160 
SELECTED ARTICLES. 
served by Wohler, which is, perhaps, a third isomeric modi- 
fication of arsenious acid. 
If the transparent acid is treated in the above mentioned 
manner and proportions, and the crystals have been formed 
accompanied by phosphorescence, and the whole been allowed 
to cool perfectly, the phosphorescence can be obtained once 
more, and sometimes even very powerfully, if the whole is 
again heated to the boiling point and slowly cooled. How- 
ever, the light is much more feeble than that first observed, 
and is only caused by the muriatic solution still containing 
portions of the transparent arsenious acid, and which, during 
crystallization, evolves this feeble light. Moreover, the quan- 
tity of dilute muriatic acid in the mixture above described is 
not sufficient to dissolve all the arsenious acid; and there re- 
mains, therefore, a small portion in the vitreous state. 
But still the appearances of light which have been observ- 
ed cannot be explained on the principle of a new arrange- 
ment or formation, and I myself hold this hypothesis to be 
one which requires the evidence of more facts to establish 
its probability. Thus, Berzelius observed phosphorescence 
during the crystallization of fluoride of sodium out of a solu- 
tion which held the same salt already in solution. 
Jlrcana of Science. 
