Analyses  of  Stourbridge  Clay.

Sillca.

Alumina.

Peroxide  Iron.

Alkalies,  loss,
etc.

1,
2
3
4
5,
6
7
8,
9,

66.47
65.65
65.50
67.00
63.42
65.08
65.21
58.48
63.40

26.26
26.59
27.35
25.80
31.20
27.39
27.82
35.78
31.70

6.63
5.71
5.40
4.90
4.70
3.98
3.41
3.02
3.00

.64
2.05
1.75
2.30
.68
3.55
3.56
2.72
1.90

.  —  ■—  '.

Limit.  Grover  very  justly  points  out  "  that  the  infusibility
  of  any  substance  depends  not  merely  upon  the  Chemical ­
  nature  of  its  constituents,  but  also  upon  the  manner
in  which  those  constituents  are  combined  with  one  another.
For  example,  granite  per  se  is  infusible  at  ordinary  high
temperatures,  whilst  pounded  granite  can  bo  rcadily  melted
by  the  same  degree  of  heat.  Thus  it  would  seem  that  a
porosity  in  structure,  brought  about  by  a  coarseness  of  elementary
  particles,  would  enhance  the  chemical  infusibility
of  a  material;  and  that  in  fire-clay  goods  a  close  uniform
structure,  though  pleasing  to  the  eye,  is  not  favorable  to
their  refractory  powers,  since  the  component  particles
should  have  a  facility  for  contraction  or  expansion  under
hiffh  temperature,  and  the  air  cavities  act  as  valuable  nonconductors
  of  heat.  Hence  it  will  be  evident  that  to  determine
  accurate  conclusions  respecting  these  wares,  a  fire
fest  is  as  essential  as  chemical  aualysis.