FIRE CLAYS AND FIRE-BRICK INDUSTRY. 325 



connection with the fire clay. These ingredients are commonly 

 tempered in ring pits, but sometimes in pug mills, and then molded 

 either by hand or machine. If the former is used, the bricks are 

 molded very soft ; if the latter is employed, a soft-mud machine is 

 favored, although a stiff-mud machine is used at a few works. In 

 every case the brick are re-pressed, and after re-pressing they are 

 commonly hacked up to dry, and are then placed in the kilns. 

 Hand- or machine-molded bricks are usually spread out on brick 

 drying floors, warmed by flues passing underneath, and after re- 

 maining there a short time are re-pressed. This not only com- 

 presses the brick, but smoothens the sides and straightens the 

 edges. The following dimensions, given in inches, indicate the 

 amount of compression that takes place in re-pressing. 



Before re-pressing, g]A. by 4J/2 by 2%. 



After re-pressing, 9^ by 4^ by 2^. 



The loss in weight and decrease in size of a stiff-mud fire brick 

 is shown by the following figures, obtained at another works : 



Conditions. Dimensions in. inches. Weight. 



Freshly molded, . . . . 9^ by 2|-J- by 4}§ 9 pounds. 



Re-pressed, 9! by 2 T 5 5 by 4} .8 do 12 ounces. 



Dried, 9§ by 2| by 4f 7 do 2 do 



Burned, 9 by2J by4 6 do 2 do 



Most of the fire-brick manufacturers burn their product in cir- 

 cular down-draft kilns, although one factory has a continuous kilri, 

 and a few works have rectangular kilns. A few of the fire-brick 

 makers in New Jersey use Seger cones as a guide in burning, but 

 the majority do not. A number of cones were, therefore, dis- 

 tributed among the different fire-brick manufacturers for placing 

 in their kilns. From these, and those used regularly at some of 

 the works, it was found that the New Jersey fire brick were burned 

 at from cone 9 to cone 12. There is no reason to believe that those 

 manufacturers whole kilns were not tested, burn at a much higher 

 cone, although it is probable that in the hottest parts of the kiln 

 a slightly higher cone may sometimes be melted. At one factory 

 cone 16 has been melted when placed opposite the flue leading 

 from the fireplace. The firing commonly takes three to four days, 



