4 BULLETIN 373^ U. S. DEPARTMENT OF AGEICULTUEE. 



inches. For " end-cut " brick the cohimn has a cross section approxi- 

 mately 4 inches by 4^ inches and is cut into sections about 10 inches 

 long. 



In order that the successive courses in a brick paA'ement may be 

 uniformly spaced, it is necessary that suitable lugs be formed on the 

 brick either at the time they are cut, or later by means of re-press 

 molds. Special shapes, such as nose brick for use next to car tracks, 

 and hillside block, which have one side thicker than the other and 

 which are used on steep grades in order to give the pavement a 

 rough surface, may be made either by special die or special re-press 

 molds. 



The next step in the process of manufacture consists in drying the 

 brick. In a properly systematized plant the brick are stacked upon 

 drier cars as they leave the presses in such manner as to permit a 

 free circulation of air between them. The loaded cars are imme- 

 diately run into a tunnel drier, the temperature of which is main- 

 tained at about 100° F. at the entering end. As cars containing 

 " green " brick enter one end of the tunnel, which is usually more 

 than 100 feet long, other cars containing dry brick are being removed 

 at the opposite end. Air circulation in the drier is effected by means 

 of fans or high stacks. During drying the brick lose an amount of 

 moisture equivalent to from 1.5 to 20 per cent of their own weight. 



The brick leave the drier ready for burning, which is the last and 

 undoubtedly the most important step in the process of manufacture. 

 Upon the burning depends largely the quality of the finished product, 

 and it requires the greatest skill so to regulate the temperatures and 

 firing periods as to obtain the best results from a given material. 

 Experience alone can demonstrate the manner in which the burning 

 must be modified in order to suit varj^ing sets of conditions. The 

 kilns in which the burning is done are made of brick and are provided 

 with numerous furnaces. The brick are placed in the kilns so as to 

 jDermit a free circulation of the gases of combustion and the heated air. 



PHYSICAL CHARACTERISTICS. 



GENERAL REQUIREMENTS. 



Paving brick should be uniform in size, reasonably perfect in shape, 

 free from ragging due to friction in the die, and from deep kiln 

 marks caused by impressions from overlying brick in burning. They 

 should be tough in order to resist crushing, hard in order to resist 

 abrasion, and uniformly graded in order that the pavement may wear 

 evenly. Each brick should be homogeneous in texture and free from 

 objectionable laminations or seams. Fire cracks, caused by too rapid 

 firing, should be limited in number and extent, and the entire brick 

 should be vitrified and should contain neither unfused nor glassy 

 spots. 



