100 Dr. H. Morton on the Fluorescent Relations of certain 



trail is of a faint indigo tint, penetrates but little into the liquid, 

 and begins decidedly below G. 



In a former paper attention was drawn to the effect which an 

 exposure to sunlight produced upon the bands of absorption 

 exhibited by commercial anthracene. A cold solution of that 

 substance, showing its bands with great distinctness, loses them 

 entirely by an exposure of ten minutes to the direct rays of the 

 sun. Thallene similarly treated loses its lower band in five mi- 

 nutes, but its upper one (i. e. the broad double band) only after 

 thirty minutes' exposure. 



A saturated hot solution under like conditions loses its lower 

 band in thirty minutes, and its upper one in about two hours. 

 By placing it, however, near the focus of a large burning-glass 

 of 15 inches diameter, ten minutes sufficed for this effect. When 

 a solution of anthracene so exposed for one minute is allowed to 

 cool, it deposits white pearly scales (of pure anthracene), which 

 show no trace of a banded spectrum by fluorescence. 



When a solution of the yellow anthracene (obtained by wash- 

 ing the crude material with benzine, dissolving in hot benzole, 

 filtering, and crystallizing by cooling), which contains much 

 chrysogen, is similarly treated, after ten minutes' exposure in the 

 focus of the lens, it deposits on cooling crystals of anthracene 

 nearly white, but still showing a banded spectrum ; the bands 

 are w r eaker than before, but occupy exactly the same positions ; 

 the general fluorescence of the substance is also greatly reduced. 



Thallene, however, under similar conditions (that is to say, 

 exposed in hot solution in a 4-ounce flask for ten minutes near 

 the focus of the large lens and allowed to cool) deposits crystals 

 almost white but having a slight grey shade ; and these show a 

 distinctly banded spectrum, whose bands are located in almost 

 the same positions as those of an etherial solution, but are a little 

 more elevated. 



Their centres are in fact located as follows: — 7*34, 9*13, 11*17, 

 omitting the lowest band, which is too broad to be well indi- 

 cated in this way. 



The general colour of the fluorescent light emitted by this 

 substance is light blue ; and to distinguish it I would propose 

 the name Petrollucene. 



A solution of this in benzole shows a slight further elevation 

 of bands, as 7*38, 9*2, and 11*24; and when a pure spectrum is 

 thrown on this solution only two trails of light are seen — one 

 about four fifths of the way from F to G, and the other above G. 

 These are blue and indigo in colour respectively. 



As illustrations of the action of fluorescence, these substances 

 (thallene and petrollucene) surpass, I think, any bodies hereto- 

 fore known. 



