solid Hydrocarbons found in Petroleum Distillates. 101 



The green light emitted by thallene surpasses in intensity that 

 furnished by any other substance, the only one which approaches 

 it being platinocyanide of barium in a peculiar condition, which, 

 however, is by no means under control. 



There are in the collections of the Stevens Institute of Tech- 

 nology some screens and words painted with this salt on cards 

 of a few inches area, prepared by Albert Sohn, of Frankfort- on- 

 the- Maine, which approach thallene in brilliancy; but the pure 

 salt, even when forming fine crystals, is very inferior in the 

 energy of its fluorescence. 



Anthracene forms, as is well known, a compound with chlorine 

 (bichloranthracene), whose solutions in alcohol and benzole 

 fluoresce brightly and give a spectrum (banded in the upper 

 regions) which has been studied by Hagenbach (PoggendorfFs 

 Annalen, vol. cxlvi. p. 385. 



This led me to attempt the preparation of a like compound 

 with thallene. 



A quantity of bichloranthracene having been first made, to 

 ensure accuracy in the method of working, thallene was sub- 

 mitted to the same treatment, i. e. was mixed with benzole 

 and subjected to a current of chlorine for about an hour, and 

 was again exposed in the dry state to the action of chlorine. A 

 strong reaction was shown, considerable heat being developed, 

 and the entire substance acquiring a chocolate colour. The pro- 

 duct, however, showed no tendency to crystallize. In its tarry 

 state and in solution its fluorescence is moderately strong, but 

 yields a continuous spectrum from about C to E. 



Having next prepared some bibromanthracene and examined 

 its fluorescence, I submitted thallene to an identical treatment. 

 But here also, though a compound was formed crystallizing in 

 very minute needles from its hot benzole solution, neither the 

 solid nor the solution showed any indications of fluorescence. 



I found moreover that, while anthracene combines with about 

 twice its weight of picric acid to form the picrate, which crystal- 

 lizes in long needles of a rich strawberry colour, thallene requires 

 fully four times its weight of picric acid to saturate it. On 

 cooling from hot solution, a granular mass of minute crystals is 

 •formed ; having a rich orange-red colour. Examined under the 

 microscope, these crystals are seen to be short prisms with well- 

 defined pyramidal terminations. 



Sulphuric acid of density 60° B., which rapidly blackens an- 

 thracene even at the ordinary temperature, gives thallene a rich 

 grass-green colour, which remains unchanged even after stand- 

 ing for weeks and exposure to a temperature of 60° C. 



In this condition it continues to give a bright fluorescence, 



