Packing the sample tube

When packing a special sample tube to a length of approximately 2.5 cm, it is important that the column of substance in the tube should be uniformly packed. This is best achieved by placing the substance in the tube a little at a time and tapping the tube gently on a rubber bung between each addition. Crystalline specimens may require powdering, but the grinding process may cause the sample to gain electrostatic charge and this will prevent accurate measurements on the balance. To minimise this samples should be ground using a plastic spatula and then left for at least 15 minutes after grinding to allow the static charge to subside before packing. An antistatic gun may be used if available.

Operation of the magnetic susceptibility balance

1)    Turn the left-hand knob to RANGE 1, and allow 5-10 min. for the apparatus to warm up. [If the apparatus is to be used frequently, it should be left on all day].
2)    Adjust zero knob until display reads 000.
3)    Gently place the sample tube into the holder and take reading R₀ in cm².  This value should be negative since glass is diamagnetic.
4)    Weigh the sample tube.
5)    Pack the sample tube as explained above and weigh the combination of sample tube and sample to obtain the sample mass, m, in g.
6)    Gently place the sample tube into the holder and take reading R in cm². If the measurement goes off scale, remove the sample tube turn the RANGE knob to X10 (measurement divided by 10). Rezero the instrument. Reinsert the sample tube and record the reading. Multiply the reading by 10.
7)    Remove the tube and gently tap the tube on a rubber bung.
8)    Place the tube back in the balance and record the reading.
9)    Repeat steps 8) and 9) until a constant reading is obtained.
10)    Measure sample length, l, in cm.  Record the ambient temperature, T, in K.


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