If water vapour is to be removed from gases external to the instrument, calcium chloride
(CaCl
2
) is an inexpensive and efficient chemical to use. When absorbing moisture however, it
forms a corrosive liquid and therefore the container should be made of glass, with a moisture
trap.
‘Silica gel’ is a good indicating drier, but can ‘hang on’ to some gases, especially C0
2
, giving
false readings, and is not generally recommended.
2.8.2 Carbon Dioxide
To remove C0
2
, usually in a C0
2
Instrument, indicating ‘soda lime’ is used. Soda lime consists
of about 80% calcium hydroxide ((Ca (0H)
2
)), 4% sodium hydroxide (NaOH) and 0.2%
indicator (green to brown).
In use, soda lime changes from green to brown and must be changed when green is no longer
visible. It is not recoverable. Replacement supplies are available from ADC (Spares & Service)
Ltd or their local authorised agents.
Other chemicals may produce corrosive by-products which can damage the instrument.
2.8.3 Precautions
Any chemical intended for use in the instrument is provided with it in a separate container,
labelled with international identification labels. Under normal use, the quantity supplied will last
for about 6 months to a year. Replacements can be obtained from ADC (Spares & Service)
Limited who will also advise on the use of chemicals obtainable by the User.
When handling chemicals, refer to the ‘Safety Letter’ enclosed in the manual for precautions
against possible health risk. For all chemicals, avoid skin and eye contact and do not taste or
swallow them.
As Magnesium Perchlorate is an oxidising agent, do not bring it into contact with
combustible material and dispose of it in a sealed glass container.
2.9 Pre-operation Checks
Before connection power to the instrument, check:
1. The voltage indicated on the voltage selector matches the local supply
2. That gas connections are leak free
3. That the exhaust gas venting arrangements are safe for the gases in the sample
4. That the instrument is properly grounded (earthed).
2.10 General Advice
2.10.1 Use of Gas Cylinders
Before use, Gas Cylinders must be checked to ensure that -
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