284 Dr. R. A. Lehfeldt on the 



light is a striking one, to be compared with the fact that in 

 the vena contracta of a gas escaping from an orifice the 

 maximum velocity attainable is nearly that of the agitation 

 of the average molecule in the containing vessel or of sound 

 in the gas. 



It appears as though a complete theory of electricity would 

 be a kinetic theory, in which the place of the atoms or mole- 

 cules of the kinetic theory of matter is taken by the electrons. 

 The ion appears as a sort of molecule formed by the union of 

 an atom or radical to an electron. But such large questions 

 can hardly be opened up in the present connexion. We may 

 summarize the contentions of the preceding pages in the two 

 propositions : — 



The cathode and Lenard rays are streams, not of ions, but 

 of free negative electrons. 



The Rontgen rays are caused by the internal vibrations of 

 free electrons. 



Melbourne, Nov. 1898. 



XXI. Properties of Liquid Mixtures. — Part III.* Partially 

 Miscible Liquids. By R. A. Lehfeldt, D.Sc] 



THE phenomena of complete mixture between two liquids, 

 about which so little systematic knowledge is yet in 

 existence, are connected with the phenomena of ordinary 

 solution by an intermediate stage, that in which two liquids 

 dissolve one another to a limited extent only. The study of 

 such couples seems a promising field of investigation, on 

 account of the intermediate position they occupy; it seems 

 to offer the chance of extending some of the laws arrived at 

 with regard to simple solution to the more complicated cases; 

 I have therefore attempted to get some information on the 

 equilibrium between incomplete mixtures and the vapour 

 over them, and especially at the " critical point," i. e., the 

 point at which incomplete miscibility passes over into com- 

 plete. A recent short paper by Ostwald % draws attention 

 to the importance of that point in the theory of mixtures. 



Choice of Liquids. 



The first point is to obtain suitable pairs of liquids for 

 experiment. In order to study the properties of the critical 

 point with ordinary vapour-pressure apparatus, it is necessary 



* Part I. Phil. Mag. (5) xl. p. 398; Part II. Phil. Mag. (5) xlvi. 

 p. 46 ; reprinted, Proc. Phys. Soc. xvi. p. 83. 



t Communicated by the Physical Society : read Nov. 25, 1898. 

 X Wied. Ann. lxiii. p. 336 (1897). 



