3B SCIENTIFIC PHYSICS U104001 Instructions D'utilisation page 22

the water bath and the measuring cell must attain the
desired temperature first.
8.5 Determining the mass of gas:
Blow the gas out of the measuring cell into a gas-tight
plastic bag and then weigh it:
•
If necessary, remove the gas supply pipe and
attach gas connection fittings.
•
Wind out the handwheel, say to 46 mm.
•
Open the regulating valve a little and release the
gas through the gas connection fittings into the
plastic bag.
•
Shut the regulating valve.
•
Determine the mass of the released gas. In doing
this, take into consideration the empty weight of
the bag and the buoyancy of air.
•
Reduce the volume of the measuring cell till the
pressure in the measuring cell has reached its
original value.
•
Calculate the original mass of gas from the vol-
ume difference before and after emptying the
measuring cell and the volume which is still pre-
sent in the measuring cell.
Comparison with quoted values:
Using tabulated values, e.g. Clegg et al. [4], it is alter-
natively possible to calculate the mass of gas in the
measuring cell from the measurements of ϑ, p, and V.
8.6 Evaluation:
We can clearly see from Fig. 5 that, despite the rela-
tively simple equipment, it is possible to achieve
measurements which match closely to the reference
values plotted on the graph.
8.7 Bibliography:
[1, 2] Sulphur Hexafluoride, in-house publication,
pp. 27 [1], 30 [2], Solvay Fluor und Derivate GmbH,
Hannover, Germany, 2000
[3] Otto and Thomas: Landolt-Börnstein – Numerical
Data and Functional Relationships in Science and
Technology, Vol. II, Section 1, Springer-Verlag, Berlin,
1971
[4] Clegg et al.: Landolt-Börnstein – Numerical Data
and Functional Relationships in Science and Technol-
ogy, Vol. II, Section 1, Springer-Verlag, Berlin, 1971.
[5] Din, F.: Thermodynamic Functions of Gases, Vol. 2,
Butterworths Scientific Publications, London, 1956
[6] Vargaftik, N.B.: Handbook of Physical Properties of
nd
Liquids and Gases, 2
Corporation, Washington, 1983
[7] Nelder, J. and Mead, R.: Comp. J., Vol. 7, p. 308,
1965
ed., Hemisphere Publishing
9. Storage for long periods without use
If no experiments are to be conducted over a long
period, the test gas should be released and the piston
should be turned to its rest position where the conical
rubber seal is only very slightly curled and does not
press against the walls of the measuring cell.
•
If necessary, allow the equipment to cool. Wind
the handwheel back till the lowest possible pres-
sure is present.
•
Release the test gas through the flush valve.
•
Turn the handwheel to move the piston to its
"rest position", at approx. 5 mm.
•
Shut the flush valve again.
•
Before storing away the equipment, the hydraulic
fluid needs to be degassed (as described in chap-
ter 10) if the equipment has been in use over a
long period of time.
•
Store the equipment in a safe place where it is
not exposed to direct sunlight.
•
The thermal medium should be kept in the appa-
ratus during storage, as the additives inhibit cor-
rosion and efflorescence caused by electrochemi-
cal potentials between the different materials. Al-
ternatively, the apparatus can be flushed with de-
ionised water and then dried using compressed
air (oil-free, max. 1.1 bar).
8