OHAUS Pioneer PX Serie Manual De Instrucciones página 17

PX Series Balance
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 Density Than Water
For density determination of solids with a density less than 1 g/CM
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.
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 0.5 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 CM3 of air weighs approximately 1.2 mg (depending on the physical condition). As a consequence, in the
weighing in air, each solid experiences buoyancy of this magnitude (the so-called "air buoyancy") per cm
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
calculated result:
Calculated density + 0.0012 g/cm
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 (P/N: 83034024) 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)
3
, the bottom of the Weigh Below Hook for solids
3
air buoyancy = effective density
3
volume of the body) is added to the
EN-15
3
of its