5U 



liquid hydrogen the difliciillj lies in the circumstance, that the 

 boiling-point and melting-point of neon are only a few degrees apart. 

 The construction of our apparatus is specially designed to meet the 

 difficulty arising from the almost unavoidable freezing of the neon. 

 If we had applied Lindk's pi'inciple of liquefaction on neon, cooled 

 only in liquid air, and had thus liqiietied neon in the same manner 

 as Dewak first showed, how to liquefy hydrogen, this difficulty 

 of the neon freezing would not he encountered. But in that case the 

 other difliculty would make ilself felt, that only a part of the 

 available gas appears as liquid in the bath. As long as neon is still 

 so difficult to obtain as at present, this objection weighs very much 

 more than that inherent in the principle of our apparatus. Moreover 

 as we have the excellent hydrogen-cycle ready at our disposal, it 

 would be much more conq)licated conslruciing a separate neon-cycle 

 with liquid-air cooling only, than following the method adopted. In 

 future, when neon will be equally easily obtained as at present 

 hydrogen and there will thus be no necessity for anxiously guarding 

 against the smallest loss and such a loss will be considered in the 

 same light as a loss of hydrogen is now, it will become more 

 profitable to prepare the liquid hydrogen itself by means of a neon- 

 cycle. For that case a purifying-ap|)aratus of neon by means of 

 liquid neon, similar to that of hydrogen described in Comm. 109, 

 will be practically a necessity. If the neon is not completely deprived 

 beforehand of the less volatile admixtin-es, such as nitrogen, (he 

 narrow tubes of the regenerator-spiral, through which the gas is 

 made to flow during its expansion, would be apt to get plugged. In 

 the method chosen by us it is of no account, whether the neon 

 still contains a few percentages of the less volatile constituents, like 

 nitrogen. Without obstructing the passages they are deposited on the 

 less cooled upper parts of the spiral, while the neon is liquefied or 

 solidified on the lower coils. If the temperature of the cooling spiral 

 is so regulated that the va|)oui--pressure of neon at that temperature 

 is above one atmosphere, while the solid nitrogen and oxygen have 

 still only a negligible vapour- pressure, all the liquid and solid neon 

 which might be present will evaporate and the less volatile admix- 

 tures of the neon can all be retained in the apparatus and so 

 removed from it. This procedure may be utilized for the purification 

 of the neon (see § 3). We will however at present adhere to the 

 supposition, made in the beginning of our description, that the neon 

 is already pure. 



The liquid neon flowing down from the spii'al is caught (fig. 1) 

 in the silvered vacuum-vessel with silvered draw-off-tube Eaks and 



