ON ARGON AND ITS COMPANIONS. 
69 
Fig. 5. 
Cr* 
the stop-cock at the top of the reservoir; the bulb was cooled ; and the pressures 
were read on the gauge on a mirror-scale, c, parallax being thus avoided. 
For high pressures, a pressure-apparatus was 
made use of, similar to the one depicted in a 
memoir on Ethyl Oxide, published in the ‘ Trans¬ 
actions ’ for 1887 (A, vol. 178, p. 59). The tube con¬ 
taining the gas, however, was bent twice at right- 
angles, and was a small-bore capillary; for the 
amounts of gas at our disposal for compression 
were small (about 3 cub. centims.) because the 
total volume of the screw displacing the mercury 
did not admit of the compression of a greater 
amount; and, moreover, the amount of xenon in 
our possession was not greater than 3 cub. centims. 
The end of the capillary tube dipped into the 
cooling liquid ; it was, of course, impossible to 
measure the volume of the lic^uefied gas, for care 
had to be taken to keep the mercury in the 
compression-tul)e sufficiently far away from the 
cold region, in case of its freezing. 
.Details of Results.—Ileliiiui and Neon .—These 
gases have been liquefied only at tlie temperature 
of liquid hydrogen. Dewar states that helium 
was licpiefied at that temperature under a pressure 
of eight atmospheres ; and our experiments show 
that even at that temperature, neon possesses a 
vapour-pressure of a few millimetres. Attempts 
were made to liquefy neon by compressing it to 
about 100 atmospheres at the temperature of air 
boiling in vacuo (about — 205°). The pressure 
rose continuously on decrease of volume, and no 
liquid could be detected in the tulje. Tiie critical 
temperature of neon, therefore, lies in the un¬ 
bridged interval between the boiling-point of 
liquid hydrogen, and that of air under reduced 
pressure. 
Argon .—The lowest temperatures were obtained Ijy the use of liquid nitrogen, 
boiling in a vacuum-jacket under atmospheric pressure; and the low-pressure 
apparatus was employed. Liquid air was added from time to time, and the rise of 
pressure consequent on the rise of temperature was noted. The range was from 
77’3° to 87'8° abs. ; the pressure from 215 to 821 milliins. At the lower tempera- 
