130 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



2. — Determination of the Specific Gravity. 



The specific gravity of the water at 17'5° C. (p 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. 



