NEW JERSEY BRICKMAKING INDUSTRY. 265 



ring and shows many ash fragments on the broken surface. Its 

 strength is the lowest of any tested, due to the loam used to 

 temper the clay. Better results would be obtained by the use of 

 sand. 



22. Common bricks made from a mixture of lignitic clay and 

 surface loam. The clay mixture is moderately plastic, has 

 moderate tensile strength and low shrinkage. The bricks are 

 dried on open yards and burned in scove kilns. The cubic air 

 shrinkage is 26.2 per cent., and the cubic fire shrinkage 7.3 per 

 cent. The bricks show a somewhat coarse grain, and some have 

 a black centre. 



23, 24, 25. Common bricks made from a sandy, open-burning, 

 Pleistocene surface clay. They were molded in a horsepower 

 machine, dried on an open yard and burned in a scove kiln. The 

 three samples represent different mixtures and banks. 



26. A machine-molded common brick made from the clay 

 loam used so extensively about Trenton. It was dried in the sun 

 and burned in an up-draft Dutch kiln. The fracture shows 

 numerous small pebbles. 



27. The same clay, with the addition of some more plastic 

 material, but brick re-pressed after molding. It shows a more 

 even grain. The cubic air shrinkage was 19.9 per cent, and the 

 cubic fire shrinkage 0.6 per cent. 



28. Common bricks from the Hackensack district, made of a 

 mixture of clay and sand. The clay has a moderate tensile 

 strength and burns dense at a low temperature, viz., cone 01. 

 The mixture is tempered in ring pits, dried on open yards and 

 burned in scove kilns. The fracture is moderately fine-grained 

 and homogeneous and showed few pebbles. 



29. Common bricks made from sandy glacial clay. It is tem- 

 pered in ring pits, dried on open yards and burned in scove kilns. 

 Only one sample was tested, which represented a normally burned 

 brick. 



30 and 31. Two common bricks from' the same yard, the 

 second one re-pressed. They were made from- a red-burning, 

 laminated Raritan clay, of moderate tensile strength. The re- 

 pressed bricks show higher strength, due in large part to harder 

 burning. 



