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Installation and Configuration Manual 7
Introduction
Installation Procedure Accuracy ConsiderationsElectrical ConnectionsIntroduction
1.5 Physical properties of gas compounds
1.6 Applications
The following are typical applications where specific gravity measurement is an essential parameter.
1.6.1 Supplementary gas supply
This system is used to top up normal supplies during peak periods. Specific gravity monitoring of a
propane/air mixture, for example, enables accurate control to be exercised over the ratio of the
mixture, therefore ensuring that the correct burning characteristic/calorific value is maintained.
Table 1-1 Physical properties of gas compounds
Compound Formula Molecular Weight
(1)
(1) Based upon 1961 atomic weights, referred to Carbon-12 Isotope (12 AMU), recommended by the International Commission of
Atomic Weights and the International Union of Pure and Applied Chemistry.
Specific Gravity
(2)
(2) Perfect gas specific gravity represents the ratio of molecular weight of compounds to the molecular weight of air.
Hydrogen H
2
2.01594 0.069600
Helium He 4.00260 0.138189
Water Vapour H
2
O 18.01534 0.621976
Nitrogen N
2
28.01340 0.967157
Carbon Monoxide CO 28.01055 0.967058
Oxygen O
2
31.99880 1.104752
Argon Ar 39.94800 1.379197
Air
(3)
(3) Molecular weight of air based upon components of atmospheric air given in Handbook of Chemistry & Physics, 53rd Edition
(1972–1973). Value of 28.96469 differs from figure 28.966 provided by NBS Circular 564 due to minute differences in component
content and changes in atomic weights of the elements given in 1961 (NBS value based upon 1959 atomic weights).
– 28.96469 1.000000
Hydrogen Sulphide H
2
S 34.07994 1.176603
Methane CH
4
16.04303 0.553882
Ethane C
2
H
6
30.07012 1.038165
Propane C
3
H
8
44.09721 1.5522447
i-Butane C
4
H
10
58.12430 2.006730
n-Butane C
4
H
10
58.12430 2.006730
i-Pentane C
5
H
12
72.15139 2.491012
n-Pentane C
5
H
12
72.15139 2.491012
Hexane C
6
H
14
86.17848 2.975294
Heptane C
7
H
16
100.20557 3.459577
Octane C
8
H
18
114.23266 3.943859