226 HISTORY OF COLD AND THE ABSOLUTE ZEEO. 



the necessity for extreme caution in extending our inferences regard- 

 ing the properties of matter near the zero of temperature. I^ord 

 Kelvin evident!}" anticipates t':c possibility of more remarkable elec- 

 trical properties being met Avith in the metals near the zero. A theo- 

 retical investigation on the relation of "electrions" and atoms has led 

 him to suggest a hypothetical metal having the following remarkable 

 properties: Below 1 absolute it is a perfect insulator of electricity; 

 at 2'-^ it shows noticeable conductivity, and at 6° it possesses high con- 

 ductivity. It ma}' safely be predicted that liquid hydrogen will l)e 

 the means l)y which many obscure problems of physics and chemistry 

 will ultimately be solved, so that the liquefaction of the last of the old 

 permanent gases is as pregnant now with future consequences of great 

 scientific moment as was the liquefaction of chlorine in the early years 

 of the last century. 



The next step toward the absolute zero is to tind another gas more 

 volatile than hydrogen, and that we possess in the gas occurring in 

 clevite, identified by Ramsay as helium, a gas which is widely distrib- 

 uted, like hydrogen, in the sun, stars, and nebuki?. A specimen of 

 this gas was subjected by Olszewski to liquid air temperatures, com- 

 bined with compression and subsequent expansion, following the 

 Cailletet method, and resulted in his being unable to discover any 

 appearance of liquefaction, even in the form of uiist. His experi- 

 ments led him to infer that the boiling point of the substance is proli- 

 ably below 9 -' absolute. After Lord Rayleigh had found a new source 

 of helium in the gases which are derived from the Bath springs, and 

 liquid hydrogen became available as a cooling agent, a specimen of 

 helium cooled in liquid hydrogen showed the formation of fluid, but 

 this turned out to be owing to the presence of an unknown admixture 

 of other gases. As a matter of fact, a year before the date of this 

 experiment I had recorded indications of the presence of unknown 

 gases in the spectrum of helium derived from this source. When sub- 

 sequently such condensable constituents were removed, the purified 

 helium showed no signs of liquefaction, even when compressed to SO 

 atmospheres, while the tube containing it was surrounded with solid 

 hydrogen. Further, on suddenly expanding, no instantaneous mist 

 appeared. Thus helium was definitely proved to be a much more 

 volatile substance than hydrogen in either the liquid or solid condition. 

 The inference to l)e drawn from the adiabatic expansion etfected 

 under the circumstances is that helium must have touched a temper- 

 ature of from 9° to 10^ for a short time without showing any signs 

 of liquefaction, and consequently that the critical point must be still 

 lower. This would force us to anticipate that the Ijoiling point of the 

 liquid will be about 5° absolute, or liquid helium will l)e four times 

 more vohitile than liquid hydrogen, just as liquid hydrogen is four 

 times more volatile than liciuid air. Although the liquefaction of the 



