EXAMINATION OF BITUMINOUS ROAD MATERIALS. PA 
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 aid 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, untii 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 mimutes, 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 fiask should be added to the weight of 
msoluble matter in the crucible. The total weight. of insoluble mate- 
rial may include beth organic and mimeral 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 msoluble in carbon disulphide and the weight of substance 
taken equals the total bitumen, and the percentage weights are cal- 
‘culated and reported as total bitumen, and organic and imorganic 
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 mimeral matter 
on an asbestos felt. Itis, therefore, generally more accurate to obtain 
the result for total mineral matter by direct ignition of a 1-gram sample 
im a platinum crucible or to use the result for ash obtamed im the 
fixed carbon test. The total bitumen is then determined by deduct- 
ing from i100 per cent the sum of the percentages of total mineral 
matter and organic matter insoluble. Hf 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 deter- 
mination with afew drops of ammonium carbonate solution, drying at 
100° C., then heating for a few mimutes at a dull red 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 
