CLAYS OF MIDDLESEX COUNTY. 465 



Burning tests of a fire-proofing clay, Keasbey. 



Cone 05 01 



Fire shrinkage, 2.5% 



Color, reddish red 



Condition, not hard steel-hard 



As an illustration of the variation in some deposits, two ex- 

 amples may be taken from a bank of the National Fireproofing 

 Company near Keasbey (Loc. 46). The first represents a black 

 "flue clay," which is used for making fireproofing and hollow 

 brick. The second, termed "bottom pipe clay," is found in the 

 lower portion of the bank, and is used in the mixture for conduits. 



The flue clay forms the greater portion of the bank and is less 

 dense burning than the pipe clay, which fact is shown by the dif- 

 ference in shrinkage and absorption of the bricklets. It is more 

 sandy than the pipe clay, but has a higher tensile strength. The 

 flue clay slakes quite fast and works up with 28 per cent, of water 

 to a mass of good plasticity, whose air shrinkage was 4 per cent., 

 and whose tensile strength ranged from 75 to 100 pounds per 

 square inch. Its burning qualities were as follows : 



Burning tests of a flue clay, National Fireproofing Company, Keasbey. 

 Cone. 3 5 



Fire shrinkage, 7-3% 12% 



Absorption, . ... 8.81% 6.10% 



Color, brownish red dark gray 



The bottom or pipe clay is much denser and finer grained than 

 the upper clay. It feels plastic but its tensile strength was low, 

 running from 50 to s 55 pounds per square inch. It slaked 

 moderately fast in water and required 30 per cent, to temper. 

 The air shrinkage of the bricklets was 6 per cent. Its chief value 

 lies in the dense-burning quality which it possesses, but it has to 

 be heated slowly on account of the large amount of organic matter 

 contained in it. Its behavior in burning was as follows : 



Burning tests of a pipe clay, National Fireproofing Co., Keasbey. 

 Cone 1 3 5 



Fire shrinkage, 7-3% 9% 9-3% 



Absorption, 1.58% 1.00% 0.78% 



Color, light brown red gray 



30 CL G 



