The whole is kept at a gentle temperature for an hour or an hour and a
half, so as to allow the decomposition to commence very slowly; the
first portions of acid which come over are rejected as they carry with
them traces of water remaining in the salt. The platinum receiver is
then attached, and the heat increased, allowing the decomposition to
proceed with a certain degree of slowness. The receiver is then
surrounded with a mixture of ice and salt, and from this moment all
the hydrofluoric acid is condensed as a limpid liquid, boiling at
19.5 deg., very hygroscopic, and, as is well known, giving abundant fumes
in presence of the atmospheric moisture.
During this operation the platinum U tube, dried with the greatest
care, has been fixed with a cork in a cylindrical glass vessel
surrounded with chloride of methyl. Up to the moment of introducing
the hydrofluoric acid, the leading tubes are attached to drying tubes
containing fused caustic potash. To introduce the hydrochloric acid
into the apparatus, it may be absorbed through one of the lateral
tubes in the receiver in which it is condensed.
In some experiments we have directly condensed the hydrofluoric acid
in the U tube surrounded with chloride of methyl; but in this case
care must be taken that the tubes are not clogged up by small
quantities of fluoride carried over, which would infallibly lead to an
explosion and projections, which are always dangerous with so
corrosive a liquid.
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