POTTERY OR STONEWARE CLAYS. 177 



The compositioa of this clay is: 



Analysis of Clay, Henry Co., Ho. 



Silica 67.49 



Alumina 21.11 



Water 5.95 



Ferric oxide 2.45 



Lime . . . .* .17 



Magnesia .63 



Alkalies 2.83 



100.63 



Total fluxes 6.08 



Specific gravity 2.23 



The shrinkage in both drying and burning is sx per 

 cent, and the tensile strength in 110 on the average, with 

 a maximum of 127. Incipient fusion begins at 2000° F. 

 complete vitrifir ation at 2300°F., and viscosity at 2400° F. 



(No. 68 S.) 



POTTEKY CLAY (REFRACTORY). 



SHIELEY 8 MILL, PAYETTE CO. 



A fine grained, compact clay, with lit' le coarse grit, but 

 considerable fine sand. Color drab. It slakes very 

 slowly to scaly grains. 



Three per cent, of water were required to make a work- 

 able paste which was quite plastic. This paste shrunk 

 10 per cent, in drying and 4 per cent, in burning, giving 

 a total shrinkage of 14 per cent. 



The tensile strength of the air dried briquettes showed 

 an average of 106 lbs. per square inch, and a maximum 

 of 123 lbs. 



The clay burns to a yellowish white body. Incipient 

 fusion occurs at 2000° F., vitrification at 2200° F., and 

 viscosity at 2400° F., The composition of the clay is as 

 given below: 



