52 ME. A. FOWLER ON THE SPECTRUM OF SCANDIUM, 



intensity in the ordinary arc spectrum, as well as in the spark spectrum. Why this 

 should be so is not quite clear, but scandium is not a'lone in this behaviour, as 

 reference to the spectra of calcium, strontium, and barium will show, though this 

 point has received little attention hitherto. In the case of the iron arc, the enhanced 

 lines are almost insignificant in the integrated light, but they appear with consider- 

 able intensity close to the positive pole, and with less intensity near the negative 

 pole.* It would seem that in the case of scandium and the other elements named 

 the region of the arc in which enhanced lines are produced is of greater extent than 

 in the case of such substances as iron. However that may be, the H and K lines of 

 calcium, the lines 4078, 4215 of strontium, the lines 4554, 4934 of barium, and the 

 lines of scandium in question, have all the other characteristics of enhanced lines and 

 may be properly regarded as such. They are weakened in the flame, relatively 

 brightened in the spark, and are isolated from the other lines of the arc spectra when 

 observed in the upper chromosphere and in certain stellar spectra. The enhanced 

 lines are, in fact, to be regarded as forming a distinct spectrum of scandium, which 

 may or may not co-exist with the other lines according to circumstances. A separate 

 list of these lines is given in Table V. 



The Arc-Flame Spectrum. 



An economical method of producing an approximation to the flame spectrum was 

 suggested by the observations of the spectrum of euxenite, to which reference has 

 already been made. It was felt that the material available was inadequate for the 

 effective use of the oxyhydrogen flame, or even for the comparatively long exposures 

 required for the outer part of the flame of an ordinary arc. 



The method of purposely introducing other substances into the arc was therefore 

 adopted, the idea being to produce a " flaming arc " without unduly increasing the 

 number of impurity lines in the spectrum. For this purpose silicate of soda, silicate 

 of potash, and sodium chloride were separately tried and found to be effective if used 

 in sufficient quantity. A very long "arc" was thus obtained (the P.D. between the 

 poles falling to about 30 volts), and photographs were secured in which the enhanced 

 lines, including even the strong line 5527, were reduced to mere traces. In the blue 

 end of the spectrum the strong enhanced lines were much enfeebled in other 

 photographs covering this region, and it might have been possible to abolish these 

 lines also if more material had been available for continued experiments. 



It should be mentioned that the spectrum fluctuated considerably, the enhanced 

 lines occasionally coming in as in the ordinary arc, but, so ,far as possible, the exposures 

 were only made in the intervals when visual observations showed that the enhanced 

 lines were absent from the spectrum. The desired condition could be restored, in a 

 general way, by adding more of the supplementary substance. 



* FOWLER, ' Monthly Notices R.A.S.,' vol. 67, p. 154 (1906). 



