SAMPLING AND TESTING HIGHWAY MATERIALS. 39 



After being weighed, the Gooch crucible containing the felt is set up over the dry- 

 pressure flask, as shown in figure 18, 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 neces- 

 sary, with a feather or "policeman" to remove all adhering material. The contents 

 of the crucible are washed with carbon disulphide, until the washings run colorless. 

 Suction is then applied until there is practically 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 insol- 

 uble material may include both organic and mineral p 

 matter. The former, if present, is burned off by 

 ignition at a red heat until no incandescent parti- 

 cles 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 are calculated and reported as total bitu- 

 men, 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 practically impossible 



to retain all of the finely divided mineral matter 



on an asbestos felt. It is, therefore, generally more 



accurate to obtain the result for total mineral matter _ ,» ' . , A * 



Fi3. 18. — Apparatus for determining 

 by direct ignition of a 1-gram sample in a platinum soluble bitumen. 



crucible or to use the result for ash obtained in the 



fixed carbon test. The total bitumen is then determined by deducting 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 suspected, the percentage of mineral matter 

 may be most accurately obtained by treating the ash from the fixed carbon determi- 

 nation 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 again. 



When difficulty in filtering is experienced — for instance, when Trinidad asphalt is 

 present in any amount — a period of longer subsidence than 15 minutes is necessary, 

 and the following method proposed by the Committee on Standard Tests for Road 

 Materials of the American Society for Testing Materials is recommended : 



From 2 to 15 grams (depending on the richness in bitumen of the substance) is 

 weighed into a 150-cubic centimeter Erlenmeyer flask, the tare of which has been 

 previously ascertained, and treated with 100 c. c. of carbon disulphide. The flask is 

 then loosely corked and shaken from time to time until practically all large particles 

 of the material have been broken up, when it is set aside and not disturbed for 48 

 hours. The solution is then decanted off into a similar flask that has been previously 

 weighed, as much of the solvent being poured off as possible without disturbing the 



