1870.] 



Erbia and some other Earths. 



551 



tensely heated in the oxyhydrogen jet only a continuous spectrum was 

 seen*. 



" 2. Experiments with Lime. — A platinum wire of the same thickness as 

 the last was moistened with the phosphoric acid, some calcium nitrate was 

 then taken up in the loop, and heated in the hydrogen flame until a residue 

 of lime was obtained. At the outset the calcium-spectrum was observed, but 

 the light speedily gave only a continuous spectrum. The lime and loop of 

 wire were kept well enveloped in the hydrogen flame for nearly half an hour 

 in order to ensure the complete decomposition of the nitrate. During this 

 time no lines could be detected on the background of the continuous 

 spectrum, or in the spectrum of the flame surrounding the lime. More 

 hydrogen was now turned on and oxygen slowly admitted, the light being 

 examined with the spectroscope during the time. When the proportion of 

 oxygen had reached a certain point, faint traces of the two brightest Ca 

 lines appeared on the bright background, and the intensity of these lines 

 increased with the amount of oxygen admitted up to a definite extent. 

 When a certain proportion of oxygen was exceeded, the lines became less 

 distinct. The best results were obtained when the hydrogen was decidedly 

 in excess of the oxygen in the flame, that is to say, more than in the pro- 

 portion of 2 : 1 . 



" When the slit of the spectroscope was pointed in such a way that only 

 the light from the flame surrounding the incandescent lime entered the 

 instrument, all the Ca lines and bands were observed with great ease with- 

 out a continuous spectrum. On looking at the mantle of flame with the 

 naked eye it was easy to perceive a reddish tinge. I next maintained the 

 small fragment of lime at the highest temperature its supporting wire was 

 capable of resisting for three hours ; at the end of this time the Ca lines 

 were as strongly marked as before, and the lime on the wire had very 

 appreciably diminished in amount. The same results were obtained when 

 no phosphoric acid was employed to attach the calcium nitrate to the wire 

 in the first instance. 



"xlgain, a piece of well-burned quicklime, of very small size, was heated 

 alone on a platinum wire for more than an hour, and the bright Ca lines 

 were seen during the whole time. 



" From the results of these experiments, we must draw the conclusions(l) 

 that when lime is sufficiently heated the light which it emits is derived in 

 part from the incandescent solid, and partly from ignited vapour ; (2) that 

 lime is either volatile as such, or that in the first instance it suffers reduc- 

 tion by the excess of hydrogen in the flame, the luminous vapour of calcium 

 then giving its own peculiar spectrum. 



"3. Experiments with Erbia. — The specimen of erbium nitrate which 



* " Since writing the above, I have succeeded in observing the bright lines described by 

 Mr. Huggins as occurring in the spectrum of the flame surrounding the incandescent 

 magnesia. In the earlier experiments I probably admitted too much oxypjen to the 

 mixed gas-flame in the first instance." 



