CRYOLITE. 
195 
few,  and  the  ingredients  which  are  used  so  pure  in  themselves, 
that  no  difficulty  exists  in  obtaining  these  chemical  products  in 
quantities  of  hundreds  of  tons,  and  in  a  state  of  almost  absolute 
purity,  that  were  before  considered  of  impossible  attainment  in 
quantities  greater  than  those  which  could  be  obtained  in  an 
analytical  laboratory. 
In  order  to  separate  the  alumina  and  soda,  the  following  pro- 
cess must  be  resorted  to  ;  and  for  the  extraction  of  the  soda,  and 
the  manufacture  of  its  carbonate  and  separation  of  the  alumina, 
the  so-called  dry  process  is  used.  This  consists  first  in  grinding 
together  under  vertical  mill-stones  or  chasers,  a  mixture  composed 
of  one  equivalent  of  cryolite  (previously  powdered,  and  sifted 
through  fine  wire  gauze),  along  with  a  little  more  than  6  eq.  of 
carbonate  of  lime,  or  slaked  lime.  This  mixture,  which  must  be 
an  intimate  and  perfect  one,  is  then  exposed  in  quantities,  about 
1000  lbs.  at  a  time,  to  a  low  red  heat  in  furnaces  constructed  in 
a  peculiar  manner,  with  double  fireplaces,  one  at  each  end ;  the 
flame  from  one  passing  under  the  hearth,  and  then  uniting  with 
the  other,  and  both  together  passing  over  the  mixture  of  cryolite 
and  lime,  in  order  that  the  heat  may  be  kept  uniform  throughout 
the  mass.  This,  is  then  continued  for  about  two  hours,  though 
care  must  be  taken  to  avoid  the  materials  fusing  together.  The 
ash  thus  produced  is  taken  out  and  allowed  to  cool,  when  it  is 
then  placed  in  large  iron  leach-tanks,  with  false  bottoms,  and 
leached  with  hot  water  until  all  soluble  matter  is  removed.  Now 
the  insoluble  residue  in  the  tanks  consists  of  fluoride  of  calcium, 
6  eq.,  which  is  dried,  and  has  now  become  an  article  of  great 
value  to  metallurgists  in  reducing  gold  and  other  ores,  and  as 
a  good  flux  for  silicates.  The  solutions  resulting  from  the  leach- 
ing processes  are  collected  into  large  iron  tanks,  and  when  mixed 
together  should  have  the  sp.  gr.  of  about  30°  Baum6\  The  so- 
lution consists  of  equal  quantities  of  aluminate  of  soda,  and  also 
either  carbonate  or  hydrate  of  soda,  as  one  of  the  other  forms  of 
lime  have  been  used. 
In  order  to  separate  the  alumina  and  convert  the  soda  into  the 
carbonate,  the  solution  is  now  pumped  into  large  horizontal 
cylindrical  vessels,  which  are  from  40  to  50  feet  in  length,  and 
are  provided  with  machinery  for  agitating  through  their  contents 
