1870.] 



Erbia and some other Earths. 



549 



merits show that the luminous vapour is the same as that produced by the 

 exposure of the chlorides of the metals to the heat of the Bunsen gas- 

 flame. The character common to these spectra of bands of some width, in 

 most cases gradually shading off at the sides, is different from that which 

 distinguishes the spectra of these metals when used as electrodes in the 

 metallic state*. 



Roscoe and Clifton have investigated the different spectra presented by 

 calcium, strontium, and barium, and they " suggest that at the lower tem- 

 perature of the flame or weak spark, the spectrum observed is produced by 

 the glowing vapour of some compound, probably the oxide, of the difficultly 

 reducible metal ; whereas at the enormously high temperature of the in- 

 tense electric spark these compounds are split up, and thus the true spectrum 

 of the metal is obtained. In none of the spectra of the more reducible 

 alkaline metals (potassium, sodium, lithium) can any deviation or disap- 

 pearance of the maxima of light be noticed on change of temperature "j\ " 



As the experiments recorded in this paper show that the same spectra 

 are produced by the exposure of the oxides to the oxyhydrogen flame, 

 Roscoe and Clifton's suggestion that these spectra are due to the volatiliza- 

 tion of the compound of the metal with oxygen is doubtless correct. 



The similar character of the spectrum of the bright lines seen when erbia 

 is rendered incandescent would seem to suggest whether this earth may not 

 be volatile in a small degree, as is the case with lime, magnesia, and some other 

 earths. The peculiarity, however, of the bright lines of erbia, observed by 

 Bahr and Bunsen, that they could not be seen in the flame beyond the limits 

 of the solid erbia, deserves attention. My own experiments to detect the 

 lines in the Bunsen gas-flame, even when a very thin wire was used, so as 

 to allow the erbia to attain nearly the heat of the flame, were unsuccessful. 

 The bright line in the green appears, indeed, to rise to a very small extent 

 beyond the continuous spectrum, but I was unable to assure myself 

 whether this appearance might not be an effect of irradiation. 



It is perhaps worthy of remark that the chlorides of sodium, potassium, 

 lithium, caesium, and rubidium give spectra of defined lines which are not 

 altered in character by the introduction of a Leyden jar, and which, in the 

 case of sodium, potassium, and lithium, we know to resemble the spectra 

 obtained when electrodes of the metals are used. Now all these metals 

 belong to the monad group ; it appeared therefore interesting to observe 

 the behaviour of the other metal belonging to this group. 



Chloride of silver when introduced into the Bunsen flame gave no 

 lines. The chloride was then mixed with alumina, which had been found 

 to give a continuous spectrum only, and exposed to the oxyhydrogen 



* For the spectra of metallic strontium, barium, and calcium, see Phil. Trans. ISG4, 

 p. 148, and Plates I. and II. Both forms of the spectra of these substances are repre- 

 sented by Thalen in his • Spektralanalys.' 



t Roscoe's Spectrum Analysis, p. 175, and Proc. Lit. & Phil. Soc. Manchester, April 

 1, 1862. See also A. Mitscherlicb, 1 Ueber die Spectren der Verbindungen,' S. 10. 



