142 The Philippine Journal of Science i9i4 



material remain as free lime,^ whereas the coarse or underburned 

 particles of cement rock are more apt to possess the more 

 desirable properties of such products as hydraulic limes and 

 Eoman cements. However, it should be borne in mind that, as 

 an impure limestone requires less siliceous material than a purer 

 one, the relative cost of quarrying, crushing, and grinding the 

 different raw materials might make it advisable, from an eco- 

 nomic standpoint, to use the purest available limestone in spite of 

 these advantages of impurity. 



The data in Table I show that the available crystalline lime- 

 stones 46 and 50 contain only 3.91 and 6.44 per cent, respectively, 

 of clay substance and fluxing materials. Such pure limestones 

 are practically nonfusible, and they must be ground to extreme 

 fineness to enable them to unite thoroughly with the pulverized 

 siliceous materials at cement-kiln temperatures. On the other 

 hand, the coralliferous limestones 35, 37, and 39 are more closely 

 related to cement rock. They contain on the average about 13.2 

 per cent of clay substance and fluxes, and combine so much more 

 readily with siliceous material that their use is advantageous and 

 involves less danger from free lime and kiln troubles. In addi- 

 tion, they are the most conveniently located and the most easily 

 quarried and pulverized of the calcareous materials. These ad- 

 vantages are especially significant here, because clay 47 is the 

 most conveniently located and desirable of the available siliceous 

 resources. 



Clay 47 has the highest content of free silica. Ordinarily, this 

 would be disadvantageous, but in this instance the grain is so 

 fine and the content of total silica so high (70.28 per cent) 

 that, as a whole, the silica content is very satisfactory. Iron 

 in quantities above that required for fluxing purposes is not 

 desirable. Clay 47 contains the least iron, but sufficient to 

 produce, without excessive treatment, a well-burned cement (2b) 

 with a hydraulic index as high as 2.31. Clay 47 can be combined 

 with limestones 46 and 50 to produce good cement, but much 

 more satisfactory results are obtained by combining it with the 

 coralliferous limestones. This is more or less apparent from 

 the data given in Table XII. 



° The evil effects of free lime and the manner in which it affects the 

 physical and chemical properties of Portland and other hydraulic cements 

 have been thoroughly discussed in previous publications. Cf. Reibling, 

 W. C, and Reyes, F. D., This Journal, Sec. A (1910), 5, 117-142; ibid. 

 (1911), 6, 207-252; ibid. (1912), 7, 135-191. 



