48 BULLETIN 1216, U. S. DEPABTMENT OF AGBICULTURE. 
3. From 1 to 2 grams of bitumen or about 10 grams of an 
asphalt topping or rock asphalt are now placed in the Erlennieyer 
flask, which has been previously weighed, and tbe accural e weight 
of the sample is obtained. One hundred cubic centimeters of 
chemically pure carbon disulphide are poured into the flask in 
small portions, with continual agitation, until all lumps d s- 
appear and nothing adheres to the bottom. The flask is then 
corked and set aside for 15 minutes. 
4. After being weighed, the Gooch crucible containing the felt 
is set up over the dry-suction flask, and the solution of bitumen in 
carbon disulphide is decanted through the felt with light suction 
or 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 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 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 
material may include both organic and mineral matter. The for- 
mer, 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 are calculated and reported as total bitumen, 
and organic and inorganic matter insoluble, on tbe basis of tbe 
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 impossible 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 most accurately obtained 
by treating the ash 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. 
0. When difficulty in filtering is experienced — for instance, 
when Trinidad asphalt is present in any amount — a period of 
Ipnger subsidence than 15 minutes is necessary, and the follow- 
ing method proposed by the committee on standard tests for road 
materials of the American Society for Testing Materials i< 
recommended : 
7. From 2 to 15 grams (depending on the richness in bitumen 
of the substance) are weighed into a 150 cubic centimeter Krlen- 
meyer flask, the tare of which has been previously ascertained, 
and treated with 100 cubic centimeters of carbon disulphide. Tbe 
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 residue. The first flask is again 
