SAMPLING AND TESTING HIGHWAY MATERIALS. 57 



The dish of bitumen should then be set in a hot-air oven maintained at 105° 0. for 

 about an hour, after which it is allowed to cool. Its general character is noted and 

 any tests for bitumens that are necessary are then made upon it. 



The difference between the final aggregate and the original amount taken gives 

 the amount of bitumen extracted, which is subject to correction, dependent on the 

 amount 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 quartz. 

 The solvent is evaporated over a very low flame and the residual coke is then ignited 

 with a burner capable of furnishing high temperature, such as a Meker. (Caution: 

 When an inflammable solvent is used evaporation should be conducted on a steam 

 bath and care should be taken that no flames are in the immediate vicinity.) The 

 dish and contents are then cooled in a desiccator and the percentage of ash calculated. 



B. HOT EXTRACTION METHOD. 



The New York Testing Laboratory extractor consists of a large brass cylinder, 

 through the bottom of which projects a 16-candlepower incandescent carbon-filament 

 bulb to supply heat to the extraction apparatus proper, which is held in the upper 

 portion of the cylinder. This apparatus is composed of a cylindrical brass vessel for 

 holding the solvent, a cylindrical wire basket made of 80-mesh wire cloth, suspended 

 in the cylinder, and an inverted conical condenser which serves as a top. 



The aggregate is prepared for analysis by heating it in a tin dish on the hot plate 

 until it is sufficiently soft to be disintegrated Dy means of a large spoon. The disin- 

 tegrated aggregate is then allowed to cool. Five hundred grams of aggregates contain- 

 ing particles larger than one-half inch in diameter and 300 grams of aggregates with 

 all particles smaller than one-half inch are then closely packed in the wire basket 

 and covered with a disk or wad of absorbent cotton or felt. From 175 to 200 c. c. 

 of carbon disulphide are next placed in the inside vessel, in which the wire basket 

 should be suspended. The top is then placed in position and cooling water circulated 

 through it. Heat is applied by means of the electric-light bulb. The solvent is 

 boiled in the lower part of the extractor and condenses on the under surface of the 

 top, from which it drips upon the wad of absorbent cotton and then percolates through 

 the sample. A complete extraction may be made in three hours. At the end of 

 this time the apparatus is allowed to cool and the basket containing the extracted 

 aggregate carefully removed. After thoroughly drying, the aggregate is placed 

 upon a pan of the rough balance and weighed. The difference between this weight 

 and the original weight taken shows the amount of bitumen extracted which is cal- 

 culated upon a percentage basis of the original. This figure should be corrected for 

 fine mineral matter which passes through the meshes of the wire basket as follows: 

 The solution of extracted bitumen is thoroughly agitated and measured in a glass 

 graduate. Five or ten cubic centimeters are then poured into a weighed platinum 

 crucible or dish, burned, and ignited to ash. The amount of mineral matter in the 

 entire solution may then be calculated from the amount of ash produced from that 

 portion ignited. The total percentage of such ash is then deducted from the per- 

 centage of bitumen already calculated in order to obtain the true percentage of bitu- 

 men. The amount of this correction will ordinarily vary from 0.1 per cent in uni- 

 formly coarse aggregates to 1 or 2 per cent in the analysis of aggregates containing a 

 considerable amount of very fine mineral matter. 



SUGGESTED METHOD FOR EXAMINATION OF BITUMINOUS MORTARS. 



Bituminous mortars may be extracted by the use of bronze tubes which ^re capable 

 of being whirled in the type of centrifuge similar to the Babcock milk tests. This 

 method is based on decantation of the supernatant solvent. The difference between 



