138 



PRINCIPLES OF CHEMISTKY 



fog, hydrogen in expanding forms a fog, thus indicating its passage into 

 a liquid state. But as yet it has been impossible to preserve this 

 liquid, even for a short time, to determine its properties, notwithstanding 

 the employment of a temperature of 200 and a pressure of 200 atmo- 

 spheres, 33 although by these means the gases of the atmosphere may be 

 kept in a liquid state for a long time. This is naturally dependent 

 on the fact that the absolute boiling point of hydrogen lies lower than 

 that of all other known gases, which is related to the extreme lightness 

 of hydrogen. 34 



was seen from the formation of cloud-like drops, like a fog, which rendered the gas opaque. 

 Thus Cailletet proved the possibility of the liquefaction of gases, but lie did not isolate 

 the liquids. The method of Cailletet allows the passage of 

 gases into liquids being observed with greater facility and 

 simplicity than Pictet's method, which requires a very 

 complicated and expensive apparatus. 



The methods of Pictet and Cailletet were afterwards 

 improved by Olszewski, Wroblewski, Dewar, and others. 

 In order to obtain a still lower temperature they employed 

 liquid ethylene or nitrogen instead of carbonic acid gas, 

 whose evaporation at low pressures produces a much lower 

 temperature (to 200). They also improved on the 

 methods of determining such low temperatures, but the 

 methods were not essentially altered ; they obtained nitro- 

 gen and oxygen in a liquid, and nitrogen even in a solid, 

 state, but no one has yet succeeded in seeing hydrogen in 

 a liquid form. 



55 The investigations of C. Wroblewski in Cracow 

 clearly proved that Pictet could not have obtained liquid 

 hydrogen in the interior of his apparatus, and that if he 

 did obtain it, it could only have been at the moment of its 

 outrush due to the fall in temperature following its sud- 

 den expansion. Pictet calculated that he obtained a tem- 

 perature of 140, but in reality it hardly fell below 120, 

 judging from the latest data for the vaporisation of car- 

 bonic anhydride under low pressure. The diffei*ence lies 

 in the method of determining low temperatures. Judging 

 from other properties of hydrogen (see Note 34), one would 

 think that its absolute boiling point lies far below - 120, 

 and even ~ 140 (according to the calculation of Sarrau, on 

 the basis of its compressibility, at - 174). But even at -200 

 (if the methods of determining such low temperatures be correct) hydrogen does not give 

 a liquid even under a pressure of several hundred atmospheres. However, on expan- 

 sion a fog is formed and a liquid state attained, but the liquid does not separate. 



54 After the conception of the absolute temperature of ebullition (tc, note 211) had 

 been worked out (about 1870), and its connection with the deviations from Mariotte's law 

 had become evident, and especially after the liquefaction of permanent gases, general 

 attention was turned to the development of the fundamental conceptions of the gaseous 

 and liquid states of matter. Some investigators directed their energies to the further 

 study of vapours (for instance, Ramsay and Young), gases (for instance, Amagat), and 

 liquids (for instance, Zaencheffsky, Nadeschdin, and others), especially to liquids near tc 

 and pc ; others (for instance, Konovaloff and De Haen) endeavoured to discover the rela- 

 tion between liquids under ordinary conditions (removed from tc and pc) and gases, 



forliuef In*'* ases 



