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9.—DETERMINATION OF THE SPECIFIC GRAVITY. 
The specific gravity of the water at 17°5° C. (0 17°5) was 
determined by means of areometers made by Stegel at Kiel, 
a salinometer of Hicks, and in a few cases by a hydrometer 
of Negretti and Zambra. 
Several observations were made with the Kiel areometers 
at different temperatures, and these values were then cor- 
rected for temperature and the glass of the instrument by 
means of Knudsen’s Hydrographical Tables. 
The temperature of the water at the time of the observa- 
tions was observed by means of a thermometer made by 
Stegel of Kiel, and graduated to 0°2° C. . 
By means of these determinations at different tempera- 
tures it was hoped that some of the errors due to a single 
observation would be avoided. The Negretti and Zambra 
hydrometer was a small pocket instrument, and it is remark- 
able how good are the values obtained by it, but at the same 
time it must be noted that all values obtained with it are 
about 0°0014 too low. This presumably is due to the scale 
not being accurately placed in the stem. 
The values of the Kiel areometers are given to five decimal 
places, but the last place is obtained in the correction above 
mentioned, and is not read on the instrument except in a 
very few cases. 
In the annexed table the values obtained with these in- 
struments are given, and also, for comparison, that calculated 
from the chlorine value. In the case of the areometer read- 
ings the maximum and minimum are given so as to show 
the error between the readings at different temperatures. 
The density of the water at 0° C. referred to distilled 
water at 4° C. was calculated from the above figures, and is 
given in the tables at the end of the paper. 
