20 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE. 
The sample should now be placed in the oven, where it is allowed to 
remain for a period of five hours, during which time the temperature 
as shown by the thermometer in bitumen should not vary at any 
time more than 2° C. from 163° C. The sample is then removed from 
the oven, allowed to cool, and reweighed. From the difference 
between this weight and the total weight before heating, the per- 
centage of loss on the amount of material taken is calculated. 
The general appearance of the residue should be noted, especiall 7 
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. 
Highly volatile and nonvolatile materials should not be subjected 
to this test at the same time in the same oven owing to a tendency 
on the part of the latter to absorb some of the volatile products of 
the former. 
R USE OF THE VOLATILIZATION TEST. 
The volatilization test, as above described, is made on practically 
all bitumens with the exception of tars, for which the distillation test 
answers a similar purpose. The test is also frequently made at 105° 
C. for five hours, and with products containing small amounts of water — 
it is usually necessary to make a test at the lower temperature before 
the material can be heated at 163° C. without foaming over. In the 
case of emulsions it is customary to determine the loss on a 20-gram 
sample at reom temperature for 24 hours, after which the sample is 
heated at 105° C. for five hours. This additional loss is obtained and 
all determinations are made on the dried residue and reported 
accordingly. 
The volatilization test is also occasionally made at 205° C. for five 
hours on a fresh sample in order to show the effect of this higher 
temperature as compared with the results at 163° C. 
Because of the fact that after the volatilization test it frequently 
happens that a penetration test can not be made upon the residue of 
a 20-gram sample in the container specified, it has been suggested 
that the volatilization test be made upon a 50-gram sample in a tin 
box 54 centimeters in diameter and 33 centimeters in depth. In 
many cases, however, the percentage loss by volatilization and the 
consequent hardening will be found to vary materially from that 
obtained with a 20-gram sample owing to differences in the ratio of 
exposed surface area to total volume of material. This fact should 
_ be borne in mind if the test is made with a 50-gram sample. - 
