( 168 ) 



The lefthand part agrees then perfectly with Bakhuis Roozeboom's 

 spacial figure, Oa and Ob not representing the melting-points under 

 vapour-pressure, but the transition points of the two components 

 under vapour pressure, i.e. the points where the ordinary crystalline 

 state passes to the fluid crystalline state under the pressure of its 

 vapour. 



If this spacial figure is cut by a plane of constant pressure, we 

 get, at least if this pressure is chosen high enough, the simplest 

 imaginable 7-A-figure of a system of two components, each of which 

 possesses a stable fluid-crystalline modification. 



The other possible cases may be easily derived from this spacial 

 figure. 



Amsterdam June 1908. Anorg. Chem. Laboratorium 



of the University. 



Physics. — "The liquefaction of helium". By Prof. H. Kamerlingh 

 Onnes. Communication N°. 108 from the Physical Laboratory 

 at Leiden. 



§ 1. Method. As a first step on the road towards the liquefaction 

 of helium the theory of van der Waals indicated the determination 

 of its isotherms, particularly for the temperatures which are to be 

 attained by means of liquid hydrogen. From the isotherms the critical 

 quantities may be calculated, as van der Waals did in his Dissertation 

 among others for the permanent gases of Faraday, which had not 

 yet been made liquid then, either by first determining a and b, or 

 by applying the law of the corresponding states. Led by the consi- 

 derations of Comm. N°. 23 (Jan. 1896) 1 ) and by the aid of the critical 

 quantities the conditions for the liquefaction of the examined gas may 

 be found by starting from another gas with the same number of 

 atoms in the molecule, which has been made liquid in a certain 

 apparatus. By a corresponding process in an apparatus of the same 

 form and of corresponding dimensions the examined gas may be 

 made liquid. 



x ) [Developed in view of the statical liquefaction of hydrogen and the obtaining 

 of a permanent bath of liquid hydrogen (Comm. N°. 94/") at which I was working 

 then]. 



By [] will be designed additions made in the translation. 



