44 



BULLETIN 1)49, U. S. DEPARTMENT OF AGRICULTURE. 



26. FIXED CARBON DETERMINATION. 



This determination is made in accordance with the method described for coal in 

 the Journal of the American Chemical Society, 1899, volume 21, page 1116. One 

 gram 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 22. The crucible should be sup- 

 ported on a platinum triangle with the bottom from 6 to 8 cm. above the top of the 

 burner. The flame should be fully 20 cm. high when burning freely, and the deter- 

 mination should be made in a place free from drafts. The upper surface of the cover 

 should burn clear, but the under surface should remain covered with carbon, ex- 

 cepting 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 min- 

 eral is suspected, the percentage of mineral matter 

 may be most accurately obtained by treating the ash 

 with a few drops of ammonium 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 has a 

 cover with a flange 4 mm. wide, fitting tightly over 

 the outside of the crucible, and weighs complete 

 about 25 grams. Owing to sudden expansion in burn- 

 ing some of the more fluid bitumens, it is well to 

 hold the cover down with the end of the tongs until 

 the most volatile products have burned off. 



Some products, particularly those derived from 

 Mexican petroleum, show a tendency to suddenly 



expand and foam over the sides of the crucible in 

 Fig. 22. — Apparatus for determining -, . .,. j-I ,. ■■ .-. j » ■, 



Kr , , s making this determination, and no method of ob- 



fixed carbon. ° .... 



viating this trouble without vitiating the result has 



thus far been forthcoming. Recent experiments in the laboratory of the Bureau of 



Public Roads indicate that the difficulty may be overcome by placing a small piece 



of platinum gauze over the sample and about midway of the crucible. The gauze 



should be so cut or bent as to touch the sides of the crucible at all points, and is of 



course weighed in place in the crucible before and after ignition. 



27. SPECIFIC VISCOSITY DETERMINATION. 



The viscosity of fluid bituminous road materials may be determined at any suitable 

 temperature by means of the Engler viscosimeter. This apparatus is shown in figure 

 23, and may be described as follows- a, is a brass vessel for holding the material to 

 be tested, and may be closed by the cover, b. To the conical bottom of a is fitted 

 a conical outflow tube, c, exactly 20 mm. long, with a diameter at the top of 2.9 mm. 

 and at the bottom of 2.8 mm. This tube can be closed and opened by the pointed 

 hardwood stopper, d. Pointed metal projections are placed on the inside of a at 



