Sartorius YDK03 Betriebsanleitung Seite 12

Air Buoyancy
A volume of 1 cm 3 of air has a weight 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 cm
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
air under standard conditions (temperature
20°C, pressure 101�325 kPa)�
12 12
3
of its volume�
+ ρ (a)�
3
= Density of
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 =
corr [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 (90 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)