478 



of solid and liquid ai'gon. besides some results which may be deduced 

 from these observations. 



The experimental material now at our disposal is put together 

 in table I. (see p. 487). 



The determinations in P^ebr. 1910 have already been published^), 

 and are onl}' included here to facilitate the complete survej' of all 

 the vapour pressure determinations, and because we shall need them 

 in the following discussion of the results. 



The observations in May 1912 were made on the occasion of the 

 determinations of the straight diameter ^) ; as regards the apparatus 

 we can therefore refer to the papers concerning this. We need only 

 remark that the pressure deter-.ninations were made with an open 

 standard manometer '). 



The measurements in Dec. 1912 were made with the apparatus 

 already described") for the determination of vapour pressure ai low 

 pressures, which on this occasion also proved highly satisfactory. 



As regards this last series of measurements we make the following 

 remarks. Before we proceeded to a measurement we waited until 

 the constancy of the pressure showed that the equilibrium betw^een 

 the phases was established. During this period the temperature was 

 of course kept as carefully as possible constant. The measurement 

 then consisted in reading the manometer and barometer several 

 times alternately. As a rule the pressure in the apparatus remained 

 almost completely constant during a measurement. 



The values given for the temperature of the bath of liquid oxygen, 

 boiling under atmospheric and under reduced pressure, in which 

 these measurements were made, w^ere based upon a new comparison 

 of the standard platinum resistance thermometer Pi/ with the hydrogen 

 and the helium thermometers, shortly to be published by Kamerlingh 

 Onnes and Holst. This gives results that ditfer slightly from the 

 former calibration ^) but for none of the temperatures are they more 

 than 0^.05 and they are of a completely systematic character. The 

 cause of this difference is not yet clear. A dii-ect determination of 

 the difference between the boiling point of argon and of oxygen 

 will throw more light upon it. 



1) G. A. Grommelin, Proceedings May 1910, Gomm. No. 115, and Thesis 

 Leiden, 1910. 



2) E. Mathias, H. Kamerlln'gh Onnes and G. A. Grommelin, Proceedings Oct. 

 1912. Gomm. No. 131a. 



3) H. Kamerlingh Onnes, Proceedings Nov. 1898, Gomm. No. 44. 



■*; H. Kamerlingh Onnes and C. Braak, Proceedings Oct. 1908, Gomm. No. 107a. 



"I H. Kamerlingh Onnes and J. Glay, I'roceedings Sept. 1906, Gomm No. 95c and 



II. Kamerlingh Onnes, G. Braak and J. Glay, Proceedings Dec. 1907, Gomm. N". 101a. 



