1919.] 
Departmental Reports. 
215 
was to take a large sample of the clay after it had been analysed by the 
combined method and to separate it by means of the Schoene elntriator 
into two fractions, the “ clay fraction ” and the “ sand fraction ” 
respectively. These were then reblended in various proportions, the com¬ 
position of the new samples being calculated from the known composition 
of the fractions. 
Samples of the synthetic products were then fired in a Seger gas 
furnace, the temperature of the firing-chamber being recorded by Seger 
cones. In all cases quoted in this paper the temperature was raised until 
cone No. 14 wilted (about 1410° C.), and then the gas was extinguished. 
The results in the case of sample No. 1 are shown in Table IY and 
fig. 1. It is seen that the fire shrinkage is approximately inversely 
proportional to the amount of the tempering-material in the mixture. 
The reason for the air shrinkage increasing again above 60 per cent, of 
the tempering-material has not ye been investigated. By “ tempering- 
material ” is meant all material in the mixture other than the actual clay. 
Table IV. 
Clay Fraction 
(per Cent.). 
Sand 
Fraction 
(per Cent.). 
Total 
Tempering - 
material 
Shrinkage (Percentage of 
Original Volume). 
Porosity 
(Percentage 
of Total 
(per Cent.). 
Air. 
Fire. 
Volume). 
75 
25 
35-1 
20*5 
28-5 
6-3 
45 
55 
611 
17-0 
11-5 
30-5 
30 
70 
74-0 
22-0 
0-0 
34-0 
50 40 50 60 70 20 
Tempering material 
Fig. 1. 
