CLAYS OF MIDDLESEX COUNTY. 439 



HIGHLY REFRACTORY CLAYS. 



Clays which are sufficiently refractory to merit this classifica- 

 tion are found chiefly in the Woodbridge clay bed, and mostly in 

 the vicinity of Woodbridge. Two- grades are dug, No. 1 fire clay 

 and ball or ware clay, but not all the clays known by these trade 

 terms can rightfully be called highly refractory. 



Fire clays. — At the middle or base of the section in many pits, 

 there are often two grades of fire clay, known to the miners as the 

 No. 1 and No. 2. The No. 1 is generally a fat, bluish clay, while 

 the No. 2 is commonly mottled red and white, yellow and white, 

 or sometimes bluish, but differing usually from No. 1 in being 

 more sandy. 



The character of the No'. 1 fire clay found in the different pits 

 varies somewhat, especially in point of refractoriness, as is shown 

 by the detailed tests given below. 



No. 1 fire clay is used in the manufacture of the best grades of 

 fire brick, and there is consequently considerable demand for the 

 material. Some of the No. 1 fire clays are also sold for saggers, 

 the producers claiming to receive from $3.00 to< $3.50 per ton for 

 it. The supply of it is rather limited in the region around Wood- 

 bridge, and this is unfortunate, since it represents the most re- 

 fractory type of clay found in Middlesex county, or even in New 

 Jersey. As the Woodbridge fire-clay bed is followed to the south- 

 westward it is found that the No. 1 clays drop off considerably in 

 their fire-resisting qualities. 



Detailed tests. — No. 1 fire clay, from pit of M. D. Valentine & 

 Bros. Company (Loc. 14). This is a bluish clay (Lab. No. 382) 

 with very little grit, even texture and smooth fracture, passing 

 entirely through a 100-mesh sieve and slaking fairly fast. The 

 air shrinkage was 7 per cent, when tempered with 25 per cent, 

 of water, but the briquettes invariably cracked in drying, so that 

 it was impossible to measure their tensile strength. The burning 

 tests were as follows : 



Burning tests of No. i tire clay. M. D. Valentine & Bros. Co., Woodbridge. 

 Cone 3 5 10 



Fire shrinkage, 5.5% 6.5% 13% 



Absorption, 24.25% 19-65% 7-76% 



Color, nearly white whitish light buff 



