Standard and tentative methods of sampling and testing highway materials : recommended by the Second Conference of State Highway Testing Engineers and Chemists, Washington, , Feb 23-27, 1920 . e settling of any fine mineral matter that is sometimes carried through the felt ringin the extractor. The solution is then decanted into the flask a, and the solvent isdriven off by means of heat from an incandescent lamp until the residue is of a thicksirupy consistency. Meanwhile the solvent is condensed and recovered in the flask residue is poured into an 11-cm. porcelain evaporating dish a
Standard and tentative methods of sampling and testing highway materials : recommended by the Second Conference of State Highway Testing Engineers and Chemists, Washington, , Feb 23-27, 1920 . e settling of any fine mineral matter that is sometimes carried through the felt ringin the extractor. The solution is then decanted into the flask a, and the solvent isdriven off by means of heat from an incandescent lamp until the residue is of a thicksirupy consistency. Meanwhile the solvent is condensed and recovered in the flask residue is poured into an 11-cm. porcelain evaporating dish and evaporated ona steam bath. The most scrupulous care must be taken at all times that no flamesare in its immediate vicinity. Evaporation is carried on at a gentle heat, with con-tinual stirring, until foaming practically ceases. It is advisable to have a largewatch glass at hand to smother the flames quickly should the material ignite. As thefoaming subsides, the heat of the steam bath may be gradually raised, and evapora-tion is continued until the bubbles beaten or stirred to the surface of the bitumenfail to give a blue flame or odor of sulphur dioxide when ignited by a small gas n^ir^ Fig. 31.—Recovery apparatus. SAMPLING AND TESTING HIGHWAY MATERIALS. 57 The dish of bitumen should then be set in a hot-air oven maintained at 105° C. forabout an hour, after which it is allowed to cool. Its general character is noted andany tests for bitumens that are necessary are then made upon it. The difference between the final aggregate and the original amount taken givesthe amount of bitumen extracted, which is subject to correction, dependent on theamount of ash determined from the washings. Ash correction shall be made in the following manner: The total solution of bitu-men, well stirred, is rapidly measured and an aliquot portion taken, usually 100 c. c,and poured into a previously weighed suitable flat-bottom dish, preferably solvent is evaporated over a very
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