Composition of Brittle Platinum. 89 



Measurements made by Dr. Adeney have been communi- 

 cated to me prior to publication. The iron lines are very 

 closely in agreement with Kayser's wave-lengths while the 

 numbers for the platinum lines prove their identity with those 

 quoted above. 



Adeney's Measurements. 



Ikon lines 2628-396 and 2625-724 



Platinum lines 2628-172 ,, 2625-400 



I conclude that the lines have not a common origin, but 

 are different lines with only approximately the same wave- 

 lengths. Some trouble was taken to prove the presence 

 or absence of silicon. The strongest lines of silicon, namely 

 2881*6, 2516*0, and 2506*7, have been sought for, but they 

 appear to be absent from all the platinum-spectra. This 

 does not, however, quite dispose of the question, because there 

 are two lines on Adeney's spectrum of platinum with wave- 

 lengths approximately 2514*20 and 2515*65, the former and 

 more refrangible line being the stronger of the two, the former 

 comes very near to one of the weaker lines of silicon 2514*4, 

 and the latter near to the stronger line 2516*0. Exner and 

 Haschek give two corresponding lines in platinum with 

 wave-lengths 25138 and 2515*4. 



Jn a subsequently published list of wave-lengths determined 

 with greater accuracy (Mittheilung vi.), the former line 

 alone is given as being a strong line with the wave-length 

 2513*98. The order of the relative intensities of the two 

 silicon lines is the reverse of that of the platinum lines, and 

 it is only the weaker line of the silicon spectrum that 

 approximates in wave-length the stronger line of the platinum. 

 There can be no doubt whatever that silicon is absent. 



This investigation has proved in a forcible manner, 1st 

 the utility for practical purposes of spectrograph^ analysis 

 by means of the spark ; 2nd, the importance of determining 

 the wave-lengths of arc and spark lines of pure elements 

 with extreme accuracy ; and 3rd, the advantage of being 

 able to distinguish between two spark lines of very nearly 

 the same wave-length by the difference in their characters. 

 In conclusion 1 desire to express my thanks to Dr. Adeney 

 for his courtesy in communicating his measurements of the 

 platinum and iron lines. 



Royal College of Science, Dublin, 

 April 9th, 1902. 



