262 CLAYS AND CLAY INDUSTRY. 



the cubical fire shrinkage is 8.9 per cent., since the decrease in 

 size occurs in the other two dimensions. The bricks were fine- 

 grained, laminated, with a black centre, showing- many fragments 

 of burned lignite or coal. Their surface was rather rough. The 

 average modulus of rupture is much better proportionately than 

 the average crushing strength. The absorption is low. 



6. Common brick made of a mixture of loam, black sandy 

 clay, and yellow sandy laminated clay. None of the three indi- 

 vidually have very high tensile strength (although that of the 

 black clay is good) nor high fire shrinkage. The last two contain 

 scattered limonite nodules. The bricks are molded in a stiff-mud 

 machine, with little or no water added to> the clay, and hacked up 

 in the sun to dry. They are burned in Dutch kilns. The cubic 

 air shrinkage is 5.5 per cent, and the cubic fire shrinkage 14. 1 

 per cent. Many of the bricks showed fire cracks, which seemed to 

 have affected the modulus of rupture rather than the crushing 

 strength. The former was also no doubt lowered by the pebbles 

 of one-fourth to one inch in size, which were visible on the 

 fracture. 



7. Common brick made from a mixture of black laminated 

 clay, separated by thin layers of white sand and surface loam. 

 The clay burns fairly dense and has good tensile strength. The 

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

 are fine-grained, but slightly laminated and with few lumps or 

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

 fire shrinkage 15.1 per cent. 



8. Common brick made from a mixture of black, plastic Pleis- 

 tocene clay, and loamy clay, with some loam. The clays have a 

 high tensile strength and burn quite dense at a temperature but a 

 few cones higher than that at which the bricks are burned. The 

 product is fine-grained, but those with low fracture showed many 

 clay nodules ranging up to one-half an inch in size. 



9. Common bricks, made from a mixture of slightly weathered 

 Alloway clay, and about one-third surface loam. The bricks, 

 after molding, are hacked up to dry under sheds, then burned in a 

 down-draft kiln, and are somewhat harder than the general run of 

 common brick. The clays used are very plastic, have a high 

 tensile strength and burn to a good red color. The crushing 



