46 BULLETIN 1216, U. S. DEPARTMENT OF AGRICULTURE. 
B. Pycnometeb Method (Used fob Viscous Fluid and Semi- 
solid Bitumens and Emulsions). 
Pycnometer 4. The determination of specific gravity shall be made with a 
method. Bubbard-Carmick pycnometer or weighing bottle, which shall 
consist of a conical or Erlenmeyer-shaped llask approximately 45 
millimeters high, 40 millimeters in diameter at the bottom, and 25 
millimeters in diameter at the mouth, carefully ground to receive 
an accurately fitting solid glass stopper with a hole «.r about 1 
millimeter bore in place of the usual capillary opening. The 
lower surface of the Stopper is made concave in order to allow 
all air bubbles to escape through the bore. The depth of the cup- 
shaped depression shall be about 4.8 millimeters at the center. 
The stoppered flask has a capacity of about 25 cubic centimeters 
and when empty weighs about 25 grains. 
5. Before making a determination, the pycnometer with stopper 
shall first be calibrated by weighing it clean and dry upon an an- 
alytical balance. This weight is called a. It shall then be filled with 
freshly boiled distilled water at a temperature of 25° C. (77° F.), 
the stopper firmly inserted, all surplus moisture wiped from the 
surface with a clean, dry cloth, and again weighed. This weight 
LS culled t). 
6. W hen determining the specific gravity of road oils or road 
tars which flow readily, the material shall be brought to a tem- 
perature of 25° C. (77° F.) and poured into the pycnometer until 
it is full, with care to prevent the inclusion of air bubbles. The 
stopper is then firmly inserted and all excess of material forced 
through the opening is carefully removed with a clean dry cloth 
The pycnometer and contents are then weighed and this weight 
is called c. The specific gravity of the material shall be calculated 
from the formula : 
c — a 
Specific gravity ^ r— - 
7. When determining the specific gravity of tar and asphalt 
products which are too viscous for the method described in sec- 
tion 4, a small amount of the material shall be brought to a fluid 
condition by the gentle application of heat, care being exercised 
to prevent loss by evaporation. When sufficiently fluid, enough is 
poured into the clean, dry pycnometer to aboul half fill it. Pre- 
cautions shall be taken to keep the material from touching the 
sides of the tube above the final level and to prevent the inclusion 
of air hubbies. The tube should be slightly warmed before filling. 
The pycnometer and contents are then cooled to room temperature 
and weighed with the stopper. This weight is called C. The 
pycnometer is next removed from the balance, filled with freshly 
boiled distilled water, and the stopper firmly inserted, it is then 
completely immersed for not less than 30 minutes in a beaker of 
distilled water maintained at 25° C. (77° BY), after which it is 
removed, and all surplus water is wiped off with a clean (doth. 
It is immediately weighed. This weight is called d. The specific 
gravity of the material shall be calculated from the formula: 
s, 
:peciricgravity= (ftn) _ (rf . c) 
8. When making the specific gravity determination it is impor- 
tant that : 
(a) Only freshly boiled distilled water shall be used. 
(b) When weighing the pycnometer completely filled, the tem- 
perature of its contents shall be within 1° C. (1.8° P.) of 25° <\ 
(77° V.). 
(o Precautions shall he taken to prevent expansion and over- 
flow of the contents from the heat of the hand when wiping the 
surface of the pycnometer. 
( (I ) The presence of all air bubbles shall be eliminated in filling 
the pycnometer and inserting the stopper. 
