218 The N.Z. Journal of Science and Technology. [May 
Table VIII. 
Clay 
Fraction 
(per Cent.). 
Sand 
Fraction 
(per Cent.) 
Total 
Tempering- 
material 
(per Cent.). 
Shrinkage (Percentage of 
Original Volume). 
Porosity 
(Percentage of 
Total Volume). 
Air. 
Fire. 
100 
0 
42-2 
17-0 
45-0 
0-9 
Natural 
sample 
55-9 
16-5 
40-5 
11-0 
60 
40 
65-3 
12-5 
40-0 
11-5 
50 
50 
71T 
15-5 
37-5 
17-0 
35 
65 
79-8 
14-0 
33-0 
21-0 
40 50 60 70 80 
Tempering material -*> 
Fig. 4. 
The porosity of the fired samples of the clays under consideration is 
shown graphically in fig. 5. It is obvious that the porosity of a series of 
samples of a given clay decreases as the fire shrinkage increases. 
Fig. 5. 
