22,6 Nelson: The Solid Bitumens of Leyte 625 



carbon is 11.04 per cent. The stickiness and the viscosity of 

 the rock bitumen is entirely due to the ethyl acetate soluble 

 (paraffins) which, when extracted, was found to possess these 

 characteristics, while the ethyl acetate insoluble (asphalt) was 

 in all respects similar to the ethyl acetate insoluble of Leyte pure 

 bitumen. 



This difference between the paraffinaceous constituents of 

 Leyte pure bitumen and of Leyte bituminous rock could be ex- 

 pected since mineral aggregate mixed with bitumen prevents to 

 a certain extent any evaporation from the bitumen. Originally, 

 as may be supposed, both varieties of bitumen were very similar, 

 except perhaps in the content of the asphaltic ingredient, which 

 may or may not have been increased in the rock bitumen at the 

 expense of the paraffinaceous portion by the catalytic action of 

 the mineral aggregate. At present, the rock bitumen differs 

 from the pure bitumen by the presence of relatively volatile par- 

 affin hydrocarbons, some of which are liquid and others semi- 

 fluid. This difference apparently illustrates the relative stabil- 

 ity to the action of atmospheric agents conferred upon bitumens 

 by the admixture of mineral matter. 



Natural asphaltic rocks seldom contain a sufficient quantity 

 of bitumen to make them suitable for use as a paving material. 

 In most cases bituminous fluxes have to be introduced to supple- 

 ment this deficiency. Mastics containing as much as 15 and 20 

 per cent of bitumen are used in countries of temparate climate ; 

 but in tropical countries a much smaller percentage of bitumen 

 is required. On the other hand, the amount of bitumen must 

 also be regulated to the amount and character of the traffic. 

 Pavements subjected to light traffic will require less rock than 

 those destined to support heavy traffic. The properties of the 

 flux to be mixed with our Leyte rock, if fluxing is found 

 advisable, must be carefully considered, as it is a well-known 

 fact that the cementing properties of bitumen fluxes depend 

 greatly on their composition which should be largely asphaltic. 

 As our Leyte bitumen is largely paraffinaceous, the use of fluxes 

 derived from asphalt-base petroleum, such as the Trinidad 

 epure or heavy residues of distillation of asphaltic oils, is 

 advisable. 



The examination of the mineral aggregate which is penetrated 

 with bitumen has considerable importance in the road-build- 

 ing industry, in as much as the quality and the characteristics 

 of the road surface are mainly dependent on the character of 

 the sand which is cemented, and we have seen that this sand 



