Physics. — “/sothermals of monatomic substances and their binary 
mixtures. XX. Isothermals of neon from + 20° C. to —217° C.” 
By C. A. CROMMELIN, J. Paracios Martinez, and H. KAMERLINGH 
Onnes. Communication N°. 154a from the Physical Laboratory 
at Leiden. 
(Communicated in the meeting of June 29, 1918). 
§ 1. /ntroduction. This paper is the continuation of a previous pre- 
liminary communication '). The reduction of the neon-isothermals 
has now progressed so far, that what follows may be looked upon 
as a pretty nearly completed whole. The measurements refer to 
pressures up to about 90 atmospheres and as regards the temperature 
go from + 20°C. down to — 217°C.; they therefore embrace the 
region between the ordinary temperature down to the lowest tem- 
perature to be reached with liquid oxygen. The region from — 218° C. 
to —246° C., which can now also be covered by means of the hydrogen 
vapour cryostat’), is here left out of account; we hope shortly to 
be able to continue our measurements in this region. As regards the 
importance of such determinations as will be communicated on this 
occasion and the apparatus which have been used for the purpose 
we may refer to previous communications on the isothermals of 
hydrogen and of argon. *) 
For the sake of completeness and of a better survey of the whole 
work we have included in the table the material published in the 
previous communications on neon, quoted above, viz. the series I, I, 
STEVEN TME VIL and IX. 
§ 2. The results of the measurements are given in table I, where 
6 =the temperature on the international *) Cuxstus-seale, i.e. the 
temperature on the international Keivin-scale diminished by 273.09 ; 
p =the pressure in international atmospheres (for Leiden 1 inter- 
national atmosphere = 75.9488 cms mercury); 
d4 = the density expressed in the normal density (0° C. and 1 atm.) ; 
va = the volume expressed in the normal volume (0° C. and 1 atm.). 
1) H. KAMERLINGH ONNES and C. A. CROMMELIN, Comm. NO. 147d; these 
Proc. XVIII (1) p. 515. 
2) H. KAMERLINGH ONNES, Comm. N°. 15la@; these Proc. XIX (2) p. 1049. 
3) Comp. H. KAMERLINGH Onnes and H. H. FRANCIS HynpMAN, Comm. N°. 69; 
these Proc. III p. 481; H. KAMERLINGH Onnes and CG. BRAAK, Comm. N’. 97a 
these Proc. IX p. 754; C. BRAAK, Dissertation, Leiden, 1908; C. A. GRoMMELIN, 
Dissertation, Leiden, 1910. 
4) Comp. H. KAMERLINGH Onnes, Comm. Suppl. NO. 34a. § 5. 
