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A 1 0280 , i
U.oooi = —— (x — I.00002754)
X = 1.000124
that is: only in casé the coefficient of expansion of the water
was = 0.000124 or greater, would the rise of temperature from
0° to + Io C have any perceptible influence 011 the areometric
determination of the spec, gravity. According to Ekmans
determinations, which are graphically represented in plate
23, the volume at + Io of 1 cc. of the sea-water in question
is about
X = 1.000060
the coefficient of expansion between 0° and + Io C being less
than 0.000062. We would therefore obtain with our instrument
precisely the same result at + Io C as at zero, and the
number found at + Io C can be used indiscriminately to denote
the specific gravity at 0°. Pursuing this calculus further we
find, that we need not apply any correction on account of
the temperature to
water of I.0280 spec. gr. from a few degrees below 0° to + 3° C
» » l.ono » » » 0° ...............to +5° C
» » 1.0090 » » » 0° ...............to + 9°.5 C.
I have tested the truth of this experimentally with the Vega
areometer and 3 samples of sea-water of different spec, gravity
1.02819, 1.02548 and 1.01703 and found, that the instrument floats
quite immovably in these waters between the aforesaid limits
of temperature.
We may infer from this, that the freezing point of water
theoretically and practically is the best adapted
starting-point for areometric measurements of the specific gravity of
all kinds of sea-water, as the instrument in the vicinity of zero
is freed from the disturbing influence of variations of temperature.
If experimenting a few degrees above or below zero, as was
usually the case on board the Vega, we need not mind the
temperature at all, 1 the readings on the scale of the
areometers denote without corrections the true specific gravity at
ó"’ or ipr5 O — provided the instrument was originally adjusted
to these standards of temperature. Otherwise, as in the case
of the Vega areometer, which is graduated at qrjT’ a sPec’a^
correction is necessary, which can only be supplied by
experiment. For the numbers representing the specific gravity
1 Not even to keep it constant!
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