This error, of course, makes the yield from the sample
appear higher than it actually is. Its effects may be compensated by
allowing time for the water in the generator or gasholder to cool to its
original temperature before the final reading is made.
With regard to the measurement of the temperature of the evolved gas in
the bell gasholder, it is usual to assume that the reading of a
thermometer which passes through the crown of the gasholder suffices. If
the thermometer has a very long stem, so that the bulb is at about the
mid-height of the filled bell, this plan is satisfactory, but if an
ordinary thermometer is used, it is better to take, as the average
temperature of the gas in the holder, the mean of the readings of the
thermometer in the crown, and of one dipping into the water of the holder
seal.
The following table gives factors for correcting volumes of gas observed
at any temperature and pressure falling within its range to the normal
temperature (60 deg. F.) and normal barometric height (30 inches). The
normal volume thus found is, as already stated, not appreciably different
from the volume at 15 deg. C. and 760 mm. (the normal conditions adopted
by Continental gas chemists).
Pages:
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694