86 
PROFESSOR W. RAMSAY AND DR. M. TRAVERS 
Hydrogen. 
Fluorine. 
Chlorine. 
Bromine. 
Iodine. 
0-473 
0-05 ? 
0-073 
0-048 
0-048 
Lithium. 
Sodium. 
Potassium. 
Rubidium. 
Csesium. 
0-13 
0-048 
0-051 
0-036 
0-038 
Compressiihhties. —On referring to the jDlate (Plate 2) it will be seen that at the 
lower tera 2 )eratnre, 11'2°, the value of P.Y. for a perfect gas is 17,710 metre-cnhic- 
centiins. The values for nitrogen are taken from Amagat’s results, and thev deviate 
very little from the theoretical. The compressibility of helium decreases Avith rise of 
jiressure, or in other Avords the Amine of P.Y. increases. This is also the case Avith 
hydrogen, though in a less degree. Neon is a more perfect gas than nitrogen, though 
at high j^ressures, it, too, becomes too little compressible. Argon, on the other hand, 
is more compressible than the former, and krypton still more ; though the shape of 
the cur Am indicates that at still higher pressures their P.Y. AA-onld become normal at 
some point. Xenon is below its critical temperature, and its compressibility is there¬ 
fore Amry great. 
At higher temperatures the results are difficult to interpret. Measurements made 
Avith nitrogen shoAv that it retains nearly a uniform P.Y. as pressure rises ; hut of all 
the other gases the P.Y. diminishes and then increases. And the order of position 
of the cuiwes is not in accordance AA'ith the densities of the gases. That the measure¬ 
ments are fairly correct may be inferred from the tAvo sets for argon Ijeing nearly 
identical. Although these obserAmtions at a high temperature cannot he taken as of 
great importance in themselAms, yet they shoAv the necessity of a careful comparison 
of the behaAuour of diatomic gases as regards their compressibility. 
The results of the measurements are reproduced on Plate 2. 
Vapour-pre^isiires. — As already remarked, it AAms found impossible to liquefy neon, 
except by the aid of liquid h^nlrogen; and as the constants for hydrogen are 
unknoAA'ii, it Avas useless to attempt a measurement of its A’apour-pressure. The same 
remarks apply to helium. The diagram sIioaa's that tlie A’apour-pressure curA'es of the 
remaining three elements exhibit a gradual progression. 
Using the formula of Ramsay and YorxG, as described on p. 68, the ratios 
betAA'een the absolute temperatures of these liquids, and that of methyl alcohol at equal 
pressures for all are expressible by straight lines, AAdien mapped against the absolute 
temperature of the alcohol. The slope of such a line affords a physical constant, 
which is j)eculiar to each substance. The Amines of AR At for the three elements, 
argon, krypton and xenon, are :— 
Argon. Kiypton. Xenon. 
0 0350 0'0467 0'0675 
Here again a progression is noticeable; it does not, hoAA’eA’er, appear to be possible to 
