VITEIFIED BRICK AS MATERIAL FOR COUN-TRY ROADS. 3 
indicate its fitness or unfitness for paving brick. The reason for this 
is that the quality of the brick after "firing" is no less dependent on 
the physical arrangement of the minerals than on the chemical 
composition of the material. 
THE MANUFACTURE. 
The general processes of manufacture are the same for both fire 
clays and shale. The raw material in either case is crushed to com- 
paratively small fragments and conveyed by some convenient means 
to a grinding machine, known in the industry as a dry pan. Briefly, 
this machine consists of a solid iron plate, approximately 5 feet in 
diameter, surrounded by a perforated iron surface about 2 feet wide. 
Outside the perforated surface is a rim some 15 inches in height which 
serves to prevent the material from escaping otherwise than through 
the perforations. Upon the solid plate rest two massive crushers or 
mullers, each weighing from 2-J to 3 tons. The pan is revolved 
rapidly, causing the mullers to rotate by friction. The material is 
ground between the mullers and the plate and thrown out by cen- 
trifugal force toward the rim, where it escapes through the perforated 
surface into an elevator, by means of which it is conveyed to the 
screens. 
The particles too large to pass the screens, which should not exceed 
three-sixteenths inch in mesh, are returned to the dry pan, while 
the screened material is passed to the mixing machine or pug mill 
by means of conveyors. In the pug mill, water is admixed with the 
clay to form a stiff mud, which is fed continuously into the brick 
machine proper. 
The brick machine is an extremely heavy mechanism. It con- 
sists essentially of an auger or propeller conveyor, a tapering barrel, 
and the die or former. The material is forced by means of the auger 
conveyor into the tapering barrel, which terminates in the die, and 
issues from the die in a solid column under heavy pressure. For 
"side-cut" brick this column is approximately 4| inches by 10 
niches in cross section, and the brick are formed by cutting through 
the column, by means of an automatic device, at intervals of about 
3 J inches. For "end-cut" brick the column has a cross section 
approximately 4 inches by 4J inches and is cut into sections about 
10 inches long. 
Paving brick, whether end or side cut, have usually in the past 
been re-pressed. This process smooths and rounds the corners, and 
forms on one side of each brick small lugs or projecting trademarks 
which serve to produce uniform spacing between the courses of the 
pavement. Suitable lugs may also be formed at the time the brick 
are cut, however, and the process of re-pressing is then omitted. 
Much discussion has taken place as to which of these methods pro- 
