462 CLAYS AND CLAY INDUSTRY. 



Where both retort and fine fire clay are found in the same bank, 

 a mixture of the two is sometimes made for the use of manufac- 

 turers of chemical stoneware and other grades of pottery. Such 

 a mixture from J. H. Leisen's bank (Loc. 16, Lab. No. 381) was 

 tested with the following results : Water required for mixing, 34 

 per cent. ; air shrinkage, 6 per cent. ; average tensile strength, 

 91.5 pounds per square inch. It behaved as follows in burning: 



Burning test of a mixture of retort and fire clay, I. R. Leisen, Woodbridge. 



Cones 15 8 



Fire shrinkage, 4-6% 8% H.3% 



Absorption, 19.51% 9-79% 6.69% 



Color, cream light buff light buff 



The bricklets burned steel-hard at cone 1, and showed a slight 

 tendency to warp at cones 5 and 8. At cone 27 the material was 

 vitrified, so that it is more refractory than a retort clay, and less 

 so than a No. i fire clay of this district. This mixture burns 

 denser than did the No. 1 fire clay alone from the same bank/ 

 and has higher tensile strength. 



Among the various grades of clay seen in McHose Brothers' 

 pits, near Florida Grove, one sample selected for testing was a 

 bright-red clay (Lab. No. 403), which, from its color, appears to 

 be quite ferruginous, and in fact contains 12.45 P er cen t- of ferric 

 oxide (Fe 2 3 ). It slaked slowly and worked up with 32 per 

 cent, of water to a mass whose air shrinkage was 6.6 per cent. 

 The tensile strength averaged 75 pounds per square inch. Its 

 behavior on burning was as follows : 



Burning tests of a bright-red clay, McHose Bros., Florida Grove. 



Cone 01 12 



Fire shrinkage, 6% 6.3% 6.6% 



Absorption, 14.28% 13.00% .... 



Color, red red red 



The clay was nearly steel-hard at cone 2. It has been used in 

 pipe manufacture, but is not refractory enough to be classed as a 

 fire clay. 



