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, 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. 



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. 



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 room 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 5 J centimeters in diameter and 3^ 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. 



