1886.] 



On Radiant Matter Spectroscopy. 



11 



III. "On Radiant Matter Spectroscopy: Note on the Spectra of 

 Erbia." By William Crookes, F.R.S. Received Jan. 7, 1886. 



I have recently succeeded in getting the earth erbia in a sufficiently 

 pure state to allow me to examine its phosphorescent spectrum without 

 the interference which might be produced by the presence of yttria, 

 samaria, holmia, thulia, Y« or ytterbia. As in the case of yttria* 

 the spectrum is best seen when erbic sulphate is heated to redness and 

 submitted to the electric discharge in a high vacuum. The addition 

 of calcic sulphate interferes with the purity of the spectrum. In this 

 respect erbia differs from samaria, as the latter earth seems to require 

 the presence of some other metal to develop its phosphorescent 

 properties. 



The phosphorescent spectrum of erbia consists of four green bands, 

 of which the following measurements have been taken : — 



Scale of 



X 



1 



Remarks. 



spectroscope. 







9-750° 



5564 



3230 



Approximate centre of a wide 

 band, shading off at each side. 



9 -650° 



5450 



3367 



Approximate centre of a band, 

 narrower and somewhat fainter 

 than the first band. 



9-525° 



5318 



3536 



Approximate centre of a narrow 

 band, bright and moderately 

 sharp on each side. 



9-400° 



5197 



3702 



Approximate centre of a band, 

 similar in appearance to the 

 first band, but brighter. 



Fig. 1 shows the erbia phosphorescent spectrum drawn to the — 

 scale. 



These bands do not correspond in position to any in either the 

 yttrium or samarium spectrum. The nearest approach to a coinci- 

 dence is between the first erbia green and the samarium green, but 

 when the two spectra are examined one over the other it is seen that 

 the samarium band is less refrangible than the erbium band. 



The first green of Ya occurs midway between the first and second 

 greens of erbia, and the second Yx green comes between the second 

 and third erbia greens. 



Pure erbia is of a beautiful rose- pink colour. j When illuminated 



* " Phil. Trans.," vol. 174, p. 913, par. 71. 



t Rose-coloured erbia has already been obtained by Professor Cleve, who a year 

 ago presented me with a specimen of the earth as pure as the one which is the sub- 

 ject of this paper. 



