( 277 ) 



at lower temperature, and passes then into a plait crossing in a slanting 

 direction 1 ). 



For this distinction a-xM'twM w &s always supposed so small in 

 connection with the value of b^M'buM, that the plaitpoint curve crosses 

 from K x to the line v =b and that three phase equilibria not yet 

 occur at the temperatures under consideration '). 



Now that the estimations concerning the a and b of helium justify 

 the supposition that the plaitpoint curve') crosses from j: = to the 



') Kundt, Berl. Sitzb. Oct. 1880, S. 812—824 was of opinion that it would 

 always be possible to convert a liquid to the gas state by pressing in a gas. 

 This view was maintained in van Eldik's thesis (Leiden 1898, p. 7, cf. Comm. 

 Phys. La'i. Leiden, Suppl. N'. 3, p. 45), where it says that the operation mentioned, 

 if it is realized, would be the determination of the plaitpoint pressure corresponding 

 to the temperature of observation of the pair of substances which is subjected to 

 the experiment. There it was tacitly assumed that with sufficiently high pressure 

 the plaitpoint state could be reached for every temperature between the critical 

 temperatures of the components as e.g. for mixtures of methyl chloride and carbonic 

 acid, even though it would have to be found above 750 atmospheres for hydrogen 

 ami ether, as van Eldik derived taking into account the diminution which with increasing 

 pressure is found in the decrease of the surface tension caused by one and the 

 same increase of pressure (Kundt loc. cit. p. 818, van Eldik Thesis, p. 5, cf Suppl. 

 N°. 3, p. 52). If we pay attention to the possibility now foreseen by the theory, 

 that this diminution continues outside the region of observation, it seems probable 

 in the light of the observations mentioned, that it would not be possible — here 

 we treat as infinite, pressures which exert forces on the molecules greater than 

 those joining the parts of them — to reduce the surface tension to for the 

 pair of substances mentioned (and the same remark applies to hydrogen and 

 ethylalcohol) at the temperature of observation (Kundt 21 ', van Eldik 9°.5), so 

 that already at that temperature a plait crossing obliquely from x = to v=b 

 would exist on the d>-surfacp. 



In fact we should also derive from van Laar's figure cited p. 274 footnote 3 that ether- 

 hydrogen (and also alcohol-hydrogen) belong to van Laar's type I, while according to 

 the criteria laid down by us, they should belong to case (c) of this type. Van deb Waals' 

 equations Contin. II p 43, however, would point out a critical temperature of complete 

 miscibility of about — 200C in the supposition of ai2iu= v an m a-2s.ii , so that according 

 to these suppositions an obliquely crossing plait would only make its appearance 

 below this temperature. If the existence of an obliquely crossing plait at the tem- 

 perature of the above mentioned experiments should be confirmed, this might, 

 among other things point to the fact that ai2H would be considerably smaller than 

 1 «iii/«j2.v for the pair of substances mentioned (cf. p. 280). 



2 ) According to this restriction case (c) cannot occur e.g. for baM/buM larger 

 than a certain value (cf. Suppl. N°. 15 These Proc. March '07, p. 797). 



s ) Kuenen, These Proc. Febr. '03, p. 473 was the first to find experimentally 

 a plaitpoint curve starting from x = 0, and directed to the side v = b for mixtures 

 of ethane and methylalcohol. 



