NEW JERSEY BRICKMAKING INDUSTRY. 253 



termed the modulus of rupture, which is calculated from the 

 following formula. : 



3 w 1 



R = ° 



2 b h 2 

 in which R = Modulus of Rupture. 



W = Pressure necessary to break the brick. 

 1 = Distance between the supporting knife-edges, 

 b = Breadth of the brick, 

 h = Thickness of the brick. 



That is, three times the pressure in pounds multiplied by the 

 distance between the supports is divided by twice the breadth 

 of the brick, multiplied by the square of the thickness. If the 

 pressure necessary to break a brick was 2,000 pounds, distance 

 between supports 6 inches, width of brick 4 inches, and thick- 

 ness 2 inches, the modulus of rupture would be calculated as 

 follows : 



3 x 2 °°° X 6 



2 x 4 X 2 2 



— 1 1 25 pounds. 



Absorption tests. — An absorption test is made for determining 

 how much water a brick is capable of absorbing. This indicates 

 the degree of porosity which it possesses. Vitrified brick which 

 are impervious, or nearly so, will absorb little or no> water. 

 Many common brick may absorb an amount of water equal to 

 15 per cent., or even 20 per cent, of their dry weight. It is 

 easily understood that if a brick of high porosity is exposed to 

 a freezing temperature when its pores are filled with water, 

 the expansion of the latter, when changing to ice, may be suffi- 

 cient to disrupt the brick, either after one freezing, or after re- 

 peating freezings following periods of thawing. A moderate or 

 low absorption is therefore desirable. 



In making the absorption determinations on New Jersey brick, 

 the test was carried out on a half brick. The advantage of doing 

 this is that the surface of the brick is sometimes slightly denser 

 than the interior and acts as a protective skin against percolating 

 water. If, therefore, a whole brick is tested, we do not always 

 get its true absorptive capacity. In use, this outer skin may get 

 worn off wholly, or in part, especially if the brick is exposed to 

 abrasive action, as in pavements. 



