212 The Philippine Journal of Science 1916 



Burning tests. — The change in porosity of clays with increas- 

 ing heat treatment is an important factor in determining their 

 value for paving-brick manufacture. This test is considered 

 by many to be the best that has been so far devised. The test 

 in this laboratory is, in general, carried out according to the 

 method used by Purdy.'* A number of small bricks, 2.5 by 2.5 

 by 5 centimeters, are molded and thoroughly dried. They are 

 then placed in a kiln in a row parallel with a row of Seger 

 cones." As each cone fuses, the corresponding brick is removed 

 from the kiln, allowed to cool slowly, and then marked with the 

 number of the cone. The heating is usually continued until 

 the fusing point of the clay is reached or the specimens begin 

 to crack badly. The burning tests described here were made 

 in a small gasoline muffle kiln. 



The test bricks are weighed and placed on end in distilled 

 water, with the upper surface exposed to facilitate the escape 

 of air. After remaining overnight, they are boiled in water 

 under reduced pressure for about six hours. They are then 

 removed from the water and reweighed. The suspended weight 

 is taken by weighing each specimen while suspended in water. 

 From these data the porosity may be calculated.^* 



^'Bull. III. State Geol. Surv. (1908), No. 9, 141. 



" It is customary to give temperatures in terms of Seger cones, although it 

 is well known that the fusing points of these cones depend to some extent 

 on the rate of applying heat and on various other kiln conditions. [See, 

 for instance, The melting points of pyrometric cones under various con- 

 ditions, Geijsbeek, S., Trans. Am. Cer. Soc. (1912), 14, 849.] However, 

 since the cones and the test piece are subjected to the same heat treatment, 

 they are in general use in ceramic processes. The approximate fusing 

 points of the cone's employed in this work are here given: 



me No. 



Temper- 

 ature, °C. 



Cone No. 



Temper- 

 ature, °C. 



Cone No. 



Temper- 

 ature, °C. 



Cone No. 



Temper- 

 ature, °C. 



010 



950 



03 



1090 



5 



1230 



12 



1370 



09 



970 



02 



1110 



6 



1250 



13 



1390 



08 



990 



01 



1130 



7 



1270 



14 



1410 



07 



1010 



1 



1150 



8 



1290 



15 



1430 



06 



1030 



2 



1170 



9 



1310 







05 



1050 



3 



1190 



10 



1330 







04 



1070 



4 



1210 



11 



1350 







" Percentage porosity = 



W-D 

 W-S 



xioo. 









Where, W=wet weight, D=:dry weight, S = suspended weight. 



