340 Lord Ruylrigli. On <tn Anomaly encountered in [Apr. l[ 



April 19, 1894. 

 The LORD KELVIN, D.C.L., LL.D., President, in the Chair. 



A List of the Presents received was laid on the table, and tl 

 ordered for them. 



Professor Dewar made an oral communication stating that he 

 observed that many bodies cooled to between 180 C. and 200 

 after stimulation by light become remarkably phosphorescent, 

 only in increased intensity, bnt in duration, and that liquid oxyg 

 itself always shows faint but distinct phosphorescence. He stat 

 that the details of experiments would be shortly communicated 

 the Society. 



The following Papers wei-e read : 



I. "On an Anomaly encountered in Determinations of 

 Density of Nitrogen Gas." By LORD RAYLEIGH, Sec. 

 Received February 16, 1894. 



In a former communication* I have described how nitrogen, 

 pared by Lupton's method, proved to be lighter by about 1/1000 

 than that derived from air in the usual manner. In both cases a 

 hot tube containing copper is employed, but with this difference, 

 the latter method the atmospheric oxygen is removed by oxidatic 

 of the copper itself, while in Lupton's method it combines with 

 hydrogen of ammonia, through which the air is caused to pass on it 

 way to the furnace, the copper remaining unaltered. In order 

 exaggerate the effect, the air was subsequently replaced by oxyj 

 Under these conditions the whole, instead of only about one-sever 

 part of the nitrogen is derived from ammonia, and the discrepai 

 was found to be exalted to about one-half per cent. 



Upon the assumption that similar gas should be obtained by 

 methods, we may explain the discrepancy by supposing either 

 the atmospheric nitrogen was too heavy on account of imperfect 

 moval of oxygen, or that the ammonia nitrogen was too light 

 account of contamination with gases lighter than pure nitrogen. In- 



" On the Densities of the Principal Gases," ' Roy. Soc. Proc.,' vol. 53, p. 146, 

 803. 



