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 = 10.9-1^9.9_ 

 Total bitumen _ 1 00- 1 ~~ 99 = 



23. VOLATILIZATION TEST. 



10 per cent. 



Fig. 19. — New York Testing Laboratory oven. 



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 H. I) may be used. The bulb of one of the thermometers h 

 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 163° C. as registered by 

 the thermometer in ah. A 

 tin box b\ cm. in diameter 

 and Z\ 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 hours, 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 reweighed. 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. Tt 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. 



