FIRE CLAYS. 139 



be counteracted to a large extent by the addition of 

 quartz and it would also be necessary to mix it with 

 some plastic clay, if it was to be molded when wet. 



No. 2. This is similar to No. 1 in its color and tex- 

 ture. It is however much more plastic than the 

 other although it only required 31.25 per cent, of 

 water to mix it, the tensile strength however is very 

 low, and in this case bears no relation to the plastic- 

 ity, the air shrinkage of the clay is 3 per cent; at 

 about 2200 F., the total shrinkage was 10 per cent, 

 and the bricklet was still absorbent although incipient 

 fusion had just begun, while the color was yellowish 

 white; at about 2250 F., the total shrinkage was 14 

 per cent., the bricklets had an absorption of about 5.7 

 per cent, and the color still a yellowish white. At 

 about 2300 F. the total shrinkage was 16 per cent., 

 the absorption only 2 per cent, while its color was a 

 very f ain<t yellowish gray ; the total shrinkage was 17 

 per cent, at 2400 F., and the bricklet which appeared 

 nearly vitrified, was gray in color. 



In the Deville furnace at cone 30, the form of the 

 clay was still perfectly sharp, and while it was thor- 

 oughly vitrified it showed no evidence of becoming 

 viscous. 



The rational composition of the clay was : 



Clay substance^ 94.54 



Quarts 5.80 



Ferric oxide .26 



No. 3. This is likewise a white clay but one con- 

 taining much fine grit, not very porous, and slaking 

 quickly to a powder. It is also a very plastic clay, 

 and took 36.50 per cent, of water to work up, but the 

 tensile strength again is very low, being not over 5 

 pounds. The air shrinkage was 3 per cent. ; at about 



