OHAUS PJX Serie Manual De Instrucciones página 16

EN-14 PJX Series Balance
The density Q is the quotient of the mass m and the volume 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:
The balance allows direct determination of the buoyancy P (P =A - B) and consequently the above formula can be
simplified:
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).
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.
Solid Density Determinations for items Less Dense Than Water
For density determination of solids with a density less than 1 g/CM3, the bottom of the Weigh Below Hook for
solids must be used as it holds the solid body below the surface of the auxiliary liquid. If the buoyancy of the solid
is greater than the weight of the Weigh Below Hook, the Weigh Below Hook must be weighted by placing an
additional mass on the submerged part of the Weigh Below Hook as shown.
Weigh the sample in air first as explained in the previous procedure.
After loading the additional mass, tare the balance and start the weighing again. Wait until the balance has
reached stability and note the displayed weight P (buoyancy of the solid).
Improving the Accuracy of the Result of Solid Density
The following tips should help you improve the accuracy of the results in the density determination of solids.