CLAYS OF NEW YOKK 729 



occur in the clay, and a special apparatus is used to extract tliem. 

 The clay and a certain percentage of shale are ground in a dry pan, 

 tlien carried up to an inclined screen. Those particles which 

 pass through are mixed by means of wheels and scrapers at- 

 tached to a revolving arm. The bricks are molded on stiff mud 

 machines and repressed on a hand-power machine. Ohamber driers 

 axe used and burning done in down-draft kilns, scove-kilns or a 

 continuous kiln. The clay burns to a buff brick; farther burning 

 at a higher heat gives a hard, greenish yellow brick, which is 

 smaller, but sold for paving purposes. The pavers made at this 

 yard are a mixture of clay and shale, while the building brick are 

 clay alone. The following is a report of tests made on these brick 

 in the laboratory at Cornell university. All the bricks were tested 

 on edge, as used for the purpose of paving. The sides were dressed 

 to parallel planes on an emery wheel, so as to get a uniform bearing 

 over every part. Single layers of thick paper were placed between 

 the brick and the machine. 



