( 1H8 ) 



smaller molecuhir coni[)rcssil)ility, or with plioiiomciia wliicli would 

 result fioin a]ipreefable deviations froni true spheres in the shape of' 

 the iHolecides, which coiiid therefoi'e, at higher densities, he packed 

 more closely than would be possible with spheres, of which the 

 radius is ecpial to the average radius, which is to be ascribed (o the 

 molecules in the gaseous state. For isopentane, then, a prolate molecnio 

 might be assumed. But since carbon dioxide also belongs to the 

 substances under consideration which agree well with VII. 1, and as 

 it is not necessary to assume tor it a molecule which is either 

 particularly |)rolate or particularly oblate, the <liagram seems to show 

 that in this case it is really molecular incompressibility which deter- 

 mines the behaviour of' argon. 



Physics. — " fsotlwnns of inouaUnnic su/jsfances and ofthcir hiiKH'ij 

 mirtiircs. XT. Remarls upon tlw critical temperature of neon 

 and upon the meltinp point of o.vi/r/en.'' By Prof. H. Kameri.ingii 

 Onnes and C. A. Croinimklin. Comm. N". 121'' from the physical 

 Laboratory at Ijeiden. 



(Gommiinicaled in the meeting of May ^7. 1011). 



Foi' some time past we have been busy with an investigation of 

 the erpiation of state for neon in which a ]>lace of importance is 

 taken by the isotherms for the tempei-atures which are repeatedly 

 used with liquid oxygen in our cryostat, viz. — 182° 0. to — 217° (-. 

 It is obvious that for the purpose of this branch of the investigation 

 one should be able to take advantage of a knowledge of the critical 

 temperature. 



Before, therefore, proceeding to determine a series of isotherms 

 which would be specially arranged with a view to the deduction of 

 the critical temperatui-e from these isotherms which is the ob\ions 



method of obtaining a i-eliable estimate when the direct detei-minafion 

 cannot be made with a bath of lirpiid oxygen — we have first 

 ascertained if the critical tempei'ature of neon lies above oi' below 

 the melting point of oxygen. Such an investigation is necessary i)ecause 

 the critical temperature of neon is not yet definitely knowni, and the 

 estimates which have been made of it differ w^idely. Tk.weks, Skntkk 

 and Jacqukkod ^), who start with the assumption that the critical 

 temperature of neon nuist lie below — 213° C. obtain the \alue 

 — 223"^ C, while A. (). Ivankink found a short time ago from two 



ij M. W. Travers, G. Senter and A. .Jacquerod, Phil. Trans. A. 200, 105, 1902 



