716 
MR. W. CROOKES ON RADIANT MATTER SPECTROSCOPY. 
spectrum of 42 samaria and 58 yttria, and is built up of some of the component bands 
of the spectrum of each earth : whilst in fig. 9, the spectrum of 39 samaria and 61 
yttria is seen to be almost the yttria spectrum. 
Fig. 9. 
152. I have already shown (86) that one part of yttrium can be detected spectro¬ 
scopically in the presence of a million parts of calcium, and the reaction is almost as 
sensitive if other earths are taken instead of lime. Again, the spectrum test for 
samarium is, if possible, even more delicate (156 to 163), one part being detectible 
when mixed with more than two million parts of calcium. 
Fig. 10. 
153. The accompanying diagram (fig. 10) shows at a glance the remarkable effect 
these two earths have of masking each other’s spectrum reactions. The ordinates 
above the horizontal zero line represent the percentages of samaria in the mixtures 
examined, and the lower ordinates show the percentages of yttria present. The dots 
