solid Hydrocarbons found in Petroleum Distillates. 93 



With solutions in tanks the same plan was followed, a small 

 piece of card with a needle-hole being moved into the required 

 position and the transmitted light then measured. 



Observations. 



Spectrum of Fluorescent Light from Solid Thallene. 



When a portion of the yellow crystalline substance above de- 

 scribed, and which, to avoid circumlocution, I shall hereafter call 

 thallene, in allusion to the brilliant green colour of its fluores- 

 cence, is examined in the manner first described and represented 

 in fig. 1, we obtain a spectrum such as is indicated in fig. 5. 



Fig. 5. 



7 



This begins with a very broad bright space in the orange and 

 yellow ; then, separated by shades or bands of less brilliancy, 

 follow two green spaces, and lastly one of blue, much less bril- 

 liant than the others, and best seen when the violet glass is 

 added to the blue tank (see fig. 1). The scale employed in the 

 above and subsequent drawings of spectra is that with milli- 

 metre-divisions introduced by Bunsen. 



This spectrum, it will be seen, differs from that of impure an- 

 thracene, or chrysogen as found in commercial anthracene, in 

 two respects. First, there is no decided separation of the orange 

 and yellow rays from the red by a dark space in this thallene- 

 spectrum as in the other. Second, there is found in this spec- 

 trum a strong bright band in the blue under circumstances in 

 which it cannot be recognized in the spectrum given by the 

 former substance. 



Absorption-spectrum of Solid Thallene. 



At a temperature of about 460° ¥., thallene fuses without de- 

 composition ; and we may thus obtain a translucent plate of it 

 between slips of mica or on glass in a condition convenient for 

 the study of its absorption in the manner shown in fig. 3. But 

 we may also dissolve it in melted paraffine, or spread it by rub- 

 bing on filter-paper, or mix it with varnish and so coat paper 

 with it. In any of these shapes, when examined by transmitted 

 light, as in fig. 2, it shows an absorption-spectrum such as is 

 represented in lig. 6. 



