464 CLAYS AND CLAY INDUSTRY. 



As pointed out in Chapter XIII, however, some of the clays 

 used in hollow ware and conduit mixtures are a low grade of 

 fire clay and these are discussed under "Semirefractory clays." 

 A number of samples were collected for testing at different local- 

 ities and are taken up in their geographic order. 



Woodbridge. — Hollow-brick clays are dug in both W. H. 

 Cutter's pits (Loc. 29) and J. H. Leisens pit (Loc. 16) near 

 Woodbridge, but no tests were made of them. A considerable 

 quantity has also been dug at Spa Spring from a pit (Loc. 33) im- 

 mediately west of the works of the Staten Island Clay Co. 



North side of the Raritan river. — This same class of clay is 

 dug at several points not far distant from the river, especially 

 east and west of Florida Grove, and northwest of Keasbey. 

 They belong to the laminated clay and sand series in the upper 

 part of the Woodbridge clay bed, and are dark, thin-bedded clays, 

 usually with much finely divided carbonaceous matter, mica 

 scales and scattered lumps of pyrite, limonite and lignite. While 

 the clays usually show this impure character throughout the bank, 

 there are at times layers which are less gritty and contain fewer 

 impurities than are found in other parts of the bank. 



A test made on a sample from the bank of the National Fire- 

 proofing Company at Perth Amboy gave the following results. 

 Clay laminated, bluish black, with considerable mica and scattered 

 lumps of pyrite and limonite. Air shrinkage 5 per cent. ; average 

 tensile strength, 145 pounds per square inch. It behaved as fol- 

 lows in burning : 



Burning tests of a fire proofing clay, National Fireproofing Co. 



Cone 05 01 3 15 



Fire shrinkage, 1.6% 2% 2.9% viscous 



Color, grayish red red red 



Condition, not steel-hard steel-hard steel-hard 



Another sample from Keasbey (Lab. No. 451) behaved simi- 

 larly. Air shrinkage, 5.5 per cent. ; average tensile strength, 112 

 pounds per square inch. Behavior in burning: 



