CHAPTER XVI, 



THE FIRE CLAYS AND FIRE-BRICK 

 INDUSTRY. 



CONTENTS. 



Properties of fire clays. 



Definition. 



Chemical composition. 

 Effect of silica. 

 Effect of titanium. 



Other properties. 

 Mineral impurities. 

 Uses of fire clays. 

 History of the fire-brick industry. 

 Method of manufacture. 

 Tests of New Jersey fire brick. 



PROPERTIES OE EIRE CEAY. 



Definition. — Strictly speaking a fire clay is one whose fusion 

 point lies at least above that of cone 27, but the term' is some- 

 what loosely used and often applied to- clays of even low refrac- 

 toriness. Aside from refractoriness, which is the most important 

 property of a fire clay and the one possessed by all true ones, they 

 vary widely, showing- great differences in plasticity, density, 

 shrinkage, tensile strength and color. Since the resistance of 

 a fire clay to heat is governed primarily by its chemical composi- 

 tion, and secondarily by its fineness of grain, it may be well to 

 consider first the former property. 



Chemical composition,. — Fire clays (see Appendix C, Middle- 

 sex county), contain practically all the substances usually deter- 

 mined by the ultimate analysis, 1 but in every good fire clay the 



1 See p. 49; also, pp. 315, 319, 320. 



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