II

li

I

310

FLUIDITY AND PLASTICITY

of equal size and employ the tare method in weighing.

Strictly, it is necessary to measure the density at only one
temperature by this method. The working volume of the vis-
cometer has to be adjusted each time that the temperature of the
liquid is raised. By noting the expansion of this working volume
for each temperature interval it is readily possible to calculate
the specific volume and density. The portion of the viscometer
HO, Fig. 29, is graduated in millimeters. By filling the viscometer
with mercury from A to (?, and weighing this mercury, the work-
ing volume V can be actually determined. And by filling a
given length of the capillary HG with mercury, the volume vf of
the capillary per centimeter is easily determined. The density
of mercury is given in Table III.

TABLE VII.—DENSITY AND VOLUME OF MERCURY IN GRAMS PER

MILLILITER

Temperature, degrees
Density
Logarithm density
Specific volume

10
13.570
1.13260
0.073687

15
13.558
1.13220
0.073757

20
13.546
1.13181
0.073822

25
13.534
1.13142
0.073887

30
13.522
1.13104
0.073954

If, therefore, the specific volume of the liquid is s0 at temperature
t0 and on forcing the meniscus at the left just up to the trap, the
right meniscus is a distance d away from its proper level (?, then
at the new temperature t, the specific volume s must be
= i (10)
With this volumeter it must be remembered that the errors
are cumulative. On the other hand with the pycnometer method
care must be taken to wipe off drops of liquid which may adhere
to the inside of the glass, and to prevent the evaporation of
volatile substances, on account of which a stopper is added to the
pycnometer.
Assuming that a capillary is used whose radius is 0.01 cm and
that the tube HG has a radius which is ten-fold this amount, or