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Explorer
Pro
When the Pycnometer is used, it is filled with a known volume of a liquid. The density is arrived at as follows:
Density =
+ {
}
NOTE:
pycnometer may be obtained at laboratory supply firms.
• Follow the same procedure for solid density determination except select LIQUID under the Select material display. The
balance is prepared in the same manner.
Weight of full pycnometer - Weight of pycnometer
3.14
Density (Cont.)
3.14.3 Improving the Accuracy of the Result of Solid Density Determinations
The following tips should help you improve the accuracy of the results in the density determination of solids.
Temperature
Solids are generally so insensitive to temperature fluctuations that the corresponding density changes are of no consequence.
However, as work is performed with an auxiliary liquid in the density determination of solids, their temperature must be taken
into account as the temperature has a greater effect with liquids and causes density changes in the order of magnitude 0.1 to
1% per °C. This effect is already apparent in the third decimal place of the result.
To obtain accurate results, we recommend that you always take the temperature of the auxiliary liquid into account of all density
determinations.
Air Buoyancy
1 cm
3
air weighs approximately 1.2 mg (depending on the physical condition). As a consequence, in the weighing in air, each
solid experiences a buoyancy of this magnitude (the so-called "air buoyancy") per cm
3
of its volume.
However, the air buoyancy must be taken into account only when a result is required with an accuracy of 3 to 4 decimal places.
To correct for this, the air buoyancy (0.0012 g per cm
3
volume of the body) is added to the calculated result:
Calculated density
+ 0.0012 g/cm
3
air buoyancy
= effective density
Surface Tension of the Auxiliary Liquid
Adhesion of the liquid to the Weigh Below Hook causes an apparent weight increase of up 3 mg.
As the Weigh Below Hook is immersed in the auxiliary liquid in both weighings of the solid (in air and in the auxiliary liquid) and
the balance is tared before every measurement, the influence of the apparent weight increase can be neglected.
To reduce the effect of air bubbles and to ensure the greatest possible accuracy, use a few drops of a wetting agent (not
supplied) and add them to the auxiliary liquid.
3.14.4 Liquid Density Determinations
The density of a liquid can be made using either a sinker of known
volume
or a Pycnometer. When using the sinker, the sinker
is weighed in air and then in the liquid whose density is to be determined. The density
Q can be determined from the two
weighings as follows:
Q = Density of the liquid
A = Weight of the sinker in air
B = Weight of the sinker in liquid
V = Volume of the sinker
P = Buoyancy of the sinker in the liquid ( P= A-B )
Volume of pycnometer
Air
density
V
A - B
Q =
Summary of Contents for BH350
Page 64: ...56 Explorer Pro NOTES ...
