HOLLOW WARE FOR STRUCTURAL WORK. 281 



The above tabulation is not without interest, and shows a 

 considerable variation in certain directions. The air shrinkage 

 shows little variation, but the tensile strength shows a great 

 range. Of these different samples, Nos. 447, 451 and 371 are 

 practically from the same bed. No. 408 is from the base of the 

 Raritan series and is one of the most dense-burning clays to be 

 found in that section, or even in the State. Most of these clays 

 have to be burned to cone 01 before becoming steel-hard, the one 

 exception being No. 408, which burns very hard at cone 05. 

 They all burn red. The pyrite and limonite nodules are abundant 

 in some of the layers, and in burning often swell and spall oft" 

 pieces of the ware. 



The black laminated clay which forms the upper part of the 

 Woodbridge clay bed (pp. 184-5) ^ s the most important source 

 of the terra-cotta lumber and fireproofing clays in New Jersey. 

 As shown on the map, Plate XI, they are found in the region bor- 

 dering the Raritan river, that is at Perth Amboy, Keasbey, South 

 River and Sayreville, as well as in the vicinity of Woodbridge 

 and Spa Springs. At Lorillard, east of Keyport, Clay Marl II 

 is also extensively utilized. On account or the enormous quan- 

 tity of fireproofing manufactured, a great amount of clay is dug, 

 and the excavations are very large. In some pits the clay is dug 

 with a steam shovel (PI. XXXII, Fig. 2) and loaded onto tram 

 cars, which are hauled to the works either by horsepower or a 

 small engine. 



The following analyses are representative of the general chem- 

 ical composition of the New Jersey fireproofing clays : 



Compositions of two New Jersey fireproofing clays. 



1 2 



Silica (Si0 2 ), 52.22 60.18 



Alumina (A1 2 3 ), 29.43 23.23 



Ferric oxide (Fe 2 3 ), 2.78 3.27 



Lime (CaO), 0.88 1.00 



Magnesia (MgO), 0.72 0.67 



Potash (K2O), 2.10 2.58 



Soda (Na 2 0), 0.75 0.80 



Loss on ignition, 11. 10 8.54 



99.98 100.27 



