( 235 ) 



into contact with the line x = at a certain temperature, and crosses 

 in a slanting direction front r = b to the side x = at /turn- tempe- 

 rature (§ 2 These Proc March '07 p. 787). Comparison of this result 

 with van Laar's papers induced us then to cite (p. 786 footnote 1) that 

 the latter already treated the projection of the plaitpoint curve on the 

 v , r-plane for the case of a gas without cohesion, but without 

 further investigating the shape of the spinodal curve and of the plait 

 for this case. Now that van Laar (These Proc. May '07 p. 35) says : 

 "The case that a plait starts from C\ ') to C, a ), or also at the same 

 time from C\ to 6' (when there is a minimum temperature in the 

 plaitpoint line) is not new (see Kamermngh Onnes and Keesom, p. 788 

 below), but has been before described and calculated by me in all 

 particulars", we have once more looked through his papers. 



It would have been good if Mr. van Laar had indicated the place 

 where we had to look for this description of the plait treated in 

 § 2 and indicated by van Laar in the italicized words (the italics 

 are ours) ; we have not been able to find this description in his 

 preceding papers even on this renewed careful perusal '). 



That the shape of the plait described by us occurs for tempera- 

 tures above the critical temperature of the least volatile component 

 led us to the considerations on limited miscibility in the gas state 

 mentioned in § 3 sqq. 



Always availing ourselves of the above mentioned equations of 

 van der Waals, we examined then if also with a„ ^> such a plait may 

 occur for values as they are to be expected for mixtures witli helium. 

 We saw in $ 7 (These Proc. March '07 p. 795) that for the case of 

 the plaitpoint curve running from K l to K m (called type 1 by van Laar) 

 3 cases are to be distinguished: a) that with falling temperature the 

 plaitpoint gets from K m on the if'-stirface, and proceeds regularly 

 towards K x ; l>) that with tailing temperature a plaitpoint coming 

 from A'„, and one coming from K l unite to a double plaitpoint ; c) 

 that the plaitpoint gets from K 1 on the tp-surface and proceeds 

 regularly towards K m (without double plaitpoint with minimum 



!) Our A',„. 



2 ) Our K v 



3 ) On the contrary he says in his paper These Proc. Sept. 1906 p. 231 (cf. Van Laar, 

 These Proc. May 1905, p. 42 at the bottom) : ": In former papers it lias been demon- 

 strated that in the neighbourhood of C u a minimum plaitpoint temperature makes its 

 appearance both with type 1 in the line C^Ca and with type 11 in the line C A, and 

 that therefore with decrease of temperature a separate plait begins to detach itself 

 starting from C at a definite temperature Y' (1 (the plaitpoint temperature in C ), 

 which plait will merge into the main plait (or its branch plait) later on in an 

 homogeneous double point. 



