132 DETAILED REPORT ON ALABAMA CLAYS. 



slight degree of it. They are generally of a highly 

 refractory nature, their fusing point being commonly 

 above 2700 F. and t'heir shrinkage in drying and 

 burning is extremely low. They therefore make an 

 excellent grog to add to the more plastic clays for the 

 purpose of reducing their shrinkage. Flint clays 

 have thus far not been found in Alabama, except 

 in Conecuh, Choctaw, Washington, Clarke and 

 Monroe counties. 



Plastic fire clays are widely distributed and are 

 especially abundant in the Coal Measures of many 

 states, but they may also ocsur in the Cretaceous 

 and Tertiary formations. Those of the Carbonifer- 

 ous are often of a shaly nature and to be ground be- 

 fore their plasticity can be brought forth. 



The requisite qualities of a fire clay vary some- 

 what according to the use to which it is to be put, and 

 it is still a disputed point, just what temperature the 

 fusion point of a clay should exceed in order to be 

 classed as a refractory one. As it now stands, many 

 American clays are unfortunately and erroneously 

 classed as fire clays which can not withstand a tem- 

 erature of more than 2300 or 2400 F. M&ny of the 

 New Jersey fire clays require a temperature of from 

 2500 to 2600 F. to burn them.* The fire clays of 

 Missouri fuse at from 2400 to above 2700. 



No arbitrary line can be drawn between refractory 

 and semi-refractory clays, but if such a division were 

 made it would seem advisable not to ( call any clay re- 

 fractory which is affected by a temperature of less 

 than 2700 F. Many of the Alabama fire clays con- 

 form to this definition. 



While it is desirable that fire clays should posses 

 good plasticity and low shrinkage, the main point is 

 their refractoriness. It may be said in general that 



