6 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE, 
When working with semisolid bitumens whieh are too soft to be 
broken and handied in fragments, the followmg method of deter- 
mining their specific gravity is employed. The clean, dry pyenom- 
eter is first weighed empty and this weight is called ‘‘a.” it is 
then filled in the usual manner with freshly distilled water at 25° C., 
and the weight is again taken and called ‘‘b.” A smali amount of 
the bitumen should be placed in the spoon and breught to a fluid 
condition by the gentle application of heat, with care that no loss 
by evaporation occurs. When sufficiently fluid, enough is poured 
into the dry pycnometer, which may aiso be warmed, to fill it about 
half full, without allowing the material to touch the sides of the tube 
above the desired level. The tube and contents are then aillewed to 
cool to room temperature, after which the tube is carefully weighed 
with the stopper. This weight is called “ce.” Distilled 
water, at 25° C., is then poured in until the pyenometer 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. Allsurplus 
moisture is then removed with a soft cloth, and the pyc- 
nometer and contents are weighed. This weight is called 
‘‘d.” From the weights obtained the specific gravity of 
the bitumen may be readily calculated by the following 
formula: 
c-a 
i £ r ) 25 e * prs i. BT 
Specific gravity C./25° © (bo a 
sie te Both ‘‘a” and ‘‘b” are constants and need be deter- 
nome ° . 
(Hubbara Mined but once. It is therefore necessary to make but 
type). two weighings for each determination after the first. Re- 
sults obtained according to the method given above are accurate to 
within 2 units in the third decimal place, while the open-tube method 
is accurate to the second decimal place only. 
The specific gravity of fluid bitumens 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. 
The pycnometer may be readily cleaned by placing it in a hot-air 
bath until the bitumen is sufficiently fluid to pour. ,As much is 
drained out as possible and the interior swabbed with a piece of 
cotton waste. It is then rinsed clean with a little carbon disulphide, 
and after drying is again ready for use. 
