214 CLAYS AND CLAY INDUSTRY. 



Engineering works. — Puddle; Portland cement; railroad bal- 

 last; water conduits; turbine wheels; electrical conduits; road 

 metal. 



Nearly all of the more important products are made in New 

 Jersey, and these branches of the industry are treated in some 

 detail in the following- pages. 



Classification of clays based on uses.^Cldiys are sometimes 

 classified according to their uses into the following groups : 



Kaolins or China clays. — Those burning white and used in 

 manufacture of white earthenware or porcelain. 



Fire clays. — Buff-burning clays of refractory character used 

 chiefly for fire brick. 



Stoneware clays. — Semirefractory clays, which burn to a dense 

 body and possess good plasticity and tensile strength. 



Pipe clays. — Nonrefractory clays, of good plasticity, and which 

 are vitrifiable. 



Brick clays. — Impure clays, usually red-burning. 



These do not by any means represent all the names commonly 

 met with in the clay-working industries. For this reason it may 

 be well to give at least the more important ones below. 



Kaolins. — A term applied to white-burning residual clays, used 

 in the manufacture of white earthenware, porcelain, wall tiles, 

 white floor tiles, paper making, etc. 



Ball clays. — White-burning, plastic, sedimentary clays, used 

 chiefly in the manufacture of the fine grades of pottery, viz. : 

 those having a white body. 



Ware clay. — A term applied to ball clays mined near Wood- 

 bridge. 



Fire clay. — A term loosely applied to clays considered suitable 

 for making fire brick. No standaid of refractoriness has been 

 adopted in this county, and many clays are called fire clays which 

 have absolutely no right to the name. Fire clays are often 

 classed as No. I and No. 2 grades. Since the term is so* loosely 

 used, and, furthermore, as even in New Jersey there is no uniform 

 usage of the name, in this report the fire clays have been grouped 

 as highly refractory, refractory, semirefractory (p. 100), and no 

 clay fusing below cone 27 is considered a fire clay. The terms 

 No. 1 and No. 2, when used, refer to the designations given by 



