282 CLAYS AND CLAY INDUSTRY. 



1. Clay from bank of National Fireproofing Company, Keas- 

 bey (Lab. No. 399). 



2. Clay from Sayre & Fisher's pits, Sayreville (Lab. No. 393). 



Method of manufacture. — Hollow blocks and fireproofing are 

 molded on stiff-mud machines, with either a single or double die. 

 The material is previously tempered in a wet pan, as this crushes 

 up the pyrite and sandstone lumps found in many of the clays. 

 Some firms use drying tunnels, while others employ slatted floors, 

 and the burning is done mostly in circular down-draft kilns, al- 

 though one firm uses a continuous kiln. Most of the factories do 

 not burn higher than cone 01, and as the clays used contain much 

 organic matter, the burning has to be done slowly. 



Many of the clays also' contain considerable soluble salts, which 

 come to the surface during drying, but this is of little consequence, 

 as the product is covered up when in the building. The range of 

 shrinkage in drying and burning, as determined at several works, 

 is as follows : 



Shrinkage in drying and burning fireproofing. 

 t Linear. ^ t Cubic. ^ 



Air. Fire. Air. Fire. 



34%-4-3% 3-9%-S-2% n.1%-154% 9.9%-i3-2% 



New Jersey industry. — One of the most interesting statements 

 to be found in the New Jersey Clay Report of 1878, and one 

 which serves well by comparison to show the great strides that 

 have been made in the clay industry of New Jersey, is the follow- 

 ing: "They (the hollow brick) have not been much used in this 

 country. Henry Maurer, of Perth Amboy, has begun their manu- 

 facture, and there is now an opportunity to make a trial of this 

 promising improvement in building materials." 



At the'present day there are nine factories in New Jersey whose 

 product consists largely or entirely of fireproofing, hollow blocks, 

 etc., with an output in 1901 valued at $611,864 and in 1902 at 

 $965,047. Of these the firm of Henry Maurer & Son was the 

 first to begin this manufacture as above noted (PI. XXXIII, Fig. 

 1). Four of the other factories are operated by the National 



