156 
PROFESSOR W. RAMSAY AND DR. S. YOUNG ON ALCOHOL. 
saturated vapour and of liquid. The summit of this surface, which represents volumes 
of gas in contact with liquid, if correctly drawn, would give the relation between 
temperature, pressure, and volume at the critical point. It appears to us impossible 
to obtain direct measurements of this portion of the curve. There must, therefore, 
necessarily be some uncertainty as regards all three. 
On Plate 7 the relations between the weight of one cubic centimetre of saturated 
vapour and liquid are shown. Curve No. 1 exhibits this relation between 40° and 
242\5°; and curve No. 2 between 225° and 242‘5° on an enlarged scale. 
It is evident, however, from these results that the critical temperature must lie 
within 0’5 of a degree above or below 243'6°, that the critical pressure must be nearly 
47,700 mms., and that the critical volume cannot be far from 3'5, i.e., one gramme of 
alcohol at the critical point must occupy about 3'5 ccs. ; otherwise expressed, the 
specific gravity at the critical point is nearly 0 - 28. 
Note. 
After this memoir had been read (May, 1885), an account of experiments by 
Amagat (Compt. Pend., xcix., p. 1153) on the compressibility of air was noticed. 
Amagat’s reputation and the method he adopted are a sufficient guarantee for their 
accuracy ; and, although these results differ considerably from Pegnault’s, which, 
moreover, had reference only to pressures below 20,000 mms., and were therefore not 
available for our purpose, we have felt justified in making use of them. This has 
necessitated a recalculation of all the pressures, values of p.v., and vapour-densities 
given in this paper, and has led us to modify some of the conclusions in the memoir as 
read in 1885. It was also thought advisable to use Biot’s formula, and to substitute 
numbers for pressure calculated by its help, instead of by the method of differences 
which was at first employed. The use of this formula enabled us to obtain more 
dv 
accurate values for than was possible by any graphical means, and, as a result of 
these alterations, the curve representing heats of vaporisation is much more regular 
than we at first supposed ; besides, it passes between the points obtained from direct 
measurement by Andrews, and by Favre and Silbermann. The diagrams have also 
been reconstructed so as to represent accurately the corrected numbers. 
