(1) Place a powder paper or some other suitable container on each pan and
readjust your equilibrium. Powder papers of the same size and consistency may vary in
weight as much as 60 mg and can cause errors of up to 30 percent if you do not correct
them at the beginning of the weighing.
(2) With the beam locked in stationary position, open the lid and place the
desired weight on the right-hand pan (on top of the powder paper). The weights are
always placed to the right because on the beam of the balance is a rider (additional fine
weight), which may be moved to the right a number of divisions instead of adding
extremely tiny weights to the pan. Using this rider, for example, to weigh 264.5-mg, you
could either place a 200-mg weight on the right pan and run the rider out to 64.5-mg or
simply run the rider out to 264.5-mg. The left pan is convenient for receiving the
powders from the container. Use the forceps to place the weights as close to the center
of the right pan as possible. Weights placed at the edges of the pan give erroneous
(3) Place on the left pan your best estimate of the required amount of the
substance to be weighed. At first, it will be difficult to estimate, but as you become more
proficient, you will be able to estimate rather accurately.
(4) Release the beam to see if you have too much, too little or just the right
amount of substance on the pan. If the right pan descends and the left rises, you have
not enough of the substance being weighed. If, conversely, the left pan descends and
the right rises, you have too much of the substance. Lock the securing device and
correct the error by adding or removing some of the substance until the balance is in
(5) When the weights on both pans are equal, the balance is in equilibrium,
or in balance. This may be determined in more than one way. In the fixed balance
method, which is accurate, the pointer remains fixed at the central position when the
beam is released. In the swinging balance method, which is more accurate, equilibrium
is indicated when the pointer, on release, swings an equal number of divisions to each
side of the central position. If allowed to swing until all motion ceases, the pointer will
come to rest at the central position. To weigh accurately, however, it is not necessary
for the pointer to stop swinging. If, for two or three consecutive arcs, it goes an equal
number of divisions to either side, your accuracy is sufficient.
e. Hints on Weighing. Following are a few guidelines and checkpoints for the
technique of weighing and care of equipment:
(1) Locate your balance in a light place, free from vibration, dust, corrosive
vapors, and moisture.
(2) Keep the balance cover closed except when you are using the balance.
This prevents damage to the mechanism, extends the effective life of your equipment,
and maintains its accuracy. It also keeps out drafts during the weighing process and
allows you a more nearly perfect procedure.