PART C - CARE AND USE OF BALANCES
Weighing is a task that is constantly performed by laboratory technicians. Therefore, you must ensure that the
technicians know the correct balance to use and how to use it. Erroneous weighing or the improper balance can
result in false results when performing laboratory tests. As a senior petroleum laboratory NCO, it is your
responsibility to ensure that all balances are serviceable and properly calibrated at all times.
Significance -- Weighing is a necessary part of running a test to obtain results and making solutions.
Types of Balances:
Analytical Balance-- Used for precision weighing (0.0001 gram) of small quantities. Some features on a
single-pan analytical balance include: easy-to-read display, separate sealed keys, and automatic
Harvard Trip Balance -- Precision balance used for weighing substances in the petroleum laboratory. It
should be used on a reasonably flat and level surface. In this setting a very near balance should be
attained with the beam and tare poises all the way to the left.
Torsion and Triple Beam Balances -- Used when precise weighing is not required. For instance, it would
be used when determining the appropriate weight of tubes to be centrifuged.
Use of Balances.
Use of the Analytical Balance.
Press the TARE on the balance to zero the display. Place a sheet of quantitative filter paper on the pan of
the balance.
Use a clean, dry spatula to carefully measure the required quantity of solute calculated.
Read the display weight after the display is stable, indicated by the no-motion symbol switches on or off.
Record the weight of the solute for reference.
Use of the Harvard Trip Balance.
Zero the balance. Adjust the knurled zero knob at the right end of the beam, if the scale is not balanced at
zero when set upon the working surface.
Weigh substance. Place the substance to be weighed on the left platform of the balance. Move the poises
to a position that will restore the scale to balance. The lower poise is moved to the right until the first
notch is reached which causes the right platform of the scale to drop. The lower poise is then moved
back one notch, which will cause the right platform to rise again. The upper poise is then moved to the
right until the scale is brought into balance.
Read the results directly from the beams by adding the amount indicated on the lower and upper beams.
Record the weight of the solute for reference.
Use of the Triple Beam Balance (when precise weighing is not required).
Level and zero the balance. Select a reasonably flat and level surface on which to use the balance. Adjust
the knob at the left end of the beam to obtain zero balance.
Weigh substance. Place substance to be weighed on the load receiving platform. Move the center poise
to the first notch where it causes the beam pointer to drop, then move it back one notch and the pointer
will rise.
Read the results as the weight of the substance by adding the values indicated by the poises.
Care of Balances.
Balances should be used on reasonably flat and level surfaces.
When transporting balances, take care that they do not receive any sharp blows or unnecessarily rough
treatment.
Cleaning of Balances
Balances should be kept clean at all times.
Dirt and moisture should not be allowed to accumulate in the vicinity of these balances.
Analytical Balance. Refer to manufacturer's manual for specific cleaning procedures.
Harvard Trip and Triple Beam Balances. Scale bearings should never be lubricated or oiled. Should the
bearings become dirty, attempt to clean them by blowing out with dry air blast. Occasionally, the magnet
QM 5184
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