NEW JERSEY BRICKMAKING INDUSTRY. 261 



STIFF-MUD BRICKS. 



1. A front brick, made from a plastic, gritty clay, having a 

 high tensile strength, and vitrifying at above cone 12. The bricks 

 are burned in down-draft kilns, at about cone 6 or 7. The crush- 

 ing tests ran quite uniform, and the lower figures of the trans- 

 verse tests were due to fine cracks in the bricks. 



2. A common brick made from a mixture of black clay and 

 loam, in the proportion of about two-thirds of the former and one- 

 third of the latter. Little or no water is added to the clay in the 

 stiff-mud machine. The bricks are dried on pallets and burned 

 in up-draft kilns. The brick are all fine grained, but some 

 showed a laminated structure. The minimum modulus of rup- 

 ture was caused by a one-inch pebble in one sample. 



3. Common brick made from- Cape May clay. The raw ma- 

 terial is a highly plastic, gritty and sometimes pebbly clay, with 

 an average tensile strength of 289 pounds per square inch. The 

 linear air shrinkage was 8.4 per cent, and the fire shrinkage 1.5 

 per cent. The bricks are dried on pallets and burned in scove 

 kilns. On the fracture they showed a coarse grain, with small 

 clay nodules and gravel, and also- slight laminations. 



4. A common brick made from a mixture of Raritan clay and 

 surface loam. The mixture is gritty, moderately plastic and not 

 of high tensile strength. No temperature or cone measurements 

 were made on the kiln, but the laboratory bricklet at cone 05 shows 

 about the same absorption as the large brick. The linear air 

 shrinkage is 0.7 per cent, and the fire shrinkage o per cent. The 

 cubical air shrinkage 0.7, and fire shrinkage 5.2. The bricks show 

 numerous fused specks of limonite, and the centres are sometimes 

 black and shelly. The minimum transverse break was caused by 

 a one-inch pebble. 



5. Common brick made from a dense-burning clay of high 

 tensile strength and red-burning if fired slowly. The clay was 

 molded as taken from the bank in a small stiff-mud machine, 

 stacked up to dry under sheds, and burned in up-draft Dutch kilns. 

 The linear air shrinkage in drying is 5.4 per cent, and the fire 

 shrinkage, as measured on the greatest length, is o per cent., but 



