Another  process  has  been  patented  (Barlow
&  Gore,  1851)  for  the  manufacture  of  alum
from  the  ash  or  residue  of  the  combustion  of
Boghead-coal,  which,  though  hitherto  re-
garded as  almost  valueless,  actually  contains
about  30J  of  alumina.  It  has  not,  however,
been  found  a  convenient  material  for  the  pur-
pose.
By  the  latest  and  most  approved  processes
the  least  possible  quantity  of  boiling  water  or^
liquor  is  employed  for  making  the  solutions,  so
that  they  may  crystallise  without  evaporation,
and  thus  economise  fuel;  and  the  mother-
liquors  of  previous  operations  are  constantly
employed  for  this  purpose,  when  possible.  Nor
is  anything  which  is  convertible  to  use,  from
tile  drainage  of  the  heaps,  to  the  liquor
and  slime  of  the  reaching  casks,  allowed  to  be
wasted.
By  whatever  process,  or  from  whatever
materials  alum  is  obtained,  it  is  absolutely
necessary  for  the  successful  and  economical
conduct  of  its  manufacture,  that  the  precise
composition  of  the  mineral  or  minerals  em-
ployed should  be  exactly  known.  This  can
only  be  determined  by  actual  analysis,  which
should  be  extended  to  several  parts  of  the
same  bed,  and  particularly  to  the  upper  and
lower  strata,  which  frequently  differ  in  com-
position from  each  other,  and  thus  require
different  treatment,  or  may  be  most  advan-
tageously employed  in  combinations  with  each
other.  The  necessity  of  this  will  be  seen  by
reference  to  the  composition  of  the  following
minerals,  of  which  the  top  contains  a  larger
proportion  of  iron-pyrites  than  the  bottom,
and  the  two  require  to  be  mixed,  to  equally
diffuse  the  sulphuric  acid  generated  by  the
calcination,  &c.,  to  which  they  are  subjected.
The  following  is  the  per-centage  composition
of  certain  alum  shales  : —


Wlntby,  Yorkshire.
Camp

sie,  near  Glasgow.          |

{^Richardson.)

(Ranaldl.)

*

Top  rotk.
Bottom
rock.
Top  rock.
Top  rock.
