SAMPLING AND TESTING HIGHWAY MATERIALS. 
41 
for about one hour, after which it is cooled and weighed . The percentage of bitumen 
insoluble is reported 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 insoluble in 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 follows : 
Bitumen insoluble in naphtha_ 10.9-1 
Total bitumen — 100- L 
Wq =10 per cent. 
23. VOLATILIZATION TEST. 
An oven is used that will give a uniform temperature throughout all parts where 
samples are placed. A gas oven of the type shown in figure 19 or an electric oven 
of proper design (see PL I) may be used. The bulb of one of the thermometers is 
immersed in a sample of some fluid nonvolatile bitumen, while the other is kept 
in air at the same level. 
The first thermometer 
serves to show the tempera- 
ture of the samples during 
the test, while the latter 
gives prompt warning of 
any sudden changes in tem- 
perature due to irregulari- 
ties in the heat. 
Before making the test 
the interior of the oven 
should show a temperature 
of ]63° C. as registered by 
the thermometer in air. A 
tin box 5^ cm. in diameter 
and 3§ cm. deep (American 
Can Co., gill type, deep 
pattern ointment box) is 
accurately weighed after carefully wiping with a towel to remove any grease or dirt. 
About 50 grams of the material to be tested is then placed in the box. The material 
may then be weighed on a rough balance, if one is at hand, after which the accurate 
weight, which should not vary more than 0.2 gram from the specified amount, is 
obtained. It may be necessary to warm some of the material in order to handle it 
conveniently, after which it must be allowed to cool before determining the accurate 
weight. 
The sample should now be placed in the oven, where it is allowed to remain for a period 
of five hows, during which time the temperature as shown by the thermometer in 
bitumen should not vary at any time more than 2° C. The sample is then removed 
from the oven, allowed to cool, and re weighed. From the difference between this 
weight and the total weight before heating the percentage of loss on the amount of 
material taken is calculated. 
The general appearance of the residue should be noted, especially with regard to 
any changes which the material may have undergone. Some relative idea of the 
amount of hardening which has taken place may be obtained from the results of a 
float or penetration test made on the residue, as compared with the results of the 
same test on the original sample. It is also frequently desirable to make the specific 
gravity and other tests on the residue for the purpose of identifying or ascertaining 
the character of the base used in the preparation of cut-back products. Before any 
tests are made on the residue, it should be melted and thoroughly stirred while cooling. 
New York Testing Laboratory oven. 
