1906-7.] On the Application of a Differential Densimeter. 231 
that after five or six minutes’ immersion it was practically impossible to 
detect any change in the volume of the contained water. 
The temperature of the water-bath was indicated by a Baudin thermo- 
meter graduated to of a degree Centigrade, and previously compared 
with a standard thermometer from Kew. The water-bath was large, and 
was maintained at a uniform temperature throughout by a stirrer of the type 
devised by Griffiths for his re-determination of the mechanical equivalent 
of heat ; * this stirrer, driven by a small electro-motor, proved both con- 
venient and efficient. 
The method of procedure adopted for the determination of the relative 
densities of the waters has already been described in a former communica- 
tion ; f it may, however, be stated that all the weighings of any pyknometer 
and its contents were effected with the instrument placed first in one pan 
of the balance and then in the other, suitably adjusted counterpoises being 
employed, as first advocated by Regnault. The weighings were performed 
with a short-beam Bunge balance sensitive to ^ of a milligram, and a set 
of re-standardised weights. 
After the constants of the various pyknometers had been ascertained, 
it was deemed advisable to test their accuracy by a determination of the 
relative density of some one sample of water with all five instruments ; 
and for this purpose the sample marked No. 30 was chosen, because it 
contained the largest amount of chloride, and would therefore ensure the 
detection of any discrepancy that might exist, with a greater degree of 
certainty. 
The following are the results obtained : — 
Pyknometer. 
Approximate 
Capacity. 
Relative 
Density A 18 . 
Difference from 
Mean Value. 
a. 
15*92 c.c. 
1-03188 
± -ooooo 
P- 
15-60 n 
89 
+ 1 
y- 
16-19 m 
85 
3 
8. 
18-85 ,, 
91 
+ 3 
e. 
19-64 h 
87 
1 
Mean = 
1-03188 
From the above it was inferred that the constants of the pyknometers 
were as nearly as possible correctly determined. 
* Phil. Trans ., vol. A, 1893, p. 435. 
t Proc. Roy. Soc. Edin., 1903, p. 356. 
