(543) 



while the reservoir remained cooled to — 80°. After the capillary 

 constriction at E had been fused to, part of the nitrogen tetroxide 

 was distilled ovei- from C to B, and after the two vessels Cand B 

 had been cooled again down to — 80° the connection' at D was 

 melted off. 



Now we had still to break the capillary constriction at E in a 

 rubber tube connected with the GAEDE-pump and exhausted, to melt 

 off the constriction at F^ which was made possible by the glass 

 spring G, and to admit with slow heating of B continually so much 

 air through E that the pointer does not move too far from the 

 marks to prevent breaking of the apparatus. 



5. Pressure measurement. 



For temperatures below the temperature of the room the pressure 

 was determined by surrounding B with a large vacuum vessel tilled 

 with alcohol, which was brought to and kept at the required tem- 

 perature by the insertion of small pieces of solid carbonic acid. A 

 stirrer ensured uniformity of temperature throughout the vacuum 

 vessel. The temperatures were read from an ANscHÜTZ-thermometer, 

 which was controlled by the aid of thawing ice and mercury. The 

 pressure was determined by the aid of a mercury manometer con- 

 nected with E (fig. 2) by rubber. 



For determinations at temperatures above the temperature of the 

 room the whole apparatus was immersed in a large waterbath up 

 to F, and the pressure, obtained by pumping air by means of a 

 cycle pump into the righthand part of the apparatus, was read from 

 a mercury manometer 27^ meters long, when adjustment of the 

 pointer between the two marks has been obtained. 



It may finally be mentioned that as a control experiment a not 

 filled apparatus, in which F and G were connected by means of 

 rubber, was brought at different pressures and temperatures, and it 

 was ascertained that no appreciable change of the position of the 

 pointer on the scale could be perceived, so that the zero position 

 appeared to be independent of the temperature and pressure. 



6. Results. 



The obtained results have been collected in the following table; 

 the pressures are given in millimeters of mercury of 0°, and if 

 necessary corrected to 45° N.Lat. 



It is clear from the above table and the corresponding graphical 

 representation (Fig. 3), that the P-7' line of the nitrogen tetroxyde 

 presents a perfectly normal shape; there is no question of the 



