50 



BULLETIN 691, U. S. DEPAETMENT OP AGRICULTURE. 



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 temperature of 

 the samples during the test, while the latter g'.ves prompt warning of any 

 sudden changes in temperature due to irregularities in the gas pressure, etc. 



Before making the test the interior of the oven should show a temperature 

 of 163° C. as registered by the thermometer in air. A round tin box ^ 6 

 cent-ineters in diameter and 2 centimeters deep is accurately weighed after 

 carefully wiping with a towel to remove any grease or dirt. About 20 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 deter- 

 mining 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 

 /Z . should not vary at any 



time more than 2° C. 

 from 163° C. The sam- 

 ple is then removed from 

 the oven, allowed to cool, 

 and reweighed. From 

 the difference between 

 this weight and the total 

 weight before lieating, 

 the percentage of loss on 

 the amount of material 

 taken is calculated. 



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. 



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 tests on the original sample. Before 

 any tests are made on the residue, it should be melted and thoroughly stirred 

 while cooling, 



FLOAT TEST. 



[Bulletin 314, p. 9.] 



NEW YORK TESTING LABOKATOEY FLOAT APPARATUS. 



The float apparatus consists of two parts, an aluminum float or saucer and a 

 conical brass collar (fig. 5). The two parts are made separately, so that one 

 float may be used with a number of brass collars. 



In making the test the brass collar ft is placed with the small end down on 

 a brass plate, which has been previously amalgamated with mercury by first 



Fig. 4. — New York Testing Laboratory oven. 



1 The box for a 50-gram sample should be 5i centimeters in diameter and 3J centi- 

 meters deep. 



