432      SULPHUR  IN  OIL  OF  VITRIOL  OR  SULPHURIC  ACID. 
about  5  per  cent,  of  sulphur  on  the  average,  so  that  there  is 
actually  burned  off  86  per  cent,  of  the  sulphur  of  the  Irish  ore, 
and  89  per  cent,  of  that  contained  in  Spanish  ore  of  45  per 
cent,  strength,  thus  giving  a  clear  gain  of  3  per  cent. 
Mr.  Mactear  then  referred  to  certain  disadvantages  attending 
the  use  of  pyrites  instead  of  Sicilian  sulphur  : — 
First.  A  greater  amount  of  chamber  space  is  required  for 
burning  pyrites  than  for  sulphur.  This  is  usually  taken  to  be 
in  the  ratio  of  45  to  30,  and  is  due  to  the  fact  that  the  iron  of 
the  ore  is  peroxidised  during  combustion,  and  therefore  uses 
extra  oxygen  and  nitrogen  (which  passes  on  unchanged)  ;  and 
for  the  extra  amount  of  both  of  these  gases  chamber  space  must 
be  provided. 
Second.  The  arrangements  for  burning  pyrites  are  much  more 
closely  than  for  burning  sulphur ;  the  heat  is  greater,  and 
therefore  there  is  more  wear  and  tear  of  the  chambers  and  con- 
necting-pipes. 
Third.  There  is  always  a  larger  percentage  of  nitre  required 
with  pyrites  than  with  brimstone. 
Fourth.  Owing  to  various  causes,  the  acid  produced  is  of  in- 
ferior quality. 
Fifth.  It  involves  more  labor  to  work  pyrites  than  to  work 
brimstone  ;  and  there  is  a  large  amount  of  refuse — approxi- 
mately three-fourths  of  the  weight  of  the  raw  ore— for  which 
room  has  to  be  provided. 
Sixth.  In  burning  pyrites,  and  during  transit,  much  small  is 
made,  and  this  cannot  be  burned  properly  unless  in  a  separate 
furnace.  The  most  common  form  is  a  muffle  furnace  ;  in  it  the 
4'  smalls  "  are  roasted,  wTith  free  admission  of  air,  but  the  quan- 
tity passed  into  the  chamber  is  so  great,  in  proportion  to  the  sul- 
phur, that  this  method  is  objectionable. 
Taking  all  these  disadvantages  into  account,  it  is  found  that, 
in  making  ordinary  sulphuric  acid,  one  ton  of  sulphur,  in  the 
form  of  pyrites,  costs  only  X4  10s.,  while  Sicilian  sulphur  costs 
from  <£6  to  £7.  The  ore  is  usually  sold  at  so  much  per  cent,  of 
sulphur  per  ton ;  for  some  years  the  rate  was  Is.  per  unit,  at 
present  it  is  8d. 
