THE PROPERTIES OF WATER AND OF STEAM. 
1 17 
The vapour-clensities and volumes of a gramme of saturated vapour can be given 
at temperatures above 230°. They are as follows :— 
Temperature. 
Pressure. 
Vol. of 1 grm. 
Vapour-density (H = 1). 
Vol. of 1 grm. ; 
O 
millims. 
c.c. 
read. 
smoothed. 
recalculated. 
230 
20936 
73-00 
10-23 
10-22 
73-06 
240 
25019 
60-65 
10-51 
10-40 
61-28 
250 
29734 
50-30 
10-87 
10-63 
51-43 
260 
35059 
42-40 
11-14 
10-94 
4319 
270 
41100 
37-20 
11-04 
11-36 
3615 
There is very great difficulty in reconciling the results given by Regnault at the 
highest temperatures with our own direct measurements. Regnault’s results inter¬ 
preted as vapour-density obviously increase at too slow a rate above 210°, while 
ours appear to increa.se too rapidly at 240°, 250°, and 260°. We therefore constructed 
a curve showing the relationship of vapour-densities from all sources to temperature ; 
the numbers given as “ smoothed ” are read from the curve, and the volumes of 1 grm. 
were again calculated. 
In a series of papers published in the ‘Philosophical Magazine’ (1887, vol. 27, 
pp. 196 and 435), we showed that for ether, ethyl alcohol, and carbon dioxide, the 
pressures of the vapours of these substances for constant volumes are, within limits 
of experimental error, a rectilinear function of the temperature, or p = bt — a, where 
a and b are two constants, depending on the volume, and t is the absolute temperature. 
Carl Barus, as the result of experiments with other substances, has confirmed the 
statement, both for liquid and gas. He states (‘Phil. Mag.,’ 1890, vol. 30, p. 358) 
that “below 1000 atmospheres, the curves for ether, alcohol, thymol, diphenylamine, 
and toluidine, are so nearly linear that they may be accepted as such with an error no 
larger than 2 or 3 degrees at 1000 atmospheres.” He also found that in the case of 
water the rectilinear relation does not hold. 
If an isochoric diagram be constructed from the results given on p. 116, it will be 
seen that, except at small volumes, the isochoric lines are approximately straight, but 
curve considerably on approaching the condensation points. The lines should probably, 
as Bares found, be curved throughout, but no considerable error is introduced in con¬ 
sidering them as straight during the major part of their course. Indeed, accepting 
Regnault’s determinations as correct, it would appear that at temperatures above 
140°, the curvature cannot be due to premature condensation, since the isothermal 
curves given in the diagram have been drawn, as already stated, to coincide with the 
results of Regnault’s work on the heats of vaporization, and yet coincide with our 
experimental results, except at volumes very close to those at which liquefaction takes 
place; and at such small volumes, surface condensation is unmistakeable. 
On reference to the Appendix, p. 128, an account of experiments at much lower 
