458 CLAYS AND CLAY INDUSTRY. 



This analysis is interesting as the ratio of silica to alumina is so 

 low. It also shows that there are present nearly 4 per cent, of 

 fluxes in the form of iron oxide and lime, and there is probably 

 some titanium oxide present also, which, however, was not sepa- 

 rated from the silica and alumina. Were it not for these impuri- 

 ties the clay would probably be highly refractory. It is interest- 

 ing to compare this clay with the blue fire clay from the adjoining 

 bank (p. 451), since the two resemble each other closely in ap- 

 pearance, yet differ so in fusibility. 



Fire-mortar Clay. 



Fire-mortar clay is a sandy type of clay found in not a few 

 pits, and, as its name indicates, it is used for making mortar 

 for setting fire bricks. A sample (Lab. No. 383) corresponding 

 to layer 9 of the section on p. 436 was taken from Henry 

 Maurer & Son's pit (Loc. 24, PI. VIII, Fig. 2). It was a 

 sandy, speckled, or finely-mottled clay with small mica scales, 

 and was part of a bed about 3 feet thick. When tested it slaked 

 fast and worked up with 28 per cent, of water to a mass, having 

 an air shrinkage of 5 per cent. Its tensile strength averaged 

 99 pounds per square inch, and in burning it behaved as follows : 



Burning test of a tire-mortar clay, Maurer & Son, Woodbridge. 



Cone 3 5 8 



Fife shrinkage, 3% 4% 5% 



Absorption, 10.75% 5.98% 4.20% 



Color, buff buff gray buff 



It burned steel-hard at cone 5, and became viscous at cone 27. 

 The chemical composition was : 



Chemical analysis of Maurer & Son's tire-mortar clay. 



Silica (Si0 2 ), 67.26 



Alumina ( AkOs) , 23.36 



Ferric oxide (Fe^Oa), 163 



Lime (CaO) , 0.25 



Magnesia (MgO), trace 



Alkalies (Na 2 0, K-O), 0.65 



Loss on ignition (chiefly JLO) , 6.94 



100.09 



