CLAYS OF MIDDLESEX COUNTY. 461 



fountf to be thoroughly vitrified at cone 2.7 and became viscous at 

 cone 30. It therefore stands intermediate in refractoriness be- 

 tween the No. 2 fire clay given on p. 445 and the fire mortar on 

 p. 458. 



The yellow top clay at Maurer's (Loc. 24, Lab. No. 379, and 

 layer 7 of section on p. 436) is also' a sandy clay, with many small 

 mica scales, but it leaves no residue on a ioo-mesh sieve. It slaked 

 slowly to a powdery mass in water, and in tempering only 16 per 

 cent, of water was needed, giving a gritty mass of low plasticity, 

 the tensile strength of which was 48 pounds per square inch. The 

 air shrinkage was low, being but 3.3 per cent. In burning it be- 

 haved as follows : 



Burning tests of yellow top clay, Henry Maurer & Son, Woodbridge. 



Cone 05 3 8 



Fire shrinkage, soft and underburned i% 3% 



Absorption, 18.20% 14.76% 8.90% 



Color, light red reddish reddish 



At cone 27 it became viscous, so that its refractoriness is not 

 any better than that of fire mortar, and in fact not as good. It 

 is also quite porous when burned. 



A red clay from Such's pits (Loc. 6y, Lab. No. 390) showed 

 very little grit and slaked rapidly in water. It all passed through 

 a ioo-mesh sieve and worked up with 39 per cent, of water to a 

 mixture whose air shrinkage was 4.5 per cent. Its average tensile 

 strength was 65.5 pounds per square inch, and it behaved as fol- 

 lows in the firing : 



Burning tests of a red clay. J. R. Such, Burt Creek. 



Cone 05 3 5 10 



Fire shrinkage, 1.5% 8.7% n.5% 15. 5% 



Absorption, 28.90% 13.59% 8.26% 2.19% 



Color, red red red red 



The clay burned steel-hard at cone 3, and showed small cracks 

 that had developed in firing. Since it contains 5.36 per cent, ferric 

 oxide, it is not highly refractory, but probably belongs in the 

 group of semirefractory clays. 



