961 
severe test. The nitrogen was moreover once more tested for its 
purity in the apparatus itself. For this purpose the vapour-pressure 
was measured at a temperature which was kept constant (about 
— 158°), first when only a drop of liquid was present in the appendix 
of the dilatometer and immediately afterwards with the dilatometer 
completely filled with liquid. The vapour-pressure was found in the 
two cases to be 
25.38 and 25.41 atm. 
This difference of about one thousandth of the total value is not 
far removed from the limits of accuracy of the observations and 
proves (1) that the nitrogen was very pure and (2) that the tempe- 
rature-difference near the top and near the bottom in the cryostat 
must have been inappreciable. 
In the further observations the liquid-surface was always brought 
to about the middle of the dilatometerbulb. 
==: - rr 5 = = = = en 
Te 
La 8 a ae obs. Peale. Obs.-calc. (abs.) Rests ens 
1914 eens, tm. int. (lo) 
21 Febr. |X | — 148.85 30.364 | 30.631 =<" 0961 yaaa bee 
: IX | — 152.11 | 25.889 | 26.087 | — 0.18 | — 0.8 
REM =. 155.47-| 21.620 | 21.945) | = 00188 zele 
20 Febr. | VII | — 161.31 | 15.949 | 15.949 | 0.000 0.0 
17 Febr. |V | — 173.58 | 7.3705| 7.3705 | 0.0000 0.0 
: IV. | — 170.18 | 4.8278| 4.8632 | — 0.0354 |. = 07 
16 Febr. |1 | — 182.47 | 3.7248| 3.7117 | + 0.0131 +04 
f IL | — 186.88| 2.5067| 2.4863 + 0.0204 + 0.8 
; Im |— 191.88| 1.4727] 1.4721 0.0000 | 0.0 
In the above table are given the results of the measurements and 
a comparison with a formula of the form 
b c d 
logp=a+ at aa t 
where 7’ represents the absolute temperature, the coefficients having 
the values 
a = + 5.76881 
b = — 858.522 
¢ = + 54872.3 
d = — 1783500 
Proceedings Royal Acad. Amsterdam. Vol. XVII. 
