OSMOTIC PRESSURES DERIVED FROM VAPOUR-PRESSURE MEASUREMENTS. 303 
the same cause has to be applied to the volume of the piezometer, for it is evident 
that the higher the mercury in the stem, the more the walls of the bulb are caused 
to come in towards each other. 
To obtain this correction a set of separate experiments was made with each 
piezometer, thus : the piezometer was inverted and filled (up to the graduations in 
the stem) with recently boiled water. The stem was then connected to a mercury 
manometer by means of a T-piece, so that by joining the T to an exhaust pump, the 
pressure on the water could be reduced and the amount of the reduction measured on 
the manometer. The change in volume caused by the change in pressure is given 
directly by the difference in readings of the water meniscus. These two corrections 
(together with others which will be understood readily) as applied to the experiment 
of June 12, are shown in Table I, 
Table I. 
Ob¬ 
served 
pressure. 
Correc¬ 
tion to 
pressure 
for 
excess 
of 
external 
pressure. 
A. 
Cor¬ 
rected 
pressure. 
Observed 
Correction to the volume for — 
Mean 
Mean co- 
, relative efficient 
V olume 
of co " °* 
t ,. efficient compres- 
solution 
. -i \ ot sibility 
corrected. £ J 
compres- ot 
sibility. solution. 
# 
Pressure 
range 
above 
atmo¬ 
spheric 
pressure. 
readings 
of 
mercury 
meniscus 
in 
stem. 
V olume 
of 
solution 
un- 
eorrected. 
Tempera¬ 
ture. 
Reading 
of Excess of 
mercury ( external 
meniscus [ pressure 
in upper i B. 
capillary, j 
atmo- 
atmo- 
spheres. 
c.c. 
10~ 5 X 10~ 5 x 
spheres. 
17 01 
-0 -00 
17 -01 
209 -5 
32 -42119 
o -o 
o -o o -o 
32 -42119 
2 "550 2 773 
17 to 51 
51 -03 
-0 -09 
50 '94 
132 0 
32 -39319 
-o -ooooi 
0-0 -0 -00004 
32 39314 
2.528 2-751 
51 „ 85 
85 '05 
- 0'19 
84-86 
55 -0 
32 -36541 
o -o 
0-0 - 0 -00008 
32 -36533 
2 -529 2 -751 
85 „ 51 
51 -03 
-0 09 
50-94 
131 -9 
32 39315 
+ 0 -00005 
-0 -00001 -0 00004 
32 -39315 
2 -550 2 -773 
51 „ 17 
17 01 
-0 
17-01 
T209 -41 
32 -42115 
+ 0 '00005 
o-o -o-o 
32 -42120 
estimated 
* These values are obtained by adding the coefficient of compressibility of the glass of the piezometer (=0 '223 x 10 5 ) 
to- the numbers in the preceding column. 
The Results. 
Compressibility of Mercury .—The following is a summary of our results with 
mercury. Five observations were made :— 
■With Piezometer 1 a. The mean relative coefficient at 0° C. between 
1 and 101 atmospheres was 0‘169x 10 -5 . 
With Piezometer 7. The mean relative coefficient at 1°‘8 C. between 
1 and 110 atmospheres was 0'171 x 10~ 5 . 
With Piezometer 1a. The mean relative coefficient at 29°'5 G. between 
8 and 150 atmospheres was 0'165x 10~ 5 . 
2 s 
VOL. CCXVIir.-A. 
