This fact is
now recognised by meter-makers, and meters of all suitable sizes can be
obtained. It is desirable, if an ordinary coal-gas meter is being bought
for use with acetylene, to have it subjected to a somewhat more rigorous
test for soundness than is customary before "stamping" but the makers
would readily be able to carry out this additional test.
The two types of gas-meter are known as "wet" and "dry." The case of the
wet meter is about hall-filled with water or other liquid, the level of
which has to be maintained nearly constant. Several ingenious devices are
in use for securing this constancy of level over a more or less extended
period, but the necessity for occasional inspection and adjustment of the
water-level, coupled with the stoppage of the passage of gas in the event
of the water becoming frozen, are serious objections to the employment of
the wet meter in many situations. The trouble of freezing may be avoided
by substituting for the simple water an aqueous solution of glycerin, or
mixture of glycerin with water, suitable strengths for which may be
deduced from the table relating to the use of glycerin in holder seals
given at the close of Chapter III.
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