METHODS OF TESTING. 
The following methods of testing are those to which reference is made in the 
foregoing specifications. The descriptions taken from Department of Agri- 
culture Bulletin 314 have been condensed, but not changed in any essential 
particular unless so indicated in the specifications proper. 
SPECIFIC GRAVITY. 
[Bulletin 314, p. 4.] 
HYDROMETER METHOD. 
A sufficient quantity of material is poured into a tin cup, which is then 
placed in a large dish containing cold or warm water as occasion may require. 
The material in the cup should be stirred with a thermometer until it is brought 
to a temperature of 25° C, after which it should be immediately poured into 
a hydrometer jar and its gravity determined by means of the proper hydrometer. 
In case the hydrometer sinks slowly, owing to the viscosity of the material, it 
should be given sufficient time to come to a definite resting point, and this 
point should be checked by raising the hydrometer and allowing it to sink a 
second time. The hydrometer should never be pushed below the point at which 
it naturally comes to rest until the last reading has been made. It may then 
be pushed below the reading for a distance of three or four of the small divi- 
sions on the scale, whereupon it should immediately begin to rise. If it fails to 
do so, the material is too viscous for the hydrometer method, and the pycnom- 
eter method should be employed. 
The direct specific gravity reading obtained by the foregoing method is based 
upon water at 15.5° C. taken as unity. For all practical purposes this reading 
may be corrected to water at 25° C, considered as unity, by multiplying it by 
1.002. Thus : 
Specific gravity 25° C./25° C.=specific gravity 25° C./15.5° C.X1.002. 
SPECIFIC GRAVITY. 
[Bulletin 314, p. 5.] 
PYCNOMETER METHOD. 
The pycnometer, shown in figure 1, consists of a fairly heavy, straight-walled 
glass tube, 70 millimeters long and 22 millimeters in diameter, carefully ground 
to receive an accurately fitting solid glass stopper with a hole of 1.6 millimeters 
bore in place of the usual capillary opening. The lower part of this stopper is 
made concave in order to allow all air bubbles to escape through the bore. The 
depth of the cup-shaped depression is 4.8 millimeters at the center. The stop- 
pered tube has a capacity of about 24 cubic centimeters and when empty weighs 
about 28 grams. 
The clean, dry pycnometer 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 small amount of the bitumen 
should be placed in a spoon and brought to a fluid condition by the gentle ap- 
plication of heat, with care that no loss by evaporation occurs. When suffi- 
ciently fluid, enough is poured into the dry pycnometer, which may also be 
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