32 PHOSPHORESCENCE 



teenth during the emission of light. This neces- 

 sitates a disengagement of heat, which is really 

 observed to take place, as is shown in the follow- 

 ing experiment: When chromic oxide, titanic acid, 

 or better than all, gadolinite is heated in a small 

 retort, the end of which, terminating in a capil- 

 lary tube, plunges into water, the dilated air con- 

 fined in the apparatus is expulsed through the 

 water uniformly as the heat increases, and when 

 the phenomenon of incandescence takes place, the 

 bubbles of air are, for a moment, driven out vio- 

 lently, indicating a sudden production of heat. 



With samarskite and arsenious acid (see p. 19), 

 whose densities dimmish during the experiment, 

 no heat is disengaged, as with gadolinite. Thus, 

 thinks Rose, when this phosphorescence occurs 

 without any disengagement of heat, it seems to 

 indicate a diminution of density, whilst phospho- 

 rescence with emission of heat, appears indicative 

 of an increase of specific gravity ; and ' ' probably, 

 during the diminution of density, the caloric is 

 employed to separate the atoms, instead of being 

 disengaged." 



These results, obtained at the beginning of the 

 year 1857, are exceedingly remarkable. 



In this chapter we should include also the well- 

 known phosphorescence of phosphorus, formerly 

 studied in our ' Recherches nouvelles sur le Phos- 

 phore/ The phenomenon occurs when phosphorus 



