SULPHUR  FOR  OIL  OF  VITRIOL  OR  SULPHURIC  ACID.  433 
Theoretically,  100  parts  of  pure  sulphur  should  yield  306  25 
parts  of  oil  of  vitriol,  and  in  practice  it  is  found  that  100  parts 
of  brimstone,  containing  one  per  cent,  of  impurity,  can  be  made 
to  yield  302  parts  of  acid,  while  with  pyrites  the  acid  produced 
only  amounts  to  285  parts  of  the  sulphur  actually  burned,  or 
275  parts  on  the  sulphur  actually  present  in  the  ore. 
The  author  then  referred  in  detail  to  the  several  sources  from 
which  the  required  sulphur  is  obtained.  He  spoke  of  them  in 
the  following  order,  and  illustrated  his  remarks  by  a  very  exten- 
sive collection  of  specimens  : — 
Sicilian  Sulphur. — This  is  found  chiefly  in  the  volcanic  dis- 
tricts on  the  south  coast  of  Sicily,  more  or  less  pure,  and  im- 
bedded in  lime  and  clay  marl.  It  is  extracted  from  the  crude 
mineral  in  various  ways,  according  to  the  richness  of  the  mate- 
rial. If  the  mineral  is  very  rich,  it  is  simply  melted  in  a  cast- 
iron  pot,  and  then  the  liquid  sulphur  is  ladled  out  into  moulds  ; 
but  if  the  mineral  is  poor  in  sulphur — some  kinds  containing 
only  15  to  20  per  cent. — it  is  distilled  in  earthen  retorts,  and 
usually  condensed  in  water.  As  imported  into  this  country  it 
consists  of  three  qualities — 46  firsts,"  "  seconds,"  and  "thirds." 
The  latter  only  is  used  in  making  oil  of  vitrol,  the  others  are  re- 
fined for  making  gunpowder. 
Spanish  Pyrites. — In  the  author's  opinion,  this  mineral  claims 
the  first  attention,  owing  to  its  forming  at  least  one  half  of  all 
the  pyrites  burnt  in  the  sulphuric  acid  manufacture.  It  is 
found  chiefly  in  the  province  of  Huelva ;  the  deposits  pass, 
however,  from  Spain  into  the  adjoining  part  of  Portugal.  Some 
of  the  deposits  are  nearly  a  mile  long,  of  great  depth,  and  of 
varying  width.  Till  lately,  the  great  bulk  of  pyrites  imported 
was  brought  chiefly  from  Mr.  Mason's  mines,  near  the  river 
Gaudiana.  The  owner  was  the  first  person  to  construct  a  rail- 
way as  a  means  of  transport  from  the  mines  to  the  coast,  in- 
stead of  the  antiquated  and  expensive  method  of  mule  carriage. 
Mules  are  still  employed  at  all  the  other  mines,  and  the  mineral 
is  carried  in  sacks  or  baskets  on  the  mules'  backs.  A  few  years 
since,  the  Tharsis  Mining  Company,  consisting  chiefly  of  Glas- 
gow capitalists,  was  formed  to  purchase  and  work  a  number  of 
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