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The determination of the change of volume by the melting
of the ice in experiment II miscarried. I was obliged
therefore to start from the volume of the ice (= 1.089038) at — 10° C
found in experiment I, in calculating the volumes of the frozen
water in Table II. It is evident that this circumstance does
not alter the whole character or the outline of curve II in
plate 22 in the slightest degree, although its position (i. e. the
exact value of the sp. volume of the ice) may be either a few
millionths higher or lower than the numbers given in Table II.
From the above tables and from the graphic
representation in plates 21 & 22 it will be seen, that also the purest ice,
which can be tested by experiments, is liable to premature
contraction of volume before melting. It is impossible to
decide, if absolutely pure water would be entirely free from
this weakness or not, since we can not assume that water,
which has boiled for a quarter of an hour or more in a glass
vessel, is absolutely free from minimal quantities of foreign
substances .as f. ex. sodium salts, silicia etc. For my own
part I am rather inclined to think, that absolutely pure water,
if it could be tested, would show an absolutely fixed melting
point, but I think, that this problem very much resembles
another question still undecided, viz. is absolutely pure ivater a
conducting or non-conducting substance for electricity? In fact
Kohlrausch has found, that the purer the water is, the
greater is the resistance, which it offers to the electric current,
and that we may by chemical j>urification and repeated
distillations etc. approach a point, where the resistance tends to be
insurmountable for every electromotoric force. In the
behavior of solid bodies just before their melting points I think I
have found another, almost equally sensible, proof of their
chemical purity. The regular coefficient of expansion of pure
water in the solid state (see Table I) slowly increases from
O.000165 [the average value between —17° C and — 10° C] to
O.oooi7i or O.000174 [between —4° and —3° C] but then
gradually begins to decrease and finally changes its sign between
— 0°. 15 and —0°.os C, where the ice begins to contract instead
of expanding its volume. This point of inversion is reached
by water II already between —0°.3o and —0°.os C and by III
between — 0°.35 and — 0°.25. In order to obtain a stricter
comparison we must refer to the preceding tables, as the
graphic representation on plate 22 does not give us a clear idea
of variations beyond O.ooooi of the unit of volume [1 cc. of the
water at 0°]
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