284 CLAYS AND CLAY INDUSTRY. 



The clays used are similar to those employed for making fire- 

 proofing, although they are somewhat more carefully selected 

 with regard to plasticity and freedom from pyrite and limonite 

 lumps. They must also burn dense at a moderate temperature. 



The conduits are molded in auger stiff-mud machines. They 

 are then removed from the cutting table on a pallet, and placed 

 on a stand (PI. XXXIV, Fig. i), where the ends are trimmed 

 smooth before the pieces are taken to the drying floor or drying 

 tunnel. In drying the conduits are stood on end. The burning 

 is commonly done in down-draft kilns, between cone 8 and 9, al- 

 though some manufacturers burn lower than this. The average 

 shrinkage that takes place in a long conduit is about as follows : 

 Length freshly molded, 39 inches; length air dried, 37^4 inches; 

 length burned, 35 inches. 



New Jersey conduit industry. — There has been a great demand 

 for conduits in the large eastern cities during the last two years, 

 many being used in New York city especially, in the construction 

 of the rapid transit subway, so that the following large plants 

 have been running almost exclusively on this line of work : 



The National Fireproofing Company, Standard plant, Perth Amboy; 

 The National Clay Manufacturing Company, at South River ; 

 The Globe Fireproofing Company, at Clayville. 



Conduits are also occasionally made at the fireproofing fac- 

 tories. 



