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MANUFACTURE  OF  ULTRAMARINE. 
ON  THE  MANUFACTURE  OF  ULTRAMARINE. 
By  J.  G.  Gentele. 
The  author  has  given  a  description  of  the  manufacture  of  ultra- 
marine, of  which  the  following  is  an  abstract. 
The  manufacture  consists  of  two  parts. 
I.  The  preparation  of  green  ultramarine. 
II.  The  conversion  of  green  ultramarine  into  blue. 
I.  Preparation  of  green  Ultramarine. — The  raw  materials  at 
present  in  use  are, — 
1.  An  alumina  silicate  (kaolineV 
2.  Calcined  sulphate  of  soda. 
3.  Calcined  carbonate  of  soda. 
4.  Sulphide  of  sodium. 
5.  Sulphur. 
6.  Charcoal  or  coal. 
As  an  alumina  silicate,  kaoline  is  used,  or  a  white  clay  with  a 
similar  composition.  A  certain  admixture  of  lime  and  mag- 
nesia is  not  injurious,  but  a  greater  quantity  of  oxide  of  iron 
than  1  per  cent,  is  objectionable.  The  clay  is  elutriated  in 
order  to  separate  it  from  mechanical  impurities  as  much  as  pos- 
sible. The  elutriated  clay  is  dried  and  ignited,  and  it  is  then 
easily  reduced  to  a  fine  powder. 
Sulphate  of  soda  and  carbonate  of  soda  are  obtained  sufficiently 
pure  from  the  chemical  manufactories  ;  both  are  powdered  and 
sieved.  In  cases  where  the  sulphide  of  sodium  is  obtained  in 
the  liquid  form,  it  is  evaporated  in  cast-iron  pots,  or  iron  pans, 
and  the  residue  powdered.  In  using  it,  it  is  calculated  as  mono- 
sulphide  of  sodium.  Roll-sulphur  is  used  and  is  kept  in  stock 
in  the  form  of  fine  powder. 
Wood-charcoal  or  coal  are  used ;  of  the  latter,  a  non-caking 
coal,  and  one  that  leaves  little  ash,  is  preferred.  Both  sorts  of 
carbon  are  finely  powdered  before  being  used.  In  preparing  the 
mixture,  it  is  essential  not  only  that  the  substances  be  in  the 
right  proportions,  but  also  that  they  be  very  intimately  mixed. 
With  dry  materials  the  substances  are  weighed,  then  well  mixed 
in  a  trough  by  means  of  a  shovel  and  sieved,  and  the  shoveling 
and  sifting  frequently  repeated.  Where  solutions  of  sulphate  of 
soda,  carbonate  of  soda,  and  sulphide  of  sodium  are  used,  the 
