Shrinkage. 
216 The N.Z. Journal op Science and Technology. [May 
The results for sample No. 7 are given in Table Y and fig. 2, and show 
the same regular falling-off in both air and fire shrinkage as the proportion 
of tempering-material in the mixture is increased. 
Table V. 
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. 
72 
28 
79*2 
28-0 
17-0 
12*3 
50 
50 
85-5 
24-6 
6-0 
26-0 
30 
70 
91-3 
16-0 
1-0 
32-5 
Tempering material 
In the case of sample No. 3, on the 
other hand (Table VI and fig. 3), it is seen 
that as the proportion of its own tempering 
constituents is increased the shrinkage in 
the fire steadily increases. Eeference to the 
analytical [results on p. 213 explains in 
part this unusual result, for the tempering- 
material is seen to include some 4*6 per 
cent, of alkali earths and iron which act 
as fluxes. Thus the analysis indicates 
important information to the manufacturer 
who is accustomed to regard the increase of 
“[sand ” in his clay as tending to reduce 
the shrinkage in the fire. Obviously much 
depends on the nature of the “ sand.” 
Fig. 2. 
Table VI. 
Clay Fraction 
(per Cent.). 
Sand 
Fraction 
(per Cent.). 
Total 
Tempering- 
material 
(per Cent.). 
Shrinkage (Percentage of 
Original Volume). 
Air. j Fire. 
Porosity 
(Percentage 
of Total 
Volume). 
60 
40 
70-3 
43 
9 
6-5 
50 
50 
75-3 
37 
10-5 
6-5 
30 
70 
85-2 
32 
12-5 
7-5 
