If the generation of gas is irregular, as when an apparatus of
the type described above is used, it is advisable to insert a small
gasholder or large bell-governor between the washer and the meter. The
meter must be provided with a thermometer, according to the indications
of which the observed volumes must be corrected to the corresponding
volume at normal temperature.
If apparatus such as that described above is not available, fairly
trustworthy results for practical purposes may be obtained by the
decomposition of smaller samples in the manner described below, provided
these samples are representative of the average composition of the larger
sample or bulk, and a number of tests are made in succession and the
results of individual tests do not differ by more than 10 litres of gas
per kilogramme (or 0.16 cubic foot per pound) of carbide.
It is necessary at the outset to reduce large lumps of carbide in the
sample to small pieces, and this must be done with as little exposure as
possible to the (moist) air. Failing a good pulverising machine of the
coffee-mill or similar type, which does its work quickly, the lumps must
be broken as rapidly as possible in a dry iron mortar, which may with
advantage be fitted with a leather or india-rubber cover, through a hole
in which the pestle passes.
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