CLAYS OF NEW YOEK 667 



Semi-dry process 



This differs but little from tiie dry process. Tlie clay usually 

 has a slight araount of moisture added to it. 



Clays adaptable to the different molding methods 



Few clays give good results with all the methods of molding just 

 described, and the same clay will not necessarily make a good brick 

 with any machine of the same general type. This is specially true 

 of stiff mud machines. For the dry press process a wide range of 

 clays can be used, for it works with sandy ones, or with plastic 

 materials. Coarse sandy clays however do not lend themselves 

 readily to dry pressing, on account of their very slight cohesive 

 strength. 



As an illustration of the wide range of clays used, we may com- 

 pare the two following clays, no. 1 being a clay used to a large 

 extent for making brick in western Illinois, no. 2 a black clay from 

 "Wyandance, L. I. 



Both feel gritty, but neither contains particles large enough to 

 be retained by a 100 mesh sieve. 



When subjected to a mechanical separation they yielded. 



m. 1 ITo. 2 



Fine sand '. . 5^ 84^ 



Clay substance and silt 95^ 16^ 



100^ 100^ 



The other physical tests of no. 2 are given on page 740. 



Those of no. 1 are: water reuqired for mixing 16^; air shrink- 

 age 6^. Incipient fusion began at .04 with 8^ shrinkage; vitrifica- 

 tion at 4, with a total shrinkage of 12^; at cone 6 viscosity began. 

 The soluble salts amounted to .09^. The tensile strength ranged 

 from 150 to 175 pounds a square inch. 



If the product from the dry press machine is properly burned, it 

 gives a good brick, but if not, it is apt to be easily disintegrated by 



