( 280 ) 



These Proc. April '05 p. 652 has been included in the diagram. 

 The second branch of the plaitpoint curve is not to be distinguished 

 from the straight line HK t on the scale on which the diagram has 

 been drawn. 



For the connodal curves the points of intersection with the line 

 x = representing the points of saturation for pure hydrogen have 

 been calculated. For this purpose the constants of saturation have 

 been used, which have been calculated by Dalton l ) for a substance 

 that follows the equation of state of van der Waals with constant 

 <t and b. For the rest the course of the connodal curves for which 

 for T^> Tkm also the plaitpoints are known, has been represented 

 schematically. This applies particularly to the points of intersection 

 of the connodal curve for T= 20 with the line v = b, so that 

 also the course of- the connodal curve, particularly of the gas branch, 

 is uncertain in the neighbourhood of the line v = b. The line CD 

 represents the experimentally determined barotropic tangent chord for 

 T=2Q (see Comms. N". 96" and N°. 96 f Febr. '07 p. 660 footnote 2). 



The situation of the line CD with respect to the connodal curves 

 might point to Tkm being higher than was calculated by us, which 

 ma}' be due either to the critical temperature of helium being lower 

 than was assumed by us here, or to a v2)I being <^ V<i\\u<ii2M for 

 mixtures of He — H, '). 



The course of the barotropic plaitpoints and barotropic tangent 

 chords in case (c), and also in case {b), if they occur on the plait 

 starting from x = 0, corresponds for the higher temperatures with 

 that for the case that the branch of the plaitpoint curve starting 

 from A', crosses the t^-surface from x — to x = 1, for which case 

 the course was described in Comm. N°. 96 6 . For the lower tempe- 

 ratures we meet with this difference that in the cases considered in 

 this comm. the barotropic tangent chord continues to exist on the 

 plait, till it disappears under the three phase triangle, whereas 

 in the cases considered in Comm. N°. 96 6 the barotropic tangent 

 chord may also vanish from the plait through a barotropic plaitpoint 

 (lower barotropic plaitpoint temperature, see Comm. N°. 96 4 p. 504). 

 The latter must even be the case if for T^. Jt, no three phase 

 equilibria appear as yet (cf. p. 275 note 1). 



!) J. P. Dalton, Phil. Mag. April 1907, p. 520. 



2 ) The same remark concerning ohm for mixtures of H 2 witli other substances 

 might be derived as follows: for C0 2 — H 2 (the same holds for C0 2 — 2 ) from 

 a comparison of the experimentally determined portion of the plaitpoint curve with 

 that calculated in the same way as above for He— H 2 ; for H 2 — ether and 

 H 2 — alcohol see § 1 p. 277 note 1 ). 



