Rice Lake Ohaus Explorer Pro High Capacity Instuction Manual - Manual (Page 38)

EN-34 Explorer Pro
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.
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.I 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 on all
density determinations.
Air Buoyancy
1
1 1 1 1 CM 3 of 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),
the influence of the apparent weight increase can be neglected
because the balance is tared before every measurement.
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.
Liquid Density Determinations
The density of a liquid can be made using a sinker of known
volume. 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)
Q = A - B
V
In DENSITY SETUP, set Mode to Liquid Density and enter sinker
volume in cc’s.
After weighing the sinker in air and then weighing the sinker
immersed in liquid, the balance calculates the density of the
liquid and is displayed in grams/cc.