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 Lussae’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 Valentiner® in the Institute at Munich, and resulted 
in the establishment of the foilowing empirical relation between pressure 
volume and temperature :— 
piv=InT— (h.—h,T)p, where 7 is the absolute temperature, p is the 
pressure, and v is the specific volume, the constants having values 
Ii=0.27774, h.—0.03202, and h.—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 to the experimental work of I and II, Valentiner’ has 
made use of the same apparatus used by the writer, with certain modifi- 
‘ations 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 iengths, 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 
eg OP aa (1) 
where v is the specific volume, and p is the pressure, the negative sign 
meaning that a decrease in pressure corresponds to an increase in specific 
volume. It must be remembered 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. 
Ann. der Physik, 15, p. 74. 
