( 275 ) 



certain ratio r k2 /i'ic\ for not too large Th/Tm (from up to a certain 

 value, see Table I loc. cit. p. 662) only one barotropic plaitpoint 

 occurs, which in connection with Connn. N°. 96 6 p. 503 and 504 

 pointed to the fact that for the knowledge of the course of the 

 barotropic phenomena at lower temperature considerations in which 

 only the transverse plait is taken into account, are not sufficient 

 for these mixtures ') (see Comm. N°. 96<- p. 663). 



In Comm. N°. 96? p. 660 footnote 2 an estimation 2 ) was derived 

 about the critical temperature of helium from the observation of 

 the barotropic phenomenon for a mixture of helium and hydrogen 

 described in Comm. N°. 96^ These Proc. Nov. '06, p. 459. In this 

 estimation the supposition already mentioned in Comm. N°. 96", 

 p. 460, that the molecules of helium exert only an exceedingly 

 slight mutual attraction, was found confirmed. 



This suggested the investigation already announced in Comm. 

 N°. 96 6 , p. 502 on binary mixtures one of whose components is a 

 gas the molecules of which exert no or only feeble attraction (Suppl. 

 N°. 15, These Proc. March '07, p 786). Here a plait was described 

 for the first time which at descending temperature appears on the 



1 ) For mixtures of pairs of substances as meant in table I p. 662, for which 

 0.2'9 > 2'a- 2 /K-, > 0.196, three barotropic plaitpoints will occur one of which, 

 however, does not belong to the absolutely stable region. At least for the larger 

 ones of the mentioned ratios Ta 5 /Tk x , the two others belong to a plait which 

 enters the J/-surface from K lt and crosses the ^surface as a transverse plait at 

 lower temperature. For this the considerations of Comm. N'. 96'' will hold at least 

 in so far as solid phases do not cause a disturbance. For the smaller ones of these 

 ratios one of these two barotropic plaitpoints will also fall in the not absolutely 

 stable fluid region, and so also for these we shall have to take the occurrence of 

 three phase equilibria into account. 



2 ) For the calculations in note 2, p. 6G0 of Comm. N°. 96 c we availed our- 

 selves for a and b of hydrogen of the values calculated for this by Kohnstamm 

 (LANDOLT-BoRNSTEiN-MErERHOFFER's Physik. Chem. Tables 1905), which values had 

 2^ = 38.6, pk = 20 according to Olszewski, Wied. Ann. Bd. 56, p. 133, 1895 as 

 starting point. If we derive the a and b for H 2 from Tk = 29 a 32, #£=15 

 according to Dewar (B. A. Beport 1902), the estimation for TkHe yields about 1°, 

 Olszewski's newer data, Ann. d. Phys. 17 (1905) p. 986: Ti = 32.3, pi = 14.2, 

 give it a value of more than 1° (the calculation according to note 2 1. c. yields 

 as? M/a 1 1 m = Vsoi TkHe = 1.3). 



This would bring about these modifications in the classification of the helium 

 mixtures mentioned in Suppl. K°. 15, Sept. '07, § 8, that mixtures of He with 

 HjO, 3 , A, Ne, NO, NH 3 would belong to case (b), those with H 2 , H 2 S, C0 2 to 

 case (c). For the modification which another assumption about <Xkm (cf. p. 280) 

 would cause in the circumstances under which the plait starting from v = b occurs 

 see Suppl. N'. 15 I.e. p. 234. A smaller auu might even again bring about a 

 shifting in the classification in the direction from (c) towards (a). 



18* 



