166 



The Philippine Journal of Science 



1914 



brick 7, the pulverized clay was screened through a 30-mesh 

 sieve and the surfaces remained free from rupture. 



Ground until no residue remains upon the 20-mesh sieve, or 

 finer, the clay is easy to pug, and when mixed with about 24 per 

 cent of water produces a stiff mud which is easy to mold by hand 

 or to express smoothly through an ordinary brick die. The addi- 

 tion of more water tends to produce a soft mud which is too 

 sticky and too lean to mold well in any single process. If molded 

 by pressure in the semidry or dry state, the brick disintegrates 

 with even ordinary handling or it cracks and warps while drying 

 or burning. The hand-molded, stiff-mud bricks dry fairly 

 rapidly, and in so doing shrink about 8 per cent and develop a 

 tensile strength of 133 pounds per square inch; but better den- 

 sity, strength, and appearance can be obtained by first molding 

 the stiff mud by hand or by expression, and after most of the 

 shrinkage has taken place re-pressing it at a pressure of about 

 1,000 pounds per square inch. 



Table III. — Physical properties of bricks produced from Iwahig clay by 

 different processes of manufacture. 



Item. 



Brick. 



Average of 



Nob. 1 and 2 

 made at 

 Iwahig. 



No. 3. 



No. 4. 



Process of molding . 



(a) 

 20.3X9.5X5.4 



1,807 

 1.70 

 2.93 



20.42 



1,010 



6.00 



307 



750 



(b) 



19.4X9.4X5.4 



1.821 



1.82 



2.82 



16.63 



2,250 

 6.00 



648 

 1,244 



7.6 



20.6X9.9X6 



2,153 



1.80 



2.83 



15.54 . 



2,460 



6.00 



656 



1,021 



10.00 



Dimensions in centimeters _ 



Weight in grams (dry) _ 



Apparent density (weight/volume of brick) 



Specific gravity . 



Absorption of water, per cent .. . 



Modulus of rupture: 



Transverse strength in pounds 



Distance between supports in inches _- 



3PI/2bd2 



Crushing strength in pounds per square inch 







" Pressed soft mud. 



" Ee-pressed stiff mud. 



Stiff mud molded by hand. 



There is not much difference between the handmade and the 

 re-pressed bricks except in appearance; both products are much 

 better than the brick manufactured at Iwahig. 



Bricks 3 and 4 in Plate I, fig. 1, represent the product obtained 

 by the best methods of manufacturing brick with Iwahig clay. 

 Both were molded by hand in the condition of stiff mud, but 

 No. 3 was re-pressed at a pressure of 3,000 pounds per square 



