UN EVAPORATION AND DISSOCIATION. 
91 
Our results also receive confirmation from a number of experiments by Horstmann 
(‘Liebig’s Annalen,’ Suppl. 6, 1868, p. 63), which, although not very concordant with 
each other, yet amply suffice to prove that the vapour-density is not constant, and 
that, therefore, p.v. is variable. 
It follows from the Table already given that, if Regnault’s results are correct, the 
thermo-dynamical formula does not always hold ; the same discordance was noticed in 
his observations with alcohol. 
It is possible, assuming the impurity in Regnault’s ether to have been alcohol, 
which is not unlikely, inasmuch as no mention is made of the sample of ether having- 
been purified by washing with water, to calculate the percentage which must have been 
present in order to raise the heat of vaporisation from 84‘5, calculated by us, to 90'2, 
calculated from Regnault’s formulae; it is 4 - 4 per cent., and an analysis of such a 
mixture would give 64‘3 per cent, of carbon, instead of 64’86 per cent, contained in 
pure ether. This does not, however, account for the composition of the high-boiling 
residue, which, if alcohol, should have contained 52’17 per cent, of carbon. 
From these experiments it is noticeable that with ether, although the density of the 
saturated vapour is very abnormal, even more so than with alcohol, yet there is no 
tendency towards a rise with decrease of temperature. It therefore seems probable 
that, for the same reasons which were stated in the memoir on alcohol, combination of 
gaseous molecules to form complex molecules does not take place. 
It is impossible to state accurately the temperature, pressure, and volume of any 
substance at the critical point; but the following numbers may be regarded as closely 
approximate for ether ;— 
Temperature . . . 194°. 
Pressure .... 27,060 mins. = 35‘61 atmospheres. 
Volume .... probably 4'06 cub. centims. for 1 gramme. 
Appendix. 
Received February 2, 1887. 
Since the foregoing- memoir was read, it appeared to us of importance, in consequence 
of some theoretical deductions, a short account of which has been communicated to the 
Society by Professor Stokes, to make fresh determinations of the relations between 
volume, temperature, and pressure of ether at higher temperatures and greater 
pressures than we had formerly employed. 
For these experiments a fresh stock of ether was prepared ; the volume tube was 
new ; and the air-gauges were refilled. The weight was not determined directly, but 
was ascertained by comparison with our previous results at 175°, 185°, and 195°. It 
was 0'055406 gramme. 
