Ohaus CARAT PLUS PRECISION JEWELRY BALANCES Density Determination Kit Manual - Manual (Page 4)

4
PRINCIPLE OF DENSITY DETERMINATION OF SOLIDS
The density Q is the quotient of the mass m and the volume V.
Q =
m
V
Density determinations are frequently performed by Archimedes' principle, which is
also used with the density determination kit for the balances. This princple states that
every solid body immersed in a fluid loses weight by an amount equal to that of the fluid
it displaces.
The density of a solid is determined with the aid of a liquid whose density Q
0
is known
(water or ethanol are usually used as auxiliary liquids). The solid is weighed in air ( A)
and then in the auxiliary liquid ( B). The density Q can be calculated from the two
weighings as follows:
Q
A
A - B
• Q
0
The balance allows direct determination of the buoyancy
P (
P = A - B) and consequently the above formula can be simplified:
Q = • Q
0
A
P
Q = Density of the solid
A = Weight of the solid in air
B = Weight of the solid in the auxilary liquid
Q
0
= Density of the auxiliary liquid at a given temperature (this
value depends on the temperature and must be taken from
a density table except when using a Voyager or Voyager Pro
balance, the density table is included).
P = Buoyancy of the solid in the auxilary liquid
(corresponds to A - B).
PERFORMING DENSITY DETERMINATION
For density determination of solids, use a standard lab glass beaker 250 ml and a
precision thermometer, 0°C to 30°C (not supplied).
Figure 8. Beaker and Thermometer Installation.
1. Prepare the balance for the
density determination as pre-
viously described.
2. Install the beaker as shown
in Figure 8 and suspend the
thermometer on the edge of
the beaker.
3. Suspend the Weigh Below
Hook from the Bracket into
the beaker.
density kit.pmd 8/9/2005, 1:12 PM 4