1904.] On the Ultra-violet Spectrum of Gadolinium. 421 



Wellenlangen-Tabellen fur Spektralanalytische Untersuchungen,"* 

 These observers used a material prepared by Dr. L. Haitinger, in which 

 they say holmium, samarium, and yttrium were present as impurities. 

 They give wave-lengths of 1150 lines ; I have found them to be as a 

 rule very accurate, and in the maps accompanying this I have adopted 

 most of their wave-lengths, except in cases where my own measure- 

 ments give different figures, or where lines given by them are not 

 to be distinguished on my photographs. In some cases also lines 

 ascribed to gadolinium appear to be caused by other earths as 

 impurities. 



My photographs were taken by means of the apparatus described in 

 my paper " On the Ultra- Violet Spectrum of Eadium."t The arrange- 

 ment is the same as there adopted in the maps of the radium spectrum. 

 The upper half of each strip shows the iron lines used as standards, 

 with their wave-lengths according to Rowland's latest measurements, 

 lower half contains the gadolinium lines, with their wave-lengths 

 Iculated or verified from the iron standards, according to the 

 method given in detail in the paper just quoted. Other lines, the 

 wave-lengths of which are written in red ink, are either platinum lines 

 or lines due to traces of impurity in the gadolinium oxide. These are 

 very few, and their faintness speaks well for the accuracy with which 

 M. Urbain has separated other earths from the gadolinium, for in my 

 experience I have seldom found a so-called " pure " salt of an ordinary 

 metal anything like so free from impurities as this earth proves to be. 

 Moreover, it must not be taken as certain that some of the impurities 

 assumed to be present on the strength of a strong line are really there, 

 because in some instances I have not been able to detect the presence 

 of another equally characteristic line of the same impurity. 



The rare elements allied to gadolinium, or occurring with it, which 

 I have thus found to be present, are : 



Yttrium, represented by the lines at... 3774-51 and 4177-68. 



Europium ... 3972-16, 4129*90, and 4662-08, 



Samarium ,, ,, ... 3230*65. 



Ytterbium ... 3289-52 and 3694-35. 



Scandium ... 3572-71, 3613-96, and 3630-86. 



The other elements which are present are 



Bismuth, represented by the line at 4259-85. 



Magnesium lines at 2796-62 and 2802*80. 



Calcium 3933-81 and 3968-60. 



Of these, r : the bismuth and magnesium are present from the salts 



* F. Deuticke, Leipzig and Wien, 1902. 



f ' Roy. Soc. Proc.,' vol. 72, p. 295., Aug., 1903. 



