Balances are essential laboratory instruments used for weighing substances like powders and crystals. There are two main types of balances: mechanical/rough balances and electronic balances. Mechanical balances are used to weigh larger amounts with less accuracy, while electronic balances can precisely weigh very small quantities in milligrams. Electronic balances use electromagnetism to return the balance to a null position, and have features like automatic zero tracking and temperature compensation for high accuracy. Proper use and care of balances is important for cleanliness and avoiding vibrations or moisture that could impact measurements.

1. Balance
Mohammed Siddig ALI
MSc. Clinical Chemistry

2. introduction
• Balances are essential laboratory instruments
that are widely used for weighing of various
substances (powders, crystals and others) in
the laboratory. For instance, to prepare
reagents, stains and culture media, balances
are required to weigh accurately and precisely
within the needed range.

3. Gravimetry
• Gravimetry:
• Gravimetry is the process used to measure the
mass of a substance.
• Weight is a function of mass under the
influence of gravity, a relationship expressed
by the relationship
• Weight =Mass ×Gravity

4. Types of Balances
1- Double or single-pan(mechanical)
2- electronic balances

5. • Balances in medical laboratory may be:
• A. Rough balances (mechanical balances)
• B. Analytical balances

6. A. Rough balances (mechanical balances)
• It is used:
• To weigh large amounts (up to several kilo
grams).
• When a high degree of accuracy is not
required.
• Example: 20.5 gm, 36. 5 gm, etc. The
sensitivity of a twopan balance is 0.5 gm.
• The sensitivity of a balance is the smallest
weigh that moves

7. mechanical balances
Principles of Weighing:
In practice, one of two modes of weighing is
used:
(1) analytical weights are added to equal the
weight of the object being weighed, or
(2) the material to be weighed is added to a
balance pan to achieve equilibrium with a preset
weight.

8. Electronic Balance
(principle)
• In an electronic balance, an electromagnetic force
is applied to return the balance beam to its null
position. This force is proportional to the weight
on the pan. Most electronic balances have a built-
in provision for taring so that the mass of the
container is subtracted easily from the total mass
measured.
• In addition, in many modern balances, a built-in
computer compensates for changes in
temperature and provides both automatic zero
tracking and calibration.

9. • These balances are used:
1. To weigh small quantities usually in mili
gram(mg) range
2. When great accuracy is required
Example, 2.750mg, 0.330 mg, 5.860mg, etc
• Its sensitivity is 0.5 mg to 1 mg depending on
the model.

11. Use and care of balances
1. Read carefully the manufacturer’s
instructions.
2. Always handle a balance with care.
3. Position the balance on a firm bench away
from vibration, draughts and direct sunlight.
4. Before starting to weigh, zero the balance as
directed by the manufacturer.

12. 5. Weigh the chemicals at room temperature in
a weighing scoop or small beaker. Never put the
chemicals directly on the balance pan.
6. When adding or removing a chemical, remove
the container to avoid spilling any chemical on
the balance.
7. When using an analytical double pan balance,
bring the pans to rest before adding or removing
a chemical.

13. 8. Always use forceps to add or remove weighs.
Protect the weights from dust, moisture and fungal
growth.
9. Use small brush to remove any chemical, which
may have been spilt on the balance.
10. A container of self - indicating silica gel should
be kept inside the analytical balance case to remove
any moisture present in the atmosphere.
11. Keep the balance clean, being particularly
careful not to let dirt accumulate near the pivots
and bearings.

14. Thank You