POTTERY OR STONEWARE CLAY 8. 167 



The tensile strength was on the average 154 pounds, 

 with a maximum of 170 pounds. 



The air shrinkage amounted to 8.1 per cent.; at about 

 2200 F. the total shrinkage was 14 per cent., the clay at 

 this temperature having burned nearly dense, and the 

 brick being a brown gray color; at'about 2300 F. the 

 total shrinkage was 15 per cent., the brick was very hard, 

 homogeneous, dense, and still of a brownish gray color 

 though somewhat darker; at 2500 F. the brick was thor- 

 oughly vitrified, and showed a slight swelling, the shrink- 

 age at this temperature being only 13.5 per cent, and the 

 color remained unchanged except that it was slightly 

 darker in shade. A test made of this clay in the Deville 

 furnace showed that at cone 26 it had become viscous. 



The composition of the clay is as follows : 



Analysis of Stoneware Clay, Coosada, Elmore Co. 



Silica 86.61 



Alumina 21.04 



Ferric oxide 2.88 



Lime 40 



Magnesia ' .58 



Alkalies 70 



Water.. 7.00 



Total fluxes . 



(No. 1 S.) 

 POTTERY CLAY. 



H. H. CRIBBS, TUSCALOOSA, 



This is a whitish, fine grained clay with small amounts 

 of grit, which slakes easily to small irregular grains and 

 scales ; it required 25 per cent, of water to mix it and 

 gave a moderately plastic mass whose air shrinkage was 6 

 per cent, and fire shrinkage 4 per cent., giving a total 

 shrinkage of 10 per cent.; briquettes made of this paste 



