Rice Lake Discovery Series Semi-Micro and Analytical, Ohaus - Manual (Page 23)

EN-19 Ohaus Discovery
The density Q is the quotient of the mass m and the volume V.
Q = m
V
Density determinations are performed by using Archimedes’ principle. This principle states that every solid body immersed in a fluid loses
weight by an amount equal to that of the fluid it displaces. The density table for water is included in the Discovery balance software.
The density of a solid is determined with the aid of a liquid whose density, Qo, is known (water is used as an auxiliary liquid). 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
•Q0
The balance allows direct determination of the buoyancy P (P =A - B ) and consequently the above formula can be simplified:
Q =
A
P
•Q0
Q = Density of the solid
A = Weight of the solid in air
B = Weight of the solid in the auxiliary liquid
Q0 = Density of the auxiliary liquid at a given temperature (this value depends on the temperature). The density table for water is included in
Discovery balances.
P = Buoyancy of the solid in the auxiliary liquid (corresponds to A -B).
3.5.9 Density (Cont.
Sample Weighing in Air Sample Weighing in Liquid Buoyancy Sample Weighing
Mass
Sample
Place the solid in the Weighing Pan on the Weigh Below Hook in the liquid as shown. Ensure that there are no air bubbles on the solid to be
weighed.
Close the draft shield doors and weigh the solid (buoyancy P). The display indicates the density in grams/cc.
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