METALLIC  OXIDES  IN  COMMERCIAL  AMMONIA.  163 
is  attained,  because  no  lumps  remain  which  may  be  greener  in- 
ternally than  externally.  After  roasting  again,  washing,  dry- 
ing, and  sifting,  this  ultamarine  will  be  of  the  best  quality.  The 
brighter  sorts  are  mostly  produced  by  the  addition  of  white 
substances. 
In  the  French  roasting-process,  a  sort  of  muffle-furnace  is  used, 
or  reverberatory  furnaces  so  constructed  that  the  flame  cannot 
play  on  the  mixture.  The  ultramarine  is  spread  out  in  a  uni- 
form layer  from  1J  to  2  inches  in  height,  and  heated  with  the 
door  closed  until  a  piece  of  sulphur  thrown  in  immediately 
begins  to  burn.  A  shovelful  of  powdered  sulphur  is  then  added, 
and  the  mass  kept  stirred  with  iron  rakes  until  the  sulphur  is 
burnt  off.  The  operation  is  repeated  until  the  shade  and  in- 
tensity of  the  blue  color  ceases  to  improve. 
When  blue  ultramarine  is  washed  by  displacement,  a  saturated 
sulphate  of  soda  solution  is  obtained,  which  may  be  used  in  the 
manufactory  after  the  iron  has  been  precipitated  by  lime.  Ultra- 
marine by  being  burned  with  sulphur  increases  somewhat  in 
weight,  but  on  washing  loses  a  small  per  centage. 
When  the  washing  has  been  imperfectly  performed,  the  ultra- 
marine gradually  cakes  together  in  the  casks  in  which  it  is  pre- 
served.— Chem.  Gaz.  Jan.  1,  1858,  from  Dingier' 8  Journal. 
NOTE  ON  THE  SOLUBILITY  OF  METALLIC  OXIDES  IN  COM. 
MERCIAL  AMMONIA. 
By  R.  West  Pearson. 
While  preparing  sulphide  of  ammonium,  I  have,  at  various 
times,  observed  a  black  precipitate  to  be  produced  in  the  solu- 
tion. The  physical  appearance  of  the  deposit  rendered  it  pro- 
bable that  sulphide  of  iron  was  the  compound  formed  in  this 
case,  which  assumption  was  confirmed  upon  analysis.  This  fact 
necessarily  implied,  that  iron  existed  in  the  ammonia  used,  and 
recalled  to  mind  a  remark  of  Wittstein,  that  hydrated  ferric 
oxide  is  slightly  soluble  in  caustic  potash.  Schaffner,  it  is  true, 
controverted  this  statement  by  referring  the  iron  found  to  such 
as  was  in  a  finely  divided  state  and  held  in  suspension  merely  ; 
but  the  initial  observation  of  Wittstein  seemed  to  derive  sup- 
