182 DETAILED REPORT ON ALABAMA CLAYS. 



-workable mass which shrank 5 per cent, in drying, and 

 10 per cent, ia burning, giving a total shrinkage of 15 

 per cent. The average tensile strength of air diied 

 briquettes per sq. inch is 30 lbs , and the maximum ten- 

 sile strength per sq. inch is 35 lbs. 



Incipient fusion occurs at 2160 F., vitrificataon at 2300 

 F., and viscosity at 2500 F.; the clay burns to a dense 

 yellowish white body. 



Following is the composition of the c'ay: 



Analysis of Pottery Clay J. W. Williams, Pegram, Colbert Co. (No. 55 S.) 



Total silica 86.45 



Alumina ' 18.53 



Ferric oxide 2.40 



Water 8.68 



Lime 1-50 



Magnesia 1-25 



Alkalies tr. 



Moisture -78 



99.59 



Free silica (sand) , 44.22 



Total fluxes 5.15 



Clay base 49.44 



Specific gravity 2.39 



This clay could probably be purified by washing, it 

 corresponds in general composition to a fire clay from 

 Parker and Russel's Mine* near St. Louis Mo., but the 

 latter on account of its greater coarseness, has a larger 

 refractoriness. 



BRICK CLAYS. 



The term brick clays is a somewhat elastic one for it 

 may include those used for the manufacture of common 

 brick, front or pressed brick, and paving brick. As the 

 requirements are somewhat different they can be men- 

 tioned briefly and apart. 



Clays for common brick. For this purpose almost any 



♦Missouri Geol. Survey. Vol. XI, p. 570. 



