185 



of liquid air, boiling freely under atmospheric pressure, about — 190° C, 



the gas in this series being pure nitrogen. 



Values were calculated for both series using the simple relations given 

 in equation (6), and for series I the results were in close agreement with 

 those of Wiillner. The assumption that Gay Lussac's law holds for nitro- 

 gen at low temperatures was however regarded as questionable, and re- 

 sults for series II were not at that time published. Subsequently the 

 density-pressure relation for low temperatures was investigated for nitro- 

 gen by Bestelmeyer and Yalentiner" in the Institute at Munich, and resulted 

 in the establishment of the following empirical relation between pressure 

 volume and temperature : — 



pv=li\T — (h. — JhTJp, where T is the absolute temperature, j) is the 

 pressure, and r is the specific volume, the constants having values 

 7(1=0.27774. 7(2=0.03202, and 7«5=000253. This relation introduced into 

 the general equations gives (13). Making use of (13) the data of series 

 II have been recomputed, and the results are given in table IV. 



Subsequent tp the experimental work of I and II, Valentiner^" has 

 made use of the same apparatus used by the writer, with certain modifi- 

 cations and improvements, for investigating the dependence of k upon 

 pressure, for nitrogen, at liquid air temperatures. 



Theory. — The method used was that of Kundt's dust figures. Two 

 glass tubes, maintained at different temperatures, had set up in them sys- 

 tems of standing waves by means of the longitudinal vibrations of the 

 same glass rod. The frequency of the waves was the same within both 

 tubes, and from measurements of the wave lengths, as shown by the dust 

 figures, the variations in k could be determined. 



The velocity of sound in any homogeneous medium is given by the 

 equation 



V2 = — v2 _Z. :r=: iflUl (1) 



v\'here v is the specific volume, and /; is the pressure, the negative sign 

 meaning that a decrease in pressure corresponds to an increase in specific 

 volume. It must be I'emembered that the standing wave in the tube has 

 a wave length half as great as that for the progressive wave of the same 



» Ann. der Physik, 15. p. 61. 

 lOAnn. der Physik, 15, p. 74. 



