Manchester Memoirs, Vol. xliii. (1899), No. 4. 17 



the spectrum of krypton is characterised by three con- 

 spicuous lines, one red, one yellow, and one green — this 

 last closely coinciding in wave-length with the green line 

 of the aurora borealis — that of xenon is complex, resem- 

 bling that of argon in general character, but differing 

 totally in the wave-length of its lines. Like the spectrum 

 of argon, too, it is profoundly altered by interposition of a 

 Leyden jar and a spark-gap ; the colour changes from an 

 ill-defined purple to a sky-blue, and the spectrum shows 

 the presence of many groups of green and blue lines. The 

 spectrum of krypton, however, in its behaviour towards a 

 discharge of greater intensity is more like that of helium ; 

 it undergoes only a slight change. Krypton differs from 

 argon also in its refractivity for light; the refractivity of 

 argon is nearly 0*97 ; that of krypton is about i'03; but 

 the refractivity of xenon is evidently much higher, although 

 exact measurements have not as yet been made. Even 

 though the sample we have obtained was evidently far 

 from pure, showing the spectra of both krypton and argon, 

 yet a determination of its density gave a number far in 

 excess of the density of argon. This preliminary weighing 

 proved that we may expect xenon to occupy a vacant 

 space between bromine on the one hand, and rubidium on 

 the other. Continuing the table, of which a portion has 

 already been given, we have the following arrangement: — 



Fe= 56 

 Mn= 55 Ni= 587 Cu= 63-6 Zn= 65-4 Ga= 70 Ge= 72 As= 75 Se= 79 



Co- 59 



Br= 80 ? X= 82 Rb=: 85-4 Sr= 87-6 Y = 89 Zr= 91 Nb= 94 Mo= 9 



Ru = ioi7 

 ?=ioo Rh=i03 Ag=io8-o Cd=ii2 In:=ii4 Sn=ii8 Sb=i20 Te=i28 

 Pd=io6 



1=127 ?=I30 Cs=i33 Ba=:i37 La=i38 Pr—140 Nd = i44 .? = 146 

 ? =152 

 Sa = i5o ?=i53 



? =154 etc, etc. etc. 



