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I Fordunstningsmaaleren B begynder Forsøget med
en Vandmængde af 263 cbcm. eller en Vægt af 270 Gram.
der indeholder 9.56 Gram Salt. Den største
Fordunstnings-mængde, der er maalt, er 60 cbcm. Ved Forsøgets Slutning
indeholder Skaalen 270 minus 60 eller 210 Gram Vand.
der holder 9.56 Gram Salt eller 4.55 pro Cent. Den
spe-cifiske Nægter voxet fra 1.027 til 1.0347, altsaa mere end
i det foregaaende Exempel.
Fordunstningshastigheden er, cæteris paribus,
proportional med Forskjellen mellem Vanddampenes
Maximums-tryk (E) over den fordunstende Vædske og
Vanddampenes-Tryk i Luften (e). Kaldes den i Tidsenheden fordunstede
Vandmængde f. og er a en Constant, saa har man
f = a (E—e).
Antages e constant, har man
evaporating dish. These 515 grammes ot water contain the
whole amount of salt, 22.65 grammes, or the proportion of
salt is 4.40 per cent. Hence, the specific gravity of the
. water has increased from 1.027 to 1.0336.
In the atmometer B, the experiment begins with a
volume of water of 263 ccm., or a weight of 270 grammes,
containing 9.56 grammes of salt. The greatest evaporation
measured was 60 ccm. At the end of the experiment, the
evaporating dish contained 270 minus 60, or 210 grammes
of water, with 9.56 grammes of salt, or 4.55 per cent.
Hence, the specific gravity had increased from 1.027 to
1.0347, a greater value, therefore, than in the case given
above.
The rate of evaporation is, cæteris paribus,
proportionate to the difference .between the maximum tension of the
aqueous vapour (E) above the evaporating fluid and the
tension of the aqueous vopour (e) present in the air. Let
the quantity of water evaporated in the unit of time be /
and a be a constant, we have then, j — a (E—e).
Supposing e to be constant,
df = f
dE
E-e
hvor df er den Correction, som skal lægges til f. naar E
gaar over fra E til E + dE. Trykket E over Saltvand
kan ifølge Wiillners Lov1 sættes
df=f
dE
E-e
df representing the correction to be applied to / when E
changes from E to E -)- d E. The tension E above the salt
water can, according to Wiillner’s law,1 be put —
E = E„ 1 — a
hvor E-i er Maximumstrykket af Dampene over rent Vand,
a en Constant (der for Chlornatrium er 0.601), y
Mængden af Salt og x Mængden af rent Vand. I vort
Exempel fra Fordunstningsmaaleren B have vi Temperaturen af
Fordunstningsvandet 7".6, hvortil svarer E0 = 7.mm78 og
Middelværdien af e — 5.mm15 efter Psychrometret. Man
faar saaledes følgende Regning.
■ E0 representing the maximum tension of the vapour above
fresh water, a a constant (which for chloride of sodium
is 0.601), y the amount of salt, and x the quantity of
fresh water. In the example from the atmometer B, the
mean temperature of the evaporating water was 7°.6,
corresponding to E0 = 7.ram78, and the mean value of
e zz 5.mm 15, by the psychrometer. The computation from
these data is as follows: —
Ved Begyndelsen.
(At Commencement).
V - 9-56
x — 270—9.56 = 260.44
0.0367
y _
X
0.02206
Ved Slutningen.
(At End).
9-56
210 — 9.56 = 200.44
0.0476
0.02861
Poggendorffs Annalen, Bd. lUii.
O.97794
7.62793
O.97139
7-57684
Poggendorffs Annalen, Bd. 1 Oil
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