FIRE CLA78. 149 



(No. 116.) 

 FIRE CLAY. 



NEAR VALLEY HEAD, DEKALB COUNTY. 



Occurring in the same quarry is what is known as 

 the second grade of fireclay. This is a fine grained 

 yellowish gray clay containing much fine grit. It 

 slakes quite quickly when thrown in water, and) when 

 worked up with 39 per cent, of water gave quite a 

 plastic mass, The air shrinkage of the bricklets am- 

 ounted to 8 per cent, which is greater than that of the 

 first grade, which was also less plastic. The tensile 

 strength seems to have increased with the plasticity 

 for it amounted to 20 pounds per square inch. When 

 burned to 2350 F. the total shrinkage was 17 per 

 cent, and incipient fusion took place, while vitrifica- 

 tion occurred at 2700 F. and at cone 27 in the Deville 

 furnace the clay fused but did not run. It will be 

 thus seen that it is less refractory than the so called 

 first grade, which only vitrified at this latter temper- 

 ature. Both are to be classed as fireclays however. 

 Up to incipient fusion, the clay remains v/hite, but 

 above that it begins to show a yellowish tint due to 

 the presence of iron oxide in the clay. 



The chemical composition of the clay is : 



Analysis of Fire Clay, near Valley Head, DeKalb Co. (No. 116). 



Silica 79.80 



Alumina 11.75 



Ferric oxide 1-75 



Lime 75 



Magnesia trace 



Alkalies 1.50 



Water 4.11 



99.16 



Total fluxes 3.50 



Specific gravity 2.37 



