ofErbia and some other Earths. 307 



" 2. Experiments with Lime. — A platinum wire of the same thick- 

 ness 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 proportion 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 without 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. 



" Again, 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 conclu- 

 sions: — (1) 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 reduction 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 you kindly gave me was attached to a platinum loop with 

 syrupy phosphoric acid as usual, and decomposition of the salt 

 effected in the plain hydrogen flame. After heating for a short 

 time in this way, the chief green line of erbia became visible, but 

 seen upon the continuous spectrum. Oxygen was now turned slowly 

 into the flame. As the temperature rose, two of the other bright 

 lines of the earth were seen. The best observations were made 

 when the oxyhydrogen flame had hydrogen in excess, and the erbia 

 was kept in such a position that it was very strongly ignited. The 



