443 



wliich would follow from the supposition of an increase of pressure 

 at condensation ; hence lliere is no evidence of an influence of 

 admixtures. 



The pressure in the cryostat has also been given in the table 

 (column 6). The manometer, on which this pressure was read, was 

 connected to a side tube of the cover of the cryostat ; this cover 

 had at this place the same width as the cryostat glass. At the 

 pressures marked with an * the tube, which formed the connection 

 with the manometer, was continued within the crj^ostat by a glass 

 tube which reached down into the liquid '). By this means we 

 obtained the result that the vapour pressure was measured at a 

 liquid surface where no continued vaporization (and hence cooling 

 of the upper layers) takes place. The influence of this can be clearly 

 seen: in the observations without * for all but one ^) the pressure of 

 the bath was found smaller than that in the vapour pressure appa- 

 ratus, for the observations with * just the reverse is the case. On 

 the average in these latter observations the difference is moreover 

 smaller. The temperature difference which corresponds to the largest 

 pressure differences is 0.03 degrees. If for the measurement of the 

 temperature in liquid hydrogen one is satisfied with this degree 

 of accuracy, it is sufficient for the purpose to measure the pressure 

 in the cryostat in the way indicated. 



As the triple-point could not be properly observed in the vapour 

 pressure apparatus, for determining the triple-point temperature the 

 temperature of the bath was read when the first crystals became 

 visible in the latter. The indication of Ptj then became constant; 

 1.415 52 was read. Extrapolation (over 0.8 degree) of the calibration 

 curve of Pt[ gives for the triple-point temperature — 259°. 14 C. 

 in Kej.vin degrees = 13°.95 K. The pressure of the bath was 

 5.07 cm. at this point. 



1 

 § 4. The curve which represents log p as a function ot —is slightly 



concave upwards.'') Tn the 3'^^ column the values are given of p 



1) In order to have a better guarantee that the pressure which is read belongs 

 to the temperature of a definite place in the liquid, this tube might be surrounded 

 by a heat conducting tube reaching above the liquid surface, as in the vapour 

 pressure apparatus (cf. N". 107a, Pi- J.). 



2) For this one, placed between [ ], tlie experimental data indicate tliat in the 

 vapour pressure apparatus temperature eciuilibrium probably was not yet arrived 

 at. [Added in tlie translation |. 



•5) The measurements of Travers and JAquEROD give a log p, T-i -curve 

 which is slightly convex upwards. The following table gives some numbers which 



