EXAMINATION OF BITUMINOUS ROAD MATERIALS. 



31 



1899, volume 21, page 1116. One grain of the material is placed in 

 a platinum crucible weighing from 20 to 30 grams and having a 

 tightly fitting cover. It is then heated for seven minutes over the 

 full flame of a Bunsen burner, as shown in figure 15. The crucible 

 should be supported on a platinum triangle with the bottom from 

 6 to 8 centimeters above the top of the burner. The flame should 

 be fully 20 centimeters high when burning freely, and the determi- 

 nation should be made in a place free from drafts. The upper sur- 

 face of the cover should burn clear, but the under surface should 

 remain covered with carbon, excepting 

 in the case of some of the more fluid 

 bitumens, when the under surface of the 

 cover may be quite clean. 



The crucible is removed to a desiccator 

 and when cool, is weighed, after which 

 the cover is removed, and the crucible 

 is placed in an inclined position over the 

 Bunsen burner and ignited until nothing 

 but ash remains. Any carbon deposited 

 on the cover is also burned off. The 

 weight of ash remaining is deducted from 

 the weight of the residue after the first 

 ignition of the sample. This gives the 

 weight of the so-called fixed or residual 

 carbon, which is calculated on -a basis of 

 the total weight of the sample, exclusive 

 of mineral matter. If the presence of a 

 carbonate mineral is suspected, the per- 

 centage of mineral matter may be most 

 accurately obtained by treating the ash 

 with a few drops of ammonimn carbonate solution, drying at 100° 

 C, then heating for a few minutes at a dull red heat, cooling and 

 weighing. 



An excellent form of crucible for this test is shown in figure 15. 

 It has a cover with a flange 4 millimeters wido, fitting tightly over 

 the outside of the crucible, and weighs complete about 25 grams. 

 Owing to Budder expansion in burning some of the more fluid bitu- 

 mens, it is well to hold the rover down with, the end of the tongs 

 until iIj<- mo I volatile products have burned off. 



ne products, particularly those derived from Mexican petro- 

 leum, sdow a tendency to suddenly expand and foam over the sides 

 of the crucible in making this determination, and no method of 

 obviating this trouble without vitiating the result bus thus far been 

 forthcoming. Recent experiments in the laboratory of the Office of 



Fig. 15. 



-Apparatus for determining 

 fixed carbon. 



