546  REGENERATION  OF  PURE  SULPHUR,  ETC. 
traction ;  the  mass  is  broken  up,  further  exposed  to  the  air 
for  24  hours,  and  then  exhausted  by  lixiviation,  in  three 
basins  of  brickwork  or  iron  so  that  concentrated  solutions  are 
obtained.  The  residues  are  further  oxidized  either  in  ditches 
3  feet  in  width  and  depth,  or  better  by  passing  the  gases  of 
a  chimney,  by  means  of  a  ventilator,  under  the  false  bottom  of 
the  exhausting  vessels.  In  the  latter  case  the  oxidation  is  com- 
pleted in  10  to  12  hours ;  more  hyposulphites  are  formed  than 
in  the  ditches  and  much  labor  is  saved.  The  chimney  gases, 
consisting  mainly  of  water,  carbonic  acid  and  warm  air,  are  well 
adapted  to  transform  sulphuret  of  calcium  into  polysulphuret  and 
hyposulphite.  This  oxidation  may  be  repeated  three  or  four  times, 
according  to  the  nature  of  the  soda  residues.  Too  long  continued 
oxidation  will  produce  free  sulphur  and  sulphite,  finally  sulphate. 
The  latter  will  occasion  a  loss  of  sulphur  ;  the  free  sulphur  will 
be  taken  up  by  the  concentrated  liquors. 
The  decomposition  of  the  liquors  is  effected  in  close  stone  or 
iron  vessels  by  muriatic  acid ;  CaOSgOg  +  HCl  yield  CaCl  -f 
SO2  +S  +  HO,  and  2CaS^  +  380^  yield  2CaOSA  +  S^. 
On  adding  muriatic  acid  to  the  liquor  in  the  first  vessel,  the 
polysulphurets  are  first  decomposed  with  the  separation  of  sul- 
phur and  the  extrication  of  sulphuretted  hydrogen  ;  more  mu- 
riatic acid  will  decompose  the  hyposulphite,  precipitate  sulphur 
and  liberate  sulphurous  acid  which  is  conducted  into  the  liquor 
of  the  second  vessel,  wherein  it  forms,  with  the  polysulphurets, 
free  sulphur  and  hyposulphite.  The  first  vessel  is  heated  by  in- 
jecting steam  to  drive  over  all  sulphurous  acid,  the  exhausted 
liquor  is  drawn  off  and  the  sulphur  collected,  after  which  the 
vessel  is  filled  with  a  new  portion  of  sulphur  liquor.  Now  the 
decomposition  of  the  liquor  in  the  second  vessel  is  effected  in 
the  same  way  :  however,  the  polysulphurets  having  been  com- 
pletely converted  into  hyposulphites,  no  sulphuretted  hydrogen 
is  given  off,  but  sulphurous  acid  which  is  conducted  into  the  fresh 
sulphur  liquor  in  the  first  vessel.  If  properly  conducted,  after 
the  first  decomposition,  neither  sulphuretted  hydrogen  nor  sul- 
phurous acid  must  escape  into  the  atmosphere.  The  sulphuret 
and  hyposulphite  in  the  sulphur  liquor  are  estimated  by  titra- 
tion, and  accordingly  the  soda  residues  are  oxidized  more  or 
less. 
