EXAMINATION OF BITUMINOUS ROAD MATERIALS, 29 
the flask. If difficulty is still experienced in dissolving the material, 
a rounded glass rod will be found convenient for breaking up the 
undissolved particles. Not more than one-half of the total amount 
oi naphtha required should be used until the sample is entirely 
broken up. The balance of the 100 cubic centimeters is then added, 
and the flask is twirled a moment in order to mix the contents thor- 
oughly, after which it is corked and set aside for 30 minutes. 
In making the filtration the utmost care should be exercised to 
avoid stirring up any of the precipitate, in order that the filter may 
not be clogged and that the first decantation may be as complete as 
possible. The sides of the flask should then be quickly washed down 
with naphtha and, when the crucible has drained, the bulk of insoluble 
matter is brought upon the felt. Suction may be applied when the 
filtration by gravity almost ceases, but should be used sparingly, as 
it tends to clog the filter by packing the precipitate too tightly. The 
material on the felt should never be allowed to run entirely dry until 
the washing is completed, as shown by the colorless filtrate. When 
considerable insoluble matter adheres to the flask no attempt should 
be made to remove it completely. In such cases the adhering mate- 
rial is merely washed until free from soluble matter, and the flask is 
dried with the crucible at 100° C. for about one hour, after which it 
is cooled and weighed. The percentage of bitumen insofable is re- 
ported upon the basis of total bitumen taken as 100. 
The difference between the material insoluble in carbon disulphide 
and in the naphtha is the bitumen insoluble in the latter. Thus, if 
in a certain instance it is found that the material msoluble m carbon 
disulphide amounts to 1 per cent and that 10.9 per cent is insoluble 
in naphtha, the percentage of bitumen insoluble would be calculated 
as s follows: : 
Bitumen insoluble in naphtha _ eo Okan ocak 
Total bitumen f00=17 994° F* 
USE OF NAPHTHA INSOLUBLE BITUMEN DETERMINATION. 
This test is made on all petroleums, malthas, eee and other 
solid native bitumens and their products. 
It should be noted that petroleum naphthas are by noe means defi- 
nite compounds, but are composed of a number of hydrocarbons 
which vary in character and quantity according to the petroleum 
from which they have been distilled. Their solvent powers also vary 
greatly. Thus nap>thas produced from asphaltic petroleums, con- 
sisting mainly of naphthene and polymethylene hydrocarbons, are 
much more powerful solvents of the heavier asphaltic hydrocarbons 
than are the paraffin naphthas. The density of the naphtha also 
_ affects its solvent power, for those of high specific gravity dissolve the 
