

EXAMINATION OF BITUMINOUS ROAD MATERIALS. 27 



After being weighed, the Gooch crucible containing the felt is 

 set up over the dry pressure flask, as shown in figure 14, and the 

 solution of bitumen in carbon disulphide is decanted through the felt 

 without suction by gradually tilting the flask, with care not to stir 

 up any precipitate that may have settled out. At the first sign of 

 any sediment coming out, the decantation is stopped and the filter 

 allowed to drain. A small amount of carbon disulphide is then 

 washed down the sides of the flask, after which the precipitate is 

 brought upon the felt and the flask scrubbed, if necessary, with a 

 feather or "policeman/' to' remove all adhering material. The con- 

 tents of the crucible are washed with carbon disulphide, until the 

 washings run colorless. Suction is then applied until there is prac- 

 tically no odor of carbon disulphide in the crucible, after which the 

 outside of the crucible is cleaned with a cloth moistened with a small 

 amount of the solvent. The crucible and contents are dried in the 

 hot-air oven at 100° C. for about 20 minutes, cooled in a desiccator, 

 and weighed. If any appreciable amount of insoluble matter adheres 

 to the flask, it should also be dried and weighed, and any increase over 

 the original weight of the flask should be added to the weight of 

 insoluble matter in the crucible. The total weight of insoluble mate- 

 rial may include both organic and mineral matter. The former, if 

 present, is burned off by ignition at a red heat until no incandescent 

 particles remain, thus leaving the mineral matter or ash, which can 

 be weighed on cooling. The difference between the total weight of 

 material insoluble in carbon disulphide and the weight of substance 

 taken equals the total bitumen, and the percentage weights arc cal- 

 culated and reported as total bitumen, and organic and inorganic 

 matter insoluble, on the basis of the weight of material taken for 

 analysis. 



This method is quite satisfactory for straight oil and tar products, 

 but where certain natural asphalts are present it will be found prac- 

 tically impossible to retain all of the finely divided mineral matter 

 on an asbestos felt. It is, therefore, generally more accurate to obtain 

 tin result for total mineral matter by direct ignition of a 1-gram sample 

 in a platinum crucible or to use the result for ash obtained in the 

 fixed carbon test. The total bitumen is then determined by deduct- 

 in;: from. 100 per cent the sum of the percentages of total mineral 

 matter and organic matter insoluble. If the presence of a carbonate 

 mineral is suajh cted, the percentage of mineral matter may be most 

 accurately obtained by treating the ash from tho fixed carbon deter- 

 minal ion v.ii h a few drops of ammonium carbonate solution, drying at 

 100° ('., then heating for a few minutes at a dub 1 cod heat, cooling, 

 and weighing again. 



When difficulty in filtering is experienced— for instance, when Trini- 

 dad asphalt is present in any amount — a period of longer subsidence 



