444 CLAYS AND CLAY INDUSTRY. 



Some of these, especially No. 3, agree very closely with analyses 

 recently made and given on a previous page. 



REFRACTORY CLAYS. 



According to our classification, this group includes those clays, 

 the fusion point of which ranges from cone 31 to 33 inclusive. 

 It includes a large number from all the clay members of the 

 Raritan formation except the Cliffwood clays, which are nonre- 

 fractory. They are used for a variety of purposes, and are 

 known by various names, some denoting refractoriness, as No. 1 

 fire clay, No. 2 fire clay; some their possible uses, as stoneware 

 clay, retort clay, pipkin clay, ball clay ; some their texture, as top- 

 sandy, extra top-sandy, etc. There is no fixed rule in regard to 

 the use of these names, clay which by one man is called a No. 2 

 fire clay, being termed a stoneware clay by another, and some of 

 the so-called No. 1 fire clays, when judged according to their re- 

 fractoriness, being more correctly No. 2. In the following de- 

 tailed description of tests the clays are grouped under three heads, 

 fire clays, ball clays, stoneware clays. 



Fire Clays. 



Woodbridge. — Many occurrences of fire clays (fusing at cone 

 31 to 33 inclusive are found in the pits around Woodbridge. 

 Most of them fuse between cones 31 and 32, although they show 

 a wider range in their refractoriness than the highly refractory 

 clays of the same district. Tests were made on several samples 

 as follows : 



Anness & Potter (Loc. 6, Lab. No. 372). The material is a 

 light-gray, mottled, sandy clay which slakes rather fast. It took 

 29.5 per cent, of water to> temper it, and gave a mass of only mod- 

 erate plasticity, the tensile strength of which was low. The air 

 shrinkage was 5.5 per cent. Its behavior under fire was as fol- 

 lows : 



Burning test of a sandy clay, Anness & Potter, Woodbridge. 

 Cone 3 

 Fire shrinkage,.... 5.5 % 



Absorption, 15.87% 



Color, cream white 



Cone 5 



Cone 8 



Cone 10 



5-5 % 



8.5 % 



10.5 % 



16.85% 



10.54% 



10.04% 



yellowish 



yellowish 



yellowish white, 



white 



white 



small iron specks 



