1251 
region of liquid hydrogen temperatures was each time determined 
at least at two temperatures, viz. at about 20,3 and 14° K. For 
this purpose the vapour pressure of the hydrogen in the ervostat bath 
was measured with the aid of a vapour pressure tube p. The vapour 
pressure was read (the stop-cock 4, being opened) on the manometer J/. 
For the measurement of the temperatures!) we refer to Comm. 
N°. 143 § 2 and 147a $ 1. 
The heat capacity of the calorimeter flask / (of copper) with the 
core Ajj; was determined by special measurements in liquid hydrogen 
and in liquid air. 
§ 3. The triple point of nitrogen. 
The nitrogen was prepared and treated in the same way as the gas 
which served for the measurements of Comm. N". 1454, ¢ and d (ef. Comm. 
N°. 1455 § 2), so that we may rely on a high degree of purity. In fact 
the analysis with copper in ammonia (Hempen) as well as that with 
pyrogallie potash yielded less than 0.1°/, for the admixture of oxygen. 
For the temperature of the triple point of nitrogen we found 63.06° K. 
This temperature lies higher than that found by Fiscurer and Arr®): 
— 210.50° on a hydrogen-thermometer with p, = 96 cm, lower than 
that derived by Horst *) from the measurements of v. SreMENs. 4 
1) We gladly record our cordial thanks to Messrs. P. G. Carn and J. M. Burgers 
for their aid in these measurements. 
2) K 
5) ( 
C.T. Fiscuer und H. Arr. Ann. d. Phys. (4) 9 (1902), p. 1149. 
t. Horst. Comin. NY. 148a (Sept. 15). 
tj In order to see whether transformation 
points occur in solid nitrogen, on cooling 
below the triple point the time-rate of 
froony 
the temperature was followed continuously. 
Originally on examining our cooling curves the 
presence of a transformation point had escaped 
us through a combination of fortuitous circum- 
stances. On a renewed examination, made in 
consequence of the fact that EuckEN (p. 1248 
note 1) found a transformation point, it appears 
that our observations confirm its existence. 
In fig. 5 (ordinates: galvanometer readings, 
abscissae: minutes) we give a part of one of 
the cooling curves. Three different cooling cur- 
ves point to a transformation at 35.3 , 35,4 , 
35,3° K., whereas in a temperature curve taken 
during heating an indication of the beginning 
of a transformation occurs at 36.4° K. Down 
to 14.55° K. we did not find any indication 
of the existence of a further transformation 
point. 
zi fo | 
Proceedings Royal Acad. Amsterdam. Vol. XVIJL 
