Metrohm 797 VA Computrace - Manual (Page 85)

3.4 Safety considerations concerning mercury
797 VA Computrace / Hardware-Manual 8.797.8001EN
77
3.4 Safety considerations concerning mercury
3.4.1 Properties of mercury
The most important properties of mercury (Hg) are listed in the Table below. This
compilation allows the following summary:
• Mercury is a heavy metal with a very high density and is liquid at room tem-
perature.
• Mercury is mobile at room temperature and tends to form drops because of its
high surface tension. The surface tension is around 6 times greater than that of
water; Hg is thus not wetted by water.
• Mercury has a relatively high electrical conductivity (at room temperature it is
only some 60 times lower than that of silver).
• Mercury has a relatively high vapor pressure compared with other metals.
Mercury vapor is some seven times heavier than air (so that it sinks rapidly and
specifically to the floor).
• The odor threshold is very high relative to the threshold limit value (TLV).
• Air saturated with Hg vapor (which naturally does not occur in practice) con-
tains approximately 250 times the amount of Hg specified by the TLV at room
temperature.
Properties of mercury
Property Value Ref.
Density ρ (liquid mercury) 13.5451 g/cm 3 (at Θ = 0 °C) [1]
Density ρ (mercury vapor) 8.959 g/dm 3 (at Θ = 0 °C) [2]
Melting point Θ
F
–38.86 °C (at p
air
= 1.01325 bar) [3]
Melting enthalpy Δ H
F
2.295 kJ/mol (at p
air
= 1.01325 bar) [3]
Boiling point Θ
V
356.73 °C (at p
air
= 1.01325 bar) [3]
Boiling enthalpy Δ H
F
59.1 kJ/mol (at p
air
= 1.01325 bar) [3]
Vapor pressure p 0.0253 Pa (at Θ = 0 °C)
0.17 Pa (at Θ = 20 °C)
0.391 Pa (at Θ = 30 °C)
0.81 Pa (at Θ = 40 °C)
1.69 Pa (at Θ = 50 °C)
[2, 4]
Mass concentration ρ in air
(after reaching equilibrium)
2.0 mg/m 3 (at Θ = 0 °C)
13.6 mg/m 3 (at Θ = 20 °C)
29.6 mg/m 3 (at Θ = 30 °C)
62.7 mg/m 3 (at Θ = 40 °C)
126 mg/m 3 (at Θ = 50 °C)
[2, 4]
Evaporation rate 85 μg/h·cm 2 (at Θ = 25 °C) [2]
Surface tension σ 4.67·10 –3 N/cm (at Θ = 20 °C) [5]
Electrical conductivity κ 1.044·10 4 S/cm (at Θ = 20 °C) [6]
Odor threshold 13 mg/m 3 [2]
Threshold limit value (TLV) for air
for mercury
for organic mercury com-
pounds (calculated as Hg)
0.1
mg/m 3
0.01 mg/m 3
[4, 7]
[2, 4, 7]