4
4. Error Factors
The results of measurements may be affected by various factors that could cause errors
4-1. Buoyancy Of Air
A density measurement is influenced by an upward force of 0.0010 to 0.0014 g/cm
3
(buoyancy of air).
The density of air can be obtained by the equation below:
0.0012932
P
d
=
×
1
+
0.0036728 × t
1013.25
d : Density of air (g/cm
3
)
t : Air temperature (°C)
P : Atmospheric pressure (hPa)
When measurement accuracy of three significant digits is necessary, consider the buoyancy of air, add 0.001
g/cm
3
to the measured value to compensate for the error due to the air density.
4-2. Volume Of Float
The tolerance of the measured value of the volume of the float is
±
0.01 cm
3
.
In liquid density measurement, the decimal places beyond the third decimal place of the measured value contain
errors.
When measurement accuracy to the third decimal place or beyond is necessary, measure the volume of the
float using distilled water.
A
-
B
d
=
-
0.0035
ρ
-
d
V : Volume of float (cm
3
)
A : Mass of float in air (g)
B : Mass of float in liquid (g)
ρ
: Density of distilled water at t °C (g/cm
3
)
d : Buoyancy of air at t °C (g/cm
3
)
0.0035 : Correction value for the wire (diameter of 1 mm) of the density
pan connecting the upper and lower pans (when the beaker
provided with this kit is used)
4-3. Temperature Of Liquid
The density of the liquid that is used for measuring the density of a solid varies with the liquid temperature.
Therefore, the decimal places beyond the second decimal place of the measured value contain errors.
Obtain the density of a liquid according to the temperature from Table 1 for distilled water or from other reference
documents for other liquids.
When measurement accuracy to the third decimal place or beyond is necessary, use a thermometer with a
tolerance of
±
0.2 °C or less.
