made  a  boiling  hot  solution  of  sulphate  of  magnesia,  to  which  was 
added  a  sufficient  quantity  of  carbonate  of  soda  to  form  a  small 
amount  of  carbonate  of  magnesia,  expecting  that  the  iron  would 
go  down  with  the  precipitate  and  thus  be  separated,  which,  how- 
ever, was  but  partially  the  case. 
Second  Series  of  Experiments. 
•Being  dissatisfied  with  the  results  obtained  from  the  foregoing 
experiments,  I  determined  to  try  the  feasibility  of  producing  a 
magnesia  of  good  quality  by  the  decomposition  of  chloride  of  mag- 
nesium by  heat.  The  following  quantities  I  found  convenient  to 
operate  upon : 
Take  of  Hydrochloric  acid,  (of  commerce,)  two  pints. 
Nitric  acid,  a  fluid  ounce. 
Water,  half  a  pint. 
Carbonate  of  magnesia,  a  sufficient  quantity. 
Mix  the  hydrochloric  acid  and  water  together  and  saturate  the 
dilute  acid  thus  formed  with  the  carbonate  of  magnesia.  Put  the 
solution  in  a  capsule  of  porcelain  over  a  slow  fire,  and  when  it  ap- 
proaches the  boiling  point  add  the  nitric  acid,  and  boil  the  whole 
for  ten  minutes.  An  excess  of  carbonate  of  magnesia  in  powder 
is  then  to  be  added  to  completely  neutralize  the  nitric  acid.  The 
solution  is  to  be  boiled  a  few  minutes  longer  and  then  filtered. 
After  filtering  return  the  liquid  to  the  vessel  and  evaporate  with  a 
gentle  heat  to  complete  dryness.  When  the  evaporation  is  com- 
pleted remove  the  mass  from  the  capsule,  and  having  reduced  it  to 
small  fragments,  place  them  in  a  Hessian  crucible  well  glazed  in- 
side. Expose  the  crucible  with  its  contents  to  a  moderate  heat, 
which  gradually  increase  to  a  dull  red.  Continue  the  application 
of  the  heat  for  three  hours  or  until  the  decomposition  is  complete. 
This  process,  which  was  repeated  several  times,  and  varied  in 
some  of  its  details,  furnished  the  specimens  herewith  presented 
