VEGA- EXPEDITION ENS VETENSKAPLIGA ARBETEN, 331 



^ 1.0280 



U.oooi ^ — - — (.r — 1.00002754) 



X = 1.000124 



that is: only in easé the coefficient of expansion of the water 

 was = 0.000124 or greater, would the rise of temperature from 

 0° to + 1° C have any perceptible influence on the areometric 

 determination of the spec. gravity. According to Ekmans 

 determinations, which are graphically represented in plate 

 23, the volume at + 1° of 1 cc. of the sea-water in question 

 is about 



X == 1.000060 



the coefficient of expansion between O" and + 1° C being less 

 than 0.000062. We would therefore obtain with our instrument 

 precisel}" the same result at + 1° G as at zero, and the num- 

 ber found at + 1^ C can be used indiscriminately to denote 

 the specific gravity at 0°. Pursuing this calculus further we 

 find, that we need not apply an}' correction on account of 

 the temperature to 

 water of I.0280 spec. gr. from a few degrees below 0° to + 3° C 



» » 1.0170 » » » 0^ to + 5^ C 



» » 1.0090 y » » 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 aud 1.01703 aiid 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 practicalh' is the best adapted starting- 

 point for areometric measurements of the specific gråvit}^ of 

 all kinds of sea-water, as the instrument in the vicinity of zero 

 is freeä from the clisturhing 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, ^ the readings on the scale of the areom- 

 eters denote without corrections the true specific gravity at 



(f 01" ZTJ^ C — pro vid ed the instrument was originally adjusted 

 to these standards of temperature. Otherwise, as in the case 

 of the Vega areometer, which is graduated at . ^^. C, a special 

 correction is necessar}'-, which can only be supplied by experi- 

 ment. For the numbers representing the specific gravity 



* Not even to keep it constant ! 



