LIQUEFACTION AND SOLIDIFICATION OF ARGON. 255 




Tixperiment. | Temperature. Pressure. 
| ° atmos. 
| 1 Bie — — 121°2 50°6 
2 — 121-6 | 50°6 
3 » — 120°5 50°6 
4A — 121°3 50°6 
5 = 12145 50°6 
| 6 — 1198 | 50°6 
| 7 = 1s} | 50°6 
| 



In all seven determinations the critical pressure was found to be 50°6 atmospheres ; 
but determinations of the critical temperature show slight differences. In experiments 
Nos. 3 and 6 less liquid argon was present in the tube than in the other five; in 
these the volume of liquid exceeded the volume of gas. 
In determining the vapour pressures of argon, a tabular record of which is given 
below, I noticed slight differences of pressure according as I produced more or less of 
the liquid at the same temperature. This proved that the sample of argon contained 
an inconsiderable admixture of another gas, more difficult to liquefy ; it is doubtless 
the trace of nitrogen previously referred to. The mean of the seven estimations of 
the critical temperature is —121°, and this may be taken as the critical temperature 
of argon. . 
At lower temperatures the following vapour-pressures were recorded :— 







Experiment. | Temperature. Pressure. Experiment. | Temperature. Pressure. 
° atmos. | | ° atmos. 
8 —128°6 38:0 13 | —134:4 29°8 
9 —129°6 30'8 | 14 | —135:1 29-0 
10 | —129-4 30°8 | 15 | —136:2 27°3 
11 | —129°3 39°8 16 —188°3 25°3 
12 —129°6 308 | 17 | —139'1 23°7 

In Experiments Nos. 9, 10, and 17 the quantity of liquefied argon was very small, 
for it filled the tube only to a height of 3 to 5 millims., and in the other experiments 
the column of liquid argon was 20 millims. or more. 
Determination of the Boiling- and Freezing-Points. 
Two hundred cub. centims. of liquid oxygen, prepared in my large apparatus,* was 
poured into a glass vessel with quadruple walls, so as to isolate the liquid from 
* ‘Bulletin International de Académie de Cracovie,’ June, 1890; also WispEMANN’S ‘ Beiblatter,’ 
yol, 15, p. 29, 
