48 



BULLETIN" 691, U. S. DEPARTMENT OF AGEICULTURE. 



^ 



warmed, to fill it about half full, Avithout allowing the material to touch the 

 sides of the tube above the desired level. The tube and contents are then 

 allowed to cool to room temperature, after which the tube 

 is carefully weighed with the stopper. This weight is 

 called " c ". Distilled water, at 25° C, is then poured in 

 until the pycnometer is full. After this the stopper is 

 inserted, and the whole cooled to 25° C. by a 30-minute 

 immersion in a beaker of distilled water maintained at 

 this temperature. All surplus moisture is then removed 

 with a soft cloth, and the pycnometer and contents are 

 weighed. This weight is called " d ", From the weights 

 obtained the specific gravity of tlie bitumen may be readily 

 calculated by the following formula : 



Specific gravity 25° C./25° C.=: 



Fig. 1. — Pycnometer 

 (Hubbard type). 



'{b-a)-{d-c) 



The specific gravity of fluid bitumen may be determined 

 in the ordinary manner with this pycnometer by completely 

 filling it with the material and dividing the weight of the 

 bitumen thus obtained by that of the same volume of water. 



FLASH POINT. 



[Bulletin 314, p. 17.] 

 OPEN-CUP METHOD. 



The open-cup oil tester, shown in figure 2, consists of a brass oil cup a of 

 about 100 cubic centimeters capacity, and an outer vessel b which serves as an 

 air jacket ; a suitable thermometer c is suspended from 

 the wire support d directly over the center of the cup so 

 that its bulb is entirely covered with oil but does not 

 touch the bottom of the cup. The testing flame is obtained 

 from a jet of gas passed through a piece of glass tubing, 

 and should be about 5 millimeters in length. 



The test is made by first filling the oil cup with the 

 material under examination to within about 5 millimeters 

 of the top. The Bunsen flame is then applied in such a 

 manner that the temperature of the material in the cup 

 is raised at the rate of 5° C. per minute. From time to 

 time the testing flame is brought almost in contact with 

 the surface of the oil. A distinct flicker or flash over the 

 entire surface of the oil shows that the flash point is 

 reached and the temperature at this point is taken. 



SPECIFIC VISCOSITY. 



[Bulletin 314, p. 7.] 

 ENGLER VISCOSIMETER METHOD. 



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The specific viscosity of fluid bituminous road materials 

 is determined at the specified temperature by means of 

 the Engler viscosimeter. This apparatus shown in figure 

 3 may be described as follows: a is a brass vessel for 

 holding the material to be tested, and may be closed by 

 the cover 6. To the conical bottom of a is fitted a conical outflow tube c, 

 exactly 20 millimeters long, with a diameter at the top of 2.9 millimeters and 

 at the bottom of 2.8 millimeters. This tube may be closed and opened by the 



Fig. 2. — Open-cup oil 

 tester. 



