XI. A, 5 



Witt: Philippine Paving-brick Materials 



211 



sistency is used in making the other tests described here, and 

 the method of drying is the same. 



Drying shrinkage. — The clay is molded in the form of a bar 

 2.5 by 2.5 by 15 centimeters. Two parallel scratches, one near 

 each end, are made with a pair of dividers. The distance be- 

 tween them is measured and recorded. After the bar has been 

 dried, the distance is again measured and the shrinkage calcul- 

 ated on the basis of the dry weight.^* 



Slaking time. — A 2.5-centimeter cube is molded and dried; it 

 is placed in a small wire basket and immersed in water. The 

 time required for complete disintegration is recorded as the 

 slaking time. 



Tensile strength. — In making the tensile-strength determina- 

 tions the Fox method ^^ was followed, in general. The clay is 

 mixed with water and is allowed to stand for a day or two. It is 

 then rolled out in the form of a thick slab and cut into briquettes 

 with a cutter similar to a biscuit cutter. The clay is forced into 

 the molds and pressed into shape, and the excess is removed 

 by a spatula. After drying for several days at room tem- 

 perature, the briquettes are thoroughly dried in an air oven and 

 then kept in a desiccator until broken. The width and thickness 

 of each briquette at the narrowest point is measured before 

 breaking and the results are calculated to tensile strength per 

 unit area. 



The physical tests on the raw clays are given in Table III. 



Table III. — Tests of clays in raw state. 



No. and source of sample. 



Water of 

 plasti- 

 city, a 



Linear 

 drying 

 shrink- 

 age, a 



Slaking 

 time. 



Tensile strength. 



Drying qual- 

 ities at room 

 temperature. 



Kilos per 

 square 

 centi- 

 meter. i> 



Pounds per 

 square 

 inch. 



1. Mabolo, Cebu 



Per cent. 

 23.26 

 45.96 

 59.00 

 59.97 

 36.91 

 30.96 

 37.46 

 27.87 

 38.96 



Per cent. 



3.75 

 10.87 

 14.29 



9.09 

 11.11 

 10.05 

 13.21 

 10.09 

 10.09 



Minutes. 

 34 

 62 



3 

 65 



8 

 13 



6 



25 

 36 



24.2 



12.2 



nil 



nil 



nil 



21.7 



5.8 



31.3 



10.8 



345 

 176 



Very good. 



Good. 



Poor. 



Do. 

 Good. 



Do. 

 Poor. 

 Good. 



Do. 



2. Pasig River . 



3. Laguna Province .. 



4. Masbate 





5, Mindoro 







308 



83 



447 



156 



7. Jaro River, Iloilo 



9. Abra Bubprovince 



» Calculated to the basis of the dry weight. 



■> Average of six briquettes. 



See Bull. Oklahoma Geol. Surv. (1911), No. 7, 37. 

 'See Bull. III. State Geol. Surv. (1908), No. 9, 163. 



