392 CLAYS AND CLAY INDUSTRY. 



variable and in places may form streaks running from 6 to 15 

 inches in thickness, but occasionally thickening out to 4 feet. The 

 material is no doubt equal to a No. 2 sandy fire clay. There is 

 no evidence of pyrite in it, although it might occur in some of the 

 dark lignitic streaks seen in the pits towards the western end 

 of Hylton's excavation. A sample of this clay (Lab. No. 621) 

 gave the following physical tests : Plasticity, fair ; clay, very 

 gritty; water required for tempering, 20 per cent.; air shrinkage, 

 5.3 per cent. ; average tensile strength low, being 65 pounds per 

 square inch. 



Burning tests of fire clay, H. Hylton, Palmyra. 



Cone 



05 



5 



8 



15 



Fire shrinkage, 



1.3% 



1.3 % 



2 % 



2-3% 



Absorption, . . 





14.52% 



12.82% 



8.4% 



Color, 



buff 



buff 



buff 



buff with small 

 black specks 



Hardness, .... 



not steel-hard 



nearly steel-hard 



steel-hard 





At cone 27 the brick was well vitrified, and was viscous below 

 cone 30. These clays show that the material should be classed 

 as a fire clay of medium refractoriness, such as would be used 

 in No. 2 fire bricks, or only in small quantities in a No. 1 brick. 

 Its fire shrinkage is very low, but at the same time it is not dense 

 burning, as can be seen from its absorption at cone 15. Its com- 

 position was as follows: 



Chemical composition of a lire clay, H. Hylton, Palmyra. 



Silica (SiOo), 7772 



Alumina (AI2O3), 15.74 



Ferric oxide (Fe 2 3 ) , 0.49 



Lime (CaO), trace 



Magnesia (MgO), 0.81 



Alkalies (Na-O, K-O), trace 



Ignition, 5.62 



100.38 



Hylton's pits were being worked at the time the earlier New 

 Jersey Clay Report was written (1878), and an analysis is there 

 given of the fine white sand and also of the clay. 



