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at —0°.25 C. Still more easily this contraction may be followed
by the deflection of the curve III (marked with red) on plate 22.
I next proceeded to the examination of entirely pure
water, prepared by repeated distillation of water from the well
of St. Eric in Upsala, which according to the analyses of Prof.
Almén gives the purest drinking water in Sweden. Two
separate experiments were made with such water. The volumes
of the ice are found in tables I & II and are graphically
represented in plate 1 22 by the red curves I & II. These
measurements were taken with two different dilatoineters, but this
circumstance will hardly suffice to account for the marked
discrepancy of the curves of volumes. The real cause seems
to be, that in experiment II the water was boiled for more
than an hour by the operation of filling the instrument and
therefore has dissolved a trace of the substance of the glass
reservoir. In experiment I, which I undertook last of all, I
purposely restricted the boiling operation to the least possible
time. Still the inflection of curve I on plate 21 & 22 clearly
shows, that the purest water, which can be employed in
dila-tometric experiments, also contracts its volume before melting.
». . . . Bei Abnahme der Temperatur fand stets eine Ausdehnung und
bei Zunahme der Temperatur stets eine Zusammenziehung statt, und zwar
ergab sich, wenn die Längenausdehnung bei — 1° R = 1 gesetzt wird,
die lineare Ausdehnung im mittel für Erkältung um 1° R
in d. 2ten Versuchsreihe, bei Erkält, v. —2’R bis —7’.s R zu O.oooäc..
» » 3ten » » » » » —2° » » —7° » » O.oooio..
» » 4ten » » » * ■> —2° » » —8° » »O.00037..
etc...» [Beiträge zur Geognosie von Tyrol, Leipz. 1843].
If Petzholdt had employed ice from salt water in his experiments,
we would find no difficulty in explaining the negative coefficient of expansion.
In chapter 4 we will meet with some specimens of sea ice, which show
very considerable contractions, when cooled. But as lie asserts, that the ice
of his experiments was formed from pure water (»luftfreies destillirtes
Wasser»), which does not show any abnormal contraction below —0°.3 C,
we must admit the justness of the remark of Brunner, who in 1845
re-jieated the experiments of Petzholdt and found the coefficient of
expansion of ice to be positive and greater than that of any other solid:
»II résulte donc de mes expériences, que la glace se contracte par le
froid, ainsi que les autres corps solides, ce qui est directement opposé aux
observations de Mr. Petzholdt» (Bibliothèque universelle de Genève T. LVI).
Notwithstanding this, some of the observations of Petzholdt on
glaciers highly merit our attention. If we confine the application of his theory
to those limits, where a contraction by heat really takes place in the
glacier-ice, i. e. to temperatures in the immediate vicinity of zero, we certainly can
not deny, that this phenomenon must have something to do with the
movement of the glaciers.
’ For the sake of distinctness the curve II is left out in plate 21.
18
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