920 Transactions of the American Institute. 



On exposure fee sunlight in hot solution, anthracene loses this 

 banded spectrum, which is thus proved to belong to a body first 

 observed by Fritzsche, and called by him chrysogen (see Comptes 

 Rendus, tome 54, p. 910), and which is decomposed by exposure 

 to sunlight. 



It thus appears that the bright bands observed by Becquerel in a 

 yellow hydrocarbon obtained from Fritzsche (see La Lumiere, by E. 

 Becquerel, vol. 1, p. 382), as well as the bands described by Hagen- 

 bach in Paggendorff's Annalen, 1872, vol. 26, p. 286, as belonging to 

 Photen (anthracene), are not due to that substance in a pure state, but 

 are due, probably in both cases, to traces of chrysogen. 



When the solution of thallene in boiling benzole is exposed for sev- 

 eral hours to the direct rays of the sun, or, better, for ten to fifteen 

 minutes in the focus of a large burning glass some eighteen inches 

 in diameter, it does not lose its fluorescent bands, but has them all 

 moved upward in the spectrum, as is shown in JSTo. 3, of Plate III, 

 and then emits not a green but a blue light by fluorescence. 



A similar effect to this, varying in degree, is produced by solution. 

 Thus the solutions in benzole and chloroform, which take up about 

 the same amount of thallene, give an upward displacement of the 

 bands nearly as great as the permanent one effected by sunlight. 



Bisulphide of carbon which dissolves much more, shows a less dis- 

 placement, and ether and turpentine, which dissolve very little, dis- 

 place the bands most of all. 



So far, this relation of solubility to displacement of bands is the 

 only one which I have been able to trace, no relation seeming to exist 

 between the densities or refracting powers of the solvents and this 

 movement of the bands. 



In the case of impure anthracene (chrysogen), an exactly similar 

 change in the position of its fluorescent bands, by solution, is to be 

 noticed, varying with a change of solvents in the same way as does 

 thallene, but the exposure to sunlight, in place of elevating the bands 

 as with thallene, removes them altogether, and renders the spectrum 

 of its fluorescent light continuous. 



No. 4, Plate III., shows the fluorescent spectrum of chrysogen dis- 

 solved in benzole. 



Beside, the fluorescent spectra, anthracene, or we should more cor- 

 rectly say chrysogen and thallene, have absorption spectra, but these, 

 unlike the absorption bands of the uranium salts, are in every way 

 intimately connected with the bands of fluorescence. 



Thus No. 5, Plate III., shows the absorption spectrum of solid 



