ON THE USE OF THE HYDROMETER OF TOTAL IMMERSION. 25/ 



determinations. ^ The length of their body was a Httle more 

 than 15 cm., their diameter 35 cm. Both were furnished with 

 a stem 3 cm. in length, and 1'5 mm. in diameter, graduated 

 into millimetres. Küchler No. 1 weighed about 120 gr., and 

 its volume was 118 cub. cm.; Küchler No. 3 weighed about 

 121 gr. and its volume was 118 cub. cm. The stem of No. 3 

 was broken in October, 1900, and that of No. 1, with which 

 the majority of the determinations were made, was broken in 

 April, 1901. The object of the thin, graduated stem was, that 

 the number of millimetres of the stem above the water surface 

 might give the observer almost at once some idea of the number 

 of milligrammes with which the hydrometer would have to be 

 loaded in order to sink. 



In practice this has pi'oved to be unneccessary, as with a 

 little experience it is easy to judge of the additional weight 

 required from the rapidity with which the hydrometer rises 

 through the liquid, when it has gone below the surface. It is 

 therefore recommended that the hydrometer of total immersion 

 be made with a thick, strong stem, about 1 cm. in length, so 

 that the instrument cannot easily be broken. 



The object of the stem is solely to afford a safe and con- 

 venient place for the platinum spiral, as PI. 23, fig. 3 shows. 



At first I made some of the determinations in a Dewar's- 

 cylinder, some in a glass cylinder placed in a water bath. I 

 soon found that the bath gave the more constant temperature, 

 and therefore the more reliable determinations. During the 

 winter there was no fire in the laboratory at night, and the 

 water-samples were therefore much cooled down by the morning, 

 generally 8 or 10° C. below the day-temperature of the room. 

 In a Dewar's cylinder the temperature of the water-sample rose 



^ For control tests four hydrometers of Jena Glass No. 59 m made by 

 C. Richter (Berlin) have been used. These instruments have volumes 

 about 66 ccm. and their specific gravities are about 1"000 at 17"5° C. 

 Their absolute weight and volume have been determined at the Reichs- 

 anstalt, at Charlottenburg. 



Nyt Mag. f. Naturv. XXXIX, HI. 17 



