OHAUS PJX Serie Bedienungsanleitung Seite 17

PJX Series Balance
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 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 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)
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. See illustrations below for placement of the sinker. When the sinker is
immersed in the liquid, it must not come into contact with the bottom of the beaker.
3
air buoyancy = effective density
3 volume of the body) is added to the
EN-15
3 of its