1887.] 



Crimson Line of Phosphorescent Alumina. 



27 



It is known that spinel (magnesium aluminate) phosphoresces with 

 a red light, and shows a crimson line in its spectrum.* On examina- 

 tion in the high power spectroscope the spectrum of the light emitted 

 bj spinel under the radiant matter test is seen to differ from that 

 emitted by ruby and alumina under the same test, and to closely 

 approximate to the description given by E. Becquerel in 1859. 



The spectrum first shows, in the extreme red, a faint double band, 

 then a narrow crimson line, which, however, is not double like the 

 alumina line, neither is it quite so bright and sharp. Four hazy red 

 bands follow, the fourth being wider and more indistinct than the 

 others. Here the spectrum of most spinels fades away. Sometimes, 

 however, a spinel is seen to glow with a greenish tiut ; in these the 

 spectrum is the same as the others up to this point, and there is also 

 seen a bright concentration of light in the green. 



The measurements of the spinel spectrum are given in the following 

 table : — 



Scale of 



X. 



1 



Remarks. 



spectroscope. 



& 



10 -610° 



7096 



1986 



Approximate commencement of first com- 

 ponent of ill-defined double band. 



10-595 



7055 



2009 



Approximate end of ditto. 



10-580 



7017 



2031 



Commencement of ill-defined second com- 

 ponent. 



10-550 



6942 



2075 



End of ditto. 



10-515 



6857 



2127 



Centre of sharp crimson line. 



10-490 



6798 



2164 



Approximate commencement of broad 

 hazy band. 



10 -450 



6707 



2223 



End of ditto. 



10-440 



6683 



2239 



Commencement of second component of 

 group. 



10-405 



6608 



2290 



End of ditto. 



10-400 



6598 



2297 



Commencement of third component. 



10 -380 



6555 



2327 



End of ditto. This band is somewhat 

 sharper and brighter than the other com- 









ponents of this group. 

 Commencement of fourth component of 

 ditto. 



10-370 



6534 



2342 



10-330 



6454 



2401 



End of ditto. 



9-730 



5541 



3257 



Approximate commencement of luminous 

 concentration in the gi-een seen in some 



9-440 







spinels. 



5234 



3650 



Position of maximum luminosity of this 

 concentration of light. From this point 

 the spectrum appears to be continuous, 

 shading off gradually towards the blue 

 and violet. 



The drawing (fig. 2) shows the spectrum, drawn to the — scale. 



* E. Becquerel, ' Annales de Chimie et de Physique,' vol. 57, p. 58 ; W. Crookes, 

 ' Roy. Soc. Proc.,' vol. 32, p. 208. 



