THE PROPERTIES OF WATER AND OF STEAM. 
129 
At 50°, at which the vapour-pressure is 92 millims., the vapour-densities are all 
high, but do not rise rapidly after the first one. The highest pressure registered 
(7075) approached the vapour-pressure. 
At 40° the vapour-pressure is 54"9 ; the highest pressure read was 54T. The rise 
of vapour-density is slow at first, and afterwards more rapid. 
At 30° the vapour-pressure is 31'55 millims., while the highest pressure read was 
3T05 millims. The vapour-densities are very high, and rise rapidly with decrease of 
volume; and at 25° the vapour-pressure is 23'55 millims., the highest pressure read 
being 23'35. Again, there is a rapid increase of density with diminishing volume. 
These pressures are all somewhat lower than the values given by Regnatjlt. 
( b ). Weight = 0'00295 grm. 
The tube was heated to 100°. 
Tempera¬ 
ture. 
Pressure. 
Volume. 
Vapour- 
density. 
o 
millims. 
c.c. 
100 
25-1 
152-4 
8-94 
287 
131-3 
9-08 
34-1 
110-4 
9-08 
41-45 
9113 
9-05 
52-4 
72-34 
9-02 
The tube was then cooled with the mercury at the same height as at the last 
reading, and then, without drawing down the mercury, the tube was heated to 40°. 
In this case there was no possibility of condensation of vapour on the lower part of 
the tube, while previously, when readings were begun at the largest volume, con¬ 
densation might have taken place on the lower part of the tube. If, therefore, the 
high vapour-densities are due to adhesion and condensation, the value of this reading 
at 40° should be lower than it was found in the first series. This is in fact the case, 
as is shown by the following determinations :— 
Tempera¬ 
ture. 
Pressure. 
Volume. 
V apour- 
density. 
o 
millims. 
C.C. 
40 
42-05 
71-7 
9-52 
45-75 
64-63 
9-70 
51-6 
55-41 
10-04 
53-95 
49-83 
10-67 
54-8 
42-0 
Condensed. 
In the first series, at volume 71*1 cub. centims., the vapour density was 9'99, as 
against 9'52 in the second at volume 71'7 cub. centims. The largest volume in the 
mdcccxcii.—a. s 
