38 



BULLETIN W9, U. S. DEPARTMENT OF AGRICULTURE. 



C. DISPLACEMENT METHOD (USED FOR HARD SOLID BITUMENS). 



For materials which- are hard enough to he broken and handled in fragments at 

 room temperature, the following method will prove convenient. A small fragment 

 of the bitumen (about 1 c. c.) is suspended by means of a silk thread from the hook 

 on one of the pan supports, about H inches above the pan, and weighed. This weight 

 is called a. It is then weighed immersed in water at 25° C, as shown in figure 17, 

 and this weight is called 6. The specific gravity may then be calculated by means 

 of the following formula: 



Specific gravity = — -r 



20. DETERMINATION OF BITUMEN SOLUBLE IN CARBON DISULPHIDE. 



This test consists in dissolving the bitumen in carbon disulphide and recovering 

 any insoluble matter by filtering the solution through an asbestos felt. The form of 

 Gooch crucible best adapted for the determination is 4.4 cm. wide at the top, tapering 

 to 3.6 cm. at the bottom, and is 2.5 cm. deep. 



For preparing the felt the necessary apparatus is arranged as shown in figure 18, 

 in which a is the filtering flask, b a rubber stopper, c the filter tube, and d a section 



Fig. 17. — Displacement method of determining specific gravity. 



of rubber tubing which tightly clasps the Gooch crucible, e. The asbestos is cut 

 with scissors into pieces not exceeding 1 cm. in length, after which it is shaken up 

 with just sufficient water to nour easily. The crucible is filled with the suspended 

 asbestos, which is allowed to settle for a few moments. A light suction is then apj:>lied 

 to draw off all the water and leave a firm mat of asbestos in the crucible. More of 

 the suspended material is added, and the operation is repeated until the felt is so 

 dense that it scarcely transmits light when held so that the bottom of the crucible 

 is between the eye and the source of light. The felt should then be washed several 

 times with water and drawn firmly against the bottom of the crucible by an increased 

 suction. The crucible is removed to a drying oven for a few minutes, after which 

 it is ignited at red heat over a Bunsen burner, cooled in a desiccator, and weighed. 

 From 1 to 2 grams of bitumen or about f0 grams of an asphalt topping or rock asphalt 

 is now placed in the Erlenmeyer flask, which has been previously weighed, and the 

 accurate weight of the sample is obtained. One hundred cubic centimeters of chemi- 

 cally pure carbon disulphide is poured into the flask in small portions, with continual 

 agitation, until all lumps disappear and nothing adheres to the bottom. The flask 

 is then corked and set aside for 15 minutes. 



