NEW JERSEY BRICKMAKING INDUSTRY. 263 



strength is excellent for a common brick and the transverse 

 strength is very fair. The bricks have a cubic air shrinkage of 

 19.3 per cent, and a cubic fire shrinkage of 14.8 per cent. 



10. Common brick made from a. mixture of light gray sandy 

 Raritan clay, a black sandy clay of late Pleistocene age, and Cape 

 May sandy loam; in the proportion of one to> one and one-half. 

 The clays are put through a short pug mill, without previous dis- 

 integration, and after molding are hacked up to dry and burned in 

 Dutch kilns. The cubic air shrinkage is 9.7 per cent, and the 

 cubic lire shrinkage 15.1 per cent; the bricks are commonly even 

 and fine-grained, with little trace of lamination. If the Raritan 

 clay does not get thoroughly broken up in the pug mill it shows as 

 white spots in the brick. 



11 and 12. Common brick made from a mixture of Clay Marls 

 I and II, with a small amount of surface clay added. The clays 

 are charged directly into the stiff-mud machine and the drying is 

 done either on racks or in tunnels. They are burned in circular 

 down-draft kilns to about cone 1. In the normally burned brick 

 the cubic air shrinkage is 14.6 per cent, and the cubic fire shrink- 

 age 3.1 per cent. The bricks are fine-grained and dense, although 

 some showed scattered pebbles on the fracture. No. 12 shows an 

 increased strength due to harder burning. 



13. Common brick made from- a mixture of Clay Marls I 

 and II and loam. The loam; is first screened through a sieve with 

 one-inch mesh, but this fails to remove many pebbles. The bricks 

 are dried in tunnels and burned in up-draft kilns. They show 

 few laminations. The cubic air shrinkage is 4.7 per cent, and the 

 cubic fire shrinkage 12.3 per cent. The modulus of rupture is 

 rather high as compared with the crushing strength. 



14. Front bricks made from a gritty, plastic clay of moderate 

 tensile strength. The brick, after molding are re-pressed and 

 dried in tunnels. They are burned in down-draft kilns at about 

 cone 1. The cubic air shrinkage is 19.2 per cent and the cubic 

 fire shrinkage 5.2 per cent. The strength is good and absorption 

 not high. 



15. Common bricks made from, more or less weathered beds 

 of Clay Marl II. After molding they are hacked under sheds 

 to dry, and burned in up-draft scove kilns. The bricks are 



