MR. W. CROOKES ON RADIANT MATTER SPECTROSCOPY. 713 
The third kind of spectrum is given by calcium mixed with samarium. Here the 
red and green are single, and the orange double. Aluminium would also fall into this 
class were it not that the broad ill-defined green band is also doubled. The calcium- 
samarium spectrum, already illustrated in fig. 4 (140), is a good illustration of this 
type. 
Fig. 5. 
Fig. 6. 
Mixed Samarium and Yttrium Spectra. 
146. It was interesting to ascertain what spectrum a mixture of samarium and 
yttrium would give. A mixture of 90 parts of samaria to 10 of yttria was treated with 
sulphuric acid and then ignited, and afterwards examined in the radiant matter tube. 
The result was as remarkable as it was unexpected. Scarcely a trace of the yttrium 
spectrum could be detected. The powder phosphoresced with moderate intensity, 
but the spectrum was almost the facsimile of that given by pure samaric sulphate 
(137, fig. 3), except that the sharp orange line, which in the spectrum of pure samaric 
sulphate is only just visible, had gained sufficiently in intensity to be measurable, and 
was found to lie at 2693. I next tried a mixture of samaria 80, and yttria 20. The 
spectrum was identical with the one last observed, with one striking difference—the 
2693 line now shines out with great brilliancy of a fine orange-red colour, as sharp as 
a gas line, and so unlike the bands usually met with in the spectra of phosphorescent 
earths as to suggest the explanation that some other spectrum-forming body was 
present in the mixture. 
The next tube experimented with contained 70 parts of samaria and 30 parts of 
yttria. The spectrum was identical with the one last observed. The sharp orange 
line was present in full intensity. 
147. Mixtures were now made of samaria 60, yttria 40; samaria 60'63, yttria 39'37 
(equivalent proportions of the two earths); in this last a slight division could be 
