465 



Physics. — " Fsothennnls of di-atomic substances ami their binary 

 mixtures. XVII I. The Isothermal of hydrogen at 20° C. from 

 60 — 100 atmospheres." By H. Kamerlingh Onnes, C. A. 

 Crommeijn and Miss E. I. Smid. (Communication 1466 from 

 the Physical Laboratory at Leiden). 



(Communicated in the meeting of June 26, 1915). 



1. Introduction. The measurements communicated in this paper 

 are a revision and extension of those of the preceding communication. 

 Tliey are to be looked upon as a first part of a more accurate 

 investigation to obtain a bridge between the accurate isothermal at 

 20^ C. and between 4 and 60 atmospheres, determined by Schalkwijk'), 

 and Amagat's isothermals '), wliich only begin at 100 atmospheres. 



Previous determinations by Kamkrlingh Onnks and Hyndman ') were 

 made with the same ultimate aim in view. They were made with 

 the piezometers for low temperatures and gave the same values as 

 Schalkwijk's measurements witii the piezometers for ordinary tem- 

 perature. On this ground measurements at 0° C. with the same 

 piezometers for low temperatures could be undertaken with confi- 

 dence. In the paper by Kamkrlingh Onnes and Hynuman quoted above 

 a determination of the isotiiermal for 0° C was published which 

 was replaced by a more accurate one in a later communication *). 

 It will be necessary to repeat the latter investigation and extend it 

 to 100 atmospheres in order to obtain the desired connection with 

 Amagat's work. In addition it will be necessary to undertake a 

 determination with Schai.kwmk's piezometer IV, provided with a 

 vessel of twice the volume, and thus extending from 60 to 120 

 atmospheres ; as a continuation of work with a somewhat different 

 object, viz. the investigation of the isothermal of 20° C. arranged 

 to reach a higher accuracy. For it will now also be our object to 

 know this isothermal from 60 to 120 atmospheres with an accuracy 

 of 1 in tenthousand. 



In the mean time, while this investigation of the highest accuracy 

 is still in abeyance, the necessary calibration of the working mano- 



') .1. G. Schalkwijk, These Proceedhigs 4, p. 107, 1901, Comm. 70 (cont.), 

 Dissertation, Amsterdam, 1902. 



2) E. H. Amagat. Ann. de chim. et de phys. (6). 29. p. 68, 505, 1893 



^) H. Kamerlingh Onnes and H. H. V. Hyndman, These Proc 4. p. 761, 

 1902, Gomm. 78. 



*) H. Kamerlingh Onnes and G. Braak, These Proc. 10, p 413, 1907, Gomm. 

 100a and lOüö. G. Braak, Dissertation, Leiden, 1907. 



