THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 





[FIFTH SERIES.] 



\FEBRUARY 1890. 



XIII. The Pressure- Variations of certain Higli-Temperature 

 Boiling-Points. By Carl Barus *. 



1. TN the following pages I briefly describe a practical 

 JL method for the calibration f of thermocouples by aid 

 of boiling-points, and then apply it in measuring the vapour- 

 tensions of zinc, cadmium, and bismuth. During the course 

 of the work a neglected principle of Groshans J is advan- 

 tageously employed. I must state at the outset tbat it is not 

 the object of this paper to furnish accurate values for boiling- 

 points. My purpose is to investigate the probable nature of 

 the relation of boiling-point to pressure, throughout very 



* Communicated, with the permission of the Director of the U.S. 

 Geological Survey, by the Author. 



t The literature of the subject, which is very voluminous, may be 

 omitted here, because I give a full account of it in the Bulletin of the 

 U.S. Geological Survey, no. 54, pp. 23 to 55, 1889. Among recent 

 authors H. Le Chatelier (cf. Bull. Soc. Chim. Paris, n. s. xlv. p. 482, 

 1886 ; ibid, xlvii. pp. 2, 300, 1887 ; C. R. cii. p. 819, 1886 ; Jonrn. de. 

 Physique, vi. p. 23, 1887, and elsewhere) is particularly active in pro- 

 moting thermoelectric high-temperature research. In the ' Bulletin ' 

 I describe methods of standardization by aid of boiling-points (pp. 84 to 

 125), and by direct comparison with Deville and Troost's porcelain air- 

 thermometer (pp. 165 to 248). I also submit an independent method of 

 my own, based on the high-temperature viscosity of gases (pp. 248 to 

 306). Experiments made conjointly with my colleague, Dr. William 

 Hallock, on capacious high-temperature vapour-baths, are discussed in 

 another part of the ' Bulletin ' (pp. 56 to 83). 



% Groshans, Pogg. Ann. lxxviii. p. 112, 1849. 



Phil Mag. S. 5. Vol. 29. No. 177. Feb, 1890. M 



