Micromeritics Gemini VII 2390a Operator's Manual page 344

Appendix E
b.) Determine the number (n) of glass beads needed to equal the sample volume:
where
3. Outgas the sample in the sample tube at an appropriate temperature for an appropriate amount of
time.
4. Install the sample tube (containing the outgassed sample) onto the analysis port and the sample
tube (containing the glass beads) onto the balance port.
5. Specify a one-point measurement (P/Po = 0.05 to 0.1) so that the initial free-space measurement
can quickly be determined; then perform the measurement.
6. Using the measured free space absolute value and the following relationship, determine the mass
of glass beads to remove from (or add to) the balance tube to reduce the free-space imbalance:
free space cm
---------------------------------------------------------------------------- -
where
2.515 g/cm
3.53 = thermal correction (no units)
Note that the volume of one glass bead is approximately 0.014 cm
measured free space is less than 0.02 cm
7. Use a beaker of warm water to bring the balance tube to room temperature before removing it
from the balance port of the Gemini to remove (or add) glass beads. This prevents condensation
of moisture from the laboratory atmosphere onto the cold glass beads.
8. Remove the balance tube:
• If the measured free space is negative (–), add the calculated mass of glass beads into the
balance tube.
• If the measured free space is positive (+), remove the calculated mass of glass beads from the
balance tube.
E-2
v
------------------------ -
=
n
3
0.014 cm
3
0.014 cm = approximate volume of one bead
3 3

2.515 g/cm
=
mass of glass beads g
3.53
3
= density of glass beads
 
3
, it is unnecessary to correct the free space.
Gemini VII
3
. Therefore, if the
239-42828-01 - Dec 2012