404 CLAYS AND CLAY INDUSTRY. 



Most of the clay is dark, almost black in color, with occasional 

 layers of coarse black sand and much organic matter. Lumps of 

 lignite are not uncommon, but pyrite was not noticeable. The 

 upper limit of the black clay varies, and at the end of the excava- 

 tion nearest the factory there is a 2-foot layer, low in organic 

 matter and sand, which is sufficiently plastic for pottery purposes 

 and has been used for stoneware. 



It is found in actual practice that it is undesirable to use the 

 black clay alone, and that a certain amount of loam must be added 

 tO' it. This decreases the fire shrinkage and makes the clay easier 

 to burn, for the black clay alone has considerable organic matter. 



The physical properties of the black and of the brick mixture 

 can best be compared by placing them in parallel columns. 



Physical characters of clays from Fish House. 



Black clay. Brick mixture. 

 Lab. No. 668. Lab. No. 639. 



Water required, 37.1 % 27.5 % 



Air shrinkage, 6 % 7.0 % 



Tensile strength, lbs. per square in., 243 258 



Cone 05 



Fire shrinkage, 3.00% 



Absorption, 9.96% 



Cone 03 : 



Fire shrinkage, 7-3 % 5.0 % 



Color, red red 



Condition, steel-hard steel-hard 



Absorption, 5-96% 6.83% 



Cone 1 : 



Fire shrinkage, 7.60% 6.0 % 



Color, deep red brown 



Absorption, 4-90% 3-o8% 



Cone 3 : 



Fire shrinkage, 6.3% 



Color, deep red brown 



Absorption, 0.02% 



The black clay, in spite of its high tensile strength, does not feel 

 very plastic when wet, and the brick mixture is much more sticky. 



The following analysis was made of a green brick, as represent- 

 ative of the run of the bank : 



