960 
state of nitrogen at low temperatures. Moreover several of these 
data were required for the computation of the corrections of the 
diameter-measurements. 
In the region here dealt with so far all experimental data were 
lacking, at least if we leave out of account two old determinations 
by v. Wrostewski’), which differ considerably from mine. Vapour- 
pressures have been measured by Baty’) between — 196° and 
— 182°, by FiscHer and Aur®) between —195° and — 210° and 
by von SIEMENS“) between —.192° and — 205°, but, as will be seen, 
they all refer to regions of low temperatures and pressures. 
The nitrogen was liquefied in the same dilatometer and by the 
same compression-cylinder, which had been used in the diameter- 
measurements of argon and nitrogen. It should be mentioned, that 
this dilatometer was not provided with a stirring-arrangement, so 
that the determinations were made without stirring. It is possibly 
due to this circumstance, that the vapour-pressures of nitrogen seem 
to be a trifle less accurate than those of oxygen. ’) 
As in the previous measurements the temperature was determined 
by means of two platinum-thermometers which had been compared 
with the standard resistance-thermometer Pf). As regards all this 
we may therefore refer to previous communications"). The pressures 
above 20 atm. were determined by means of the closed hydrogen- 
manometer’), those below 20 atm. with the open standard-mano- 
meter °). 
The calculations do not call for special remarks. The atmosphere 
at Leiden was taken equivalent to 75.9488 cms. mercury. , 
The nitrogen with which the experiments were made was, as 
mentioned in connection with the diameter-measurements, the same 
as was used for the determinations of the critical constants. By these 
determinations the purity of the substance had been submitted to a 
1) S. v. WroBLEwsKI, C. R. 102. (1886) p. 1010. 
2) E. C. C. Baty, Phil. Mag. (5) 49 (1900) p. 517. 
) 
wo 
K. T. FrscHer and H. Aur, Ann. d. Phys. (4) 9 (1902) p. 1149. 
4) H. von Stemens, Ann. d. Phys. 42. (1913) p. 871. 
5) H. KAMERLINGH Onyes, C. DoRsMAN and G. Horst, This number of the 
Proc. Comm. No. 1450. 
6) E. Marrias, H. KAMERLINGH Onnes and C. A. CROMMELIN, Proc. Oct. and 
Dec. 1912 and Jan. 1913. Comm. No. 13la (argon) and these Proc. above Comm. 
No. 145c (nitrogen). 
7) H. KAMERLINGE ONNEs and H. H. F. Hynpman, Proc. April 1902, Comm. 
No. 78 (§ 17) and ,H. KAMERLINGH ONNES and C. BRAAK, Proc. March 1907, 
Comm. No. 97a (§ 3). 
5) H. KAMERLINGH ONNes, Proc. Nov. 1898, Comm. No. 44. 
