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the regular expansion of the solid hydrates HCOOH and
CH3COOH for many degrees below their melting point. The
considerable change of volume accompanying the melting
process of these compounds then begins at a premature stage
of temperature and gradually increases, until the whole mass
is transformed into the liquid state.
In the same degree that the acetic acid was purified from
adhering traces of water, these signs of premature melting
rapidly diminished, and the curve of regular expansion of
volume began to extend to the vicinity of the real melting
point, but nevertheless the purest hydrate, which I could
prepare by repeated distillation and crystallisation from 10
kilogrammes of ordinary acid. acet. puriss. did not show a
sudden transition, at any definite temperature, of the specific
volume of the solid into that of the liquid substance. I
therefore suspected, that a slight trace of foreign substances would
cause a similar anomaly in the melting-process of the ice, to
that, which a trace of water occasions in the behavior of the
solid acetic or formic hydrate; and that the negative results,
hitherto obtained by Plucker and Geissler as well as by
myself, were due to the absolute purity of the water. I resolved
first to try ordinary distilled water from one of the glass
reservoirs of the laboratory. The water had been kept there more
than a week, protected from dust etc., but in communication
with the air of the laboratory room. Silver nitrate and chlorid
of mercury with carbonate of sodium occasioned a faint
opalisa-tion in the fluid; other agencies were powerless. A drop of
the water, cautiously evaporated on a glass plate, left a visible
residue. I concluded that, with the exception of slight traces
of ammonium salts and of chlorine, the water was pure. The
volumes of ice from this sample of water are recorded in table
III. In the vicinity of the melting point the ice shows a
remarkable contraction of volume, 1 which seems to begin already
1 This fact recalls to our mind the old hypothesis, once supported by
Muschenbroek and de Mairan, that the ice expands its volume, when
cooled, and contracts, on being heated. Although this opinion was refuted
by the experiments of Placidus Heinrich already in the beginning of
this century, it was revived by Petzholdt in 1843, who tried to explain the
movement of the glaciers by the dilatation of the ice, caused by the winter
cold, and its contraction by the heat of the summer.
In order to corroborate his theory, Petzholdt determined the
expansion of ice by weighing a silver bottle filled with pure frozen water in ether
at different temperatures (from — 2° to — 8 R°) below zero. In fact the
coefficient of expansion was found to be negative at all temperatures.
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