METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 65 
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 material may include both organic and mineral matter. 
The former, if present, is burned off by ignition at a red heat until no in- 
candescent 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 are calculated and reported as total 
bitumen, and organic and inorganic matter insoluble, on the basis of the weight 
of material taken for analysis. 
5. This method is quite satisfactory for straight oil and tar products, but 
where certain natural asphalts are present it will be found practically impos- 
sible to retain all of the finely divided mineral matter on an asbestos felt. It is 
therefore generally more accurate to obtain the results for total mineral matter 
by direct ignition of a 1-gram sample in a platinum crucible. The total bitumen 
is" then determined by deducting from 100 per cent the sum of the percentage 
of total mineral matter and organic matter insoluble. If the presence of a 
carbonate mineral is suspected, the percentage of mineral matter may be m<>sr 
accurately obtained by treating the ash with a few drops of ammonium car- 
bonate solution, drying at 100° C. then heating for a few minutes at a dull red 
heat, cooling, and weighing again. 
6. 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. 
7. From 2 to 15 grams (depending on the richness in bitumen of the sub- 
stance ) are weighed into a 150 cubic centimeter Erlenmeyer flask, the tare of 
which has been previously ascertained, and treated with 100 cubic centimeters 
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 de- 
canted off into a similar flask that has been previously weighed, as much of the 
solvent being poured off as possible without disturbing the residue. The first 
flask is again treated with fresh carbon disulphide and shaken as before, when 
it is put away with the second flask and not disturbed for 48 hours. 
8. At the end of this time the contents of the two flasks are carefully decanted 
off upon a weighed Gooch crucible fitted with an asbestos filter, the contents of 
the second flask being passed through the filter first. The asbestos filter shall 
be made of ignited long-fiber amphibole, packed in the bottom of a Gooch 
crucible to the depth of not over one-eighth of an inch. After passing the 
contents of both flasks through the filter, the two residues are shaken with more 
fresh carbon disulphide and set aside for 24 hours without disturbing, or until 
it is seen that a good subsidation has taken place, when the solvent is again 
decanted off upon the filter. This washing is continued until the filtrates or 
washings are practically colorless. 
9. The crucible and both flasks are then dried at 125° C. and weighed. The 
filtrate containing the bitumen is evaporated, the bituminous residue burned, 
and the weight of the ash thus obtained added to that of the residue in the 
two flasks and the crucible. The sum of these weights deducted from the weight 
of substance taken gives the weight of bitumen extracted. 39 
45. METHOD OF TEST FOR PERCENTAGE OF BITUMEN 
INSOLUBLE IN CARBON TETRACHLORIDE 
1. This determination is conducted in exactly the same manner as described 
under "Method of test for percentage of bitumen" (see p. 64), using 100 cubic 
centimeters of chemically pure carbon tetrachloride as a solvent in place of 
carbon disulphide. 
2. The percentage of bitumen insoluble is reported upon the basis of total 
bitumen taken as 100, as described tinder " Method of test for percentage 
of bitumen insoluble in paraffin naphtha." (See p. 66.) 
% This method for recovery of mineral material should also be used in case of asphalt 
topping and rock asphalt if analyzed as previously described. 
104022°— 28 5 
