ON AEGON AND ITS COMPANIONS. 
87 
extrapolate the results, and so to obtain means of calculating the vapour-pressure 
curves of neon and helium. 
Melting-points, Boiling-points and Critical Temperatures .—During the deter¬ 
mination of the vapour-pressures and the atomic volumes of argon, krypton, and 
xenon, we have frequently solidified these elements. The melting-points are as 
follows :— 
Argon. 
187-9° C. 
85-1° abs. 
Krypton. 
— 169° C. 
104° abs. 
Xenon. 
—140° C. (approx.) 
133° abs. 
The melting-point of argon was determined by aid of a platinum thermometer 
immersed in liquid air ; that of krypton in liqnid methane; and that of xenon in 
ethylene cooled below its boiling-point. As already mentioned, the temperatures 
are reduced to the hydrogen standard ; a portion of the vapour-pressure curve of 
solid krypton was measured, but only two points were obtained, viz., at 9-00 and at 
17-4 millims. pressure. The ratios calculated from these two points and plotted on 
curve-pajDer, cuts the line representing the ratios for the vapour-pressures of the 
liquid at a point representing the ratio for the melting-point; it corresponds to the 
temperature —166-6° C., a fairly near concordance with the found number —169° C. 
(See Ramsay and Young, ‘Trans. Chem. Soc.,’ vol. 49, p. 460.) 
The boiling-points at 760 millims., calculated by the method of ratios, are :— 
Argon. Krypton. Xenon. 
—186-1° C. -151-67° C. -109-1° C. 
86-9° abs. 121-33° abs. 163-9° abs. 
The critical temperatures and pressures are ;— 
Tenqjeratures . 
Pressures. 
Argon. 
-117-4° C. 
155-6° abs. 
40,200 millims. 
Krypton. 
-62-5° C. 
210-5° abs. 
41,240 millims. 
Xenon. 
+ 14-75° C. 
287-75° abs. 
43,500 millims. 
The boiling-point and melting-points of the inactive elements also show periodicity ; 
it has not been deemed necessary, however, to insert diagrams illustrative of this. 
Suffice it to remark that these constants place the elements at the bottom of the 
descending point of such a curve as accompanies Lot ear Meyer’s ‘ Modern Theories 
of Chemistry; ’ and that here, too, they fall into jjlace. 
Atomic Volumes .—-So far as is known, the following table gives the atomic volumes 
at their boiling-points of tlie elements of interest m connection with those of the 
argon group. 
