1885.] 



On Radiant Matter Spectroscopy. 



421 



It will be remarked that a sudden change of spectrum occurs 

 between very narrow limits of mixture. 



The spectrum of a mixture of 44 parts samaria and 56 parts yttria, 

 except for the orange line, is the pure samarium spectrum. The 

 spectrum of 42 samaria and 58 yttria is built up of some of the com- 

 ponent bands of the spectrum of each earth ; whilst the spectrum of 

 39 samaria and 61 yttria is almost a pure yttria spectrum, the sharp 

 orange line ruuning across them all. 



Tlie Delicacy of the Spectrum Test for Samarium. 



Experiments were now commenced with the object of getting some 

 approach to a quantitative estimate of how small a quantity of 

 samarium could be detected. 



A mixture was first made in the proportion of one part samarium 

 to 100 parts of calcium. The spectrum is very brilliant, and but 

 little inferior in sharpness to the spectrum given by a 50 per cent, 

 mixture. 



A mixture was now prepared containing 1 part of samarium to 

 1000 parts of calcium. Very little difference can be detected between 

 the spectrum of this mixture and that of the last. The bands are, 

 however, a little less sharp. 



A mixture containing one part of samarium to 10,000 parts of 

 calcium was now tested. The bands are now getting fainter, the 

 second green band is fading out, and the continuous spectrum of 

 calcic sulphate is getting brighter. 



The next mixture tried contained one part of samarium in 100.000 

 parts of calcium. Here the green is almost gone, being overshadowed 

 by the continuous spectrum of calcium which has spread over it. 

 The red band has likewise almost disappeared in the greater bright- 

 ness of the continuous red of the calcic spectrum. The double 

 orange band is still very prominent, and the black space, 2942. 

 between it and the green is very marked. 



The next mixture, one part of samarium to 500,000 parts of 

 calcium, gives a spectrum which is fainter than the last, but the 

 .orange bands are still distinctly visible. The blank space between 

 the yellow and green is strongly marked, but narrower than before. 



A mixture of one part of samarium in 1,000,000 parts of calcium 

 was next subjected to experiment. In this the samarium spectrum is 

 very feeble, and the orange bands are only to be seen with difficulty. 

 Now the most striking characteristic of this spectrum is the black 

 space which still cuts out the greater portion of the yellow. 



A mixture of one of samarium in 2,500,000 parts of calcium was 

 now taken. In the spectrum shown by this mixture the bands of 

 samarium have entirely gone, and its presence now is apparent only 



