Sartorius YDK 01-0D Betriebsanleitung Seite 18

To correct the liquid density for
temperature, proceed as follows:
– measure the temperature of the liquid
using the thermometer that comes
with the kit
– use the table at the back of this manual
to find the density of the most commonly
used liquids, water and ethanol, at
the temperature measured, and use this
density for the value ρ (fl).
Air Buoyancy
3
A volume of 1 cm
of approximately 1.2 mg, depending
on its temperature, humidity and air
pressure. When weighed in air, a solid
is buoyed by a corresponding force per
3
cm of its volume. The error that results
if the air buoyancy is not allowed for
shows up in the third decimal place and
should therefore be corrected.
The following formula allows
for air buoyancy:
W (a) · [ρ (fl) – ρ (a)]
ρ =
W (a) – W (fl)
Where ρ (a) = 0.0012 g/cm
Density of air under standard
conditions (temperature 20°C,
pressure 101.325 kPa).
18
of air has a weight
+ ρ (a).
3
=
Depth of Immersion
The pan for holding and/or immersing the
sample during weighing in liquid is rigidly
attached to two wires and is immersed
approximately 30 mm below the surface
of the liquid. Since the balance is tared
before each measurement, the additional
buoyancy caused by the immersed part
of the measuring device is not allowed for
in the specific gravity determination.
When a solid sample is weighed in liquid,
a volume of the liquid will be displaced
which corresponds to the volume of the
solid sample. This causes the attachment
wires of the pan hanger assembly to be
immersed deeper and generate additional
buoyancy which introduces an error in
the specific gravity determination.
Use the following formula to correct
this error:
W (a) · [ρ (fl) – ρ (a)]
ρ =
0.99983 [W (a) – W (fl)]
Since the correction factor is determined
exclusively by the geometry of the
measuring device setup, be sure to only use
the large diameter beaker (76 mm) from
the kit when determining the specific
gravity of a solid. The "Supplement"
to this manual shows how this correction
factor is derived.
+ ρ (a)