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:—W hen chromic oxide, titanic acid, 
or better than all, gadolinite is heated m a small 
retort, the end of which, terminating im a capil- 
lary tube, plunges into water, the dilated air con- 
fined in the apparatus is expulsed through the 
water uniformly as the heat mcreases, 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 diminish during the experiment, 
no heat is disengaged, as with gadolmite. 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 dimimation 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 
