166 
Chemistry. — ‘Determinations of the vapour tension of nitrogen 
tetroxide’. By Dr. F. E. C. Scarrrer and J. P. Trevs. (Com- 
municated by Prof. J. D. Van per Waals). 
(Communicated in the meeting of May 25, 1912). 
* 
1.-In a previous treatise’) we communicated the results of an 
inquiry into the vapour tensions of nitrogen tetroxide. In these deter- 
minations we made use of a method which had been applied before 
by different investigators (LADENBURG, Ramsay and Youne, BODENSTEIN, 
Jounson and JACKSON) in measurements of vapour tensions of substances 
which could not be brought into contact with mercury. Of the forms 
of the manometer proposed by the said investigators we chose that 
described by Jackson, because this manometer can be very easily 
constructed, and the accuracy which we wanted to reach, can be 
easily obtained by means of this apparatus. Moreover by means of 
this manometer it seemed possible to us to devise a method to determine 
the vapour pressures of substances attacking mercury up to the 
critical pressure. As a sequel to the determinations to three atmos- 
pheres given in the preceding paper, we shall give a description here 
of this method for higher pressure, and state the results which make 
the vapour tension line of the nitrogen tetroxide up to the eritical 
temperature known to us. 
2. Critical temperature. Before entering upon the description of 
the vapour tension determinations at higher pressure, we will first 
mention a determination of the critical temperature, which we did 
not carry out with the measurements of the vapour tension, but in 
another way independent of these. A thickwalled tube of combustion 
glass provided with a capillary constriction was connected by means 
of a ground glass junction with the reservoir with nitrogen tetroxide. 
After the tube had been evacuated by means of the GAEDE-pump (with 
cooling of the nitrogen tetroxide with a carbonic acid alcohol mixture), 
and the connection with the pump had been melted off, the tube 
was filled by the liquid being distilled over, so that the liquid took 
up a volume that was somewhat smaller than half that of the tube. 
Then the latter was melted off at the capillary constriction, and 
heated in a bath of paraffin oil. 
The liquid, which is almost colourless in the neighbourhood of 
1) These Proc. Vol. 14, p. 536. 
